Automotive Systems: Principles and Practice 9781000262018, 1000262014

Table of contents :
Cover
Half Title
Title Page
Copyright Page
Dedication
Table of Contents
Preface
Acknowledgements
Abbreviations
Authors
Chapter 1 Automobile Evaluation and Market Review
1.1 Introduction
1.2 History and Evolution of Vehicles
1.3 Indian Automotive Market
1.4 Global Automotive Market
1.5 Automotive Research Perspectives
1.6 Indian and Global OEMs
1.7 Indian and Global Auto Components Manufacturers
1.7.1 Industry Scenario
1.7.2 Global Automotive Components Manufacturers
Summary
Multiple Choice Questions
Review Questions
Chapter 2 Vehicle Classification, Structure and Layouts
2.1 Introduction
2.2 Classification of Vehicles
2.3 Constructional Details of Vehicle Chassis and Body
2.4 Basic Terminology and Legislative Requirements of a Vehicle as per CMVR and MVA
2.4.1 Lead Dimensions of a Vehicle
2.5 Various Systems of the Vehicle and Their Functions
2.6 Various Types of Chassis Frames: Their Construction and Material
2.7 Various Loads Acting on the Vehicle Chassis Frame, and Its Deformation
2.8 Types of Chassis and Vehicle Layouts, Advantages and Disadvantages
Summary
Multiple-Choice Questions
Review Questions
Chapter 3 Vehicular Engines
3.1 Introduction
3.2 Working Principle and Terminology of the Engine
3.3 Components of the IC Engine and Their Constructional Details
3.3.1 Piston and Rings
3.3.2 Connecting Rod and Bearings
3.3.3 Crankshaft Assembly and Bearings
3.3.4 Cylinder Head and Gasket
3.3.5 Cylinder Block, Crankcase and Head
3.3.6 Crankshaft Assembly and Main Bearings
3.3.7 Crankshaft Torsional Vibration Dampers
3.3.8 Valve Train
3.4 Classification of IC Engines
3.5 Two-Stroke and Four-Stroke Engines
3.6 Comparison of Engines
3.7 Selection of Engine as Per Functional Requirement
3.8 Fuel Supply System for SI Engines: General Layout and Components
3.9 Principles of Carburetion and Fuel Injection in SI Engines
3.10 Types of Carburettors and Their Constructional Details
3.10.1 Multiple and Compound Carburettors
3.10.2 Electronically Controlled Carburettors
3.10.3 Fuel Injection System
3.11 Continuous and Timed Injection System
3.12 Single-Point TBI and MPFI Systems
3.13 Fuel Supply System for CI Engine: General Layout and Components
3.14 TDI and CRDI System
3.15 Types of Fuel Injection Pumps and Their Constructional Details and Testing of Fuel Pumps
3.15.1 Distributor Fuel Injection Pump
3.15.2 Testing of Fuel Injection Pump
3.16 Fuel Injectors and Nozzles
3.17 Electronically Controlled Unit Fuel Injection System
3.18 Injection Timing and Its Importance
3.19 Spray Characteristics
3.20 Principles of Lubrication Systems
3.21 Friction and Wear Mechanics
3.22 Lubricants: Their Composition and Properties
3.23 Wet Sump Lubrication Device
3.24 Dry Sump Lubrication System
3.25 Mist Lubrication System
3.26 Principles of Cooling System
3.27 Liquid Cooling System
3.27.1 Pressurised Water Cooling System
3.27.2 Components of a Water Cooling system
3.28 Air Cooling System
3.29 Current Advancements in Cooling Systems
3.30 Principles of Air Intake and Exhaust
3.31 Air Cleaners and Silencers
3.32 Intake and Exhaust Manifolds
3.32.1 Intake Manifolds
3.32.2 Exhaust Manifolds
3.33 Tailpipe Emissions from Vehicular Engines
3.34 HC, CO, NO , PM Formation Process
3.34.1 Formation of Nitrogen Oxides
3.34.2 HC Emission
3.35 Methodologies Adopted to Reduce Emission
3.36 Current Advancements in Emission Control and Reduction
3.37 Principles of Turbocharging and Supercharging
3.37.1 Naturally Aspirated Engines
3.37.2 Forced Induction
3.38 Types of Superchargers and Their Constructional Details
3.39 Types of Turbochargers and Their Constructional Details
3.40 Engine Electronics and Management System
Summary
Multiple-Choice Questions
Review Questions
Chapter 4 Automotive Clutches
4.1 Introduction
4.2 Necessity and Functions of the Clutch
4.3 Working Principle of the Clutch
4.4 Classification of Clutches
4.5 Requirements of the Clutch
4.6 Torque Transmission Capacity of the Clutch
Number of Friction Surfaces
Surface Area/Size of the Friction Plate (Which Depends on the Mean Radius of the Friction Plate)
Pressure over the Disc
Coefficient of Friction of the Material Used
Elements of the Clutch and Their Construction
4.7 Construction and Working of the Single Plate Clutch
Construction
Diaphragm Clutch
4.8 Construction and Working of the Multi-Plate Clutch
4.9 Construction and Working of the Centrifugal Clutch
Centrifugally Operated Clutches
4.10 Construction and Working of Electromagnetic Clutch
4.11 Operating Mechanism of the Clutch
Mechanically Operated Clutch Linkage
Cable-Operated Clutch
4.12 Operating Mechanism of the Clutch: Hydraulic
4.13 Design Aspects of the Automotive Clutch
Summary
Multiple-Choice Questions
Review Questions
Chapter 5 Manual Transmission and Transaxles
5.1 Introduction
5.2 Various Types of Resistances
5.3 Motive Power, Traction and Tractive Efforts
5.4 Necessity of the Gear Box
5.5 Calculation of Gear Ratios
5.6 Construction and Working of the Constant Mesh Gear Box
5.7 Construction and Working of the Sliding Mesh Gear Box
5.8 Construction and Working of the Synchromesh Gear Box
5.9 Overdrive
5.10 Transfer Box Construction and Working
5.11 Heavy Vehicle Gear Boxes
5.11.1 Splitter Drive Gear Boxes
5.11.2 Range Change Gear Boxes
5.12 Gear Shifting Mechanisms
5.13 Gear Box Lubrication and Sealing
5.14 Transaxle Construction and Working
Summary
Multiple-Choice Questions
Review Questions
Chapter 6 Semiautomatic and Automatic Transmission
6.1 Introduction
6.2 Fluid Flywheel
6.2.1 Limitations
6.3 Torque Convertor
6.4 Planetary Gear Box
6.5 Continuous Variable Transmission System
6.6 Automatic Transmission System for Passenger Cars
6.7 Automatic Transaxles
6.8 Automatic Transmission System for Heavy Vehicles
6.9 Hydraulic Control System
6.10 Electrohydraulic Control System
6.11 Automated Manual Transmission System
Summary
Multiple-Choice Questions
Review Questions
Chapter 7 Propeller Shaft, Differential and Rear Axles
7.1 Introduction
7.2 Driveline Arrangements
7.2.1 Hotchkiss Drive
7.2.2 Torque Tube Drive
7.3 Propeller Shaft
7.4 Universal Joint
7.5 Slip Joint
7.6 Constant Velocity Joints
7.7 Final Drive Gears and Bearings
7.7.1 Bearings
7.8 Differential
7.8.1 Limited Slip Differential
7.9 Rear Axle Construction
7.10 Types of Rear Axles
7.11 Various Types of Loads Acting on the Rear Axles
7.12 Tandem Axle Drive for Heavy Vehicles
Summary
Multiple-Choice Questions
Review Questions
Chapter 8 Suspension System
8.1 Introduction
8.2 Basic Ride Considerations of the Vehicle
8.3 Functions of the Suspension System
8.4 Classification of the Suspension System
8.5 Independent Suspension System
8.6 Dependent Suspension Systems
8.6.1 Advantages of Axle Beam Suspension
8.6.2 Disadvantages of Axle Beam Suspension
8.7 Air Suspension
8.8 Rubber Suspensions
8.9 Types of Springs Used in the Suspension System
8.9.1 Leaf Springs
8.9.1.1 Benefits of Leaf Springs
8.9.2 Coil Springs
8.10 Dampers
8.11 Adaptive Suspension System
8.11.1 Soft Mode
8.11.2 Firm Mode
Summary
Multiple-Choice Questions
Review Questions
Chapter 9 Braking Systems
9.1 Introduction
9.2 Classification of Brakes
9.3 Drum Brakes and Disc Brakes
9.3.1 Leading and Trailing
9.3.2 Twin Leading Shoes
9.3.3 Duel Servo
9.3.4 Advantages of Drum Brakes
9.3.5 Disadvantage of Drum Brakes
9.3.6 Disc Brakes
9.4 Hydraulic Braking System Construction and Working
9.5 Air Brakes
9.5.1 System Actuation
9.6 Antilock Braking Systems
9.6.1 Wheel Speed Sensors
9.6.2 Operation
9.6.2.1 Normal Braking Condition
9.6.2.2 Pressure Holding
9.6.2.3 Pressure Reducing
9.6.2.4 Pressure Increasing
9.7 Parking Brakes
Summary
Multiple-Choice Questions
Review Questions
Chapter 10 Vehicle Body Engineering
10.1 Introduction
10.2 Functions of the Vehicle Body
10.3 Requirements of the Vehicle Body
10.4 Classification of Vehicle Body
10.5 Car Body Construction
10.5.1 Passenger Vehicles
10.5.2 Under Body Section
10.5.3 Body Side Assemblies
10.5.4 Shroud and Dash Panel Assembly
10.5.5 Roof
10.5.6 Back Window Aperture Panel
10.5.7 Rear End Assembly
10.5.8 Frontend Assembly
10.5.9 Front Wings
10.5.10 Front Door Panel Assembly
10.5.11 Bonnet Panel Assembly
10.6 Bus Body Construction
10.7 Body Mounting
10.7.1 U Bolts
10.7.2 Balata Packing
10.8 Body Materials
10.9 Various Loads Acting on the Vehicle Body and Their Analysis
10.9.1 Symmetric Vertical Load
10.9.2 Asymmetric Vertical Load
10.9.3 Longitudinal Loads
10.9.4 Side Loads
10.10 Anthropometric and Ergonomic Considerations
10.11 Upcoming Trends in Vehicle Body Manufacturing
Summary
Multiple-Choice Questions
Review Questions
Chapter 11 Front Axle and Steering Systems
11.1 Introduction
11.2 Functions of the Front Axle
11.3 Constructional Details of the Front Axle
11.4 Requirements of Steering
11.5 Principle of Correct Steering
11.6 Ackerman’s Steering Gear Mechanism
11.7 Steering Linkage Arrangements
11.8 Axle Beam Suspension Steering System Layout
11.9 Independent Suspension Steering System Layout
11.10 Steering Gear Boxes
11.11 Power-Assisted Steering
11.11.1 Introduction
11.11.2 The Need for Power-Assisted Steering
11.11.3 Hydraulic Power-Assisted Steering
11.11.4 Features of the Power-Assisted Steering System
11.11.5 Hydraulic Power-Assisted Steering Components
11.11.6 Speed-Sensitive Hydraulic Power-Assisted Steering
11.11.7 Electrohydraulic Power-Assisted Steering
11.11.8 Electrical Power-Assisted Steering
11.11.9 Electrical Power-Assisted Steering Components
11.11.9.1 Electrical Motor
11.11.9.2 Actuating System
11.11.9.3 Steering Input Sensors
11.11.9.4 Electronic Control Unit
11.11.9.5 Types of Electrical Power-Assisted Steering
Summary
Multiple-Choice Questions
Review Questions
Chapter 12 Wheels and Tyres
12.1 Introduction
12.2 Requirements of the Wheel
12.3 Classification of Wheels
12.4 Construction of Wired and Pressed Disc Wheels
12.5 Types of Rims and Their Constructional Details
12.5.1 Rim Designs
12.5.2 Well-Base Rims
12.5.3 5° Seat-Angle Well-Base Rim
12.5.4 Drop-Centre 15° Taper Rim
12.5.5 Detachable-Rim Wheels
12.5.6 Semi-Drop-Centre Two-Piece Rim
12.5.7 Wide-Base Two-Piece Rim
12.5.8 Wide-Base Three-Piece Rim
12.5.9 Divided Flat-Base Rim
12.6 Wheel Alignment and Balancing
12.6.1 Wheel Alignment
12.6.2 Wheel Balancing
12.7 Tyre Characteristics
12.7.1 Tyre
12.7.2 Tyre Properties
12.7.2.1 Non-Skidding
12.7.2.2 Uniform Wear
12.7.2.3 Load-Carrying Capacity
12.7.2.4 Cushioning
12.7.2.5 Tyre Noise
12.7.2.6 Balance
12.8 Cornering Properties of the Tyre
12.8.1 Static Load and Standard Wheel Height
12.8.2 Contact Patch
12.8.3 Cornering Force
12.8.4 Slip Angle
12.8.5 Pneumatic Trail and Self-Aligning Torque
12.8.6 Camber Thrust
12.9 Requirements of Tyres
12.10 Classification of Tyres
12.10.1 Tubed Tyres
12.10.2 Tubeless Tyre
12.10.3 Cross Ply Type
12.10.4 Radial Ply Type
12.10.5 Belted Bias Type
12.11 Tyre Construction
12.12 Tyre Treads
12.12.1 Symmetrical Tread Pattern
12.12.2 Asymmetrical Tread Pattern
12.12.3 Directional (Unidirectional) Tread Pattern
12.12.4 Asymmetrical and Vertical Tread Patterns
12.12.5 Non-directional Tread Patterns
12.13 Tyre Size and Designations
12.14 Factors Affecting Tyre Life
12.14.1 Selection of Correct Tyre and Its Installation
12.14.2 Tyre Pressure
12.14.3 Loading Capacity
12.14.4 Wheel Alignment
12.14.5 Car Speed
12.14.6 Tyre Temperature
12.14.7 Chassis Status
12.14.8 Road Conditions
12.14.9 Seasonal Factors
12.14.10 Driving Habits
12.14.11 Vehicle and Tyre Maintenance
12.15 Tyre Material
12.16 Tyre Re-treading
Summary
Multiple-Choice Questions
Review Questions
Chapter 13 Vehicle Aerodynamics
13.1 Introduction
13.2 Air Flow Fundamentals
13.3 Drag Forces
13.4 Lift Forces
13.5 Aerodynamic Stability
13.6 Car Body Drag Reduction
13.7 Aerodynamic Lift Control
13.8 Wind Tunnel
13.8.1 Open Loop
13.8.2 Closed Loop
13.9 Aerodynamics of Commercial Vehicles
13.10 Aerodynamics in Two-Wheelers
Summary
Multiple-Choice Questions
Review Questions
Chapter 14 Battery Electric, Hybrid Electric, and Fuel Cell Vehicles
14.1 Introduction
14.2 General Layout of a Battery Electric Vehicle
14.3 Basic Systems of Battery Electric Vehicles
14.4 General Layout of Hybrid Electric Vehicles
14.5 Basic Systems of HEVs
14.6 Operation and Types of Fuel Cell Vehicles
14.6.1 Polymer Electrolyte Membrane Fuel Cells (PEMFCS)
14.6.2 Direct Methanol Fuel Cells (DMFCs)
14.6.3 Alkaline Fuel Cells (AFCs)
14.6.4 Phosphoric Acid Fuel Cells (PAFCs)
14.6.5 Molten Carbonate Fuel Cells (MCFCs)
14.6.6 Solid Oxide Fuel Cells (SOFCs)
14.7 General Layout of Fuel Cell Vehicles
14.8 Characteristics of BEVs, HEVs and FCVs
14.9 Current Advancements in BEV, HEV and FCV Technology
Summary
Multiple-Choice Questions
Review Questions
Chapter 15 Vehicle Maintenance Practices
15.1 Introduction
15.2 Necessity of Maintenance
15.3 Types of Maintenance
15.3.1 Preventive Maintenance
15.3.1.1 Scheduled Preventive Maintenance
15.3.1.2 Condition-Based Preventive Maintenance
15.3.1.3 Predictive Maintenance
15.3.1.4 Proactive Maintenance
15.3.2 Breakdown Maintenance
15.4 Procedure and Methodologies Adopted
15.5 Maintenance Documentation
15.6 Advanced Techniques and Tools Used
15.6.1 Modern Tools Used
15.6.1.1 On-Board Diagnostics
15.6.1.2 Handheld
15.6.1.3 PC/Laptop with Scan Tool
15.6.1.4 Mobile Device (Phone or Tablet) Application
15.7 Recent Trends in Routine Maintenance
Summary
Multiple-Choice Questions
Review Questions
Bibliography
Index

Citation preview

Automotive Systems

Automotive Systems Principles and Practice

G. K. Awari, V. S. Kumbhar, and R. B. Tirpude

First edition published 2021 by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 and by CRC Press 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN © 2021 Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, LLC Reasonable efforts have been made to publish reliable data and information, but the author and ­publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material ­reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, access www.copyright. com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. For works that are not available on CCC please contact mpkbookspermissions@ tandf.co.uk Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging‑in‑Publication Data Names: Awari, G. K. (Engineer), author. | Kumbhar, Vijay S., author. | Tirpude, Raju B., author. Title: Automotive systems : principles and practice / G K Awari, Vijay Kumbhar, and Raju Tirpude. Description: First edition. | Boca Raton, FL : CRC Press/Taylor & Francis Group, LLC, 2021. | Includes index. Identifiers: LCCN 2020032529 (print) | LCCN 2020032530 (ebook) | ISBN 9780367498429 (hardback) | ISBN 9781003047636 (ebook) Subjects: LCSH: Automobiles—Design and construction. | Automobiles—Equipment and supplies. Classification: LCC TL240 .A95 2021 (print) | LCC TL240 (ebook) | DDC 629.2—dc23 LC record available at https://lccn.loc.gov/2020032529 LC ebook record available at https://lccn.loc.gov/2020032530 ISBN: 978-0-367-49842-9 (hbk) ISBN: 978-1-003-04763-6 (ebk) Typeset in Times by codeMantra

The book is dedicated to the late Sau. Shashikala K. Awari, for her divine blessings and inspiration.

Contents Preface....................................................................................................................xvii Acknowledgements..................................................................................................xix Abbreviations...........................................................................................................xxi Authors..................................................................................................................xxvii Chapter 1 Automobile Evaluation and Market Review.........................................1 1.1 1.2 1.3 1.4 1.5 1.6 1.7

Introduction................................................................................1 History and Evolution of Vehicles.............................................. 1 Indian Automotive Market.........................................................2 Global Automotive Market.........................................................5 Automotive Research Perspectives.............................................7 Indian and Global OEMs.......................................................... 12 Indian and Global Auto Components Manufacturers.............. 15 1.7.1 Industry Scenario........................................................ 15 1.7.2 Global Automotive Components Manufacturers......... 18 Summary.............................................................................................20 Multiple Choice Questions.................................................................. 21 Review Questions................................................................................ 21

Chapter 2 Vehicle Classification, Structure and Layouts..................................... 23 2.1 2.2 2.3 2.4

Introduction.............................................................................. 23 Classification of Vehicles......................................................... 23 Constructional Details of Vehicle Chassis and Body...............24 Basic Terminology and Legislative Requirements of a Vehicle as per CMVR and MVA..............................................25 2.4.1 Lead Dimensions of a Vehicle.....................................25 2.5 Various Systems of the Vehicle and Their Functions...............26 2.6 Various Types of Chassis Frames: Their Construction and Material.............................................................................. 29 2.7 Various Loads Acting on the Vehicle Chassis Frame, and Its Deformation......................................................................... 30 2.8 Types of Chassis and Vehicle Layouts, Advantages and Disadvantages........................................................................... 32 Summary............................................................................................. 36 Multiple-Choice Questions................................................................. 36 Review Questions................................................................................ 37

Chapter 3 Vehicular Engines............................................................................... 39 3.1 3.2

Introduction.............................................................................. 39 Working Principle and Terminology of the Engine................. 39 vii

viii

Contents

3.3

3.4 3.5 3.6 3.7 3.8 3.9 3.10

3.11 3.12 3.13 3.14 3.15

3.16 3.17 3.18 3.19 3.20 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29

Components of the IC Engine and Their Constructional Details..............................................................40 3.3.1 Piston and Rings..........................................................40 3.3.2 Connecting Rod and Bearings.................................... 41 3.3.3 Crankshaft Assembly and Bearings............................ 41 3.3.4 Cylinder Head and Gasket.......................................... 42 3.3.5 Cylinder Block, Crankcase and Head......................... 42 3.3.6 Crankshaft Assembly and Main Bearings.................. 42 3.3.7 Crankshaft Torsional Vibration Dampers................... 43 3.3.8 Valve Train.................................................................. 43 Classification of IC Engines..................................................... 43 Two-Stroke and Four-Stroke Engines......................................44 Comparison of Engines ...........................................................46 Selection of Engine as Per Functional Requirement................ 47 Fuel Supply System for SI Engines: General Layout and Components ............................................................................. 49 Principles of Carburetion and Fuel Injection in SI Engines..... 49 Types of Carburettors and Their Constructional Details......... 50 3.10.1 Multiple and Compound Carburettors........................ 52 3.10.2 Electronically Controlled Carburettors....................... 52 3.10.3 Fuel Injection System.................................................. 52 Continuous and Timed Injection System................................. 53 Single-Point TBI and MPFI Systems ...................................... 53 Fuel Supply System for CI Engine: General Layout and Components.............................................................................. 56 TDI and CRDI System............................................................. 57 Types of Fuel Injection Pumps and Their Constructional Details and Testing of Fuel Pumps........................................... 58 3.15.1 Distributor Fuel Injection Pump.................................. 58 3.15.2 Testing of Fuel Injection Pump................................... 58 Fuel Injectors and Nozzles....................................................... 59 Electronically Controlled Unit Fuel Injection System.............60 Injection Timing and Its Importance........................................60 Spray Characteristics ...............................................................60 Principles of Lubrication Systems............................................ 61 Friction and Wear Mechanics................................................... 62 Lubricants: Their Composition and Properties........................ 63 Wet Sump Lubrication Device ................................................64 Dry Sump Lubrication System................................................. 65 Mist Lubrication System.......................................................... 65 Principles o f Cooling System................................................... 67 Liquid Cooling System............................................................. 67 3.27.1 Pressurised Water Cooling System............................. 68 3.27.2 Components of a Water Cooling system..................... 68 Air Cooling System.................................................................. 70 Current Advancements in Cooling Systems............................. 71

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Contents

3.30 Principles of Air Intake and Exhaust....................................... 71 3.31 Air Cleaners and Silencers ...................................................... 71 3.32 Intake and Exhaust Manifolds.................................................. 72 3.32.1 Intake Manifolds......................................................... 72 3.32.2 Exhaust Manifolds...................................................... 72 3.33 Tailpipe Emissions from Vehicular Engines............................ 72 3.34 HC, CO, NOx, PM Formation Process..................................... 72 3.34.1 Formation of Nitrogen Oxides.................................... 72 3.34.2 HC Emission............................................................... 73 3.35 Methodologies Adopted to Reduce Emission........................... 74 3.36 Current Advancements in Emission Control and Reduction.... 74 3.37 Principles of Turbocharging and Supercharging...................... 74 3.37.1 Naturally Aspirated Engines ...................................... 75 3.37.2 Forced Induction......................................................... 75 3.38 Types of Superchargers and Their Constructional Details...... 75 3.39 Types of Turbochargers and Their Constructional Details...... 77 3.40 Engine Electronics and Management System.......................... 77 Summary............................................................................................. 79 Multiple-Choice Questions................................................................. 79 Review Questions................................................................................ 81 Chapter 4 Automotive Clutches........................................................................... 83 4.1 4.2 4.3 4.4 4.5 4.6

Introduction.............................................................................. 83 Necessity and Functions of the Clutch..................................... 83 Working Principle of the Clutch...............................................84 Classification of Clutches......................................................... 85 Requirements of the Clutch...................................................... 85 Torque Transmission Capacity of the Clutch........................... 86 Number of Friction Surfaces.................................................... 86 Surface Area/Size of the Friction Plate (Which Depends on the Mean Radius of the Friction Plate)................................ 86 Pressure over the Disc.............................................................. 86 Coefficient of Friction of the Material Used............................ 86 Elements of the Clutch and Their Construction....................... 87 4.7 Construction and Working of the Single Plate Clutch............. 89 Construction............................................................................. 89 Diaphragm Clutch ...................................................................90 4.8 Construction and Working of the Multi-Plate Clutch..............90 4.9 Construction and Working of the Centrifugal Clutch.............. 91 Centrifugally Operated Clutches.............................................. 91 4.10 Construction and Working of Electromagnetic Clutch............92 4.11 Operating Mechanism of the Clutch........................................92 Mechanically Operated Clutch Linkage...................................92 Cable-Operated Clutch.............................................................92 4.12 Operating Mechanism of the Clutch: Hydraulic...................... 93

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Contents

4.13 Design Aspects of the Automotive Clutch............................... 93 Summary.............................................................................................94 Multiple-Choice Questions.................................................................94 Review Questions................................................................................94 Chapter 5 Manual Transmission and Transaxles................................................. 95 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 5.10 5.11

Introduction.............................................................................. 95 Various Types of Resistances................................................... 95 Motive Power, Traction and Tractive Efforts...........................96 Necessity of the Gear Box........................................................97 Calculation of Gear Ratios....................................................... 98 Construction and Working of the Constant Mesh Gear Box....99 Construction and Working of the Sliding Mesh Gear Box.... 100 Construction and Working of the Synchromesh Gear Box.... 101 Overdrive................................................................................ 103 Transfer Box Construction and Working................................ 104 Heavy Vehicle Gear Boxes..................................................... 104 5.11.1 Splitter Drive Gear Boxes ........................................ 105 5.11.2 Range Change Gear Boxes........................................ 105 5.12 Gear Shifting Mechanisms..................................................... 106 5.13 Gear Box Lubrication and Sealing......................................... 107 5.14 Transaxle Construction and Working..................................... 107 Summary .......................................................................................... 108 Multiple-Choice Questions............................................................... 108 Review Questions.............................................................................. 109

Chapter 6 Semiautomatic and Automatic Transmission.................................... 111 6.1 6.2

Introduction............................................................................ 111 Fluid Flywheel........................................................................ 111 6.2.1 Limitations................................................................ 114 6.3 Torque Convertor.................................................................... 114 6.4 Planetary G  ear Box................................................................ 115 6.5 Continuous Variable Transmission System............................ 116 6.6 Automatic Transmission System for Passenger Cars............. 117 6.7 Automatic Transaxles............................................................. 118 6.8 Automatic Transmission System for Heavy Vehicles............. 119 6.9 Hydraulic Control System...................................................... 119 6.10 Electrohydraulic Control System............................................ 120 6.11 Automated Manual Transmission System.............................. 121 Summary........................................................................................... 122 Multiple-Choice Questions............................................................... 123 Review Questions.............................................................................. 123

xi

Contents

Chapter 7 Propeller Shaft, Differential and Rear Axles.................................... 125 7.1 7.2

Introduction............................................................................ 125 Driveline Arrangements......................................................... 125 7.2.1 Hotchkiss Drive......................................................... 125 7.2.2 Torque Tube Drive..................................................... 126 7.3 Propeller Shaft........................................................................ 126 7.4 Universal Joint........................................................................ 127 7.5 Slip Joint................................................................................. 127 7.6 Constant Velocity Joints......................................................... 128 7.7 Final Drive Gears and Bearings............................................. 131 7.7.1 Bearings.................................................................... 132 7.8 Differential............................................................................. 132 7.8.1 Limited Slip Differential........................................... 133 7.9 Rear Axle Construction.......................................................... 134 7.10 Types of Rear Axles............................................................... 135 7.11 Various Types of Loads Acting on the Rear Axles................ 136 7.12 Tandem Axle Drive for Heavy Vehicles ................................ 136 Summary........................................................................................... 137 Multiple-Choice Questions............................................................... 137 Review Questions.............................................................................. 138 Chapter 8 Suspension System............................................................................ 139 8.1 8.2 8.3 8.4 8.5 8.6

Introduction............................................................................ 139 Basic Ride Considerations of the Vehicle............................... 140 Functions of the Suspension System...................................... 140 Classification of the Suspension System................................ 140 Independent Suspension System............................................. 141 Dependent Suspension Systems............................................. 145 8.6.1 Advantages of Axle Beam Suspension..................... 146 8.6.2 Disadvantages of Axle Beam Suspension................. 146 8.7 Air Suspension........................................................................ 146 8.8 Rubber Suspensions ............................................................... 148 8.9 Types of Springs Used in the Suspension System.................. 148 8.9.1 Leaf Springs.............................................................. 149 8.9.1.1 Benefits of Leaf Springs ........................... 150 8.9.2 Coil Springs............................................................... 151 8.10 Dampers.................................................................................. 152 8.11 Adaptive Suspension System.................................................. 154 8.11.1 Soft Mode.................................................................. 155 8.11.2 Firm Mode................................................................. 155 Summary........................................................................................... 156 Multiple-Choice Questions............................................................... 156 Review Questions.............................................................................. 156

xii

Contents

Chapter 9 Braking Systems................................................................................ 157 9.1 9.2 9.3

Introduction............................................................................ 157 Classification of Brakes.......................................................... 157 Drum Brakes and Disc Brakes............................................... 158 9.3.1 Leading and Trailing................................................. 158 9.3.2 Twin Leading Shoes.................................................. 160 9.3.3 Duel Servo................................................................. 160 9.3.4 Advantages of Drum Brakes..................................... 160 9.3.5 Disadvantage of Drum Brakes.................................. 162 9.3.6 Disc Brakes............................................................... 162 9.4 Hydraulic Braking System Construction and Working.......... 162 9.5 Air Brakes.............................................................................. 167 9.5.1 System Actuation...................................................... 168 9.6 Antilock Braking Systems...................................................... 169 9.6.1 Wheel Speed Sensors................................................ 169 9.6.2 Operation................................................................... 170 9.6.2.1 Normal Braking Condition........................ 170 9.6.2.2 Pressure Holding........................................ 170 9.6.2.3 Pressure Reducing..................................... 171 9.6.2.4 Pressure Increasing.................................... 171 9.7 Parking Brakes ...................................................................... 171 Summary........................................................................................... 172 Multiple-Choice Questions............................................................... 172 Review Questions.............................................................................. 173

Chapter 10 Vehicle Body Engineering................................................................ 175 10.1 10.2 10.3 10.4 10.5

Introduction............................................................................ 175 Functions of the Vehicle Body............................................... 175 Requirements of the Vehicle Body......................................... 176 Classification of Vehicle Body............................................... 176 Car Body Construction........................................................... 178 10.5.1 Passenger Vehicles.................................................... 178 10.5.2 Under Body Section.................................................. 179 10.5.3 Body Side Assemblies............................................... 179 10.5.4 Shroud and Dash Panel Assembly............................. 179 10.5.5 Roof........................................................................... 180 10.5.6 Back Window Aperture Panel................................... 180 10.5.7 Rear End Assembly................................................... 180 10.5.8 Frontend Assembly.................................................... 181 10.5.9 Front Wings............................................................... 181 10.5.10 Front Door Panel Assembly...................................... 182 10.5.11 Bonnet Panel Assembly ............................................ 183 10.6 Bus Body Construction .......................................................... 184 10.7 Body Mounting....................................................................... 185 10.7.1 U Bolts....................................................................... 186

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10.7.2 Balata Packing........................................................... 186 10.8 Body Materials....................................................................... 187 10.9 Various Loads Acting on the Vehicle Body and Their Analysis........................................................................ 188 10.9.1 Symmetric Vertical Load.......................................... 189 10.9.2 Asymmetric Vertical Load........................................ 189 10.9.3 Longitudinal Loads................................................... 190 10.9.4 Side Loads................................................................. 190 10.10 Anthropometric and Ergonomic Considerations ................... 190 10.11 Upcoming Trends in Vehicle Body Manufacturing .............. 191 Summary........................................................................................... 192 Multiple-Choice Questions............................................................... 193 Review Questions.............................................................................. 193 Chapter 11 Front Axle and Steering Systems...................................................... 195 11.1 Introduction............................................................................ 195 11.2 Functions of the Front Axle ................................................... 195 11.3 Constructional Details of the Front Axle............................... 196 11.4 Requirements of Steering....................................................... 196 11.5 Principle of Correct Steering ................................................. 197 11.6 Ackerman’s Steering Gear Mechanism.................................. 199 11.7 Steering Linkage Arrangements............................................ 199 11.8 Axle Beam Suspension Steering System Layout...................200 11.9 Independent Suspension Steering System Layout.................. 201 11.10 Steering Gear Boxes............................................................... 201 11.11 Power-Assisted Steering......................................................... 203 11.11.1 Introduction............................................................. 203 11.11.2 The Need for Power-Assisted Steering...................203 11.11.3 Hydraulic Power-Assisted Steering.........................204 11.11.4 Features of the Power-Assisted Steering System....204 11.11.5 Hydraulic P  ower-Assisted Steering Components....204 11.11.6 Speed-Sensitive Hydraulic Power-Assisted Steering.....................................................................205 11.11.7 Electrohydraulic Power-Assisted Steering.............. 205 11.11.8 Electrical Power-Assisted Steering.........................205 11.11.9 Electrical Power-Assisted Steering Components....206 11.11.9.1 Electrical Motor......................................206 11.11.9.2 Actuating System....................................206 11.11.9.3 Steering Input Sensors............................206 11.11.9.4 Electronic Control Unit .........................207 11.11.9.5 Types of Electrical Power-Assisted Steering ..................................................207 Summary...........................................................................................207 Multiple-Choice Questions...............................................................208 Review Questions..............................................................................209

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Chapter 12 Wheels and Tyres.............................................................................. 211 12.1 12.2 12.3 12.4 12.5

Introduction............................................................................ 211 Requirements of the Wheel.................................................... 211 Classification of Wheels......................................................... 212 Construction of Wired and Pressed Disc Wheels.................. 212 Types of Rims and Their Constructional Details .................. 213 12.5.1 Rim Designs.............................................................. 213 12.5.2 Well-Base Rims......................................................... 214 12.5.3 5° Seat-Angle Well-Base Rim................................... 214 12.5.4 Drop-Centre 15° Taper Rim...................................... 214 12.5.5 Detachable-Rim Wheels........................................... 214 12.5.6 Semi-Drop-Centre Two-Piece Rim........................... 215 12.5.7 Wide-Base Two-Piece Rim....................................... 215 12.5.8 Wide-Base Three-Piece Rim.................................... 215 12.5.9 Divided Flat-Base Rim.............................................. 215 12.6 Wheel Alignment and Balancing........................................... 215 12.6.1 Wheel Alignment...................................................... 215 12.6.2 Wheel Balancing....................................................... 216 12.7 Tyre Characteristics................................................................ 217 12.7.1 Tyre............................................................................ 217 12.7.2 Tyre Properties.......................................................... 217 12.7.2.1 Non-Skidding............................................. 217 12.7.2.2 Uniform Wear............................................ 217 12.7.2.3 Load-Carrying Capacity............................ 218 12.7.2.4 Cushioning ................................................ 218 12.7.2.5 Tyre Noise ................................................. 218 12.7.2.6 Balance ..................................................... 218 12.8 Cornering Properties of the Tyre............................................ 218 12.8.1 Static Load and Standard Wheel Height................... 218 12.8.2 Contact Patch ............................................................ 218 12.8.3 Cornering Force ....................................................... 219 12.8.4 Slip Angle.................................................................. 219 12.8.5 Pneumatic Trail and Self-Aligning Torque .............. 219 12.8.6 Camber Thrust ......................................................... 219 12.9 Requirements of Tyres............................................................ 219 12.10 Classification of Tyres ........................................................... 220 12.10.1 Tubed Tyres............................................................... 220 12.10.2 Tubeless Tyre............................................................. 220 12.10.3 Cross Ply Type .......................................................... 222 12.10.4 Radial Ply Type......................................................... 222 12.10.5 Belted Bias Type........................................................ 222 12.11 Tyre Construction................................................................... 223 12.12 Tyre Treads ............................................................................ 223 12.12.1 Symmetrical Tread Pattern ......................................224 12.12.2 Asymmetrical Tread Pattern ....................................224

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12.12.3 Directional (Unidirectional) Tread Pattern ............224 12.12.4 Asymmetrical and Vertical Tread Patterns ............224 12.12.5 Non-directional Tread Patterns ..............................224 12.13 Tyre Size and Designations ...................................................224 12.14 Factors Affecting Tyre Life.................................................... 225 12.14.1 Selection of Correct Tyre and Its Installation......... 225 12.14.2 Tyre Pressure........................................................... 225 12.14.3 Loading Capacity.................................................... 226 12.14.4 Wheel Alignment.................................................... 226 12.14.5 Car Speed................................................................ 227 12.14.6 Tyre Temperature.................................................... 227 12.14.7 Chassis Status......................................................... 227 12.14.8 Road Conditions...................................................... 227 12.14.9 Seasonal Factors..................................................... 227 12.14.10  Driving Habits........................................................ 227 12.14.11  Vehicle and Tyre Maintenance................................ 227 12.15 Tyre Material.......................................................................... 227 12.16 Tyre Re-treading..................................................................... 228 Summary........................................................................................... 229 Multiple-Choice Questions............................................................... 229 Review Questions.............................................................................. 230 Chapter 13 Vehicle Aerodynamics...................................................................... 231 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8

Introduction............................................................................ 231 Air Flow Fundamentals.......................................................... 231 Drag Forces............................................................................ 232 Lift Forces.............................................................................. 233 Aerodynamic Stability............................................................ 234 Car Body Drag Reduction...................................................... 234 Aerodynamic Lift Control...................................................... 236 Wind Tunnel........................................................................... 237 13.8.1 Open Loop ................................................................ 237 13.8.2 Closed Loop.............................................................. 238 13.9 Aerodynamics of Commercial Vehicles................................. 238 13.10 Aerodynamics in Two-Wheelers............................................ 239 Summary...........................................................................................240 Multiple-Choice Questions...............................................................240 Review Questions.............................................................................. 241

Chapter 14 Battery Electric, Hybrid Electric, and Fuel Cell Vehicles................ 243 14.1 14.2 14.3 14.4

Introduction ........................................................................... 243 General Layout of a Battery Electric Vehicle......................... 243 Basic Systems of Battery Electric Vehicles ...........................244 General Layout of Hybrid Electric Vehicles.......................... 245

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14.5 Basic Systems of HEVs.......................................................... 245 14.6 Operation and Types of Fuel Cell Vehicles............................246 14.6.1 Polymer Electrolyte Membrane Fuel Cells (PEMFCS) ................................................................ 247 14.6.2 Direct Methanol Fuel Cells (DMFCs) ...................... 247 14.6.3 Alkaline Fuel Cells (AFCs) ......................................248 14.6.4 Phosphoric Acid Fuel Cells (PAFCs) .......................248 14.6.5 Molten Carbonate Fuel Cells (MCFCs) ...................248 14.6.6 Solid Oxide Fuel Cells (SOFCs)................................248 14.7 General Layout of Fuel Cell Vehicles..................................... 249 14.8 Characteristics of BEVs, HEVs and FCVs............................. 249 14.9 Current Advancements in BEV, HEV and FCV Technology ..... 250 Summary .......................................................................................... 251 Multiple-Choice Questions............................................................... 251 Review Questions.............................................................................. 251 Chapter 15 Vehicle Maintenance Practices......................................................... 253 15.1 Introduction............................................................................ 253 15.2 Necessity of Maintenance ..................................................... 253 15.3 Types of Maintenance............................................................ 254 15.3.1 Preventive Maintenance............................................ 254 15.3.1.1 Scheduled Preventive Maintenance........... 254 15.3.1.2 Condition-Based Preventive Maintenance............................................ 255 15.3.1.3 Predictive Maintenance............................. 255 15.3.1.4 Proactive Maintenance.............................. 255 15.3.2 Breakdown Maintenance........................................... 256 15.4 Procedure and Methodologies Adopted................................. 257 15.5 Maintenance Documentation................................................. 258 15.6 Advanced Techniques and Tools Used................................... 258 15.6.1 Modern Tools Used................................................... 259 15.6.1.1 On-Board Diagnostics............................... 259 15.6.1.2 Handheld.................................................... 259 15.6.1.3 PC/Laptop with Scan Tool......................... 259 15.6.1.4 Mobile Device (Phone or Tablet) Application ............................................... 259 15.7 Recent Trends in Routine Maintenance ................................260 Summary........................................................................................... 261 Multiple-Choice Questions............................................................... 262 Review Questions.............................................................................. 262 Bibliography.......................................................................................................... 263 Index....................................................................................................................... 273

Preface The term “automotive” or “automobile” is used to refer to a vehicle which can be moved by itself. In other words, an automobile is a self-propelled vehicle. It is used for the transportation of passengers and goods from one place to another on the ground. It consists of a frame supported by a body and power-producing and powertransmitting units. These units are further supported by tyres and wheels, which are connected by springs and axles. In general, the required power is produced by internal combustion engines, and this power is transmitted to the rear wheels through various transmission systems, such as clutch, propeller shaft, gear box, differential units, etc. The various units are held together and arranged on the frame in proper positions. The automobile is propelled through the friction between tyre and ground. The superstructure or body of the automobile provides protection and comfort to the passengers. Modern automobiles are produced using complex components and machinery and therefore careful attention is needed to make them perform the required functions in a safe, economical and efficient way. Thus, any mechanical or automobile engineer is required to have an in-depth knowledge of the various ­components and functions of automobiles. The organisation of the chapters is as follows (1) Automobile Evaluation and Review (2) Vehicle Classification Structure and Layouts (3) Vehicular Engines (4) Automotive Clutches (5) Manual Transmission and Transaxles (6) Semiautomatic and Automatic Transmission (7) Propeller Shaft, Differential and Rear Axles (8) Suspension System (9) Braking Systems (10) Vehicle Body Engineering (11) Front Axle and Steering Systems (12) Wheels and Tyres (13) Vehicle Aerodynamics (14) Battery-Electric Vehicle and Fuel Cell Vehicles (15) Vehicle Maintenance Practices. All the topics are treated elaborately with examples of advance vehicles running today. A continues change in the various technologies in automobile engineering and integration of various systems has made the job of engineers and technician more challenging. This book intends to be more accessible to readers who have not had formal training in physical sciences and mathematics (as well as those who have) to understand the functional operation of automotive systems. Many new diagrams (two- and three-dimensional) as well as photographs have been added to make the learning more simple. Introduction to Automotive Systems: Principles and Practice, covers all areas of automotive systems including modern automotive system introduced in the last decade. The text presents all systems together, making it easier for the reader to see how automotive systems are intertwined and connected. The book’s 15 chapters divide the content into individual topics to make it easier for budding technicians and engineers to learn and master the material. Offering a solid foundation in the basics, this text uniquely addresses complete solutions to automotive systems procedures without being overwhelming. The present book has a strong engineering focus, including electronic components/subsystems and systems found in contemporary automobiles, and it emphasises on what students need to know about the vehicles of yesterday, today and tomorrow. xvii

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Preface

This book is presented to the students and teachers community, containing c­ omprehensive treatment of the subject matter in a simple, lucid manner. It encompasses a large number of systems properly graded, including typical examples, from an examination point of view. The book is mainly targeted at diploma, graduate and postgraduate courses in engineering in most of the universities in USA and Asian continent. This book serves as an ideal resource for students of Mechanical, Automobile, Production, and Mechatronics engineering and practising technicians and engineers. However, to err is human, so some errors and omissions may be encountered in the book. The authors will be highly indebted to and welcome suggestions to improve the book. At the end of each chapter, multiple-choice questions and review questions have been added to make the book a comprehensive unit in all respects. This book is also useful to prepare the readers for competitive examinations like GATE, IES, UPSC, MPSC and other public sector undertaking exams. Salient features of the book: i. Each chapter contains learning objectives, self-review questions and ­exercises with answers. ii. It progresses from beginner to more advanced material at an easy-to-follow pace, the book utilises examples throughout to aid readers. iii. The book contains an in-depth coverage of concepts and techniques in its 15 chapters, including future generation vehicles, i.e. electric vehicles. iv. Throughout the text, tables, figures and assembly drawings are presented to illustrate the concepts and techniques. At the end of each chapter, to test conceptual understanding of the subject and put theory into practice, review questions are included. v. The book follows a simple and lucid style.

Acknowledgements Accomplishing a task is never a solo effort; it is the result of valuable contribution of numbers of individuals in a direct or indirect manner. This helped us in making this book a success. We extend our gratitude and acknowledge those guiding lights that imbibed in us the right ingredient and helped us to accomplish this task. Automotive Systems: Principles and Practice is the outcome of classroom experiences of the authors in department of Automobile Engineering, Government Polytechnic, Nagpur. We are grateful to Dr. Abhay Wagh, Director, Directorate of Technical Education, Mumbai MS (India), Dr. Vinod Mohitkar, Director, MSBTE, Mumbai, MS, Dr. Ram Nibudey, Joint Director, Technical Education, Regional office, Nagpur, for their inspiration, guidance and support to develop the comprehensive book for the benefit of students and teaching fraternity. We are also thankful to Dr. C. S. Thorat, Principal of Government Polytechnic, Jalna, Dr. M. B. Daigavane, Principal Government Polytechnic, Brahmapuri, and Prof. D. S. Kulkarni, Principal of Government Polytechnic, Nagpur, for extending the laboratory facilities of the institute and support to pursue the research work. In preparing the manuscript of this book, we have benefitted immensely from referring to many books, publications and online sources, such as website and open source material. We express our gratitude to all those authors, publications, and publishers; many of them have been listed in the bibliography. If anybody is left out inadvertently, we seek their pardon. The authors are grateful to Prof. Dr. Sandeep Salodkar, Punajb engineering college, Chandigarh, Prof. Dr. Jaji Varghese, Aryabhat Polytechnic, New Delhi, Prof. Dr. S. Velumani, Velalar College of Engineering and Technology, Erode, Prof. Dr. Yusuf Ali, Director, Lords Institute of engineering, Hyderabad and Dr. S. W. Rajurkar, Government college of engineering, Chandrapur, Dr. K. S. Dixit, Government polytechnic, Nagpur for their constant motivation and consistent help while developing this text. We sincerely acknowledge with deep sense of gratitude to our mentors Dr. D. G. Wakde, Dr. L. B. Bhuyar, Dr. D. K. Parbat, Dr. G. V. Gotmare, Dr. D. N. Kongre, Dr. Achal Shahare and Dr. H. N. Warhatkar, who have supported us and have been a source of inspiration. We are obliged to all leading automobile manufacturers of Nagpur region for their support and help during the entire project duration. We thank CRC Press, Taylor & Francis Group, especially Dr. Gagandeep Singh, Editor who has kept our morale high and helped us in preparing and maintaining our schedules, for facilitating the work, for the regular updates and for standing behind us patiently during this entire project. We acknowledge our sincere thanks to Ms. Saranya PN, Project Manager, for copyediting the manuscript and extending the assistance at each stage of project. We are also grateful to Prof. Vidhyadhar Kshirsagar, Prof. Sandesh Goswami and Prof. Yogesh Ramteke for extending the CAD facilities for figures and drawings in the book. We are indeed grateful to our family members Mrs. Jaya Awari, Master Vedant Awari, Mr. Keshavrao Awari, Mr. Shankar Kumbhar, Mrs. Ranjana Kumbhar, Mrs. Shubhangi Kumbhar, baby Vedashree Kumbhar, and MAA Sheela, mother Laxmibai, xix

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Acknowledgements

Mrs. Dr. Pranali Tirpude, Master Pushpak Tirpude, Ms. Anushka Tirpude, for their timely help in all endeavours of this book, without which this book would not have seen the light of day. Last but most important, we bow our heads to the greatness of Almighty God and our parents for making this experience one of the most technologically gratifying moments of our lives. We hope that the book serves its purpose to its readers and that we will continue to get their support and suggestions. Suggestions and comments to improve the book in content and style are always welcome and will be appreciated, acknowledged and incorporated in future editions of the book.

Abbreviations ABC ABS ABDC AC A/C ACL ACT A/F AIR ALB ARCS ASD ASF ASR ATC ATDC ATF AWD AWS BAS BBDC BDC BEV BHP BMEP BOFT BSFC BTDC CAD CAFE CAG CATS CB CBE Cd CD CFC CGI CI CN CNG

Active body control (Mercedes-Benz) Anti-Blockier-System (German) – anti-lock braking system After bottom dead centre (engine timing) Alternating current Air-conditioning Automatic chassis lubrication (commercial vehicles) Air charge temperature Air/fuel ratio Air injection reactor (emission control) Anti-lock brakes (Honda) Active roll control system (Citroen) Automatic slip-control differential Audi space frame (aluminium body construction) Antriebs-Schlupf-Regelung (German) – anti-slip regulation or traction control Automatic temperature control After top dead centre (engine timing) Automatic transmission fluid All-wheel drive (also 4WD) All-wheel steering (also 4WS) Brake assist system Before bottom dead centre (engine timing) Bottom dead centre (engine timing) Battery-electric vehicle Brake horsepower Brake mean effective pressure Bearing oil film thickness Brake-specific fuel consumption Before top dead centre (engine timing) Computer aided design Corporate average fuel economy (American) Computer aided gearshift (Scania) Computer active technology suspension (Jaguar) Contact breaker Cab behind engine (commercial vehicles) Coefficient of drag (vehicle aerodynamics) Capacity discharge (ignition system) Chlorofluorocarbon (refrigerant) Compact graphite iron Compression ignition (diesel engines) Cetane number (diesel fuel ignition rating) Compressed natural gas (fuels) xxi

xxii

CO CO2 COE CP CR CRS CTX CV CVT Cw Cx DC DERV DI DIS DISI DOHC DRP DSC DSG DWB EBA EBFD EBS ECI ECM ECS ECT ECU EDC EFI EGR ELV EMS EP EPAS EPHS EPS ESP ETC ETS EUI EVC EVO FCEV

Abbreviations

Carbon monoxide (emission control) Carbon dioxide (global warming) Cab over engine (commercial vehicles) Centre of pressure (vehicle aerodynamics) Compression ratio (engine) Common rail system (diesel fuel injection) Continuously variable transaxle (Ford) Constant velocity (universal joints) Continuously variable transmission Coefficient of drag (German) – vehicle aerodynamics Coefficient of drag (French) – vehicle aerodynamics Direct current Diesel engine road vehicles (fuel) Direct injection Direct ignition system (no distributor) Direct injection spark ignition Double overhead camshafts Dynamic rear proportioning (brakes) Dynamic stability control Direct shift gearbox (Volkswagen group) Double-wishbone suspension Emergency brake assist Electronic brake force distribution Electronic braking system (air brakes) Electronically controlled injection Electronic control module Evaporative control system (fuel system); electronically controlled suspension Engine coolant temperature Electronic control unit Electronic diesel control Electronic fuel injection Exhaust gas recirculation (emission control) End-of-life vehicle (materials recycling) Engine management system Extreme pressure (lubricants) Electrical power-assisted steering (NSK-RHP) Electrically powered hydraulic steering (TRW) Electric power steering Electronic stability programme Electronic traction control Enhanced traction system (General Motors) Electronic unit injector (Lucas Diesel) Exhaust valve closed (engine timing) Exhaust valve open (engine timing) Fuel cell electric vehicle

Abbreviations

FHP FWD GCW GCWR GDI GRP GTW GV GVW GVWR GWP HC HDC HEV HFC HGV HT HUCR HVAC IFS IHP INJ IOE IPM IRS IVC IVO KPI LCV LGV LI LNG LPG LS LSD MAF MAP MOFT MON MPI MPV NO NOAT NVH OAT OBD

Friction horsepower Front-wheel drive Gross combination weight (articulated vehicles) Gross combined weight rating (vehicle and trailer) Gasoline direct injection (Mitsubishi) Glass-reinforced plastics Gross train weight (drawbar vehicles) Governor valve (automatic transmissions) Gross vehicle weight (rigid vehicles) Gross vehicle weight rating Greenhouse warming potential (refrigerants) Hydrocarbons (emission control) Hill descent control (ABS system) Hybrid-electric vehicle Hydrofluorocarbon (refrigerant) Heavy goods vehicle High tension Highest useful compression ratio Heating, ventilation and air-conditioning Independent front suspension Indicated horsepower Injection (timing mark) Inlet over exhaust (obsolete valve layout) Integrated power module (hybrid electric vehicles) Independent rear suspension Inlet valve closed (valve timing) Inlet valve open (valve timing) King-pin inclination (steering) Light commercial vehicle Large goods vehicle Load index (tyres) Liquefied natural gas (fuels) Liquid petroleum gas (fuels) Leading shoe (drum brakes) Limited slip differential Mass air flow (engines) Manifold absolute pressure Minimum oil film thickness Motor octane number (more demanding ON test) Multi-point injection Multi-purpose vehicle (people carrier) Nitrogen oxides (emission control) Nitrite organic acid technology (coolants) Noise, vibration and harshness (vehicle refinement testing) Organic acid technology (coolants) On-board diagnosis

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OD ODP OHC OHV ON PAS PBD PCM PCV PEM PFI PM PR PSV PTFE PTO PVC PZEV RC RON RTV RWD SAMT SBC SBR SCA SCR SCS SEFI SFC SFI SG SI SLA SOHC SPI SRS SUV SV TAC TBI TC TCI TCM

Abbreviations

Overdrive Ozone depletion potential (refrigerants) Overhead camshaft Overhead valves Octane number (petrol anti-knock rating) Power-assisted steering Polybutadiene (tyres) Power train control module (engine and transmission) Positive crankcase ventilation (emission control) Polymer electrolyte membrane (fuel cells) (or proton exchange membrane) Port fuel injection (petrol engines) Particulate matter (diesel emission control) Ply-rating (tyres) Public service vehicle Polytetrafluoroethylene Power take-off (commercial vehicles) Polyvinyl chloride Partial zero emission vehicle Roll-centre (suspension geometry) Research octane number (less demanding ON test) Room temperature vulcanizing (sealant) Rear-wheel drive Semiautomated mechanical transmission (Eaton) Stand-by-control (electronic transmission control ZF) Styrene-butadiene rubber (tyres) Supplemental coolant additives Selective catalytic reduction (emission control) Stop control system (girling) Sequential electronically controlled fuel injection (Ford) Specific fuel consumption Sequential fuel injection Spheroidal graphite (high-strength cast iron) Spark ignition (petrol engines) Short and long arm (American) – suspension linkage Single overhead camshaft Single point injection (petrol engines) Supplemental restraint system (airbags) Sports utility vehicle Side valves (obsolete valve layout) Thermostatic air cleaner Throttle body injection (SPI) Twin carburettors Transistorized coil ignition Transmission control module

Abbreviations

TCS TDC TDI TEL TML TPS TS TV TVS TWC TXV UJ ULEV VCP VCU VDC VGT VI VIP VIVT VKPI VSC VTG VTT VVT VVTL WOT ZEV

Transmission controlled spark (engine intervention system) Top dead centre (engine timing) Turbocharged direct injection (diesel engines) Tetra ethyl lead (petrol anti-knock additive) Tetra methyl lead (as above) Throttle position sensor Trailing shoe (drum brakes) Throttle valve (engine and automatic transmissions) Thermal vacuum switch (exhaust gas recirculation) Three-way catalyst (emission control) Thermostatic expansion valve (refrigeration) Universal joint Ultra-low emission vehicle Variable cam phasing (valve timing) Viscous coupling unit (transmission) Vehicle dynamics control (Bosch) Variable-geometry turbocharger Viscosity index (lubricants) Vehicle intrusion protection (Toyota) Variable inlet valve timing Virtual king-pin inclination (steering) Vehicle skid control Variable turbine geometry (turbocharging) Variable twin turbo (turbocharging) Variable valve timing Variable valve timing and lift Wide-open throttle Zero emission vehicle

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Authors Dr. G. K. Awari received his BE from RTM Nagpur University, Nagpur, Maharashtra, India, in 1991 and an ME from Thapar University, Patiala, Punjab, India, in 1995, both in Mechanical engineering. He earned his PhD from Sant Gadgebaba Amravati University, Amravati, Maharashtra, India, in 2007. He has more than 25 years of teaching experience at the diploma, undergraduate, postgraduate and research levels. He has taught various subjects, such as fluid power and machinery, computer graphics, automation engineering, operation research, and machine design. His areas of interest are graphical modelling of computational fluid dynamics (CFD) and vehicle dynamics. Dr. Awari has 221 citations, including 33 international journal publications, 22 international conference publications, 11 national conference publications, 3 patents and 1 product developed for the automobile manufacturing industry to his name. Seventeen research scholars have completed PhD in mechanical engineering under his supervision in three Indian universities. He is also a recipient of “Best Principal Award” and “Best paper award” at various national and international conferences. He has contributed to the development of academics as a Board of Study (BOS) Member at Goa University, Goa; SG Amravati University, Amravati; and RTM Nagpur University, Nagpur. He is presently a BOS member in Yeshwantrao Chavan College of Engineering (YCCE, an autonomous institute), Nagpur, RTM Nagpur University, Nagpur, GH Raisoni University, Chindwara (MP) and BOS Chairman of Automobile Engineering at Government Polytechnic (GP), Nagpur. He is also recognised by AICTE, New Delhi as “Margdarshak for NBA Accreditation” of mentee institutes. Dr. Awari has authored eight books, two with CRC Press, Taylor & Francis Group, London, and others with renowned international publishers like Mercury International Publication, New Delhi, and New Age India Publisher Ltd. New Delhi. He has also developed more than 20 video tutorials/e-content modules for the benefit of students/teachers and his method of presentation/lecture modules is appreciated by many staff and students. Prof. V.S. Kumbhar r eceived his BE and ME in automobile engineering from Shivaji University Kolhapur, Maharashtra, India, in 2007 and 2013, respectively. His 13 years of experience in the field include: 4 years of industrial experience in automobile manufacturing engineering and 8 years of teaching experience at the undergraduate level. Professor Kumbhar is pursuing Ph.D. in Mechanical Engineering at GH Raisoni University, Amravati. He has taught various subjects like automobile engines, automobile systems, automobile design, machine design, strength of materials, advanced engines and xxvii

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automobile engineering. His areas of interest are fuels and combustion and emission control systems. He has more than 10 international journal publications to his credit. He has contributed to the development of Academics as Subject Expert for Maharashtra State Board of Technical Education (MSBTE), Mumbai. Professor Kumbhar is presently BOS member of Automobile Engineering at Government Polytechnic (GP), Nagpur. He is currently working in the Automobile Engineering Department at Government Polytechnic, Nagpur. Prof. R.B. Tirpude received his BE in mechanical engineering from RTM Nagpur University, Nagpur, Maharashtra, India, in 1998 and an ME in CAD/CAM from Sant Gadgebaba Amravati University, Amravati, Maharashtra, India, in 2008. He did his diploma in management in 2003 and MBA (operations) at Delhi University Delhi, India, in 2007. He is currently pursuing PhD in mechanical engineering at RTM Nagpur University, Nagpur, Maharashtra, India. Professor Tirpude has more than 20 years of teaching experience at the undergraduate and research levels. He has taught various subjects like computer-aided drafting, hydraulics and pneumatics, operation research, fluid power, machine design and automobile engineering. His area of interest is emission control systems. He has 20 international journal publications, 10 international conference publications, 11 national conference publications and 7 patents to his name. He has received “ISTE Narsee Munji Best Project Award”. He is also a recipient of “Best Teacher Award” from Government Polytechnic, Nagpur, as well as from the Dr. Babasaheb Ambedkar National Association of Engineers, Nagpur chapter. Professor Tirpude has contributed to the development Academics as Board of Study (BOS) member at MSBTE and various autonomous institutes of the government of Maharashtra. He is presently BOS member of Automobile Engineering at Government Polytechnic (GP), Nagpur. He is currently working in the Automobile Engineering Department at Government Polytechnic, Nagpur, and handling various collaborations of the department with leading automobile manufacturing industries.

