Patent ID: 8504247

Claim:
A vehicle steering device comprising: a steering mechanism that steers a wheel of a vehicle upon steering operation of a steering handle; an electric motor that is supplied with source power from an electric power supply device in which a first electric power source and a second electric power source are interconnected in parallel, and that generates assist force that assists in the steering operation of the steering handle; a steering torque detection device that detects steering torque that is input to the steering handle by a driver of the vehicle; a motor control device that controls driving of the electric motor based on an assist characteristic in which a relation between the steering torque and the assist force is set so as to have a characteristic that the assist force changes according at least to the steering torque; and a control device having a first electric power source abnormality detection portion that determines whether or not source power supply from the first electric power source is abnormal, a second source power supply capability detection portion that detects source power supply capability of the second electric power source, an assist characteristic switch portion that switches, when it is determined that the source power supply from the first electric power source is abnormal, the assist characteristic from the assist characteristic set for a time when the source power supply from the first electric power source is normal stepwise to an abnormality-time assist characteristic in which the assist force relative to the steering torque is set lower than in the assist characteristic set for the time of normality, and an assist characteristic alteration portion that alters, after the assist characteristic is switched stepwise to the abnormality-time assist characteristic by the assist characteristic switch portion, the abnormality-time assist characteristic so that the assist force relative to the steering torque further declines continuously in accordance with declines in the source power supply capability of the second electric power source detected by the second source power supply capability detection portion.