Patent ID: 7828112

Claim:
An electric power steering apparatus, comprising: a torque sensor which detects a steering torque applied to a steering shaft by a driver; a motor which applies an assist torque for assisting steering to said steering shaft; a vehicle speed sensor which detects a vehicle speed; an assist command calculation unit which calculates an assist command in response to the steering torque detected by said torque sensor and the vehicle speed detected by said vehicle speed sensor; a motor controlling device which controls the assist torque of said motor in response to the assist command calculated by said assist command calculation unit; an abnormality detection unit which detects an abnormality generated in an electric power steering apparatus body; an assist command switching unit which switches the assist command and an assist command at an abnormal time; and a steering burden estimation unit which estimates a steering burden of the driver on a basis of at least any one signal of a rotational angular velocity of said motor detected from said motor, the steering torque, and the vehicle speed, wherein, in a case said abnormality detection unit detects the abnormality, said assist command switching unit switches the assist command to the assist command at an abnormal time, thereby continuing a control of the assist torque of said motor in response to the assist command at abnormal time; the assist command at the abnormal time is set smaller than that at a normal time when there is no abnormality in a first range where the steering burden estimated by said steering burden estimation unit is small; the assist command at the abnormal time is increased equally to that at a normal time when there is no abnormality in a second range where the steering burden estimated by said steering burden estimation unit is larger than the first range; and the assist torque is increased or decreased in response to the steering burden.