Patent ID: 7628247

Claim:
An electric power steering device for a vehicle comprising: a motor working to produce a steering assist torque when a steering wheel of a vehicle is being rotated in a rotational direction, the steering wheel assist torque urging rotation of the steering wheel in the rotation direction; a torque sensor working to measure a steering torque; a vehicle speed sensor working to measure a speed of the vehicle; a steering velocity determining circuit working to determine a steering velocity of the steering wheel; a motor control working to control an operation of said motor based on the steering torque, as measured by said torque sensor, and the speed of the vehicle, as measured by said vehicle speed sensor; a decision-making circuit working to decide whether condition parameters related to preselected operating conditions of the vehicle meet given requirements or not; and an automatic rotation controller working to perform an automatic steering control to maintain said motor to produce the steering assist torque to rotate the steering wheel in the rotation direction based on the steering velocity determined by said steering velocity determining circuit and the speed of the vehicle; wherein when the steering torque and the speed of the vehicle have fallen within given ranges, respectively, said decision-making circuit deciding that the condition parameters have met the given requirements, and said automatic rotation controller including means for initiating the automatic steering control to maintain said motor to produce the steering assist torque to rotate the steering wheel in the rotation direction and means for holding the steering velocity of the steering wheel constant; and when said decision-making circuit decides that the condition parameters have been shifted from the given requirement, said automatic rotation controller deactivating the automatic steering control.