1

Automobile Evaluation and Market Review

OUTCOME Learning Objectives • History and evolution of the automobile industry • Brief review of Indian/global automotive and automotive components manufacturers • Recent developments in vehicular technologies • Indian and global OEMs

1.1 INTRODUCTION The development of automobiles is associated with the process of civilization and ­overall growth of the human race. The self-propelled vehicle used for the ­transportation of goods and passengers is called a motor vehicle. Industries ­associated with the motor vehicle are engaged in its design, development and manufacturing as per the rules and regulations laid out by various authorities and as per customer needs. The global automotive industry and its allied industries are major contributors to the world’s economy and employment. Enhancement of technologies has enhanced their market potential as well. There are various manufactures related to these ­industries located across the globe. Currently, the automotive industry is in a phase of transformation due to v­ arious socioeconomic factors, global policies, emerging markets trends, etc. E-mobility, sharing of vehicles, electrical vehicles and connected cars are some of the trends in the automotive industry.

1.2 HISTORY AND EVOLUTION OF VEHICLES The journey of transportation started from the invention of the wheel, initially from the oxcart to high-speed vehicles. Generally, an automobile consists of a ­number of assembly and subassembly parts. Germany is considered the ­birthplace of the ­automobile, as most of the research in automobile has been carried out there. Captain Nicolas Cugnot, a Frenchman, is considered to be the father of a­ utomobiles. He built the first self-propelled vehicle in 1969–1970. Self-propelled steam engine vehicles developed in France were named Cugnot’s artillery tractors. The first practical steam car was built by Richard Trevithick of England using a crankshaft in 1802.

1

2

Automotive Systems

Julius Griffiths of England designed the first comfortable steam-powered vehicle in 1821. The gas-engine-powered car was built in 1863. Carl Benz of Germany also ­developed a three-wheel, or three-wheel-drive, vehicle powered by an Otto-cycle internal ­combustion engine. Carl Benz, the German invented a completely new form of vehicle in 1894. The engine was mounted in front of the frame, connected to the clutch, the transmission of the sliding gear and the differential. The vehicle also had brake pedals and an accelerator. Charles E. Duryea and his brother Frank Duryea of Massachusetts successfully operated the first gasoline-powered vehicle in America on September 12, 1892. The vehicle was powered by a 4-­horsepower (2.9 kW) ­gasoline engine. It became known as the “horseless buggy”. Henry Ford began the d­ evelopment of the “quadricycle” in 1895, which was powered by a two-cylinder ­gasoline engine. The same year, 300 cars were manufactured in the USA. The first front-mounted power units were installed in Columbia in 1900. In 1901, Oldsmobile began development of its framed curved car wash. The Cadillac Company was founded in 1902. The Brick Motor Company and the Ford Motor Car Company were founded in 1903 and the Packard Company relocated to Detroit. In year 1902, Cadillac produced 1,895 units and Oldsmobile 4,000 units. In 1905, Brick produced 750 cars. In 1908, Ford placed 20,000 of its Model T vehicles on the roads. From 1900 onwards, the improved design of automobiles completely awakened the public to the greater utility of this modern mode of transport. During 1900–1906, the manufacture and sale of these automobiles became widespread. In America alone, there were 121 car manufactures. The years that followed, 1906–1920, are considered the era of mass production in the automotive industry. A typical car produced in 1910 was the first diesel vehicle on the roads of the UK was a Mercedes lorry in 1928, the first diesel car in series production was the 1936 Mercedes 260 D. In the meantime, a diesel-powered vehicle, the Bentley, competed the RAC Rally in 1932 at an average speed of 128 km/h. In the mid-1970s, Volkswagen fitted a 1.5 L indirect injection engine (IDI) to the Golf (Rabbit in the USA).

1.3 INDIAN AUTOMOTIVE MARKET The first car on Indian roads appeared in 1897, and the first Indian to own a car was Jamshedji Tata, in 1901. It was in 1942, before India gained its independence, that Hindustan Motors produced India’s first car. Today, India is a core pillar of the global automotive market. India’s policies, actions and initiatives have a direct impact on the global automotive landscape. The automotive industry is a pillar of Indian economy and a key driver of macro-­ economic growth and technological advancement. Currently, the automotive industry contributes more than 7% to the total GDP, and as per the Automotive Mission Plan (AMP) 2016–2026, its contribution is projected to increase to 12%. India is expected to emerge as the world’s third-largest passenger vehicle market by 2021. The estimated employment potential is about 32 million people, directly and indirectly. The milestones of the Indian automotive industry are as follows:

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• The industry currently manufactures 25 million vehicles, of which 3.5 ­million are exported. • India has a good place in the international heavy vehicles arena as it is the top in tractor manufacturing, second in bus manufacturing and third in heavy trucks manufacturing in the world. • Sale of passenger vehicles has increased by 2.7%, two-wheelers by 4.86% and three-wheelers by 10.27% during 2018–2019vis-à-vis2017–2018. In April–March 2019, total vehicle exports increased by 14.5%. The overall commercial vehicles segment reported a rise of 17.6% in April–March 2019. • The sector received $22.4 bn FDI during April 2000–June 2019; accounting for 5.1% of the overall FDI inflow. • 100% FDI is allowed under automatic route. • India is expected to be the world’s third-largest automotive market in terms of volume by 2026. Just like in many other countries, the Indian automotive industry is set to witness major changes in the form of electric vehicles (EVs) and intelligent transport s­ ystem (ITS) with aims to alleviate existing concerns, including traffic congestion, fuel dependency and air and noise pollution. In March 2016, the Government of India set the country’s target to have 100% EVs fleet on its roads by 2030. Growth drivers of the Indian automotive market are as follows: • Increasing income: 3 × increase in average household income from $6,393 in 2010 to $18,448 in 2020. • Demographic potential: Demographic potential of India offers an unprecedented edge to its economy and India is set to become the youngest country by 2025 with an average age of 25 years. • Vehicle penetration: projected to cross 72 vehicles per 1,000 people by 2025. • Rising R&D hub: India accounts for 40% of the total R&D expenditure. The five trends impacting the Indian automotive industry and market potential are as follows (Figure 1.1):



1. Rapidly evolving customer expectations: Per capita income of the middleclass people is continuously changing, and they are shifting towards the higher middle class. These people are very possessive of their lifestyle, having high expectations of the services they seek and value for their money, as the effect of this is the creation of organizational capabilities in line with evolving consumer needs and the delivery of these needs accordingly. 2. Disruptive impact of technology: The car of the future is constantly updated with advancements in technology. They are electrified, automated, shared, connected and updated yearly to make driving easier, safer, cheaper and more comfortable. New waves of emerging technologies are on the cusp of affecting the industry at three levels:

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Automotive Systems

FIGURE 1.1  Impact on Indian auto industry and market potential.



a. Vehicles (electrical, driverless and connected; smart sensors, real-time vehicle tracking, geo-fencing, driver analysis and remote diagnostics). b. Supply chain and processes (digitised trucking, future distribution centres, automated warehouses, automation, virtual reality, and IoT). c. Business models (mobility as a service and car sharing). The Indian Government’s target is to ensure that only EVs are sold in the country over the next few years. The Ministry of Heavy Industries has selected 11 cities in the c­ ountry to incorporate EVs into their public transport networks under the Faster Adoption and Manufacturing of (Hybrid and) Electric Vehicles (FAME) Scheme in India. The first phase of the scheme was extended until March 2019. In February 2019, the Government approved the FAME-II scheme with a fund allocation of INR 10,000 crore (US$ 1.39 billion) for FY20–22. The number of vehicles funded under the FAME scheme increased from 5,197 in June 2015 to 192,451 in March 2018. 3. Dynamic regulatory environment: India, a developing country, has historically been seen as a desirable destination for low-cost manufacturing. The following significant regulatory actions are planned: a. Adoption of BSVI standards in Delhi/NCR by 2019 and PAN India by 2020 for all new four-wheeler vehicles sold. b. Shift in the tax structure – GST and associated costs. c. Government spending in the automobile sector and its infrastructure growth plans (Pradhan Mantri Gram Parivahan Yojana, Bharatmala Pariyojana, etc.).

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d. The implementation of health criteria in compliance with international norms. e. Formulation of end-of-life or scrap policy. f. Implementation of Corporate Average Fuel Efficiency requirements as per which manufacturers need to increase their fuel efficiency by 10% between 2017 and 2021 and by 30% or more by 2022. g. The adoption of EVs and alternative fuels by means of the FAME-2 String vehicle-related standards is contributing to a change in vehicle technology. Automotive organizations therefore need to invest in improving the various technological skills that are important to cope with these changes. 4. Changing the face of mobility infrastructure: self-driving cars, ride-­hailing services  and other technologies are transforming mobility. Creation of alternative modes of transport (e.g. autonomous  cars and EVs) alongside smart infrastructure (e.g. smart cities, optimization of parking spaces, artificial intelligence (AI)-driven traffic lights and focusing on smart enablement of EV-charging infrastructure) is projected to transform the mobility infrastructure. In this sense, India’s efforts to support EVs are likely to concentrate on two-wheelers, public transport and fleet operations, such as taxis and three-wheelers. According to the Bloomberg New Energy Finance (BNEF) report, India will see much progress over the next 10 years in electric twowheelers, rickshaws and electric busses, and by 2040, EVs will make up 40% of the country’s total fleet of passenger vehicles. Globally interconnected sector: Regional and local markets give the Indian automotive sector a sustainable growth opportunity. The rise in FDI in India and the emergence and acceptance of emerging global megatrends and technologies in the country are expected to result in the country becoming more dependent on other countries at every step of the automotive value chain, for example, R&D, purchase of raw material, power electronics, manufacturing support and sales. Therefore, automotive organizations’ ability to put in place and implement effective global and local strategies to manage risks and build their capability to drive their strategies will be of paramount importance.

1.4 GLOBAL AUTOMOTIVE MARKET Global profits for automotive OEMs (original equipment manufacturers) are ­projected to increase by almost 50% by 2020. The majority would come mainly from growth in emerging markets and, to a lesser degree, in the USA. Europe, Japan, and South Korea should be sluggish in terms of growth in earnings. The age of the linked car has already arrived. In response to demands of an ever-connected mobile society, millions of cars are fitted with built-in connectivity. The US auto market will cross 42 billion dollars by 2025 alone, while the US customer preference for partially autonomous and fully autonomous vehicles is 55% and 44%, respectively. Investment in driverless cars and infrastructure applications is also on the rise from

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Automotive Systems

various players worldwide. Hybrid cars are becoming very popular in the UK, and manufacturers are investing more and more capital in technology. Almost every car manufacturer has a hybrid in its catalogue. Automotive suppliers are under pressure to automate processes and implement new technology to meet OEM demand and optimise supply chains for secure and timely delivery. Due to increase in demand, several opportunities of creation remain unfilled. In some cases, OEMs are seeking new suppliers outside the traditional model. According to the forecast, with 57% of the world’s population unable to imagine their lives without a vehicle, and given the low rate of motorization in developing countries such as India or China, the demand for passenger cars will continue to rise in the coming years. Growth is tempered by the high rate of motorization in “­developed” countries. Global sales of passenger cars hit 78.6 million vehicles in 2017. Next to China, the USA is among the largest automobile markets worldwide, both in terms of p­ roduction and sales. About 6.9 million passenger cars were sold to US customers in 2016, while 4 million cars were domestically produced in the same year. Toyota, Volkswagen and Daimler topped the list in 2016, while the automotive supplier industry was ­dominated by Bosch, Continental, Denso and Magna. Most analysts expect the global automotive market size to keep growing, powered by electrification and by car autonomy. According to the Global Automotive Outlook 2017, the industry will reach 114 million in worldwide sales annually by 2024, an increase of 45% over the 2017 level (Figure 1.2)

FIGURE 1.2  Revenue of major car manufacturers.

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1.5 AUTOMOTIVE RESEARCH PERSPECTIVES







1. Green automotive and e-mobility Design of more lightweight metallic and composite materials that will improve powertrain efficiency and reduce fuel consumption and polluting emissions • Light weighting • New metallic and composite materials: innovation, employability and fastening • Innovative design and simulation • Electric motors, reducers, inverters, batteries and other electrical equipment: testing, validation and certification. Vehicle hydrogen storage design and manufacturing • Complete powertrain performance, tribology and lubrication ecodesign and “Reach” compliance 2. Intuitive Human Machine Interface (HMI) smart life on board Minimise noise, vibration and harshness of materials. Development of Internet of Things (IoT) applications to bring ever greater levels of comfort and safety in driving • NVH approach (testing and simulation) • Feeling of material • Ageing test • Added value through industrial IoT applications (comfort, safety, etc.) 3. Getting design and production right the first time Bring state-of-the-art expertise to the design of components, systems and manufacturing processes. Through modelling and multi-physical ­simulations, Cetim can accelerate testing cycles and tighten protocols. • Durable construction and fastening, sealing • Mechanical damage and durability • Product of Exponentials (PoE), automation and multi-physical simulation • Process simulation • Acceleration checking and procedure tightening • Number of tests reduced • Aging, fatigue and vibration, life, efficiency and friction tests 4. Excellence in execution Offers technical advancement and development, but also optimises ­organization and processes through • Lean management • Process efficiency and risk management • On-line controls: NDT, dimensional inspection and cleanliness survey • Robotics • Defect rate reduction (PPM) • Exceeding quality recognition and quality drift management

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Automotive Systems

• Reduction in cost of ownership • Manufacturing facilities Technological developments defining the future of automotive manufacturing and assembly: minimizing polluting emissions, maximizing energy efficiency and, above all, ensuring the highest standards of safety at work • Machine safety and ergonomics at work • New process innovation and tuning • 3D printing, intelligent and smart machines • Process qualification and risk management • Robot, exoskeleton • Identification and suppression of non–value adding tasks • Environmental concerns • Reduction of lubrication • Air pollution and waste management • Process energy efficiency • Human resources • Audit and training • Knowledge management 1. Current and upcoming technologies used in vehicles Driver assistance technology, integrating navigated highway ­driving with hands-off single-lane driving capabilities: Designed for on-ramp to ­off-ramp (ramp-to-ramp) highway driving, this new system uses the ­vehicle’s ­navigation system to help the vehicle work on a predefined path on designated roads. The system also allows hands-off driving while cruising on a single lane for the first time. In order to activate the latest functions of the new system, drivers must first set their destination in the navigation ­system, creating a predefined travel route. Once the car enters the ­highway, the new system’s navigated driving becomes available. After activation using a ­predefined path, the device will assist the driver to proceed on a multi-lane highway until reaching the highway exit on a predefined ­path-helping with driving and lane changing and exiting. 2. Automatically switches headlights from high beam to low beam and back to minimise driving burden This device automatically changes the headlights setting from high beam to low beam when it detects a vehicle ahead. Frequent use of high beams allows for faster identification of pedestrians, enabling safer driving (Figure 1.3). System operation When driving with the headlight switch in the AUTO mode, the high beam of the vehicle stays on when low light is detected. When an oncoming or leading vehicle is observed, the headlights will be shifted automatically from high beam to low beam. When there is no oncoming vehicle or the leading vehicle is at a safe distance ahead, the headlight will return to high beam.

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FIGURE 1.3  Automatic switching headlights system.

3. Assists drivers in smooth cornering by adjusting power output to the front and rear wheels The vehicle predicts the cornering line that the driver expects and adjusts torque distribution for a natural and smooth cornering line, even on s­ lippery road surfaces. The intelligent 4 × 4 automatically controls torque ­distribution between the front and rear wheels to provide cornering as per the ­driver’s intentions predicted by steering wheel input. Vehicle yaw m ­ ovement control technology realises smooth, ideal cornering while turning. 4. Variable compression ratio engine that simultaneously achieves high efficiency and high power while synchronizing with the driver’s intentions The VC-Turbo engine uses a multi-link mechanism that continuously varies piston top dead centre (TDC) and bottom dead centre (BDC) positions, allowing free control of the compression ratio of the critical factor of power and performance on demand. It makes it the world’s first production engine to achieve both remarkable high power and remarkable fuel efficiency – two performance characteristics that normally contradict each other. Lane Departure Warning warns the driver if they are about to leave the lane. If there is a risk that the vehicle will leave the lane accidentally, the device will include visual and audio warnings to prompt the driver to take action. System operation The system visually tracks the left and right lane markers of the driving lane. If there is a possibility that the vehicle will change lane accidentally, the device will flash an indicator and sound an alarm chime.

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Automotive Systems

5. Helps the driver prevent collisions with approaching vehicles and objects while reversing This device warns the driver with a visual and auditory warning when there is a chance of collision with an object behind the vehicle or with a vehicle approaching from the side. If the driver attempts to reverse further under those conditions, then in addition to the initial visual and audible warning, the system automatically activates the brakes for a moment to help the driver prevent a collision. 6. Assists the driver to prevent a change of collision with the lane by detecting vehicles in a blind spot When the device detects a vehicle driving in an adjacent lane ­approaching the rear of the driver’s vehicle (a typical blind spot), the driver is alerted with an indicator light. If the driver begins changing lanes, the device warns the driver with a chime and flashes the indicator light continuously while ­applying a slight braking force to help return the vehicle to its original lane. 7. Simple driving using only the accelerator pedal • The e-pedal helps the driver to start, accelerate, slow down and stop using only the accelerator pedal. • Press the accelerator pedal hard for fast acceleration. Lift off the pedal and the e-pedal mimics on the brake pedal, allowing the vehicle to slow down and even stop completely. • In stop-and-go city traffic, the e-pedal dramatically eliminates the need to switch from one foot to the other, making driving safer and more appealing. It also makes sporty driving on winding roads, making the driving process more exciting. 8. An advanced automated parking system The newly developed Pro-PILOT Park assists the driver to park in three easy steps by controlling the steering, accelerator, brakes, gear shift and even the parking brake. This advanced automated parking system can recognise the type of parking space and guide the car into front or back-in parking spots, as well as parallel parking. 9. Lightweight, compact and high-efficiency powertrain for EVs The e-Powertrain powers EVs and eliminates the need for an internal combustion engine. It is a lightweight, compact system that produces extremely low vibrations and generates instant torque. These elements combine to deliver a high-quality, smooth and highly responsive driving experience. The main components of the e-Powertrain are its inverter, high-power electric motor, speed reduction and load supply (PDM) module. The device has been built to function in diverse environments around the world, ­exhibiting high efficiency and high reliability in all of them (Figure 1.4). 10. Direct adaptive steering Direct adaptive steering transmits the driver’s steering input, moving the tires by translating the driver’s steering into electronic signals and independently controlling the angle of the tires and the steering force.

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FIGURE 1.4  Powertrain for electric vehicles.

The technology provides a sense of strong propulsion on a variety of road surfaces, and gives a feeling of being in contact with the road. For example, the technology is helpful on bumpy roads or bad road surfaces where the driver is forced to grip the steering wheel tightly. The amount of vibration transferred to the driver through the steering wheel is reduced, helping the driver to more easily maintain a straight line of travel. When travelling along highways, the system automatically makes small adjustments to steering, reducing the need for manual steer inputs. This leads to a more confident and relaxed driving experience. 11. Intelligent seat belt The motor stretches the seat belt tongue to the driver and the front passenger, and when the belt is on it, it removes the extra webbing of the belt and helps control fit. Upon unbuckling, the belt is immediately put into place. The system’s tight design helps ensure that both the driver and the front passenger feel comfortable during skids or sudden manoeuvers. 12. Parking assistance and wireless charging This system frees an EV of the need for a cable when charging, further advancing the convenience of EVs for charging at home or work. As the car can be parked always in a designated location, the steering can be operated automatically, greatly reducing the hassle of parking. Technology functionality Parking misalignment is minimised by combining the Advanced Parking Assist with the EV Wireless Charging System, which changes the efficiency of charging as per the parking location. An EV can always be charged at maximum efficiency (Figure 1.5).

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Automotive Systems

FIGURE 1.5  Wireless charging system.

Wireless Charging System: When charging an EV, there is no need for a charging cable, with the vehicle charged just by parking at a predetermined location. 13. Emergency assistance in pedal misapplication When the vehicle is stationary or drives at a low speed (up to 15 km/h) and there is a wall, a stopped car or other obstacle in the direction of travel, and when the driver inadvertently pushes the accelerator pedal instead of the brake pedal or is late in braking, the system can help the driver prevent a collision by automatically suppressing acceleration and by applying the brakes. Regarding wall detection, the system can detect glass surfaces, such as the glass walls of a convenience store in addition to typical wall structures. Wall detection operates both when driving forward and reversing. In addition to this function, some models such as LEAF provide assistance in preventing collisions when there is a vehicle, pedestrian or other obstacle in front and the driver operates the wrong pedal at speeds of up to 25 km/h. 14. Alternator regenerative control technology An alternator is a power generator inside a vehicle, functioning as the power source of the electricity used in a car, such as in the audio or airconditioning unit. As it uses the power of the engine to work, it consumes more fuel when generating electricity. Previously, alternators generated power all the time, but this new ­alternator increases fuel consumption of the engine by means of r­ egenerative control technology that regenerates power when the vehicle decelerates and by reducing consumption by not generating power at certain times (Figure 1.6).

1.6 INDIAN AND GLOBAL OEMs The Indian automotive sector is divided into three: commercial vehicles, cars and multi-utility vehicles, and two- and three-wheelers.

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FIGURE 1.6  Alternator regenerative engine technology.

The majority of India’s car manufacturing industry is based around four clusters: I. Delhi-Gurgaon-Faridabad-Ghaziabad-Gautama Buddha Nagar (North) II. Mumbai-Pune-Nasik-Aurangabad-Thane (West) III. Chennai-Bangalore-Dharmapuri-Vellore-Kanchipuram-Thiruvallur (South) IV. Kolkata-Jamshedpur (East) (Figure 1.7 and Table 1.1).

FIGURE 1.7  Global automotive manufactures and their market share.

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Automotive Systems

TABLE 1.1 Variety of Products of Automobile Manufacturers Sr. No.

Name of Company

1 3

Ford India Pvt Ltd Tata Motors

4

Hyundai

5

Maruti

6

Mahindra

7

Honda Cars India Ltd

8

Nissan

9 10

Fiat India Automobiles Ltd Volkswagen

11

Skoda

12

Toyota

13 14

Mitsubhishi Audi India

15

BMW India Pvt. Ltd

16

Kia Cars

17 18 19 20

Renault MG Motor Cars Datsun Volvo

21

Jeep

22 23

Jaguar MINI

Products (Cars/SUVs) Eco-Sport, Mustang, Aspire, Freestyle, Endeavour, Figo Nexon, Harrier, Tiago, Tigor, Strome, Hexa, Zest, TiagoNRG, TiagoJTP, Bolt, Altroz, Gravitas, H2X Eon, Terracan, Santro, Xcent, Accent Eco, Grand i10, Elantra, Hyundai Verna, Getz Prime, i20 Sportz, Venue, Elite i20, Creta, Grand i10 Nios, Tucson, Aura, Palisade, Nexo Swift, Swift Desire, Jimny, Alto, Altok10 Omni, Eeco, Astar, SX4, Baleno, Gypsy, 800, Ritz, Ertiga, Wagon R, Versa, Ertiga, Baleno, Vitarabreza, Spresso, XL6, Celerio, Grand Vitaraciaz, Scross, Ignis, Celeriox, Baleno RS Xylo, Bolero, Scorpio, Voyager, xuv500, Thar, VeritoVibe, Quanto, Duster, Scala, Fluence, Pulse, Koleos, xuv300, TUV 300, Marazzo, KUV100NXT, Verito, Aero City, CR-V, Accord, Civic, Jazz, Brio, TIF, Amaze, WRV, BRV, HRV Vezel Micra, MicraActive, GT-R, Sunny, Terrano, Leaf, X-Trail, Terraklics PuntoEVO, AbarthAvventura, Aventura Urban Class, Linea, AbarthPunto, Cronos Vento, Polo, Tiguan, Ameo, Troc, Virtus, T-Cross, TiguanAllspace Rapid, Octavia, Kodiaq, Superb, Kamiq, Citigo, Scala, Karoq, VisionX, VisionIN Innova Crysta, Glanza, Fortuner, Platinum Etios, Corolla Altis, EtiosLiva, Yaris, Camry, Land Cruiser, Etios Cross, Land cruiser Prado, PriusVellfire, CorollaC-HR Pajero Sport, Outlander, Xpander, Eclipse Cross A3, A4, A6, RS5, S5, A5 A6, R8, Q5, Q3, Q7, A3 Cabriolet, TT, Q2, A7, Q8, Q4, Q3, A8 X1, 7Series, 3 Series, Z4, X5, X3, 5Series, 3SeriesGT, 6 Series, X4, M2, X7, M Series, 8Series, i3, X6, 2Series Seltos, QYI, Rio, Carnival, Picanto, Soul, Stinger, Spotage, Stonic Triber, Kwid, Duster, Captur, Lodgy, HBC, Zoe, Arkana Hector, RX5, ZS, Baojun510, GS, D90, ERX5 Go Plus, GO, redi-GO XC90, S60 Cross Country, S90, S60, XC40, V90 Cross Country, X60 Wrangler, Compass, Cherokee, Compass Trailhawk, Renegade XE, XJ, FType, F-Pace, XF, I-Pace, Epace Cooper Five Door, Cooper Three Door, Countryman, Clubman, Convertible (Continued)

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Automobile Evaluation and Market Review

TABLE 1.1 (Continued) Variety of Products of Automobile Manufacturers Sr. No.

Name of Company

24 25 26 27

Bajaj Cars ISUZU Lamborghini Mercedes-Benz

28 29 30 31 32 33 34 35

Rolls Royce Tesla Cars DC cars Bugatti Lexus Aston Martin Maserati Bentley

Products (Cars/SUVs) RE60 D-Max V-Cross, MUX Huracan, Aventador, Urus, Huracan EVO G-Class, C-Class, S-Class, E-Class, GLAClass, GLS, CLA, E-Class All-Terrain, V-Class, A-Class, AMG GT, GLE, CLS, GLC, B-Class, GLB Dawn, Phantom, Cullinan, Wraith, Ghost Model 3, Model Y, ModelX, ModelS, Cybertrunk Avanti Chiron, Divo, Veyron LS, NX, RX, LX, ES, UX, LC DB11, Rapide, DBS Superleggera, MartinDBXZagato Levante, GranTurismo, Ghibil, Quattroporte Continental, Bentayga, Mulsanne, Flying Spur

1.7 INDIAN AND GLOBAL AUTO COMPONENTS MANUFACTURERS The auto components industry accounted for 2.3% of India’s Gross Domestic Product (GDP) in 2017–2018. At the same time, 1.5 million workers were employed directly and 1.5 million indirectly in the auto components industry. The automotive ­components market has seen good growth with a turnover of US$ 51.2 b­ illion in FY18 and an expected turnover of US$ 200 billion in FY26.By 2021, India’s auto ­components exports could account for as much as 26% of the industry. Auto ­components ­production is expected to increase by 12%–14% in FY19 in ­2018–2019, following strong growth in both domestic and export markets. A number of favourable government policies, such as the Auto Policy 2002, the Automotive Mission Plan 2016–2026, the National Automotive Testing and R&D Infrastructure Projects (NATRiPs), have helped the Indian auto components industry achieve significant growth. The government also extended the FAME (Faster Adoption and Manufacturing of [Hybrid and] Electric Vehicles in India) scheme from September 2018 to March 2019 (Figure 1.8). India is emerging as a global hub for auto components sourcing. A cost-effective manufacturing base keeps costs lower by 10%–25% relative to operations in Europe and Latin America. Relative to competitors, India is geographically closer to key automotive markets like the Middle East and Europe.

1.7.1 Industry Scenario The $51.2 billion auto components industry in India is expected to grow to $200 ­billion by 2026.

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FIGURE 1.8  Various auto components.

Auto components industry exports, which are currently valued at $13.5 billion, are expected to grow at an annual rate of 23.9% to reach $80 billion by 2026. The USA, Germany, Turkey, UK and Italy are the top export destinations. Aftermarket segment, which includes tyre, battery and brake parts, is expected to reach $32 billion by 2026 from the current $9.2 billion. The global industry, which currently accounts for 2.3% of India’s GDP, is expected to become the third largest in the world by 2025. • Expanding Research and Development hub: India has accounted for 40% of global manufacturing and R & D activities. • Emerging global sourcing hub: Proximity to markets such as ASEAN, Europe, Japan and Korea Price competitive: excessive vehicle duty reduction would boost demand. The sixth largest vehicle producer in the world. India is expected to be the third largest market by 2026. • Favourable trade policy:100% FDI is allowed and no import-export restrictions Investments and expansions in the Indian Auto component sector – • In April 2019, Durr, a German automotive painting and sealing company, entered into a partnership with Patvin to provide automated two-or threewheel and agricultural solutions. • The capital expenditure of domestic automotive component manufacturers is estimated to be around INR 24,000 crore (US$ 33.26 billion) over FY19 and FY20. • As of December 2018, Kesoram Industries has decided to expand its tyre sector to unlock value and raise capital for expansion. The restructuring

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Automobile Evaluation and Market Review

•

• • • • • •

•

•

would allow the company to enter the high-margin automotive radial tyre market. The firm expects the sector to be finished by July 2019. As of December 2018, the German automotive giant Continental is p­ reparing to spend INR 180 crore (US$ 25.65 million) to set up a premium surface materials plant in Pune. The facility will have an initial capacity of five ­million square meters and is scheduled to start production in 2020. In October 2018, the company inaugurated its second largest manufacturing facility in the Asia Pacific region. The business plans to expand its product and technological portfolio over the next few years. In September 2018, the air compressor manufacturer Elgi Equipments will spend INR 18 crore (US$ 2.56 million) to set up a power plant in India. The building is scheduled to be opened in Q1 FY20. In January2019, Lite Auto Components Pvt Ltd, a part of Hindustan Magnesium Products Pvt Ltd, invested INR 500 crore (US$ 69.30 million) to set up a magnesium-based manufacturing plant in Andhra Pradesh. In June 6, 2019, Tata Group’s automotive parts subsidiary Tata Auto Comp Systems Limited entered into a 50:50 joint venture (JV) with SECO Seojin of South Korea to design, develop and manufacture clutch systems in India. In April 29, 2019, automobile components manufacturer Valeo  increased its manufacturing capacity to  500,000 units  annually and shall cater to the OEMs and aftermarket segments in the country. In August 2018, the Board of Directors of Amara Raja Batteries authorised the establishment of an INR 700 crore (US$ 99.74 million) greenfield ­automotive battery plant with a production capacity of 6.5 million units per year. As of October 2018, the company agreed to further raise the plant’s capacity to 10.8 million units in phases. In August 2018, JK Tyre and Industries Ltd opened its state-of-the-art global development centre in Mysore. Work at the centre will concentrate on various aspects of tyre technology, including the development of advanced laboratory tyre performance predictors and the identification of crucial lifesaving inputs for rubber products. As of August 2018, Rico Auto Industries will soon be signing a JV ­agreement with HZ Manufacturing to manufacture automatic transmission for scooters.

Sr. No.

Name of the Group

1

Bharat Forge Ltd

2

Motherson Sumi Systems Ltd

3 4

Lucas-TVS Ltd Rico Auto

Component Category Crankshafts, front axle beams and steering knuckles (forged and machined), connecting rods, camshafts and rocker arms (forged) Automotive wire manufacturers, automotive rear view mirrors, injection-moulding tools, sunroofs, vehicle air-conditioning systems, lighting systems, cabins for off-highway vehicles, cutting tools and thin film coating metals Auto-electrical equipment High-precision fully machined aluminium and ferrous components and assemblies (Continued)

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Automotive Systems

Sr. No.

Name of the Group

5

Rane Group

6

Shriram Piston and Rings Ltd Pricol Ltd Sundaram Fasteners Ltd

7 8

9 10 11

Sona Koyo Steering Systems Ltd Minda Industries Ltd Bosch India

12

Denso India

13 14

Continental AG Magna

15 16 17

Cummins Visteon Automotive Systems Delphi

18 19 20

Same Deutz-Fahr ArvinMeritor Valeo

Component Category Manual steering and suspension systems, engine valves, tappet, brake linings, disc pads, clutch facings, brake blocks and pads, power steering systems, seat belt systems, etc. Automobile pistons, piston rings, engine valves and piston pins Auto-electrical equipment High-tensile fasteners, powder metal components, hot forged components, radiator caps, automotive pumps, gear shifters, gears and couplings, hubs and shafts, tappets and iron powder Steering systems Auto-electrical components Auto-electrical belts, braking systems and pads, clutch plates, gear pumps, etc. Auto-electrical components, alternators, starters, wiper motors, engine cooling fans, washer pumps, etc. Chassis, power trainand interior equipment Automotive interior, seating, metal body and chassis, electronic equipment, powertrain components, etc. Engines and components AC systems, alternators, panel instrument assembly and plastic components Electronic and safety systems, evaporative emissions canisters, air-conditioning systems, oil filters, radiators, etc. Tractors, engines and agricultural machinery and components Engines and components Wiper systems, clutches, lighting and signalling, braking, ignition, etc.

1.7.2 Global Automotive Components Manufacturers According to experts, the global auto components industry is a highly diversified field involving manufacturers of engines and auto components, including m ­ anufacturers of aftermarket parts, suppliers, dealers and retailers. The production of auto ­components is gradually shifting to Asian countries such as China, India and others due to higher market potential and low-cost manufacturing options. In China and India, OEMs are focused on helping suppliers develop and expand their companies. Strong growth in the industry has attracted a pool of companies, including major foreign companies, to operate on the Chinese auto components market. The growing importance of e­ lectronics and the practical incorporation of green components and sustainable goods would drive growth in the industry. The Global Auto Parts & Accessories Manufacturing industry consists of electrical systems, steering, suspensions and wheels, brake systems, transmission systems,

19

Automobile Evaluation and Market Review

interior products, metal stamping services, exhaust, airbag and HVAC systems and other parts. Over the 5 years to 2019, the Global Auto Parts & Accessories Manufacturing industry is expected to benefit from improving global economic conditions. Per capita income rates have risen across the globe, and the burgeoning middle classes in developing economies have been looking to purchase their own vehicles. As demand for new vehicles is increasing, OEMs have requested more components from the operators of the industry. In addition, aftermarket auto parts helped generate revenue as average vehicle age increased. The demand for this segment tends to increase with the number of vehicles in use; therefore, as more people take to the roads, the demand for spare parts increases. Sr. No.

Company Name

1

Robert Bosch GmbH

2

Denso Corp.

3 4

Magna International, Inc. Continental AG

5

ZF Friedrichshafen AG

6

Aisin Seiki Co.

7

Hyundai Mobis

8 9

Lear Corp. Valeo SA

10

Faurecia

11 12

Adient Yazaki Corp.

13

Panasonic Automotive Systems Co. Sumitomo Electric Industries

14

Product Name Powertrain solutions, chassis systems controls, electrical drives, car multimedia, electronics, steering systems & battery technology Thermal, powertrain control, electronic & electric systems, small motors, telecommunications Body exteriors & structures, power & vision technologies, seating systems & complete vehicle solutions Advanced driver assistance systems, electronic brakes, stability management, tires, foundation brakes, chassis systems, safety electronics, telematics, powertrain electronics, injection systems & turbochargers Transmissions, chassis components & systems, steering systems, braking systems, clutches, dampers, active & passive safety systems, driver-assist systems, including camera, radar &lidar Body, brake & chassis systems, electronics, drivetrain & engine components Automotive electronics, infotainment, ADAS, EV systems, module systems, lighting, airbags& brakes Seating & electrical systems (e-systems) Micro hybrid systems, electrical & electronic systems, thermal systems, transmissions, wiper systems, camera/sensor technology, security systems, interior controls Micro hybrid systems, electrical & electronic systems, thermal systems, transmissions, wiper systems, camera/sensor technology, security systems, interior controls Seating & seating systems & components Wiring harnesses, connectors, junction boxes, power distribution boxes, instrumentation & high-voltage systems Premium audio systems, navigation systems, compressors, batteries, motors, monitors, sensors, switches & HUDs Electrical distribution systems, electronics & connection systems (Continued)

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Automotive Systems

Sr. No.

Company Name

15

MAHLE GmbH

16 17

Yanfeng Toyota Boshoky Corp.

18 19

JTEKT Corp. ThyssenKrupp AG

20

BASF SE

21

Aptiv*

22

Schaeffler AG

23

Samvardhana Motherson Group

24

Autoliv, Inc.

25

BorgWarner, Inc.

26

Plastic Omnium

27

Gestamp

28

Magneti Marelli S.p.A.

29

Calsonic Kansei Corp.

30

Hitachi Automotive Systems

*

Product Name Piston systems, cylinders, valve trains, alternators, air & liquid management systems, vehicle climatization, engine & powertrain cooling, battery cooling, actuators, electric drives & starters Interiors, exteriors, electronics, seating & safety Seats, door trim, carpet, headliners, oil & air filters, door panels, fabrics & substrates Bearings, steering systems, driveline systems & machine tools Steering, dampers, springs & stabilisers, camshafts, forged machined components, bearings, undercarriage components, axles, forged crankshafts & drivetrain components, high-strength lightweight steel & electrical steel Coatings, catalysts, engineering plastics, polyurethanes, coolants, 21 (49) 621-60-0, brake fluids, lubricants, battery materials Electrical & wiring products, body controls, infotainment, safety & autonomous driving technologies Anti-friction bearings; engine, chassis & transmission components; wheel & axle bearings; clutch & transmission systems; dampers & e-mobility products Rear view mirrors, plastic modules cockpits/IPs, door trims & bumpers, wiring harnesses, plastic parts, rubber components, lighting, air intake manifolds, pedals, shock absorbers, HVAC systems & roof hatches Airbags, seat belts, safety electronics, steering wheels, brake control systems, radar, night vision, camera vision systems Turbochargers, electric motors, electronic control units, engine valve timing, ignition systems, thermal systems, transmission -clutch systems, transmission-control & torque management systems Fascias, front-end modules, rear-end modules, fenders, body panels & fuel systems Metal components & assemblies, body-in-white, chassis & mechanisms Lighting, powertrain, electronics, suspensions systems, shock absorbers, exhaust systems & plastic parts Climate control, engine cooling & exhaust systems; instrument clusters, console boxes, cockpit modules, instrument panels & front-end modules Engine management, electric powertrain & drive control

It is a Jersey-registered auto part company headquartered in Dublin, Ireland.

SUMMARY • The journey of transportation started from the invention of the wheel, ­initially from the oxcart to high-speed vehicles.

Automobile Evaluation and Market Review

• Charles E. Duryea and his brother Frank Duryea, of Massachusetts, successfully developed the first gasoline-powered vehicle in America on September 12, 1892. • India holds a strong position in the international heavy vehicles arena as it is at the top in tractor manufacturing, second place in bus manufacturing and third in heavy trucks manufacturing in the world. • Various government policies, such as the Auto Policy 2002, the Automotive Mission Plan 2016–2026, and the National Automotive Testing and R&D Infrastructure Projects (NATRiPs), have helped the Indian auto components industry achieve considerable growth and maintain the right track. • The autonomous car market will hit $42 billion by 2025 in the USA alone, and consumer sentiment for partially autonomous and fully autonomous vehicles in the USA is at 55% and 44%, respectively.

MULTIPLE CHOICE QUESTIONS 1. Various technologies available in the modern automotive systems are a. Safety b. Vehicle dynamics c. Environmental pollution d. All of the above 2. Which of the following are new waves of emerging technology in automotives? a. Vehicles b. Supply chain and operations c. Business models d. All of the above 3. The largest tractor manufacturer in the world a. India b. France c. Italy d. Japan 4. Which trends of the following are impacting on the Indian Automotive Industry and Market Position? a. Rapidly evolving customer expectation b. Changing the face of the mobility infrastructure c. Impact of technology d. All of the above

REVIEW QUESTIONS • • • • •

Describe briefly the history of automobile industry. Describe current research perspectives of the automotive industry. Describe various incoming vehicular technologies. Describe various current technologies available on the market. List the growth drivers of the global automotive technology.

21

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Automotive Systems

• How does the Indian automotive sector contribute to the growth of the global automotive market? • Describe the role of government policies on the automotive market. • What are the regulatory inventions related to the global automotive industry? Answers to MCQs: (1) d (2) d (3) c (4) d

2

Vehicle Classification, Structure and Layouts

OUTCOME Learning Objectives • • • •

Classification of vehicles Various vehicular systems Types of chassis and chassis frames Various vehicle layouts

2.1 INTRODUCTION The progress of the human race is accelerated by developments in transportation; this transportation may be for either goods or passengers. A self-propelled vehicle is known as an automobile. A vehicle is an assembly of the proper design of various machines and mechanisms which perform intended functions for the transportation of passengers and goods in an economical and efficient manner. It consists of an engine, transmission and suspension systems, steering and braking systems all mounted on a chassis with frame. The power produced by the engine is transferred through the clutch, gearbox, propeller shaft, final drive, differential, axles and finally to the wheels.

2.2 CLASSIFICATION OF VEHICLES

1. According to Use a. Goods vehicle b. Passenger vehicle 2. According to capacity a. Heavy transport vehicle, e.g. truck and bus b. Light transport vehicle, e.g. car, jeep c. Medium-duty vehicle 3. According to fuel used a. Petrol vehicle, e.g. scooter b. Diesel vehicle, e.g. car, truck, bus c. Gas vehicle, e.g. auto-rickshaw  d. Solar vehicle, e.g. car 4. According to number of wheels a. Two-wheelers, e.g. bike, scooty b. Three-wheelers, e.g. auto-rickshaw 23

24



Automotive Systems

c. Four-wheelers, e.g. car, jeep d. Vehicles with six and more wheels, e.g. bus and heavy truck 5. According to drive layout a. Left-hand drive b. Right-hand drive 6. According to transmission systems a. Conventional type b. Semiautomatic c. Fully automatic 7. According to engine location and drive layouts a. Front engine front wheel drive layout b. Rear engine rear wheel drive layout c. Transverse under floor engine 8. According to body construction a. Closed car b. Open car

2.3 CONSTRUCTIONAL DETAILS OF VEHICLE CHASSIS AND BODY In the case of heavy vehicles, vehicle without body is called as chassis; it consists of the following systems (Figure 2.1):

1. Engine system 2. Transmission system 3. Braking system

FIGURE 2.1  Various systems in a vehicle.

Vehicle Classification, Structure and Layouts



4. Suspension system 5. Wheels and tyres 6. Steering system 7. Electrical and electronics systems 8. Vehicle body system

2.4 BASIC TERMINOLOGY AND LEGISLATIVE REQUIREMENTS OF A VEHICLE AS PER CMVR AND MVA 2.4.1 Lead Dimensions of a Vehicle Following are the basic dimensions of a vehicle: Wheel Base This is the distance between the centreline of the front axle to the centreline of rear axle. It is viewed from side of the vehicle. Wheel Track The dimension measured between the centrelines of tyres of the same axle. It is viewed from the front of the vehicle. Vehicle Length It is the dimension measured from the front of the vehicle to the rear-most end of the vehicle, including the towing hook, trailer coupling, number plate, ladder, etc. Body Length The dimensions measured from the rear edge of the cowl to the rear end of the body. Overall Width Maximum width of the vehicle includes the mudguard, wheel hub, and door handles, as shown in Figure 2.2. The dimension measured from the rear edge of the cowl to the rear end of the front. Front Overhang The dimension measured from the centreline of the front axle to the front of the vehicle body, including protrusion of any components like number plate, bumper, fog lamp, etc. Rear Overhang It is the dimension measured from the centreline of the rear axle to the rear of the vehicle body, including protrusion of any components like number plate, bumper, etc.

25

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Automotive Systems

FIGURE 2.2  Dimensions of a vehicle.

2.5 VARIOUS SYSTEMS OF THE VEHICLE AND THEIR FUNCTIONS A vehicle consists of different systems and subsystems. The details of the systems and their functions are as follows: 1. Power Plant A vehicular engine is the power plant of an automobile. It is a mechanical device which converts chemical energy of the fuel into heat, light and sound energy. According to the method of ignition, engines can be divided into spark ignition and compression ignition engines. An engine includes various other systems like ignition, cooling, lubrication, fuel supply, intake, exhaust system, etc. a. Cooling system In an engine produces power, and therefore heat. About one-third of the heat produced in the combustion chamber will be converted into brake power, one-third will be carried by the exhaust gases and remaining heat will be carried by the engine cooling system. If the temperature of the engine continuously increases, it increases the thermal stresses on the vehicular components, ultimate resulting in engine seizure and failure of the components. A cooling system is of two types: air cooling and water cooling. b. Lubrication system The lubrication system distributes lubricants to moving parts to reduce friction when they rub against each other; this prolongs the life

Vehicle Classification, Structure and Layouts

of those components and enables smooth driving. An engine lubrication system has the following important functions: – Lubrication, thus reducing friction – Cools various engine parts – Seals the combustion chamber – Cleans the engine – Aids in preventing corrosion – Serves as a cushion between impacting parts The following parts of an engine require lubrication – Cylinder piston and piston rings – Main bearings – Crankshaft – Crank pin and piston pin – Big end and small end connecting rod – Camshaft – Valves and other components c. Air Intake, Exhaust Intake and exhaust systems are important components of ventilation in an engine. For optimum performance of an engine, supply of sufficient clean air is essential, because if atmospheric air that contains dust particles gets sucked into the engine, it may create friction, ultimately affecting engine performance. Removal of exhaust also helps in better performance, because if not removed from the combustion chamber it can form carbon deposits and affect the volumetric efficiency of the engine. 2. Transmission system As road conditions change, traction requirement of the vehicle also changes. The function of the transmission system is to adapt to and fulfil such requirements. It consists of components like clutch, gearbox, propeller shaft, final drive, differential, axle, and wheels. a. Clutch The clutch is a mechanical element used to connect the two coaxial (collinear axis) shafts having relative motion (different speeds). The word “clutch” means to grip tight. The clutch engages and disengages the engine and the transmission system from the gear box. It is always in the engage position, at the time of starting from stationary position position or necessary changes required in gear box till the operator/driver press the clutch pedal then it disengages. b. Gear box Gear box is an important part of the transmission system. It is an assembly of gears, shafts, shifting mechanisms, etc. Gear boxes can be classified as constant mesh, sliding mesh or synchromesh. c. Propeller shaft Power from the gearbox is transferred to the final drive with the help of the propeller shaft. It consists of a slip joint, a universal joint and a

27

28

Automotive Systems

shaft. The universal joint permits the transmission of power not only at one angle but when angle varies continuously as well. d. Differential While cornering, inner wheel rotates at a lower speed than the outer wheel. The differential allows for this difference in speed between the two wheels of a vehicle. e. Rear axle Function of the rear axle is to transfer from differential to the wheels. According to bearing locations it can be classified into semi-floating, three quarter and full floating axle. f. Wheels and tyres The function of the wheels and tyres is to support, propel and steer the vehicle as per requirement, when rolling over the road surface. The tyres provide a cushioning effect to the wheels against small road shocks and also transmit driving and braking forces between the wheel and the road surface. 3. Braking The function of the braking system is to retard or stop the vehicle progressively or rapidly. Brakes consist of a shoe and drum or disc or pad arrangement, when the driver applies the brake, due to friction between the shoe and drum, kinetic energy in the vehicle is converted to mechanical and heat energy, resulting in the retardation or stopping of the vehicle. There are two types of brakes (1) service brakes, to stop/retard the vehicle (2) parking brakes, used for parking. 4. Suspension system Different types of road surfaces subject a vehicle to dynamic loads, cornering forces, etc. The vehicle’s frame and body are connected through a spring and shock absorber, the suspension system, to provide comfort to the occupants. If the chassis is connected directly to the transmission components, then these dynamic loads will be directly transferred to the occupants resulting in sever discomfort, also the whole structure of the vehicle may be subjected to excessive fatigue, and it may breakdown. Therefore it is important that vehicle components are properly suspended. 5. Steering system The steering wheel enables controlling the angular motion of the front wheels as per requirement, to maintain directional stability of the vehicle. 6. Lighting and electrical accessories Lighting and electrical systems are important in an automobile in terms of vehicle safety. The headlights allow for visibility in the dark. As far as visibility is concerned viper and the air bags actuation are the important accessories in automotives. As visibility concern viper while air bags actuation are the important accessories. The vehicle is equipped with a horn as well as direction indicators, etc. Modern systems like cruise control, antilog braking system, fuel engine system, etc. are part of the electronic control systems. The vehicle consists of an electrical power point which supplies

Vehicle Classification, Structure and Layouts

the voltage required by the vehicular electrical and electronic system. Generally, a vehicle’s electrical system is divided into the following: a. Distribution storage and generation system b. Charging system c. Starting system d. Electrical ignition system e. Lighting and accessory system 7. Vehicle body and frame Vehicle body work generally depends on the following • Comfortable accommodations of the passengers/goods and driver • Maximum utilisation of space • Aesthetics • Suitable protection from wind and weather • Minimum resistance during operations • Type of load vehicle has to carry • Special applications for specific industries such as trucks that contain a concrete mixer and have a tipping mechanism, trucks with refrigerators, or trucks used to transport vehicles.

2.6 VARIOUS TYPES OF CHASSIS FRAMES: THEIR CONSTRUCTION AND MATERIAL Frame The frame holds the important parts of the chassis. It is made up of two long side members riveted together with the help of number of cross members. It is also called the underbody. Types of Chassis Frames Ladder type This is also known as a non–load carrying frame. Here the load is transferred to the suspension by the frame. It is made up of two long side members riveted together with the help of a number of cross members. These types of ladder construction is used in trucks. Tubular Frame A tubular space frame chassis is made up of circular section tubes, positioned in different directions to provide mechanical strength against force from anywhere. It is complex in nature and difficult to maintain; this type of frame is used in sports vehicles. Dropped Frame A drop frame floor assembly is used in trailers and similar vehicles. It includes a frame assembly, a floor assembly and a lift assembly. The lift is connected to the frame for elevating and lowering the floor assembly with respect to the frame (Figure 2.3).

29

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Automotive Systems

FIGURE 2.3  Nomenclature of the chassis frame.

Monocoque Monocoque construction is one piece construction i.e. body and frame. This type of construction is of less weight. It does not involve separate conventional frame for various attachments. Integral Construction In these types, the body and the frame form one integral part and they cannot be seen separately. This type of car body is produced from overlapping sheet metal, fastened by a multiplicity of spot welds often robotically applied. The side longitudinal members are not present here; transverse members are designed for higher strength. Such types of construction can be used for buses and luxury coaches. Materials used for chassis frame

1. Mild steel 2. Carbon steel 3. Nickel alloy steel 4. Aluminium alloy

2.7 VARIOUS LOADS ACTING ON THE VEHICLE CHASSIS FRAME, AND ITS DEFORMATION The chassis frame is the main part of the vehicle; it holds the important parts of the chassis. It is made up of two long side members riveted together with the help of a number of cross members. It is also called an under body. The frame must have

Vehicle Classification, Structure and Layouts

31

enough rigidity and strength to withstand road shocks, acceleration, braking thrust, driving torque and different types of stresses and vibrations. The vehicle frame must be sufficiently strong and light to withstand load without distortion. The chassis design includes a selection of suitable shapes and cross sections for its frame. A chassis frame can bear different types of loads. Functions of the Frame • To support the chassis components and body • To withstand static and dynamic loads due to deflection and distortion Loads Acting on the Chassis Frame • Flexural load produced in the vertical plane of the side members due to laden weight and unladen weight of the vehicle • Engine and braking torque • Flexural load which also develops in the lateral plane of the side members due to • Road camber • Cornering force • Side wind Flexural load causes flexural stresses, which can be either tensile or compressive in nature. Compressive stress is restricted by placing thrust-bearing members between the frame and the back axle. The tension is resisted by using material of sufficient strength. Torsional loads are caused by vertical loads when the vehicle goes over a road bump. The twisting induces a shear stress in the frame. The frame is designed strong enough to resist torque by providing • • • •

Torque resisting members Cross members A radius rod Benzo frame–type torque members

Vertical Loading Laden and unladen weight of the vehicle applies load to the middle portion of the wheel base. When the vehicle is subjected to bump, a bending movement occurs in middle portion the vehicle (Figure 2.4). Longitudinal Torsion When diagonally opposite wheels are subjected bump, they twist the frame in a longitudinal direction. Horizontal Bending When the chassis is subjected to lateral force that may be due to a road camber, horizontal bending occurs. Such a bending can occur also when cornering.

