Adaptive Global Fast Sliding Mode Control for Handling Improvement of Steer-by-Wire System Road Vehicles

Abstract

A steer-by-wire (SbW) system, also known as a Next-generation steering system, is one of the core elements of autonomous driving technology. SbW system’s modular design, tuneable steering feel, variable steer ratio and active steering capabilities fully unlock the potential of modern vehicles and future autonomous vehicles. Particularly, SbW system enhances the functionalities of Advanced Driving Assistance Systems (ADAS) to the next level, and provides the foundation to implement the Level-5 fully automated driving system. Navigating a SbW system road vehicle in varying driving conditions requires an adaptive and robust control scheme, to compensate the uncertain system parameters variations and external disturbances effectively generated due to the tire-road contact and steering geometry. Also, the control scheme also self-sufficient to avoid the high-frequency chattering and rejects control overshoots without saturating the electronic controller, and ensures the closed-loop stability while tracking the reference steering signal provided by the driver or any automated navigation system. Therefore, this study proposed an adaptive global fast sliding mode control (AGFSMC) for SbW system vehicles with unknown steering parameters. First, the cooperative adaptive sliding mode observer (ASMO) and Kalman filter (KF) are established to estimate the vehicle states and cornering stiffness coefficients simultaneously. Second, based on the best set of estimated dynamics provided by the ASMO and KF, the AGFSMC is designed to stabilize the impact of nonlinear tire-road disturbance forces and at the same time to estimate the uncertain SbW system parameters. Due to the robust nature of the proposed scheme, it can not only handle the tire-road variation, but also intelligently adapts to the different driving conditions and ensures that the tracking error and the sliding surface converges asymptotically to zero in a finite time. Finally, the simulations are carried out over the different maneuvering tests, and the successive results are compared with other recognized control techniques that validate the excellent performance of the proposed scheme.