Research on Friction Compensation Control for Electric Power Steering System

With motor and reduction mechanism applied to Electric Power Steering (short for EPS) system of automobile, the frictional loss torque of steering system is increased. The common friction compensation control through the sign function of angular velocity or the saturation function of angular velocity is conducted to reduce the frictional loss torque of steering system. However, when the motor used in steering system generates assist torque based on the common friction compensation control, the longitudinal intercepts of steering torque change obviously at different steering wheel angles. The driver will get different frictional loss torque of steering system at different steering wheel angle. The information of steering torque contains the change of steering reaction torque and the frictional loss torque of steering system, so the change of frictional loss torque can cause the fuzzy of road feeling. In this paper, the variable friction compensation control is proposed to make the longitudinal intercepts of steering torque same at different steering wheel angles and make the driver have similar feeling of frictional loss torque. So road feeling has nothing to do with the frictional loss torque of steering system and is only influenced by EPS assist torque, which makes it easier to get good road feeling.