Patent ID: 8823305
Filing Date: 2014-09-02
Classification: B62D

Abstract:
1. An electric power steering system that includes a motor that applies assist force to a steering system, comprising: a rotation angular velocity acquisition unit that acquires a corresponding rotation angular velocity that corresponds to a rotation angular velocity of the motor; an induced voltage calculation unit that calculates an induced voltage of the motor as an estimated induced voltage at the same time that the corresponding rotation angular velocity is acquired; a back electromotive force constant calculation unit that calculates a back electromotive force constant based on the corresponding rotation angular velocity and the estimated induced voltage; and a rotation angular velocity calculation unit that calculates a rotation angular velocity of the motor as an estimated rotation angular velocity based on a current of the motor, a voltage of the motor, the back electromotive force constant and a resistance of the motor, wherein when a magnitude of the corresponding rotation angular velocity is higher than a threshold, an amount of change in the corresponding rotation angular velocity is smaller than a reference chance amount and an absolute value of a difference between a first corresponding rotation angular velocity and a second corresponding rotation angular velocity is smaller than a set value, the estimated induced voltage is calculated.