Analytic Nonlinear Observer Based Design for Antilock Braking Systems

Abstract

This paper describes an observer based design for control of vehicle traction that is important in providing safety and obtaining desired vehicle motion in longitudinal vehicle control. Since vehicle traction force depends on the friction coefficient between road and tire, which in turn depends on the wheel slip and road conditions, we may influence traction force by varying the wheel slip. A robust adaptive sliding mode controller is designed to maintain the wheel slip at any given value. Simulations show that this longitudinal traction controller is capable of controlling the vehicle with parameter deviations and disturbances. The direct state feedback is then replaced with nonlinear observers in order to estimate the vehicle velocity from the output of the system which is the wheel velocity. The nonlinear systems model is shown to be locally observable. Extended Kalman filter and sliding observer are the two methods used for estimation. The effects and drawbacks of these observers are shown via simulations. The sliding observer is found to be promising while the extended Kalman filter is unsatisfactory due to unpredictable changes in the road conditions.