Electric power steering system designed to generate torque for assisting driver's turning effort

摘要

In an electric power steering system installed in a vehicle and designed to generate, by a motor (6), assist torque for assisting the driver's turning effort of the steering wheel, a self-aligning torque determiner (110) determines a value of self aligning torque applied to the vehicle. A commanded-value generator (120) determines a value of an assist ratio based on a predetermined relationship between a variable of the self aligning torque and a variable of the assist ratio. The assist ratio represents a ratio of share of torque by the motor (6) for compensating the self aligning torque. The commanded-value generator (120) generates, based on the self aligning torque and the value of the assist ratio, a commanded value for the assist torque. An assist torque determiner determines the assist torque based on the commanded value for the assist torque generated by the commanded-value generator (120).