The Effect of Tyre Dynamics on Wheel Slip Control Using Electromechanical Brakes

This paper investigates the response of the wheel slip to brake torque perturbations during a braking manoeuvre as the wheel slip state and the vehicle speed change. Its purpose is to better understand and model the wheel slip response characteristics during braking and to inform the development process of an antiskid wheel slip controller. The developed controller is implemented in the Simulink environment on a half-car vehicle model using a nonlinear electromechanical brake (EMB) model. A linearised analysis of the wheel slip response to brake torque perturbations about a nominal “trim” condition is first performed, based on a quarter-car vehicle model. It is shown that the inclusion of first-order tyre dynamics (characterised by the so-called “relaxation length”) has a significant effect on the dynamics of the “plant” seen by the slip controller and these dynamics vary significantly with the trim value of the slip and the vehicle speed. The implications of these variations for controller design are discussed, taking into account the EMB actuator dynamics. A gain-scheduled PID wheel slip controller is developed and an analysis of the antilock performance of this controller is presented.