High Speed Off-Road Vehicles E-Book

Bruce Maclaurin

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Serie: Automotive Series
• Sprache: Englisch

Seitenzahl: 372

Veröffentlichungsjahr: 2018

Beschreibung

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.

Leseprobe

Table of Contents

Cover

Dedication

Series Preface

Acknowledgements

Introduction

Chapter 1: Tracked Vehicle Running Gear and Suspension Systems

1.1 General Arrangement

1.2 Transverse Torsion Bars

1.3 Coil Springs

1.4 Hydrogas Suspensions

1.5 Dampers

References

Chapter 2: Vehicle Track Systems

2.1 Link Tracks

2.2 Flexible Tracks

References

Chapter 3: Tracked Vehicle Suspension Performance: Modelling and Testing

3.1 Human Response to Whole‐Body Vibration (WBV) and Shock

3.2 Terrain Profiles

References

Chapter 4: Controllable Suspensions

4.1 Height and Attitude Control

4.2 Actively Controlled Damping (Semi‐Active Suspensions)

4.3 Active Suspension Systems

4.4 DERA Active Suspension Test Vehicles

4.5 Conclusions

References

Chapter 5: Wheeled Vehicle Drivelines and Suspensions

5.1 Unarmoured Vehicles

5.2 Armoured Vehicles

5.3 Interconnected Suspensions

References

Chapter 6: Wheeled Vehicle Suspension Performance

6.1 Quarter‐Car Model

6.2 Wheelbase Filter

6.3 DROPS Truck Ride Measurements

Reference

Chapter 7: Steering Performance of Tracked and Wheeled Vehicles

7.1 Tracked Vehicles

7.2 Comparing Skid and Ackermann Steered Wheeled Vehicles

Appendix A: Equations of Motion

Appendix B: Power Flow Equations

References

Chapter 8: Soft‐Soil Performance of Wheeled and Tracked Vehicles

8.1 Basic Requirements

8.2 Models for Soft Cohesive Soils

8.3 Models for Dry Frictional Soils

8.4 Space Efficiency of Running Gear Systems for Armoured Vehicles

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

References

Chapter 9: Effect of Free, Locked and Limited‐Slip Differentials on Traction and Steering Performance

9.1 Types of Lockable and Limited‐Slip Differentials

9.2 Relationships for Frictional Limited‐Slip Differentials

9.3 Traction Performance

9.4 Steering Performance on a Road Surface

Reference

Chapter 10: Articulated Vehicles

10.1 Articulated Tracked Vehicles

10.2 Articulated Wheeled Vehicles

References

Chapter 11: Vehicle Rollover Behaviour

11.1 Basic Considerations

11.2 Methods to Reduce the Likelihood of Rollover

11.3 Truck Rollover: A Case Study

References

Notation

Abbreviations

Bibliography

Index

End User License Agreement

List of Illustrations

Chapter 1

Figure 1.1 Warrior running gear layout.

Source:

Courtesy of Ministry of Defence.

Figure 1.2 Leopard 2 running gear layout.

Source:

Courtesy of ATZ.

Figure 1.3 The principle of presetting a torsion bar.

Figure 1.4 Panther torsion bar arrangement.

Figure 1.5 Torsion tube over bar arrangement.

Source:

Courtesy of Ministry of Defence.

Figure 1.6 Cromwell MBT suspension unit.

Source:

Courtesy of Ministry of Defence.

Figure 1.7 Chieftain bogie suspension unit.

Source:

Courtesy of Ministry of Defence.

Figure 1.8 Merkava 4 suspension unit.

Source:

Courtesy of MANTAK.

Figure 1.9 Challenger hydrogas suspension unit.

Source:

Courtesy of Ministry of Defence.

Figure 1.10 Challenger suspension characteristics at 0.8 Hz as measured, a fitted curve and a typical design curve.

Figure 1.11 Ratio of specific heats for nitrogen at different pressures.

Source:

Din, 1961 [1.3]. Reproduced with permission of Butterworths.

Figure 1.12 Measured ratio of specific heats at different frequencies.

Figure 1.13 Challenger suspension unit damper characteristics from differential pressure across damper valve.

Figure 1.14 Challenger suspension unit damper characteristics from flow rig.

Figure 1.15 Diagram of interaction between hydrogas suspension and track tension.

Figure 1.16 Effect of temperature on hydrogas suspension ride height.

Figure 1.17 Diagram of two‐stage hydrogas suspension unit.

Figure 1.18 Two‐stage hydrogas suspension load/deflection characteristic.

Figure 1.19 Diagram of hydrogas suspension with counter‐spring.

Figure 1.20 Load–deflection characteristic of hydrogas suspension with counter‐spring.

Figure 1.21 Leclerc MBT opposed piston suspension unit.

Source:

Courtesy of Nexter Systems.

Figure 1.22 Diagram of In‐arm suspension unit.

