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Design of High Speed Off-Road Vehicles

Design of High Speed Off-Road Vehicles

Bruce Maclaurin

ISBN: 978-1-119-25882-7

Jul 2018

272 pages

Description

A concise reference that provides an overview of the design of high speed off-road vehicles

High Speed Off-Road Vehicles is an excellent, in-depth review of vehicle performance in off-road conditions with a focus on key elements of the running gear systems of vehicles. In particular, elements such as suspension systems, wheels, tyres, and tracks are addressed in-depth. It is a well-written text that provides a pragmatic discussion of off-road vehicles from both a historical and analytical perspective. Some of the unique topics addressed in this book include link and flexible tracks, ride performance of tracked vehicles, and active and semi-active suspension systems for both armoured and unarmoured vehicles.

The book provides spreadsheet-based analytic approaches to model these topic areas giving insight into steering, handling, and overall performance of both tracked and wheeled systems. The author further extends these analyses to soft soil scenarios and thoroughly addresses rollover situations. The text also provides some insight into more advanced articulated systems.

High Speed Off-Road Vehicles: Suspensions, Tracks, Wheels and Dynamics provides valuable coverage of: 

  • Tracked and wheeled vehicles
  • Suspension component design and characteristics, vehicle ride performance, link track component design and characteristics, flexible track, and testing of active suspension test vehicles
  • General vehicle configurations for combat and logistic vehicles, suspension performance modelling and measurement, steering performance, and the effects of limited slip differentials on the soft soil traction and steering behavior of vehicles

Written from a very practical perspective, and based on the author’s extensive experience, High Speed Off-Road Vehicles provides an excellent introduction to off-road vehicles and will be a helpful reference text for those practicing design and analysis of such systems.

