Patent ID: 8909429

Claim:
A vehicle steering system in which an operating member that is operated for steering is not mechanically coupled to a steering mechanism and the steering mechanism is driven by a steered system motor formed of a brushless motor, the vehicle steering system comprising: a rotation angle sensor configured to detect a rotation angle of a rotor of the steered system motor; and a processor programmed to: estimate the rotation angle of the rotor of the steered system motor based on an induced voltage of the steered system motor; compute a target rotor angle that is a target value of the rotation angle of the rotor of the steered system motor based on a steering state; superimpose a rotation maintaining command signal for continuously rotating the steered system motor on the computed target rotor angle; detect an occurrence of a malfunction of the rotation angle sensor; and in response to a detected malfunction of the rotation angle sensor, change a control mode from: a first control mode, in which the steered system motor is controlled based on the target rotor angle or the target rotor angle on which the rotation maintaining command signal has been superimposed by the processor and a value detected by the rotation angle sensor, to a second control mode, in which the steered system motor is controlled based on the target rotor angle on which the rotation maintaining command signal has been superimposed by the processor and the estimated rotation angle of the rotor.