Figure 1.23 Suspension with an external hydrogas or liquid spring strut.

Figure 1.24 Warrior rotary damper cross–section.

Source:

Courtesy of Horstman Defence Systems.

Figure 1.25 Leopard 2 suspension.

Source:

Courtesy of ATZ.

Figure 1.26 Leopard 2 suspension characteristics.

Source:

Courtesy of ATZ.

Chapter 2

Figure 2.1 Dry single‐pin track.

Source:

Courtesy of Ministry of Defence.

Figure 2.2 Single‐pin rubber‐bush track.

Source:

Courtesy of Ministry of Defence.

Figure 2.3 Double‐pin, three‐connector, single‐body rubber‐bushed track.

Source:

Courtesy of Ministry of Defence.

Figure 2.4 The relationship between nominal ground contact area and vehicle mass.

Figure 2.5 Three‐quarter‐track multi‐role 7 tonne carrier type ZgKW.

Figure 2.6 Track of the multi‐role carrier type ZgKW.

Figure 2.7 Two‐connector double‐pin track.

Source:

Courtesy of Ministry of Defence.

Figure 2.8 Double‐pin double‐body three‐connector track (Tank Automotive Research, Development and Engineering Centre).

Figure 2.9 Cross‐bend loading on track link/pins.

Figure 2.10 Double‐pin track with in‐body drive (left) and the ‘bayonet’ method of replaceable track pad insertion (right).

Source:

Courtesy of DST Defence.

Figure 2.11 Comparing different track pad conditions: (a) new pad; (b) abrasive wear; (c) ‘cutting and chunking’; and (d) thermal blow‐out (Tank Automotive Research, Development and Engineering Centre).

Figure 2.12 Track tensile force duty cycle for 1000 km on road and 1000 km on cross‐country.

Figure 2.14 FV 432 rolling resistance: dry‐pin and rubber‐bushed tracks (RB). MWP: metal wheel path; RWP: rubber wheel path.

Figure 2.15 Scorpion towed rolling resistance with track system in different configurations.

Figure 2.13 Chieftain rolling resistance: dry‐pin and double‐pin rubber‐bushed track.

Figure 2.17 Effect of isolating components of the running gear on sound pressure levels.

Figure 2.18 Flexible trailing link sprocket drive.

Source:

Courtesy of Ministry of Defence.

Figure 2.16 Chordal action of the track impacting on the idler wheel.

Figure 2.19 Resilient idler mounting.

Source:

Courtesy of Ministry of Defence.

Figure 2.20 Sound pressure levels with the compliant mountings fitted.

Figure 2.21 Average vibration levels with the compliant mountings fitted.

Figure 2.22 Diagram of idler carried on a four‐bar linkage with resilient mounts.

Figure 2.23 Citroen–Kegresse half‐track truck as used in desert conditions.

Source:

Audouin‐Dubreuil A, 2006 [2.8]. Reproduced with permission of Dalton Watson Fine Books 2006.

Figure 2.24 M3 track system.

Figure 2.25 A jointed track on an oversnow vehicle.

Figure 2.26 Caterpillar high speed earth‐mover with flexible track.

Source:

Courtesy of Ministry of Defence.

Figure 2.27 Segmented track system showing the connectors used for joining adjacent segments.

Source:

Courtesy of DST Defence.

Figure 2.28 Cross‐section of segmented flexible track showing the steel‐wire longitudinal reinforcement, composite transverse stiffeners and steel‐plate reinforced guide horn.

Source:

Courtesy of DST Defence.

Figure 2.29 Spartan fitted Soucy Mark 1 flexible tracks.

Source:

Courtesy of Ministry of Defence.

Figure 2.30 Spartan fitted with Soucy Mark 2 flexible tracks showing ‘back‐driving’ on the sprocket. Applied torque is anti‐clockwise.

Source:

Courtesy of Ministry of Defence.

Figure 2.31 Spartan fitted with Mark 3 Soucy tracks and UHMW plastic sprocket. There is no sign of back‐driving.

Source:

Courtesy of Ministry of Defence.

Figure 2.32 ASCOD fitted with Soucy flexible tracks.

Source:

Courtesy of General Dynamics European Land Systems ASCOD.

Chapter 3

Figure 3.1 HRV BS6841 and ISO2731 weighting filters in linearised format for vertical vibration on seat base.

Figure 3.2 NATO Reference Mobility Model (NRMM): general layout (US Army Engineer Research and Development Centre).

Figure 3.3 HRV weighting functions for vertical vibration on seat base, including absorbed power.

Figure 3.4 Comparing the absorbed power and ISO 2631 weighting filters on vehicle ride values (US Army Engineer Research and Development Centre).

Figure 3.5 Heave wheelbase filter for a six‐axle vehicle.

Figure 3.6 Heave response filter for a six‐axle 4.8 m wheelbase vehicle at 10 m s

–1

.

