ABSTRACT
Active Front Steering (AFS) system controls steering ‘gear ratio’ of vehicle, which is defined as a ratio of ground wheel steer to steering wheel angle, in order to improve vehicle agility in low speed and directional stability in high speed; AFS raises the gear ratio in low speed, and lowers the gear ratio in high speed. However, a low gear ratio in high speed could compromise yaw rate responsiveness of AFS vehicle, especially in obstacle-avoiding maneuver. Lead Steer Control has been introduced to compensate the yaw rate responsiveness of AFS vehicle in high speed. In this paper, a Lead Steer Control logic is developed based on the lead-lag compensator. Performance and stability of the control logic are designed based on the ‘vehicle-control logic’ model in closed-loop manner, and verified by real vehicle tests. The verification result shows a significant improvement in responsiveness and directional stability of AFS vehicle in high speed driving.
