Tyre curve estimation in slip controlled braking
Progress in reducing actuator delays in pneumatic brake systems creates an opportunity for advanced anti lock braking algorithms to be used on heavy goods vehicles. However, these algorithms require knowledge of variables that are impractical to measure directly. This paper introduces a braking force observer and road surface identification algorithms to support a sliding mode slip controller for air braked heavy vehicles. Both the force observer and the slip controller are shown to operate robustly under a variety of conditions in quarter car simulations. A non linear least squares algorithm was found to be capable of performing regressions on all the parameters of the tyre model from the University of Michigan Transportation Research Institute when used 'in the loop' with the controller and the observer. A recursive least squares algorithm that is less computationally expensive than the non linear algorithm was also investigated but gave only reasonable estimates of the tyre model parameters on high friction smooth roads.