Patent ID: 8272474

Claim:
An electric power steering system comprising: a motor that applies a steering assisting force to a steering mechanism; an electric current command value-calculating section that calculates an electric current command value that is used to control the motor; a motor control signal generating section that outputs a motor control signal based on the electric current command value calculated by the electric current command value-calculating section; a motor drive circuit that outputs electric power for drive to the motor based on the motor control signal; an abnormal external force application-determining section that determines whether an abnormal external force equal to or greater than a predetermined value is applied to a steered wheel based on one of or both of a motor rotation angular speed and a motor rotation angular acceleration of the motor; and a motor rotation angular speed-reducing section that outputs a speed reduction command value that is used to reduce a rotation angular speed of the motor when the abnormal external force application-determining section determines that the abnormal external force is applied.