Figure 3.7 Heave response to different wavelengths for different wheelbase six‐axle vehicles.

Figure 3.8 Pitch input at different wavelengths of constant amplitude for vehicles of different wheelbase.

Figure 3.9 Quarter‐car model

Figure 3.10 Comparing the ride response of single‐ and six‐axle vehicles on a random terrain at different speeds. Also shown are the effects of the ISO 6841 and ISO 2631 weighting filters.

Figure 3.11 The weighted PSD accelerations on a random terrain for the single axle at 5 m s

–1

and the six‐axle vehicle at 10 m s

–1

. Also shown are the effects of the ISO 6841 and ISO 2631 weighting filters.

Figure 3.12 Tracked vehicle computer model.

Source:

Courtesy of Ministry of Defence.

Figure 3.13 Damper characteristics of the Warrior suspension computer model and the trials vehicle.

Figure 3.14 Comparing the computer modelled and trials results of a Warrior suspension test vehicle.

Figure 3.15 Scorpion damper characteristics.

Fig 3.16 Scorpion computer modelling results.

Figure 3.17 Challenger suspension test vehicle on the random course at 8.5 m s

–1

.

Source:

Courtesy of Ministry of Defence.

Figure 3.18 Pitch response on the 7 m sinewave course of the Challenger suspension test vehicle.

Figure 3.19 Weighted RMS acceleration on the random course of the Challenger suspension test vehicle.

Figure 3.20 Front‐wheel displacement on the random course of a Challenger suspension test vehicle at 8 m s

–1

.

Figure 3.21 Relative pitch stiffness of vehicles with different numbers of axles but the same wheelbase and heave stiffness.

Figure 3.22 Forces acting on a tracked vehicle body when braking.

Figure 3.23 Predicted pitch angles for Scorpion when braking.

Figure 3.24 Scorpion braking at 0.5 g deceleration.

Source:

Courtesy of Ministry of Defence.

Figure 3.25 Scorpion track tension either side of sprocket when braking.

Figure 3.26 Challenger pitch angles when braking for single‐stage and two‐stage suspension units, and with and without track.

Figure 3.27 Forces acting on a compensating idler when braking.

Figure 3.28 General arrangement of the sprung idler test vehicle (SITV).

Source:

Courtesy of Ministry of Defence.

Figure 3.29 The sprung and compensating idler linkage.

Source:

Courtesy of Ministry of Defence.

Figure 3.30 SITV on the 30% ramp at 8.5 m s

–1

.

Source:

Courtesy of Ministry of Defence.

Figure 3.31 SITV on the random course at 8.5 m s

–1

.

Source:

Courtesy of Ministry of Defence.

Chapter 4

Figure 4.1 The Swedish S‐tank showing the gun in the fully depressed condition.

Source:

Courtesy of The Tank Museum.

Figure 4.2 The steering and gun azimuth control system of the S–tank.

Source:

Courtesy of R Ogorkiewicz.

Figure 4.3 Diagram of an active suspension.

Source:

Courtesy of Ministry of Defence.

Figure 4.4 Dowty Rotol in‐arm liquid spring suspension unit and control actuator for FV 432.

Source:

Courtesy of Ministry of Defence.

Figure 4.5 Diagram of AP active suspension system.

Source:

Courtesy of Ministry of Defence.

Figure 4.6 The AP control valve.

Source:

Courtesy of Ministry of Defence.

Figure 4.7 Suspension test vehicle with passive suspension.

Source:

Courtesy of Ministry of Defence.

Figure 4.8 Active suspension fitted to the suspension test vehicle.

Source:

Courtesy of Ministry of Defence.

Figure 4.9 Results from the single‐wheel laboratory rig with AP control valve; PSD of body acceleration with random road input and body response to step force input.

Source:

Courtesy of Ministry of Defence.

Figure 4.10 Scorpion test vehicle fitted with Lotus active suspension.

Source:

Courtesy of Ministry of Defence.

Figure 4.11 Lotus active suspension on Scorpion test vehicle.

Source:

Courtesy of Ministry of Defence.

Figure 4.12 Comparison of the ride performance of the Lotus active suspension test vehicle with the Scorpion with uprated passive suspension.

Chapter 5

Figure 5.1 Diagram of I‐ and H‐driveline layouts. E, engine; GB, gearbox; TB, transfer box; D, differential..

Figure 5.2 DROPS general layout..

Figure 5.3 MAN SX truck coil spring rear suspension..

Figure 5.4 Pinzgauer 4×4 general layout..

Figure 5.5 Pinzgauer final drive and swing axle pivot..

Figure 5.6 Layout of Alvis Stalwart..

Figure 5.7 Stalwart double‐wishbone torsion bar suspension..

Figure 5.8 Principle of the liquid spring..

Figure 5.9 Comparison of the compressibility of various liquids..

Figure 5.10 Detail of the Dowty pressure seal..

Figure 5.11 Panhard AML armoured car transmission layout and limited‐slip differential..

