Controller design of a new active front steering system

An AFS (active front steering) on the basic of a C-EPS (column electric power steering) system was developed. Based on the mathematical model of essential components, the AFS controller was designed covering two units: an EPS actuator unit was used to reduce the steering torque requirement to the driver; an AFS actuator unit was used to compensate the steering angle for steering characteristics and vehicle stability. In contrast to the conventional stability control, both the sideslip angle and the yaw rate were fed back to this AFS controller and the stability performance has been optimized with LQR (linear quadratic regulator). In addition, tire stiffness uncertainties have been taken account in the LQR controller to provide the control robustness. Finally, HILS (Hardware-in-the-Loop Simulation) tests were conducted to demonstrate the performance of the designed AFS controller. Experiment indicates that the proposed AFS system can improve vehicle stability and compensate the steering reaction torque effectively. Key-Words: Active front steering (AFS), Electric power steering (EPS), Linear quadratic regulator (LQR), Sideslip angle, Yaw rate, Vehicle stability