High Speed Off-Road Vehicles

BRUCE MACLAURIN initially worked in the aircraft industry on structural design and analysis and then spent over 35 years on the research and design of the automotive systems of military vehicles. His main area of research is tracked and wheeled vehicle steering systems, suspensions and tracks including design, computer modelling, and performance measuring. He is now retired from the Ministry of Defence in the UK.

• Series Preface xiiiAcknowledgements xvIntroduction xvii1 Tracked Vehicle Running Gear and Suspension Systems 11.1 General Arrangement 11.2 Transverse Torsion Bars 21.3 Coil Springs 61.4 Hydrogas Suspensions 81.4.1 Challenger MBT Hydrogas Unit 81.4.2 Measured Characteristics of a Challenger Unit 91.4.2.1 Spring Characteristics 91.4.2.2 Damper Characteristic 111.4.2.3 Differential Pressure Across the Damper Valve 111.4.2.4 Force/Displacement Loop 111.4.2.5 Flow Rig 121.4.2.6 Suspension Damping of a Multi‐Wheeled Vehicle 131.4.3 Temperature Effects 131.4.3.1 Two‐Stage Units 151.4.3.2 Counter‐Spring Units 171.4.4 Other Types of Hydrogas Suspension 181.4.4.1 Twin‐Cylinder Units 181.4.4.2 In‐Arm Units 181.5 Dampers 201.5.1 Hydraulic Dampers 201.5.2 Friction Dampers 20References 222 Vehicle Track Systems 232.1 Link Tracks 232.1.1 Single‐Pin Tracks 262.1.1.1 Dry‐Pin Tracks 262.1.1.2 Rubber‐Bushed Tracks 272.1.2 Double‐Pin Tracks 282.1.3 Rubber Track Pads, Road Wheels and Track Tensioners 312.1.3.1 Rubber Track Pads 312.1.3.2 Road Wheels 322.1.3.3 Track Tensioners 332.1.4 Track Loadings 332.1.4.1 Centrifugal Tension 332.1.4.2 Final‐Drive Torque Measurements 342.1.4.3 Lateral Horn Load 352.1.5 Rolling Resistance: Analytical Methods 352.1.5.1 On a Metal Wheel Path 352.1.5.2 On a Rubber Wheel Path 362.1.6 Rolling Resistance: Experimental Measurements 372.1.6.1 Chieftain 382.1.6.2 FV 432 392.1.6.3 Scorpion and Spartan 402.1.6.4 Summary 422.1.7 Noise and Vibration 422.1.8 Approaches for Reducing Noise and Vibration 432.1.8.1 Finite Element Analysis and Experimental Sprockets 432.1.8.2 Fully Decoupled Running Gear 442.1.8.3 Flexible Rubber Tracks 442.1.9 Reducing Noise and Vibration 442.1.9.1 Stage (a): Establishing the Principal Noise Sources 452.1.9.2 Stage (b): Design and Production of the Resilient Mountings 462.1.9.3 Stage (c): Test Results with the Resilient Mountings 472.2 Flexible Tracks 482.2.1 Earlier Flexible Tracks 492.2.2 Contemporary Flexible Tracks 502.2.3 ‘Proof‐of‐Principle’ Flexible Tracks for a Spartan APC 512.2.3.1 Mark 1 Tracks 532.2.3.2 Mark 2 Tracks 542.2.3.3 Mark 3 Tracks 552.2.3.4 Durability Trials 572.2.4 Later Developments 57References 583 Tracked Vehicle Suspension Performance: Modelling and Testing 593.1 Human Response to Whole‐Body Vibration (WBV) and Shock 593.1.1 BS 6841:1987 and ISO 2631‐1 (1997) 593.1.2 Further Standards Relating to WBV 613.1.2.1 Absorbed Power 613.1.2.2 The European Physical Agents (Vibration) Directive 2002/44/EC 643.1.2.3 ISO 2631‐5 (2004) 643.2 Terrain Profiles 643.2.1 Characterisation 643.2.2 DERA Suspension Performance Test Courses 653.2.3 Response of Multi‐Wheel Vehicles 663.2.4 Quarter‐Car Model 683.2.5 Computer Modelling 713.2.5.1 Parameter Specification 733.2.5.2 Assumptions 743.5.2.3 Examples of Use of the Model 743.5.2.4 Comparison with Trials Data 753.5.2.5 Upgrading the Suspension Performance of the Scorpion Family of Vehicles 763.2.6 Ride Performance Trials of a Challenger Suspension Test Vehicle 763.2.7 Pitch Response to Braking and Accelerating 793.2.7.1 Compensating Idler 833.2.8 Sprung Idler Test Vehicle (SITV) 85References 884 Controllable Suspensions 894.1 Height and Attitude Control 894.1.1 Tracked Vehicles 894.1.2 Wheeled Vehicles 914.2 Actively Controlled Damping (Semi‐Active Suspensions) 914.2.1 Adaptive Damping 914.3 Active Suspension Systems 914.4 DERA Active Suspension Test Vehicles 934.4.1 Narrow‐Bandwidth Systems 934.4.1.1 Wheeled Vehicle 954.4.1.2 Tracked Vehicle 974.4.1.3 Laboratory Test Rig 974.4.2 Broad‐Bandwidth System 974.5 Conclusions 100References 1015 Wheeled Vehicle Drivelines and Suspensions 1035.1 Unarmoured Vehicles 1035.1.1 Leyland DAF DROPS 8×6 Logistic Load Carrier 1035.1.2 MAN SX 8×8 High‐Mobility Load Carrier 1055.1.3 Pinzgauer 4×4 and 6×6 Light Trucks 