Figure 5.12 Panhard EBR light tank transmission layout..

Figure 5.13 Piranha APC with coil spring and torsion bar suspension..

Figure 5.14 Piranha APC driveline and hydrogas suspension..

Figure 5.15 Luchs reconnaissance vehicle cross section..

Figure 5.16 Luchs reconnaissance vehicle steering arrangements..

Figure 5.17 Luchs reconnaissance vehicle coil spring suspension system..

Figure 5.18 Different methods of interconnection, (a‐d) in roll and pitch, (e‐g) in heave, using torsion bars, coil springs, hydrogas springs and torsion bars, and (i) in roll and pitch using torsion bars.

Figure 5.19 Citroen 2CV pitch interconnected suspension system..

Figure 5.20 Simplified Citroen 2CV pitch interconnection system.

Figure 5.21 Zero‐warp stiffness anti‐roll bar system using torsion bars and balance beams..

Figure 5.22 Hydraulically interconnected zero‐warp anti‐roll system using hydrogas springs.

Figure 5.23 Six‐wheeled vehicle zero‐warp arrangement.

Figure 5.24 Mars Curiosity rover showing rocker‐bogie linkage..

Figure 5.25 Effect of the position of the bogie pivot on the rearwards tilt angle.

Chapter 6

Figure 6.1 Quarter‐car model: the effect of undamped natural frequency and damping ratio on weighted RMS acceleration.

Figure 6.2 Quarter‐car model: the tradeoff between weighted RMS acceleration and RMS suspension displacement for different undamped natural frequencies and damping ratios.

Figure 6.3 Quarter‐car model: the effect of unsprung weight and tyre pressure on weighted RMS acceleration and RMS suspension displacement for different damping ratios.

Figure 6.4 Quarter‐car model: the effect of unsprung weight and tyre pressure on weighted RMS acceleration and RMS tyre loading ratio.

Figure 6.5 Effect on weighted RMS acceleration of the heave response of vehicles with two, three and four equi‐spaced axles compared to a single axle.

Figure 6.6 Effect on the heave acceleration of a four‐axle vehicle for different undamped natural frequencies and damping ratios.

Figure 6.7 Comparison of the effect of the BSI and ISO weighting filters on the heave RMS acceleration of a four‐axle vehicle compared to a single axle.

Figure 6.8 Effects of the BSI and ISO weighting filters on the PSD acceleration of the four‐axle vehicle compared to a single axle.

Figure 6.9 Weighted RMS acceleration on the DROPS vehicle frame and on the cab floor under the driver's seat with standard and half‐standard tyre pressures.

Figure 6.10 Weighted RMS acceleration on the vehicle frame over the rear suspension at standard and half‐standard tyre pressures.

Figure 6.11 Weighted acceleration PSD on the vehicle frame over the front and rear suspensions at a speed of 4.4 m s

–1

.

Figure 6.12 Friction and stiffness measurements on a DROPS rear suspension spring.

Source:

Courtesy of Ministry of Defence.

Chapter 7

Figure 7.1 Simplified diagram of a double differential.

Figure 7.2 1899 Vedovelli Priestley electric taxi with double differential steering (Cassell & Co. Ltd).

Figure 7.3 A simple steering model.

Figure 7.4 The two basic types of double differential (diff).

Figure 7.5 (a) The Renk transmission (gearbox and steering) as used on Leopard 2 and (b) a simplified diagram of the steering system.

Source:

Courtesy of RENK AG.

Figure 7.6 The Merritt skid steering model.

Figure 7.7 The primary parameters of the Magic Formula.

Figure 7.8 The different curves that can be produced by altering parameter

C

in the Magic Formula.

Figure 7.9 Experimental traction force–slip curve of a Spartan vehicle compared to its Magic Formula representation. Also shown for comparison are a calculated traction force–slip curve and a calculated traction–slip stiffness.

Figure 7.10 The force–slip relationships at static load for new pads, worn pads and on a low‐friction surface.

Figure 7.11 The forces acting on the model vehicle: only those acting on the front outer and rear inner wheels are shown.

Figure 7.12 The relative steering wheel displacements required for two different control arrangements to cause a 0.2 g lateral acceleration at various speeds.

Figure 7.13 The slewing moments at slow speed for new pads, worn pads and on the low‐friction surface on turns of increasing radius.

Figure 7.14 The effect on slewing moment of the five different track conditions as a function of lateral acceleration on a 15 m radius turn.

Figure 7.15 The front and rear track angles as a function of lateral accelerations on a 15 m radius turn with suspension and track pretension.

Figure 7.16 Specific track speed difference d

v

/

V

as a function of lateral acceleration on a 15 m radius turn for the model with different track conditions.

Figure 7.17 The various power flows in the steering system as a function of lateral acceleration on a 15 m turn with new pads.

Figure 7.18 Slewing moment as a function of lateral acceleration on a 15 m radius turn with new pads, worn pads and on the low‐friction surface.

