Research on the All-Wheel Steering Control Strategy for Multi-Axle Vehicles Based on Super-Twisting Sliding Mode Control

All-wheel steering is an effective means to improve the high-speed handling stability and low-speed mobility flexibility of multi-axle vehicles, and the control strategy is a major factor affecting the steering characteristics. In view of the numerous nonlinearity (such as system coupling nonlinearity, tire nonlinearity), uncertainties (such as vehicle parameter uncertainty, modeling uncertainty, external disturbance, etc.), as well as the chattering phenomenon of steering system easily caused by traditional sliding mode control, this paper proposes a novel super-twisting sliding mode control strategy for all-wheel steering system of multi-axle vehicles. Firstly, a 11-DOF nonlinear uncertain dynamic model, nonlinear tire model, and random road surface model for the multi-axle vehicle are established. Secondly, an ideal reference model for the multi-axle vehicle is built by simultaneously considering the low-speed and high-speed steering performance. Thirdly, a continuous control law for the multi-axle vehicle is synthesized based on the super-twisting sliding mode control idea and the finite-time separation principle, which can overcome the effects of nonlinearity and uncertainty, suppress jitter phenomenon, and compel the system sates to converge in finite time. Finally, the finite-time stability of all-wheel steering system is systematically proven by using Lyapunov theory and finite time stability theory. The simulation results under three typical working conditions show that, in contrast to front axle steering control, proportional control and discontinuous switching sliding mode control, the designed controller posses faster convergence speed, and can improve the high-speed steering stability and low-speed steering mobility of multi-axle vehicles significantly.