Handling Enhancement through Active Rear-Wheel Steering with 4WS Vehicle Reference Model

Active Rear Steering (ARS) is an effective means to enhance vehicle steering responsiveness. To fully explore the handling characteristics of four-wheel steering (4WS) vehicles, this paper proposes an ARS control approach founded on a time-varying parameter reference model for 4WS vehicles, with the controller employing model predictive control (MPC). This reference model is established by analyzing rear-wheel steering characteristics and defining the front and rear wheel steering angle reference ratio coefficient. Through serpentine slalom tests, combined with the driver manoeuvring intentions, the vehicle state response at different speeds and front-to-rear wheel steering angle ratios is analyzed. A two-dimensional reference map, accounting for vehicle speeds and driver manoeuvring intentions, is designed to enable real-time updates of the vehicle reference model. The experiment results indicate that the ARS controller with the designed 4WS vehicle reference model can enhance the vehicle's yaw rate response, reduce the peak steering wheel angle for the driver, and greatly improve the vehicle's maneuverability performance under normal conditions.