Electric power steering apparatus

Abstract

An electric power steering (EPS) apparatusincludes a motor, an EPS actuator, a torque sensor, and an ECU. The EPS actuatoruses the motoras a drive source to apply assist force to a steering system, thereby assisting a steering operation. The torque sensordetects a steering torque τ of the steering system. The ECUcontrols the operation of the EPS actuator. Based on the steering torque τ detected by the torque sensor, the ECUcomputes a basic shift amount εts_b of the assist force applied to the steering system. The ECUdetermines which one of returning, holding, and turning is the state of the steering operation. When the state of the steering operation is returning or holding, the ECUexecutes compensation control for correcting the steering torque τ, which is used in the computation of the basic shift amount εts_b of the assist force, thereby increasing the assist force applied to the steering system. The ECUsubjects the steering torque shift control amount εts to a filtering process using a low pass filter, thereby inhibiting the steering torque shift control amount εts from sharply changing. When the state of the steering operation is turning, the ECUchanges a filter constant of the low pass filter so as to reduce the filtering effect.