Figure 7.19 Specific track speed difference d

v

/

V

as a function of lateral acceleration on a 15 m turn with new pads, worn pads and on the low‐friction surface.

Figure 7.20 Track forces from sprocket and idler to ground as a function of lateral acceleration at 15 m s

–1

on turns of varying radii.

Figure 7.21 The specific track speed difference d

v

/

V

as a function of lateral acceleration at 15 m s

–1

on turns of varying radii.

Figure 7.22 Power flows in the steering system as a function of lateral acceleration at 15 m s

–1

on turns of varying radii.

Figure 7.23 Diagram of the QinetiQ electric drive system with two drive motors and a steer motor driving through a double differential.

Source:

Courtesy of QinetiQ.

Figure 7.24 The effect of centre of gravity position on specific track speed difference d

v

/

V

as a function of lateral acceleration on a 15 m radius turn.

Figure 7.25 The GIAT AMX10RC light tank performing a clockwise pivot or neutral turn.

Source:

Courtesy of Nexter Systems.

Figure 7.26 Basic tyre force characteristics: (a) lateral force–slip angle; and (b) braking force–slip.

Source:

Courtesy of Bosch Automotive Handbook.

Figure 7.27 The derived combined slip–force characteristics used in the simulations: (a) longitudinal force–slip at various slip angles; and (b) lateral force–slip at various slip angles.

Figure 7.28 Forces acting on the skid steered vehicle during a steady‐state turn. Only the tyre forces acting on the front outer and the rear inner tyres are shown.

Figure 7.29 Slewing moment for different radii of turn at low lateral accelerations. The slewing moments of a six‐axle tracked vehicle of similar dimensions is also shown.

Figure 7.30 The steering response d

v/V

as a function of lateral acceleration for 15 and 30 m radii of turn.

Figure 7.31 The various power flows in the steering system as a function of lateral acceleration for a 15 m radius turn.

Figure 7.32 Forces acting on the Ackermann steered vehicle during a steady‐state turn. Only the tyre forces acting on the front outer and the rear inner tyres are shown.

Figure 7.33 Comparison of the steering responses of the skid and Ackermann steered vehicles for a 30 m turn at various speeds. Also shown are the responses on a low‐friction surface.

Figure 7.34 Comparison of the power requirements of the skid and Ackermann steered vehicles for a 30 m turn at various speeds.

Figure 7.35 Power required for the skid and Ackermann steered vehicles for a 0.2 g turn at various radii.

Figure 7.36 Controlled differential.

Source:

Courtesy of R Ogorkiewicz.

Figure 7.37 Effect on steering response of different degrees of differential torque transfer.

Figure 7.38 Wheel speed difference for different degrees of differential torque transfer.

Figure 7.39 Power requirements for different degrees of differential torque transfer.

Chapter 8

Figure 8.1 (a) Parameters measured during traction testing. (b) Free‐body diagram of wheel in traction condition. (c) Free‐body diagram of wheel in free‐rolling condition

Figure 8.2 DERA mobile tester in the field.

Figure 8.3 Coefficient of traction for tyres against mobility number

N

M.

Figure 8.4 Coefficient of traction for tracks against mobility number

N

T

.

Figure 8.5 VCI and VLCI values compared for a range of wheeled and tracked vehicles.

Figure 8.6 Comparison of the coefficients of traction and rolling resistance with soil strength for the Warrior vehicle as given by the VCI and VLCI models.

Figure 8.7 DERA sand pit..

Figure 8.8 EXF vehicle in sand: experimental traction values compared to predicted values for different tyre deflection ratios.

Figure 8.9 EXF vehicle in sand: experimental rolling resistance values compared to predicted values for different tyre deflection ratios.

Figure 8.10 Experimental values for traction values for a range of tracked vehicles compared to the NRMM predictive relationship..

Figure 8.11 Experimental values of rolling resistance values for a range of tracked vehicles compared to the NRMM predictive relationship..

Figure 8.12 Comparative space requirements of tracked and wheeled vehicles of similar soft soil performance. The wheeled vehicle is assumed to have H‐drive, skid steering and trailing arm suspension. The dotted line shows a possible profile for a vehicle with Ackermann steering.

Figure 8.13 Alvis Stalwart with H‐drive, Ackerman steering and wishbone suspension..

Figure 8.14 Comparison of the space requirements of tracked and wheeled vehicles of similar soft performance. Here the vehicle has an I‐drive causing the floor of the vehicle to be raised.

Figure 8.15 Typical traction curves for a tyre in soft cohesive soil as measured with the DERA mobile tester.

Figure 8.16 Coefficient of rolling resistance comparing the variable slip data with the free‐rolling data.

Figure 8.17 Peak traction coefficient given by the experimental data (Equation (8.46)) compared to that given by the Magic Formula at 0.3 slip.

