Systematic design and control of steering feel for steering-by-wire vehicles

The steering feel of a steering-by-wire (SBW) system plays a critical role in enhancing driving safety, ensuring harmony, and optimizing comfort during human-machine-environment interactions. This paper presents a comprehensive framework for the design of steering feel and closed-loop control strategies for steering torque control. Employing a strategy based on a linear single track vehicle model, this study utilizes the Kalman Filter (KF) technique to estimate the primary forces on the steering rack, facilitating the attainment of fundamental steering gradient and stiffness characteristics. To render detailed road feedback and effectively manage complex steering scenarios, a complementary strategy for observing rack force is developed, leveraging motor currents and rack displacement measurements from the road wheel actuator (RWA). The desired steering torque is determined by a two-dimensional assist curve based on the estimated rack forces. This research further introduces a robust controller designed to track the target steering torque accurately within a predefined performance envelope, and implements feedforward control to attenuate high-frequency fluctuations. Additionally, an active return module is incorporated to bolster return stability in hand-off scenarios. Extensive validation is carried out through joint simulation on the Carsim/Simulink platform and empirical testing on a real vehicle platform. Both simulated and experimental results demonstrate the effectiveness of the proposed control scheme in delivering a superior steering experience.