32

Automotive Systems

FIGURE 2.4  Load acting on chassis frame.

FIGURE 2.5  Different cross sections of the frame.

Horizontal Lozenging Due to various types of bumps, potholes, and other obstacles, the frame is subjected to distortion in a parallelogram-type movement called horizontal lozenging. The chassis frame is made up of the following steel sections: 1. Channel section: Used for long members of the chassis frame; channel ­section provides good resistance to bending (Figure 2.5). 2. Box section: Used for the short members of the chassis frame; it provides good resistance to both torsion and bending. 3. Tubular section: Used in the frames of small vehicles like mopeds, threewheelers, etc.It provides good resistance to torsion.

2.8 TYPES OF CHASSIS AND VEHICLE LAYOUTS, ADVANTAGES AND DISADVANTAGES The function of the automotive chassis is to provide sufficient strength necessary to support the laden and unladen weight of the vehicle. The various components associated with the suspension system allow the vehicle to pass over uneven roads without an

Vehicle Classification, Structure and Layouts

33

excessive amount of vibrations reaching the passengers or cargo. The steering, suspension and braking components, mounted along with the chassis, work as a control system for a vehicle. The tyres grip the road surface to provide good traction that enables the vehicle to accelerate, brake and make turns without skidding. Along with the suspension, the tyres absorb most of the shock caused by road irregularities. The body of the vehicle encloses the mechanical components and passenger compartment. All the components of chassis members are fitted with the frame with proper fitting arrangement. The chassis can be classified as follows: Conventional control: The engine is mounted in front of the driver’s cabin. Generally all cars and old trucks have this structure. This arrangement prevents noise, vibrations and heat from reaching the driver and occupants. Semi-forward control: Engine is mounted in such way that half of it is in the driver’s cabin and half in front. A part of the engine compartment can be used as the driver’s cabin. Full forward chassis: Here the engine is completely mounted inside the ­driver’s cabin, e.g. in luxury coaches and buses. The entire space of the driver’s compartment is used, but height of the vehicle increases. Rear-Wheel Drive and Front-Wheel Drive Layouts Vehicular layout means arrangement of all the drive components. Differences in layout depend on the following considerations: • • • • • • •

Interior space Ease of handling Maintaining traction Balanced barking Stability of vehicle during various types of road conditions Comfort to the passenger Other considerations like vibrations, heat dissipation, noise, etc.

FIGURE 2.6  Front engine front - wheel drive layout.

34

Automotive Systems

Generally, a vehicle has the following layout Front Engine Front-Wheel Drive The engine is mounted in the front part of the vehicle and drive is transmitted to the front wheels through proper arrangement. This type of drive arrangement has the following advantages and disadvantages. Advantages • • • •

No propeller shaft, so height so low. Floor profile can be used. The centre of gravity of the vehicle is lower, so overall height can be reduced. Engine and transmission shaft linkages are simplified. Better steering response during high wind speed, as more weight is concentrated in the front part of the vehicle.

Disadvantages • There is heavier steering as weight is concentrated in the front side of the vehicle. • While climbing a hill, traction of the front wheel may reduce due to shifting of the centre of gravity to the rear side of the vehicle. • Heat, noise, fumes may transfer to the passenger compartment (Figure 2.6). Front Engine Rear-Wheel Drive The engine mounted in the front part of the vehicle and drive is transmitted to the rear wheels through proper arrangement (Figure 2.7). This type of drive arrangement has the following advantages and disadvantages. Advantages • • • • • •

Front-mounted engine provides better safety during crash. Radiator can be mounted in front of the vehicle, enabling effective cooling. A front-mounted engine is easy to maintain. Engine and transmission linkages are simple in construction. The slope of the propeller shaft is very small so simple hook joint can be used. During hill climbing, the centre of gravity shifts towards the back side, which provides a grip on the rear wheels. • Provides good traction to the vehicle. Disadvantages • Extended sections are required to accommodate the propeller shaft • In case of muddy road this vehicle tend to plough more into the ground. • Additional universal joints and drive shafts are required because of independent rear suspension system.

Vehicle Classification, Structure and Layouts

FIGURE 2.7  Front engine rear-wheel drive layout.

Rear Engine Rear-Wheel Drive The engine is mounted in the rear side of the vehicle and drive is transmitted to the rear wheels through proper arrangement. Engine can be mounted transversally or longitudinally. This type of drive arrangement has the following advantages and disadvantages. Advantages • Due to rear mounting of the engine, passengers do not experiences noise, heat, fumes, etc. • Steering is smoother due to absence of the heavy weight in the front side. • With a compact exhaust system, span of exhaust travel is less. Disadvantages • Linkages of the clutch and gear box are required to transmit the power at the driver’s location. • Lighter weight in the front side allows for a more sensitive steering. • Lighter front end subjected to car more sensitive to steer at high wind speed. • Accommodation for the cooling system is difficult to acquire effective cooling. • Most convenient location for the petrol engine, for such type of layout is location of the petrol tank is at front, which is dangerous at the time of ­collision (Figure 2.8).

SUMMARY • In the case of heavy vehicle, the frame without the body is called as chassis. • In the case of light vehicles of monocoque construction, the whole body except additional fittings is called a chassis.

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Automotive Systems

FIGURE 2.8  Rear engine rear-wheel drive layout.

• The chassis consists of the frame, engine, vehicle control systems (­ braking, steering, suspension systems), transmission system, wheels, axles and some electrical and electronics systems for ease operation and safety of the vehicle. • The frame must have enough rigidity and strength to withstand road shocks, acceleration, braking thrust, driving torque and different types of stresses and vibrations.

MULTIPLE-CHOICE QUESTIONS

1. Vehicle without body is called a. Chassis b. Frame c. Structure d. None of the above 2. Section used for chassis frame is a. Channel section b. Box section c. Tubular section d. All of the above 3. Channel section is good in resisting a. Bending b. Torsion c. Both bending and torsion d. None of the above 4. Chassis frame used in trucks is called a. Ladder frame b. Tubular frame c. Integral construction d. None of the above

Vehicle Classification, Structure and Layouts



5. Conventionally controlled chassis consist a. Half of the engine in the driver’s compartment b. Engine is in the rear side c. Engine in the front side of the driver’s compartment d. None of the above 6. Advantages of integral construction of the vehicle are a. More space available for occupants b. Improvement in the handling characteristics of the vehicle c. Increases the load carrying capacity of the vehicle d. Both a and b 7. Integral construction can be used in a. Cars and luxury buses b. Light commercial vehicles c. Heavy commercial vehicles d. All of the above

REVIEW QUESTIONS • • • • • •

Describe the various types of chassis. List the components of the chassis. List the different types of chassis. Differentiate chassis and frame. List various types of loads coming on the chassis. Identify the types of chassis frames for the following vehicles:

(1) Rickshaw (2) truck (3) two-wheeler (4) bus (5) car Answers to MCQs: (1) a (2) d (3) a (4) a (5) c (6) d (7) a

37

3

Vehicular Engines

OUTCOME Learning Objectives • • • • •

Constructional details of vehicular engines Various systems and subsystems of vehicular engines Fundamentals of lubrication oil and coolants Emission formation and emission reduction technologies Advancements in vehicular engines

3.1 INTRODUCTION An internal combustion (IC) engine is a mechanical device which converts the chemical energy in the fuel into heat and finally into mechanical power through the working fluid. On the basis of combustion, the IC engine can be classified into two: spark i­gnition (SI) engine and compression ignition (CI) engines. After combustion of the air and fuel mixture, an IC engine produces a thrust; this thrust is transferred to the crankshaft through a to-and-fro motion of the piston. The piston moves in an up-and-down direction. This reciprocating motion of the piston can be transferred and converted into the rotary motion of the flywheel through the crankshaft to perform mechanical work. The engine consists of various types of systems, such as ignition, cooling lubrication, fuel supply, and exhaust system. As the vehicular power plant, the engine has various other applications in the field, like in stationary electric power generation, ships and aviation.

3.2 WORKING PRINCIPLE AND TERMINOLOGY OF THE ENGINE Operating Principle All combustion engines have to follow a particular sequence of operations or cycles to give the required output. There is not much difference between petrol and diesel engines. The petrol engine operates on the principle of the Otto cycle; while diesel engine operates on the basis of a diesel cycle. In an SI engine, a mixture of the air and fuel is supplied to the engine and it is ignited by a spark plug; in a CI engine, there is no need fora spark plug. On the basis of the cycle of operation an automotive engine can be classified as follows:

1. Four-stroke SI engines: In this engine, the cycle completes in two revolutions of the crankshaft. It consists of the following cycles: A. Suction: Mixture of air and fuel is sucked during this stroke. During this operation only inlet valve is open. 39

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Automotive Systems

B. Compression: Sucked air–fuel mixture is compressed; during this stroke both valves are closed. Just before the end of the compression stroke, sparking occurs and the mixture burns. C. Power: During this stroke both the valves are closed and due to high pressure, burnt gasses force the piston in a downward direction. Power is obtained during this stroke. D. Exhaust stroke: At the end of the expansion stroke the exhaust valves are open, piston travels from bottom dead centre (BDC) to top dead centre (TDC) and whatever exhaust gas present is removed. In CI engines, only air is sucked during the suction stroke and compressed during the compression stroke. Fuel is injected at the end of the compression stroke; due to the high temperature of the compressed air, the mixture burns. Various terms used in Engine are as follows: Cylinder bore: The nominal internal diameter of the cylinder. Cylinder: Cylindrical area in which piston reciprocates. BDC: The extreme downward position of the piston in a vertical engine. TDC: The extreme upward position of the piston in a vertical engine. Stroke: The distance between BDC and TDC. Displacement volume/swept volume: Volume generated when piston travels from TDC to BDC. Clearance volume: Nominal volume of the combustion chamber, when the piston is at TDC. Compression ratio: The ratio of total volume to the clearance volume. The ­compression ratio in an SI engine is about 7–14 while in a CI engine it is 14–22. Cubic capacity or engine capacity: The product of the displacement volume (or swept volume) and the number of cylinders is called as engine capacity.

3.3 COMPONENTS OF THE IC ENGINE AND THEIR CONSTRUCTIONAL DETAILS The assembly drawing of a four-cylinder IC engine is shown in Figure 3.1.

3.3.1 Piston and Rings Piston receives the combustion power and then transmits it through the piston pin and connecting rod. The assembly of the piston pin and rings seals the combustion chamber. Metal rings provided in the upper part of the piston, called piston rings, are important for proper sealing. Piston rings contain compression rings and oil rings. Compression rings are above the oil rings and perform the sealing function properly, the oil rings act as a lubrication layer between cylinder wall and piston. Piston rings also transfer excess heat from combustion chamber to cylinder walls (Figure 3.2).

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FIGURE 3.1  IC engine details.

FIGURE 3.2  Piston and piston ring.

3.3.2 Connecting Rod and Bearings The connecting rod connects the piston and crankshaft. It converts the reciprocating motion of the piston into a rotary motion. The end connected to the piston is the small end and that connected to the crankshaft the big end. Big end bearings have two liners (Figure 3.3).

3.3.3 Crankshaft Assembly and Bearings Crankshaft converts the reciprocating motion of the connecting rod into a rotary motion. One end of the crankshaft is called flywheel end and the other the gear end. In the crankcase, the crankshaft is supported by radial bearings called main bearings. Like the big end bearings, these bearings are also divided into two half liners.

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FIGURE 3.3  Connecting rod.

3.3.4 Cylinder Head and Gasket It is the upper part of the engine which accommodates the upper part of the cylinder, which provides the desired shape to the combustion chamber, the valve train and its components, injectors, spark plugs, etc. The function of the gasket is to join the cylinder and cylinder head without leakages in such a way that their oil, coolant and gas exchange passages are properly aligned.

3.3.5 Cylinder Block, Crankcase and Head Engine blocks can be considered monolithic (without liners) or heterogeneous which is nothing but with liners. The ducts provided in the upper part of the cylinder block transfer the cooling water to the crankcase. The cylinder bore has a high surface finish, which guides the piston to perform the sealing function. Due to its strength and rigidity, the cylinder bore receives high combustion pressure. The cylinder head consists of elements required for gas exchange processes.

3.3.6 Crankshaft Assembly and Main Bearings The crankshaft is an important part of the engine, which converts the reciprocating motion of the piston into a rotary motion. One end of the crankshaft is called the flywheel end while the other is the gear end. It consists of the following parts:

1. Crank web 2. Main journal 3. Pin journal 4. Gear end 5. Flywheel end

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FIGURE 3.4  Parts of crankshaft assembly and main bearing.

The number of main journals is more than pin journal because the crankshaft is ­subjected to greater bending loads due to gas pressure (Figure 3.4).

3.3.7 Crankshaft Torsional Vibration Dampers For each power stroke, the crankshaft tends to twist. At the time of sudden engaging and disengaging, the crankshaft is subjected to application of uneven forces. These forces generate vibrations. To damp the vibrations and nullify the effect of these forces, dampers are provided.

3.3.8 Valve Train The function of the valve train is to open and close the inlet and exhaust valves at a suitable time and at required intervals. It consists of valves, camshaft, crankshaft, rocker arms, pushrod, etc. The opening and closing of the inlet and exhaust valves is synchronised by the camshaft and crankshaft. Valve train arrangements are as follows: • Overhead camshaft • Camless • Cam in block

3.4 CLASSIFICATION OF IC ENGINES There are no standard methods for classifying IC engines, but they can be classified as follows. 1. According to the arrangement of engine cylinders: i. Horizontal engine ii. Vertical engine

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iii. V engine iv. In-line engine v. Opposed cylinder engine vi. Opposed piston engine vii. Radial engine 2. According to the number of cylinders: i. Single-cylinder engine ii. Multi-cylinder engine 3. According to the working cycle employed: i. Four-stroke cycle engine ii. Two-stroke cycle engine 4. According to the fuel used: i. Petrol engine ii. Diesel engine iii. Gas engine iv. Bi-fuel engine 5. According to the nature of thermodynamic cycle used: i. Otto cycle engine ii. Diesel cycle engine iii. Dual combustion cycle engine 6. According to the speed: i. Low speed engine ii. Medium speed engine iii. High speed engine 7. According to the field of application: i. Stationary engine ii. Marine engine iii. Automobile engine iv. Motor-cycle engine v. Aero engine vi. Locomotive engine, etc. 8. According to the method of ignition: i. Compression ignition engine ii. Spark ignition engine 9. According to the type of cooling system: i. Air-cooled engine ii. Water-cooled engine

3.5 TWO-STROKE AND FOUR-STROKE ENGINES A. Four-stroke engine: Cycle of operation is completed in four strokes of the piston or two revolutions of the piston. i. Suction stroke (suction valve open, exhaust valve closed): Charge consisting of fresh air mixed with the fuel is drawn into the cylinder by the vacuum pressure created by the movement of the piston from TDC to BDC.

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ii. Compression stroke (both valves closed): Fresh charge is compressed into clearance volume by the return stroke of the piston and ignited by the spark for combustion. Fuel combustion increases pressure and temperature. iii. Expansion stroke (both valves closed): The high pressure caused by burnt gasses forces the piston towards BDC and hence power is obtained at the crankshaft. iv. Exhaust stroke (open exhaust valve, closed suction valve): Burning ­gasses are ejected due to the movement of the piston from BDC to TDC (Figure 3.5). B. Two-stroke cycle engine: The complete series of events, i.e. suction, compression, power and exhaust, is achieved by two strokes of the piston, i.e.  one revolution of the crankshaft. In this engine, there are no valves. Gas movement takes place through holes in the cylinder called ports. The engine crankcase is air tight under which the crankshaft rotates. The two strokes operate as follows: • Upward stroke of the piston (suction + compression): As the piston travels upward, it covers two ports, the exhaust port and the transfer port, which are usually almost opposite to each other. This traps the load of the air fuel mixture that has already been drawn into the crankcase. Further upward movement of the piston compresses the charge and uncovers the suction port. Fresh mixture is then drawn into the crankcase via this port. The mixture in the cylinder is ignited by a spark plug just before the end of this stroke. Thus, all suction and compression events are performed during this stroke. • Downward stroke (power + exhaust): Burning of the fuel increases the temperature and pressure of the gasses that cause the piston to travel down the cylinder. When the piston moves downward, it closes the suction port, trapping the fresh charge in the crankcase during the previous

FIGURE 3.5  Cycles of a four-stroke engine.

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upward stroke. A downward movement of the piston will first expose the exhaust port and then the transfer port. Now the fresh charge in the crankcase travels to the cylinder through the transfer port, moving the burnt gas through the exhaust port. The uniquely shaped crown of the piston deflects the incoming mixture across the cylinder so that it can aid in pushing out the exhaust gasses. The piston strength and exhaust events are completed during the downward stroke.

3.6 COMPARISON OF ENGINES



Comparison of Two-and Four-Stroke Cycle Petrol Engines a. In the two-stroke engine one cycle of events completes with each revolution of the crankshaft, whereas in the four-stroke engine in two revolutions. b. Theoretically, the two-stroke engine generates double the useful power of a four-stroke engine with the same cylinder capacity. c. The mean effective cylinder pressures are lower in two-stroke engines than in equivalent four-stroke engines, because removal of exhaust gasses and charging of the fresh mixture through the crankcase in the two-stroke engine is less effective than having separate exhaust and induction strokes, as in the four-stroke engine. d. The two-stroke engine runs smoother than the four-stroke engine for the same size of the flywheel due to effect of more uniform torque output in two-stroke engine. e. As an effect of the absence of separate exhaust and induction strokes in the two-stroke engine, the piston and small end of the connecting rod have a tendency to overheat under heavy driving conditions. f. Comparatively less maintenance is expected in the two-stroke engine compared to the four-stroke engine. g. Mixed lubrication is achieved in the two-stroke engine by mixing small quantities of oil with petrol in proportions anywhere between 1:16 and 1:24. h. Two-stroke engines are generally cheaper to manufacture, as there are fewer working parts than in a four-stroke engine. i. In the two-stroke engine with inferior scavenging, there is a tendency for a. Insufficient filling of fresh charge b. Retention of large amounts of residual exhaust gas in the cylinder c. Direct release of fresh charge through the exhaust port

These undesirable performances greatly affect both power and fuel consumption and may take place under different speed and load conditions. Comparison of SI and CI Engines A comparison of SI and CI engines can be done on the basis of the following. Fuel Economy Thermal efficiency is defined as the ratio of the useful work produced to the total energy supplied and is considerably affected by the selected

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compression ratio design and the condition of the engine. Petrol engines can produce thermal efficiencies ranging between 20% and 30%, whereas diesel engines generally develop improved efficiencies, between 30% and 40%. Power and Torque A petrol engine usually has a shorter stroke and operates over a high speed range of the crankshaft than a diesel engine. Therefore, more power is obtained in the petrol engine towards the upper speed range, which matches with the requirement for high road speeds. On the other hand the diesel engine runs with slower rpm, and generally has a long stroke and an improved pulling torque over a relatively narrow speed range, which is ideal for heavy commercial vehicles. A diesel engine, therefore, provides higher torque at low speeds, but with a rough running. Reliability Diesel engines are built sturdier, tend to run cooler, and have only half the speed range of most petrol engines. Therefore, the diesel engine is more reliable and has extended engine life relative to the petrol engine. Diesel engines also require relatively less maintenance. Pollution The combustion process is quieter in the petrol and it runs smoother than the diesel engine. Diesel engines are noisy and vibrate on their mountings at the part load operation. The diesel engine’s exhaust is more noticeable, particularly if any of the injection equipment components are out of tune. The visible smoky diesel exhaust contains more NOx, and the relatively invisible exhaust gasses from the petrol engine contain HC and CO. Safety Unlike petrol, diesel fuels are not flammable at normal operating temperature, so their handling is not hazardous and there is no risk of fire. Cost Diesel engines are more expensive than petrol engines due to their heavy ­construction and injection equipment and high reliability.

3.7 SELECTION OF ENGINE AS PER FUNCTIONAL REQUIREMENT The engine can be selected on the basis of the following basic parameters

1. Power to weight ratio Power to weight ratio of an engine must be as high as possible, i.e. an engine with minimum weight must produce maximum power. 2. Power to volume ratio Power to volume ratio of an engine must be high so the space required for engine mounting is minimal.

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3. Fuel economy and availability An engine must be designed in a way that its fuel is easily available with minimum cost. 4. Easy cold starting An engine must be easy to start in all weather conditions, and it does not produce high amount of exhaust gasses. It should consume the minimum possible fuel during warm-up periods. 5. Minimum noise An engine consists of various types of parts for reciprocatory and rotary motions. During engine operation, noise generation should be minimum, to ensure comfort for the occupants. 6. Durability The trend is to reduce the weight and size of an engine and to install superchargers and turbochargers; this increases power without increasing size or volume of the engine. As a result some parts may undergo high heating, so design and material selection should be done in a way to make engine components durable. 7. Minimum emission Due to stricter emission norms, an engine should be designed to produce the least emission. 8. Economic manufacturability and low cost A new engine design always brings with it a high initial investment, so it should be done in a way that it can use existing facilities, which will reduce the market price of the engine. Advantages of IC Engines

1. Greater mechanical simplicity 2. Can be used in a variety of applications in different ranges 3. These units are compact and require less space Disadvantages of IC Engines



1. IC engines cannot use solid fuels which are cheaper. The liquid or g­ aseous fuel of the same standards may be used effectively. These fuels are r­ elatively more expensive than that of solid fuels. 2. IC engines have reciprocating sections, so balancing them is difficult, and they are also prone to mechanical vibration. 3. Air and noise pollution. Applications of IC Engines 1. Vehicular applications 2. Stationary engines for power generation 3. Shipping and aviation industry 4. Agriculture

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3.8 FUEL SUPPLY SYSTEM FOR SI ENGINES: GENERAL LAYOUT AND COMPONENTS Different systems are used for fuel supply to the cylinder. 1. Gravity system In this system the fuel tank is located at the highest point in the vehicle and due to gravity fuel is supplied to the engine. 2. Suction and gravity system The fuel is sucked from the main tank located at the rear of the vehicle by means of suction of the manifold vacuum. 3. Pump system In this system, different types of pumps, such as mechanical, electrical, diaphragm, are used to pump the fuel. Petrol Supply System The function of the petrol supply system is to store the fuel, prepare the mixture and supply the fuel to the engine as per requirement. The fuel supply system of the petrol engine consists of the following components: 1. Fuel tank The fuel tank is made from two halves of anticorrosive steel welded together. The location of the fuel tank depends on availability of space, type of fuel supply system, etc. The baffle plates provided in the fuel tank prevent surging. 2. Filters Filters are used to prevent entry of dust particles into the carburettor. The location of the filter is between the fuel tank and the pump. 3. Fuel lines The function of fuel lines is to supply fuel to the carburettor, return excess fuel to the tank and carry fuel vapour. The fuel system consists of two types of fuel lines: 1. Rigid lines: These are rigidly fixed with the frame or engine body, ­generally made from metal component. 2. Flexible lines: These are not fixed, and are generally rubber tubes and hoses. 4. Fuel pump The fuel pump transfers the fuel from the fuel tank to the carburettor through filters. There are two types of the fuel pumps: 3. Mechanically operated pump 4. Electric motor pump

3.9  PRINCIPLES OF CARBURETION AND FUEL INJECTION IN SI ENGINES In general, the SI engine uses volatile liquid fuels. Preparation of the fuel-air mixture is conducted outside the engine cylinder and the creation of a homogeneous mixture is not usually completed in the inlet manifold. Fuel droplets

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which remain in suspension tend to evaporate and mix with air during suction and compression processes. The process of preparation of mixtures is extremely important for SI engines. The purpose of carburetion is to provide a fuel mixture of air and fuel in the quantity and quality required for efficient operation of the engine under all conditions. Fuel metering, minimum fuel consumption, distribution of the mixture in equal proportions to all the cylinders, proper injection timing and atomisation of fuel and ultimately engine performance and emission are the essential parameters associated with the fuel supply system of the engine. The carburettor has various limitations, which can be minimised with the help of the fuel injection system.

3.10 TYPES OF CARBURETTORS AND THEIR CONSTRUCTIONAL DETAILS Carburettors can be classified according to the following. Float Chamber • Eccentric • Concentric Number of Units • Single • Dual • Four-barrel Metering System • Air-bleed jet • Metering rod type Type of Power System • Manually operated • Vacuum controlled Type of Venturi • Plain venturi • Double venturi • Vane venturi • Nozzle-bar venturi • Triple venturi Direction of Air Flow • Up-drought • Horizontal • Down-drought

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Carburettors The process of the formation of a combustible mixture of the proper amounts of fuel and air before admission to engine cylinder is called carburetion and the device which does this job is the carburettor. A simple carburettor consists of the following parts. Float chamber The float chamber maintains the fuel at a constant level which is necessary for normal operation of a carburettor. Float The float is a hollow and lightweight part made of plastic which helps to ­maintain the fuel level in the float chamber. Jet A jet is an element with a calibrated hole of definite diameter which provides metred quantity of fuel to the engine. Mixing chamber Mixing chamber is a straight or bent tube of which one end is connected to the engine inlet pipe and the other to the air cleaner. Venturi A venturi is a very simple device that changes air pressure by changing the velocity of air. Throttle The throttle controls the amount of air allowed to enter the engine. Choke A valve used in carburettor is a butterfly valve to increase the mixture strength at the time of starting position in cold start condition. Fixed-Choke Carburettors In such carburettors, air and fuel flow area are always maintained constant. Pressure difference allows the amount of fuel and air to vary according to the engine’s operating condition. Solex and Zenith carburettors are examples of fixed-choke carburettors. Variable-Choke Carburettor Also known as constant vacuum carburettors, in these air and fuel flow can be varied as per the demand of the engine. SU and Carter carburettors are examples of variable choke carburettors.

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3.10.1 Multiple and Compound Carburettors Maximum quantity of the mixture admitted in the cylinder depends on the size of the mixing chamber venture. Vehicles with large-capacity engines require higher quantity of charge. In modern practices multiple or compound carburettors fulfil the requirements. a. Multiple carburettors In multi-cylinder engines, engine efficiency and fuel economy depend on the mixture strength supplied to the engine. Because of the possibility of the mixture strength getting disturbed, the quantity of mixture supplied to the engine can vary due to flow restriction in manifold. The solution here is to provide a separate carburettor to each cylinder, which improves fuel economy and optimizes engine performance. But it is very difficult to match fuel economy in each carburettor as well as the initial installation cost, and fuel consumption. b. Twin-chokes carburettors In a multi-cylinder engine, a twin choke, or twin-barrel, carburettor is fixed on the banks of the engine’s cylinder. It consists of a single float chamber and throttle spindle on which both the throttle valves are maintained.

3.10.2 Electronically Controlled Carburettors Conventional carburettors with mechanical linkages between the accelerator pedal and other components like throttle, valves, etc. were disadvantages and in functioning that they caused delayed openings which affected the performance and economy of the vehicle. This problem was solved by the introduction of electronically controlled system servomotors, where an electro-pneumatic plunger operates the choke valves and throttle. Actuators received signals from the electronic control unit (ECU), which collects the information from the various sensors like engine speed, coolant temperature throttle position, etc. Electronic control over the carburettor can be applied in following ways: a. Starting and warm up: Actuators, throttle and choke valves receive information from the ECU regarding throttle valve position, speed, coolant temperature, etc., and according to this the system works. b. Idling speed: Lower stable speed can be achieved because the system works without any disturbances. c. Acceleration: The exact amount of fuel can be used for enrichment of the mixture at the time of acceleration of the vehicle.

3.10.3 Fuel Injection System Performance of the petrol engine depends on various factors, proper air fuel ratio as per engine requirement is one. A petrol engine fuel injection system provides the exact mixture strength which will improve fuel economy, emission reduction and may even increase engine life in all operating conditions. This fuel injection system consists of multiple point fuel injection system and throttle body injection system.

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3.11 CONTINUOUS AND TIMED INJECTION SYSTEM Methods of fuel injection:

1. Simultaneous injection: Injection of fuel to all cylinders occurs at the same time at every crankshaft revolution. As a result, fuel is injected twice in every four-stroke cycle. The timing of the injection is determined with respect to the location of the crank/camshaft. 2. Group fuel injection: Injectors are divided into two groups which are regulated separately. Every group injects once in a four-stroke cycle. A crankshaft revolution is the offset between the groups. 3. Sequential injection: Each injector is managed separately. The timing of injections, both with respect to the location of the crank/camshaft and the duration of the pulse, can be adjusted for each individual cylinder. 4. Continuous injection: This system is normally fitted with a rotary pump. The pump maintains a fuel line pressure of approximately 0.75–1.5 bar. The system injects the fuel through a nozzle situated in right downstream of the throttle plate. For a supercharged engine, the fuel is pumped at the entrance to the supercharger. The timing and length of the fuel injection shall be determined by the ECU, depending on the load and speed.

3.12 SINGLE-POINT TBI AND MPFI SYSTEMS



a. Throttle body injection (TBI) • The throttle body is identical to the carburettor throttle body, with the throttle valve regulating the amount of air entering the intake manifold (Figure 3.6). • The injector is located just above the throat of the throttle body. The injector sprays fuel into the air in the intake manifold where the fuel is combined with the air. This mixture passes through the throttle valve and reaches the intake manifold. b. Multipoint fuel injection (MPFI) • As per earlier discussions, the throttle injection system and the port injection system can be either pulsed systems or continuous systems. For both methods, the amount of gasoline injected depends on the speed and power requirements of the engine. MPFI systems can be divided into two types: D-MPFI and L-MPFI. • D-MPFI: The vacuum in the intake manifold is first sensed in this case. It also senses the volume of air by its density. When air enters the intake manifold, the manifold pressure sensor senses the intake manifold vacuum and sends the signal to the ECU. Simultaneously engine speed can be sensed by the engine speed sensor and signal delivered to the ECU. After receiving the signal, the ECU sends commands to the injector to control the supply of fuel for injection. As the injector sprays the fuel in the intake, the gasoline blends with the air and the mixture reaches the intended cylinder (Figure 3.7)

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FIGURE 3.6  Throttle body injection.

FIGURE 3.7  (a) D-MPFI system.

(Continued)

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FIGURE 3.7 (CONTINUED)  (b) LMPFI system.



• L-MPFI: This is a port type injection system. In this type, amount of fuel delivery can be controlled by engine speed and the quantity of air coming into the engine cylinder. This is called air-to-mass metering. As air enters the intake manifold, the air flow sensor measures the amount of air and sends signals to the ECU; the speed sensors also deliver the signals to the ECU. The ECU collects all the necessary information obtained and sends the necessary instructions to the injector in order to control the volume of the gasoline supply for injection. As injection is made, the fuel mixes with the air and the mixture reaches the cylinder. c. Direct fuel injection In a direct fuel injection system the injector is located at engine head so the fuel can be injected directly into the combustion chamber. In direct injection system, the time available for mixing the fuel in the air is very less and there is a requirement of the high air turbulence. With high injection pressure, shorter injection time is available to this direct injection system. In this system, a larger overlap period can be utilized so incoming air can sweep the exhaust gasses (Figure 3.8).

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FIGURE 3.8  Direct injection system.

3.13  FUEL SUPPLY SYSTEM FOR CI ENGINE: GENERAL LAYOUT AND COMPONENTS The diesel fuel injection system consists of the following parts:

a. Fuel tank It is mainly to store the diesel; the tank capacity depends on vehicle type and application. The fuel tank contains baffles to avoid fuel surging. b. Sedimentor The purpose of the preliminary filter is to separate larger droplets of water and abrasive matter that might be present in the fuel. c. Fuel lift pump Since fuel tank is mounted below the level of the engine’s fuel pump, a separate pump is required to pump the fuel from the fuel tank to the fuel pump. d. Main filter The main filter is used to remove the small abrasive/dust particles that may be present in the fuel. This avoids any damage to the injector. The main filter is required to be cleaned after certain kilometres. e. Fuel pipelines Fuel pipelines are of two different types: low pressure and high pressure. Low-pressure lines are connected before the pump and pipes which are ­connected from fuel pump to injector are basically the high pressure lines. f. Injectors Injectors are located in the cylinder head and open into the combustion chamber. Pressurized fuel is injected in small droplets into the combustion chamber through injectors (Figure 3.9)

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FIGURE 3.9  General layout of the fuel injection system,

3.14 TDI AND CRDI SYSTEM Turbocharged direct injection (TDI) is a combination of a common direct rail injection with a turbocharger. The turbocharger significantly enhances the peak engine output by jamming more air into the cylinders. The intercooler then cools the air that is pulled out of the turbocharger. In the final stage, the now cooled air reaches the combustion engine, where high-pressure fuel is directly pumped into the cylinders. It is this combination of cooled air and atomized diesel that makes TDI incredibly powerful. It has certain advantages: • Compactness: This leads to maximum space utilisation. • Efficiency: TDI engines can produce more power and more fuel efficiency in all operating ranges of the vehicle. • Extremely quiet: TDI engines are by far the quietest of all diesel engines due to their excellent insulation and firewall features. • Higher torque: TDI engines can produce huge torque surges, making them great for heavy transport. A common rail diesel injection (CRDI) system is used to achieve equal and high injection pressures in all the cylinders at any engine operating ­condition. CRDI consists of the following parts: a. Common rail: It is a manifold-like tube mounted at the cylinder head. It acts as a constant pressure accumulator. b. High-pressure plunger pump: The function of this pump is to maintain constant pressure at about 2000 bar in the common rail. c. Feed pump: It transfers the fuel from the supply tank to high pressure lines.

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d. Injectors: They are connected hydraulically to the ECU and the common rail. e. ECU: It controls the opening and closing of the valves and the pressure of the fuel in the common rail.

3.15 TYPES OF FUEL INJECTION PUMPS AND THEIR CONSTRUCTIONAL DETAILS AND TESTING OF FUEL PUMPS In-line fuel injection pump The main purpose of the in-line fuel pump is to deliver fuel at a pressure higher than the combustion pressure in small quantities depending on engine requirement. An in-line fuel pump consists of the following parts:



1. Pump housing The camshaft and tappet assemblies are located in the pump housing. 2. Governor housing Governor mechanism of pump is located in the governor housing, which is a part of the main pump housing. 3. Camshaft and tappet assemblies These operate to provide reciprocating motion to the plunger. In the spring-loaded pump, the plunger is lifted by cam through a tappet assembly which incorporates a roller, bush and pin to ensure smooth rolling contact with the cam. 4. Pumping elements The pumping elements are a barrel and a plunger with a helix groove, and the quantity of fuel to be delivered is controlled by its rotation.

3.15.1 Distributor Fuel Injection Pump In the case of distributor-type fuel injection system, two or more plungers are used. The fuel is directly injected into each cylinder in turn by a distributor. Rotary and axial-plunger-type pumps are used. In an axial-plunger-type distributor, the plunger is co-axial with the drive shaft and rotates with it, working also as a distributor. In rotary type, the plunger is reciprocated in the distributor head rotor while revolving around the axis. These types of pumps are generally lighter in weight and also simple and compact.

3.15.2 Testing of Fuel Injection Pump The motor-driven bench consists of an electric motor of 2–3 HP. Therefore the operating range of the pump can go up to 4,000rpm. This covers the full range of engine speed. The machine is mounted on a table, which has provisions to connect the pump at right alignments. A flexible coupling is provided to connect the shafts, eliminating even small errors in alignment. A trip plate is provided which tripsoff every 14s. The delivery pipes from the pump are connected to the injection nozzles, the valves of which are spring loaded. The fuel delivered from the nozzle is measured by the glass vessels. When testing, the shaft is rotated at the testing speed, and the pump elements

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FIGURE 3.10  Fuel injection test bench.

deliver the fuel into a tray provided above the measuring vessels. When the air in the system is completely removed then the tray is quickly swung and the fuel is allowed to be delivered into the measuring vessels. This delivery of the fuel is allowed for 200 revolutions of the camshaft by means of a counting device. After completing the above revolutions, the tray is automatically and quickly moved over to cover the tops of the measuring vessels. In this way the fuel delivered from the individual pump element can be read and compared from the measuring vessels. Finally the pump is set and calibrated as ­specified by the manufacturer (Figure 3.10).

3.16 FUEL INJECTORS AND NOZZLES Types of nozzles: Generally, nozzles used for injection depend on the shape of the combustion chamber. The main types of nozzles are as follows: Single-hole nozzles: These are used in open combustion chambers. They consist of a single hole, usually more than 0.2 mm. The hole may be central or at an angle to the centreline of the nozzle. The spray angle used in these is very low, which affects the mixing of the fuel.

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Multi-hole nozzles: Number of holes in these nozzles is about 4–18 and size varies from 1.5 to 0.35nm. They provides better atomization compared to single-hole nozzles. Pintle nozzles: The valve of a pintle nozzle has an extension that protrudes through the hole in the bottom of the nozzle body and produces a hollow cone-shaped spray. Pintaux-type nozzles: The pintaux is a variation of the basic pintle nozzle, it consists of an additional auxiliary spray hole. The auxiliary spray is directed towards a glow plug which aids ignition under cold conditions and reduces engine knock when idling.

3.17 ELECTRONICALLY CONTROLLED UNIT FUEL INJECTION SYSTEM The power output of a diesel engine depends on the amount of fuel injected, injection pressure and injection time. In the case of conventional injection systems, injection pressure depends on the speed of the engine, which may increase fuel consumption and emission. With the help of an electronic diesel control system, overall engine performance can be improved. This system senses changes in the parameters influencing the amount of diesel supply and passes on the information to the central coordinating system, which decides the amount of the fuel to be injected and this pre-decided amount of fuel can be transferred to the engine mechanically, hydraulically or electrically with the help of pumping and metering devices. These systems also incorporate a fault diagnosis system, which alerts when faults occur. Controlling parameters sense the following:

a. Engine speed b. Charge pressure c. Coolant temperature cranking speed d. Air temperature e. Altitude f. Exhaust oxygen content g. Amount of inlet air flow h. Position of the accelerator pedal

3.18  INJECTION TIMING AND ITS IMPORTANCE Injection timing is a very important parameter which significantly influences all engine characteristics. This is mainly due to the fact that injection timing influences the mixing quality of the air–fuel mixture and, consequently, the combustion process, including harmful emission. Engines come witha particular injection timing set by the manufacturer.

3.19 SPRAY CHARACTERISTICS Diesel engine sprays are typically of a full-cone form. This means that, in the idle mode, the fuel is blocked from the upstream side of the nozzle, and during injection the centre of the spray is denser than the outer regions. Liquid spray can be

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characterised by distinguishing five regimens. The first liquid core is intact from the exit of the nozzle. A few nozzle diameters farther downstream in the so-called churning flow, the liquid consists of ligaments. These liquid components are like large droplets of a size equal to the nozzle diameter. Then the ligaments split into several smaller droplets, in a dense region, where the volume and mass fraction of the liquid phase is high. Further downstream, the process of decomposition of the droplets continues and at the same time more and more of the surrounding gas is energized into the spray field. The thick zone system consists of the thin zone (low volume but still high mass fraction of liquid) and the dilute zone (low mass fraction of liquid) respectively. Fuel spray characteristics: The most important characteristics of diesel fuel spray can be categorised as follows. • Macroscopic quantities: • Spray tip penetration • Cone angle • Microscopic quantities: • Droplet size All characteristics of fuel spray affect the combustion process and engine performance.

3.20 PRINCIPLES OF LUBRICATION SYSTEMS An IC engine consists of many moving parts. Due to continuous movement of two metallic surfaces over each other, there is wearing in moving parts, generation of heat and loss of power in the engine. Hence, lubrication of moving parts is essential to prevent these harmful effects. In engines frictional losses are attributed to the ­following mechanical losses:



i. Direct frictional losses: Power absorbed due to the relative motion of different bearing surfaces such as piston rings, main bearings, camshaft bearings, etc. ii. Pumping loss: Net power spent by the piston on the gas during intake and exhaust stroke –more in the case of four-stroke engines compared to twostroke engines. iii. Power loss to power loading and scavenge components: In a four-stroke supercharged engine, the compressor delivers high-pressure air that is mechanically driven by the engine. This is perceived to be a negative frictional loss. It is used in the two-stroke engine scavenging pump, which is also powered by the engine. iv. Power loss to drive the auxiliaries: Some power is used to drive auxiliaries such as water pump, oil pump, fuel pump, cooling fan, generator, etc. v. Lubricating function: Lubrication produces the following effects: (a) reduction in frictional effect, (b) cooling effect, (c) sealing effect and (d) cleaning effect. a. Reduction in frictional effect: The primary purpose of lubrication is to reduce friction and wear between two surfaces rubbing surfaces. Continuous friction produces heat, which causes component wear and

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loss of power. In order to avoid friction, contact between the two sliding surfaces must be reduced as far as possible. This can only be achieved by proper lubrication. Lubricating forms an oil layer between two moving surfaces. Lubrication also reduces the noise produced when two metal surfaces move over each other. b. Cooling effect: Heat generated by piston, cylinder and bearings is to a large extent eliminated by lubrication. Lubricating creates a cooling effect on the engine parts. c. Sealing effect: the lubricant reaches the gap between the cylinder liner, piston and piston rings. This prevents leakage of gasses from the engine cylinder. d. Cleaning effect: Lubrication keeps the engine clean by removing dirt or carbon from inside the engine along with oil. vi. Lubrication theory: There are two hypotheses in nature concerning the application of lubricants on surfaces: i. Fluid film theory: According to this theory, the lubricant is expected to behave as a mass of globules moving in between two surfaces. This creates a rolling effect that decreases friction. ii. The principle of boundary layers: According to this theory, the lubricant is saturated in rubbing surfaces and forms an oily film over them. Thus, the sliding surfaces are kept separate from each other, reducing friction.

3.21 FRICTION AND WEAR MECHANICS There are various factors responsible for engine performance, and decrease in life expectancy due to friction is one of them. When two parts come in contact with each other with relative motion, they may be subject to friction, and rubbing friction without any lubrication causes wear, i.e. there will be removal or transfer of solid material from one to the other and constitute parts. There are various types of the wear: Abrasion: It occurs whenever hard foreign particles are present between ­r ubbing surfaces. Sometimes due to faulty or incorrect oil or air filters, ­foreign particles may enter the cylinder which may lead to excessive wearing of engine cylinder walls and piston rings. Adhesion: When rubbing surfaces are subjected to extreme contact pressure, the frictional heat may cause momentary welding of surfaces. Corrosion: It is an effect of chemical interaction between rubbing surfaces, which over time deteriorate and lead to corrosion. Fretting: This refers to formation of the corrosive debris as an effect of confined rubbing surfaces where the motion between them is almost imperceptible and typically arises from vibration. Fatigue: If there are deformations on the both rubbing and rolling surfaces due to repetitive loading then fatigue takes place in the component and it is subjected to crack initiated just below the contacting surfaces.

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3.22 LUBRICANTS: THEIR COMPOSITION AND PROPERTIES There are two fundamental aspects to lubricant performance: achieving the required level of friction and wear rates, and maintaining these standards in spite of continuous degradation of the lubricant. These aspects are associated with the properties and the composition of the lubricant. The selection and formulation of appropriate mixtures of hydrocarbons for the purposes of lubrication is a very skilled and complex process. Lubricants made from natural or mineral oils are partly refined and partly impure, and some additives can be used to radically change the properties of a lubricant and are essential to the overall performance of the lubricant. They also dictate specific characteristics of the lubricant, such as corrosion tendency, foaming, clotting, oxidation, wear, friction and other properties. These are the chemical substances which are added to the lubricating oil either to reinforce some of its natural properties or to provide it with certain new properties which it does not possess originally. Additives of lubrication oil and their function:

1. Viscosity index improvers: long chain, high-molecular-weight polymers 2. Pour point depressants: alkyl aromatic polymers 3. Antioxidant: aromatic amine compounds 4. Extreme-pressure (EP) additives: polysulphides, phosphate, dithiophosphates, and dithiocarbamates. 5. Oxidation inhibitors: organic compounds such as amines, sulphides or ­phenols with metals like tin, zinc, etc. 6. Anti-foaming additives: polyorganosiloxanes The following are the essential properties required for the suitability and the optimal performance of the engine oil in the various operating conditions.

a. Viscosity: Viscosity is a measure of the flow ability of oil under a particular temperature and pressure. b. Flash point or fire point: The lowest temperatures at which oil just flashes and catches fires (continues to burn) are known as flash or fire points. These two temperatures must be sufficiently high for any lubricating oil to avoid flash or burn during use. c. Cloud:  The low temperature at which the lubricant changes from liquid state to a semi-solid or solid state is called cloud point. d. Carbon residue:  Lubricating oils being chemical compounds of carbon and hydrogen, when burnt it deposit carbon on engine parts. This should be as low as possible for lubricating oil because such depositions may impact on engine performance. e. Corrosion: A lubricant should not corrode the working parts. f. Pour point: The lowest temperature at which the oil pours is called its pour point. Oil below this temperature cannot be used. g. Dilution of crankcase oil: Petrol vapour may escape past the piston rings during the compression stroke, which mixes with oil and affects its lubricating property. The test which determines the amount of dilution in crankcase oil indicates the suitability of such oil.

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h. Oxidation at high temperature: Lubricating oils may break down at high temperatures due to oxidation, producing hard carbon and varnish, which deposit on engine parts and impact engine performance. Therefore, lubricants must resist oxidation. i. Evaporation: Evaporation test is conducted to determine the quantity of oil that may evaporate at high temperatures. Lubricating oil should have a low evaporation characteristic. j. Sulphur content: Sulphur in a corrosive form is detrimental in lubricating oil. Thus its presence should be avoided. k. Specific gravity:  Specific gravity of lubricating oil varies considerably and hence should not be regarded as the main indication of its lubricating property.

3.23 WET SUMP LUBRICATION DEVICE The bottom of the crankcase contains an oil pan or a sump from which the lubricating oil is applied to different engine components. Upon lubrication, the oil flows back to the sump due to gravity. There are three types of wet sump lubrication systems: i. Splash system: This lubrication system stores lubricating oil in an oil sump. In the lower part of the connecting rod, a scoop or dipper is made. When the engine is working, the dipper dips in the oil at any turn of the crank shaft, and the oil is splashed on the cylinder wall. Due to the action of the engine walls and the piston ring, the crank shaft bearings are lubricated. It is used for light-duty engines (Figure 3.11). ii. Splash and pressure system: Lubricating oil is supplied under pressure to the primary camshaft bearings and pipes which guide the oil stream against the dippers on the large end of the connecting rod bearing cup and, thus, the crankpin bearings are lubricated by splashing or spraying the oil from the dipper. iii. Pressure feed system: In this lubrication system, the engine parts are lubricated under pressure feed. Lubricating oil is stored in a separate tank (in the case of a dry sump system) or in a sump (in the case of a wet sump system) from which an oil pump (gear pump) delivers oil to the main oil gallery at a pressure of 2–4 kg/cm2 through an oil filter. The oil from the main gallery goes to the main bearing, where some of it falls back to the sump after lubricating the main bearing, and some of it is splashed to lubricate the walls of the cylinder and the remaining goes through the hole to the crank pin. Due to the crank pin provided, the lubricating oil goes to the piston pin through a hole in the connecting rod, where the piston rings are lubricated. For the lubrication of the camshaft and the gears, the oil is transferred into a separate oil line from the oil gallery. The oil pressure gauge used in the machine shows the oil pressure in the machine. The oil filter and strainer in the device separate the oil from dust, metal particles and other harmful particles (Figure 3.12).

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FIGURE 3.11  Splash lubrication system.

3.24 DRY SUMP LUBRICATION SYSTEM In this system, oil is supplied from an external tank. The oil pump draws oil from the supply tank and circulates it under pressure to various bearings of the engine. The oil dripping from the cylinders and bearings into the sump is removed by a scavenging pump and is returned to the supply tank through the filter. The capacity of the scavenging pump is greater than the oil pump. A separate oil cooler is used to remove heat from oil using either air or water (Figure 3.13).

3.25 MIST LUBRICATION SYSTEM This type of lubrication is used where crankcase lubrication is not suitable, and it is mostly adopted in two-stroke petrol engines, such as in scooters and motor cycles. It is the simplest form of lubricating system. It does not consist of any separate oil pump component for lubrication purposes. In this system, the lubricating oil is blended into the fuel (petrol) when filling the fuel tank of the vehicle at a specified ratio (the fuel and lubricating oil ratio is from 12:1 to 50:10 as per manufacturer’s requirements or recommendations).

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FIGURE 3.12  Pressure lubrication system.

FIGURE 3.13  Dry sump lubrication system.

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3.26  PRINCIPLES OF COOLING SYSTEM Cooling is associated with internal temperature equalization to avoid local overheating and to extract sufficient heat energy to maintain a realistic overall working temperature. Necessity of the Cooling System The temperature of the combustion gasses in the engine cylinder is between 1,500°C and 2,000°C, which is above the melting point of the cylinder body and the engine head. Thus, if the heat is not dissipated, then the failure of the cylinder material will result. Due to very high temperatures, the lubricating oil film is oxidized to produce carbon deposits on the surface. This will result in the loss of the piston. Due to ­overheating, large temperature differences may lead to a distortion of engine components due to the thermal stress setup. This makes it necessary to keep temperature variations to a minimum. Higher temperatures also affect the volumetric performance of the engine.

3.27 LIQUID COOLING SYSTEM A water/liquid cooling system can be divided into the following two types:





a. Thermo-syphon system: The water is circulated in the water jackets provided in the cylinder block and cylinder head. The principle of the natural convectional current of water is used in this system. As the temperature of water increases, there is change in density and this enables circulation of the water. This type of cooling system is used in all automotive engines. The water is circulated in the water jackets provided in the cylinder block and cylinder head with the help of a water pump driven by a crankshaft through belt. The water absorbs heat from the engine, due to this the temperature of the water increases. This hot water is again circulated through the radiator or heat exchanger, which transfers heat from water to air and reduces the water temperature. b. Forced or pump cooling: This system is used in a large number of vehicles, such as cars, buses, trucks and other heavy vehicles. Here water is circulated in pumps with the help of convection currents. The water or coolant is circulated through jackets around the parts of the engine to be cooled, and is kept in motion by a centrifugal pump, driven from the engine through a V-belt. c. Cooling with a thermostatic regulator: • Whenever the engine is started from a cold condition, the coolant t­emperature has to be brought to the desired warmup time to avoid ­corrosion damage due to condensation of acids as well as to help easily start the engine. This can be done by the use of a thermostatic device or thermostat. • It is a kind of check valve which opens and closes with the effect of temperature. It is fitted in the water outlet of the engine. During warm up, the thermostat is closed and the water pump circulates only through the cylinder block and the cylinder head. When the usual o­ perating temperature is reached, the thermostat valve opens and allows hot water to flow to

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the radiator. Standard thermostats are designed to be opened at ­70°C–75°C and completely opened at 82°C. High-temperature ­thermostats with permanent anti-freeze solutions (Prestine, Zerex, etc.) open at 80°C–90°C and completely open at 92°C. There are three types of thermostats: i. Flexible bellows-type valve: These are filled with alcohol or ether. As the ­bellows are heated, the liquid vaporises, producing enough ­pressure to extend the bellows. The gas condenses when the device is cooled. The ­pressure decreases and the bellows fall to close the valve. ii. Bimetallic-type valve: consists of a bimetallic chain. The uneven expansion of the two metallic strips causes the valve to open and allows the water to flow into the radiator. iii. Wax-type valve: It can operate reliably within the specified temperature range: Heat is transmitted to the wax, which has a high coefficient for thermal expansion. Upon being heated, wax expands and the rubber plug presses the plunger forcing it to move vertically upwards.

3.27.1 Pressurised Water Cooling System • In the case of a typical water-cooling device where the cooling water is exposed to ambient pressure, the water boils at 212°F. But the boiling temperature of the water increases when the water is heated in a closed radiator under high pressure. Higher water temperature increases the efficiency of the engine and provides additional protection under high altitude and tropical conditions for long periods of hard driving. The pressure-type radiator cap is also used for the forced circulation cooling system. The cap is placed on the neck of the radiator with an air-tight lock. The pressure-release valve or safety valve may be opened at a pressure between 4 and 13 psi. With this rise in pressure, the boiling temperature of the water increases to 243°F (at 4 psi boiling tap 225°F and 13 psi boiling water temperature 243°F). Any change in pressure is triggered by the opening of the pressure valve or the safety valve to the atmosphere. During cooling, the vapours will ­condense and a partial vacuum will be formed, resulting in the collapse of the hoses and tubes. In order to solve this problem, the pressure release valve is connected to the vacuum valve that opens the radiator to the atmosphere (Figure 3.14).

3.27.2 Components of a Water Cooling system Water Pump The water pump is a mechanical pump that circulates the engine coolant/antifreeze through the radiator and back to the engine. Since they are mechanical pumps, they are usually driven by an accessory drive belt or by the timing belt-chain (depending on the vehicle). It consists of the following parts: 1. Impeller 2. Pump body

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FIGURE 3.14  Pressurised water cooling system.

3. Gasket 4. Shaft 5. Bearing Thermostat The thermostat is a temperature-sensitive orifice in the cooling system that opens and closes according to engine temperature to regulate the flow of coolant-­anti-freeze through the radiator and back to the engine. When the engine coolant t­ emperature is low, the valve closes to prevent the engine coolant flowing to the radiator, thus permitting the engine to warm up rapidly. After reaching a particular temperature, it opens and supplies the coolant to the engine. This allows for the engine to be run at specific temperatures to optimize the performance and emissions levels of the vehicle. Radiator The radiator is basically a finned box mounted at the front of the vehicle that the coolant is forced through so that air may pass across it and cool the anti-freezecoolant. The fins act as heat syncs to help dissipate the heat. The radiator consists of the following parts:

1. Inlet tank 2. Radiator core 3. Radiator cap 4. Hoses

The radiator holds a large volume of coolant in close contact with a large volume of air so heat will transfer from the coolant to the air.

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Cooling Fan The cooling fan is located directly behind the radiator, irrespective of front- or ­rear-wheel drive. Its job is to pull air through the radiator at lower vehicle speeds to keep it from over-heating. Cooling fans can either be mechanical (belt driven on the engine) or electric (mounted on the radiator, temperature controlled). Hoses Normally rubber hoses are used in cooling systems and they are designed to w ­ ithstand the cooling system pressure. They have very good resistance to coolant, water and temperature. Coolant is pumped by the water pump is sent through these hoses to the radiator and back to the engine. Checking the hoses for damage, crack and leakage is one of the important engine checks at the time of servicing. Advantages of the Water Cooling System

1. Heat transfer rate of water is more compared to air, so compact design of the system is possible. 2. Water-cooled engines can be placed anywhere in the vehicle. 3. Volumetric efficiency of water is more compared to air-cooled engines. Disadvantages

1. It increases weight and dimensions of the engine. 2. Warmup performance is poor. 3. Higherpower consumption. 4. Requires high maintenance.

