Patent ID: 8160777

Claim:
An electric power steering device, comprising: a steering force assisting device having a motor that functions as a drive source and providing a steering system with an assist power for assisting a steering operation; and a control device that controls an operation of the steering force assisting device through a supply of a drive power to the motor, the control device comprising: a motor control signal output part that outputs a motor control signal; a drive circuit that supplies the drive power of three phases to the motor on the basis of the motor control signal; and an abnormality detecting part that detects an electrification failure caused in each of the phases of the motor, wherein: the motor control signal output part generates the motor control signal by executing current control on the basis of a rotational angle of the motor and, upon occurrence of the electrification failure, executes output of the motor control signal by means of two electrification phases other than a phase with the electrification failure; upon occurrence of the electrification failure, the motor control signal output part executes the current control for applying each of the electrification phases with a phase current that changes in the form of a secant curve or a cosecant curve based on an asymptotic line, which is a line on which a predetermined rotational angle corresponding to the phase with the electrification failure is constant; the motor control signal output part executes current restriction for restricting the phase current within a predetermined range; and the motor control signal output part executes acceleration control for accelerating rotation of the motor, in order to prevent the rotation of the motor from stopping as a result of the current restriction.