Series Preface xiii

Acknowledgements xv

Introduction xvii

1 Tracked Vehicle Running Gear and Suspension Systems 1

1.1 General Arrangement 1

1.2 Transverse Torsion Bars 2

1.3 Coil Springs 6

1.4 Hydrogas Suspensions 8

1.4.1 Challenger MBT Hydrogas Unit 8

1.4.2 Measured Characteristics of a Challenger Unit 9

1.4.2.1 Spring Characteristics 9

1.4.2.2 Damper Characteristic 11

1.4.2.3 Differential Pressure Across the Damper Valve 11

1.4.2.4 Force/Displacement Loop 11

1.4.2.5 Flow Rig 12

1.4.2.6 Suspension Damping of a Multi]Wheeled Vehicle 13

1.4.3 Temperature Effects 13

1.4.3.1 Two]Stage Units 15

1.4.3.2 Counter]Spring Units 17

1.4.4 Other Types of Hydrogas Suspension 18

1.4.4.1 Twin]Cylinder Units 18

1.4.4.2 In]Arm Units 18

1.5 Dampers 20

1.5.1 Hydraulic Dampers 20

1.5.2 Friction Dampers 20

References 22

2 Vehicle Track Systems 23

2.1 Link Tracks 23

2.1.1 Single]Pin Tracks 26

2.1.1.1 Dry]Pin Tracks 26

2.1.1.2 Rubber]Bushed Tracks 27

2.1.2 Double]Pin Tracks 28

2.1.3 Rubber Track Pads, Road Wheels and Track Tensioners 31

2.1.3.1 Rubber Track Pads 31

2.1.3.2 Road Wheels 32

2.1.3.3 Track Tensioners 33

2.1.4 Track Loadings 33

2.1.4.1 Centrifugal Tension 34

2.1.4.2 Final]Drive Torque Measurements 34

2.1.4.3 Lateral Horn Load 35

2.1.5 Rolling Resistance: Analytical Methods 35

2.1.5.1 On a Metal Wheel Path 35

2.1.5.2 On a Rubber Wheel Path 36

2.1.6 Rolling Resistance: Experimental Measurements 37

2.1.6.1 Chieftain 38

2.1.6.2 FV 432 39

2.1.6.3 Scorpion and Spartan 40

2.1.6.4 Summary 42

2.1.7 Noise and Vibration 42

2.1.8 Approaches for Reducing Noise and Vibration 43

2.1.8.1 Finite Element Analysis and Experimental Sprockets 43

2.1.8.2 Fully Decoupled Running Gear 44

2.1.8.3 Flexible Rubber Tracks 44

2.1.9 Reducing Noise and Vibration 44

2.1.9.1 Stage (a): Establishing the Principal Noise Sources 45

2.1.9.2 Stage (b): Design and Production of the Resilient Mountings 46

2.1.9.3 Stage (c): Test Results with the Resilient Mountings 47

2.2 Flexible Tracks 48

2.2.1 Earlier Flexible Tracks 49

2.2.2 Contemporary Flexible Tracks 50

2.2.3 ‘Proof]of]Principle’ Flexible Tracks for a Spartan APC 51

2.2.3.1 Mark 1 Tracks 53

2.2.3.2 Mark 2 Tracks 54

2.2.3.3 Mark 3 Tracks 55

2.2.3.4 Durability Trials 57

2.2.4 Later Developments 57

References 58

3 Tracked Vehicle Suspension Performance: Modelling and Testing 59

3.1 Human Response to Whole]Body Vibration (WBV) and Shock 59

3.1.1 BS 6841:1987 and ISO 2631]1 (1997) 59

3.1.2 Further Standards Relating to WBV 61

3.1.2.1 Absorbed Power 61

3.1.2.2 The European Physical Agents (Vibration) Directive 2002/44/EC 64

3.1.2.3 ISO 2631]5 (2004) 64

3.2 Terrain Profiles 64

3.2.1 Characterisation 64

3.2.2 DERA Suspension Performance Test Courses 65

3.2.3 Response of Multi]Wheel Vehicles 66

3.2.4 Quarter]Car Model 68

3.2.5 Computer Modelling 71

3.2.5.1 Parameter Specification 73

3.2.5.2 Assumptions 74

3.5.2.3 Examples of Use of the Model 74

3.5.2.4 Comparison with Trials Data 75

3.5.2.5 Upgrading the Suspension Performance of the Scorpion Family of Vehicles 76

3.2.6 Ride Performance Trials of a Challenger Suspension Test Vehicle 76

3.2.7 Pitch Response to Braking and Accelerating 79

3.2.7.1 Compensating Idler 83

3.2.8 Sprung Idler Test Vehicle (SITV) 85

References 88

4 Controllable Suspensions 89

4.1 Height and Attitude Control 89

4.1.1 Tracked Vehicles 89

4.1.2 Wheeled Vehicles 91

4.2 Actively Controlled Damping (Semi]Active Suspensions) 91

4.2.1 Adaptive Damping 91

4.3 Active Suspension Systems 91

4.4 DERA Active Suspension Test Vehicles 93

4.4.1 Narrow]Bandwidth Systems 93

4.4.1.1 Wheeled Vehicle 95

4.4.1.2 Tracked Vehicle 97

4.4.1.3 Laboratory Test Rig 97

4.4.2 Broad]Bandwidth System 97

4.5 Conclusions 100

References 101

5 Wheeled Vehicle Drivelines and Suspensions 103

5.1 Unarmoured Vehicles 103

5.1.1 Leyland DAF DROPS 8×6 Logistic Load Carrier 103

5.1.2 MAN SX 8×8 High]Mobility Load Carrier 105

5.1.3 Pinzgauer 4×4 and 6×6 Light Trucks 105

5.1.4 Range Rover 106

5.1.5 Alvis Stalwart 107

5.1.6 Caterpillar Mining/Dump Truck 108

5.1.7 Euclid (Later Hitachi) Mining/Dump Trucks 110

5.2 Armoured Vehicles 112

5.2.1 H]Drive 112

5.2.2 I]Drive 113

