Patent ID: 8767364

Claim:
A vehicle steering system that applies driving force to a steering mechanism of a vehicle with use of a three-phase brushless motor that has a rotor and field coils, comprising: a drive circuit that includes three sets of series circuits which correspond to the respective three phases and each of which is formed of two switching elements that are connected in series, wherein the series circuits are connected in parallel with one another between a power supply and a ground, and regenerative diodes are connected in parallel with the respective switching elements; stop control means for, when a short-circuit fault occurs in one of the plurality of switching elements, turning off all the switching elements to stop driving of the three-phase brushless motor; first identifying means for, in a state where driving of the three-phase brushless motor is stopped by the stop control means, identifying whether the short-circuited switching element is one of the high-side switching elements or one of the low-side switching elements; second identifying means for, in a case where the short-circuited switching element is identified as one of the high-side switching elements by the first identifying means, detecting minimum phase voltages of the three phases when a steering member for steering the vehicle is operated, and comparing the detected minimum phase voltages of the three phases with one another to identify to which of the three phases the short-circuited switching element corresponds; and third identifying means for, in a case where the short-circuited switching element is identified as one of the low-side switching elements by the first identifying means, detecting maximum phase voltages of the three phases when the steering member for steering the vehicle is operated, and comparing the detected maximum phase voltages of the three phases with one another to identify to which of the three phases the short-circuited switching element corresponds.