3.28 AIR COOLING SYSTEM Air cooling is generally used for small engines, which are exposed to high air flow. Cooling fins are provided on the engine; especially in the combustion chamber, the air flow on the fins carries excess heat. This is a simple cooling system used in all motorcycle engines. The amount of heat dissipation depends on the following factors: • Surface area available: As the surface area increases, rate of heat dissipation increases. • Thermal conductivity of the material. • Temperature difference. Advantage of the air cooling system:

1. Light weight 2. No liquid coolant hence no leakage 3. No friction and wear 4. No need to add anti-freeze, etc.

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Disadvantages of the air cooling system:

1. This is not suitable for engine producing higher power because of complex nature of the fins. 2. Only used for engine directly exposed to air. 3. Engines give low power output

3.29 CURRENT ADVANCEMENTS IN COOLING SYSTEMS Today the cooling system in the car is more compact and more efficient. Modern technologies like electric thermostat, electric water pumps and viscous pumps are making engines run in narrow temperature ranges, making them more fuel efficient and less pollutant. The most important techniques now a day is that the various additives can be added to enhance the quality of the coolants.

3.30 PRINCIPLES OF AIR INTAKE AND EXHAUST The intake and exhaust system plays an important role in the breathing of an engine. Its function is to remove exhaust gasses at the end of power stroke, while suctioning the fresh charge during the next cycle. Power development of an engine is directly related tothe amount of air sucked during the suction stroke, so engine must be ­provided with a good intake system. Generally, an SI engine’s intake system consists of the following parts: • • • •

Air filter Carburettor Throttle or fuel injector Throttle or throttle with individual fuel injectors in each intake port and intake manifold.

Requirements of a good inlet manifold are to supply equal amount of the charge to all cylinders, have minimum resistance to flow, provide a direct flow to each cylinder. While exhaust manifolds are used for removal of the exhaust within minimum ­possible time, working as drainage for the heavier fraction of the exhaust and minimum possible internal friction.

3.31 AIR CLEANERS AND SILENCERS An air cleaner serves two functions: First, it works as a silencer – at the time of ­suction stroke, suction pressure is high, producing excessive noise (unwanted sound). The internal shape of the air cleaner is designed in such a way that it minimises the sound of incoming air. Second, it works as flame arrester, in case of backfiring of the engine. Generally, the efficiency of the filter is about 99%. For automobile engine filters, filtering media are paper, composite material (paper+melt blown) and synthetic.

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Generally, modern air filters consist of a system with a “raw air” pipe with an air inlet, filter housing, dampers to reduce intake noise, a filter element and a cleaned-air line with a hot-film air-mass sensor (HFM).Space required for this system is very less it does not affect engine performance.

3.32 INTAKE AND EXHAUST MANIFOLDS An automobile engine has two types of manifolds: intake manifold and exhaust ­manifold. Manifolds play an important role in the engine breathing system. If they are designed incorrectly, engine output will be affected.

3.32.1 Intake Manifolds The function of the inlet manifold is to supply equal amount of charge to each ­cylinder, without change in the air fuel ratio, to provide equal aspiration to each cylinder. There must be minimum restriction to the flow of fuel. The passages provided in intake manifold are called runners. Runners must be shaped in a way that there is a minimum restriction to the flow, such as without sharp corners in the internal wall surfaces. In the case of in-line engines, manifolds are simple in construction. Sometimes runners can supply the mixture to two adjacent cylinders, these are called Siamese runners. Manifolds used for V engines are called dual plane manifolds.

3.32.2 Exhaust Manifolds An exhaust manifold collects all the exhaust gasses from the cylinder and delivers it to the exhaust pipe. It is mounted on the cylinder head’s exhaust ports. V-type engines have two exhaust manifolds and in-line engines have one. When the intake and exhaust manifolds are on opposite sides of the engine, the head is called cross flow head. Engine exhaust manifolds are generally made up of cast iron or steel. The exhaust temperature depends on the engine’s loading condition. As the engine load increases, the temperature of the exhaust gasses increases and manifold runs red hot. Generally manifold runs cooler when idle.

3.33 TAILPIPE EMISSIONS FROM VEHICULAR ENGINES The emissions discussed so far are evaporative emissions, which are mainly of unburned hydrocarbons. Emissions from the SI engine contain CO, CO2, NOx, unburned HC, etc. Generally to achieve minimum emission, it is expected for the engine to operates at maximum power and speed and it must run with a leaner air– fuel ratio, but it cannot; it operates with a rich mixture, i.e. air supplied to the engine to complete reaction is less and as the speed of the vehicle increases; time available to complete the reaction is also very less. So there is increase in emission of the vehicle.

3.34 HC, CO, NOX, PM FORMATION PROCESS 3.34.1 Formation of Nitrogen Oxides Nitric oxide is the major component of NOx emission from IC engines. During c­ ombustion, there are three probable sources of NO formation:

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i. Thermal NO: By oxidation of atmospheric (molecular) nitrogen at high ­temperatures in the post-flame burned gasses ii. Prompt NO: Formed at the flame front within the flame reaction zone iii. Fuel NO: Oxidation of fuel-bound nitrogen at relatively low temperatures

3.34.2 HC Emission Incomplete Combustion: Even when the fuel and air entering the engine are at the optimal stoichiometric ratio, there is no complete combustion and some HC ends up in the exhaust. Volumes of Crevice: Air and fuel are squeezed into the crevice volume of the combustion chamber at high pressure during the compression stroke and early part of the combustion process. As much as 3% of the fuel in the chamber can be pushed into this amount of crevice. Later in the process, during the expansion stroke, the pressure in the cylinder is decreased below the crevice volume pressure and reverse blow occurs. Leaking past the exhaust valve: As the pressure increases during compression and combustion process, some air and fuel is pushed into the crevice volume around the edges of the exhaust valve, between the valve and the valve seat. A even small amount flow through the valve into the exhaust manifold, which is still in this crevice volume is being brought into the exhaust manifold, and there is a momentary increase in HC concentration at the start of the blast. Valve overlap: During overlapping of the valve, both the exhaust and the intake valves are opened, providing a pathway where the intake of air–fuel will flow directly into the exhaust. This flow is reduced by a well-designed engine, but a small amount can get through. The worst condition for this is idle and low speed, with the greatest overlap in real time. Deposits on the walls of the combustion chamber: Gas particles, like fuel vapour, are absorbed by the compounds on the walls of the combustion chamber. The amount of absorption is a function of the gas pressure, so that the maximum is achieved during compression and combustion. Later in the cycle, when the exhaust valve opens and the pressure of the cylinder is reduced, the absorption capacity of the deposit material is reduced and the gas particles are dissipated back into the cylinder. These particles, including some HC, are then removed from the cylinder during the exhaust stroke. Oil on the walls of the combustion chamber: A very thin layer of oil is collected on the cylinder walls of the engine to provide lubrication between the cylinder and the moving piston. The incoming air and fuel come into contact with this oil film during the intake and compression strokes. In much the same way as wall deposits, this oil film absorbs and dissipates gas particles, depending on the gas level. When the cylinder pressure is high, gas particles, including fuel vapor, are absorbed into the oil film during compression and combustion. When the pressure is later decreased during expansion and blowing down, the absorption potential of the oil is decreased and the fuel particles are dissolved back into the container. Particulate matter is a mixture of soot and other liquid- or solid-phase material that is produced as the exhaust gasses pass through the filter. It involves five processes: pyrolysis, nucleation, coalescence, surface production, agglomeration and oxidation.

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CO formation: Maximum CO formation takes place when the engine runs with the rich mixture, such as during starting and acceleration; poor mixing, rich regions and incomplete combustion also lead to formation of CO.

3.35 METHODOLOGIES ADOPTED TO REDUCE EMISSION Enhancement in quality of life, rapid economic growth and improper transportation facilities are the main reasons forthe increase in vehicle population. Automobile engines are a major source of air pollution. Constituents of the automobile engine emission are CO, CO2, unburned HC, particulate matters, etc. The emission control technology is based on the following four principles:

1. Modification in design parameters: stroke to bore ratio, compression ratio, cylinder displacement, surface to volume ratio, etc. 2. Modification in operating variables: loads, speed, spark retard, etc. 3. Exhaust after-treatment: air injection, exhaust gas recirculation, catalytic convertor, etc. 4. Fuel modifications: mixing of various types of additives, blending of the fuels, etc.

3.36 CURRENT ADVANCEMENTS IN EMISSION CONTROL AND REDUCTION Soot can be minimised with the help of DPFs (diesel particulate filters), but a DPF requires periodic regeneration (i.e. removal of the collected soot), which increases fuel consumption. Generally diesel engines work on lean to stoichiometric so UHC and CO are not available for conversion of NOx into Nitrogen by using three-way catalysts. There are devices like lean NOx traps (LNT), selective catalysts reduction (SCR) which can be used for the reduction in NOx. But the efficiency of NOx traps is up to 60%–70%. There is growing interest in supplementing LNT performance with integrated SCR, which utilizes ammonia generated in the LNT during rich regenerations. But for the engine relying on the LNT for NOx reduction must periodically operate rich to reduce the stored NOx thus the fuel efficiency reduced. In SCR technology, the reducing agent (urea) can be stored on the vehicle and injected, but this consumes energy, which increases fuel consumption.

3.37 PRINCIPLES OF TURBOCHARGING AND SUPERCHARGING Important factors on which power depends are • Amount of air sucked per unit time • Thermal efficiency • Compression ratio This amount of air can be increased by increasing the speed of the engine or ­supplying more air to the engine. The induction process in automotive engines is either ­naturally aspirated or forced.

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3.37.1 Naturally Aspirated Engines In case of naturally aspirated engines induction of air is carried out by pressure difference between the manifold and cylinder. The pumping action here can help in breathing of automotive engines. This depends on the design of the intake arrangement. Sufficient denser air may increase the mean effective pressure of the engine, therefore producing greater torque and power.

3.37.2 Forced Induction Increase in mean effective pressure increases output power and torque of the engine. This requires pressure charging. Pressure charging supplies air continuously above the atmospheric pressure, which increases the density of air. Charging of an engine supplies more oxygen to the combustion chamber, improves the combustion process and reduces emission. This can be achieved by a supercharger, which supplies air with high density to the engine, the ultimate effect of which is increase in power. It also improves the atomisation of the fuel, reduction in exhaust smoke, acceleration response of the vehicle and increasing the mechanical efficiency of the engine. Generally, pressure charging or supercharging can be carried out in the following two types • Superchargers which are driven by exhaust gasses and do not consume engine power. • Superchargers which are driven by engine power with the help of gear, belt chain and drive arrangements.

3.38 TYPES OF SUPERCHARGERS AND THEIR CONSTRUCTIONAL DETAILS The turbine used in superchargers is driven by engine power, while in turbochargers it is driven by exhaust gas. Expectation from automotive engines includes minimum possible fuel consumption and reduction in emission. Superchargers can be installed in SI engines in the following two ways”

1. Between the air cleaner and carburettor 2. Between the carburettor and the engine

Both arrangements have advantages and disadvantages. The advantages and limitations of supercharging are as follows. Advantages • It keeps the cylinder temperature as low as possible even under heavy load conditions. It reduces the thermal stresses on engine components and increases engine life. • Reduces the NOx emission by providing low inlet air temperature.

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• It increases the knock limit of an engine, and allows higher mean effective pressure. • It reduces black smoke emission at lower engine speeds and higher load conditions. • Correctly matched supercharger may reduce fuel consumption. Limitations • • • • •

Increases thermal stresses (in the case of SI engine) Increases gas loading Increases cooling requirement of the piston and valves Some part of power is required to drive the compressor In SI engines, it increases chances of detonation

There are three types of superchargers in use:





1. Centrifugal type In this type, the impeller rotates in a closed casing. It operates on the principle of centrifugal force. Due to centrifugal action, the pressure of inlet air increases. Considerable quantity of air can be delivered by relatively small size of centrifugal type superchargers. 2. Roots type It consists of two cylindrical lobes rotating in opposite directions, and in same casing. One rotor is connected to the other by gears so both rotors rotate at the same speed. The roots blower operates on the principle of gear pump. The mixture supplied to the outlet has more pressure compared to the inlet mixture. 3. Vane type It consist of a drum on which a number of vanes mounted enclosed in a casing. Against the spring force, the vanes slide in and out and maintain continuous contact with the body. The space between the drum and the inner surface of the body decreases from the inlet to the outer side of the body. The quantity of air which enters at the inlet decreases in volume, which increases outlet pressure. Construction A supercharger consists of the following parts: • Turbine • Compressor • Intercooler • Connecting shaft • Bearings and housings • Belts for drive arrangement

In cases where the supercharger turbine is driven by engine crankshaft, air with higher density can be supplied. This will supply more oxygen to the fuel, compared to a naturally aspirated engine.

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FIGURE 3.15  Details of a turbocharger.

3.39 TYPES OF TURBOCHARGERS AND THEIR CONSTRUCTIONAL DETAILS The following are the different types of turbocharger

1. Single turbo 2. Twin turbo 3. Twin-scroll turbo 4. Variable geometry turbo 5. Variable twin scroll turbo 6. Electric turbo

The turbocharger consists of a compressor wheel and an exhaust gas turbine wheel connected together by a shaft, which is used to enhance the intake air pressure of the IC engine. The exhaust gas turbine extracts energy from the exhaust gas and uses it to power the compressor and to prevent friction. Generally, in automotive applications, both the compressor and the turbine wheel are of a radial flow type. Many systems, such as medium and low-speed diesel engines, can use an axial flow turbine wheel instead of a radial flow turbine (Figure 3.15).

3.40 ENGINE ELECTRONICS AND MANAGEMENT SYSTEM Engine Electronics: As fuel economy is considered performance efficiency, recent vehicular engines are being equipped with various electronically operated systems and subsystems which are integrated with the engine management system (EMS). The various sensors and actuators associated with it are as follows: • • • • • • •

Exhaust gas or oxygen sensor Engine temperature sensor Air flow sensor Air inlet temperature sensor Throttle position sensor Manifold pressure sensor Camshaft position sensor

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Engine Management System: In a passenger car, the EMS is an electronically controlled system that uses an ECU (engine computer) to optimize engine operation at all times. Various types of sensors in the EMS detect the operating condition of the engine and transmit the information to the ECU engine which, in turn, electronically controls the different types of actuators (motors) used to operate the engine under optimum conditions. The basics of the EMS configuration are as follows: Intake system: The intake system adjusts the air volume required for combustion and detachment. The mass air flow sensor is used to measure the volume of intake air filtered by the air cleaner directly. The air volume adjustment is performed on the throttle body and the idle speed control valve (ISCV), and the air is drawn into the cylinder. The idle speed control in vehicles equipped with electronic throttle control (ETC) is carried out by ETC only without the use of an ISCV. Fuel System: The fuel system controls the supply of fuel required for combustion. After the fuel pump is drawn and the fuel is discharged, the pressure regulator keeps the fuel pressure at a constant level and the excess fuel is returned to the fuel tank. The fuel then travels through the fuel filter, which removes dust and moisture, passes through the delivery pipe, and is fed to the injectors. When the fuel is injected by the injector, there is a slight fluctuation in pressure. The pulsation damper absorbs the pulsation of the fuel pressure at that time. Air Fuel Ratio Feedback System: This system maintains the engine in an optimum condition by monitoring the exhaust gas conditions. In this system, a lambda sensor detects the concentration of oxygen in the exhaust gas and the ECU engine analyses the combustion conditions of the engine in order to control various actuators such as the exhaust gas recirculation valve for both diesel and gasoline engines to suit driving conditions. Ignition system: The ignition system generates the sparks necessary for the ignition of the air–fuel mixture. The optimal ignition timing is calculated by the ECU engine according to each driving condition. The ignition signal is then sent to the ignition coil (stick coil). The ignition coil generates a high voltage based on the ignition signal. This high voltage is then applied to the ignition plug electrodes, which generate ignition and cause the air–fuel mixture to burn within the cylinders. Exhaust Gas Treatment System (Diesel Engines): The exhaust gas treatment ­system includes a DPF to trap particulate matter in the exhaust gas, an exhaust gas temperature sensor to detect the exhaust gas temperature and a DPF pressure sensor to detect the loss of pressure in the exhaust gas. The system controls the exhaust gas temperature and fuel injections to burn the particulate matter trapped in the DPF (DPF regeneration control) system. As a result, exhaust emissions are reduced without reducing engine performance. Control system: This system uses the ECU engine to determine the optimum fuel consumption rate, timing of injection, timing of ignition, optimum control of exhaust gas, output, etc. in accordance with the operating conditions of the engine detected by the various sensors, in order to control the various actuators (Figure 3.16).

Vehicular Engines

FIGURE 3.16  Engine management system.

SUMMARY • An IC engine is a mechanical device which converts chemical energy of  the fuel into heat and finally into mechanical power through the ­working fluid. • Engines consist of cylinder block and crankcase, piston and rings, valve train, crankshaft and bearings, connecting rod and bearings flywheel, timing drive, etc. • Engine working on four stroke cycle operations suction, compression, power, exhaust stroke, at the time of suction inlet valve is open, for compression and power both the valve are closed, while for exhaust valves are closed. • Vehicular engines consist of various systems and subsystems, such as fuel supply, cooling lubrication systems, cooling systems, intake and exhaust, starting ignition systems, etc. • In a passenger car, the EMS is an electronically controlled system that uses an engine computer (the ECU) to optimise engine operation at all times.

MULTIPLE-CHOICE QUESTIONS 1. The function of the carburettor is a. To mix air and fuel inside the combustion chamber b. To mix air and fuel inside the inlet manifold c. Tomix air and fuel outside the combustion chamber d. All of the above

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2. Fuel injection system provides a. Better atomisation b. Increase in volumetric efficiency of the engine c. Reduction in emission d. All of the above 3. Injection pressure in the indirect injection system compared to direct ­injection is a. More b. Less c. Equal d. None of the above 4. The goal of supercharging is to increase the a. Density of the charge b. Quantity of the fuel c. Temperature of the charge d. None of the above 5. The compressor in a turbocharger is driven by a. Electric motor b. Exhaust gas c. Engine power d. None, it rotates automatically 6. The compressor in a supercharger is driven by a. Electric motor b. Exhaust gas c. Engine power d. None, it rotates automatically 7. Size of inlet valves compared to exhaust valves is a. Bigger b. Equal c. Small d. None of the above 8. Multi-cylinder engines are more smoother in operation compared to singlecylinder engines because a. Minimum interval of power impulses b. Bigger size c. Small flywheel d. All of the above 9. The function of the flywheel is to a. Absorb engine vibrations b. Store energy c. Both a and b d. None of the above

Vehicular Engines

REVIEW QUESTIONS • • • • • • • • • • • • • • • • •

Describe the working of a forced cooling system. Describe the working of a radiator. Describe various properties of the lubrication oil. Provide the classifications of the lubrication oil. Compare air cooling and water cooling systems. What is supercharging? What are the limitations of a supercharger? List the components of a supercharger. List the advantages and disadvantages of the pressure charging system. List the common faults in the pressure charging system. Why is a control system necessary for supercharging? List the components of the fuel supply system of a petrol engine. Explain the process of carburetion. List the disadvantages of the carburetted fuel injection system. List the advantages and disadvantages of the fuel injection system. Describe electronic throttle control. List the constructional details of the following: 1. Piston and piston rings 2. Crankshaft and flywheel 3. Cylinder block and crankcase • Explain the working principle of an IC engine. • Draw a neat sketch of an engine. • Explain valve train in brief. Answers to MCQs: (1) c (2) d (3) b (4) a (5) b (6) c (7) a (8) a (9) c

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4

Automotive Clutches

OUTCOME Learning Objectives • • • • • •

Necessity and functions of the clutch Working principle of the clutch Requirements of the clutches Construction and working of various types of clutches Operating mechanism of the clutch Design of the clutch

4.1 INTRODUCTION The clutch is a device used to connect the two co-axial (collinear axis) shafts having relative motion (different speeds). The meaning of the word clutch is to grip tight or grasp. Clutch engages and disengages the engine to the transmission system from the gear box. The clutch is always in the engage position. At the time of moving from stationary or when necessary changes are required in the gear box as per traction requirements, the driver presses the clutch pedal to disengage it.

4.2 NECESSITY AND FUNCTIONS OF THE CLUTCH Traction requirement of a vehicle continuously changes with the resistances offered by the vehicle. It is necessary to transfer the maximum torque smoothly to the wheel through the various controls of the transmission system. The clutch is the link between the engine and the transmission system, which plays an important role in the following cases:

1. When, due to certain limitations the engine is unable to run at very low rpm. The engine cannot provide sufficient torque for positive engagement of the transmission. Initially, at the time of starting the vehicle, it is in the neutral position, and when the vehicle is started, engine rotates with certain speed and the remaining transmission system from the clutch is stationery. 2. When the driver needs to shift from a lower to a higher gear and vice versa. In both these cases, when the shaft is connected directly there are chances of jerk and damage to the system. To avoid this by means of smooth engagement, the clutch is necessary.

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Functions of the Clutch

1. Smooth transmission of the rotary motion from rotating shaft to stationary or slowly rotating shaft without snatch or jerk. 2. To facilitate positive transmission at maximum engine torque when the road speed of the vehicle is high enough for the engine to be directly coupled to the transmission without it stalling. 3. Rapid engagement and disengagement of the engine from transmission while one or both shaft in motion at the time of gear change during sudden acceleration and sudden stoppage.

4.3 WORKING PRINCIPLE OF THE CLUTCH Basically all automotive clutches work on the basis of the principle of friction F = μR. Suppose there are two cases. In the first case the block is resting on the table, and the force applied due to the self-weight of the block is W1 and the reactive force acting on block in vertical direction is R1. This block is in an equilibrium condition. In second case, the same block is present but an external weight is added in the box with a magnitude W2 and the reactive force acting on this is R2. Now in the second case the total weight is W and total reactive force is R. Still the block is in stationary condition. By considering the equilibrium we can write

W = R (4.1)

Now pulling force F1 is applied to pull the first box and force F is applied to the second case. The pull required in the second case is more compared to the first due to addition of extra weight in the second case, i.e. as W2 increases the value of W also increases.

FαW (4.2)

And from equation (4.1), we can write FαW and

F = µR

where μ is the coefficient of friction, which depends on the surface of contact. During gradual engagement of the flywheel and the pressure plate, the friction between these transmits the turning mechanism from one shaft to another. The amount of power transfer depends on the percentage of slip; if slip increases, the rate of power transfer decreases. Let us assume that the two discs came into contact, as shown in Figure 4.1, the force W which is provided by the thrust springs which holds these two plates together, the rate of the transfer of frictional drag force and the turning effort depends on the grip between the two surfaces. From Figure 4.1, the frictional torque produced can be calculated as follow

Automotive Clutches

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FIGURE 4.1  Working principle of the clutch.



Frictional Torque = friction force (N) × mean radius (m)

In Figure 4.1, there is only one frictional surface, where the friction plate is used to get the desired effect of the torque transmission.

4.4 CLASSIFICATION OF CLUTCHES Clutches can be classified as follows: 1. Positive contact clutches, e.g. square jaw and spiral jaw clutches 2. Progressive engagement or friction clutches, e.g. single-plate, multi-plate, cone, centrifugal clutches 3. Electromagnetic clutches, e.g. magnetic hysteresis clutches and eddy ­current clutches 4. Fluid clutches and couplings, e.g. fluid flywheel clutch

4.5 REQUIREMENTS OF THE CLUTCH Basically, for vehicular applications friction clutches are used, i.e. single-plate, multiplate, centrifugal, or cone clutches. 1. Maximum torque transmission: It should be able to transmit maximum engine torque by providing a linkage. 2. Gradual engagement: Clutch should be able to engage gradually and ­positively without jerk. 3. Dissipation of heat: Due to rubbing action, more heat will be generated, so the clutch should be designed to dissipate maximum heat. 4. Dynamic balancing: For high-speed applications, clutch must be properly balanced. 5. Vibration damping: There should be a proper mechanism to damp ­vibrations produced due to power pulses in the engine. 6. Free pedal play: Drivers have a habit of placing their foot on the clutch pedal when not being used. To avoid improper engagement and effective load on the bearings there, should be provision for free pedal play.

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Automotive Systems

7. Less inertia: The clutch must have less moment of inertia. 8. Ease of operation: The clutch should be easy to operate.

4.6 TORQUE TRANSMISSION CAPACITY OF THE CLUTCH Torque transmission capacity of the clutch can be calculated by using the following equation: T = µWR.n

where

W- Axial Force applied, R- Mean effective radius, n- Number of points of friction and µ- Coefficient of friction. Torque transmission capacity of the clutch depends on the following factors.

Number of Friction Surfaces In the case of a single-plate clutch, there are generally two types of friction surfaces. As the number of friction surfaces increases, the torque transmission capacity of the clutch enhances for a given clamping pressure. If the number of friction plates increased up to three, the torque transmission capacity increases twice or thrice at the same spring pressure. Increase in the number of frictional surfaces increases the possibility of heat dissipation, so a higher factor of safety should be adopted in this case.

Surface Area/Size of the Friction Plate (Which Depends on the Mean R adius of the Friction Plate) When the surface area of the frictional surface is increased it may lead to increase in the inertia of the friction plate, mean radius and increases the torque transmission capacity as in case of disengagement of the clutch.

Pressure over the Disc There are certain limits for the clamping pressure applied to transmit the torque, as the clamping pressure increases, it affects the friction properties which in turn affect the life of the friction plate.

Coefficient of Friction of the Material Used There are certain materials available with high coefficient of friction which can be used as the friction ‘lining of the material but there is problem of snatch and unstability during the take up. So there is limitation to use the maximum coefficient of friction.

Automotive Clutches

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Elements of the Clutch and Their Construction Basically the clutch consists of the following three parts: 1. Driving member: The driving member consists of flywheel and pressure plate assembly. The clutch plate is in between the pressure plate and ­flywheel. Pressure plate assembly consists of the mechanism used to press the friction plate or clutch plate. The driving member of the clutch assembly is bolted to flywheel. Generally the clutch plate revolves with the flywheel but when the clutch is disengaged the flywheel as well as the pressure plates are free to rotate (Figure 4.2). 2. Driven member: Driven members consists of clutch or centre plate and it ­consists hub, friction linings, cushion spring, damper springs, etc. (Figure 4.3). 1. Cushion springs or borglite segment: To achieve axial cushioning between frictions lining, the surfaces are provided with T slots around the outer rim of the disc. In these slots cushion springs are mounted to provide progressive take up over a greater pedal travel, equal ­pressure distribution and prevent snatch. It also provides protection from the clutch feeding which will minimise the slip. 2. Hub: Hub having internal splines to adjust the axial travel of the gear box driving shaft which have external splines. 3. Torsional damper springs: Due to power pulses, an engine crankshaft is subjected to torsional vibrations. If these vibrations are transferred to the gear box, there will be wear of the gear tooth and noise ­generation. The function of the damper spring is to damp the vibrations and to transmit the torque smoothly and progressively. 4. Friction lining: Clutch friction lining is subjected to severe rubbing operation which will produce heat and may hamper torque transmission capacity of the clutch, so the material must have the following properties: – Relatively high coefficient of friction – Capability of maintaining friction properties over a lifetime – Capacity to withstand bursts of centrifugal force when gear ­changing, and high energy absorbing capacity for short periods 3. Operating mechanism: Operating mechanism includes foot pedal, linkage, bearings, releasable levers, etc. When the clutch is pressed by the driver, the mechanical linkage pushes the pressure plate away from the flywheel so the spring pressure on the clutch plate is removed and it rotates freely. 4. Withdrawal fork and bearing: The fork carrying the withdrawal bearings is pivoted on a balls, and mounted in the clutch outer casing. Clutch shaft is a component of the gearbox, since it is splined shaft to the hub of the clutch plate which is sliding on it. It has its one end supported in a spigot bush in the centre of the flywheel while the outer end carries one of the constant mesh gears (Figure 4.4).

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FIGURE 4.2  Flywheel and pressure plate.

FIGURE 4.3  Friction plate.

Automotive Systems

Automotive Clutches

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FIGURE 4.4  Operating mechanism.

4.7 CONSTRUCTION AND WORKING OF THE SINGLE PLATE CLUTCH Construction A single plate clutch assembly for transmission of power consists of a flywheel, a clutch or a friction plate, a pressure plate, a clutch cover, a release lever, a fork and a bearing and a primary or a clutch shaft. It is the most common type of clutch plate used in motor vehicles. Essentially, it consists of only one clutch plate, placed on the splines of the clutch frame. The flywheel is mounted on the engine crankshaft and rotates. The pressure plate is bolted to the flywheel by means of the clutch springs and is free to move on the clutch shaft when the clutch pedal is pressed. When the clutch is engaged, the clutch plate is trapped between the flywheel and the pressure plate. The friction liners are on either side of the clutch plate. Owing to friction between the flywheel, the clutch plate and the pressure plate, the clutch plate rotates the flywheel. As the clutch plate rotates, the clutch shaft also rotates. The clutch shaft is attached to the gearbox. As a consequence, the engine power is transferred to the crankshaft and then to the clutch shaft (Figure 4.5). When the clutch lever is pressed, the pressure plate moves back against the force of the springs, leaving the clutch plate free between the flywheel and the pressure plate. Asa result, the flywheel continues to spin as long as the engine is working and until the speed of the clutch shaft slows down and eventually stops spinning. So long as the clutch lever is pressed, the clutch is said to be engaged, otherwise it will remain engaged due to the spring forces.

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Automotive Systems

FIGURE 4.5  Working of a single-plate clutch.

Diaphragm Clutch Diaphragm clutch is similar in construction to that of a single-plate or multi-plate clutch. The only difference is that it contains a diaphragm spring, which is used instead of a coil spring to apply clamping force, as well as it acts as part of the release mechanism. Basically there are three benefits of the diaphragm clutch compact structure: increased thermal capacity of the clutch, optimum clamping pressure without affecting the degree of wear and uniform clamping pressure. It is a steel disc with a hole at the centre and radially slotted in such way that the outer ends have blunting holes. The diaphragm spring is almost flat when the clutch is in the engaged position. When the driver presses the pedal, the release bearings are pressed against the fingers of diaphragm, which leads to increase in the cone angle of the diaphragm, and spring load is released and the engine separates from the gearbox. Advantage of the diaphragm type spring is that it maintains accurate balance of the cultch assembly in all operating conditions.

4.8 CONSTRUCTION AND WORKING OF THE MULTI-PLATE CLUTCH The multi-plate clutch consists of a set of clutch plates instead of a single clutch plate, as in the case of a single clamping plate. When the number of clutch plates increases, friction surfaces also increase. The increased number of friction surfaces naturally increases the ability of the clutch to transmit torque. The plates are alternatively mounted to the shaft of the engine and gearbox. They are closely pressed by powerful coil springs and assembled in a drum. Both of the ­alternate plates slide on the grooves on the flywheel and the other side, slides on the splines on the pressure plate. Thus, each alternate plate has internal and external splines.

Automotive Clutches

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The multi-plate clutch operates in the same way as a single plate clutch by ­working the lever of the clutch. Multi-plate clutches are used for the transfer of high torque in heavy commercial vehicles, race cars and motor cycles. The multi-clutch may be dry or wet. If the clutch is worked in an oil bath, it’s called a wet clutch. When the clutch is operated without oil, it is considered a dry clutch. The wet clutch maybe used in combination with or as part of automatic transmission.

4.9 CONSTRUCTION AND WORKING OF THE CENTRIFUGAL CLUTCH Centrifugally Operated Clutches As in the diaphragm clutch, in the coil spring clutch energy is stored in the compressed springs, but in this type of clutch clamping force is either fully or partially generated through the centrifugally operated mechanism. Centrifugal clutches are divided into two: 1. Semi-centrifugal 2. Fully centrifugal The centrifugal clutch consists of bob weights attached to the outside of the levers. In the case of a semi-centrifugal clutch, after a certain speed limit, the centrifugal force exerted by weight is seen at a certain speed. It will impose additional clamping force on the spring, and there will be maximum transmission of torque. In the case of a fully centrifugal clutch, the entire clamping force exerted by the weights is applied (Figure 4.6).

FIGURE 4.6  Centrifugal clutch.

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4.10 CONSTRUCTION AND WORKING OF ELECTROMAGNETIC CLUTCH The electromagnetic clutch is a clutch (a device for the transmission of rotation) which is engaged and disengaged by an electromagnetic actuator. The flywheel consists of winding in this form of clutch. The current is supplied to the battery or dynamo winding. As the current transfers  through the winding, it generates an electric field that draws the pressure plate to the clutch. If the supply is cut off, the clutch is disconnected. The gear lever consists of a release button for the clutch. When the driver holds the gear lever to shift the gear, the button is worked by cutting off the current to the winding, which allows the clutch to disengage. At low speeds, when the dynamo output is low, the clutch is not firmly attached. Therefore, three springs are also installed on the pressure plate, which allows the clutch to be fixed at low speed. Cycling is done by turning the voltage/current on and off the electromagnet. Slippage typically happens only during acceleration. Once the clutch is fully engaged, there is no relative slip, ensuring the clutch is properly designed, and therefore the torque transfer is 100% effective. The electromagnetic clutch is ideally suited for remote operation as no linkages are needed to control its operation. It provides fast and smooth operation. However, since energy dissipates as heat in the electromagnetic actuator every time the clutch is engaged, there is a chance of overheating. As a result, the overall operating temperature of the clutch is regulated by the temperature of the electromagnet insulation.  Higher heat generation and high cost are its major drawbacks, including higher initial costs.

4.11 OPERATING MECHANISM OF THE CLUTCH The clutch unit is directly mounted to the flywheel so it rotates as a single unit with the speed of the engine, and hence is subjected to vibrations. It is essential to operate the clutch smoothly without any jerk at any stage of engagement and disengagement with the help of a very flexible linkage system which does not affect the operation of the clutch. The transmission of force and movement from the foot pedal to the clutch is carried out with the help of a mechanical and hydraulic linkage.

Mechanically Operated Clutch Linkage Mechanically operated clutch linkage consists of various types of rods and levers connected to each other. This mechanism is used in the early stages of vehicle development. Friction at the pivots is more in this mechanism and wear rate is also high. Sometimes it may cause jamming of the clutch.

Cable-Operated Clutch Later developments replaced the heavy mechanical linkage with a cable and lever system, which is more efficient.

Automotive Clutches

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4.12 OPERATING MECHANISM OF THE CLUTCH: HYDRAULIC A hydraulic clutch release mechanism uses a simple hydraulic circuit to transfer the clutch pedal action to the clutch fork. It has three basic parts – master cylinder, hydraulic lines and a slave cylinder. Movement of the clutch pedal creates hydraulic pressure in the master cylinder, which actuates the slave cylinder. The slave cylinder then moves the clutch fork. The master cylinder is the controlling cylinder that develops the hydraulic pressure. The slave cylinder is the operating cylinder that is actuated by the pressure created by the master cylinder. Hydraulically operated clutches are simple in construction; they self-lubricate and have a smooth operation. By selecting the proper size and piston travel length we can calculate the exact amount of clamping force required in case of hydraulic clutch.

4.13 DESIGN ASPECTS OF THE AUTOMOTIVE CLUTCH The following are the key factors that should be considered while designing friction clutches: i. Selection of a suitable clutch for the given type of vehicle ii. Selection of suitable friction material at the contacting surfaces iii. Designing the clutch for sufficient torque transmission capacity iv. Operation of the clutch without shock or jerk v. Provision to hold contacting surfaces together by the clutch itself without any external assistance vi. Lightweight rotating parts to reduce inertia forces vii. Provision for taking or compensating wear of rubbing surfaces viii. Provision for heat dissipation generated due to rubbing Two theories can be assumed for the friction plate design: uniform pressure theory for new friction plates and uniform wear theory for worn or used friction plates.

1. According to uniform pressure theory [r 3 − r 3 ] 2 Torque transmitted: T = µF 12 22 [r1 − r2 ] 3 2 [r13 − r23 ] 3 [r12 − r22 ] 2. According to uniform wear theory µF Torque transmitted: T = [r1 + r2 ] 2 [r − r ] Mean radius: rm = 1 2 2 Mean radius: rm =



Where r2 is the inner radius andr1 the outer radius of the friction plate, and rm the mean radius of the friction plate.

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Automotive Systems

SUMMARY • Clutch is a device used to transmit the torque developed by the engine gradually through a proper linkage. • Positive engagements, friction, electromagnetic and fluid are some types of clutches. • Friction clutches can be single-plate, multi-plate, cone, centrifugal or diaphragm clutches. • The clutch consists of driving, driven and operating members. • Hub, damper spring, cushion springs, friction lining, etc. are the components of a friction plate. • Maximum torque transmission, less moment of inertia, dynamic balancing, free pedal play, vibration damping, ease of operation, gradual engagements, etc. are the requirements of the clutch. • The torque transmission capacity of the cutch depends on the clamping pressure, coefficient of friction, frictional area, etc. • The clutch can be operated mechanically, hydraulically or pneumatically. • Two theories used in designing friction plates are uniform pressure theory and uniform wear theory.

MULTIPLE-CHOICE QUESTIONS Fill in the Blanks 1. The clutch is always in the ....................... (engage/disengage) position. 2. The clutch is located ..................... (before/after) the gear box. 3. Automotive clutches are generally................... (positive contact/friction) clutches. 4. Friction plate is a.............. (driven/driving) member of the clutch. 5. Multi-plate clutches are used in......... (light/heavy) commercial vehicles.

REVIEW QUESTIONS • • • • • • • • •

What do you mean by a clutch? List out various types of clutches used in automotive applications. List the requirements of the clutch. What are the advantages of the diaphragm clutch over the coil spring clutch? Why is a cushion spring incorporated in a friction plate? Explain the necessity of the clutch? What are the requirements of the clutch? Describe the construction and working of the single-plate clutch system. Describe the clutch operating mechanism.

Answers to MCQs: (1) engage (2) before (3) friction (4) driven (5) heavy

5

Manual Transmission and Transaxles

OUTCOME Learning Objectives • • • • •

Purpose and elements of the gear box and transaxles Types of gear boxes Construction and working of the gear box and transaxles Heavy vehicle gear boxes Gear box lubrication and sealing

5.1 INTRODUCTION The gear box is an important element of the vehicular transmission system. The main function of the vehicular transmission system is to fulfil the traction requirement of the vehicle, which varies continuously due to various types of resistances acting on the vehicle. Smooth leverage is more essential without any load on the engine for smooth vehicle operation with maximum fuel economy and transmission efficiency. The gear box consists of a set of gears mounted on shafts with a shifting mechanism to enable selection of gears. Based on construction, the different types of gear boxes for manual transmission are sliding mesh, constant mesh and synchromesh gear boxes.

5.2 VARIOUS TYPES OF RESISTANCES A vehicle has to overcome the following types of resistances during operation. 1. Air Resistance This resistance is caused by air when vehicle is in the running condition. The following factors contribute to air resistance: a. Shape of the vehicle If the front of the vehicle is directly related to the area exposed to air, or if more area is exposed to air, then the more resistance the vehicle has to overcome. In the case of commercial vehicles like open trucks, loading of goods should be done in such a way that minimum area is exposed. b. Speed of the vehicle As the speed of the vehicle increases, the resistance also increases. Air resistance is directly proportional to square of the velocity of vehicle. 95

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Automotive Systems

c. Speed of air: with increasing speed of air the opposing force increases. Ra = KaAV 2

where Ra =Air resistance (N), Ka = Coefficient of air resistance, A  =  Frontal ­projected area in m2, V = Vehicle speed in km/h, Ka = 0.02688 for passenger car, Ka = 0.023 streamline car, Ka = 0.0314 average car, Ka = 0.045 for trucks and buses 2. Road or Rolling Resistance Resistance offered by the road wheel is called road resistance. It depends on the following factors: a. Type of road: The coefficient of friction between the road wheel and the road depends on the type of structure of the road. If the structure of the road is fine, the resistance offered will be less, while a coarse structure provides more resistance against the road wheel. b. Amount of laden weight of the vehicle: If the laden weight of the vehicle is high then more frictional resistance offered by the vehicle. c. Tyre inflation pressure: The area of contact of road wheel depends on the tyre inflation pressure. If there is less inflation pressure, area of contact to the road wheel resistance increases and vice versa. d. Tread pattern: Tread pattern also plays a key role in road wheel resistance. Worn out threads of tyres offer less resistance, but it may reduce the road hold of the vehicle. 3. Gradient resistance The amount of gradient resistance depends on the gradient of the road; a larger angle results in higher gradient resistance. In the above case there are another type of resistance available, transmission resistance, the value of which is very less, but while in calculations we have to consider it as transmission efficiency.

Rg = WG = Mg G Rg = Gradient resistance (N), M = Mass of vehicle in kg, W = Weight of vehicle in (N), G = Gradient

5.3 MOTIVE POWER, TRACTION AND TRACTIVE EFFORTS To overcome the discussed resistances, the vehicle’s power and torque requirement continuously changes, also affecting vehicle speed. Power is directly proportional to vehicle speed but up to a certain limit. After achieving a particular speed, the power continuously reduces. Maximum power developed in the engine is at full throttle and at top speed. The selection of the gear depends on the amount of resistance offered by the vehicle. The range of the gear ratio is between speed at maximum torque and speed at maximum power.

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Manual Transmission and Transaxles

The force available at the contact between the drive wheel tyres and road is known as “tractive effort”. And the ability of the drive wheels to transmit this effort without slipping is known as “traction”. Suppose the power developed by the engine is P

M te - Engine torque =

60P 2πN

G = Gear ratio nf = Final drive ratio Mt = Torque available at road wheel M t = M te × G × n f

Tractive effort =

M te × G × n f M t = R R

where R is the road wheel radius In case the tractive effort F>R, the total resistance on level road, the excess tractive effort is used to accelerate, hill climb and draw-bar pull.

5.4 NECESSITY OF THE GEAR BOX Torque multiplication is the function of the gear box, to match the torque and speed of the engine to the load and speed of the road wheel. This is needed for the vehicle to overcome different types of resistances during different operating conditions. We have already studied traction and tractive force. Traction requirements continuously change due to various operating conditions, such as starting, sudden acceleration, sudden braking, transient condition, etc. In all such operations it is essential to fulfil the torque requirements. In these operations, the gearbox retains the ratio of engine speed and wheel speed to maximise efficiency. The graph in Figure 5.1 shows the relation between the tractive effort tractive resistance and gear ratio.

FIGURE 5.1  Total resistance and tractive effort vs speed.

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• The relationship between vehicle speed and total resistance, tractive effort at different gear ratios and different gradients is shown in the graph. • Curves A to F represent total resistance for a smooth road but of varying gradient to the road. • Curve A represents the level road and curve F the maximum gradient. • Curves RS, TU and VW represent tractive effort for three different types of gear ratios. • The speed of the vehicle travelling on a level road is represented by OX. • At this speed the resistance to be overcome is XY and the available traction effort is XZ. • The resistance is less than the tractive effort available so the excessive tractive effort YZ is used to increase the speed of the vehicle. • During acceleration, the resistance increases and extra effort for acceleration reduces. When the speed is OM, the total tractive effort and total resistance both are equal. So this is the limit for speed. • If the vehicle represents the gradient level represented by curve B, resistance is MN for speed OM on gradient B. • At this condition, MH is the tractive effort available, which is very small. The excess resistance MN will reduce speed to the point I at which tractive effort and resistance are same. • Now assume that the gradient is getting steeper and steeper, and so we proceed in sequence from curve B to C and so on. So the speed held lowers to points J, K, and so on. • It is shown that we can pass through the gradient at any speed, as the tractive effort at the 3rd gear is anywhere below the resistance curve. • In these situations, the gear has to be shifted to 2nd and the speed can be held at point G. Gear A is keyed to the clutch shaft and it is in constant mesh with gear B. Gears B, G, E and C are the gears of the layshaft.

5.5 CALCULATION OF GEAR RATIOS The essential parameters to be considered for setting the gear ratios are final drive reduction and the maximum performance, in terms of the ability of vehicle to climb the gradients, achievement of good acceleration through the gears and gradeability. Calculating the final drive ratio: The graphs and/or data are used to determine the engine speed at maximum road speed in the following formula for calculating the final drive ratio.



Engine rpm at maximum roadspeed =

N=

distance in meter per min × gear ratio circumference of road wheels

1,000 × kmph × nf 60 × 2πr

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Manual Transmission and Transaxles



N=

kmph × nf 0.377r



f=

0.377 × Nr kmph × n

where n = gear ratio; f = final drive ratio; and r = road wheel radius. For top gear condition apply n = 1 Calculating bottom gear ratio: This ratio is dependent on the maximum tractive effort available in the top gear, and the maximum resistance

Bottom of first gear G1 =

maximum tractive resistance maximum tractive effort in top gear



Maximum tractive effort in topgear =



Bottom of first gear G1 =

RT Tnfe/r



Bottom of first gear G1 =

R Tr Tnfe

Tnfe r

For the intermediate gear ratios it is essential to calculate the engine speed ratio. This is the ratio of engine rev/min at which maximum torque is generated to the rev/min when maximum engine power is produced.

Engine speed ratio(z) =

rpm at max torque rpm at max power



Second gear ratio G 2 = G1 × z



Third gear ratio G3 = G 2 × z = G1 × z 2

Gear ratios are in geometric progression so they can be written as

G 2 = G1 × G3



G3 = G 2 × G 4

5.6 CONSTRUCTION AND WORKING OF THE CONSTANT MESH GEAR BOX In this type of gear box, gears of main shaft and layshaft are in mesh with each other. The dog clutches are provided having internal splines and they are more freely on the main shaft. It also consist clutch gear, layshaft gears, output shaft gears etc. At the

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FIGURE 5.2  Constant mesh gear arrangements.

time of shifting the gears; operator just slides the dog clutch with the help of selector mechanism. When the operator shifts the dog clutch and engages to the first pair then power transmitted from pair of clutch gear to that particular gear pair (Figure 5.2). Helical gears are generally used in many gear boxes; these are quieter as compared to spur gears. At the time of shifting the gears, the driver has to depress the clutch pedal to disengage the Gear box from the engine change gears, while matching the engine and road speeds. This is achieved by pressing the clutch pedal twice, called double declutching.

5.7 CONSTRUCTION AND WORKING OF THE SLIDING MESH GEAR BOX The sliding mesh gear box consists of a layshaft or countershaft. Gears mounted on the layshaft are fixed while on input shafts (driving shaft) they move or slide. Output shafts (driven shaft) have external splines and sliding gears have internal splines. Generally the sliding mesh gear box contains spur gears. The major problem with this type of gear engagement is that, while attempting a gear change, to engage the gears smoothly, it is required to equalise the speed of the output shaft, layshaft and clutch shaft (input shaft). During changing of the gear from first to second, it is essential to equalise the speed of input to output shaft. The driver presses the clutch and moves the gear lever to neutral. The clutch is then re-engaged and the driver closes the throttle. The engine slows down at a faster rate than that in the layshaft assembly, so the speed reduction of the layshaft assembly is obtained. The clutch can then be disengaged again and second gear selected, thus allowing the clutch to be re-engaged and allow the second gear to transmit the power.

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FIGURE 5.3  Sliding mesh gear box arrangement.

During this operation, the driver presses the clutch twice, called double declutching. In the diagram the first pair of gear is continuously in mesh. As per requirement the driver shifts the gears on the drive shaft and meshes with the fixed gear on the layshaft through the shifting mechanism. For the reverse gear position, an additional gear is provided in the mechanism, i.e. at the time of reverse gear, three gears are in mesh with each other (Figure 5.3).

5.8 CONSTRUCTION AND WORKING OF THE SYNCHROMESH GEAR BOX Synchromesh here means to equalise the speed of gears. There is no need for double declutching as described in earlier. The construction of the synchromesh gear box is same as the constant mesh gear box, but instead of the dog clutch, a synchroniser ring

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FIGURE 5.4  Synchromesh gear box.

is fitted in the synchromesh gear box. At the time of changing gears, the synchroniser ring equalises the speed of the gears, so there is smooth engagement (Figure 5.4). Construction of the synchroniser: The main purpose of this unit is to synchronise the speed of the two gears before they are engaged. In a running vehicle, when the clutch is pressed and the gear is put in neutral position, the gears revolve. Not all gears revolve at the same speed, and when we have to engage two gears running at different speeds by shifting the lever a sound is produced caused by the clash of gears, and then it becomes difficult to engage and disengage the gears. To avoid these problems, the synchromesh device is used. Synchromesh devices are not fitted to all the gears, only to the higher gears. During synchronisation the synchroniser sleeve is moved towards selected gear pushing the block ring to the right, the ring contacts the shoulder of the driven gear and begins to synchronise the speed of the two parts. In this way, the drive shifts from the layshaft gears to main shaft gears and then to the main shaft through the synchroniser device. Working:- Neutral condition;- All synchroniser remain at the centre position and no power is transmitted to the main shaft. First gear: When the right side of synchroniser slides towards the left side, ­frictional surfaces come in contact with each other, which synchronise speed and synchroniser sleeve teeth meshes with first main shaft gear teeth and first gear ratio is obtained. Second gear: When a left side synchroniser slides towards the right side, frictional surfaces come in contact with each other which synchronise speed

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FIGURE 5.5  Synchromesh gear box gear shifting.

and synchroniser sleeve teeth mesh with second main shaft gear teeth and second gear ratio is obtained. Thirdgear: When a left side synchroniser slides towards left side there frictional surfaces comes in contact with each other which synchronise speed and synchroniser sleeve teeth mesh with third main shaft gear teeth and third gear ratio is obtained. Reverse Gear: When the right side synchroniser slides towards the right side, frictional surfaces come in contact with each other, which synchronise speed and synchroniser sleeve teeth mesh with reverse main shaft gear teeth and first gear ratio is obtained (Figure 5.5).

5.9 OVERDRIVE Overdrive enables the output shaft to rotate faster than the input shaft, i.e. the engine could be allowed to rotate at a slower speed than the propeller shaft when in top gear to reduce engine’s load and enable fuel economy when the power requirement is very less. The advantages of the overdrive gears are better drivability, higher fuel economy, less emission and longer life. Overdrive can be mounted in between the clutch and gear box, in the gear box, in between the final drive and propeller shaft or between final drive and differential. Generally epicyclic gear trains are used in overdrive, which enable overdrive or direct drive. The control of the epicyclic gear train is same as that in the automatic gear box. It consists of a ring gear, planetary gears, and sun gears, arranged in such a manner to obtain the required gear ratios.

1. Ring gear: It is a ring-shaped gear with internal teeth which transmits the final output through the connected output shaft. Internal teeth of a ring gear are meshed with the planetary gears. 2. Sun gear: This is the centre-most gear of an overdrive around which the planetary gears revolve in a direction guided by the ring gear. The sun gear is meshed with the planetary gears. Power output from the splined input

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shaft, which is in mesh with the inner splines of the sun gear, is transferred to the planetary gears through the sun gear. 3. Planetary gears: These gears revolve between the sun gear and ring gear. The planetary gears are mounted or attached over a carrier through their central axis. The carrier is itself mounted over the splined input shaft same as the sun gear. Working Overdrive disabled: The input shaft passing through the sun gear which rotates the sun gear planetary gears and then these planetary gears rotates the annulus and direct drive is obtained. Overdrive enabled: In this case the input from the input shaft is transferred through the planetary gear to the annulus due to which overdrive is obtained, due to the higher reduction ratio of planetary gears and annulus.

5.10 TRANSFER BOX CONSTRUCTION AND WORKING In the case of off-road vehicles it is required to divide the torque between the rear axle and front axle to enhance road holding and enable easy travel through uneven road conditions with maximum stability. The function of the transfer case is to transfer the drive to the front wheels whenever required with arrangement of engagement and disengagement. It facilitates the attachment of the power take off, also provides the low gear operation in emergency condition. A transfer case is similar in construction to a transmission which consists of shift forks, splines, gears, shims, bearings, etc. The transfer case has an outer case made of either cast iron or aluminium. Conventional transfer cases in heavier vehicles have a two-speed transfer gearbox which is attached to the rear of the main gearbox, or separately mounted and driven via a short coupling shaft. It can be operated with the help of a declutching device. As in auxiliary gear box the transfer gear box also provides a high and low final drive gear range. It is operated with the help of a sliding dog clutch; the sliding gear having external teeth is in mesh with the internal teeth of the constant mesh gear. Likewise, the external teeth of the front axle sliding gear are in mesh with the internal teeth of the constant mesh gear. Shifting level arrangement is provided for disengagement with the sliding gear on the front axle main shaft slide so as to disconnect to the constant mesh gear. In the case of low-range gear, the sliding gear on the transmission main shaft is disengaged from the constant mesh gear and engaged with the idler gear on the idler shaft.

5.11 HEAVY VEHICLE GEAR BOXES The torque developed by the engine is inversely proportional to the speed. In a regular transmission system where the gear ratios are fixed at some interval, shifting the gear results in a loss in power. This power loss is less in small vehicles but in the case of heavy vehicles the power to weight ratio is very small. If the step between the gears is more, then the power loss is more. To avoid loss of power between the

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intermediate gears, it is essential to provide number of gear ratios. The requirement of torque transmission in heavy vehicles is more compared to that in a light vehicle’s gear box. In order avoid power loss, heavy vehicle gear boxes may have five-speed or six-speed gear boxes. Sometimes heavy vehicles gear boxe have twin layshafts. In such types of gearboxes, torque transmission is carried out from one gear to two or more gears, instead of a single gear. It can be achieved with connecting a conventional two-speed reduction gear box with an auxiliary gear box to achieve double gear no of gear ratios. It requires a shorter shaft, which makes layout more compact. In heavy vehicles, the following types of gear boxes are used.

5.11.1 Splitter Drive Gear Boxes This type of multispeed gear box consists of two speeds. The auxiliary gear set is integrated with a typically five-speed gear box to provide ten speeds. As it is five gear ratios split into ten, it is called splitter drive. The gear ratios provided with this type of gear box are 1L, 1H, 2L, 2H, etc. So accordingly load and road condition speeds can be obtained. Auxiliary gear box is usually overhung from the front wall of the main gearbox. The gear set may be arranged in a different manner to provide an extra pair of torque transmission (Figure 5.6).

5.11.2 Range Change Gear Boxes In these types of multispeed gear boxes, the auxiliary gear box is usually overhung from the rear wall of the main gearbox. It uses a wide-ratio auxiliary gear set in conjunction with close ratios in the main gear box. The gear set is arranged in such a

FIGURE 5.6  Heavy vehicle gear box.

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way to provide direct or an under drive between the gear box main shaft and layshaft for selection of high range and low range of the gear ratio.

5.12 GEAR SHIFTING MECHANISMS A gear selector mechanism is used to select, engage and disengage a particular gear. The following types of gear selector mechanisms are used in the vehicle:



1. Multi-rail gear selector mechanism: Engagement of the gears can be carried out with the help of three guiding selected rods supported at their ends either in the actual gearbox housing or in the selector cover housing. The gear change lever or selector lever is a forged steel rod with a control knob at its upper end. The lever end has a special shape with machined flat surfaces. The selector forks slide with or over the rods and fit over saddle-like grooves of the outer sliding-dog clutch hub. When the driver pushes the selector fork it moves the required dog clutch hub over the exposed ring of the dog teeth on the gearwheel. After meshing of the hub and the gearwheel, the layshaft cluster gear is coupled to the main shaft (Figure 5.7). 2. Single rail selector rod mechanism: In single rail selector rod mechanism, gear selection and change can be carried out by both a twisting and a to-and-fro motion of the selector lever. Due to use of rocking selector lever with a crankpin, engages reverse idler gear that can be operated. It consists of sticker jaws which are inward facing. In the neutral condition, the rocking selector lever and the sticker jaws are in alignment and form an arc about the axis of the selector rod. The toand-fro motion of the lever to the selector rod thus causes either one of the forks or the rocking lever to move with it.