1055.1.4 Range Rover 1065.1.5 Alvis Stalwart 1075.1.6 Caterpillar Mining/Dump Truck 1085.1.7 Euclid (Later Hitachi) Mining/Dump Trucks 1105.2 Armoured Vehicles 1125.2.1 H‐Drive 1125.2.2 I‐Drive 1135.3 Interconnected Suspensions 1165.3.1 Methods of Interconnection 116References 1226 Wheeled Vehicle Suspension Performance 1236.1 Quarter‐Car Model 1236.2 Wheelbase Filter 1266.3 DROPS Truck Ride Measurements 127Reference 1327 Steering Performance of Tracked and Wheeled Vehicles 1337.1 Tracked Vehicles 1337.1.1 Skid Steering Mechanisms 1337.1.2 Skid Steering Models 1367.1.3 The Magic Formula 1397.1.4 Deriving the Magic Formula Parameters for the Track 1407.1.5 Steering Performance Model 1447.1.6 Results from the Model 1467.1.6.1 Driver Control Arrangements 1467.1.6.2 Pivot Turn 1467.1.6.3 Effect of Radius of Turn on Slewing Moment 1477.1.6.4 Driving on a 15 m Radius Turn at Varying Speed to Show the Effects of Track Tension and a Suspension System 1487.1.6.5 Driving on a 15 m Radius Turn at Varying Speeds with New and Worn Pads and on a Low‐Friction Surface 1507.1.6.6 Driving at 15 m s–1 on Turns of Varying Radii 1527.1.6.7 Effect of the Centre of Gravity (CG) Position 1547.1.6.8 Model Validation 1567.2 Comparing Skid and Ackermann Steered Wheeled Vehicles 1567.2.1 Tyre Force–Slip Data 1577.2.2 Choice of Tyre Model 1587.2.2.1 The Skid Steered Vehicle: Vehicle Model 1597.2.3 Results from the Model 1597.2.3.1 Neutral Turn 1597.2.3.2 Variation of Slewing Moment with Radius of Turn 1617.2.3.3 Cornering on 15 m and 30 m Radius Turns at Different Speeds 1627.2.4 Ackermann Steered Vehicle Model 1637.2.5 Model Results 1637.2.5.1 Steering Performance 1637.2.5.2 Power Requirements 1657.2.5.3 Tyre Wear 1657.2.6 Torque Vectoring 1667.2.6.1 Individual Wheel Motor Control 1697.2.6.2 Articulated Vehicles 169Appendix A: Equations of Motion 170Appendix B: Equations of Motion 173References 1758 Soft‐Soil Performance of Wheeled and Tracked Vehicles 1778.1 Basic Requirements 1778.1.1 Soil 1778.1.2 Basic Definitions 1788.1.3 Soil–Vehicle Models 1798.2 Models for Soft Cohesive Soils 1808.2.1 Vehicle Cone Index (VCI) Model 1808.2.1.1 Mobility Index for Tracked Vehicles 1818.2.1.2 Mobility Index for Wheeled Vehicles 1818.2.2 WES Mobility Number Model 1828.2.3 Mean Maximum Pressure (MMP) 1828.2.4 Vehicle Limiting Cone Index (VLCI) 1838.2.4.1 Tyres 1848.2.4.2 Tracks 1878.3 Models for Dry Frictional Soils 1898.3.1 WES Mobility Number for Wheeled Vehicles 1898.3.2 DERA Trials 1908.3.3 Tracked Vehicles 1938.4 Space Efficiency of Running Gear Systems for Armoured Vehicles 1948.5 Tractive Force–Slip Relationship for Tyres in Soft Cohesive Soils 1978.5.1 Describing Force–Slip Characteristics 1978.5.1.1 Rectangular Hyperbolae 1978.5.1.2 Exponentials 1978.5.2 The Magic Formula 1988.5.3 Development of the Modified Magic Formula 199References 2029 Effect of Free, Locked and Limited‐Slip Differentials on Traction and Steering Performance 2039.1 Types of Lockable and Limited‐Slip Differentials 2039.1.1 Lockable Differentials 2039.1.2 Using the Braking System 2049.1.3 Velocity‐Dependent Limited‐Slip Differentials 2049.1.4 Frictional Limited‐Slip Differentials 2059.2 Relationships for Frictional Limited‐Slip Differentials 2069.3 Traction Performance 2099.3.1 Traction Model 2099.3.2 Model Results 2109.3.2.1 Effect of Weight Transfer Across an Axle 2109.3.2.2 Different Soil Strengths Under the Tyres 2129.3.2.3 On a Split μ Surface 2149.4 Steering Performance on a Road Surface 2149.4.1 Steering Performance Model 2149.4.2 Model Results 214Reference 21610 Articulated Vehicles 21710.1 Articulated Tracked Vehicles 21710.1.1 Traction Forces with Skid and Articulated Steering 22110.2 Articulated Wheeled Vehicles 22210.2.1 Steering Behaviour with Ackermann, Skid and Articulated Steering 22510.2.1.1 Hard Surfaces 22510.2.1.2 Soft Soils 225References 22611 Vehicle Rollover Behaviour 22711.1 Basic Considerations 22711.2 Methods to Reduce the Likelihood of Rollover 22911.2.1 Warning Systems 22911.2.2 Electronic Stability Programmes 23011.2.3 Active Anti‐Roll Bars 23011.2.4 Driver Training 23011.3 Truck Rollover: A Case Study 23011.3.1 Calculating the Rollover Angle 231References 233Notation 235Abbreviations 243Bibliography 245Index 247