Vehicle steering system state estimation using sliding mode observers

The increasing sophistication of the electronics package available on board the modern automobile, has made viable a number of new technologies that can greatly enhance the driveability and safety of the vehicle. One area that has received much attention is the use of drive by wire steering systems that partially or in some cases (such as in some envisaged IVHS systems) completely takes over the tasks of vehicle directional control. The vehicle handling dynamics are quite nonlinear (especially for severe maneuvers and over large variations in longitudinal speed). Most steering control algorithms require knowledge of the vehicle states and in many cases are quite sensitive to the values of various vehicle parameters such as tire cornering stiffness, tire-road coefficient of friction etc. Measuring the states is usually expensive and direct measurement of the parameters is often impossible. Thus, some means of estimating these variables becomes imperative. Recent advances in sliding mode control/estimation theory have demonstrated the effectiveness of such schemes when applied to nonlinear systems. This paper presents some extensions to the theory of sliding mode observers and an application to the problem of estimating vehicle steering system states.