FIGURE 5.7  Single selector mechanisms.

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5.13 GEAR BOX LUBRICATION AND SEALING Lubrication of the gear box moving parts is carried out by pouring the correct quality and quantity of oil at the opening provided in the gearbox casing. Oil level in the gearbox is maintained in such a way that gears are submerged in the oil. Oil will flow and spread between the rotating gears, output shaft, input shaft and layshaft. The main purpose of lubrication is to avoid metal to metal contact by providing an oil film of sufficient thickness and to prevent corrosion. The lubricant oil must have sufficient viscosity. Lubrication of the selector mechanism is carried out by oil splashing through gear wheels. In special cases, such as in heavy-duty commercial vehicles, a forced feed lubrication system is used in which gear pump pressurises oil along an axial drilling in both the input/output layshaft, called oil bath lubrication, in which gearbox casing or housing forms an oil-tight reservoir for the lubricating oil, and it is also provided with a drain plug at lower side of the casing and the level plug. Excessive oil creates pressure in the box and forces out the input and output seals. Two to three oil holes are drilled radially to the gear wheels as well as axial holes are provided for a smooth flow of the lubricating oil. Sealing: The sealing of gear box components is done in two ways: 1. Components are joined together by machined pressure face joints using static seals. 2. Rotating components by using dynamic seals. A. Static seals A static seals is sandwiched between pressures faces fits face to face, and takes care of all surface irregularities of two mating surfaces, such as non-metallic gaskets, paper, synthetic-rubber O-rings, and mixed compounds of both setting- and non-setting-type seals. These seals are used between the main gearbox casing and the front, top and back covers. B. Dynamic seals To prevent oil leaking out between a rotating shaft and its bearing housing, dynamic contact radial lip seal or spiral thread clearance seals are used.

5.14 TRANSAXLE CONSTRUCTION AND WORKING The combined assembly of the transmission and differential is called a transaxle, which is a part of front-wheel-drive vehicles. Transaxle may be manual or automatic. The transaxle has certain advantages as it is a front-engine, front-wheel drive: compact structure, improved traction due to higher weight at the front side, more space in the passenger compartment, etc. The output of the transaxle through transmission and differential is given to the hubs and drive wheels with the drive axles. In manual transmission there are conventional clutch and transmission units and operating mechanisms and linkages. Input shaft or mail shaft, gear assemblies, output shaft or pinion shaft, transaxle differential, differential synchroniser are the

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FIGURE 5.8  Transaxle.

important components of the manual transaxle. The output, or pinion, shaft has a gear or sprocket for driving the differential ring gear. The transaxle differential transfers power to the axles and wheels to turn the wheels at different speeds (Figure 5.8).

SUMMARY • Gear box is part of the transmission system which fulfils the traction requirement of the vehicle. • Vehicle has to overcome various types of resistances like air, gradient and road resistances. • Gear ratio lies between the speed at maximum rpm and speed at maximum power. • Sliding, constant and synchromesh are the different types of gear boxes. • Layshaft, main shaft, gear assembly, selector mechanism, etc. are the main parts of the gear box. • Overdrive is a device which gives more output speed than input speed.

MULTIPLE-CHOICE QUESTIONS

1. The function of the gear box is to a. Fulfil the traction requirement of the vehicle b. To assist the engine to do its work c. To enable the vehicle to be reversed d. All of the above 2. As the torque increases at a particular limit a. Speed increases b. Speed reduces c. Speed remains constant d. None of the above

Manual Transmission and Transaxles



3. Double declutching means a. Pressing the clutch pedal twice b. Shifting the gears c. Providing lubrication d. All of the above 4. Sliding mesh gear box consist of a. Spur gears b. Helical gears c. Spiral bevel gears d. None of the above 5. The function of the synchroniser ring is to a. Equalise the speed b. Double the speed c. Minimise the speed d. None of the above 6. Double declutching carried out in a vehicle has a. Sliding gear box b. Constant mesh gear box c. Synchromesh gear box d. All of the above

REVIEW QUESTIONS • • • • • • •

Why gear box is necessary? Explain the various types of resistances offered by the vehicle. Differentiate the various types of gear boxes. What do you mean by overdrive gears? Write a short note on selector mechanism. Explain the working of a manual transaxle. Explain transfer case.

Answers to MCQs: (1) d (2) b (3) a (4) a (5) a (6) b

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OUTCOME Learning Objectives • • • •

Principle of operations of the fluid flywheel and torque convertor Constructional details of the fluid flywheel and torque convertor Automatic transmission systems and their controls Automated manual transmission system

6.1  INTRODUCTION A manual transmission system has many disadvantages: limited gear ratio, noise and difficulty in shifting gears which may affect the operational characteristics of the vehicle, fuel economy and comfort of the driver and occupants. Smooth and noiseless operation can be achieved with the help of an automated transmission system. This system provides multiple gear ratios as per the traction demand of the vehicle with maximum fuel economy and comfort. The system consists of various components: fluid flywheel, torque converter, multiple clutches, band brakes and epicyclic gear trains. It also consists of some electrical, hydraulic and electronic components and devices for actuations, especially in the working of the system.

6.2  FLUID FLYWHEEL The hydrokinetic fluid coupling is also called fluid flywheel and it consists of two saucer-shaped discs, an input impeller (pump) and an output turbine (runner). Both impeller and turbine consist of multiple flat radial vanes (blades) to direct the flow of fluid as required. The hydrokinetic coupling is based on the principle of relative slip between the input and output member cells facing each other, and there is continuous alignment and misalignment of the vortex flow path, created by pairs of adjacent cells, with different cells of coupling. The fluid coupling comprises two rotors with radial vanes. The casing is filled with light engine oil. The driving member is attached to the crankshaft and as this rotates the oil contained between the vanes gains some kinetic energy which pushes outwards by centrifugal force and enters the opposing vanes and loses the kinetic energy to drive the driven member, which is connected to the gearbox. There is a continuous flow of fluid from the driving member to the driven member though which power is transmitted.

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During starting of the engine, the rotation of the impeller (pump) causes the working fluid trapped in its cells to rotate with it and it gains some kinetic energy due to the centrifugal force; the fluid is pressurized and flows radially outwards. The flowing fluid has two motions: first, it is circulated by the impeller around its axis and, second, it circulates around the cells in a vortex motion (Figure 6.1). To understand the principle of fluid coupling, the circulation of a very small fluid particle between one set of impeller and turbine vanes at various points A, B, C and D is considered, as shown in Figure 6.1. A particle of fluid is at point A, which is very close to the shaft. The particle has some mass and it is located at radius r. When the engine is started and hence the impeller rotated, the radial distance of the particle from the centre of the axis increases. Through this increase in centrifugal force the particle acquires some kinetic energy. The fluid particle is forced to move outwards point B at radius R, so that it is subjected to relatively more centrifugal force as a result of R which is greater than the value of r, thereby acquiring a greater amount of kinetic energy. At this outermost position, the fluid particle possesses a high amount

FIGURE 6.1  Principle of fluid flywheel.

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of kinetic energy, it is ejected from the mouth of the impeller cell and is forced to enter the cell of the outer turbine at point C. When the particle travels at point C, it comes in contact with the turbine vanes and gives some of its kinetic energy to the turbine wheel. There is a continuous motion of the particles adjacent to the fluid across the junction of the impeller and turbine cells which pushes forcefully the first fluid particle in the slower moving turbine member with reduced centrifugal force due the reduction in the radius r, to move inwards to point D. During its travel from R to r, the fluid particle imparts most of its kinetic energy to the turbine wheel, which is directly used in propelling and motion (Figure 6.2). Advantages of Fluid Coupling • Automatic engagement and disengagement of drive to the gear box can be achieved by controlling acceleration pedal only. • Vibrations created by both the engine and shock loads of the transmission can be damped effectively. • There is no need for any adjustments and no wear and tear, since it does not have moving parts. There is no damage to any component on loading of the engine. • Smooth operation of gear shift. • Vehicle can be started and stopped by using accelerator pedal alone as the engine is not directly connected to the transmission. However, in overloading conditions, transmission efficiency is affected.

FIGURE 6.2  Fluid flywheel.

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6.2.1  Limitations As fluid coupling cannot provide a positive disengagement of drive, a drag torque must always be present between the driving and driven members of the coupling. As a result of this the fluid coupling is not compatible with a layshaft gearbox without the friction clutches. Due to this, semiautomatic and fully automatic transmissions use permanently meshed epicyclic gears.

6.3  TORQUE CONVERTOR The function of the gear box is to multiply the torque, but the limitation of manual gear boxes is that they have a limited number of gear ratios. However, a torque convertor enables continuous variations in gear ratios from lowest to highest, which is essential for the smooth operation of the vehicle in different conditions. As far as construction of torque convertor is concerned this is quite similar to that of a fluid flywheel. A fluid wheel consists two elements and a torque convertor consists of three parts: a driving member called impeller, a driven member turbine and the fixed element stator. The driving member is connected to the engine, the driven member to another transmission element and the stator is attached to the frames. The blades of both the impeller and turbine are fabricated from low-carbon steel pressings and the stator is generally an aluminium alloy casted component. The variation of the torque can be achieved with the help of the stator. To understand the principle of fluid coupling, circulation of a very small fluid particle between one set of impeller and turbine vanes at various points A, B, C and D is considered, as shown in Figure 6.3. When the impeller is rotated by the engine, centrifugal force will push the fluid particle to point A, which is very close to the shaft. The particle has some mass and is located at radius r. The radial distance of the particle from the centre of the axis will increase and through this increase in centrifugal

FIGURE 6.3  Torque convertor (principle of operation).

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FIGURE 6.4  Torque convertor.

force, the particle acquires some kinetic energy. The fluid particle is forced to move outwards to point B at radius R, so that it is subjected to relatively more centrifugal force as a result of R, which is greater than the value of r, thereby acquiring a greater amount of kinetic energy. At this outermost position, the fluid particle possess a high amount of kinetic energy. It is ejected from the mouth of the impeller cell, and is forced to enter the cell of the outer turbine at point C. During this travel to point C, the particle comes in contact with the turbine vanes and it transfers some of its kinetic energy to the turbine wheel since the turbine moves at a very low speed compared to the impeller. There is a continuous motion of the particles with a adjacent particles of the fluid across the junction of the impeller and turbine cells pushes forcefully the first fluid particle in the slower moving turbine member and gives the some kinetic energy. At turbine exit the particles still possess some amount of energy which will move to the entrance side of the stator at point F. The stator guides the fluid particle to the impeller entrance point A. As the particle comes to the entrance point of the impeller, it again imparts some kinetic energy to the impeller (Figure 6.4).

6.4  PLANETARY GEAR BOX An epicyclic gear train or planetary gear train consists of three parts. Planetary gears, sun gear, and ring gear. Sun gear is situated on the central axis of the gear train. Planetary gears are permanently in mesh with the sun gear and the annulus gear or ring gear. A simple gear train has the following functions: Idling: Idling is when one member is rotated and the remaining two are left running free. The whole unit will be idle in neutral.

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Direct drive: When any two members of the gear train are fixed and third member rotates along these two with same direction and speed. The gear train becomes solidified and acts as a direct mechanical device without increasing the torque. Forward reduction: When the annulus gear in the train is held stationary, and the sun gears are rotated, planetary gears will travel along the annulus gear and the planet carrier will therefore rotate in the same direction as the sun gear, but with reduced speed and higher torque. Reverse reduction: When the planet carrier is held stationary and the sun gear rotated, the idling planet pinion will rotate the annulus gear in the opposite direction. Epicyclic gear trains are having the following advantages over layshaft gears. • Changes from one ratio to another can be done effectively without disturbing the drive. • More number of teeth are in contact at a time, resulting in maximum torque transmission capacity. • Quieter operation, because gear-separating forces are balanced and self-contained.

6.5  CONTINUOUS V  ARIABLE TRANSMISSION SYSTEM Higher power output, higher torque, compact dimensions, driving pleasure and minimum fuel consumption are the essential parameters of the vehicle, which can be fulfilled with the use of CVT(continuous variable transmission), where transmission operates continuously avoiding the delay during shifting between fixed gears. The power output of a conventional engine varies with engine speed. At low engine speeds, the output is very less. For better vehicle performance, it is essential to run the engine at higher speeds at which it produces maximum power. Fuel economy and torque output are also essential parameters. The speed of the engine develops the maximum power and maximum torque and will deliver the maximum fuel economy at different conditions. Attaining the required constant engine speed to achieve any one of the three performance factors is not possible with a conventional manual shift gearbox, because the engine speed needs to be continually changed to match the vehicle speed. Therefore, the engine only performs at its best at the vehicle speed appropriate to produce maximum engine torque, power or economy, for which smooth variation of the gear ratios are essential and this can be managed with the help of CVT. CVT is a particular automatic transmission capable of providing a smoothly varying gear ratio. A simple CVT has three main components:

1. A variable-input driving pulley 2. An output (driven) pulley 3. A metal belt

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FIGURE 6.5  Continuous variable transmission.

• Apart from the above basic components, there are also various microprocessors and sensors and even epicyclic gearing and clutch. • Both the driving as well as driven pulleys are of variable-diameter type. • Each pulley is made of two 20° cones facing each other. • A belt is present in the groove between the two cones. • In rubber belts used earlier, there were V-shaped sections. • The modern metal belts are specially constructed to provide the required flexibility (Figure 6.5).

6.6  AUTOMATIC TRANSMISSION SYSTEM FOR PASSENGER CARS Use of automatic and semiautomatic gear-changing systems to reduce driver’s fatigue is a very old technique in vehicles. Generally automatic transmissions are usually less fuel efficient than manual transmission systems. Automatic transmission systems offer many driving advantages, especially in urban road conditions:

a. Reduction in driver’s fatigue, as there is no clutch or gear lever to manipulate, which is very beneficial in congested traffic conditions. b. Both hands of the driver can remain on the steering wheel at all times, they need to not think about shifting gears, resulting in safer driving. c. The transmission always engages the correct gear automatically based on the driving conditions and the traction demand of the vehicle, and accordingly the engine operates. Since automatic transmission systems have various drawbacks like efficiency, convenience, ease of operation, durability and reliability, the manufacturability and

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maintenance is concerned, this is not much appreciable compared to manual transmission system. Automatic transmission systems currently available in market are lighter, smaller and less expensive to manufacture, and have superior operation compared to old designs. Automatic transmission systems consist of torque convertor and multispeed planetary gear drive arrangement to fulfil traction requirement of the vehicle in various operating conditions. Multiple gear ratios can be obtained with the help of multiple clutches and band brakes by holding or by coupling various members of the gear train to provide necessary speed variations as per traction demand of the vehicle. A torque converter introduced between the engine and transmission gearing automatically decreases or increases the engine-to-transmission slip according to changes in engine speed and road conditions. The whole system operates electro-hydraulically. Due to the hydraulic pressure in the system, signals are received to the governor and throttle valves control the actual speed at which gear ratio changes are occurring in torque converter. Vehicle speed and engine load can be sensed by the governor and throttle valve, respectively. These pressure signals received by the governor valve and throttle valve are directed to a hydraulic control block which consists of an arrangement of valves and pistons. These valves and pistons help achieve the required pressure variation as per signals received. Engagements of the respective clutches or band brakes can be achieved with the help of the fluid pressure supplied by a pump. The gear up-shifts and downshifts are automatically carried out taking into account road condition, the available output of the engine and the acceleration/speed requirements of the driver.

6.7  AUTOMATIC TRANSAXLES Due to various advantages of front-mounted engine and front-wheel drive, there is wide application of the horizontally mounted front-engine front-wheel drive layout. In this layout, it is essential to combine the automatic gearbox assembly with the final drive assembly, collectively called automatic transaxle. Various components of the automatic transaxle and automatic transmission systems are the same and they work on the same operating principle. Some components are similar in manual and automatic transaxle systems. The automatic transaxle unit consists of the following components: • Transaxle torque converter: A fluid-type clutch that slips at low speed but locks up and transfers engine power at a predetermined speed; couples and uncouples engine crankshaft to transmission input shaft and gear train. • Transaxle oil pump: Develops the required hydraulic pressure to operate, actuate the various pistons and servos, lubricate, and cool the automatic transaxle. • Transaxle valve body: Contains hydraulic valves operated by the operator’s shift linkage and by engine speed and load-sensing components. The function of the transaxle vale is to control the flow of the fluid to the pistons and servos in the transaxle. • Transaxle pistons and servos: Operate the clutches and bands as per the fluid pressure transferred from the valve body.

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• Transaxle clutches and bands: Different units of the planetary gear set are operated with the help of transaxle clutches and bands provided in the unit. • Transaxle planetary gear set: Provides various sets of gear ratios in forward and reverse gear sets. • Transaxle differential: Transfers motive power from the various transmission components to the axle shafts.

6.8  AUTOMATIC TRANSMISSION SYSTEM FOR HEAVY VEHICLES Heavy vehicles have different load-carrying capacity, body style, transmissions, etc. compared to the car. Both semiautomatic and automatic transmission can be utilised in commercial vehicles. The different designs which can be utilised for automatic transmission systems are as follows: • Three- to seven-speed conventional automatic transmission system with a torque convertor and rear-mounted planetary gears • Fully automatic commercial vehicle countershaft transmission which consists of a torque convertor, rear-mounted planetary gears and a continuously variable transmission system

6.9  HYDRAULIC CONTROL SYSTEM The functions of the hydraulic control system in automatic transmission are as follows:

1. To fill and maintain the constant flow of fluid under pressure for efficient transmission of torque 2. To transfer the fluid to various hydraulic elements like valve control body and governor for regulating the engagement and disengagement of the gear set clutches and bands, according to the traction demand of the vehicle 3. To provide a means for the circulation of the heated fluid from the torque converter through a separate cooler to lubricate the gears, bearing bushes, thrust washers, multi plate clutches and one-way clutch A basic hydraulic control unit consists of a hydraulic pump, pressure regulator, and accumulators. It also contains various types of valves: boost, manual, throttle, kick-down,, governor and shift valves. An engine-driven pump works as an energy source for the hydraulic control system. It is mounted at the front of the gearbox’s main casing and is driven through either two flat or two tags from the hub of the torque converter. A positive displacement pump is used. This class of pump can only generate flow: it is the resistance to this flow offered by the circuit that creates system pressure. A positive displacement pump, such as an internal gear and crescent type, is the most widely used in current automatic transmissions. The relatively large size of the pump requires a separating crescent between the gear teeth not in mesh to ensure efficient transfer of fluid. Since the pump is driven by the engine rather than the transmission, it will not circulate fluid for gearbox lubrication if the

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vehicle is being towed. It is therefore necessary to adhere to recommendations by the manufacturer with regard to speed and distance restrictions on towing, the general preference being to tow the vehicle with the driven wheels off the ground. To regulate the hydraulic control pressure, a regulator valve is included in the system. In high gear system with the transmission in direct drive, the pressure regulator valve provides for a variable line pressure which will increase with engine torque and hence throttle opening. According to the range selected by the driver, it is essential to direct the line pressure to the various circuits of the hydraulic control system, which can be done with the help of a spool valve. The valves work mechanically through a direct-acting system of rods and levers or an enclosed cable or electrically operated servo mounted on the gearbox. Throttle pressure or throttle valve pressure receives the fluid by manual valve and metre as per the torque requirement of the engine. The throttle valve can be operated mechanically, pneumatically or electromagnetically. The throttle valve is mechanically operated with the help of the kick-down valve, controlled by the enclosed cable linkage connected to the accelerator pedal. In case of pneumatic throttle valve, there is an arrangement of the diaphragm control unit by intake manifold depression to sense engine load. The governor valve meters the pressurised fluid into the hydraulic circuits of the control systems, which requires sufficient engine speed. So the governor pressure continuously varies as per the speed of the vehicle and it adjusts the rotational speed of the gear box output shaft. Shift valves play a crucial role in the shifting of gears as per the signal received by the hydraulic control system on engine load and vehicle speed. Another important element of the hydraulic control system is the accumulator. The function of the accumulator is to restrict the flow of fluid as well as damp some of the pressure, which is essential for the smooth operation of the various linkages.

6.10  ELECTROHYDRAULIC CONTROL SYSTEM The electrohydraulic control system, or the electronic transmission control, consists of various electronic components and accessories like sensors and switches, a transmission control module (TCM) and the hydraulic controlling units, including solenoid valves. The function of the TCM is to collect, analyse and process the various signals received with the help of a stored program and manage the appropriate circuit pressure to carry out various operations like gear-shift timing, lock-up clutch operation, transmission gear changes to match the engine speed and torque and the vehicle’s weight and load, driver’s requirements and road conditions. The hydraulic control unit is located underneath the transmission gears and with the help of hydraulic pump, fluid is supplied to various hydraulic circuits. The gearshift can be controlled with the help of three electromagnetically operated open/close valves (solenoid valves) and four electro-magnetic, progressive opening and closing regulation valves. The stored program provides optimistic characteristics for gear shifting as per the traction requirements of the vehicle by coordinating various parameters for smooth operation of the vehicle (Figure 6.6).

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FIGURE 6.6  Electro-hydraulic control system.

6.11  AUTOMATED MANUAL TRANSMISSION SYSTEM Reduction in fuel consumption and improvement in driving comfort and shifting quality can be achieved with the help of vehicles with automated manual transmissions (AMT). There is difference in hardware between AMT and automatic transmission. AMTs consists of constant mesh gears, and automatic transmission consists of a planetary or epicyclic gear box. In an  AMT  or  automatic transmission, gear shifting and clutch/gears actuation is done automatically without the involvement of the driver. The actuation of the gear shift and the clutch depends on the engine load and vehicle speed. The control of clutch and gear assemblies is achieved with electrohydraulic or electric actuators controlled by dedicated electronic control modules (ECM) for transmission control system. The electrohydraulic module consists of a pump (with electric motor), hydraulic pressure accumulator, fluid reservoir, a solenoid valves block, gear selection and engagement position sensors and the fluid pressure sensor. It is essential to synchronise the engine output torque with the clutch and gear positions. The engine management system (EMS) exchanges torque and speed information with dedicated electronic control modules (ECM). The transmission control exchange of information is carried out with the communication bus called controller area network (CAN). The module consist of a level of embedded diagnostic functions, and if there is an issue regarding transmission, the control module is informed and corrective action is provided for the safety of the vehicle and the components.

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FIGURE 6.7  Automated manual transmission (AMTs).

Due to advancements in the electrical and electronics technology, economy, efficiency, performance in terms of response time and power required, there is a wider use of electric motor actuation systems for clutch and gears. The main advantages of AMT over manual transmission are as follows: • Maximum comfort to the driver (the gear shifting is done automatically) • Reduction in fuel consumption(the engine is kept in the most fuel-efficient operating zone, through the gear ratio) • Clutch wear diagnostic (the electronically controlled actuators can measure clutch wear and inform the driver) (Figure 6.7)

SUMMARY • The electrohydraulic control system or the electronic transmission control consists of various electronic components and accessories like sensors and switches, a transmission control module (TCM) and hydraulic controlling units, including solenoid valves. • Manual transmission system has various disadvantages, such as limited gear ratio, noise and difficulty in shifting the gears which may affects the operational characteristics of the vehicle, fuel economy and the comfort of the driver and occupants • Higher power output, higher torque, compact dimensions, driving pleasure and minimum fuel consumption are the essential parameters of the vehicle, which can be fulfilled with the use of CVT, which operates continuously avoiding the delay during shifting between fixed gears. • A basic hydraulic control unit consists of a hydraulic pump, pressure regulator, and accumulators. It also contains various types of valves: boost, manual, throttle, kick-down, governor and shift valves.

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MULTIPLE-CHOICE QUESTIONS

1. Limitations of the conventional transmission systems are a. Limited gear ratios b. Less comfort to the operator c. Noisy operation d. All of the above 2. As the torque increases at a particular limit a. Speed increases b. Speed reduces c. Speed remains constant d. None of the above 3. Stator is an element of a. Epicyclic gear box b. Torque convertor c. Fluid flywheel d. None of the above 4. A hydraulic control unit consist of a. Pump b. Accumulators c. Various types of valves d. All of the above

REVIEW QUESTIONS • Why automatic and semiautomatic transmission is necessary? • Describe the advantages of the automatic transmission over the conventional transmission system. • Describe epicyclic gear train. • Write a short note on torque convertor. • Explain the working of an automatic transaxle. • Describe the automated manual transmission system. Answers to MCQs: (1) a (2) d (3) b (4) d

7

Propeller Shaft, Differential and Rear Axles

OUTCOME Learning Objectives • • • •

Fundamentals of driveline Different types of driveline arrangements Differential and its types Rear axles their types and various loads acting on them

7.1 INTRODUCTION The function of a propeller shaft is to connect the gearbox to the final drive. Propeller shafts transmit speed and torque to the rear axles. They are connected at an inclination. To transmit the torque, when shafts are in inclined position, universal joints are used. Differential arrangement provides differing speeds of the driven wheels, as well as equalises axle torque of both wheels at all times. Driveline attachments provided in the vehicle are Hotchkiss and torque tube drives.

7.2 DRIVELINE ARRANGEMENTS There are different types of rear drive arrangements provided in the vehicle. The most common arrangements are as follows.

7.2.1 Hotchkiss Drive This is the most commonly used drive arrangement in the rear axle. The springs provided in this type of construction takes complete weight of the vehicle, driving torque and the braking thrust. Front and down deflection of the springs during the braking and acceleration are as shown in Figure 7.1. Driving torque is transferred from casing to the spring by the interstitial friction between the leaves of the springs and then from front end is transferred to the vehicle frame. This type of arrangement is commonly used in passenger cars and heavy commercial vehicles. The rear end of the half elliptic spring is not rigidly fixed with the body; it is supported by a shackle, while the front end of the spring is rigidly fixed with the body. Figure 7.1 shows deflection of the springs as an effect of the thrust due to acceleration and braking. The propeller shaft provided with this drive has two universal joints and slip joints. 125

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FIGURE 7.1  Hotchkiss drive.

When using a helical spring with a live rear axle, the spring cannot be in a position to take the driving thrust and have torque reaction or support the rear axle. In such situations of drive, it is necessary to take above mentioned loads by the additional arrangement like upper and lower trailing suspension arms, which further increases the additional weight of the systems but coil spring slightly reduces the unsprung weight of the vehicle.

7.2.2 Torque Tube Drive This drive is generally used in light commercial vehicles and cars. Generally, the torque tube drive provides a smoother ride compared to the Hotchkiss drive. It consists of a tubular member which encloses the propeller shaft, bolted rigidly to the axle casing. The front end of the torque tube drive is located in a ball and socket joint, which is located at the end of the gear box output shaft. Torque tube takes only torque reaction and driving torque. Spring takes only side thrust besides supporting the body weight. Forward thrust can be transferred from gear box mounting to the frame (Figure 7.2).

7.3 PROPELLER SHAFT A media or shaft through which the gearbox output power is transferred to the axle is called propeller shaft. One end of the propeller shaft is connected to the gear box output and the other end connects to the final drive through universal joints. The shaft may be a one- or two-piece construction. It consists of universal joints/constant velocity joints and slip joints. In the case of the two-piece construction, there is a rubber-mounted bearing at the mid-point. A conventional universal joint consists of two yokes, connected to each end of the propeller shaft, a central or cross piece is attached to connect the two yokes. As the angular position of the shaft changes, the cross piece connected will turn in the bearing of the yoke. To overcome this problem

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FIGURE 7.2  Torque tube drive.

of variations in speed and torque, special types of joints are provided in this assembly called constant velocity joints. The shafts used may be hollow or solid. Hollow shafts are of less weight ­compared to the solid ones and hollow shaft provides additional strength. The shaft is subjected to torsional shocks and twisting. There are certain advantages of hollow shafts over solid shafts, such as less weight, higher resistance to sagging, good resistance to torsional strength, etc.

7.4 UNIVERSAL JOINT A universal joint consists of two yokes, connected to each end of the propeller shaft; a central or cross piece is attached to connect the two yokes. Universal joints are used to connect the two rigid shafts at an angle to each other. They permit the transmission of power not only at an angle but when angle varies continuously. Generally the propeller shaft is fitted at an angle, because the gear box output is a sprung mass located above the rear axle with respect to the ground. And the angle continuously varies due to road irregularities. As a result, there is fluctuation in the output torque and speed. As the angle increases, speed and torque fluctuations will be more. The shaft must be strong enough to resist the twisting action and strong enough to withstand the sagging in very-high-speed operations.

7.5 SLIP JOINT A slip joint consists of two parts: propeller shaft with external splines called the male part and a universal joint with internal splines called the female part. Because of variations in the length of the shaft, the axle moves in forward and backward directions to provide telescopic action (Figure 7.3).

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FIGURE 7.3  Propeller shaft construction.

7.6 CONSTANT VELOCITY JOINTS We know that conventional universal joints used in vehicles to transmit the gearbox output torque to the final drive creates fluctuations in the speed and torque as the angle of inclination increases. This is because two reasons:

1. Vertical up and down movement of the vehicle body relative to the front and rear wheels 2. Horizontal movement of the stub axle about the kingpin when is vehicle steered out The solution for this is constant velocity joints, which provide equal speed and torque to the output shaft. The following types of constant velocity joints are generally used:

1. Double Hooke’s joint In a double Hooke’s-type ball-and-socket joint, a centring device is required between the driving and driven shaft. When the input and output shafts are inclined to each other and the first stage driven central double yoke is speeding up, the second stage driven also increases the speed of shaft. The speed gained or lost by one half of the joint will be lost or gained by the second half of the joint. There will be no cyclic speed variation between the input and output shaft during the operation. 2. Rzeppa joint It consists of ball-and-socket joints with grooves in which six rolling steel balls are placed on a single plane. The input shaft has a gear element which is placed in the cage. It provides better results up to an angular variation of 40° (Figure 7.4).

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FIGURE 7.4  Rzeppa joint.

FIGURE 7.5  Weiss joint.

3. Weiss It consists of four rolling steel balls and interlocking forked ends of driving and driven shafts; the balls are placed in the forked ends. The arrangement of the all four balls must lie in a plane which bisects the angle between the shafts to provide constant velocity joints. There are certain limitations in this joint in terms of torque transmission compared to Rzeppa joints because only one half of the number of balls will transmit drive in either direction of rotation (Figure 7.5).

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FIGURE 7.6  Tracta joint.

FIGURE 7.7  Tripod joint.

4. Tracta Tract a joint is a two-piece assembly in which the relative circular motion in right angle plane of the driven and driving shaft can be achieved to adjust their angular displacement to get the constant velocity drive. Instead of the rolling of the balls there is a sliding action, which is subjected to sliding friction, resulting in high heat generation during high torque transmissions (Figure 7.6). 5. Tripod This type of joint consists of a needle bearing/barrel-shaped roller mounted on a three-legged spider/three-pointed yoke instead of a ball bearing. The assembly of the rollers is mounted in a cup with three corresponding grooves connected to the differential. The rollers are positioned at 120° to one. This three-legged treadmill spider has very limited operating angles, but can fall in and out at a longer distance as the suspension travels (Figure 7.7).

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7.7 FINAL DRIVE GEARS AND BEARINGS In the modern vehicle, a bevel drive has proved to be lighter, more efficient, less expensive and equally quiet running. Generally, the following types of gearing are used in the final drive:







1. Straight bevel gears Bevel gear wheels are shaped like the frustum of a cone. The larger gear is called crown wheel, which is attached to the differential unit, while the smaller gear is called pinion, which is attached to the propeller shaft (Figure 7.8). 2. Spiral bevel gear The only difference between the straight bevel gears and spiral bevel is that at the time of meshing, more than one pair comes in contact so progressive engagement and smooth operation is possible. Another advantage is the pressure on the gear teeth surfaces is reduced because the transmitted load is shared by more than one pair of teeth in simultaneous contact. 3. Hypoid bevel tooth gear The gear teeth of the crown wheel are cut in hyperbolic curve and pinion gear meshes with crown below the axle shaft, which lowers the height of the propeller shaft. 4. Worm and worm wheel gears When worm wheel rotates, the worm slides and pushes against the crown teeth which causes the crown wheel to rotate on its axis.

FIGURE 7.8  Various types of gear drive arrangements.

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7.7.1 Bearings While transmission of the torque and meshing action of the gears; various types of loads comes on crown wheels and bearings like end thrust force on the pinion with a corresponding radial separating force on the crown wheel and end thrust force on the crown with a corresponding radial separating force on the pinion wheel some tangential forces. For these applications taper rolling bearings are used, because of their following advantages: • A greater load-carrying capacity for a given size of bearing because of line contact as opposed to the (theoretical) point contact in ball bearing • Due to their tapered construction, the operating geometry remains undistributed. • They are rigid and have the ability to withstand any combination of radial, thrust and tilting loads within the designed capacity of the bearing.

7.8 DIFFERENTIAL When the vehicle takes a turn, the outer wheel of the drive axle needs to turn with more revolutions than the inner wheel, i.e. the outer wheel travels more distance compared to the inner wheel. If not, the wheel will drag and cause tyre wear. Differential gives differing speeds of the driven wheels, as well as equalises axle torque of both the wheels at all times. There is no need of differential when the outer and inner wheels are independent as in the case of the front axle. The differential consists of sun gears, planet pinions, a cage, a crown wheel and a bevel pinion. The sun gear is fixed to the inner end of each rear axle (half shaft). A cage is fixed to the left axle. The crown gear is fixed to the cage and the cage is rotated with the crown gear. The crown gear is rotated by a bevel pinion. The crown gear and cage remain secure on the rear left axle. There are two planet pinions on a shaft that is protected by a cage. The planet pinions are meshed with the sun gears. The rear wheels are fixed to the outer ends of the rear axles. Working: As the vehicle travels in a straight line, the power is transferred from the propeller shaft to the bevel pinion that drives the crown wheel. It is then moved to the differential cage in which the set of sun gears and planet pinions are housed. It is transmitted from the sun gear to the road wheels by means of axle half shafts. In this case, the crown wheel, the differential cage, the planet pinions and the sun gear all spin as a single entity, and there is no relative motion between the sun gear and the planet pinions. The planet pinions do not rotate around their own axes. Both road wheels spin at the same speed. As the vehicle turns, the inner wheel encounters resistance and appears to spin in the opposite direction. As a result, the planet pinions continue to rotate around their own axes and around the sun gear and transmit further rotary motion to the other side of the sun gear. Therefore the outer sun gear rotates faster than the inner sun gear. As a result, the outer road wheel travels quicker than the inner road wheel and covers more distance (Figure 7.9).

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FIGURE 7.9  Various components of differential.

Differential lock: If one rear axle wheel is stuck in the mud, the open differential will focus on turning the stuck wheel, which is the disadvantage of the traditional differential. A lock differential is designed to overcome this key disadvantage of the standard open differential by effectively “locking” both wheels together on the axle as if they were on a single shaft. It can drive the vehicle with the aid of the torque available on the free wheel. This forces both wheels to rotate in unison, regardless of the traction (or lack of traction) available to either wheel individually. Once the differential is unlocked (open differential), it allows each wheel to spin at various speeds (e.g. once negotiating a turn), thus preventing suffocation of the tyre. The open (or unlocked) differential always gives the same torque (rotational force) to each of the two wheels on the axle. So, while the wheels can rotate at different speeds, they exert the same rotational force, even if one is fully stationary and the other is spinning.

7.8.1 Limited Slip Differential A limited slip differential (LSD) is very similar to the open differential model but has an additional component that prevents wheel spinning and loss of traction, the regular differential provides maximum torque to the wheel with minimum traction. The limited slip differential delivers maximum torque to the wheel with maximum traction, particularly in off-road vehicles. The limited slip differential clutch pack uses a set of friction disks and steel plates to lock the axles together if one of the drive wheels experiences uncontrolled slip. The friction disks are sandwiched between the steel plates inside the differential case. The steel plates are rotated with the differential case while the friction disk is splined and rotated with the differential side gears.

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The springs (Belleville springs, coil springs or leaf springs) force the friction disk and the steel plates together. As a consequence, both rear axles attempt to rotate with the differential case. The clutch pack combines the spring force and the momentum of the spider gears. Under high torque conditions, the rotation of the pinion gears forces out the side gears of the axle, which move the axle side of the gears on the clutch disks. This action helps to lock the disk and keep both wheels turning.

7.9 REAR AXLE CONSTRUCTION Function of the rear axle: Axles are designed to carry the vehicle’s weight and sometimes they transmit the driving effort to the road wheels. Axles may be classified into • Live axles • Dead axles Live axles transmit the torque as well as carry the vertical load, they consist of various types of gears and mechanisms to drive the road wheels. The two main components installed in the live axles are differential and the final drive. A dead axle carries only vertical loads and supports the vehicle’s weight. Functions • To provide a rigid structure on which wheels can be mounted and final drive, brakes, differential bearing arrangements can be installed • To carry load and sometimes torque transmission (i.e. in the case of live axles only) • To carry break thrust Axle Casing 1. It provides a rigid means for mounting the road wheels, final drive arrangements and brake assemblies, relative to the vehicle rear suspension system and driveline. 2. It takes the vertical load acting on the vehicle. Mostly, today’s vehicles are equipped with a banjo-or carrier-type casing 1. Carrier-type axle It consists of two halves connected to each other directly or indirectly, has a robust construction and is generally used for 4×4 vehicles. The crown wheel and pinion are mounted on a rigid central housing. The advantage of this type of construction is that there is enhancement of the stability of the crown wheel. The central housing or carrier is made up of malleable cast

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iron. This type of axle casing can be used for various types of tracks by adjusting the length of the half shafts. 2. Banjo-type axle This is a one-piece construction. It has a centrally located flangemounted housing which accommodates the final drive and differential unit. The tubular axle section of this casing is built with steel pressing suitably strengthened to withstand bending loads. It is generally used in light-duty applications (Figure 7.10).

7.10 TYPES OF REAR AXLES Rear axle hub can be classified as follows:

1. Semi-floating axle The wheel is located at the extended part of the axle and a tapered roller of ball-type single bearing is located between the axle casing and axle. The inner end of the axle is carried by the side gears in the differential housing. The semi-floating axle is used in passenger vehicles and light trucks. These types of axle half shafts take the following loads: • Driving torque • Vertical load • End thrust due to side force generated by road camber, cornering, wind, etc. • Bending due to resistance offered by the tyre on the ground when end thrust exists (Figure 7.11).

FIGURE 7.10  Rear axle casing.

FIGURE 7.11  Types of rear axles.

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2. Three-quarter floating axle In this type of arrangement, the bearing is located between axle casing and hub secured in position by a large nut. The wheel is bolted to the hub. The inner end of the half shaft is splined to the final drive assembly. These types of axle half shafts will take the following types of loads: • Driving torque • Side thrust • Axle casing will take vertical loads 3. Full-floating axle Here, two-tapered roller bearings are fitted between the hub and ­casing. In this arrangement, the axle housings bear the entire weight of the vehicle and absorb all the stresses or final thrust generated by spinning, skidding and pulling, and the axle half shaft only takes the driving torque. The axle shaft is attached to the drive wheel by means of a bolted flange, which allows the axle shaft to be removed for maintenance without having to remove the wheel.

7.11 VARIOUS TYPES OF LOADS ACTING ON THE REAR AXLES The axle shaft transmits the drive from the differential sun wheel to the rear hub. The various types of shafts can be measured on the basis of the stress they can withstand. The basic car shaft must withstand the following stresses:

1. Moving thrust: The moving torque produced by the engine allows the thrust to be produced in the road wheels, which must be transferred from the axle housing to the chassis frame and to the body of the vehicle. 2. Torque reaction: If the rear axle stays rigid while the road wheels stop rotating (due to driving needs or road conditions), the bevel pinion of the final drive tends to rotate around the crown wheel. It generates a tendency for the entire vehicle to rotate about the rear axle or to rise off the front of the car. This phenomenon is referred to as a torque reaction. 3. Braking torque or thrust: The axle housing experiences a brake torque when the brakes are applied to the wheels of the vehicle. 4. Side thrust: When the vehicle is spinning, the rear axle undergoes side thrusts or pulls due to any side load on the shaft. 5. Body weight: The rear axle is a plate supported by a weighted end. This weight causes bending and shearing forces in the axle shaft.

7.12 TANDEM AXLE DRIVE FOR HEAVY VEHICLES In the tandem axle drive system, the engine power is distributed equally to both axles. Power is supplied to the transfer case between the axles in special, military and heavy-duty vehicles and transferred to them by means of the drive shafts. In over-road trucks, such as semi-tractors, the power is delivered first to the front differential. A power splitting unit, such as an interaxle differential or, two-speed

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system, a gear reduction unit is bolted to the front differential. The interaxle differential is used to allow the front and rear axles to travel at differing speeds when cornering.

SUMMARY • Propeller shaft connects the gear box output and the final drive • Propeller shaft consist of universal joints, slip joints, shaft, etc. • To transmit the torque when shafts are in inclined position, universal joints are used. • A constant velocity joint avoids fluctuations in speed and torque. • The different driveline attachments provided to the vehicle are Hotchkiss and torque tube drives to avoid adverse effects of various types of forces.

MULTIPLE-CHOICE QUESTIONS

1. Propeller shaft is used to connect a. Engine and final drive b. Engine and differential c. Gear box and rear axle d. Gear box output and final drive 2. The function of the slip joint is to a. Adjust the length of the shaft b. Provide angle to the shaft c. To connect two shafts d. To connect shafts having unequal diameters 3. Universal joints are used a. To connect two shafts b. To connect shafts of different lengths c. To connect shafts of different diameters d. To connect shafts with inclination 4. Constant velocity joints are used a. To provide additional strength for universal joints b. To avoid mismatch between two shafts c. To avoid speed and torque fluctuations during vehicular applications d. To increase the speed of input shaft 5. Front-engine front-wheel drive layout provides a. Minimum ground clearance b. Proper traction during hill climbing c. Both a and b d. None of the above 6. In a Hotchkiss drive the front end of the spring is a. Rigidly attached to the body b. Placed in shackle c. Hanged to the body d. None of the above

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REVIEW QUESTIONS

1. Describe the construction of the propeller shaft. 2. List the advantages and disadvantages of the • Front-engine front-wheel drive • Front-engine rear-wheel drive • Rear-engine rear-wheel drive 3. List the functions of • Universal joint • Slip joint Answers to MCQs: (1) a (2)d (3)a (4)d (5)a (6)a

Automotive Systems

8

Suspension System

OUTCOME Learning Objectives • • • •

The need for and functions of the suspension system Classification of the suspension system Classification of the different types of springs used in automotive suspension Construction and working of various types of suspension systems

8.1 INTRODUCTION While on the road, the vehicle has to face different types of road surfaces, due to which it is subjected to dynamic loads, cornering force, etc. If the chassis is connected directly to the transmission components, then these dynamic loads are directly transferred to the occupants. The entire structure of the vehicle may be subject to excessive fatigue, and it may breakdown. Therefore, it is essential to isolate the entire vehicle from such forces, loads and shocks due to road irregularities. It is also essential to maintain vehicle stability, control and proper road holding during all operating conditions such as braking acceleration, cornering, etc., which depends on tyre–road friction. The factors responsible for this type friction are type of road, weight of the vehicle and the coefficient of friction. If the dynamic load acting on the vehicle exceeds the tyre–road friction then the tyre may slip or skid and be subjected to scrub. To avoid and minimise the effects of this dynamic effect the suspension system is incorporated in the vehicle. If the suspension elements are designed to withstand large deflections then it absorbs these bumps and allows the body to run smooth. A suspension with limited deflection bounces the vehicle body. When the vehicle is subjected to an obstacle, the resulting bump compresses the suspension spring, which is called jounce. A jounce stores energy in the spring, and forces the spring to return to its original position. During returning it overruns the neutral position, which is called rebound. During this operation the spring starts to oscillate. It is necessary to stop this oscillation, which can be done with the help of shock absorbers. Sometimes they are mounted at an angle to help sideways control. Some of the requirements of the suspension systems are as follows: • Provide chassis isolation and ensure the wheels follow the road profile with minimum tyre load fluctuation • Ensure that steering control is maintained during travel by proper positional and directional attitude with respect to the road surface

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• Ensure that the vehicle responds favourably to control forces produced by the tyres as a of result the forces generated in various operating conditions by resisting squat, dive and roll of the vehicle body • Provide isolation from high-frequency vibration arising from tyre excitation and road noise • Provide required structural strength to resist the loads imposed on the suspension A vehicle’s frame and body are connected through spring elements, various links and damping mechanisms to provide comfort to the occupants, and is called suspension.

8.2 BASIC RIDE CONSIDERATIONS OF THE VEHICLE Ride quality is basically related to human comfort which is associated with the sensation or feel of the passenger in the environment of a moving vehicle. The vehicle environment may be affected by the following:

1. Engine vibrations 2. Road surface 3. Aerodynamic forces 4. Vibrations in the driveline 5. Imbalance and variations in stiffness of the rod and wheel assembly 6. Improper suspension and other factors.

Ride considerations are related to human response to vibrations, vibrational behaviour of the vehicle and road surface. There are various parameters related to how a suspension system can affects the ride characteristics of the vehicle, such as stiffness of the spring elements, mountings, deflection, resilience, etc.

8.3 FUNCTIONS OF THE SUSPENSION SYSTEM The functions of the suspension system are as follows:

1. To absorb road impacts to provide comfort to the occupants 2. To minimise suspension motions like pitching, rolling, yawing 3. To reduce un-sprung mass 4. To reduce impact stresses on the vehicle’s various mechanisms 5. To maintain directional stability of the vehicle 6. To maintain correct wheel alignment to avoid tyre wear 7. To help in maintaining road holding

8.4 CLASSIFICATION OF THE SUSPENSION SYSTEM Generally, the suspension system can be broadly classified into A. Rigid axle suspension system B. Independent suspension system

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8.5 INDEPENDENT SUSPENSION SYSTEM There are certain limitations in the rigid beam suspension system. In the case of the independent suspension system, the rise or fall of one wheel does not affect the others. The following are the advantages of the independent suspension system:

a. Compared to the axle-beam, relatively softer springs can be used in case of independent suspension without affecting body roll, which provides greater range of suspension movement. The soft springs are more sensitive to any small bump the vehicle has to overcome and will not transmit the shock to the vehicle body and passengers, and hence provide better ride comfort. b. Increased passenger space: The height of the engine and chassis structure can be lowered with the help of independent suspension so the power unit can be mounted further forward in the car, which will provide more space for the passenger compartment, and hence the luggage compartment. c. The capacity to store the stain energy for given weight in a coil or torsionbar spring is greater than for a semi-elliptic multi-leaf spring. Hence the lighter springs can be used with independent wishbone suspension because the spring has to only support vertical loads, absorb shocks and suspension linkage alone can sustain the driving, braking and lateral forces. d. Independent suspension usually lowers the roll centre, hence the body rolls before the wheels break away from the road, providing a warning to the driver. e. Because of the less un-sprung mass of independent suspension systems, road wheels follow the contour of the road irregularities at higher speeds, compared to that of heavy rigid-axle-beam. This type of suspension system also reduces the tyre scrub and wear. f. An anti-roll bar in conjunction with independent suspension provides the necessary resisting stiffness to oppose body roll during cornering, and hence softer springs can be employed for normal vertical loads. g. In independent suspension system on the sides of the car there is limited interaction between the opposite roads wheels so that there is less chance of wheel wobble due to vibrational resonance. It gives large amounts of kinematic and elasto kinematic configuration freedom. The following are its disadvantages:

a. The wheel cambering with body roll reduces concerning power, and wheel load equalisation during cornering is only possible using a stabiliser bar. b. There is a slight change in wheel track when the one wheel subjected to bounce causes tyre scrub. c. A more rigid chassis or sub-frame structure is required. d. A more complicated suspension and steering linkage and pivot joints are necessary, his makes it more expensive, but tends to more wear. e. Effects of the unbalanced wheel assembly are transmitted to the steering wheel more easily and are also more pronounced. f. Steering geometry alignment is critical and requires frequent attention.

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Different Types of Front Wheel Suspension Systems 1. MacPherson strut type This is most the common type of suspension widely used in the front and rear axles but mostly used in the front wheels. It consists of a strut, which includes shock absorber and coil spring. It has two links, one taking the lateral and the other the drag loading. It consists of only the lower wishbone. The wishbone is hinged to the cross member to resist it and positions the wheel as well as resists accelerating, braking and side forces. The advantages of this suspension are that it takes less space horizontally and as a result, it leaves generous room for packaging of the engine compartment and passenger cabin. Its compact and lightweight design reduces the overall weight of the vehicle. Low cost and ease of manufacturing are added advantages of this suspension system. 2. Wishbone-type independent suspension If the wheel is suspended between two lateral links, in order to resist all the forces and moments acting on the wheel, one link must be above the wheel centre and another below the wheel centre, so there is a necessity for a third link to control the toe and steering, this configuration is called double wishbone suspension or lateral link suspension. It consists of two wishbone arms pivoted to the frame. The upper wishbone arm is shorter than the lower arm. This helps maintain the wheel track stable, to avoid tyre scrub and reduce tyre wear. In such an arrangement, a minor shift in the chamber occurs. The coil spring is positioned between the lower wishbone and the underside of the cross member. The weight of the vehicle is transmitted from the body and the cross-beam to the coil spring from which it passes to the lower wishbone. The shock absorber is mounted within the spring of the coil and attached to the cross member and to the lower wishbone. If the vehicle hits a bump and  the  wheel begins to travel upwards, the lower and upper arms (control arms) travel upwards and the coil spring is squeezed so that the shock absorber (damper) dampens the shocks (which arises due to ground irregularities) in the coil spring. The double-wishbone-type suspension provides a large amount of design freedom; roll centre and pitch axis can be chosen freely; there is limited change in camber and track width; it provides high lateral stiffness and very good ride and handling (Figure 8.1). 3. Multilink suspension Multi-link suspensions are nowadays common in passenger cars from mid-range models and upward. This suspension uses three or more lateral arms and one or more longitudinal arms, which do not have to be of equal length and can be angled away from their natural direction. They are designed in a way to give a more complete control over wheel positioning. Multi-link arrangements are used on both front and rear suspensions, but the former replaces a lateral arm with a tie-rod that connects the rack or steering box to the wheel hub.

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FIGURE 8.1  Wishbone-type suspension system.





The design of multilink suspensions changes as per the manufacturer. Some BMW setups look like the letter Z and sport four links, while Honda’s multi-link is like a double wishbone suspension but with an added fifth control arm. Audi A4’s front suspension also has four links and is extremely similar to the double wishbone one. The Hyundai Genesis sport front and rear five-link system is shown in Figure 8.2. The front suspension has two upper links, two lower links and a tie-rod, and in the rear suspension, there are two upper links, a lower link, a trailing link and a toe control link. The various arrangements of the multilink suspension are shown in Figure 8.3. 4. Independent rear suspensions In the case of independent rear axle suspension systems, the selection of the suspension system is based on whether the axle is driven or non-driven, packaging space availability (effected by both differential and a need to minimise intrusion into the boot space) and torque-steer effects. Some independent systems used in the rear wheel independent suspension system are as follows: 1. Trailing arm suspension Trailing arm suspension  (the upper picture) employs two trailing arms which are pivoted to the car body at the arm’s front edge. The arm is triangular shaped and relatively large compared to other suspensions control arms because it is a single piece and the upper surface supports the coil spring. It is rigidly fixed to the wheel at the other end elastically in the longitudinal direction, which enhances the longitudinal springing characteristics to improve ride comfort. The link transmits longitudinal and lateral forces and allows the wheel carrier to rotate

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FIGURE 8.2  The Hyundai Genesis Sport front and rear five-link systems.

FIGURE 8.3  Multi-link suspension system.

about an angled horizontal axis. The links are in tension during braking and in ­compression during acceleration. The links must be extremely rigid in order to minimise the resulting changes in toe, camber, etc. The ­compact structure of the link provides additional room for the fuel tank, spare tyre and exhaust system, but during cornering there are chances of tilting of the wheel.

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2. Swing axle suspension A swing axle is basically a rigid axle that has been separated in the middle, and the two halves of the axle can be used as lateral links pivoted at the centreline in the axle drive housing. The length of the swing axle controls the camber behaviour, and enables the use of half-shafts with universal joints instead of CV joints. The large camber changes during compression and rebound causes excessive tyre wear in case of wheel travel and also there is problem of jacking in the case of swing axle suspension system. As a result of jacking there is very limited use of such type of this system in modern vehicles. 3. Semi-trailing arm systems In the case of semi-trailing arm suspension system, the link is d­ iagonally oriented with two chassis-side pivot joints separated by a large offset. This design is a cross between a pure trailing arm and a swing axle. In this design, the pivot angle is of about 10°–15° to the vehicles lateral axis (viewed from top) and 5° to the longitudinal axis (viewed from the side). The kinematics can be changed by varying both the angles to optimise the performance.

8.6 DEPENDENT SUSPENSION SYSTEMS In dependent suspension systems, movement of one wheel directly affects the other wheels. In dependent front-wheel suspension systems, a beam-type rigid axle is used to support the two stub axle pivots at a fixed distance. This is also called a solid axle, live axle or dependent wheel control system rigid axle. Rigid axles have some advantages due to their simplicity, economy and cost-effective integration of the rear differential into the axle body. They provide wide loading surface to the non-driven axle, robustness and large loading capacity. The beam-type axle is used to support two stub axle pivots. With the beam axle suspension, the wheel alignment is maintained most effectively because it does not demand more rigidity at the front-end structure of the chassis frame. There is less tyre wear as the track distance remains constant and the front wheels remain perpendicular to the road in the presence of body roll. The use of a beam axle also ensures that the ground clearance of a commercial vehicle remains constant in both unladen and laden conditions. In the case of front side of the vehicle, non drive rigid beam axle can be used which is attached to the stub axle for steering mechanism. Likewise in case of rear side of the vehicle the system can be used with the drive axle. In this case separate drive half shafts are enclosed with tubed structure. The axle beam has a T section between the spring saddles which provides resistance to bending. To sustain twisting, braking and acceleration reactions, the springsaddles and I section of the stub-axles changes to a round section. Rigid axle beam suspension consists of a semi-elliptical leaf spring assembly clamped with U-bolts to the axle provided with the mounting brackets, shackle-pins, bump stops, etc. to both sides of the axle. Bump stops are used to stiffen suspension during violent bouncing or excessive body rolls. The rubber bump stops are usually clamped on top of the axle or spring using U-bolts.

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Axle beams are provided with flat spring saddles or spring beds on which the semi-elliptical spring can be seated. The vehicle’s weight and payload are transmitted to the front and rear mounting brackets, shackle-pins, leaf springs and to the un-sprung axle-beam, through the sprung chassis. Since the suspension system is dependent, if one wheel is subjected to bump or falls in a ditch the movement is transmitted to the other wheels but the average height of the vehicle cab be maintained.

8.6.1 Advantages of Axle Beam Suspension Axel beam suspension is simple in construction with fewer parts, simple in design, easy to maintain, provides compact steering, gives better off-road performance and has a large load-carrying capacity. The rigid construction of the axle provides support against bouncing and other movements due to the side forces acting on the vehicle body. There is enhancement in tyre life because in the rigid axle beam suspension system the wheels remain perpendicular to the road surface. This provides good road grip through proper road contact between the tyre tread roads as well as by maintains the wheel alignment. Road clearance is essential when the vehicle travels on a rough road; the rigid axle suspension supports to maintain constant ground clearance in both the loading and unloading conditions and also when the body rolls or goes over a bump or pothole.