5.3 Interconnected Suspensions 116

5.3.1 Methods of Interconnection 116

References 122

6 Wheeled Vehicle Suspension Performance 123

6.1 Quarter]Car Model 123

6.2 Wheelbase Filter 126

6.3 DROPS Truck Ride Measurements 127

Reference 132

7 Steering Performance of Tracked and Wheeled Vehicles 133

7.1 Tracked Vehicles 133

7.1.1 Skid Steering Mechanisms 133

7.1.2 Skid Steering Models 136

7.1.3 The Magic Formula 139

7.1.4 Deriving the Magic Formula Parameters for the Track 140

7.1.5 Steering Performance Model 144

7.1.6 Results from the Model 146

7.1.6.1 Driver Control Arrangements 146

7.1.6.2 Pivot Turn 146

7.1.6.3 Effect of Radius of Turn on Slewing Moment 147

7.1.6.4 Driving on a 15 m Radius Turn at Varying Speed to Show the Effects of Track Tension and a Suspension System 148

7.1.6.5 Driving on a 15 m Radius Turn at Varying Speeds with New and Worn Pads and on a Low]Friction Surface 150

7.1.6.6 Driving at 15 m s–1 on Turns of Varying Radii 152

7.1.6.7 Effect of the Centre of Gravity (CG) Position 154

7.1.6.8 Model Validation 156

7.2 Comparing Skid and Ackermann Steered Wheeled Vehicles 156

7.2.1 Tyre Force–Slip Data 157

7.2.2 Choice of Tyre Model 158

7.2.2.1 The Skid Steered Vehicle: Vehicle Model 159

7.2.3 Results from the Model 159

7.2.3.1 Neutral Turn 159

7.2.3.2 Variation of Slewing Moment with Radius of Turn 161

7.2.3.3 Cornering on 15 m and 30 m Radius Turns at Different Speeds 162

7.2.4 Ackermann Steered Vehicle Model 163

7.2.5 Model Results 163

7.2.5.1 Steering Performance 163

7.2.5.2 Power Requirements 165

7.2.5.3 Tyre Wear 165

7.2.6 Torque Vectoring 166

7.2.6.1 Individual Wheel Motor Control 169

7.2.6.2 Articulated Vehicles 169

Appendix A: Equations of Motion 170

Appendix B: Equations of Motion 173

References 175

8 Soft]Soil Performance of Wheeled and Tracked Vehicles 177

8.1 Basic Requirements 177

8.1.1 Soil 177

8.1.2 Basic Definitions 178

8.1.3 Soil–Vehicle Models 179

8.2 Models for Soft Cohesive Soils 180

8.2.1 Vehicle Cone Index (VCI) Model 180

8.2.1.1 Mobility Index for Tracked Vehicles 181

8.2.1.2 Mobility Index for Wheeled Vehicles 181

8.2.2 WES Mobility Number Model 182

8.2.3 Mean Maximum Pressure (MMP) 182

8.2.4 Vehicle Limiting Cone Index (VLCI) 183

8.2.4.1 Tyres 184

8.2.4.2 Tracks 187

8.3 Models for Dry Frictional Soils 189

8.3.1 WES Mobility Number for Wheeled Vehicles 189

8.3.2 DERA Trials 190

8.3.3 Tracked Vehicles 193

8.4 Space Efficiency of Running Gear Systems for Armoured Vehicles 194

8.5 Tractive Force–Slip Relationship for Tyres in Soft Cohesive Soils 197

8.5.1 Describing Force–Slip Characteristics 197

8.5.1.1 Rectangular Hyperbolae 197

8.5.1.2 Exponentials 197

8.5.2 The Magic Formula 198

8.5.3 Development of the Modified Magic Formula 199

References 202

9 Effect of Free, Locked and Limited]Slip Differentials on Traction and Steering Performance 203

9.1 Types of Lockable and Limited]Slip Differentials 203

9.1.1 Lockable Differentials 203

9.1.2 Using the Braking System 204

9.1.3 Velocity]Dependent Limited]Slip Differentials 204

9.1.4 Frictional Limited]Slip Differentials 205

9.2 Relationships for Frictional Limited]Slip Differentials 206

9.3 Traction Performance 209

9.3.1 Traction Model 209

9.3.2 Model Results 210

9.3.2.1 Effect of Weight Transfer Across an Axle 210

9.3.2.2 Different Soil Strengths Under the Tyres 212

9.3.2.3 On a Split μ Surface 214

9.4 Steering Performance on a Road Surface 214

9.4.1 Steering Performance Model 214

9.4.2 Model Results 214

Reference 216

10 Articulated Vehicles 217

10.1 Articulated Tracked Vehicles 217

10.1.1 Traction Forces with Skid and Articulated Steering 221

10.2 Articulated Wheeled Vehicles 222

10.2.1 Steering Behaviour with Ackermann, Skid and Articulated Steering 225

10.2.1.1 Hard Surfaces 225

10.2.1.2 Soft Soils 225

References 226

11 Vehicle Rollover Behaviour 227

11.1 Basic Considerations 227

11.2 Methods to Reduce the Likelihood of Rollover 229

11.2.1 Warning Systems 229

11.2.2 Electronic Stability Programmes 230

11.2.3 Active Anti]Roll Bars 230

11.3 Truck Rollover: A Case Study 230

11.3.1 Calculating the Rollover Angle 231

References 233

Notation 235

Abbreviations 243

Bibliography 245

Index 257