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Tyre characteristics and modelling 267 Braking force F x (N) Dry road Good tread on wet road Slip angle = 0 Camber angle = 0 Poor tread on wet road Aquaplaning 0.0 Fig. 5.20 Slip ratio 1.0 The effect of road contamination on braking values of braking force as expected reduce and that for a locked wheel with poor tread a dangerous situation known as hydroplaning or aquaplaning can arise where the tyre runs on a film of water and traction is effectively lost. The curves of braking force can also be categorized by two coefficients of friction associated with the peak braking force and that associated with total sliding at a slip ratio of 1.0. On dry roads it is possible to obtain a coefficient of friction for good tyres in excess of 1.0, on wet roads this would typically reduce to about 0.5 or lower for tyres with poor tread while a road contaminated with ice may only achieve a peak value of 0.1. It can be seen when examining the curves in Figure 5.20 that the longitudinal stiffness is relatively unaffected by surface contamination. This is particularly dangerous for a road with ice or the poor tyre on a wet road. In these conditions the peak braking force occurs rapidly at low slip ratio causing the vehicle to skid before any possible corrective action from the average driver. In addition to the above it is also known that an increase in vehicle speed will reduce peak values of braking force and that other parameters such as tyre inflation pressure will have an effect, a more detailed treatment of which is given by Gillespie (1992). 5.4.5 Driving force During driving the transmission will impart a driving torque T D to the rotating wheel as shown in Figure 5.21. As the angular velocity of the wheel increases a driving force is generated that tends to move the contact patch forward relative to the wheel centre. This effect will introduce circumferential compression in the tread just before entering the contact patch and tension on leaving as opposed to braking. As the wheel is driven the tread entering the contact patch will initially bend forward under the action of shear stresses for a short distance. As the tread approaches the rear of the tread the pressure begins to unload releasing
268 Multibody Systems Approach to Vehicle Dynamics T D O V = R e Tension Rear Tread deformation Front Compression F D x {X SAE } 1 F z Pressure distribution Longitudinal slip Longitudinal shear stress Fig. 5.21 Generation of force in a driven tyre the deformation in the tread and progressive sliding develops. These actions produce distributions of pressure, slip and longitudinal shear stress of the type shown at the bottom of Figure 5.21. It can also be seen that when driving, the pressure distribution tends to differ from that in a braked tyre as the peak, and hence resultant tyre load, move further to the rear in the tyre contact patch reducing the offset x. If the resulting driving force is maintained the angular velocity of the tyre will increase from its free rolling value and will eventually begin to spin.
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Multibody Systems Approach to Vehic
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Multibody Systems Approach to Vehic
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Contents Preface Acknowledgements N
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Contents vii 4.10.1 Problem definit
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Contents ix 8.2.1 Active suspension
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Preface This book is intended to br
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Preface xiii vehicle design process
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Acknowledgements Mike Blundell In d
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Nomenclature xvii {z I } 1 Unit vec
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Nomenclature xix O n Frame for part
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Nomenclature xxi p Magnitude of re
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1 Introduction The most cost-effect
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Introduction 3 subsequent ‘classi
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Introduction 5 Fig. 1.4 Linearity:
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Introduction 7 While apparently a s
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Introduction 9 3. The body yaws (ro
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Introduction 11 Aspiration Definiti
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Introduction 13 Decomposition: Synt
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Introduction 15 The best multibody
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Introduction 17 shows good correlat
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Introduction 19 generated in numeri
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Introduction 21 1.9 Benchmarking ex
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2 Kinematics and dynamics of rigid
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Kinematics and dynamics of rigid bo
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3 Multibody systems simulation soft
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4 Modelling and analysis of suspens
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Tyre characteristics and modelling
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Modelling and assembly of the full
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7 Simulation output and interpretat
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Simulation output and interpretatio
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down and even more difficult to asc
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8 Active systems 8.1 Introduction M
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Active systems 443 mechanical actua
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Active systems 445 Table 8.1 MSC.AD
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Active systems 447 Body acceleratio
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Active systems 449 impressions of t
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Active systems 451 For this reason,
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Appendix A: Vehicle model system sc
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Appendix B: Fortran tyre model subr
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Appendix C: Glossary of terms Agili
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Appendix C: Glossary of terms 489 a
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Appendix C: Glossary of terms 495 m
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Appendix C: Glossary of terms 501 s
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References 503 Blundell, M.V. The m
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References 505 Hudi, J. AMIGO - A m
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References 507 Palmer, D. Course no
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References 509 European ADAMS News
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Index Abuse loads, 148 3 g bump, 14
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Index 513 Elk Test, 1 El-Nasher, 29
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Index 515 generalised translational
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Index 517 steer axis inclination, 1
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