8.6.2 Disadvantages of Axle Beam Suspension As both wheels are connected, a vehicle with one wheel encountering a bump or depression on the road sends a shock wave across the entire rear (or front) of the vehicle, leading to passenger discomfort and possible “shimmy”. There is no camber adjustment made during heavy cornering to keep the wheels off their edges and firmly in contact with the road. Its high un-sprung weight leads to harsher vehicle ride and passenger discomfort.

8.7  AIR SUSPENSION In air suspension, air springs, also called bellows, are used instead of metal springs. A suspension that uses both metal springs and air springs is not referred to as air suspension. • Better cushioning and ride comfort can be achieved because suspension bounce frequency between unladen and laden operating condition is much narrower and it is much closer to the ideal frequency for passenger comfort. It protects fragile loads. It also lowers stresses imposed on the vehicle because high peak axle loads are eliminated. • Air springs maintain a constant vehicle ride height irrespective of whether the vehicle is unladen or fully laden. • Air springs have a longer life compared to steel springs. • Maintenance is minimum as there is no need for lubrication.

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Air suspension consists of the following parts:

1. Air supply: Supply of compressed air through compressor, air tanks, valves, and air lines. 2. Air bellows: A bladder which holds the compressed air. 3. Height-controlled valves: these help in controlling the air in the system as per requirement, height controlled valves may be mechanically or electronically operated.

The engine compressor supplies air to the reservoir tank through the unloaded valve and the pressure regulator valve. The pressure required for the suspension is less than the pressure required for the airbrake so the pressure regulator valve is used between the unloader valve and suspension reservoir valve to reduce the delivery pressure to approximately 540 kPa required for the suspension. Air flows from the suspension reservoir to both the front and rear suspensions through a single central levelling valve at the front and a pair of levelling valves which actuate by an arm and link rod attached to the axles on each side of the first tandem axle. The height of the axle can be sensed by the levelling valve and then there is increase or decrease in air pressure supply to the air springs and the height can be maintained in the range of 540–245 kPa according to the loading condition. The air can be supplied to the left- and right-side air springs with the help of isolating valve. It also supplies more air when needed and slows down the transfer of air from the outer spring to the inner spring when the vehicle body rolls (Figure 8.4).

FIGURE 8.4  Air suspension system.

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8.8 RUBBER SUSPENSIONS As rubber can store more energy per unit mass than any other type of spring material, possesses a useful amount of inherent damping due to the internal friction of its material, does not corrode, and weighs less, it proves a good suspension component. It also contributes to the reduction of noise transmission through the suspension system. Suspension characteristics can be enhanced by using both rubber and metal springs. Rubber springs can be used as a main suspension spring for compression or shear loads acting on suspension system. In general, the advantages seen in rubber suspension of tandem axles are as follows: a. There is no metal-to-metal contact of the working parts, which provides quieter operation and better ride experience. b. There is no wear and maintenance is low because there is no need for lubricating or checking the bolt tightness of leaf spring fittings. c. The tyre life can be enhanced by virtue of the suspension being more compliant with cornering and manoeuvring scrub loads, and the rubber bolsters are failsafe in operation. d. Due to hysteresis losses, the energy released from the rubber spring after deflection is considerably less than that imparted to suspension. Hence lower-duty dampers can be used. There are certain limitations to rubber springs called settling, caused by primary and secondary creep from static and dynamic loads. However various arrangements are possible using rubber springs, such as alternatively bonded layers of rubber blocks and steel reinforcement plates sandwiched between inclined mounting plates to the linkages, which subjects the rubber to both shear and compressive forces. This arrangement can overcome the drawback of rubber suspensions.

8.9 TYPES OF SPRINGS USED IN THE SUSPENSION SYSTEM The spring is incorporated between the wheels and the vehicle body, which allows the body to move independently with respect to the wheel. When vehicle is subjected to bump, the severity of the impact stress that can be transferred to the occupants can be reduced due to the spring. The spring is an important component of the suspension system. When the vehicle is subjected to bump, the spring deflects and stores some of the energy, and after the bump has passed the spring starts to oscillate at its natural frequency. It is necessary to stop this oscillation and this can be done with the help of shock absorbers. Different types of springs are used in this suspension system:

1. Leaf spring a. Semi-elliptical leaf spring b. Quarter-elliptical leaf spring c. Three-quarter elliptical leaf spring d. Transverse leaf spring

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e. Full elliptical leaf spring f. Platform-type leaf spring 2. Coil spring 3. Torsion spring 4. Air spring 5. Rubber spring

8.9.1 Leaf Springs Leaf springs are subdivided into longitudinal and transverse leaf springs (Figure 8.5). Longitudinal leaf springs are used only on rigid axles, more commonly on commercial vehicles and trailers. Leaf springs can be used in the rear suspension system. The mounting of the leaf spring to the vehicle structure through shackle or fixed arrangement depends on the type of drive arrangement. An assembly of spring consists of a number of leaves and their lengths continuously vary depending on the arrangement. These leaves are held together with the help of a centre bolt. Leaf springs have certain advantages and disadvantages. A leaf spring can be of many shapes: such as semi-elliptical, elliptical, quarter elliptical, transverse elliptical and three-quarter elliptical. Semi-elliptical leaf springs are used in majority of applications. The various types of leaf spring arrangements are described as follows:



a. Semi-elliptical leaf spring: Here the upper leaf is called master leaf and it consists of an eye; the remaining are full-length leaves and graduated leaves. To maintain equal stress in all leaves they are pre-stressed. The ends are supported and load is applied at the centre. This shape is mostly used in heavy-duty vehicles for rear suspension of the wheels, such as in railway coaches. b. Elliptical leaf spring: Two semi-elliptical springs are joined at the eyes to form an elliptical shape. This combination offers more deflection than semielliptical for the same load. It is commonly used in rickshaws.

FIGURE 8.5  Constructional details of the leaf spring.

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c. Quarter elliptical leaf spring: This shape is just half of the semi-elliptical spring. One end has an eye and the leaves are clamped in the centre. d. Three-quarter elliptical leaf spring: A combination of semi-elliptical and quarter elliptical springs forms a three-quarter elliptical spring, as shown in Figure 8.6. e. Transverse leaf spring: They have the shape as semi elliptical leaf spring. However these springs fit under a truck with the base of curve towards chassis, rather than facing the ground. f. Platform leaf spring: Platform leaf spring uses a pair of semi elliptical leaf spring-one facing down and the other pointing up. When affixed to the vehicle, the spring supports three points of the vehicle’s weight along each side.

8.9.1.1 Benefits of Leaf Springs Leaf springs are the easiest configuration, with the fewest number of moving parts to be worn out. Like coil springs, the leaves are used to hold the rear axle in place such that the need for complicated suspension links is eliminated. If a lot of weight is being carried by the vehicle, leaf springs can distribute the load more uniformly around the chassis of the vehicle than coil or torsion bar springs. In addition, the friction produced between multiple leaves as they slide helps to damp the natural up-down rebounding effect of springs, making the ride steadier and minimising the work of shock absorbers.

FIGURE 8.6  Various arrangements of leaf spring.

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Drawbacks of Leaf Springs When leaf springs are bolted directly to the rear axles, the torque produced during hard acceleration or braking may cause the axle to wind up, creating vibration, backend squatting, and nose-diving. This mounting often requires leaf springs to have a stiffer spring rate, reducing the amount of ride comfort those softer springs can offer.

8.9.2 Coil Springs Coil springs are made of hardened and tempered steel, wound in a spiral shape. Most new passenger cars produced in the last few decades use coil springs for all four wheels, and a growing number of pick-ups and SUVs are now mounted both in the front and in the rear. Coil springs absorb energy when compressed while vehicle moves over road bumps, called jounce. After this jounce the spring starts to oscillate the energy. On MacPherson-type struts, a coil spring is mounted around a shock absorber – both of which are attached to the strut itself. On other vehicles without struts, coil springs and shock absorbers are mounted separately. Coil springs are mainly subjected to torsion. Failure of the coil spring occurs due to shear. The stress varies uniformly, from maximum at the surface to zero at the centre of the circular cross section. Advantages of Coil Springs a. Coil springs are better than leaf springs as they can absorb almost double the energy per unit volume compared to leaf springs. b. They are compact and require less space than leaf springs and can be used in very constricted spaces. c. Coil springs are lighter in weight for the same load.

Torsion Spring Torsion bar is a straight bar with a circular or square section fixed to the frame at one end, and a lever or wishbone-shaped member connects its other end to the wheel. Instead of being flattened out like a leaf spring or compressed like a coil spring, it twists elastically along its axis, or length, when the vehicle is subjected to bump, and at normal conditions it comes back to its original position. The spring rate of the torsion bar is determined by the thickness of the bar, its overall diameter, length and its material, usually steel alloy (Figure 8.7).

FIGURE 8.7  Torsion bar suspension system.

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Air Springs The air spring is often referred to as the variable stiffness spring. Air springs provide adjustable spring rate, adjustable load carrying capacity, ease of height control and low friction. The two key types of air springs are a moving lobe (sometimes called reversible sleeve) and a convoluted bellow. The rolling lobe spring uses a single rubber bladder, which folds inward and rolls outward, depending on how far and in which direction it goes. The roller lobe air spring is available with a very high stroke length, but it is limited in strength due to its propensity to bulge and thus has a limited capacity for force. Rubber Springs Rubber springs are used in suspension as they save more energy per unit weight than steel. They are more lightweight than any other spring. They have excellent vibration damping properties. The main advantage of using the rubber spring is that it does not suddenly fail like steel, so the risk is less. It does not rust. It also contributes to the reduction of noise transmission through the suspension system. The various types of rubber springs are as follows:

a. Compression spring: This type of spring is often used because it is reliable, simple in design, can withstand occasional overload of a large magnitude and has a strong damping effect. b. Compression shear spring: In this type of spring, the load is borne partly by shearing and partly by compression. c. Steel-reinforced spring: This spring consists of a steel helical spring attached to a rubber core. Steel springs hold just 20% of the load. d. Progressive spring: It has initially an exceedingly small rate and which further rises rapidly as the central cavity closes.

8.10 DAMPERS While moving on road, when the vehicle is subjected to obstacles and other forces, the spring provided is subjected to jounce, which stores the energy, when vehicle crossed the obstacle and then release of energy. This further leads to produce starts to roll or bounce i.e. this is due to springs provided in a suspension system, springs and their associated masses start to oscillate. There is a need to stop these movements within the minimum possible time to ensure good tracking and braking performance, and for this purpose shock absorbers or dampers are incorporated in the vehicle. Those that offer resistance during both compression and rebound of the spring stroke are called as double-acting shock absorber. While the one that resists only rebound is called single-acting cylinder. Vibration dampers are arranged parallel to the vehicle suspension, and are of the following types: A. Monotube dampers The main oil supply chamber is located in the same single cylinder tube in the case of the monotube shock absorber. The damping valves for both the rebound and compression stages are located on the piston. The oil and gas are separated by a moving separating piston with an O-ring seal.

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Road irregularity causes vehicle vibration which leads to compression of the shock absorber. The piston valve exerts pressure on the oil flowing upwards from the piston chamber below the piston, which prevents the piston going downwards. The gas cushion compresses the pressure of the piston rod coming in. Rebound vehicle movements cause the shock absorber to expand. The piston valve exerts pressure on the oil coming down from the chamber above the piston, which prevents the piston going upwards. The gas cushion raises the strength of the retracting piston rod (Figure 8.8). B. Twin tube dampers There are two chambers in twin tube shock absorber: one formed by the main cylinder and the outer tube, and another by the main chamber in the main cylinder and the oil supply chamber (reservoir) located between the main cylinder and the outer tube. The movement of the piston and the piston rod takes place in the main chamber. The annular oil supply chamber maintains the oil volume in the main chamber caused by the movement of the piston rod (Figure 8.9). For damping, two valves are used: the piston valve and the bottom valve. These valves consist of an arrangement of spring disks, helical springs and valve bodies with restriction holes. Compression: Vehicle vibrations compress the shock absorber, with the base valve doing the damping. When the piston rod moves in, the oil it displaces flows into the compensation chamber, while the base valve resists this flow and thus slows down the piston. The piston valve is open. It functions as a non-return valve during this stage.

FIGURE 8.8  Monotube dampers.

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FIGURE 8.9  Twin tube dampers.

Rebound: Vehicle vibrations cause the shock absorber to extend, with the piston valve assuming the damping function. The piston valve exerts pressure against the oil flowing down from the chamber above the piston, thus slowing the upward movement of the piston. The oil flows unobstructed out of the compensation chamber through the non-return valve back into the working cylinder where it is needed.

8.11 ADAPTIVE SUSPENSION SYSTEM Adaptive suspension system is electronically controlled with a continuously adaptive damping system. It consists of various types of sensors and switches to provide the information to the ECU (electronic control unit), according to which the system works. In this system, instead of springs and dampers computer controlled hydraulic actuators are used to take the suspension loads. So when the vehicle is subjected to bumper due to any road irregularity, then the hydraulic actuators come in action and raise or lower the wheels to restrain any movement of the vehicle body, in accordance with signals received by the computer from strategically positioned sensors. With this type of suspension system both the spring and shock damper characteristics are continuously self-adjusted to get optimum ride and road holding. The Hydra active suspension system developed by Lotus consists of an additional gas-spring/hydraulic-damper unit which can be switched into operation between the two main front units and another between those at the rear for the two different modes – soft and firm –in which the spring flexibility and the amount of the damping can be varied

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FIGURE 8.10  Adaptive suspension system.

according to the requirement. In this computerised control system various signals are received from the various sensors (Figure 8.10). There is a single, three-way and spring-loaded solenoid valve which provides a connection between the central hydraulic power system and two slide valves termed “firmness regulators”, there being one for each of the additional spring/damper units. The two modes are described next.

8.11.1 Soft Mode In the soft mode, solenoid admits fluid under pressure to open the slide valves of the firmness regulators, which then allow the movements of the suspension linkages to be hydraulically transmitted to the additional as well as the main gas spring units. The effect of increasing the quantity of gas under compression is to permit greater suspension flexibility, as well as allows the fluid to be transmitted to the linkage. This permit for movement of fluid to flow twice the number of restricts or orifices, which is acting in parallel and reduces the amount of shock damping.

8.11.2 Firm Mode In the firm mode, the fluid previously trapped under pressure returns to the reservoir of the central hydraulic power system and allows the slide valves of the firmness regulators to return to their closed positions. Due to this isolation of the additional spring/damper units from their associated main ones, the front and rear suspension linkages each act against only two instead of three spring/damper units, thereby reducing spring flexibility and increasing shock damping.

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SUMMARY • A vehicle frame and body are connected through a spring and shock absorber to provide comfort to the occupants, called suspension. • Ride quality is concerned with the human comfort during vibration. • Independent, semi-dependent and dependent are types of suspension systems. • Coil springs, metal springs, air springs and rubber springs are types of suspension springs. • Handling characteristics are nothing but response of the vehicle to the force associated with the steering and some environmental factors. • The function of shock absorbers is to damp vibrations. • An electronically controlled suspension system is called adaptive suspension system.

MULTIPLE-CHOICE QUESTIONS 1. The function of the suspension system is a. To maintain the height of centre of gravity b. To maintain the directional stability of the vehicle c. To provide comfort to the occupants d. All of the above 2. Coil springs are used in a. Dependent suspension b. Independent suspension c. Tandem axle suspension d. Adaptive suspension 3. Ride considerations include a. Vibration of the driveline b. Noise produced c. Road surface d. All of the above 4. The function of the spring shackle is to a. Adjustment of the length b. Support the spring c. Control side thrust d. All of the above

REVIEW QUESTIONS • • • • • •

Define suspension system. Classify vehicular suspension systems. Describe various arrangements of the leaf spring suspension system. Describe wishbone suspension system. Describe monotube suspension system. Describe adaptive suspension system.

Answers to MCQs:(1) d (2) b (3) d (4) d

9

Braking Systems

OUTCOME Learning Objectives • Fundamentals of automotive braking systems • Different types of brakes, their construction and working • Special provisions to brakes, like retarders, etc.

9.1 INTRODUCTION The braking system is an integral part of the vehicle control system. It is specifically related to the complete stopping or slowdown of the vehicle without affecting the comfort of the occupants; with minimum possible noise; without disturbing the stability; in the minimum possible time in any operating condition, i.e. very high speed, cornering, moving over a slope, etc.; and with minimum effort from the driver. When the driver pushes the brake pedal, brake converts this kinetic energy into heat energy by friction. An automobile is fitted with two types of brakes:

1. Service brakes 2. Parking brakes

To stop the vehicle/retard the vehicle service brakes are used, and of parking, parking brakes are used. Automotive brakes must perform the following functions: 1. Minimum possible stopping distance After the brakes are applied, the vehicle must stop at the shortest possible distance. 2. Control of the vehicle at cornering At the time of cornering, driver does not want to change the speed of the vehicle, so along with steering, the driver uses brakes just to preserve the stability of the vehicle. 3. Retardation of the vehicle As per the requirement and road conditions, it is important to reduce the speed and then brake to retard the vehicle.

9.2 CLASSIFICATION OF BRAKES Brakes can be classified according to certain criteria as follows: 1. According to purpose a. Service brakes b. Parking/hand brakes 157

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2. According to number of wheels a. Two-wheel brakes b. Four-wheel brakes 3. According to moment of cylinders/braking contact a. Internal expanding brakes b. External contracting brakes 4. According to method of applications of force a. Single acting b. Double acting 5. According to nature of power a. Hydraulic b. Mechanical c. Air 6. Other a. Electrical b. Electromagnetic c. Hydrostatic

9.3 DRUM BRAKES AND DISC BRAKES These types of brakes fall under the category of “internal expanding” brakes that consist of two shoes subject to expansion when the brake pedal is pressed. The shoes are attached to a back-plate with the help of anchors which prevent the rotating of brake shoes with the drums when brake is applied. The back-plate is also called as torque-plate as it absorbs the entire braking torque reaction of the shoes. The shoes have a semi-circular shape with a T segment (Figure 9.1). One end of the shoe is connected to a mechanical type of cam, or a hydraulic cylinder in the case of an assisted braking system. The other end of the shoe is on the pin where the shoe acts as a pivot. There is an arrangement of springs to return the shoes to their original position when the brake pedal is released. The cam or the hydraulic cylinder works as a shoe expander. The internal cylindrical surface of the drum has a smooth finish on which the rubbing action takes place. Due to this rubbing action a high amount of heat is generated, so the drum is positioned in such a way that there is maximum exposure to air, as the high temperature will affect the friction properties of the liner material, leading to inefficient braking. It is very essential to preserve the clearance between the brake shoe and the internal surface of the brake drum after certain duration of operation. If the clearance between the brake drum and the shoes is more, then there is increase in brake pedal play, which may be dangerous in the sudden braking conditions. In drum brakes there are different shoe arrangements (Figure 9.2).

9.3.1 Leading and Trailing In the stationary condition, i.e. when the brake drum is stationary, when brakes are applied, both the shoes expand and equal force is applied by each of shoe. But when the wheels are rotating, the drums also start rotating and equal pressure cannot be applied due to the motion of the drums. As an effect of friction drag, one shoe is

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FIGURE 9.1  Working of drum brakes.

FIGURE 9.2  Working of brakes.

pressed hard in the direction of motion of the drum, called leading shoe, and the other is pushed in off position in the direction opposite to the direction of drum rotation, called trailing shoe. As a result of this the braking torque produced by the shoes is in the ratio 4:1. In such a condition, the rate of wear of the trailing shoe is more than the leading shoe. The leading and trailing shoes provide equal braking both in the forward and in the reverse direction (Figure 9.3).

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FIGURE 9.3  Leading- and trailing-type shoes.

9.3.2 Twin Leading Shoes In these arrangements both the shoes act as leading shoes and a separate cylinder is provided to each shoe. The Hydraulic linkages are arranged in such way that they provide equal hydraulic pressure. This type of arrangement was used in front wheels before adoption of disc brakes. As an effect of equal pressure acting on both the shoes, there is equal wear of both linings, which also leads to good fade resistance and better braking due to equal servo action. Another important thing is that due to equal loading of both the shoes there are no unbalanced loads acting on the wheel bearings. A disadvantage of this brake is that at the time of reversing both the shoes act as trailing shoes if special attachments are not provided. This type of arrangement is very sensitive to the friction level between the friction lining and the drum. (Figure 9.4).

9.3.3 Duel Servo In this type of arrangement, movement of one shoe (primary shoe) is transferred to the other shoe (secondary shoe) with the help of a floating adjuster. This brake arrangement is also known as the self-energising brake. Boosting the force applied by the driver by drum energy is the principle of this type of brake. Here, the doubleacting cylinder attached to the back plate transmits the pressure to each adjacent shoe whereas the opposite shoe tip ends are joined together by the floating adjustment. This brake equally acts in the forward or reverse direction (Figure 9.5).

9.3.4 Advantages of Drum Brakes Simpler construction, easy maintenance, simpler design and longer life are some advantages of drum brakes.

Braking Systems

FIGURE 9.4  Twin leading shoe.

FIGURE 9.5  Duel servo.

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9.3.5 Disadvantage of Drum Brakes Sometimes the diver has to operate the brakes frequently for a long time; especially when the vehicle descends a long, steep hill or when vehicle’s operating condition necessitates sudden braking. In such a condition the frictional material used is called brake fade and does not work effectively. Due to the brake fade, the driver has to apply more force. Stopping distance is more in this case or sometimes it is very difficult to control the vehicle.

9.3.6 Disc Brakes As discussed, the brake drum is highly prone to fading with continuous use. In the case of disc brakes, a very small area comes in contact with disc and friction pad, during braking operation. Exposure to air in the case of disc brakes is more compared to drum brakes, so the heat is easily dissipated into air, and because of this disc brakes are not sensitive to heat and can be operated continuously for long durations. A disc brake comes under the category of external contracting brakes. A disc brake consists of an air exposed disc (grey iron, cast aluminium, carbon fibre pellets, and ceramic reinforced with carbon fibre), which is attached to the hub flange. The discs may be either solid or ventilated. The Discs rotate at the speed of the road wheels. The disc brakes are predominantly made as partial disc brakes as they do not cover the entire circumference of the disc (Figure 9.6). The disc is located between the two friction pads of the brake calliper. During application of brakes, hydraulic pressure is applied which moves the friction pad and comes in contact with the rotating brake disc which retards the wheel due to the action of friction. Uniform wear rate of the friction pad, reduction in fade, easy maintenance and operation, simple construction and design and the absence of the self-servo action (which renders the brake torque available directly proportional to applied force) are the important advantages of the disc brake (Figure 9.7).

9.4 HYDRAULIC BRAKING SYSTEM CONSTRUCTION AND WORKING A braking system in which force applied by the driver is transmitted to the braking unit with the help of fluid is called hydraulic braking system. It operates on Pascal’s law, which applies for incompressible fluids. The hydraulic braking system consists of the following elements:

a. Fluid tank for storage of the fluid b. A master cylinder c. Wheel cylinders d. Pipeline and hoses to convey the fluid (Figure 9.8)

Braking Systems

FIGURE 9.6  Disc brakes.

FIGURE 9.7  Disc brake details.

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FIGURE 9.8  Hydraulic brakes.



1. Master and tandem master cylinder Hydraulic pressure is required to operate this braking system. Force is applied to the brake drum through the master cylinder. The master cylinder develops the required pressure to operate the system. Single master cylinders are used in racing cars. Due to the regulation of the duel circuit brakes, the tandem master cylinder is incorporated in single housing with two master cylinders connected in series. It controls the pressure variation in both the circuits. The reservoir in this system maintains the level of oil in the cylinder which may be disturbed due to temperature or limited leakages. Master cylinders are of two types Lockheed master cylinder and girlingtype cylinder (Figure 9.9). Lockheed master cylinder The middle region of the master cylinder is always full of fluid to maintain a certain level of pressure. When the brakes are released the pressure in the pipeline and wheel cylinder is 55kN/m2. The purpose is to maintain the residual pressure in the cylinder and to ensure quick response during their initial operation and that the ingress of air past the wheel cylinder seals when the brakes are released. This type of master cylinder is employed in lightweight commercial vehicles. The leakage from both the ends is prevented with the help of a rubber ring, which acts as a lip seal. A seal is fixed to the return-spring end of the piston which is a highpressure cup seal and slips into a recess groove around the piston. Seals are fitted to the push-rod piston end called primary and secondary seals, respectively. A thin washer is placed between the cup seal and the piston

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FIGURE 9.9  Master cylinder.

to prevent the cup from being drawn into the recuperation holes drilled around the piston head. A rubber boot encloses the push-rod end of the cylinder, which prevents the entry of dust into the cylinder bore. As the foot pedal is operated by the driver, the push rod pushes the piston, which encloses the bypass port, trapping the fluid. As a result, the pressure developed in the cylinder pushes the lips of the check-valve cup away from the metal body so that the fluid is forced to flow through the pipelines to actuate the wheel cylinders for braking. When the foot-pedal is released by the driver, the master cylinder return spring moves the piston back against its stop washer and circlip faster than the return of fluid from the disc or drum wheel cylinders, which develops a pressure drop in the master cylinder. Simultaneously the primary seal attains its original shape, and the recuperation hole is opened. Fluid flows through the recuperation holes and equalises the pressure on the two sides of the piston head. At the same time, the pistons wheel cylinder retract and the fluid pushes the whole check-valve body away from its rubber seat and flows back into the master cylinder. The fully returned piston then uncovers the bypass port and releases fluid to the reservoir. Girling-type master cylinder This type of master cylinder contains a pressure chamber and an end fluid reservoir. The piston operates in the pressure chamber whereas the

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reservoir permits additional fluid to enter into or return from the system to maintain a constant volume of fluid. In this type of master cylinder after releasing the brakes the hydrostatic pressure is maintained in the pipeline and wheel cylinder due to pressure head of the brake fluid in the system. The piston of the master cylinder is of a plunger shape with a hollow stem. A spring retainer is fitted over the piston stem end. To prevent leakages there are two types of seals: primary seals installed near the return spring and secondary seals placed at the push-rod end. When the driver pushes down the brake pedal, the pushrod is forced against the piston. Initially the piston will push the edge of the spring retainer around the mouth of the piston stem’s central hole away from the valve stem head. During this time the pressure of the fluid trapped in the hollow piston increases and it pushes the valve stem assembly towards the inlet port. The valve assembly and seal closes the inlet port. Further movement of the piston forces the fluid to operate the brakes through the brake pedal. When the brakes are released, the wheel-cylinder pistons retract so that fluid is displaced back to the master cylinder. Before the piston travels to the end of its stroke, the spring retainer clipped to the piston stem catches and pulls the valve stem and valve assembly away from the inlet port. Fluid then flows freely between the reservoir and the pressure chamber. 2. Wheel cylinders Wheel cylinders consist of a piston assembly, primary and secondary cups, coil spring and check valves at the mouth of the cylinders. Wheel cylinders are mounted on the backplate. The brake line from the master cylinder is attached to the inlet port, and a blender screw with a cover is provided to bleed air from the system whenever required. When brakes are applied the fluid under pressure from the master cylinder enters the inlet port and forces the pistons to move outwards to push the shoe against the drum. Similarly when brakes are released, the brake shoe retractor spring forces the brake fluid out of the wheel cylinder by pushing the pistons inwards (Figure 9.10). Advantages • Simple in construction. • The hydraulic brake system works on the principle of Pascal’s law, i.e. it applies equal pressure everywhere in the circuit. • Provides an increased braking effort. • Self-lubricated system. • More flexible linkages. • Provides mechanical advantages without long and heavy levers. Disadvantages • Even small leakages, which can fail the system.

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FIGURE 9.10  Wheel cylinder details.

9.5 AIR BRAKES For heavy vehicles, vacuum and servo-assisted braking systems cannot provide ­adequate braking to the vehicle. Here is where the air brake comes into play. It consists of the following major units: 1. Compressor and air reservoir: Air brakes require compressed air, which is generated by the compressor driven by the engine, and air stored in the reservoir under specified pressure is supplied as per requirement. A safety valve is provided to the reservoir to regulate air pressure. A drain plug is also provided at the bottom to drain the reservoir periodically to remove impurities and water deposited at the bottom. 2. Brake chamber: When the driver applies a force through the pedal, ­compressed air is supplied to the brake chamber through pressure pipes. The function of the brake chamber is to convert the energy stored in the compressed air into mechanical force by using suitable arrangement. There are different types of controls in an air brake system as follows:

a. Foot-operated brake valves: The function of this valve is to control the pressure of the brake cylinders during braking operations in proportion to the driver’s effort.

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b. Pressure-regulating valves: This valve regulates the proper pressure in the system. Excess or insufficient pressure could be dangerous. c. Check valves: There are two types of check valves. i. Single check valve: Single check valve allows the flow of air in one direction only and acts as a non-return valve. This type of valve is fitted at the entry to the air reservoirs as per requirement of the system. ii. Double-check valve: It allows air under pressure from either one of two control valve systems to supply a brake actuator, while isolating the other at the time of failure. d. Relay valves: The function of relay valves is to maintain equal pressure in the brake cylinders for effective braking. e. Differential protection valves: the function of the differential valve is to avoid simultaneous operation of both parking and service brakes. f. Quick release valves: These are exhaust valves that let out air from the brake cylinders when brakes are released.

9.5.1 System Actuation Brake chambers are nothing but actuators. They are mounted externally to each wheel brake. Through the medium of the diaphragm they convert the energy stored in compressed air into mechanical force to actuate the brake shoes. Due to their bulky shape they cannot be accommodated within the brake drums, and therefore act upon either lever or cam arrangements (Figure 9.11).

FIGURE 9.11  Working of air brakes.

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Air brakes used in automobiles offer the following advantages:

1. Air is the operating fluid, which free of cost and available anywhere 2. Small, acceptable leakages 3. Sufficient force for operating the expanding cylinders 4. Compressed air can operate various types of ancillaries associated with the vehicle.

9.6 ANTILOCK BRAKING SYSTEMS Road grip depends on the vertical weight imposed on the wheel and the frictional resistance between the tyre and road wheel. Maximum effective braking depends on the retarding force imposed between the tyre and road surface. As the road condition changes, force required for braking continuously changes, making it difficult for the driver to control the vehicle at various speeds, especially on slippery or muddy roads. If extra force is applied to the wheel, then there are chances of locking the wheel, resulting in the vehicle skidding, slipping or tyre scrubbing. To avoid such individual locking of the wheel, the driver should apply and release brakes quickly to attain the safe working speed relative to the road condition. The function of the antilock braking system (ABS) is to avoid the locking of wheels, which will reduce the chances of the vehicle skidding or slipping. ABS senses the speed of retardation of the individual wheel and automatically delivers the pipeline pressure to increase or decrease the tendency of skidding, and the vehicle stops within the minimum possible time. ABS has an electronic control unit (ECU) which receives signal from the road wheel sensors and according to this operates the valves to hold or reduce the build-up of wheel brake pressure. From the sensors mounted on the wheels, it computes the rotating mean speed of all the wheels and the rate at which the speed of the wheels changes. After processing, the response is sent to the solenoid valve, to open or close the individual supply and discharge valves. Control of the on/off operation of solenoid valve relay and pump motor relay can be performed with the help of the ECU. If the problem persists in the system, warning lights turn on and system reverts to the conventional braking system.

9.6.1 Wheel Speed Sensors A wheel speed sensor has two main components: the exciter and the pickup. Other components include associated wiring and mounting equipment. The exciter is a ring with notched teeth. The most commonly used exciter has 100 evenly spaced teeth, but the number of teeth can vary depending on the system design. The component is known by several names: sensor ring, tooth wheel and tone ring. The pickup is commonly called “the sensor”. It contains a wire coil/magnet assembly, which generates pulses of electricity as the teeth of the exciter pass in front of it. The ECU uses the pulses to determine wheel speeds and rates of acceleration/ deceleration (Figure 9.12).

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FIGURE 9.12  Antilock braking system.

9.6.2 Operation 9.6.2.1 Normal Braking Condition In this condition, fluid flows from the master cylinder to the wheel cylinder without any restriction to slow down the car. In the case of braking in normal running condition, four solenoid supply valves are opened to each of the solenoids due to the effect of the energising current from the ECU, whereas the solenoid valves remain undercharged and closed. 9.6.2.2 Pressure Holding If the rate of speed reduction exceeds the predetermined values then there are chances of the wheel locking, which is very dangerous at high vehicle speeds. The wheel sensors send signals to the ECU about the rate of speed reduction, and immediately the current supplied to the corresponding wheel solenoid valve is interrupted and the valve is closed. Due to this, fluid flow from the master cylinder to the wheel cylinder subjected to skidding is completely stopped. The trapped brake fluid between the solenoid supply valve and the respective calliper holds the pressure.

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9.6.2.3 Pressure Reducing A pressure reducing valve for a vehicle braking system, comprises of inlet and an outlet communicating with each other through a radial port and an elastomeric seal movable relative to the port between a closed position in which the seal covers port and an open position. After holding the pressure, if the wheel speed sensor still sends signals to the ECU about the abnormality of the rapid speed reduction to lock the wheel then the current will send to the corresponding solenoid discharge valve to open and permit the flow the fluid. Immediately the pressure hold in the pipeline gets collapsed and again the wheels subjected to increase the speed and establish the grip with the road. 9.6.2.4 Pressure Increasing As the speed of the wheel changes from the deceleration to acceleration, then the individual wheel sensor signals the ECU to close the respective solenoid discharge valve and at same time to open the solenoid supply valve, i.e. the fluid flows from the master cylinder to the respective wheel calliper cylinder to increase the pressure and brake application. The sensitivity and the response time of the solenoids are such that the pulsating regularity is about four to ten times per second.

9.7 PARKING BRAKES Service brakes stop the vehicle while parking brakes hold it stationary. The power required for parking brakes is very less as compared to service brakes. These brakes are used for only two wheels. The parking brake is normally fitted to the rear brakes. For small and medium vehicles, the parking brakes are located between the front seats of the vehicle and are operated by hand. They are mechanically actuated. The lever operates two separate, replaceable cables connected to the rear brakes. When the lever is pulled, the actuating lever on the calliper applies pressure to the rear brakes (Figure 9.13).

FIGURE 9.13  Parking brakes.

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SUMMARY • Braking is a vehicle control system which retards, stops, maintains stability and controls the vehicles at different road conditions. • Automobile brakes are of two types: service brakes and parking brakes. • The effectiveness of a braking system depends on the type of friction material, coefficient of friction, brake diameter, brake surface area, shoe geometry and pressure applied by the driver. • Service brakes can be classified as mechanical, hydraulic, air, electrical, exhaust, servo, etc. • The function of retarders is to slow down the vehicle, used mostly in heavy vehicles.

MULTIPLE-CHOICE QUESTIONS

1. The function of the automotive brake is to a. Stop the vehicle b. Retard the vehicle c. Control the vehicle d. All of the above 2. The function of retarders is to a. Stop the vehicle b. Reduce speed of the vehicle c. Both a and b d. None of the above 3. The function of the air reservoir is to a. Store compressed air b. Compression of air c. Release air pressure whenever required d. All of the above 4. Failsafe brakes are activated when a. Pressure in the reservoir reduces b. Pressure is excess c. Vehicle is stationary d. All of the above 5. Identify correct statement related to parking brake. a. Parking brakes are applied only for two wheels b. It applies to only when vehicle is stationery c. Less pressure will be applied d. All are correct 6. Hydraulic brakes are based on the principle of a. Pascal’s law b. Newton’s third law of motion c. Faraday’s law d. Einstein’s principle of energy

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7. Antilock braking system is used to a. Minimise driver’s effort b. Avoid slip and skid of the vehicle c. Increase braking force d. Minimise stopping distance 8. Braking efficiency depends on the a. Speed of the vehicle b. Pressure applied by the driver c. Weight of the vehicle d. All of the above

REVIEW QUESTIONS • List the functions of the braking system. • List the components of the following braking systems (a) Air brakes (b) hydraulic brakes (c) parking brakes • List the components on which braking efficiency depends. • Explain the working of a retarder. • What are the features of the antilock braking system over a conventional barking system? Answers to MCQs: (1) d (2) b (3) a (4) a (5) d (6) a (7) b (8) d

10

Vehicle Body Engineering

OUTCOME Learning Objectives • • • • •

Objectives of passenger vehicle body design Nomenclature of body components Different types of commercial vehicle bodies Constructional details of commercial vehicle bodies Constructional details of passenger vehicles

10.1 INTRODUCTION An automobile’s body can be defined as the portion of the vehicle which encloses the systems, subsystems, components and occupants space with maximum safety, comfort, convenience and security. A vehicle can be designed to carry passengers as well as luggage. Design of the vehicular body depends on the application and use. An automobile body consists of metal panels, glasswork, wood work, roof, seating, flooring, etc. The body should be designed considering the aesthetics and ensuring minimum air resistance and higher strength to weight ratio. Body parts may also contribute to the structural integrity (safety and strength) of the vehicle. Vehicle body can be made from steel, aluminium, fiber glass, plastic, or composite (a combination of materials like carbon fibre). The body is normally painted to give the vehicle an appealing shiny colour and appearance.

10.2 FUNCTIONS OF THE VEHICLE BODY • To protect the occupants as well as its systems and subsystems from changing weather conditions, and to provide reasonable safety by absorbing energy in case of accidents as well as through active safety systems. • To provide convenience and comfort against distracting noise, heat and vibrations with proper interior arrangements and insulation. • To cover various chassis components like engine, suspension elements, transmission systems, etc. and to provide the means for attachment of these components. • To carry and transfer air drag forces during different operations which helps in reducing fuel consumption and enhancing handling of the vehicle. • To provide accessibility to occupants to board and alight from the vehicle, i.e. doors, and accommodate luggage, as well as ensure proper visibility for the driver and occupants. 175

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10.3 REQUIREMENTS OF THE VEHICLE BODY The vehicle body is an important component that contributes to the performance, safety, comfort and styling of the vehicle. The following are the important requirements of the vehicle body. • • • • • • • • • • • • • • • • •

Ride comfort Ergonomics/convenience Structural stability Torsional stiffness Braking and acceleration behaviour Crash behaviour Reparability Styling and beauty Safety Weight to volume ratio Aerodynamics Insulation Visibility Cost effective and easy to manufacture Light in weight Maximum space utilisation Minimum number of components

10.4 CLASSIFICATION OF VEHICLE BODY Vehicles can be broadly classified into the following categories: • Passenger vehicles • Goods vehicles Applications and use of the above categories decides the body type.While designing the body, the following should be considered. Aesthetics: Aesthetics is related to the look of the vehicle, it should have pleasing appearance. This can be achieved with good surface quality and body style. Absorption of stresses: Vehicle body consists of various types of fixed and attachable components. They must be of sufficient strength to withstand different types of stresses the vehicle may be subjected to. Ergonomics and roominess: Ergonomics provides easy access. Sufficient space should be made available to the driver, passengers and goods. Safety: The body should be designed in such way that at the time of collisions there is minimum possible impact on the occupants. Aerodynamics: For economy and stability of the vehicle, there must be ­minimum possible air drag.

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Insulation: To provide the maximum possible comfort to the occupants against noise, heat and vibrations, the vehicle body must be properly insulated. Visibility: Vehicle body arrangement should be in such a way that there is highest possible visibility during night and day. 1. Passenger Vehicles A. Cars • No of doors 1. Two door 2. Four door • Occupant capacity 1. Two 2. Four 3. More than four • Comfort level 1. Luxurious 2. Semi-luxurious • Privacy to the owner 1. Normal 2. Limousine • Shape of the car 1. Saloon 2. Estate 3. Hatchback 4. Pickup 5. Van, etc. • On the basis of roof structure 1. Open 2. Close 3. Convertible • Construction of the frame 1. Monocoque 2. Semi-integral 3. Frame on body • Purpose 1. Passenger transport 2. Goods transport (pick up)

2. Goods vehicles:

Goods transport vehicles include large and small trucks, articulated lorries, vans and pick-up vehicles. They contain a rear open or closed cargo area, and the smallest vehicles in the family are derived from car platforms. Goods vehicles may be light or heavy commercial vehicles. Heavy commercial vehicles may be of open type, closed type or just platforms. This depends on purpose and use.

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Some special types of heavy commercial vehicles are as follows: • • • • • • •

Tippers Concrete mixtures Refrigerators Poultry transport Car carriers, scooter carriers Fire tenders/equipment Ambulances

10.5 CAR BODY CONSTRUCTION Construction of the vehicle body: Generally, vehicular components can be categorised into three: 1. Movable components: includes detachable components fitted to the body –doors, deckled, lift gate, hood, fuel filler flap and related locks and hinges 2. External components: components externally mounted on the vehicular body –bumpers, windshield, windows, weather strips, grilles, spoilers, mouldings, mirrors, lamps, windshield wipers and lamp wipers 3. Interior trim: includes instrument panel, seats, carpets, trim panels, safety belts, air bags, etc.

10.5.1 Passenger Vehicles • A passenger vehicle is a road motor vehicle other than motorcycle intended for a carriage of passengers and designed to seat no more than nine passengers including driver. The term passenger car therefore covers microcars, taxis and hired passenger cars provided that they have fewer than ten seats. This category also includes pick-ups. • Car body: Generally all car bodies are provided with an integral construction, consisting of the following components: • Window and door pillars: These pillars form the part of the body structure which supports the roof. • Windscreen and rear window rails: A windscreen rail connects the windscreen pillars while a rear window rail connects the rear window pillars. • Contrails: These support the roof and connect the pillars of the wind screen and rear windows. • Roof: It is the top closing surface of the vehicle body. • Upper quarter panel or window: This is the vertical side panel or window which occupies the space between the rear side door and the rear window. • Floor seat and boot pans: Floor seat is the lower portion in the passenger compartment. Boot pan is the portion behind the rear wheel arch, and the raised portion between the rear wheel arch is called seat pan. • Central tunnel: A central tunnel occupies the transmission elements and propeller shafts. • Sills: The side members of the body are called as sills (Figure 10.1)

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FIGURE 10.1  Various body panels.

10.5.2 Under Body Section The unibody underneath the frame contains the floor pan, the trunk pan, the rocker panels, the cross section, the front and rear members and other the associated sections. This large assembly must be resistant to rusting and add strength to the structure of the unibody. The underbody is vital to the structural integrity of the unibody vehicle. Since the front-side and front-crossing members of the front-underbody front section directly impact the front-wheel alignment, they are also assembled into a boxed segment.

10.5.3 Body Side Assemblies The sides of the body are connected to the front and the roof panels to form the passenger compartment. These panels transfer loads from the underbody to the upper part of the vehicle and avoid left and right bending during side impacts or collisions. Side body members also serve as door protection and protect the dignity of the passenger compartment if the vehicle is overturned. Since the sides are compromised by wide door openings, they are strengthened by connecting the inner and outer panels, which form a very solid box-shaped structure (Figure 10.2).

10.5.4 Shroud and Dash Panel Assembly The dash panel, also referred to as a firewall or front bulkhead, is a panel that separates the front portion and the middle passenger compartment. Normally, it welds in place. The firewall helps protect people in the car in the event of fuel leakage and any ensuing engine fire.

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FIGURE 10.2  Body side assembly.

10.5.5 Roof The roof cover is a wide panel that fits over the passenger compartment. It is usually welded to the pillars. Oftentimes it contains sunroof or adjustable top parts, called T-tops. The roof panel is one of the largest of all major body panels, and is also one of the easiest to build. The area enclosed by the roof varies between various car manufacturers and models. The roof panel stops at the windscreen on some vehicles. The roof is normally attached to the body side frames, consisting of longitudinal rails or stringers and a pair of can trails that form the door openings. The interior lighting and wiring as well as the repair of the interior trimming should be installed in the roof building.

10.5.6 Back Window Aperture Panel The wide side panel of a vehicle consisting of a rear fender, a door frame and a side window frame is called the back window aperture panel The centre column or back window aperture panel is connected to the side members of the main floor assembly and supports the cantrails  of the roof structure. It provides a shut face for the front door, a place for the door lock, a striking plate and a buffer or a dovetail, and also a hinge face for the back door; as with the front pillar, provision is made for door hinges and door check.

10.5.7 Rear End Assembly The inner structure of the rear side of the vehicle consists of the rear wheel arch and the rear seat heelboard. It offers protection for the rear seat squab in a saloon car; whether the vehicle is a hatchback or an estate car, the two rear seats will be folded flat

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FIGURE 10.3  Rear body structured components.

and the seat squabs do not require support. This area is known as the rear bulkhead of the car; it provides additional transverse strength between the parts of the wheel arch and provides protection for the rear seat. The rear bulkhead also serves as a partition between the luggage compartment and the passenger compartment. (Figure 10.3).

10.5.8 Frontend Assembly The front end assembly consists of two front side component assemblies designed to bear the weight of the engine, the suspension, the steering gear and the radiator. The suspension system used would have an effect on the design of the panels, but whatever the system uses, the loads must be transferred to the wing valances and to the body panels. The front cross-beam assembly is mounted on the front of the car and houses the radiator and headlamp components. The side valance assemblies form a frame for the wheels, a mating edge for the bonnet and a solid box portion for attaching the front wings. All the side frames and the valance assemblies are connected to the cowl or dash panel and the front panel is fixed to the main floor of the toe panel. The cowl or dash panel forms the front bulkhead of the body and is typically created by combining the smaller panels (the upper panel of the cowl and the side panel of the cowl) to form the integral unit (Figures 10.4–10.6).

10.5.9 Front Wings The wing is a part of the body that covers the wheel. Apart from covering the ­suspension structure, the wing stops the wheels from dumping water and mud onto the frame. The front wings (or the fender assembly) are usually connected to the wing valance of the front end assembly by means of a flange the length of the wing, which is turned inwards from the outer surface and fixed either by welding

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FIGURE 10.4  Unibody nomenclatures.

FIGURE 10.5  Front body structural members.

or by bolts. Adjustment of the front wing is usually done by slotting the bolt holes so that the wing can be pushed forwards or backwards by loosening the fastening bolts. This modification cannot be made when the wing is welded to the main body structure.

10.5.10 Front Door Panel Assembly The door consists of two main panels, the outer panel and the inner panel, both of all-steel construction. The door derives much of its strength from the inside wall, as it is designed primarily to serve as a door frame. The outer panel flanges over the inner panel along all its edges to form a single assembly, which is then welded or, in some cases, bonded to the frame with adhesive. The inner panel has holes

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FIGURE 10.6  Front body structural components.

or openings for the door trim attachment. The trim consists of a window regulator assembly and a door lock mechanism. These assemblies are mounted through the wide openings in the centre of the inner plate. Most of the thickness of the door is due to the depth of the inside frame, which is required to fit the door grip and the window mechanism. The inside panel is created by the lock pillar and also by the hinge pillar portion of the door. Tiny angles of reinforcement are generally used between the outer and inner doors, both where the lock is inserted through the door and where the hinges are connected to the door. The outer panel is either fitted with an opening from which the outer door handles protrudes, or is recessed to give a more streamlined effect, thereby providing better aerodynamics. The upper portion of the door has a wide crack, which is covered by glass. The glass is rigidly retained by the window regulator assembly and, when it is raised, slides through the channel in the space between the outer and inner panels in the upper portion of the frame. The window seats can be closed tightly in this door panel assembly for effectively sealing out the air.

10.5.11 Bonnet Panel Assembly The bonnet is the panel that covers the engine compartment where it is situated at the front of the vehicle or the boot compartment of the rear-engine vehicle. There are many types of bonnets in use on various makes of vehicles. The bonnet consists of an outer panel and an inner reinforcement, formed in an H-shaped or cruciform pattern, which is a spot welded to the outer panel on the flanged edges of the plates. The reinforcement is essentially a top-hat portion to give the bonnet  its stiffness. In certain cases, the outer panel is bound to the inner panel by epoxy resins. This method prevents the dimpling effect of spot welding on the outer surface of the seal.

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10.6 BUS BODY CONSTRUCTION The important aspects of a bus body construction are maximum utilisation of floor space and highest possible comfort level to the occupants. The bus body may be a separate body or framed construction or an integral body or frameless construction. In the case of framed construction, the main framing is of lightweight members of thin gauge material shaped by folding, pressing, stretching, rolling or extrusion and linked by gussets usually riveted to the structure framework, which is added to the inside part of the framing. The panels used in bus body construction are mild steel (MS) and aluminium sheets. The bus body shape and size varies according to various parameters. Classifications of the types of buses are as ­follows (Figure 10.7). Based on Distance Travelled

a. Town buses b. Suburban buses c. Intercity coaches d. Touring coaches Based on Capacity of Passengers

a. Mini-bus 8–15 (number of seats) b. Small coaches for long distance 16–30 c. Small buses for town up to 40 d. Medium coach for long distance 31–45

FIGURE 10.7  Bus body structure.

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e. Medium buses for town 41–60 f. Large coaches for long distance 46–60 g. Large buses for town 61–80 h. Very large buses for town>80 Based on Style



a. Normal control type b. Single Decker c. Double Decker d. Two level e. Split level f. Articulated bus

10.7 BODY MOUNTING The frame members are joined to the side and cross members by welding, riveting and bolting. Welding provides the most rigid joint, but this method has thus far been generally uneconomic for the assembly numbers involved, especially since machine welding would be required to ensure the necessary weld uniformity. Welding is therefore usually confined to the fabrication of individual cross members. Rivets are widely used for joining the frame members, and it is used under cold operation cold instead of hot so as to avoid the rivets contracting during cooling and developing clearances in their holes. Bolting is additionally popular and may be simpler than riveting as regards rigidity because the tightness with which the frame members are clamped together is often  accurately controlled. A possible disadvantage is that screwed connections may loosen if not properly installed. A combination of riveting and bolting is sometimes employed; for example, a bolted connection may be confined to the front cross member so that it can be readily removed to facilitate engine replacement. Brackets Types of brackets used for in the vehicle are • • • •

Bumper-mounting brackets Suspension-mounting brackets Radiator core support–mounting brackets Body-mounting brackets

Brackets can be mounted by welding, riveting or bolting. Body-mounting brackets are used along with body-mounting hardware to attach the body with the frame, usually by welding (Figure 10.8).

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Automotive Systems

FIGURE 10.8  (a) Exploded view of body mountings. (b) Body mountings.

10.7.1 U Bolts U bolt mounting is the least secure mounting system but its ease of installation makes it popular with builders of truck bodies. Here, a semi-flexible material is placed between the body and the frame. There are three primary benefits of adding this material: first it protects the frame flange from damage, it makes the vehicle very flexible and finally, it helps to spread the load along the length of the frame without causing any localised stress points on the frame. The U bolt goes over a subframe and attached to the body and below both sides of the frame rail. The U bolt is then clamped at the bottom flange of the rail. Sheet or piece of wood or polyurethane is clamped between the body sub frame and the actual chassis frame. U bolt-mounting systems use friction between the frame, the spacer and the body to locate the body longitudinally. As a result the body can sometimes move relative to the frame. When U bolt mounting is used, it is also recommended that solid spacers be inserted inside the frame C channel to stop the frame flanges from collapsing when they are clamped by the U bolt. Steel spacers are recommended over wood because; overtime wooden blocks may contract and fall out.

10.7.2 Balata Packing Balata packing is waterproof and high resistant to acidic and alkaline material; hence balata packing’s are used in automotive applications. Balata packing is often used for bus body and chassis building and coach fabrication to avoid the inter friction

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between the metallic surfaces i.e. bus body and chassis and also to provide damping characteristics. It is used in other heavy machinery, like trucks, three-wheelers, agricultural machinery, etc.

10.8 BODY MATERIALS To fulfil the essential requirements of fuel economy, emission control through weight reduction and selection of proper body material is important. Functional requirements of the components, legislation requirements, economics and commercial factors, and in-service behaviour of the components are the various parameters taken into consideration. Some of the materials used in manufacturing vehicle body are as follows: 1. Steel Different types of steels are used in the automotive body industry. Constructional members are generally made of low carbon steel. There is wider use of high-tensile steels for bolts and nuts, which will be subjected to heavy load applications. Specially produced deep-drawn steel, including micro-alloyed steel, is used for complex forms of large body panels. A thickness range between 0.8 and 1.5mm can be used for sheet panels. Zinc-coated steel sheets are increasingly being specified for automobile body and chassis parts, as improved corrosion protection is addressed. Stainless steel is used for its non-rusting property, hard wearing and decorative qualities. The advantages of steel as an auto body material include • Low cost • Easy formability • Consistency of supply • Antirust properties with zinc coatings • Ease of joining • Recyclable • Good crash energy absorption The main disadvantages of steel in auto body applications are • Heavier than alternative materials • Corrosion if uncoated 2. Aluminium Weight of aluminium is approximately one-third that of steel, with an ultimate tensile strength in the range of 340–620 MN/m2. In modern vehicles a lightweight body is very important as far as fuel efficiency is concerned. Aluminium offers considerable weight reduction as the thickness of the sheets is doubled. Due to its non-rusting quality, aluminium is widely used in bodywork. The major advantages and disadvantages of aluminium as an auto body material are as follows:

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Advantages • Low density • Corrosion resistance • Strong supply base • Recyclability • Less weight Disadvantages • High and fluctuating cost • Poorer formability than steel • Less readily welded than steel 3. Timber Various types of timber are used in commercial vehicle body building today, especially in trucks/goods carriers for lightweight and attractiveness. Timber sections are also used together with other materials such as metal and plastic materials to generate segments for special reasons, which include heat and sound insulating material. Advantages of Timber As a Body Material • Light weight • Low cost • Quick erection times • Reduced site labour • Less production facilities required • Easily available 4. Magnesium Magnesium is 33% lighter than aluminium and 75% lighter than steel/cast iron components. Magnesium’s tensile yield strength is nearly the same as that of aluminium but it has lower ultimate tensile strength, fatigue strength and creep strength. The hardness in magnesium alloys is lower than aluminium and the coefficient of thermal expansion is higher. Magnesium alloys have other distinct advantages over aluminium, including increased processing strength; longer life of dies used in production process and quicker solidification and good machinability. Magnesium must be alloyed with other elements like aluminium, manganese and zinc for enhanced strength. 5. Composite materials Fibre-reinforced composites offer a wide range of advantages and applications in the automotive industry. They have the potential for lowering weight and fuel consumption due to their low density.

10.9 VARIOUS LOADS ACTING ON THE VEHICLE BODY AND THEIR ANALYSIS There are various types of forces and moments acting on the vehicle body structure, or the chassis, during operation. It is essential to fulfil the traction requirements, as well as to maintain the stability of the vehicle, when the vehicle subjected to different

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momentary loads like braking, cornering, sudden acceleration, road irregularities etc. Dynamic forces can be calculated as



 a Fdy = Fst    g

Force can be calculated as

Fx = m x (Fin − Fun )



Fy = m y (Fin − Fun )



Fz = m z (Fin − Fun )

These forces cause twisting, bending and bending along the yz axes. However, the value of bending along the yz axes is negligible.

10.9.1 Symmetric Vertical Load When the two front wheels are simultaneously subjected to obstruction, the vertical loads acting on the body and the vertical acceleration are symmetrical to the ­longitudinal axis. The vertical force acting on the body is given by

Fzs = m zs (Fin − Fun )

where m zsis the dimensionless coefficient of the inertial force, which depends on the load and speed of the vehicle. Finis the total weight of the car and Fun is the weight of the un-sprung weight of the vehicle.

10.9.2 Asymmetric Vertical Load When the two front wheels are subjected to obstruction at different times as an effect of uneven road surface, then the vertical asymmetrical loads act on the body about the longitudinal axis. The wheels of the same axis subjected to different loading conditions may produce torsional moments as well as bending moment along the longitudinal axis of the vehicle. The vertical force acting on the body is given by

Fzas = m zas (Fin − Fun )

where the mzas is the dimensionless coefficient of the inertial force, which depends on the load and speed of the vehicle. Fin the total weight of the car and Fun is the weight of the un-sprung weight of the vehicle.