Figure 8.18 Triaxial cohesion compared to cone index (lb f/in

2

) for a lean and a heavy cohesive soil at different moisture contents. Lean clay denoted by open symbols, heavy clay by closed symbols (US Army Engineer Research and Development Centre).

Chapter 9

Figure 9.1 The basic control system for engagement of differential dog clutches..

Figure 9.2 The GKN Viscodrive..

Figure 9.3 A typical torque–temperature relationship at constant speed difference between inner and outer plates, showing the ‘hump’ effect.

Figure 9.4 Load‐proportional frictional limited‐slip differential.

Figure 9.5 Load‐proportional limited‐slip differential showing shaft torques and speeds.

Figure 9.6 Effect of tyre load on gross and net traction and rolling resistance for a soil strength of 325 kPa.

Figure 9.7 Effect of weight transfer across an axle with free and locked differentials.

Figure 9.8 Gross traction–slip curves for some of the soils and surfaces considered.

Figure 9.9 Net traction–slip curves for some of the soils and surfaces considered.

Figure 9.10 Effect of soil strength on peak gross, net and rolling resistance forces for a tyre load of 30 kN.

Figure 9.11 Net traction on the individual wheels for different soil strengths across an axle.

Figure 9.12 Transfer ratio

K

d

required to lock the differential for the road and soil surfaces considered.

Figure 9.13 Transfer ratio

K

d

required to lock the differential for the soils and surfaces considered.

Figure 9.14 Effect of different differentials on front‐wheel steer angle on a 15 m radius turn at various speeds.

Figure 9.15 Effect of different differentials on vehicle power requirements on a 15 m radius turn at various speeds.

Chapter 10

Figure 10.1 Types of vehicle articulation..

Figure 10.2 The Tucker SNO‐CAT..

Figure 10.3 The COBRA test vehicle..

Figure 10.4 US experimental system for coupling two M113s together as an articulated vehicle..

Figure 10.5 US proposal for an articulated tank..

Figure 10.6 The Swedish UDES XX20 demonstrator vehicle..

Figure 10.7 The Russian Vityaz DT‐30 articulated vehicle..

Figure 10.8 Simple ‘bicycle’ steering model for an articulated vehicle, showing forces acting on wheels.

Figure 10.9 Comparing the traction forces required for a skid and an articulated vehicle on turns of various radii.

Figure 10.10 US 8 tonne GOER vehicle..

Figure 10.11 US experimental vehicle train MARV (multi‐element articulated vehicle)..

Figure 10.12 Lockheed Twister experimental vehicle..

Figure 10.13 Longitudinal forces on tyre for different slip angles with a tyre/soil mobility number

N

of 2.

Figure 10.14 The total longitudinal force on the outside wheels in soft soil at different radii of turn

Chapter 11

Figure 11.1 Forces and dimensions affecting vehicle rollover: rigid and with suspension deflection.

Figure 11.2 Vehicle on tilt platform.

Figure 11.3 Lateral acceleration of a DROPS truck on a rough‐terrain test track.

Source:

Courtesy of Ministry of Defence.

Figure 11.4 DROPS roll moments as functions of side force/weight ratio.

Figure 11.5 DROPS roll moments as functions of side force/weight ratio with increased roll stiffness on the front axles.

Guide

Cover

Table of Contents

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High Speed Off-Road Vehicles

Suspensions, Tracks, Wheels and Dynamics

Bruce Maclaurin

Retired ex Ministry of Defence UK

Copyright

This edition first published 2018

© 2018 John Wiley & Sons Ltd

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Library of Congress Cataloging-in-Publication Data

Names: Maclaurin, Bruce, author.

Title: High speed off-road vehicles : suspensions, tracks, wheels and dynamics / Bruce Maclaurin.

Description: Hoboken, NJ : John Wiley & Sons, 2018. | Series: Automotive series | Includes bibliographical references and index. |

Identifiers: LCCN 2018007653 (print) | LCCN 2018012003 (ebook) | ISBN 9781119258803 (pdf) | ISBN 9781119258810 (epub) | ISBN 9781119258780 (cloth)

Subjects: LCSH: Off-road vehicles.

Classification: LCC TL235.6 (ebook) | LCC TL235.6 .M25 2018 (print) | DDC 629.228/8-dc23

LC record available at https://lccn.loc.gov/2018007653

Cover Design: Wiley

Cover Images: Background: © solarseven/Shutterstock; Left: Range Rover Sport Offroad Presentation by Wachauring is licensed under CC BY-SA; Middle: © Rockfinder/Gettyimages; Right: Reservists Train to be Challenger tank crew, WMID-2013-044-350 © Crown Copyright 2013

Dedication

To the late Professor David Crolla, whose advice, knowledge, encouragement and humour are sorely missed.

To my wife Jacqueline, for her encouragement and tolerance of my many hours communing with journals, papers, books and my computer.

