Modelling the vehicle and its subsystems

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Tyre factors influencing braking performance

Undulations in the road surface cause wheel and body motions that result in varying vertical wheel loads. Due to the nonlinear characteristics of tyres, it may result in decreased longitudinal forces generated at the tyre-road interface. This may have the effect of increased stopping distances on uneven or rough roads due to a loss in the longitudinal friction force. The rougher the road, the higher the loss of longitudinal friction force is. This phenomenon significantly complicates the modulation of brake pressure by an anti-lock braking system (Breuer and Bill, 2008).
Jaiswal et al. (2010) used a 14 degree of freedom (DOF) vehicle model to study the influence of tyre model transience on ABS braking. They used three, single-point contact transient tyre models, a stretched-string tyre model, a modified stretched-string tyre model, and a contact mass transient tyre model. Straight-line braking and brake-in-turn manoeuvres were simulated on smooth road surfaces. Different road surface conditions were simulated, namely a dry road, a wet road and a dry snowy road. Jaiswal et al. (2010) concluded that the accurate modelling of the tyre transient dynamics is crucial to the accurate simulation of ABS braking.
Adcox et al. (2013) investigated the effect of the tyre’s torsional dynamics on the performance of ABS. A rigid-ring tyre model with a LuGre friction model was used in the simulation environment and a quarter-car test rig was built. Included in their investigation was a sensitivity analysis where low-pass filtering the wheel speed, the sensitivity to sidewall torsional stiffness and the sensitivity to wheel and tread ring inertia (of the rigid ring model) were considered. Their investigation showed that the low-pass filter’s cut-off frequency had a significant effect on the braking distances achieved. The selection of the cut-off frequency was also tyre dependent and it influenced the robustness of the ABS performance to variations in tyre inertia and torsional stiffness.

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List of Figures xi
List of Tables xv
List of Symbols xvii
Chapter 1 Introduction and problem statement 
1.1 Introduction
1.2 Initial experimental investigation
Chapter 2 Literature review 
2.1 Tyre force generation
2.1.1 Longitudinal force characteristics
2.1.2 Lateral force characteristics
2.1.3 Combined lateral and longitudinal force generation
2.1.4 Tyre models
2.1.5 Tyre factors influencing braking performance
2.2 Braking
2.2.1 Load transfer during braking
2.2.2 Vehicle stability during braking
2.2.3 Anti-lock brake systems (ABS)
2.2.4 Factors that influence ABS performance
2.2.5 Brake models
2.3 Research question and conclusion from literature review
Chapter 3 Modelling the vehicle and its subsystems 
3.1 Experimental vehicle
3.2 Vehicle model
3.2.1 Road profiles
3.2.2 Tyre model
3.2.3 Braking system
3.2.4 Experimental model validation
3.3 Conclusion and next steps
Chapter 4 Braking performance evaluation 
4.1 Introduction
4.2 Exploiting the tyres’ physics
4.3 Existing ABS performance assessment criteria
4.4 Existing directional stability assessment criteria
4.5 Proposed ABS performance evaluation technique
4.6 Illustrating the ABS performance evaluation technique on smooth roads
4.6.1 Straight line braking results
4.6.2 Brake-in-turn results
4.6.3 Split-mu braking results
4.6.4 Discussion of the proposed performance evaluation technique
4.7 Application of performance evaluation technique on rough roads
4.8 Conclusion
4.9 Next steps
Chapter 5 ABS algorithm inputs 
5.1 Introduction
5.1.1 Kinematic rolling radius
5.1.2 Kinetic rolling radius
5.1.3 Approach
5.2 Experimental setup
5.3 Experimental results
5.3.1 Kinematic rolling radius
5.3.2 Kinetic rolling radius
5.4 Conclusions
5.5 Next steps
Chapter 6 The influence of tyre force generation on the braking performance 
6.1 Introduction
6.2 The influence of suspension configuration on braking distance
6.2.1 Parallel corrugations braking simulation results
6.2.2 Angled corrugations braking simulation results
6.2.3 Belgian paving braking simulation results
6.2.4 Discussion of results
6.3 Conclusion
Chapter 7 Improving the braking performance: The WiSDoM algorithm 
Chapter 8 Conclusions and recommendations 

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