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The torsion is expressed in terms of

m s = m zas (R fl − Ffr )r/2

where (R fl − Ffr ) are the difference between the forces acting on the both the wheels of the front axle which depends on the bump height of the vehicle. Bump height depends on the suspension elements and the track width of the vehicle. r is the track of the front wheel. The value of torsion depends on the difference between the forces acting on both the wheels of the front axis and the track length of the vehicle. And the value mzas depends on the type of the vehicle.

10.9.3 Longitudinal Loads Longitudinal loads are developed due to braking and acceleration of the vehicle. The longitudinal force acting on the body is given by

FX = ± m zs (Fin − Fun )

The maximum value of positive acceleration can be taken when the engagement of the clutch is equal to the deceleration produced during the braking of the vehicle. mx = 0.7–1.0, which is the dimensionless coefficient of the longitudinal forces.

10.9.4 Side Loads A side force develops from the driving on a curved track or the cornering of the vehicle. The maximum side force is an effect of centrifugal force acting on the outer wheel as compared to the inner wheel of the vehicle. Tan r = r/2h = Fin/mzs.Fb where the h is the height of the centre of gravity above the ground, F b is the lateral component of the inertial force, Fin the total weight of the car and mzs is the dimensionless component. With these conditions, the vehicle is also subjected to various combinations of loading forces, such as combined bending and torsion, etc.

10.10 ANTHROPOMETRIC AND ERGONOMIC CONSIDERATIONS Ergonomics is the science of making human organ-friendly and human anatomy products. The word “ergonomics” is derived from two Greek words ergon, meaning job, and nomoi, meaning natural laws. Ergonomists research human capacities in relation to job demands, or simply explain the relationship between human and machine. In recent years, numerous researchers have attempted to identify postures that mitigate repetitive static work and reduce the forces acting on the body and their

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adverse effects. For a healthy working environment, numerous ergonomic guidelines must be followed • All activities should encourage the worker to follow a variety of specific, but equally good, less energy-consuming safety requirements. • The necessary muscle strength should be exercised by the largest appropriate muscle groups available, providing ample linkages. • All operations with the joints should be done at roughly the mid-point of their range of motion. This refers in particular to the head, chest and upper limbs. For best practice design, researchers use data and techniques from a variety of disciplines: • Anthropometry: body sizes, shapes; body height, populations and variations • Biomechanics: muscles, movements, powers, joints • Environmental physics: noise, light, heat, cold, radiation, body vibration systems: sound, vision, sensation • Applied psychology: ability, learning, mistake, difference • Social psychology: communities, contact, learning, behaviour Anthropometry can be defined as the calculation of dimensions of the human body. Static anthropometry involves the measurement of human beings in fixed, uniform positions (e.g. static arm length is equal to the anatomical length). Static anthropometric data is used in the design of equipment for the workplace where body movement is not a significant variable, e.g. seat width, depth and height. Dynamic anthropometry involves the estimation of human beings and the strength requirements at work or in motion (e.g. the length of the upper arm, lower arm and neck, as well as the range of movements at the knee, elbow, wrist and fingers). Dynamic anthropometric data can be used to determine control positions using reach envelopes for the hands and legs and positions of head restraints, seat belts and air bags using data on arcs identified by different parts of the body under crash conditions. Biomechanics is the calculation of the length, power, endurance, speed and precision of human movements and this data is often used in the design of controls to determine adequate ranges of control movements and operating forces.

10.11 UPCOMING TRENDS IN VEHICLE BODY MANUFACTURING Important aspects of vehicle body structures are crash safety, noise and vibration, fuel economy and overall cost. With advancements in materials used in vehicular body, some new techniques have been introduced in their manufacturing and joining methods. The details of this are as follows. Manufacturing Method • Hot-formed steel: For complex shapes it is essential to improve the ductility without cracking with the controlled heating.

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• Warm-formed aluminium: Flexibility of aluminium is enhanced by heating it up to a temperature of approximately 200°C–300°C and then cooled to increase strength. • High-pressure thin-walled aluminium die casting: Panels of a vehicular body can be manufactured with the help of high-pressure aluminium die casting. • Resin transfer moulding: With the help of a transfer moulding process, the various complex geometries can be manufactured. • 3D printing: Various parts and complex shapes can be 3D printed using various materials like plastics and composites. • Adhesives: These are widely used in joining plastic and fibre reinforced plastics parts of the vehicle body and structural components. • Tailor-welded/rolled blanks and laser-welded blanks: With the help of these, combinations of several grades, thicknesses and coatings of steel for the various locations can be attained. • Laser spot welding: This welding is used to fuse metal parts together for a rigid connection. • Flow drill screws: It uses self-piercing and extruding fastener for joining layers of sheet metal. These have a combined property of friction drilling and thread forming and the screw acts as both a fastener and a drilling-andtapping tool.

SUMMARY • Generally, vehicular body construction depends on application and use. • Vehicular body consists of metal panels, glasswork, wood work, roof, seating, flooring, etc. • Vehicular components can be categorised into exterior parts, interior trim and movable parts. • Large and small trucks, articulated lorries, vans and pick-up vehicles are examples of goods vehicles. • Goods transport vehicles have a rear open or closed area for carrying goods. • Functional requirements of the components, legislation requirements, economics and commercial factors and in-service behaviour of the components are the various parameters taken into consideration in the manufacture of vehicle body. • Ergonomics refers to human–machine relationship. Ergonomics in vehicles is related to the comfort of the driver and occupants. The driver’s seat should be located in such away that the controls are easily accessible while providing maximum comfort. This is good ergonomics in vehicles.

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MULTIPLE-CHOICE QUESTIONS

1. Factors considered while designing the vehicle bodies are a. Aesthetics b. Ergonomics c. Safety d. All of the above 2. The windshield in a vehicle is a. A movable part b. An interior trim c. An exterior part the vehicle d. None of the above 3. The part which separates the drivers’ compartment is called a. Bulkhead b. Sill c. Contrails d. All of the above 4. Generally, a car body has a. An integral construction b. A conventional frame-like structure c. A semi-integral construction d. None of the above

REVIEW QUESTIONS • • • • •

List the factors taken into consideration while designing the vehicle body. Draw a neat sketch of the car body construction. Explain car body types with neat sketches. List the various components of a car body. List the various types of materials used for the construction of the vehicle body. • Describe recent trends in vehicle body manufacturing. • Describe various loads acting on the vehicle body. Answers to MCQs: (1) d (2) a (3) a (4) a

11

Front Axle and Steering Systems

OUTCOME Learning Objectives • Need for power assistance in steering • Principle of the power-assisted steering system • Different types of steering systems

11.1 INTRODUCTION The front axle is an important component of the vehicle and may be live or dead depending on the layout of the vehicle. Normally it consists of an “I” beam. The functions of the front axle are as follows: 1. Carrying the weight of the front part of the vehicle. 2. Facilitates steering and absorbs road shocks due to surface roughness through the suspension system. The function of steering is to provide angular motion to the front wheel as per requirement; which maintains directional stability and control of the vehicle, while maintaining perfect steering conditions.

11.2 FUNCTIONS OF THE FRONT AXLE

1. It turns the front wheels easily. 2. It provides a cushioning effect though a spring. 3. It takes the weight of the front of the vehicle. 4. It provides steering action. 5. The spring transmits a cushion effect to the vehicle. 6. It controls the ride through shock absorbers. 7. It facilitates the braking system. 8. It transmits power to the front wheels in the case of four-wheel drive. 9. It carries both the hub and wheels.

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11.3 CONSTRUCTIONAL DETAILS OF THE FRONT AXLE An important component of the vehicle, front axles can be live or dead. Live axles transmit power while dead axles do not. In the case of front-wheel drive, the front axle is live, which consist of differential mechanisms for power flow to the wheel through the half shaft which consists of constant velocity joints to facilitate the turning of the wheel round the kingpin. In the case of rear-wheel drive, the front axle is dead. The steering spindle and steering knuckle assemblies are hinged on the end of the axle through which the wheels are steered. Normally it consists of an “I” beam at the centre. The ends are either circular or elliptical. The I beam construction carries bending caused by the load of the vehicle and torque from braking of wheels. The centre portion of the front axle has a downward sweep to maintain the chassis height low (Figure 11.1). There are two types of the front axles based on the axle beam:

1. Straight axle 2. Double drop axle 3. Full drop axle (Figure 11.2)

11.4 REQUIREMENTS OF STEERING The requirements of steering are • To provide accurate and light steering control with minimum steering wheel movement. • Minimum shocks to the driver. • At the time of moving from parking, steering effort of the driver should be minimum. • It must be possible to drive the vehicle accurately, i.e. without any unusual steering corrections. • There should not be any play in the mechanical parts of vehicle. . • The entirety of the mechanical transmission devices must be able to take all types of loads in all operating conditions.

FIGURE 11.1  Constructional details of axle beam.

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FIGURE 11.2  Types of front axles.

• The steering linkage must have sufficient strength to withstand the ­failures and cracks during unusual driving manoeuvres, such as driving over obstacles and road irregularities. • In case of failure of assisted steering, the force required to actuate the ­system mechanically should not exceed beyond the capacity of the driver.

11.5 PRINCIPLE OF CORRECT STEERING It is essential that there is no tyre scrub or tyre slip during cornering. This can be achieved with the help of modified Ackerman steering linkages by pure true rolling of the wheels. When the direction of wheel motion is perpendicular to its axis, then there will be pure rolling. In this case, the inner wheel has a greater angle than the outer wheel. Requirement for perfect steering The prerequisite for perfect steering is that all four wheels must turn around the same instantaneous axis. When forming a curve, the inner wheel has a greater angle of turn than the outer wheel. Extreme positions on either side are called lock positions. Turning circle is the smallest circle within which the vehicle can be turned (Figure 11.3).

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FIGURE 11.3  Principle of correct steering.

For correct steering

cotϕ =

y+c y c c = + = cotθ + b b b b cotϕ − cotθ =

c b

For inner front wheel R IF =

a − c b − sin θ  2 

R OF =

b a − c −  sin ϕ 2 

R IR =

b a − c − tan θ  2 

For outer front wheel

For inner rear wheel



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For outer rear wheel



R OR =

b a − c −  tan ϕ 2 

where a = wheel track, L = wheel base, w = distance between the pivots of front axles

ϕ-angle of outside lock



θ-angle of inside lock

11.6 ACKERMAN’S STEERING GEAR MECHANISM Ackerman’s steering principle is based on two wheels being pivoted at the ends of an axle beam. When moving on a turn, for true rolling condition, the inner wheel should ideally turn at a greater angle than the outer wheel (angles A and B); this is because the inner wheel has a tighter turning path to follow than the outer wheel, the point of intersection of the perpendicular lines drawn from each wheel lies on the extended line which passes through the rear axle. The point of intersection is called as instantaneous centre. The position of the instantaneous centre continuously varies based on the angular positions of the front wheels but it lies on the extended line of the rear axle. In the original Ackerman’s steering linkage, when the vehicle followed a curved path, the wheels swivelled at equal angles and the projected lines did not meet at the single point effect of this parallel action, because of scrubbing of the wheels with the ground and heavy steering operation. In the modified linkage there are inclined track rod arms due to which inner the wheel turns more compared to the outer wheel, and the projected lines from the stub axle lie on the imaginary line drawn from the rear wheel.

11.7 STEERING LINKAGE ARRANGEMENTS The steering linkage consists of an assembly of kingpin, drop arm, drag link, track rod, etc. (Figure 11.4). Kingpin or Swivel pin The steering spindle and steering knuckle assemblies are connected to the ends of the axle beam in order to permit wheels to be turned by the steering gear. This pin is known as kingpin or steering knuckle pin or swivel pin. The pins are made of good quality case-hardened steels used to secure the stub axle to the axle beam. Steering gear box The steering gear box provides enough leverage, to move the steering linkage as required with minimum possible effort.

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FIGURE 11.4  Steering linkages.

Drop arm Drop arm connects the output of the steering box to the drag link. Track rod The two stub axle arms of the front axle are connected to the ends of a track rod through knuckle or ball joints known as track rod ends. To ensure adjustment, the connection is made with a screw arrangement. The left-hand and the right-hand threads are produced at each end of the stub axle. Toe-in is increased by lengthening of the rod and decreased by shortening it. Pull and push rod or drag link Pull and push rod, also called drag link, has a tubular cross section between the steering arm of the front axle and the drop arm of the steering frame. At each end, spring-loaded ball sockets are given. One end is attached to the steering arm of the stub axle, while the other end is attached to the steering drop arm.

11.8 AXLE BEAM SUSPENSION STEERING SYSTEM LAYOUT In the case of heavy vehicles, the load carried by the front axle is very less ­compared to the real axle. In such vehicles the driver is seated above the front wheel or slightly in front of the wheel. As an effect of this the steering gear box is located ahead of the front axle. In this type of steering system, steering effort is transferred through the drop arm and drag link directly to the stub axle of one wheel, which is pivoted at the end of the axle beam. Both stub axles are joined together by a track rod.

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11.9 INDEPENDENT SUSPENSION STEERING SYSTEM LAYOUT In the case of independent front suspension system, if both stub axles are connected by a single track rod, then at the time of bump, both wheels lift, which leads to changes in toe-in or toe-out. To overcome this problem, a three-piece track rod is used, which consist of a relay rod, an idler arm and a drop arm. The idler rod is connected to the body structure, while drop arm is connected to the steering output. In this case, vertical movements are carried by tie rods connected to a tie rod arm, while the relay rod manages horizontal movements.

11.10 STEERING GEAR BOXES There are different types of steering gear arrangements provided in the steering gear box. Some of them are as follows:





1. Rack and pinion The rotary motion of the steering wheel is transmitted to the pinion of the steering gear, which is in mesh with the rack. The circular motion of the pinion is transferred to the linear travel of the rack which is transferred to the stub axles through the ball joints and tie rods (Figure 11.5). 2. Worm and worm wheel In this system the steering wheel turns the worm wheel, which turns the worm. A drop arm is connected to the worm wheel; the rotational movement of the steering wheel corresponds to the linear motion of the drop arm, which turns the wheel through the linkages attached. Sometime instead of worm wheel, only sectors are used, called worm and sector gears (Figure 11.6). 3. Recirculating ball type (Figure 11.7) In the re-circulating ball-type mechanism, a nut is mounted on the worm and in grooves provided between the worm and nut. It consists of sets of balls to minimise wear during steering wheel movement. When the steering

FIGURE 11.5  Rack and pinion steering gear box.

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FIGURE 11.6  Worm and worm wheel steering gear box.

FIGURE 11.7  Recirculating ball-type steering gear box.

wheel rotates; the balls provided in the worm grooves move the nut. The worm sector is in mesh with the nut, which is further connected to the drop arm and this result in the required movement of the wheels.

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4. Worm-and-nut-type steering gear In a worm-and-nut-type mechanism, a nut is mounted on the worm. When the steering wheel rotates the worm, it causes a linear movement of the nut. The worm sector is in mesh with the nut, which is further connected to the drop arm and this results in the required movement of the wheels.

11.11 POWER-ASSISTED STEERING 11.11.1 Introduction As resistance of the road wheel increases, the effort required to steer the vehicle also increases. Drivers experience more fatigue when steering the vehicle from a standstill position. Power-assisted steering helps minimise such fatigue.

11.11.2 The Need for Power-Assisted Steering Resistance offered by the front wheel of the vehicle depends on the number of ­factors: locations of the engine, caster provided to the wheel, tread pattern, etc. A transverse mounted engine exerts about 65% load on the front wheel. Driver’s difficulty in steering when moving the vehicle from a stand still condition is minimised with power steering. This system provides the following advantages: • Reduces driver’s effort • Reduces number of turns required • Permits heavier loading on the front wheels, allowing maximum room for goods or passengers (Figure 11.8).

FIGURE 11.8  Hydraulic power-assisted steering.

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11.11.3 Hydraulic Power-Assisted Steering When the turning effort exceeds the predetermined value, the servo mechanism comes into operation, which reduces the effort required to steer the vehicle. Hydraulic fluid is supplied forcefully to the servo mechanism to build the required pressure. At the time of turning the steering wheel, the hydraulic valve is operated through proper linkage and effort applied by the driver is transmitted to the road wheel. Hydraulic power assistance provides the following advantages: • • • • •

Self-lubricating system Large force can be transferred to the vehicle Precise control Occupies less space Close loop control system avoids contamination

11.11.4 Features of the Power-Assisted Steering System Safety: Hydraulic systems always comes with a failsafe system, due to this ­reason power steering superimposes mechanical steering system. Suppose there is a problem with the power steering, the vehicle must be steered in the conventional way. Sensitivity: Power assisting system must be sensitive. A sensitive power system enhances maneuverability, comfort and boosting safety. Power assistance is at its highest at low speed, when parking or maneuvering, making the car very easy to handle. At higher speeds, an electronic sensing system gradually reduces the level of power assistance. This will control the car at high speed and keep it on chosen course even more accurately than with conventional power steering. Maintenance: Proper care and routine maintenance is required for power-assisted steering.

11.11.5  H  ydraulic Power-Assisted Steering Components A hydraulic power-assisted steering system consists of the following components:





1. Hydraulic pump The function of the hydraulic pump is to supply hydraulic energy to the power-assisted steering system; it can be driven by V belt and pulley; a crankshaft drive is provided to the pump. Pump may be of rotary type or vane type. 2. Control valve The function of the control valve is to redirect the fluid as per requirement for power assistance. There are two types of control valves: linear type and rotary spools. 3. Power cylinder The function of the power cylinder is to develop the hydraulic force as per the steering requirement of the vehicle.

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11.11.6 Speed-Sensitive Hydraulic Power-Assisted Steering Generally, as road resistance increases there is increase in the effort required to steer the vehicle. This effort increases further when the vehicle is stationary. A speedsensitive system provides the required variations in power assistance, which can be achieved by flow control and a reactive system, both of which incorporate electronically controlled valves.

11.11.7 Electrohydraulic Power-Assisted Steering Electrohydraulic-assisted steering is electrically powered. The pump provided in this system is driven by a separate electric motor, and it has following advantages:

1. Compact unit 2. Integrated arrangement for simpler installation 3. Less energy required 4. Cost-effective design (Figure 11.9)

11.11.8 Electrical Power-Assisted Steering Electrical power steering system uses an electrical motor to assist steering. It consist of different types of sensors: torque sensor, engine speed sensor, steering angle position sensor and an electronic control unit. An electrical power-assisted system has the following advantages:

1. Improvement in fuel economy as the motor operates only when power assistance is required. 2. Occupies less space

FIGURE 11.9  Electrohydraulic power-assisted steering.

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FIGURE 11.10  Electric power-assisted steering system.



3. Simpler components eliminate the need for a hydraulic system, and hence priming or filling of the hydraulic fluid. 4. Less weight 5. In some cases, power assistance remains available even though engine is not running. 6. There are no leakages in this system (Figure 11.10).

11.11.9 Electrical Power-Assisted Steering Components An electrical power-assisted steering system has the following components: 11.11.9.1 Electrical Motor The electric motor used in power steering is a dc machine and it consists of a rotating armature. The current supplied to the motor is varied according to the power assistance required and the direction of the motor can be controlled by changing the polarity of the signal received by the motor. Control of the current can be carried out by the electronic control unit. 11.11.9.2 Actuating System The function of the actuating mechanism is to transmit the force required to assist the steering system in a rotary or linear sense. It also amplifies the torque output of the motor. Sometimes electromagnetic clutches can be used to disengage the motor when power assistance is not required, during high-speed operation. 11.11.9.3 Steering Input Sensors The steering torque sensor is an important part of the electrical power-assisted ­steering system, which provides information regarding the torque required to the

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steering wheel in the terms of the rotary torque transmitted and the direction in which steering wheel can be rotated. It is also fitted with a steering speed sensor, which detects the speed at which the steering wheel rotates and its direction. This data can be transferred to the electronic control unit. 11.11.9.4 Electronic Control Unit The electronic control unit receives all the data provided by the various sensors, such as the steering torque sensor, vehicle speed sensors and engine speed sensors. The data is processed further, according to which the ECU calculates the required power assistance and controls the current supply to the motor. The ECU also controls the failsafe and self-diagnosis processes. 11.11.9.5 Types of Electrical Power-Assisted Steering There are four types of electrical power-assisted steering systems:

1. Column-assist type: The power assist unit, the controller and the torque sensor are located in the steering column. 2. Pinion-assist type: The power assist unit is mounted to the steering gear pinion shaft in this configuration. The unit sits outside the passenger compartment of the car, making it possible to significantly increase assistance torque without increasing the noise of the interior compartment. 3. Rack-assist type: The power assist unit is mounted to the steering gear rack in this system. 4. Direct-drive type: The steering gear rack and the power assist unit form a single unit in this system. The steering system is lightweight and fits comfortably into the configuration of the engine compartment. Direct assistance to the rack allows for low friction and inertia, which in turn provides an ideal steering feel.

SUMMARY • Front axle carries the steering system and the weight of the vehicle’s front part. • Ackerman’s steering principle is used in automobiles. When vehicle moving on a turn then for true rolling condition, point of intersection of the perpendicular lines drawn from the each wheels lies on extended line which passes through the rear axle, called as instantaneous centre. • The steering system consists of a track rod, a tie rod, a front axle, a drop arm, etc. • The function of the steering gear box is to provide leverage, which consists of rack and pinion, recirculating ball-type mechanism, worm and worm wheel, etc. • Steering air bag protects the driver’s face and chest, and it transfers the force exerted by the driver’s face and chest to the atmosphere by using gas as a medium. • Electric steering is more economical, and easier to package and install than conventional hydraulic power steering systems.

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• Electric and electrohydraulic power steering systems are also lighter and more compact than conventional hydraulic systems. • Resistance offered by the front wheel of the vehicle depends on a number of factors, such as the location of the engine, caster provided to the wheel, tread pattern, etc. • The electrical power-assisted system can be classified into four types: column assisted, rack assisted, pinion assisted and direct drive according to the location of the power assistant unit.

MULTIPLE-CHOICE QUESTIONS

1. The function of the steering system is to a. Minimise tyre wear b. Provide directional stability to the vehicle c. Both a and b d. None of the above 2. The function of the front axle is to a. Carry the front weight of the vehicle b. Carry steering attachments c. Take front break thrust d. All of the above 3. The types of gearings used in a steering gear box are a. Rack and pinion b. Bevel and pinion c. Spur gears d. All of the above 4. Function of the steering air bag is a. To protect the passenger b. To control the vehicle c. To protect the driver’s face and chest at the time of impact d. To absorb road shocks 5. In the independent suspension steering system a. Three-piece tie rod is used b. Idler arm and drop arms are used c. Both a and b d. None of the above 6. Resistance offered by the front wheel depends on the a. Amount of weight at front side b. Engine location c. Caster provided to the front wheel d. All of the above 7. Disadvantage of the power steering system compared to conventional steering is that it a. Requires hydraulic fluid b. Will not work when vehicle is stationary c. Both a and b d. None of the above

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8. As road resistance increases the force required to steer the vehicle a. Increases b. Reduces c. Does not change d. None of the above 9. The pump used in hydraulic steering systems is driven by a. Battery b. Engine c. Both a and b d. None of the above 10. The advantage of electrical power steering over hydraulic steering is a. It occupies less space b. The electrical motor operates only when power assistance is required c. Less energy consumption d. All of the above 11. The advantage of power steering is a. Reduction in driver’s effort b. Reduction in the number of rotations c. More room for passenger and goods as more weight is carried in the front. d. All of the above 12. The advantage of the hydraulic power steering system is a. Self-lubrication b. Ability to transfer large force to the vehicle c. Precise control d. All of the above

REVIEW QUESTIONS • • • • • • • • • • •

What do you mean by live axles? What are the functions of the steering system? What do you mean by sensitive power steering? List the different types of gear arrangements used in automotive steering system. What is the difference between axle beam suspension and independent front suspension steering system. Why power steering is required? What are the different types of power steering? Explain the working principle of the steering system. List the various components of the hydraulic steering system and explain themin brief. What are the advantages of the hydraulic power-assisted steering system over the conventional steering system? What are the advantages of the electrical power-assisted steering system over the hydraulic steering system?

Answers to MCQs: (1) c (2 ) d (3) a (4) c (5) c (6) d (7) c (8) a (9) b (10) a (11) d (12) d

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Wheels and Tyres

OUTCOME Learning Objectives • • • • • •

Requirements of wheels and tyres Types of wheels, tyres and their constructional details Characteristics and properties of tyres Wheel alignment and balancing Factors affecting on tyre properties Tyre material, tread and re-treading procedure

12.1 INTRODUCTION The function of the wheels and tyres assembly is to support, propel and steer the vehicle as per requirement when rolling over the road surface. Proper assembly of the wheels and tyres directly affects the steering geometry and disturbs the comfort level of the driver as well as occupants. It provides cushioning effect to the wheels against small road shocks and also transmits both the driving and braking forces between the wheel and the road surface. Wheels: Wheel is an most important structural member of the vehicular suspension system that supports the static and dynamic loads generated during various operating conditions of the vehicle. A wheel is a circular device that is capable of rotating on its axis, facilitating movement or transportation while supporting a load.

12.2 REQUIREMENTS OF THE WHEEL Lightweight: Wheels are directly connected to the un-sprung mass of their suspension mechanism. If the height of the wheels is low then it is easier for dampers to control their bouncing movements when they are subjected to bump. Strength and rigidity: Selection of wheels is based on various factors: one of them is application. During braking reactions, wheels have to overcome vertical loads as well as cornering forces. A wheel must have sufficient strength to resists all types of deformation and accidental damage during operation and all normal service loads imposed upon it. Tyre and wheel retention: The wheel rim is designed in such way that the mounting and removal of the tyre must be easy and it must be maintained in secure position of tyre when inflated. For this purpose the tyre rims are made with two or three pieces. Sometimes tapered seating is also provided so that the beads of the inflated tyre are forced to climb these tapers, thus wedging themselves against the insides of the rim flanges. The wheel rim must also accommodate the tyre valve assembly. Wheels must be easily removable from the wheel hub. 211

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Proper balancing: Wheels must be well balanced so they can smoothly rotate at high speeds without wobbling or affecting steering geometry. Cost: Wheels should be made out of cheaper materials that can easily be fabricated, cast or forged with minimum machining. They should also have a better finish and appearance and should not easily weather or deteriorate with age.

12.3 CLASSIFICATION OF WHEELS Wheels used for automotive applications can be classified into

1. Wired wheels 2. Steel disc wheels 3. Alloy wheels

12.4 CONSTRUCTION OF WIRED AND PRESSED DISC WHEELS





a. Disc wheel This type of wheel has two parts, a steel rim and a pressed steel disc. As per the design the rim and the disc may be permanently attached or detachable. A pressed steel disc is welded to the rim. There is provision of the taper on seat of the rim for proper sealing of tubed or tubeless tyres. There is provision of slots without disturbing the strength of the disc to facilitate brake drum cooling. The disc also has provision to be mounted to the axle. Wheel discs transmit braking as well as driving torque and take care of cornering forces and side thrusts. There is provision of a hole in the disc to accommodate the tube valve (Figure 12.1). b. Wire wheel In this type of wheel the hub is attached to the rim through a number of long, thin-wired spokes. The purpose of the spokes is to bear weight, to transmit the driving and braking torques, to withstand side forces when cornering and to avoid bending or compressive loads acting on the wheel. The rim of a wired wheel is not capable of fitting tubeless tyres. Special skill is required to fit wheels with spokes. The initial tension of the spokes can be changed by means of screw nipples, which are often used to attach the spokes to the bottom. The spokes are mounted in a complicated criss-cross fashion installed on three planes. The advantages of this type of wheel are light weight and high strength and easy to change whenever required. c. Light alloy cast or forged wheels These wheels are made of magnesium and aluminium, the main purpose of which is to reduce weight. Compared to steel, magnesium alloy is 50% lighter but has similar strength. Reduced weight enhances fuel economy. Light alloys are better conductors of heat than steel, so that they transfer any heat generated by the tyre or brake more quickly, which improves tyre life. Magnesium alloys exhibit very good fatigue properties and excellent resilience, due to which they are capable of resisting vibrational and shock loading better than both aluminium alloy and steel. These wheels are

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FIGURE 12.1  Types of wheels.

manufactured with a single-piece rim and disc. As regards the cost, light alloy wheels are more expensive to manufacture than pressed steel wheels. Aluminium alloy wheels are cheaper than magnesium alloy wheels. Usually aluminium alloy wheels are preferred for passenger cars and trucks, and magnesium alloy wheels for sports and racing cars.

12.5 TYPES OF RIMS AND THEIR CONSTRUCTIONAL DETAILS The rim is the outer edge of the wheel, carrying the tire. This is the outside circular shape of the wheel on which the inner edge of the tire is placed on vehicles such as automobiles. The rim used in car wheels is cold-rolled from flat steel strip while for heavier commercial vehicles they are hot-rolled to the section from steel bars. The portion of the rim where the tyre sits has a 5° taper due to which, as the tyre is inflated, the beads are forced up the taper providing a wedge fit, and a good seal is obtained with tubeless tyres.

12.5.1 Rim Designs Rims designs differ from one another (depending upon the type of tire) in terms of number of parts and cross-sectional rim shape. The most important rim components are: rim flange, rim bead seat and rim base. Rims have the following different crosssectional shapes: • Drop centre, • Flat base

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• 5° tapered bead seat • 15° tapered bead seat

12.5.2 Well-Base Rims These rims are designed to minimise dislodging of tyres when subjected to heavy cornering. Originally the rim was tapered from the rim flange to the edge of the well so that the pressure acting over a short length of the bead would force back the tyre bead into the well (Figure 12.2).

12.5.3  5° Seat-Angle Well-Base Rim These rims are only used for vans and small commercial vehicles. They have high wall flanges, which protect the tyre beads and walls from damage from external interference. Generally both tube and tubeless tyres are fitted on these rims.

12.5.4 Drop-Centre 15° Taper Rim In this type single-piece well-base wheel rims are used, with relatively shallow flanges at the edge of 15° taper bead-seats. This profile of the rim provides a good joint and sound seal between the tyre bead and the rim taper.

12.5.5 Detachable-Rim Wheels In case of heavy commercial vehicles, due to high loads, tyres used are bulkier in the bead region. In order to ensure the proper mounting of the tyre the rims for these tyres have one removable side-flange, which allows the wheel tyres to slide into position, and then the flange can be replaced and locked at proper place.

FIGURE 12.2  Types of rims.

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12.5.6 Semi-Drop-Centre Two-Piece Rim This rim forms an intermediate class between the well-base and wide-base rims. This type of rim has inner and outer tapered tyre-bead-seating surfaces separated by a shallow central or near central well. The inner flange can be removed at the time of tyre fitting. It can accommodate too rigid heavier beads for fitting on the full well-base type.

12.5.7 Wide-Base Two-Piece Rim This type of rim is used mainly on medium-size commercial vehicles. In this type of rim one split detachable flange and one fixed flange are integral with the rim base. A taper of 5°is provided to tyre beads, the one on the detachable flange side being integral with the flange. The outer detachable flange is sprung into a continuous groove formed along the outer edge of the rim base to retain the flange in its working position. At the time of inflation of the tyre the bead sits over the detachable-flange taper to holds its position.

12.5.8 Wide-Base Three-Piece Rim This rim is used on large commercial vehicles. It contains one detachable endless flange, a separate flange-retaining split lock-ring and one fixed flange integral with the rim base. A taper of 5°is provided to seats for tyre-bead location, on the ­detachable-flange side. It is usually being an extension of the spring lock-ring. At the time of inflation of the tyre, the bead sits over the extension of the spring lock-ring, holding it in position.

12.5.9 Divided Flat-Base Rim These rims are used primarily for defence vehicles. This type of rim is an integral part of the wheel. Two halves of the wheels are divided by dismantling the outer ring of bolts at the time of fitting a tyre.

12.6 WHEEL ALIGNMENT AND BALANCING 12.6.1 Wheel Alignment Front wheel alignment is the angular relationship between the front wheels of the vehicle, the suspension and the ground, the objective of which is to allow the wheels of the vehicle to roll without dragging, cupping, scuffing or slipping. The proper alignment ensures ease of steering and reduces load on suspensions and tyres. The poor alignment of tyres can result in a less-than-enjoyable driving experience. Four angles are involved in the proper alignment of the wheel: caster, camber, toe-in, toeout on the turns and inclination of the steering axis. There are also warning signs for when the alignment needs to be adjusted, as follows: • Irregular and uneven tyre wear • Heavy steering

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Fatigue to the driver’s steering Vehicle wandering or difficult to maintain along a straight line Vehicle steering wheel not returning to exact centre One side pulling of the vehicle

Correct alignment • • • • • •

Prevents excessive, uneven and early wear of the tyre Increases fuel economy Enhances cornering and general handling Reduces driver fatigue Enhances tyre life Improves the life of suspension elements

12.6.2 Wheel Balancing For smooth operation of the wheel, long tyre life, and proper alignment of the wheel to minimise its own vibrations requires balancing of the wheel. Wheel balancing is done in order to gain consistent stability and to prevent instability in cars by applying balancing weights to the rim in order to distribute the mass of the wheel equally during rotation. Imbalance in mass distribution around the wheels may be caused by the following:

a. Tyre moulding may not be placed concentrically on the tyre surface. b. Lateral wheels wear out or wheel rim become bulky c. Some manufacturing flaws in the rubber. d. The high rate of uneven tyre wears due to lower or higher inflation

If anyone or a combination of these issues occurs, one section of the wheel will undergo uneven wear and the tyre may become lighter on one side and heavier on the other. Due to this the wheel receives unequal centrifugal force on each side; if these forces are cancelled on the other side of the wheel, they are said to be in balance. Balancing is of two forms: 1. Static balancing: This is the simplest way to test for inspection and correction. If one of the front wheels is jacked up and rotates slowly, the hardest component at the lowest point will come to rest. When the position of the heaviest part has been determined, it must be marked with a chalk. Nevertheless, in the case of a wire wheel, the short length of the lead wire may be wrapped around one or more spokes at a point opposite to the chalk mark. The length of the wire must be adequate to achieve a suitable balance. 2. Dynamic balancing: A wheel may be in perfect static balance but dynamically unbalanced. This dynamic imbalance occurs when the wheel is rotated and the centrifugal forces acting in different heavy spots become unbalanced because they are not acting through the same line.

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12.7 TYRE CHARACTERISTICS 12.7.1 Tyre The tyre is a cushion for a car axle. This consists mostly of the outer shell, i.e. the interior of the tyre and tube. The assembly of the tyre tube is mounted on the wheel rim. It is the air inside the tube that bears the entire load and provides cushioning effect. The tyre performs the following functions:

1. Supports vehicle load 2. Provides shock-absorbing cushion 3. Transmits driving force and braking force to road 4. Provides cornering strength for smooth steering

While moving on the road, the tyre has to sustain various types of forces in longitudinal, vertical and lateral directions. Considering this, the characteristics that a tyre should possess are as follows. Cushioning ability: Road wheels provide ride comfort to the vehicle by acting as a spring element. Tyre is not as flexible as the springing components of the suspension system. The flexibility of the tyre depends on elasticity of the material used and inflation pressure. Rolling resistance: Resisting forces are encountered due to tyre deformation, uneven road surfaces and friction force developed due to scrubbing action of the road. Rolling resistance is affected by inflation pressure. This in turn is related to area of contact to the road wheels. Minimum rolling resistance will improve performance and fuel consumption. Directional stability: Pneumatic tyres are flexible in nature. During free rolling, lateral forces act on the vehicle and deviates it from its straight path. This deviation is known as the slip angle. Factors such as load, tyre inflation road surface, etc. affect the slip angle. Minimum slip angle is desirable. Self-aligning property: Due to presence of slip angle, the trailing portion of the tyre contact patch has more lateral deformation than the leading portion, which shifts the centre of pressure, and cornering forces act just behind the rotational axis of the wheel, and as a result the wheel produces self-aligning torque.

12.7.2 Tyre Properties 12.7.2.1 Non-Skidding This is one of the most important tyre properties. The tread pattern on the tyre must be suitably designed to permit least skidding even on wet roads. 12.7.2.2 Uniform Wear In order to preserve the non-skidding property, it is highly necessary that the wear of the tyre be uniform. Tyres designed with a ribbed tread help accomplish this.

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12.7.2.3 Load-Carrying Capacity Throughout each rotation of the wheel, the tyre is subjected to alternating stresses. The material and design of the tyre must be able to ensure that the tension is borne by the tyre. 12.7.2.4 Cushioning The tyre should be able to withstand high-frequency vibrations produced by the ground surface and thus have a cushioning effect. An automobile tyre consumes some amount of power due to friction between the rubber surface and the road surface and also due to hysteric losses from the constant fixing and release of the tyre. The tyres should be designed to consume least power of the engine. It is seen that synthetic tyres absorb more power during rolling than those made of natural rubber. 12.7.2.5 Tyre Noise The unbalanced tread depths cause tyres to emit loud noises while driving. Usually sounds heard during driving are caused by uneven wear coming from one tyre. This will cause irregular tyre movement and make the sounds coming from the air chamber louder. A bad wheel bearing is one of the more serious issues that cause  tyre noise. The noise of the tyre must be of a certain pattern, a series or a noisy rug. In any case, it is important that noise produced by tyres should be minimum. 12.7.2.6 Balance Balance is a very critical factor for tyres. Since the tyre is a revolving component of the vehicle, it must be balanced both statically and dynamically. The absence of balance gives rise to peculiar oscillations, called wheel tramp and wheel wobble.

12.8 CORNERING PROPERTIES OF THE TYRE 12.8.1 Static Load and Standard Wheel Height The static load of the vehicle will be carried by the wheel. The effect of this load on the tyre casing is radially distorted from circular to flat in the contact between tyre thread and road interface, which is called contact patch. The contact patch shape is roughly elliptical. This will be directly impacted by the height of the vehicle. Generally, the deflection of the tyre should be proportional to the load acting on the axle.

12.8.2 Contact Patch As the inflation pressure of the tyre increases, the contact patch area decreases and the height of the tyre increases. So as the inflation pressure of the tyre increases, the deflection of the tyre will be reduced. The vibration and ride quality of the tyre is directly associated with the inflation pressure as well as the loads acting on the wheel.

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12.8.3 Cornering Force Tyres are subjected to vertical forces as well as side (lateral) forces when the wheels are in motion due to road camber, side winds, weight transfer and centrifugal force caused by travelling round bends and steering the vehicle on turns. During the action of lateral force, the tyre tread contact patch and road surface will oppose any sideways motion. This resisting force generated at the tyre–road interface is known as cornering force; its magnitude is equal to the lateral force but it acts in the opposite direction of lateral force.

12.8.4 Slip Angle The angle made between the direction of the wheel plane and the direction in which it travels is known as the slip angle. Provided the slip angle is small, the compliance of the tyre construction will allow each element of tread to remain in contact with the ground without slippage.

12.8.5 Pneumatic Trail and Self-Aligning Torque Pneumatic trail is caused by the progressive build-up of lateral force along the length of the contact patch, such that lateral forces are greater towards the rear of the contact patch (though less so when the rear of the contact patch begins sliding) and this creates a torque on the tyre called the self aligning. Self aligning torque helps steered tyres to return to the original position after negotiating a turn on the road. Self-aligning torque (SAT) may be defined as the product of the cornering force and the pneumatic trail.

12.8.6 Camber Thrust Camber thrust is the movement of a tyre perpendicular to the direction it is rolling in. In simple terms, camber thrust, or camber force, acts on a tyre in the direction of a tyre’s sidewall. If a tyre is mounted on a vehicle, camber thrust forces a tyre left or right.A positive camber reduces the cornering force for a given slip angle relative to that achieved with zero camber, but a negative camber raises it.

12.9 REQUIREMENTS OF TYRES Pneumatic tyres must satisfy the following requirements:

1. Support the weight of the vehicle and distribute it over a road surface. 2. Have minimum rolling resistance so as to minimise the fuel consumption. 3. Absorb shock 4. Have maximum tread life under varied running conditions 5. Ability to generate traction, braking and good response to steering 6. Stability even at high speeds 7. Low noise generation at high speeds

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12.10 CLASSIFICATION OF TYRES There are generally two types: solid and pneumatic (or air filled). Solid tyres are generally used for special industrial applications. Tyres are also classified into tubed and tubeless, cross ply and radial ply constructions.

12.10.1 Tubed Tyres

1. Tubed tyre or traditional tyre consists of an inner tube that assumes the form of a tyre after inflation. The valve stem attached to the vent is used to either inflate or deflate it. It consists of two essential parts, the carcass and the tread. The inner tube is vulnerable to sharp objects like rough cut stones or nails (Figure 12.3).

12.10.2 Tubeless Tyre This type of tyre does not need a separate tube; rather, the air under pressure is filled into the tyre through anon-return valve attached to the rim. The inner construction

FIGURE 12.3  Tubed tyre.

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of the tyre is similar to that of a tubed tyre, except that inside it has a specialised airretaining lining (Figure 12.4). Tubeless tyres have the following benefits over traditional tubed tyres:

1. Less un-sprung weight: This makes the tyre lighter, which minimises and eventually decreases the bouncing of the drum. 2. Better cooling: In the case of tube tyres, heat in compressed air must pass through the tube material, i.e. rubber, which is not a good heat conductor. Since there is no tube in the tubeless tyres, heat transfers directly into the atmosphere resulting in better cooling, increasing the life of the tyres. 3. Slower air leakage: As the inner lining in tubeless tyres is not extended like in tubed tyres, the air is better preserved, resulting in its slower leakage. 4. Simpler assembly: As it is just one layer of tyre that has to be installed in the vehicle, there is no danger that the tube will be punctured during assembly. 5. Improved protection: In the case of any minor holes in the tyre, it can be patched easily by plugging in a very short time, although in the case of traditional tyres, it takes quite some time to remove the tube for repair. Apart from this, the tubeless tyre maintains air pressure for a longer period of time even when punctured by a nail, as the nail is kept in place.

FIGURE 12.4  Tubeless tyre.

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Carcass Types: The carcass or skeleton of a tyre is of three types:

1 Cross ply or bias ply 2 Radial Ply 3 Belted bias type

A tyre is named after the unique type of carcass it contains because it is the main stress-taking component in operation.

12.10.3 Cross Ply Type In this type, the ply cords of the material (rayon  or nylon) are woven at an angle (30°–40°) to the axis of the tyre. There are two layers going in opposite directions. The number of plies depends on the size of the tyre and the load to be transported. This design makes it easier for the tyre body to stretch and allow a more comfortable ride on rough terrain. However, the design is flawed at highway speeds, disallowing good traction and increasing rolling resistance. The problem of overheating occurs in this type of tyre.

12.10.4 Radial Ply Type In this ply, cords run in the radial direction, i.e. in the direction of the tyre axis. Radial ply tyres have much more flexible sidewalls as the casing cords do not cross over each other. A radial tyre has less rolling resistance as it moves over the road surface. There are no heavy plies to distort, and flexing of the thin casing generates little heat, which is easily dispersed. A radial ply tyre runs cooler than a comparable cross-ply tyre and this increase tread life (Figure 12.5).

12.10.5 Belted Bias Type In this type of tyre there is a combination of cross ply and radial ply tyres. This construction gives mores strength to the sidewall and greater stability to the tread. Due this type of construction, these tyres have a longer life.

FIGURE 12.5  Types of tyres.

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12.11 TYRE CONSTRUCTION Inner tube: A tyre’s inner tube is a flexible tube, which assumes a circular shape when inflated; it will expand indefinitely like a balloon. A tube is protected by an outer cover of textile material and rubber. The purpose of the inner tube is to store the trapped air for a long time. An automotive tyre cover consists of the following elements (Figure 12.6): Carcass: Carcass consists of a inner horseshoe-shaped lining made up of a number of layers of textile cord piles. The tread bead and walls all are moulded on these cord piles. Bead: This is the inner edge of the tyre which provides rigidity and strength necessary to support the carcass. Side wall: The portion between the bead and tread is known as side wall. Degree of protection depends on wall thickness. Tread: This is the part of the tyre that contacts the road surface when the wheel rolls. Breaker: The breaker of a bias tyre is rubber-coated layers of cord between the tread and carcass, binding the two together. The breaker prevents cuts in the tread from reaching the carcass and helps absorb shocks. 

12.12 TYRE TREADS The tread of a tyre or track refers to the rubber on its circumference that makes contact with the road or the ground. As tyres are used, the tread is worn off, limiting its effectiveness in providing traction. A worn tyre can often be retreaded. Tyres usually

FIGURE 12.6  Tyre terminology.

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fall into one of the following categories: symmetrical, asymmetrical, directional and non-directional. Directional tread patterns are designed to provide a variety of functions under different driving conditions.

12.12.1 Symmetrical Tread Pattern The symmetric tread pattern is the most common and consists of continuous ribs or individual tread blocks around the entire tread face.

12.12.2 Asymmetrical Tread Pattern The criteria for dry grip and water dispersal/snow traction are combined in this form of design. Asymmetric tread designs typically contain larger tread ribs/blocks on the outboard side to improve cornering stability on dry roads by providing greater contact space.

12.12.3 Directional (Unidirectional) Tread Pattern A directional (also called unidirectional) tread pattern is built in such a way that the tread has to roll in one direction only. It consists of lateral grooves on both sides of the centreline of the tyre that point in the same direction and results in V-shaped tread blocks. Such lateral grooves improve hydroplaning resistance at high speeds by pumping water more effectively through the tread pattern.

12.12.4 Asymmetrical and Vertical Tread Patterns In this tread pattern, there are V-shaped tread grooves that are offset to the middle line of the tyre (Figure 12.7).

12.12.5 Non-directional Tread Patterns Non-directional tyres have a tread pattern that is designed to perform equally well regardless of the tires' rotational direction. These types of tyres win the tread wear comparison other tread patterns. Non directional tyres can be rotated (swapped), to different sides of the vehicle, extending their life, and making uneven tread wear easier to correct. However, directional tires can only be rotated front to back on the same side of the car.

12.13 TYRE SIZE AND DESIGNATIONS Selection of tyres is very important to achieve maximum performance. The size of a tyre must satisfy some basic conditions related to rim parameters and load-carrying capacity. All manufacturers mould the information about the tyre into its sidewall. The bead diameter must suit the wheel rim diameter to carry cornering forces and sealing of tyres. Section width must be suitable for use on the wheel rim and large enough to have a suitable load-carrying capacity for the vehicle. The overall tyre size

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FIGURE 12.7  Different tyre tread patterns.

must allow sufficient clearance between the tyre and the vehicle frame. The method of designation of a tyre is shown in Figure 12.8.

12.14 FACTORS AFFECTING TYRE LIFE The tyre is an essential component of a vehicle as it connects the vehicle to the road. The overall cost of the tyre is about 10% the cost of the vehicle. So it is essential to pay equal attention to its maintenance and longevity. There are many factors which affect the life of a car tyre.

12.14.1 Selection of Correct Tyre and Its Installation It is important that the same types of tyres are installed in one car. Every tyre has a different pattern, size and loading capacity, which varies according to the brand. Combination of different technologies and construction techniques of different brands as well as improper installation of tyres disturbs the entire balance and performance between the four tyres and negatively impacts the lives of all four tyres as well as overall performance of the vehicle.

12.14.2 Tyre Pressure Both over-inflation and under-inflation pressure acting on the tyre badly affect its performance and life span. When under-inflated, the sidewalls come in contact with the road and are subjected to rapid wear, compared to the central portion of the tyre.

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FIGURE 12.8  Tyre size and designation.

According to some operators over-inflation pressure of the tyre is good for heavy load, but as the inflation pressure increases it also reduces the contact area so the load is concentrated at the central zone of the tyre and the rate of wear is more, which again shortens tyre life.

12.14.3 Loading Capacity Tyre’s load index relates to its maximum carrying capacity (in kg). Every type of tyre has a specific loading capacity. For example, a tyre with a load index of 91 can carry 615 kg of weight. The load rating is generally found after the diameter reading and before the speed rating on the sidewall marking. Any extra load beyond the limit specified for the tyre affects tyre life.

12.14.4 Wheel Alignment Suspension geometry is also essential for the life of the tyre as well as the connections of the wheel assembly. Faulty suspension geometry reduces tyre life, as a result of uneven loading of the vehicle.

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12.14.5 Car Speed If the speed of the vehicle is beyond the limit specified by the manufacturer, then tyre life will continuously reduce.

12.14.6 Tyre Temperature Tyres are highly prone to adverse effects if the temperature is high. As tyres move on the road at high speeds, they become exposed to optimum stretch, compression and friction. A direct consequence of this is rise in tyre temperature, which easily exacerbates and even punctures the rubber material and wears out the tyres.

12.14.7 Chassis Status There are various assemblies and disassembles of various systems and subsystems. Malfunctioning of any of these directly changes the loads acting on the road wheel assemblies and there will be uneven loading conditions at various operating conditions, which generate uneven stresses on the wheels and reduce tyre life.

12.14.8 Road Conditions Road conditions are an important aspect related to tyre wear. A well-maintained road reduces additional friction required to maintain proper traction between the road and road wheel. A road with potholes and ditches, hilly terrain places additional loads on the wheels and tyres.

12.14.9 Seasonal Factors Various parameters such as the surrounding temperature and other climatic factors like wind speed, pollution, period of non operation of vehicle and geographical region affect tyre efficiency and life.

12.14.10 Driving Habits Driving habits such as frequent sudden braking, sharp steering, driving at high speeds even on bad roads, hitting against curbs and parking barriers are highly dangerous and severely affect tyre life.

12.14.11 Vehicle and Tyre Maintenance Regular and predesigned maintenance of the vehicle as per the manufacture’s recommendations, and the tyre rotations at regular interval, leads to equal wear of all tyres and enhances the life of the vehicle.

12.15 TYRE MATERIAL A tyre consists of various layers of inextensible cords which help hold the air pressure and restrict deformation in various operating conditions. The essential requirements

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of the cord material are high stiffness, sufficient rigidity, high strength-to-weight ratio and good adhesion to rubber. There is ongoing research on new tyre materials and improvements in existing tyre materials to meet the essential requirements and the growing demands for better fuel economy of the vehicle. Various types of fabric cord materials are widely used for tyre cord piles, such as cotton, rayon, nylon, polyester and glass, but also steel and polyaramid. Tyre liner is usually made of  butyl rubber,  which is intended to minimise the loss of air, because it has low permeability to gas. The requirement of the sidewalls is resistance to scraping, flexing and attack by ozone in the air. Constituents of the sidewalls are 50 parts butadiene rubber (for abrasion resistance), and 50 parts carbon black  (for reinforcement), along with small amounts of processing oil, antioxidant and protective wax.

12.16 TYRE RE-TREADING Re-treading is a special procedure that involves adding fresh thread material to the old casing and vulcanizing it into plies, and only the casing that is in good condition can be m certainly-coated. Re-covering requires special equipment. The tyre is cleaned and the tread layer is roughed up by rubbing or buffing it with a wire ring. Then a strip of new rubber treadmill called camel black is put in the recapping unit. The unit is clamped shut and heat is applied for a specified time. This vulcanises the new tray into the existing casing. The methodology of hot re-treading and cold re-treading processes is as follows: Step 1: Tyre arrives at the re-treading core. It is thoroughly washed with water so that dirt, dust and mud are all effectively extracted. Step 2: Tyre is left to dry for some time or a dryer is used. Step 3: Initial inspection is carried out to ensure whether the casing is appropriate for re-treading. This is thoroughly checked both inside and outside. Step 4: Buffing – The main purpose of buffing is to clean the worn out surface of the tyre. The original tread configuration and some of the under-treads are also removed to provide the housing with the requisite dimensions and surface texture. It adjusts the coefficient of friction of the un-treaded surface so that it can keep the cushion and sole of the new treads securely. Step 5: The tyre is made to constantly spin and the width of a paint brush containing vulcanised rubber solvent is placed over the surface of the tyre, for a uniform spread. If required, another dip of the solvent with the brush. After the application of ample solvent, the cushioning strip is permanently fixed and the tyre is slowly rotated such that the entire circumference of the tyre is enclosed and the uncured tread compound is extruded or added directly to the casing as a strip of required size. Step 6: Hot re-treading process –The tyre is placed in the mould and the air pressure is maintained so that it expands the uncured rubber at a mould temperature of 150°C on the tray, and after a certain time the mould is opened and the tyre is removed from the mould. Such moulds are used in

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the manufacture of new tyres. A new mould is needed for every size of tyre, which makes it an expensive process and almost out of date. Cold re-treading process – The tyres are removed from the machines and suspended with supports. The tyre is placed under the cover so that the uncured cushion has to be vulcanised in the pre-moulding process, while the premoulded tread has to be held in place. Tyres are pushed by hoists and chains placed in a fixed location into a horizontal furnace. The tip of the pressure nozzle is attached to the air pressure shield and the furnace lid is closed. The on/off button is switched on. A temperature of 99°C is maintained for 3–4 h. This results in an adhesive contact between the vulcanised surface and the rubber pad and the sole of the treads. After 4 h, the furnace is switched off and the tyre is left to cool in the furnace for 1–2 h. The tyre is removed from the furnace and allowed to cool some more before the worker is able to remove the envelope from the tyre. Step 7: Final inspection – This step ensures that all defects reported prior to the process have been eliminated. When the tyres pass the final test, they are stored in the warehouse until supply requirement.

SUMMARY • The function of the wheels and tyres assembly is to support, propel and steer the vehicle as per requirement, when rolling over the road surface. • Wheel balancing is done in order to gain consistent stability and to prevent instability in cars by applying balancing weights to the rim in order to distribute the mass of the wheel equally during rotation. • Selection of tyres is very important to achieve maximum performance. The size of a tyre must satisfy some basic conditions related to rim parameters and load-carrying capacity.

MULTIPLE-CHOICE QUESTIONS 1. The function of a tyre is to a. Absorb road shocks b. Absorb cornering thrust c. Both a and b d. None of the above 2. While travelling on a straight road, an over-inflated tyre will wear at a. Corner b. Middle c. Edge d. None of the above 3. While travelling on a straight road, an under-inflated tyre will wear at a. Corner b. Middle c. Edge d. None of the above

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4. Rims used in heavy vehicles are a. Flat-base divided b. Semi-drop centre c. Well-base rim d. None of the above 5. Wheel balancing is carried out to a. Stabilise the vehicle b. Reduce wear c. Both a and b d. None of the above

REVIEW QUESTIONS • • • • • • •

List the requirements of the tyre. Describe the construction of the tyre. List the various types of rims. What do you mean by wheel balancing? Explain its necessity. Describe the necessity and effect of wheel alignment. Describe the various types of wheels. Describe cross section of the rim.

Answers to MCQs: (1) c (2) b (3) c (4) a (5) c

13

Vehicle Aerodynamics

OUTCOME Learning Objectives • • • •

Basics of aerodynamics Fundamentals of air flow Wind tunnel testing Aerodynamics of passenger and commercial vehicles and two-wheelers and their drag reduction techniques

13.1 INTRODUCTION Moving vehicles are always subjected to air flow, which may have an adverse effect on fuel economy, vehicle performance, noise level, road holding and stability. This opposing force of air, frontal area of vehicle exposed, are directly associated with the aerodynamics. So it is essential to provide the styling to the vehicle with accommodating functional power train, suspension elements, passenger as well as luggage space engine, wheels etc. Aerodynamics is the branch of the science which deals with solid bodies moving through the atmosphere and the interaction between body surfaces and surrounding air with varying relative speeds and wind direction.