Series Preface

The automobile is a part of our society, and tightly linked to many aspects of our daily lives. We see a wide variety of vehicles every day, passing us on the streets in our cities and on our motorways. There is of course a vast plethora of different vehicles used for different aspects in our daily lives, and in more special applications. Perhaps some of the more interesting and exciting applications are those that are far removed from our everyday lives. Two of the more famous and popular vehicle applications in the automotive sector are high speed vehicles such as race cars and off‐road vehicles such as large earth‐moving equipment. Being in the field for over 30 years, many of those years as a faculty member, I can testify to the fact that most people get very excited when they are inspecting a top‐rated race car or see these vehicles on the track. The same is true when standing next to or watching large earth‐moving equipment in operation. There is nothing quite like seeing an earth‐mover that is capable of effortlessly hauling the volume of several large sedans up a steep grade out of a mining operation. Of course, the combination of these two areas into High Speed Off‐Road Vehicles is an amalgamation that is not only extremely exciting from an engineering perspective, but one that presents unique challenges to vehicle designers that are not faced in many other automotive sectors.

High Speed Off‐Road Vehicles is an excellent and 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 also provides spreadsheet‐based analytical approaches to modelling these topic areas, providing 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.

It is quite clear that this text is a unique and valuable addition to the Automotive Series whose primary goal is to publish practical and topical books for researchers and practitioners in industry, and postgraduate/advanced undergraduates in automotive engineering. The series addresses new and emerging technologies in automotive engineering, supporting the development of next‐generation transportation systems. The series covers a wide range of topics, including design, modelling and manufacturing, and provides a source of relevant information that will be of interest and benefit to people working in the field of automotive engineering.

High Speed Off‐Road Vehicles is written from a very pragmatic perspective, based on the author’s extensive experience, and provides an excellent introduction to off‐road vehicles. Simultaneously, it is a strong reference text for those practising design and analysis of such systems. No other text covers the concepts and vehicle systems that are presented in this book. It is an excellent read, very understandable and highly informative. The bottom line is that this book covers a very interesting topic area and is highly unique in its content, making this book a welcome addition to the Automotive Series.

April 2018

Thomas Kurfess

Acknowledgements

I would like to extend my gratitude to:

the UK Ministry of Defence, for sponsoring most of the work described in this book;

the many colleagues at DERA who contributed, and in particular Robert Gray, Robin Warwick, Peter Cox, Narinder Dhillon and Matt Williams; and to my nephew Peter Maclaurin for producing some of the line drawings.

the team at John Wiley and Sons, including Eric Willner and Anne Hunt (commissioning editors), Nithya Sechin and Blesy Regulas (project editors), P. Sathishwaran (production editor) and Elaine Rowan (freelance copy editor).

Introduction

To a large extent, this book reflects my time and experience working at the UK Ministry of Defence Military Vehicle Establishment at Chertsey, Surrey. During this time it was variously known as FVRDE (Fighting Vehicles Research and Development Establishment), MVEE (Military Vehicles Engineering Establishment), RARDE Chertsey (Royal Armaments Research and Development Establishment), DRA (Defence Research Agency) and DERA (Defence Engineering and Research Agency) before it was closed in 2002 and split between QinetiQ and DSTL (Defence Science and Technology Laboratory). For the purposes of the book, the establishment is generally called DERA. The term ‘high speed’ in the title of the book is used somewhat loosely, but is meant to exclude mainly unsprung vehicles. The vehicles described are largely military because they are the most common type of off‐road vehicles, although wheeled logistic vehicles spend much of their time on roads.

The book mainly describes the running gear systems of vehicles, that is, the suspension systems, tracks, wheels and tyres and their effects on vehicle performance in off‐road conditions. The book does not review vehicle power trains, except for describing the mechanisms used for providing the differential track speeds required for steering tracked vehicles. The engines used in wheeled vehicles, logistic and armoured, are typically uprated commercially available engines. For main battle tanks (MBTs), more specialist units are required because of the need to combine high power (up to about 1100 kW) with very compact dimensions. Apart from the Abrams tank, which uses a gas turbine engine, the diesel engine technology used is still fairly conventional. The transmissions of tracked military vehicles tend to be specialist because of the need to combine the drive engagement and ratio‐changing functions with the system used for providing differential speeds to the tracks. The drive engagement and ratio‐changing systems remain largely conventional. The units also need to be mounted transversely. As described in Chapter 7, electric drive and steering systems are now being investigated for these functions.

Much use has been made in the book of spreadsheet analysis using Microsoft Excel, and particularly the Solver routine for solving equations of motion. Although the Excel/Solver approach can be somewhat laborious at times, an advantage is that the equations of motion need to be written from first principles, particularly those for tracked vehicles, requiring careful analysis of and good insight into the systems being studied.

The book is partly descriptive of past and present systems and partly analytical. It is not an academic book, or intended to be so, but hopefully some of the methods shown will be of use to vehicle designers.

