ELECTRIC POWER STEERING SYSTEM

摘要

Provided is an electric power steering system that achieves a more appropriate steering feel. An ECU of the electric power steering system calculates a basic assist component (T a1 *) and a target pinion angle (¸ p *) based on at least steering torque (T h ). The ECU calculates a correction component for the basic assist component (T a1 *) through feedback control in which an actual pinion angle is caused to match the target pinion angle (¸ p *). The ECU calculates an assist command value by adding the correction component to the basic assist component (T a1 *). The ECU corrects a hysteresis controlled variable (T hy *) and a viscosity component (T vi *) according to the rate of change (gradient) in a spring component (T sp *) with respect to a change in absolute value of the target pinion angle (¸ p *). Specifically, the ECU multiplies the hysteresis controlled variable (T hy *) and the viscosity component (T vi *) by gains (G hy , G vi ) that have a larger value as the rate of change in spring component (T sp *) increases.