Simultaneous vehicle-handling and path-tracking improvement using adaptive dynamic surface control via a steer-by-wire system

This paper deals with the simultaneous vehicle-handling and path-tracking improvement through a steer-by-wire system, using non-linear adaptive dynamic surface sliding control. The designed adaptive dynamic surface controller, which is insensitive to system uncertainties, offers an adaptive sliding gain to eliminate the precise determination of the bound of uncertainties. The sliding-gain value is obtained using a simple adaptation law that does not require an extensive computational load. Achieving the improved vehicle-handling and path-tracking characteristics requires both accurate state estimation and well-controlled steering inputs from the steer-by-wire system. A second-order sliding-mode observer provides accurate estimation of the lateral and longitudinal velocities while the yaw rate is available from the angular rate sensor. A driver control model is also presented according to the preview or look-ahead strategy to generate appropriate steering angles using the vehicle state feedback and future information about the path to be followed. Moreover, because of the inertia and viscous damping of the steering mechanism, and the effects of the Coulomb friction and self-aligning moment of the front tyres, the steering-system controller is designed based on the proposed adaptive dynamic surface scheme, to control the front steering angle. A complete stability analysis based on the Lyapunov theory is presented to guarantee closed-loop stability. The simulation results confirmed that the proposed adaptive robust controller not only improves the vehicle-handling and path-tracking performance but also reduces the chattering problem in the presence of uncertainties in the tyres' cornering stiffnesses.