Advanced control strategy for electric power steering system to improve steering assist torque stability

Abstract

The EPS (electric power steering) system has been used to replace the conventional HPS (hydraulic power steering) system in vehicles. This system assists the steering effort of the driver using an electric motor and a gear force reduction. In a previous study, an EPS control method was proposed that used the driver's steering input torque and vehicle velocity. In addition, many papers have introduced estimation and control methods for the EPS motor's angular velocity or angular torque to reduce the sense difference for the HPS. Therefore, this paper proposes an advanced control strategy for EPS that uses the lateral force of the front wheels. In addition, we experimented with this proposed control algorithm using a simulation and confirmed that it reduced the assist torque and saved motor power. Although it is difficult to obtain the lateral wheel force of the tires for the proposed method, it is able to reduce the torque ripple of the EPS actuator, as well as troublesome problems with steering wheel vibration. Moreover, this EPS control strategy can improve a vehicle's dynamic stability.