Adaptive fast non-singular terminal sliding mode control for a vehicle steer-by-wire system

Steer-by-wire (SbW) systems in road vehicles require an effective controller to provide accurate and robust steering performance. For this purpose, this study proposes an adaptive fast non-singular terminal sliding mode (AFNTSM) controller for an SbW system by combining an adaptive estimation law with a fast non-singular terminal sliding mode (FNTSM) control scheme. First, the authors present a model to identify the dynamics of the SbW system, in which the self-aligning torque and friction-related forces are treated as external disturbances. Second, the AFNTSM control design is elaborated, which is proved to be able to guarantee high tracking accuracy via effectively estimating the self-aligning torque, fast convergence rate owing to its exponential stability, strong robustness against system and road surface uncertainties, and inherently smooth control inputs. Subsequently, the selection criteria of the control parameters are given in details. Finally, experimental results are shown to demonstrate that the designed AFNTSM controller has great superiority in comparison with an FNTSM controller without adaptation and an adaptive sliding mode controller based on conventional sliding mode.