Chapter 1 describes the suspension systems that are and have been used on tracked vehicles. In particular, the properties of the hydrogas unit used on the Challenger tank are examined in detail.

Chapter 2 describes vehicle track systems, both link tracks, and the flexible tracks that are increasingly being used. Performance aspects considered include rolling resistance and the noise and vibration caused by link tracks.

Chapter 3 examines the ride performance of tracked vehicles, including human response to vibration, terrain profiles, wheelbase filtering and computer modelling. Pitch response to braking is also considered.

Chapter 4 examines the potential advantages of active and semi‐active suspension systems and describes two DERA test vehicles and their ride performance.

Chapter 5 describes the driveline and suspension systems of wheeled vehicles, both unarmoured and armoured. Interconnected suspension systems are also described.

Chapter 6 considers the suspension performance of wheeled vehicles including the use of quarter‐car models and the effect of using the different ISO 2631 and BS 6841 HRV filters. Also described are some ride performance measurements of a logistic vehicle.

Chapter 7 examines the steering performance of tracked and wheeled vehicles. The Magic Formula, widely used for describing the force–slip characteristics of pneumatic tyres, is used here to describe the force–slip properties of a track system in a skid steering model. Results are shown for steering response and also for the power flows through the double‐differential steering system. Similar models are shown for comparing the steering performance of a skid steered and an Ackermann steered wheeled vehicle. The effects of torque vectoring are also considered.

Chapter 8 examines the soft‐soil performance of wheeled and tracked vehicles. Most predictive methods are empirically based, particularly for wheeled vehicles, because of the difficulty of directly modelling the behaviour of a pneumatic tyre in a soft yielding soil. The results of DERA field trials with single pneumatic tyres and a track rig are described together with the predictive models developed. A tractive force–slip relationship for a tyre in a soft cohesive soil is also developed from the field trial results.

Chapter 9 describes the effects of limited‐slip differentials on the traction and steering performance of vehicles. Relationships are developed to describe the effects of frictional limited‐slip differentials on tractive performance on different surfaces and soils. Results are compared with those for free and locked differentials. The effects on steering performance on a road surface are also examined.

Chapter 10 describes some previous, experimental and current articulated vehicles, both tracked and wheeled. The traction forces required to steer skid and articulated tracked vehicles are compared. Similarly, the traction forces required to steer articulated wheeled vehicles on hard and soft soils are compared with those for skid and Ackermann steered vehicles.

Chapter 11 examines the basic relationships that determine the likelihood of a vehicle to rollover. Methods to reduce the likelihood of rollover are reviewed. A study of a rollover incident with a logistic vehicle is described. A model is developed to predict the rollover angle of the vehicle and compare it with the measured vehicle tilt angle.

The author has made every reasonable effort to trace copyright holders and to obtain permissions to reproduce images in the book. Apologies are made if suitable permissions have not been obtained; copyright holders should then contact the publishers so that corrections can be made in any further print editions.

1Tracked Vehicle Running Gear and Suspension Systems

The running gear systems used on high speed, mainly military, tracked vehicles provide four essential functions:

the transmission of drive to a relatively large number of road wheels;

the distribution of the weight of the vehicle over a relatively large area;

a large suspension displacement to allow high speeds over rough terrains; and

a particular requirement of military armoured vehicles, the running gear system should occupy the minimum space in the overall vehicle envelope in order to maximise internal hull volume (as will be shown in

Section 8.4

, this is a particular attribute of tracked vehicles compared to wheeled vehicles of similar soft‐soil performance).

In addition, the running gear must be of minimum weight, reliable, easy to maintain, and compared to some other vehicle components, relatively cheap to produce.

1.1 General Arrangement

Figure 1.1 shows the running gear of the Warrior Infantry Fighting Vehicle (IFV) and is typical of modern practice. Trailing suspension arms carry rubber‐tyre road wheels and operate transverse torsion bars which run across the floor of the vehicle. Rotary vane hydraulic dampers are incorporated into the pivots of the front, second and rear road wheel stations. Link tracks run under the road wheels and around hull‐mounted drive sprockets and return idlers. Track pretension is adjusted by means of oil‐filled rams reacting against the idlers, which are carried on short pivoting arms. The drive sprockets are front‐mounted but could be at the rear of the vehicle, depending on the position of the power pack. Small diameter rollers support the top run of the track. The track link pivots are rubber‐bushed and the links are fitted with replaceable rubber road pads to minimise road damage and reduce noise and vibration.

Figure 1.1 Warrior running gear layout. Source: Courtesy of Ministry of Defence.

Figure 1.2 shows the arrangement on the Leopard 2 Main Battle Tank (MBT). Rotary friction dampers are built into the front three and rear two axle arm pivots. The vehicle is fitted with rubber‐bushed double‐pin tracks (see Chapter 2).

Figure 1.2 Leopard 2 running gear layout. Source: Courtesy of ATZ.