13.2 AIR FLOW FUNDAMENTALS When a vehicle is subjected to air flowing in the surrounding, then air will pass the vehicle and around as well as through the vehicle. Air has viscosity as well as inertia, and as a result this there is friction between adjacent layers and loss of energy. Air flowing around the solid body, forms a thin boundary layer between the main stream and surface of a body. There is a relative motion between adjacent layers of the body and the surface of the body within the boundary layer. In the case of laminar flow of air, there is a shearing of adjacent layers of air. The velocity of the layer farthest away from the body surface up to unrestricted flow is having highest velocity and at the surface it will be zero. This is because the layer of flowing air comes in contact with the surface of the body, the air particles loosely attaches this viscous drag to the surface resulting in zero velocity at the surface. The velocity of the adjacent layer is slightly higher as it slides over the surface. The general characteristics of air flow are as follows: • Air moves from high pressure regions to low pressure regions. • Air has inertia and, hence, changes direction only when obstructed (it does not always travel in a straight line). 231

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FIGURE 13.1  Air flow fundamentals.

• Friction is developed when moving air comes in contact with surfaces and this causes the air stream to slow down and form eddies. • Airflow is laminar, but when it comes into contact with the surface of acar or other obstructions, it turns turbulent. It depends on the surface finish of the vehicle (Figure 13.1).

13.3 DRAG FORCES Drag force is the opposing force that the vehicle has to overcome during the operation. Drag force is a result of pressure distribution over the body surface and forces caused by skin friction developed due to fluid viscosity. Noticeable vehicle resistance to drag occurs above 50–70 km/h of vehicle speed. A number of parameters related to the design of the frontal area of the vehicle are responsible for drag force.

The drag can be calculated from = CdAP/2

where Cd is the coefficient of drag,

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A is the characteristic area of the body which is the largest projected area of body on a plane perpendicular to the direction of the air, P/2 is called the dynamic pressure of the air flow. Drag Coefficient Aerodynamic drag coefficient is a measure of the effectiveness of the streamlined aerodynamic body shape in reducing air resistance to forward motion of the vehicle. Drag force can be divided into the following:

a. Pressure drag or form drag: This type of drag arises because of the shape or form of the body. The magnitude of this drag depends on the frontal area exposed. Bodies with a large cross-sectional area experience more drag compared to streamlined bodies. b. Induced drag: It is 8% of the total force. It forms vertices at the side of the vehicle and travelling downwards. The vertices in turn are caused by the aerodynamic lift of the vehicle body. c. Skin friction drag: It contributes about7%–10% of the aerodynamic drag and is caused by the friction force between boundary layer and body surface. The magnitude of skin friction drag depends on the surface area and the degree of smoothness of the surface of the body. d. Interference drag: It contributes 15% of the total drag. It includes such elements as projecting door handles and mirrors badges which project out of the normal surface of the vehicle body. e. Cooling and ventilation drag: It contributes around 10% of the total drag. With careful attention to the design of ducting in the vehicle, it is possible to reduce this value considerably and theoretically to use the energy given to air flow by the radiator to secure a positive forward force for a vehicle.

13.4 LIFT FORCES When the vehicle travels on the road, air flows around the vehicle, from the top, bottom and through the vehicle. The moving air has more restriction through the vehicle and at the bottom of the vehicle compared to the stream of the air which is flows from the upper side of the vehicle. These restrictions are due to the suspension, wheels, and exhaust systems, some extruding parts of the chassis and ground clearance of the vehicle. As the frontal area of the vehicle is subjected to airflow, the shape of the vehicle is also a contributor to the lift forces. As a result of this, the moving vehicle body develops different pressure regions. The difference in pressure between the upper and lower parts of the vehicle body develops the lift force. The magnitude of the lift force is not that much of a problem during normal running of the vehicle but it may cause serious problems at high speeds. Positive lift, i.e. higher pressure at the rear bottom of the vehicle compared to the upper side, disturbs the contact between the road and road wheel and the vehicle loses traction. Positive lift tends to increase with the square of the vehicle speed. Disturbed road holding of the vehicle may affect the stability of the vehicle. It may also cause uneven loading of the vehicle, which leads to adverse effects braking performance. The lift force also disturbs the steering

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ability of the vehicle by varying the slip angles of the front and the rear wheels due to uneven loading.

13.5 AERODYNAMIC STABILITY The handling performance of the vehicle consists of various aspects, such as high speed cornering stability, braking stability, road holding, cross wind stability, etc. During operation, the vehicle is subjected to roll, pitch and yaw moments as well as side force aerodynamic lift and drag force. Aerodynamic stability of the vehicle is controlling the adverse effects of these parameters, which affect the overall performance of the vehicle. Aerodynamic stability is especially important during high speed operations of the vehicle, and depends on various factors such as weight distribution, suspension geometry and design, wheels and the styling of the vehicle. At the time of braking at high speeds, lift of the vehicle front as well as rear axle is very important. Too little lift may lead to more responsive steering and discomfort for drivers and too much lift leads to less steering response and comfort. In case of rear axle too much lift reduces the vertical loading on the rear tyre and less lateral grip on the tyre, and high yaw. Generally, an increase in lift of the front axle reduces the rear lift and vice versa. Reduction in rear lift improves stability but reduces the steerability of the vehicle. The magnitude of changes on the front lift will be reflected by an opposite change of between 50% and 75% on the rear lift. Changes in the rear side of the car reduce the real axle lift by 0%–30%. The effect of side forces due to cross winds is also important in terms of aerodynamic stability of the vehicle. Directional changes in the wind may increases the drag and lift forces. Drag caused by exterior elements may affect the stability of the vehicle during braking and enhances yaw tendency. It is essential to reduce and avoid changes in the areas where there is sudden change in drag forces and flow separation (Figure 13.2).

13.6 CAR BODY DRAG REDUCTION Car body drag reduction is very essential in terms of fuel consumption, noiseless operation, maintenance of road holding and comfort of the driver etc. Certain techniques can be used to reduce drag.





1. Profile edge rounding and chamfering Drag and lift forces can be minimised with rounded edges and chamfers to the corners, but it can be done limited to certain range of the radius of the chamfer. 2. Bonnet shape and windscreen rake Increasing the slope of the bonnet up to 10° reduces drag forces considerably. Increasing the rake angle also reduces drag forces. But too much an increase in the rake angle affect the styling of the vehicle. 3. Roof and side panel cambering Cambering of roof and the side panels reduces drag force but up to certain extent. Excessive camber of the pan shows small reduction in the drag

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FIGURE 13.2  Aerodynamic lift.



forces but it may lead to more of the front area being exposed to air flow, thereby increasing the total drag experienced by the vehicle. 4. Rear side panel taper Tapering on inner side of the rear side panel of vehicle reduces the drag coefficient. 5. Underbody rear end upward taper Tilting on upper side under floor rear end produces a diffuser effect which will reduce the drag coefficient 6. Rear end tail extension The vehicle must have extended tails which will reduce aerodynamic drag force. 7. Underbody Roughness Air flow from the underside of the vehicle generates lift force. If the extended portions of the underbody are covered with plastic, drag force can be reduced considerably (Figure 13.3).

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FIGURE 13.3  Car body drag reduction techniques.

13.7 AERODYNAMIC LIFT CONTROL As discussed earlier, if the lift of the front axle is increased, the lift of the rear axle reduces. The ground clearance is an important parameter on which the amount of air flowing through the vehicle body depends. The lift is an important criterion of aerodynamics, which is responsible for the handling characteristics of the vehicle. A moderate lift is needed to maintain the stability of the vehicle as well as effective and equal wear of tyres. Upward force produces positive lift and downward force produces negative lift. Both lifts have certain advantages and disadvantages. There are various techniques employed to control lift of the vehicle. Underbody dams located at the rear side increase the pressure at the rear side and increase positive lift and those at the front end decrease the pressure at the front side produce adown thrust, resulting in a negative lift. Negative lift produced at the front side of the vehicle increases the rear side positive lift. The effect on control of the lift depends on the height of the dam. Wheel exposed to airflow is another parameter. As an effect of the viscosity of the flowing air and tread pattern of the tyres, air moves with the rolling of the road wheel, which gets trapped between the mudguard and the wheel, creating more pressure at the front side of the wheel compared to its rear side. It creates a differential pressure. Sufficient clearance between the wheel arch and the wheel will result in a loss in the momentum of air expelled at the backside of the wheel, which reduces the lift force. With the change in the body profile of the rear end of the vehicle, a smooth and fast continuous streamlined flow can be achieved. This produces an upward suction at the rear end. It is essential to cut this flow by providing a spoiler at the rear end to increase the local air pressure which will increase the negative lift at the rear end of the car. This will slightly increase positive lift at the front side. In the case of racing cars, it is essential to maintain proper grip between the road wheel and the tyres. To maintain the road holding of the car, the negative lift wings are incorporated at the cost of increasing the drag force.

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13.8 WIND TUNNEL Wind tunnels are used in aerodynamic science to analyse the effects of air moving around fixed objects. The wind tunnel consists of a tubular passage in which the device under examination is placed in the centre. Air is allowed to move past an object by means of a strong fan or other device. For the test specimen, aerodynamic forces, pressure distribution are calculated and other aerodynamic characteristics are plotted with the use of wind tunnel. Wind tunnels can be graded on the basis of design into open loop and closed loop.

13.8.1 Open Loop There is an intake and an exhaust in the open loop wind tunnel. There is no need for corners and long diffusers, but the power required to drive the wind tunnel is high due to the loss of energy in the out-flowing air. The open circuit wind tunnel is the simplest and most inexpensive to construct. In these tunnels, air is expelled directly to the laboratory and usually re-invested after flowing through the tube, although some tunnels use a compressed gas source instead. In addition to their low cost, open-circuit tunnels are also beneficial because they are relatively immune to temperature fluctuations and significant disruptions in the return flow, given that the volume of the laboratory is much greater than that of the tunnel (Figure 13.4).

FIGURE 13.4  Wind tunnel.

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There are two basic types of open circuit tunnels: a. Suck down b. Blower

13.8.2 Closed Loop As the name implies, closed-circuit tunnels (also called closed-return tunnels) form an enclosed loop in which the exhaust flow is directly returned to the tunnel inlet. In a closed-loop wind tunnel, the air is re-circulated to improve the efficiency of highspeed testing. These tunnels are typically larger and more difficult to build. These must be carefully built to optimise the efficiency of the return flow. These types of tunnels are operated by axial fan(s) upstream of the test section and often include multi-stage compressors, which are sometimes needed to produce trans-sonic and supersonic air speeds. Closed-circuit wind tunnels re-circulate the air and thus usually require less power to achieve a given low speed and above all promote the achievement of well-controlled in the test segment. Presently low-speed tunnels are used for research investigations of the closed-circuit category.

13.9 AERODYNAMICS OF COMMERCIAL VEHICLES Minimum fuel consumption is essential for profitable operations of the commercial vehicle fleet. In commercial vehicles like intercity buses, coaches and vans, it is essential to optimise body shape by considering the principles of aerodynamics. Generally, vehicles with a high loading capacity are used for construction and agricultural purposes, where aerodynamics becomes a secondary aspect. In the case of commercial vehicles, a larger part of the frontal area is exposed to air compared to cars. The frontal areas of a high-bodied truck, bus, light van and car are in the ratio of about 9:7:4:2 and there is too much difference between the drag coefficient of a car and a commercial vehicle. Generally, during overtaking, the speed of the commercial vehicle reduces due the effect of cross wind. Various techniques are used to minimise drag force in commercial vehicles but it is not as easy as in cars because of the cuboid or box-type structure of commercial vehicles and some legislative restrictions. As usual the rounding and provision of the sharp edges reduces drag force considerably up to a certain radius, beyond this there is that much advantages for the reduction in drag force. The slope of the front panel is also important in the reduction of drag force as an effect of flow separation observed during streamline flow for both cab roof and also in side panels. Height of the vehicle, the gap between the tractor and trailer combination, body pressure distribution and cab to trailer body height are also important parameters in aerodynamics. As the cab to trailer body height ratio increases the drag coefficient increases. There are various types of devices used for the reduction of drag, such as roof deflectors: due to the tilted roof deflector the airflows smoothly over the body surface. Roof deflectors are beneficial in the case of front air flow, but in the case of cross winds, they are not of much use. Certain other

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FIGURE 13.5  Commercial vehicle drag reduction techniques.

arrangements like baffles can be used to minimise the effect of side winds. In the case of a combination of various types of trailers attached to the tractor, may create different drag forces because of height variations. The shape, inclination, profile and the height to weight ratio of the deflector plate are very important parameters in drag reduction. When studying the effect of cross winds, it is essential to consider velocity and angle of attack with the speed of the vehicle. Another technique is to attach corner vanes on each side of the cab. This minimises the drag produced due to the air flowing around the vehicle. The corner vane is set away from the rounded vertical edges with several evenly spaced internal baffles to accommodate the gap between the cab and corner vane walls. Sealing of the gaps between the cab and trailer, providing skirting and proper loading of the vehicle are some ways to reduce drag in commercial vehicles (Figure 13.5).

13.10 AERODYNAMICS IN TWO-WHEELERS India is the second largest two-wheeler manufacture in the world, and around 80% of vehicles on Indian roads are two-wheelers. Along with fuel consumption and rider and passenger comfort, manoeuvrability, suspension travel, weight distribution, fuel capacity, luggage capacity, engine accessibility and ease of maintenance and shape of two-wheeler are also important aspects. Normally, the maximum speed of two-wheelers is about 100 km/h and weight is about 100–125 kg. At high speeds maintaining aerodynamic stability is very essential, because when at two-wheeler is passed by a heavy vehicle, its stability is disturbed, which may be dangerous for the rider. Due to this, while studying the aerodynamics of the two-wheeler, the effect of straight as well as cross winds should be treated equally.

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Frontal area of vehicle exposed to environment, includes the headlight, wheel assembly, mirrors, the cambered surface of the fuel tank, faring rider and its position are important for fuel efficiency, drag reduction as well as reduction in weight of the components. At a speed of 30 km/h the aerodynamic drag influences vehicle stability as well as power consumption. At a speed of 100 km/h, 80% of a motorcycle’s energy is spent just overcoming air resistance. In the case cars, the body is well streamlined and the driver or the passenger does not contribute in opposing the motion of the vehicle. The motorcycle is a collection of random engineered parts and a human body which together form a shape almost perfectly suited to disrupt smooth air flow. The body work of motorbikes vary from a simple plastic mudguard to fully enclosed fairing systems for drag reduction. Medium size fairing offers more in terms of weather protection and aerodynamics, compared to having bigger screen which can be hidden behind to eliminate wind blast. On most sports bikes which have a full body work, the fairing will include air scoops and ducts to direct air under pressure into the air box. Large touring fairings are designed to completely isolate the rider from weather effects allowing all day riding at high speeds in an upright and comfortable position. But they must do so without increasing drag and weight and without upsetting the handling. Fairings are often extended around and under the engine in the form of fairing side panels and belly pans, giving an enclosed racing look. These are primarily designed for aerodynamics.

SUMMARY • Vehicular aerodynamics consists of the interaction of the vehicle body with the air flow and its effects on performance, especially vehicular thermodynamics, passenger comfort and handling characteristics of the vehicle. • Drag and lift forces are the two parameters related to aerodynamics. Drag affects performance and lift affects handling of the vehicle. • Computational fluid dynamics and wind tunnel testing can be utilised for the optimisation of the different aerodynamic parameters. • Skin friction drag and pressure or form drags are the main components of drag forces. • Provision of around shape, chamfering, cambering roof, door panels, covering underbody components are some techniques used to reduce drag forces. • Two-wheeler aerodynamics is more complex compared to that in other vehicles.

MULTIPLE-CHOICE QUESTIONS

1. Drag force is associated with a. Fuel consumption b. Ride characteristics of the vehicle c. Handling characteristics of the vehicle d. None of the above

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2. Lift force is associated with a. Fuel consumption b. Ride characteristics of the vehicle c. Handling characteristics of the vehicle d. None of the above 3. Study of aerodynamics is essential because of a. Reduction in fuel consumption b. Thermodynamics of the vehicle c. Improvement in the handling characteristics of the vehicle d. All of the above 4. Drag force can be minimised with a. Chamfering at the corners b. Cambering the roof panels and side panels c. Providing a rake angle to the windscreen d. All of the above

REVIEW QUESTIONS • • • •

Describe the various methods used for drag reduction in cars. Describe the importance of an aerodynamic study. Describe two-wheeler aerodynamics. What are the various techniques used for the reduction of drag in commercial vehicles. • How does aerodynamic lift affect vehicle performance? • Why optimisation of vehicular shapes is important? Answers to MCQs: (1) a (2) c (3) d (4) d

14

Battery Electric, Hybrid Electric, and Fuel Cell Vehicles

OUTCOME Learning Objectives • • • •

Requirements and growth drivers of electromobility Components/systems of BEVs, HEVs, FCVs Various types of fuel cells Developments in BEV, HEV, FCV technology.

14.1 INTRODUCTION Vehicular density in the world is continuously increasing as a result of enhancement of quality of life, increasing population and transportation need. The share of energy consumption of the transportation sector is far more than other sectors. It is essential to reduce the consequences of this scenario, such as climate crisis, emissions-related health problems, dependability on another country for fossil fuels and many other contributing factors. Various survey reports and studies say that nearly 333 million tons of carbon dioxide is emitted by transportation sector alone every year, which is approximately 20% of the world’s total sources of carbon dioxide. About 4.6 million people die each year from causes directly attributed to air pollution, which is more than those who die from automobile accidents, noise pollution, mental health issues, a trial fibrillation, heart failure and stroke. Conventional IC engine vehicles are part of these. Majority of the countries across the globe have chosen electromobility as a new mode of transportation. Electromobility has certain advantages such as reduction in air and noise pollution, lower running cost of the vehicle and less maintenance and lubrication requirements due to fewer parts, which ultimately reduces economical losses due to the downtime.

14.2 GENERAL LAYOUT OF A BATTERY ELECTRIC VEHICLE The journey of the electrical vehicle (EV) began in1881, the first EV was built by Frenchman Gustave Trouve, which was a tricycle which operated on 0.1 HP motor and lead acid battery. As regards to the commercialisation of EVs, a lot of research has been done in the area of new batter chemistry , weight reduction through use of new and advanced materials, advanced drive train systems, infrastructural developments 243

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FIGURE 14.1  Layout of battery-operated vehicles.

and several other factors of its utilisation. Initial developments in electrical vehicles were conversion of existing ICE vehicles into the electrical vehicles. The ICE and the fuel tank were replaced by battery and electric motor for conversion to electrical vehicles. However, more weight, issues in the interaction between electrical components, flexibility and poor performance led it to fade out. Since then, there have been drastic changes in electric vehicles in the area of performance build up, battery chemistry for the enhancement of range extension, charging technology and components developments as a result of the need for clean mobility across the world. But basic research states that there is still scope for further developments in EVs to compete with liquid fuel engines. Battery-operated electric vehicles are also called pure electric vehicles. They consist of various energy storage systems, power train architecture, etc. The layout of EV systems is as follows (Figure 14.1).

14.3 BASIC SYSTEMS OF BATTERY ELECTRIC VEHICLES Auxiliary battery: Different types of vehicle accessories like lightning, multimedia, etc. are operated with the help of an auxiliary battery (12V) incorporated in the vehicle. Charging port: The charging port of the vehicle is used to connect to external power supply to charge the traction battery pack. DC/DC converter: The vehicle accessories and the auxiliary battery require a lower voltage. This device is used for conversion from higher to lower DC power. Electric traction motor: With the help of the electrical energy from the traction battery pack, this electric motor drives the vehicle’s wheels. Some vehicles use motor generators that perform both the drive and regeneration functions. Induction, switched reluctance and permanent magnet (PM) brushless motors are used in EVs. Onboard charger: This is used to charge the traction motor; there are various types of chargers according to time required for charging the battery. Power electronics controller: This unit controls the flow of electrical energy delivered by the traction battery, controlling the speed of the electric traction motor and the torque it produces as per the requirement.

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Battery management system: This system plays two important roles, first is maintaining the health of the battery, i.e. the ability of the battery to deliver the specific power. Secondly it maintains a proper operating temperature of the engine, electric motor, power electronics and other components for efficient performance. Traction battery pack: This works as an energy storage device for the EV. The stored energy can be utilised for the propulsion of the vehicle. The battery is the essential component of the battery-operated vehicle. Battery chemistry is an important factor in terms of range extension and battery life and safety. There are various battery chemistries available, such as lithium-ion batteries. Transmission system: With the help of the transmission architecture, the mechanical power can be transmitted to the road wheel.

14.4 GENERAL LAYOUT OF HYBRID ELECTRIC VEHICLES Hybrid vehicles have a very old history in automotive development. Hybrid vehicles have more than one energy source. In hybrid electric vehicles (HEVs), one source of power is battery and another is ICE. The advantages of HEV technology are range extension, fuel economy, low pollution, higher efficiency and best utilisation of power as per the operating conditions and traction requirement of the vehicle. According to torque management, energy management and electric propulsion, the hybrid vehicle technology can be classified as follows: • Stop-start: When the vehicle is stopped for a short time, such as at a traffic signal or other operating conditions, there is no torque requirement, as this technology stops the engine and starts whenever required. • Mild hybrid: It provides limited boosting and power regeneration with the stop-start feature. • Medium hybrid: There is increasing micro hybrid capability and electric assistance which minimises the load on the engine, which in turn allows downsizing of the engine. • Full hybrid: This provides a limited distance drive as a pure EV. • Plug-in HEVs (PHEV): These vehicle have the capability to be recharged through a mains supply with the help of a socket. • Extended range EV: This is primarily an EV with an onboard electricity generator which gives an extended range of power. • Kinetic hybrid systems: These high power density devices are used to recover and re-use substantial braking and coast-down energy.

14.5 BASIC SYSTEMS OF HEVs Generally HEVs are classified into four categories: series hybrids, parallel hybrids, series-parallel hybrids and complex hybrids, as per the arrangement of the mechanical and electrical components. In the series hybrid configuration, an ICE is mechanically coupled with an electric generator and the generator is connected to the electric motor and an electrochemical battery pack through a power electronic converter.

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In a  parallel hybrid configuration, both the engine and electric motor are connected to the drive shaft. It consists two clutches. The power is supplied by the engine, the traction motor or both. The ICE and the electric motor are connected in parallel to deliver power to the wheel. In the series and parallel configuration, advantages of both the series and parallel configuration can be achieved by additional mechanical link and an additional generator. In the complex hybrid configuration, the axles are driven separately, and there is no mechanical contact between them. This bidirectional motion can be achieved with the help of this configuration. The basic system of HEVs is the prime mover or ICE. This is the main energy storage device for HEVs, it may be a spark ignition, a compression ignition or a fuel cell. The size of the engine depends on application requirements, emission, fuel economy and availability. An HEV consists of the following systems/ components: Battery (auxiliary): In an electric drive vehicle, the auxiliary battery provides electricity to start the car before the traction battery is engaged and also powers all vehicle accessories. The auxiliary battery is about 12 V. DC/DC converter: The vehicle accessories and the auxiliary battery require a lower voltage. This device is used for conversion from higher to lower DC power. Electric generator: In some vehicles, an electric generator is used for the ­generation of the energy for propulsion of the vehicle. It also generates energy from a regenerative braking system. Electric traction motor: Traction motors are used to propel the vehicle. Power electronics controller:  This unit controls the speed of the electric ­traction motor and the torque it produces. Traction battery pack:  This works as an energy-storage device for the EV. The stored energy can be utilised for the propulsion of the vehicle. The battery is the essential component of a battery operated vehicle. Battery chemistry is an important factor in terms of range extension and battery life and safety. There are various battery chemistries available, such as lithiumion batteries. Transmission (electric): The transmission transfers mechanical power from the electric traction motor to drive the wheels. Electrical continuously variable transmission (ECVT) and power split transmission (PST) are used for transmission in HEVs. It consists of more than two planetary gear sets, which provide an additional mechanical power path, so that the electric motor/generator can directly power. (Figure 14.2).

14.6 OPERATION AND TYPES OF FUEL CELL VEHICLES A fuel cell consist two electrodes located on either side of the electrolyte. It converts chemical energy into electrical energy by a combination of hydrogen and oxygen. Hydrogen is supplied from the hydrogen storage or it can be formed by the fuel

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FIGURE 14.2  Layout of hybrid electric vehicles.

reforming process. During the chemical process, hydrogen atoms give up electrons at the anode and become hydrogen ions in the electrolyte, and the electrons released at anode move to the cathode through the external circuit. These electrons can be diverted for the generation of power, which is used to drive the traction motor. This chemical process is called electrolysis. At the cathode the hydrogen ions combine with oxygen molecules to produce heat and water. There are various parameters, such as types of chemical reactions, catalysts required, operating temperature, fuel required, etc. There is a continuous development in the fuel cell technology for better performance. According to the type of electrolyte material, fuel cells can be classified as follows.

14.6.1 Polymer Electrolyte Membrane Fuel Cells (PEMFCS) This type of fuel cell consists of a platinum catalyst with a thin, permeable polymer electrolyte sheet and porous carbon electrodes. It is widely used in various applications like passenger cars and buses. The main feature of this fuel cell is low operating temperature, faster start-up time, higher power density, lower weight. Use of solid and flexible electrolyte avoids the issue of the leakage. But there are certain limitations to this type of fuel cell, such as rare availability of platinum, which leads to high cost. Also, platinum is more prone to CO poisoning, so requires additional CO-reducing reactors. It requires a certain amount of water for functioning, but if the membrane gets too wet or too dry it will affect the efficiency as an effect of polarisation.

14.6.2 Direct Methanol Fuel Cells (DMFCs) Direct-methanol fuel cells  or  DMFCs  are a subcategory of  proton-exchange fuel cells  in which  methanol  is used as the fuel. Their main advantage is the ease of transport of methanol, energy-dense yet reasonably stable liquid at all environmental conditions. The direct methanol fuel cell is a relatively new member of the fuel cell  family. It is similar to the polymer  electrolyte  membrane (PEM) cell in that they both use a polymer membrane as the electrolyte.  Since DMFCs has lower efficiency this type of fuel cell gives high specific energy density in some vehicular

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applications. This is a subtype of PEMFCs in which instead of hydrogen, pure methanol is used with steam and fed to fuel cell’s anode. The use of methanol has no issues with storage and transportation. Compared to PEMFCs, DMFCs consist of a thicker membrane and high-density catalysts. Slow dynamic behaviour, water management, and high CO2 generation compared to normal and petrol engines are some issues related to this type of fuel cell.

14.6.3 Alkaline Fuel Cells (AFCs) Low cost, high performance, reasonable efficiency and lower working temperatures are the important features of this type of fuel cell. AFCs uses potassium hydroxide (alkaline) solution as the electrolyte. For electric vehicle application, variety of nanoparticles are used as a catalyst at the anode and cathode. AFCs have certain issues, such as leakage of potassium hydroxide, which is highly corrosive, requirement of pure oxygen because even a small amount of CO2 can disrupts function; complicated structure, and low durability of metals.

14.6.4 Phosphoric Acid Fuel Cells (PAFCs) This fuel cell consists of liquid phosphoric acid as the electrolyte, porous carbon electrodes and platinum as the catalyst. It has very less efficiency when used for electricity generation but in the case of co-generation of electricity and heat, its efficiency is more than 85%. At the same weight and volume it has less power density compared to other types of fuel cells.

14.6.5 Molten Carbonate Fuel Cells (MCFCs) Instead of pure hydrogen, this type of fuel cells uses hydrocarbon. A high-temperature operation is used to convert hydrocarbons into hydrogen, which reduces the overall cost of the fuel cell. Another important advantage of this type of fuel cell is that it is not sensitive to CO or CO2 poisoning. It uses a mixture of molten carbonate source as catalysts. Decreased life of the components due to the corrosive nature of the electrolyte, high operating temperature which creates the problem of start-stop and it requires the provision for heat retention and safety, which are the limitations of these fuel cells.

14.6.6 Solid Oxide Fuel Cells (SOFCs) A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer startup times and mechanical and chemical compatibility issues. These fuel cells consist of zirconium as an electrolyte which is a non-porous material. It operates at very high

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temperatures, which eliminates the need for a precious metal catalyst, as well as it allows for reforms in the fuel and can be used in the variety of the fuels. There is no issue of the CO or CO2poisoning.Durability and requirement for thermal shielding are the key issues related to this type of fuel cell.

14.7 GENERAL LAYOUT OF FUEL CELL VEHICLES Dependence on battery as the only power source has its limitations and affects range extension, charging time and charging infrastructure. Therefore the application of fuel cells in EVs continuously increases. FCVs uses a fuel cell to generate electricity by using hydrogen fuels generated through certain electro-chemical reactions. Like in battery-operated vehicles, fuel cells cannot store energy. Whatever power is developed by the fuel cell is used directly for propulsion though traction motors, or it can be stored in a separate onboard storage system for further use. An important advantage of the FCV is its higher extended range of operation compared to battery operated vehicles. The range directly depends on the amount of hydrogen available in the tank. The size of the fuel cell depends on the transmission requirements of the vehicle. There are various advantages of the FCVs compared to battery-operated vehicles, such as longer life, no need for a charging infrastructure and charging time, etc. But as FCVs are operated on hydrogen fuel, storage and transportation is more challenging. Storage, infrastructure reliability, safety and durability are some limiting factors of FCVs. They consists of fuel cells, energy storage device or battery pack, controller traction motors, etc. The functions of these components are the same as in the case of electric or hybrid vehicles (Figure 14.3).

14.8 CHARACTERISTICS OF BEVs, HEVs AND FCVs Various characteristics are essential for optimum performance in terms of maintenance and cost considerations depending on type of application in BEVs. HEVs and FCVs are the integration of various mechanical, electrical and electronic c­ omponents.

FIGURE 14.3  Layout of fuel cell vehicles.

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Optimum performance will depend on the proper synchronisation of the various components in the various domains like energy storage, power train technologies, etc. The various characteristics of the BEVs, HEVs and FCVs are as follows.

Characteristics

BEV

Drive given by

Electric motor

Energy storage device

Battery

Energy source Infrastructure required Features

Electrical energy Charging

Limitations/issues

No emission Energy efficient High initial cost Low operating cost Less capability of the battery Charging infrastructure Cost of battery Battery chemistry

HEV Electric motor ICE • Battery • Ultra capacitor • ICE generating unit Gasoline Electric grid charging facilities Less emission High fuel economy Longer rage of the battery (depends on the type of hybridisation) Higher cost Control optimisation and combined energy management Battery sizing

FCV Electric motor Fuel cells Need battery/ultra-capacitor to enhance power density Hydrogen Hydrogen production and transportation infrastructure Ultra-low emission High energy efficiency High cost

Hydrogen storage and structure In some cases requires a heating shield

14.9 CURRENT ADVANCEMENTS IN BEV, HEV AND FCV TECHNOLOGY There is widespread research in the area of new battery chemistry to enhance power density, which is suited for various vehicles as per applications, range extension, battery management system, power train configuration, smarter energy systems and their management, materials, combinations of the various technologies .These technologies directly affect the electromobility market. As regards battery chemistry, there is development of the second- and third-generation Li-Ion batteries. In the second-generation battery technology, a higher voltage capacity cathode material can be utilised. In the third generation, the power densities of batteries are three to five times that of Li-ion batteries. Advanced materials can be used as electrolyte in these batteries. Due to the upcoming compact and high-density batteries, the thermal loads will continuously increase, and therefore various cooling systems, such as direct two-phase refrigerant cooling with PCM, heat pipe and thermoelectric systems, are made available. In the case of FCV technology, research is focused on the use of new catalyst materials, effect of atmospheric impurities on performance degradation, chemical degradation of the electrolyte membrane, water ­content ­optimisation, etc.

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SUMMARY • Electromobility has certain advantages, such as reduction in air and noise pollution, lower running cost of the vehicle and less maintenance and lubrication requirements due to fewer parts, which ultimately reduces economical losses due to downtime. • HEVs are classified into four categories: series hybrids, parallel hybrids, series-parallel hybrids, and complex hybrids, as per the arrangement of the mechanical and electrical components. • There are various advantages of FCVs compared to BEVs, such as longer life, no need for a charging infrastructure or charging time, etc. • In the case of FCV technology, research is focused on the use of new catalyst materials, effect of atmospheric impurities on performance degradation, chemical degradation of the electrolyte membrane, water content optimisation, etc.

MULTIPLE-CHOICE QUESTIONS 1. The growth driver of electromobility is a. Increasing pollution b. Advanced technologies related to electromobility c. Lower running cost of the vehicles d. All of the above 2. The major challenge in complete electric vehicles is a. Capability of the battery b. Body material c. Drivetrain d. None of the above 3. Important elements of EVs are a. Traction motor b. DC convertor c. BMS d. All of the above 4. HEV drive is given by a. Electric motor b. ICE c. Both a and b d. None of the above

REVIEW QUESTIONS • • • •

Describe various growth drivers of electromobility in India. Describe the layout of the battery operated vehicle What are the important characteristics of hybrid vehicles? What are the recent trends in battery technology?

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• Describe functions of the various battery elements. • Describe various types of fuel cells used in vehicles. • Describe the features of BEV, HEV and FCV. Answers to MCQs: (1) d (2) a (3) d (4) c

Automotive Systems

15

Vehicle Maintenance Practices

OUTCOME Learning Objectives • • • • •

Necessity of maintenance Different types of the vehicle maintenance Various types of documents used in vehicle maintenance Advanced techniques and tools used for maintenance Recent trends in vehicular maintenance

15.1 INTRODUCTION Vehicular maintenance can be defined as the process of keeping the vehicle in useable condition by checking or repairing it on a regular basis and whenever required, or the work that is carried out to maintain the vehicle in order to enable its continued use and function, above the minimum acceptable level of performance, over its design service life, without unforeseen renewal or major repair activities. Various activities are required to maintain the vehicle in working condition with an acceptable level of performance. It includes observations and inspections, lubrication, replacement of components, adjustments, setting the positions, reconditioning, etc. There are various types of maintenance based on various aspects. Regular maintenance activities are essential for the performance of the vehicle, including safety, comfort and economy.

15.2 NECESSITY OF MAINTENANCE The vehicular population of the world is continuously increasing, and various technologies are incorporated in vehicles to optimise performance. Continuous use of a vehicle deteriorates its performance. This deterioration is due to friction, wear, temperature, weather conditions, method of operating the vehicle, etc. Maintenance activities can restore the performance of the vehicle in terms of economy, safety, reliability, comfort and overall capability. It also ensures the expected life of the systems and components. Maintenance activities ensure the following: • Efficient operation and performance enhancement: Continuous use of the vehicle affects performance and effectiveness in terms of cost of operation, comfort level, etc. Maintenance activities will maintain the expected level of performance or restore efficient operation.

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• Physical integrity and reduction in unplanned stoppages: The vehicle is an assembly of various components, systems and subsystems. These systems may be mechanical, electrical, electronic, etc. These systems are integrated with each other for intended and smooth functioning. Proper maintenance activities ensure the integrity of the components. • Reduction in operating cost: Regular maintenance reduces the operating cost of the vehicle. • Risk management: Regular maintenance activity can keep the vehicle at a safe operating condition and it also ensures the comfort of the occupants. Regular maintenance will enhances the reliability and life-span of the vehicle. • Aesthetic preservation: Maintenance activities related to the vehicle body can maintain the aesthetics. Preservation of the aesthetics may increase the reselling price of the vehicle.

15.3 TYPES OF MAINTENANCE We know that regular maintenance and repair result inefficient vehicle operation as per requirements. The types of vehicle maintenance are as follows: A. Preventive maintenance 1. Scheduled preventive maintenance 2. Condition-based preventive maintenance a. Predictive maintenance b. Proactive maintenance B. Breakdown maintenance

15.3.1 Preventive Maintenance Maintenance performed to prevent possible future breakdown or other vehicle trouble on the road is called preventive maintenance. The policy here is “prevention is better than cure”. The intensionis to identify and eliminate unplanned stoppages of the vehicle like breakdowns and accidents due to failure of various systems and components and reduce repair cost, unavailability of the vehicle, etc. Routine or daily maintenance is a type of preventive maintenance. Daily maintenance is needed to keep the vehicle in proper working condition. Tyre inflation, battery, brakes, clutch, smoke colour, steering system, ignition system and lights are checked in daily maintenance. 15.3.1.1 Scheduled Preventive Maintenance Preventive maintenance can be planned or scheduled beforehand. It includes predefined inspections and replacements of certain elements which maybe the cause of major accidents. The critical components, systems and subsystems can be inspected at regular intervals. It is also called periodic maintenance or operative maintenance. It is the attention provided to the vehicle after it being in operation for a specified time or distance covered. This maintenance may be done daily, weekly, quarterly, yearly or after covering every 500, 1,000, 2,000, 4,000 or 8,000 km of running. In

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garages, this work is done on the basis of prescribed schedules so as to avoid road failures and to minimise breakdown during use. 15.3.1.2 Condition-Based Preventive Maintenance Technical condition-based maintenance is gaining importance since past decades with the expansion of technical diagnostics. It is preventive maintenance comprising of monitoring performance or parameters and of consequent measures. Its main benefit resides in consistent removal of failures. Worn out parts and parts or whole assemblies at risk of failure are repaired or replaced optimally in advance. 15.3.1.3 Predictive Maintenance Predictive maintenance is a technique to predict the future failure point of a vehicle component, so that the component can be replaced, based on a plan, just before it fails. Thus, vehicle downtime is minimized and the component/vehicle lifetime is maximized. This is condition-based maintenance conducted on the basis of a forecast obtained from the study and evaluation of important deterioration parameters. Action shall be taken on an object only if it is scientifically and organisationally adequately acceptable to optimise the technological reliability of the essential component and, at the same time, an unintended accident has been avoided. In other words, this maintenance is based on the declaration that it is only necessary to fix an element when it is indispensable. Maintenance itself is based on regular assessment of the technical situation. Maintenance processes applied to the vehicle provide details on changes in the mechanical condition of the components being controlled. This information is processed with the intention of estimating the remaining durability and thus beginning the process of technical remedial action. The use of specialised tools designed to collect and evaluate information is needed for monitoring the signs of harm development and condition monitoring of vehicles. Such methods use technical diagnosis systems and the vehicle shall be continuously, or at least regularly, tracked and evaluated. 15.3.1.4 Proactive Maintenance Proactive maintenance is another higher level of maintenance. This is based solely on predictive maintenance, which it further enhances such that its basis is the use of more advanced scientific diagnostics. This is essentially the top-of-the-line variant of predictive maintenance focused on the current state of the system being run. Any good preventive maintenance programme has the following advantages:

a. Reduction in unplanned stoppages and increase in reliability of the vehicle b. Enhancement in the safety c. Reduction in operating cost of the vehicle d. Increasing the availability of the vehicle Disadvantages • In the case of scheduled-based maintenance, some components may be replaced unnecessarily. • Economic losses due to unavailability of the vehicle and parts replacements.

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15.3.2 Breakdown Maintenance In breakdown maintenance, attention is given to a vehicle only when it is completely immobilised due to faults during running. A breakdown is the impossibility of a material, structure or system to perform the task it was defined for in a safe and orderly manner. These faults are starting difficulties, puncture, electrical faults, carburettors and fuel supply faults, overheating, fan beltings, breakage and accidents, etc. Generally, the basic causes of such a maintenance are as follows: • • • • • • • • • • •

Excessive contamination of the lubricating oil Leakage of oil Short circuits Improper lubrication Chemical instability in the fluid Physical instability in the fluid Cavitation Instability in the temperature of the fluid Severe conditions of wear and tear Excessive heating of the components Deformation or fracture of the components

The various types of breakdown maintenance are as follows: • Catastrophe breakdown • A catastrophic failure is a sudden and total failure from which recovery is impossible.  The term is most commonly used for structural failures, but has often been extended to many other disciplines in which total and irrecoverable loss occurs. Catastrophe breakdown is a condition of sudden, complete interruption of operations and total deterioration of functions of vehicle. • Sudden breakdown It is a condition of accelerated deterioration of both the material and performance, which translates into partial weakening of functions. • Imminent breakdown A perceivable condition of deterioration of the material, in the presence of serious deterioration of performance is called as imminent breakdown. • Incipient breakdown A condition in which the use of appropriate means of detection permits the identification of first signs of deterioration, without the user being aware of any modification in the performance of the machine is said to be incipient breakdown. • Conditional breakdown A pre-alarm in which the deterioration has not yet occurred, either in the material or in performance, but it is such that, if the situation persists, a functional breakdown will inevitably occur.

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Among these, catastrophic breakdown is not in the operator’s control. The part can be removed, repaired or replaced as per the usual practice of maintenance.

15.4 PROCEDURE AND METHODOLOGIES ADOPTED Vehicular maintenance procedure is a structured and well-organised set of written instructions associated with disassembly, assembly and precautionary measures. It is the systematic method of providing solutions to minor stoppages without affecting the overall efficiency or impacting on related components or subsystems. There are certain advantages of a maintenance procedure, such as reduction in down time, maximum safety of the vehicle within its operating range, reliability and assurance of maintaining vehicle capability and life-span. Implementation of standard maintenance procedures enhances the quality of service and directly helps in increasing the customer satisfaction index. Maintenance procedures can be prepared incoordination with various authorities like manufactures, designers, suppliers of equipment and tools, etc. The procedures must be technically accurate, verified and timely upgraded and validated. Proper utilisation and implementation of this procedure are part of the methodologies in quality maintenance practices. Various methodologies can be adopted; craftsman training is one of them. Customer satisfaction is an important concern in vehicle maintenance. To achieve the set targets of the quality parameters of maintenance and repair activities, some methodologies need to be implemented, as follows: • Recruitment of skilled manpower The vehicle is an integration of mechanics, electronics and IT with various advanced technologies. Effective maintenance can be achieved by recruiting sufficiently skilled personnel through a proper screening process to ensure they have the required knowledge in these areas. • Staff training There is continuous development in vehicle technology, and it is necessary to enhance the skill and confidence of the service personnel. Maintenance procedures and its related skills must be transferred in maintenance personnel with sufficient seriousness. • Effective implementation of the maintenance schedule This is essential because it is directly related to inventory management, energy consumption, overtime, workload issues and finally on the reliability of the firm. • Regular up gradation of machineries and their effective use Machines can be upgraded as per the standard norms and latest versions of the software with proper data security provisions and continuous monitoring for their effective utilisation. Provisions should also be made for technical support. • Overall coordination Overall coordination of all the staff for planning and implementation of the policies can be achieved by increasing staff morale by providing incentives and reducing absentee rate, proper distribution of tasks, etc.

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Automotive Systems

• Use of IoT-based coordinating systems • The IoT allows physical objects to communicate in real-world to exchange data for achieving coordinated service composition module. These entities became smarter by implementing related technologies like cloud computational technology, networking technology, data acquisition technology,  IoT  protocol and other applicability. Overall activities can be ­managed with the help of various commercial software available in ­automotive sector.

15.5 MAINTENANCE DOCUMENTATION The following documents can be maintained in the service station or the workshop:

1. Vendor service work order: This contains information about the vehicle and its owner, the work to be performed, the list of spare parts and their prices and labour costs incurred. 2. History sheet: This is useful for understanding how much money is spent on repairs. While maintaining the history sheet it is essential that the maintenance column should be filled in with a remark stating the reason for maintenance control. History sheet provides the complete information of past vehicle repairs and their reasons. 3. Activity file: This is useful for reviewing unpaid jobs, identification of warranty claims, analysis of accident liability and injury reporting, type of repair and equipment used. 4. Instruction manual for the maintenance of the vehicle: This contains directions useful for the maintenance of the vehicle. It sets out the specifics, data, limits and guidelines required for maintenance work. 5. Procurement register: This is used to determine the need for replacement parts. 6. Defect register: Defective goods are recorded in this document.

15.6 ADVANCED TECHNIQUES AND TOOLS USED There are wider uses of mechatronics and advanced technologies and their integration in vehicles. Therefore, the aspects of maintenance of such systems are different from the regular mechanical maintenance practices followed in the routine maintenance of vehicles. For integrated systems, correct diagnosis is very important. Continuous monitoring and analysis of the data is an important technique used in the maintenance of vehicles. This maintenance procedure is focused on the following techniques: • Visual inspection for potential signs of fatigue, welding faults, misalignment, etc. • Inspection of interaction with friction, flow, temperature and speed verification requirements, which take into account values similar to design values

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• Monitoring of vibration and noise • Monitoring of debris from use

15.6.1 Modern Tools Used 15.6.1.1 On-Board Diagnostics On-board diagnostics (OBD) is a collection of regulations, software and hardware for the specific purpose of monitoring powertrain components/systems whose functionality has an effect on the amount of toxic emissions of exhaust gases. In other words, if a particular powertrain feature contributes to increased levels of toxic exhaust emissions in the event of a defect/failure; it must be controlled by OBD. The majority of vehicles currently in use are OBD compliant, which means that they have on-board inspection features for devices and modules that have an effect on the level of harmful exhaust emissions. There are currently three main types of diagnostic instruments (scantools, testers) in the market: 15.6.1.2 Handheld It’s a stand-alone device that doesn’t need to be driven from an external source because it uses OBD power supply pins. It can be used regardless of the vehicle type, as long as both are OBD2 compliant. The benefit of the handheld scan tool is that it is compact and easy to use, just “plug and play”. 15.6.1.3 PC/Laptop with Scan Tool ScanTool is diagnostic software for OBD compliant vehicles and a PC/laptop, which has this software essentially becomes a device that uses an external interface to connect to the OBD port of the car. The main drawback compared to the portable one is that you need a PC/laptop with an operating system to install and use diagnostic tools. Therefore, it still needs an OBD adapter (also called an “interface”), which converts the data between the computer and the vehicle to the correct format. The link between the OBD adapter and the laptop can be either serial (USB orRS-232) or wireless (Bluetooth). The benefit of this diagnostic tool is mainly related to the memory and data processing power of the laptop/PC. Huge amounts of data can be logged in and stored; data plots and other functions (acceleration time, fuel consumption, etc.) can be incorporated into the main program. 15.6.1.4 Mobile Device (Phone or Tablet) Application This third type, a mobile device scantool, is a combination of the handheld and the PC/laptop-based solutions. It still needs an OBD adapter between the mobile device and the car, but it has the benefit of being compact. Most of these devices use a wireless connection (Bluetooth) for the OBD adapter. Irrespective of the type of diagnostic tool, OBD modes of operation (also known as diagnostic services) describe how the data is requested from the vehicle and how the vehicle responds to the request. You can see the OBD modes of operation as the

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Automotive Systems

FIGURE 15.1  OBD schematic.

description of the “language” to be used by all parties (scantool and vehicle) when requesting and sending data (Figure 15.1). Diagnosis of the repair/service treatment is done according to the following standards: • ISO 15031-5: Road vehicles – Communication between vehicle and external equipment for emissions-related diagnostics, Part 5: Emissions-related diagnostic services. • SAE J1979: E/E Diagnostic Test Modes

15.7 RECENT TRENDS IN ROUTINE MAINTENANCE Recent trends in routine maintenance are associated with the safety, economy, energy saving and optimistic performance of the vehicle and ultimately customer satisfaction. The competitiveness of the vehicle manufacturer depends on these factors. Vehicles manufactured nowadays are more reliable than even before. New technologies like digitisation, automation, electrification, etc. incorporated in the vehicle are more reliable and requires less maintenance. Due to various systems with advanced technologies a lot of routine maintenance activities have been reduced. In the case of change in lubricants and coolant technologies, there is reduction in the frequency of periodic inspection. Synthetic engine oils are developed for long-lasting use; the vehicle can travel thousands of miles or even function for years before the need for oil change arises. Whatever components and the systems used in vehicles now have high reliability and longer life compared to olden days. Widespread use of information and communication technology in vehicles is continuously increasing. Various software are apart of vehicles, so regular up gradation of software is part of routine maintenance. Another aspect of OBD is the ability to collect huge vehicle data. Various indicators and warning signals are available right on the dashboard.

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Advanced notifications can be received through these indicators on distance travelled and remaining hours of function. Based on the seriousness of failure, cost consideration and availability of time the maintenance of vehicle can be carried out. The current trend in maintenance is proactive maintenance rather than reactive maintenance. Reactive maintenance is carried out when the operator reports a problem in the vehicle. But the recent trend is proactive diagnosis and replacement of parts based on risk level. The risk level can be analysed by the vehicle itself on the basis of stresses developed and the way of driving. Proactive maintenance includes the following activities: • Monitoring of key indicative parameters of system performance (i.e. operating conditions relative to primary causes of failure), e.g. the degree of contamination of lubricating fluids • Determination of threshold values, i.e. maximum appropriate values for each parameter, e.g. the average level of contamination • The detection and analysis of any abnormal values of certain main parameters, which signify a certain instability in the operating conditions, such as the degree of contamination above a threshold • The specification of the means and methods to be used to correct the primary causes of failure and to restore stability to the system, e.g. improving the filtering system With the recent systematic and smart routine maintenance practices, there is reduction in unscheduled, catastrophic maintenance, unnecessary maintenance carried out based incorrect diagnosis and guesswork. The trend of maintenance will be according to data and information urgency of the routine maintenance. Widespread use of IoT helps in deciding the required combination of parts and service and telematics provides real-time data. All this changes the overall scenario of routine maintenance of vehicles.

SUMMARY • Regular maintenance activities are essential for the performance, safety, comfort and economy of vehicles. • Planned and unplanned maintenance are the important types of the maintenance. • Maintenance performed to prevent possible future breakdown or other ­vehicle trouble on the road is called preventive maintenance. • There are certain advantages of a maintenance procedure, such as reduction in down time, maximum safety of the vehicle within its operating range, reliability and assurance of maintaining vehicle capability and life-span. • Recent trends in routine maintenance is associated with the safety, economy, energy saving and optimistic performance of the vehicle and ultimately customer satisfaction. • There is widespread use of telematics, communication technologies and OBDs in the routine maintenance vehicles.

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MULTIPLE-CHOICE QUESTIONS

1. Vehicular maintenance is essential to a. Enhance fuel economy b. Reduce unplanned maintenance c. Enhance the safety of the passenger d. All of the above 2. Recent trends in routine maintenance are associated with a. Safety b. Economy c. Optimistic performance d. All of the above 3. The different types of maintenances are a. Preventive maintenance b. Breakdown maintenance c. Periodic maintenance d. All of the above 4. Unplanned breakdowns can be reduced by a. Preventive maintenance b. Time-based maintenance c. Breakdown maintenance d. Both a and b

REVIEW QUESTIONS • • • • •

Define the term vehicular maintenance. Describe advanced techniques used in vehicular maintenance. Describe the various types of maintenance. Describe the advantages of the preventive maintenance Describe recent trends in vehicular routine maintenance.

Answers to MCQs:(1)d(2)d(3)d(4)d

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Index accumulators 119, 122, 123 automatic transmission 17, 91, 111, 114, 115, 117, 118, 119, 121 Ackerman 199, 197, 207 adaptive suspension system 154, 155, 156 speed sensitive 205 air bag 207 steering wheel 9, 11, 20, 28, 117, 141, 196, 201, 204, 207, 216 air brakes 167, 169 electronically controlled 52, 60, 78, 122, 154, 205 principles 40, 61, 67, 71 system actuation 168 air cleaner 51, 71, 75, 78 silencer 71 air conditioning systems 17, 18 passenger cars 6, 117, 125, 142, 151, 178, 213, 249 air cooling 70 air suspension 146, 147 suspension springs 156 alternative fuels 5 basic components 117 types of system 39 tyres 25, 26, 33, 97, 140 arrangement of engine cylinders 43 in-line 44, 58, 72 automatic transaxles 118 continuously variable 119, 246 torque converter 111, 118, 119 axles 125, 127, 129, 131, 132, 133, 134, 135, 136, 142, 145 balancing 211, 212, 215, 216, 229 crankshaft 41, 42, 43 fluid coupling 111, 112, 113, 114 propeller shaft 26, 27, 34, 103, 125, 126 road wheels 132, 134, 136, 141, 162, 217 ball joints 200 steering and suspension 18 lubrication and sealing 95, 107 battery electric vehicles 244 brake drums 168 brake fluids 20 geometry 77, 132, 141, 172, 211, 212, 226, 234 carburettors 50, 51, 52 cold starting 48 correction 196, 216

electronically controlled 52, 60, 78, 122, 154, 156 fixed-choke 51 forced induction 75 mixing chamber 52 mixture strength 51, 52 multiple 52 variable-choke 51 chassis frame, commercial vehicles 3, 12, 47, 91, 97, 107, 119 clutches 83, 118, 119, 206 centrifugally operated 91 diaphragm spring 90 direct release 46 friction linings 87 manual transmission 95, 107, 111, 117, 121, 122 multiplate 85 release bearings 90 combustion chambers 59 common rail 57, 58 connecting rod 18, 27, 40, 41, 42, 64 constant velocity 126, 127, 128, 129 double Hooke’s 128 cooling systems 70, 71 advantages of air cooling 70 advantages of water cooling 70 air cooling system 70 anti-freeze solutions 68 engine coolant 68, 69 countershaft 100, 119; see also layshaft gearboxes cross-ply tyre construction 222 cushioning ability, tyres 228 cylinder blocks 42, 67, 79 cylinder head 67 limited-slip differentials 133 direct injection 55, 56, 57 Hotchkiss drive system 125, 126 tandem axles heavy vehicles 148 torque-tube drive system 125, 126 utilization of torque-tube drive 125, 126, 127 drive shafts, front wheel 126 emission control, diesel engines 74, 187 exhaust gas recirculation 74, 78 particulate filters 74 engine capacity 40 engine lubrication 27 dry sump system 64 friction and wear 61, 62, 70

273

274 emission control, diesel engines (cont.) lubricating oil 64, 65, 67, 107 pistons 118, 165, 166 wet sump system 64 engine torque 84, 85, 97, 116, 120 band brakes 111, 118 exhaust gas recirculation 74, 78 exhaust manifold 71, 72, 73 exhaust system 144 silencer 71 fans 18, 70 depth 183 magnetic 85 separation 234, 238 surface 74, 86, 87 final drives 97, 98, 103, 118, 125, 128, 131 operating principle 39, 118 servicing 70 flywheel 84, 85, 87 forced induction 75 supercharging 74, 75 four-wheel drive 195 types of system 3 front engine, front-wheel drive 33, 34 front engine, rear-wheel drive 34, 35 fuel cell vehicles 246, 249 direct injection 2, 55, 57 distributor fuel injection pump 58 electronic diesel control 60 in-line fuel injection pump 58 sequential injection 53 gear box lubrication 107 hypoid bevel 131 spiral bevel 131 gear trains 103, 111, 116 constant mesh 95, 98, 99, 101 handbrake systems 157; see also parking brake systems range change 105 splitter drive 105 tandem axle 136, 147, 148 twin layshaft 105 two-speed 104

Index Hotchkiss drive system 125 hub mountings live axles 134 fully-floating 28, 136 semi-floating 135 three-quarter floating 136 hybrid electric vehicles 245 hydraulic brake systems 164, 166 brake fluids 20 single master cylinders 164 wheel cylinders disc brakes 165, 166 wheel cylinders, drum brakes 165, 166 hydraulic pump 205 ignition system 29, 78, 254 ignition timing 78 independent front suspension, IFS 201; see also suspension system independent rear suspension, IRS 143; see also suspension system advantages and disadvantages 7, 32, 33, 34, 75, 81, 138, 149, 187, 236 variable choke 51 layshaft gearboxes 99, 102, 114, 116 multiple carburettors 52 advantages 122, 123, 127, 132, 138, 141 internal gear 119 pintle 60 parking brake systems 10, 28, 157, 171 Rzeppa 128, 129 suspension system 23, 28, 32–33, 139–156, 181, 201, 211, 217 Tracta 130 tripot 130 Weiss 129 Continuously variable transmission, CVT 119, 246 electro-hydraulic control system 121 hydraulic control system 120