Patent ID: 8571757

Claim:
A steering apparatus for a vehicle which has a steering mechanism for steering steerable road wheels by means of a steering wheel that is operated by a driver and an auxiliary steering angle superposition mechanism by which an auxiliary steering angle can be superposed, said apparatus characterized by comprising: a transmission characteristic setting unit that sets a transmission characteristic between a steering angle of said steering wheel and a steered angle of steerable road wheels in accordance with a traveling condition of the vehicle; a steering wheel angle detection unit that detects a steering angle of said steering wheel operated by the driver; an auxiliary steering angle detection unit that detects an auxiliary steering angle to be steered by said auxiliary steering angle superposition mechanism or a steering angle detection unit that detects the steered angle of the steerable road wheels; a target driving amount calculation unit that generates a target auxiliary steering angle or a target steering angle added by said auxiliary steering angle superposition mechanism based on a steering-wheel steering angle detected value from said steering wheel angle detection unit and said transmission characteristic, and calculates a target amount of driving of said electric motor so as to make said target auxiliary steering angle and an auxiliary steering angle detected value from said auxiliary steering angle detection unit coincide with each other or so as to make said target steering angle and a steering angle detected value from said steering angle detection unit coincide with each other; an electric motor driving unit that drives said electric motor in accordance with said target amount of driving; a relay unit that inhibits the rotation of said electric motor by short-circuiting opposite terminals of said electric motor under a predetermined condition; a failure detection unit that detects at least a failure of said electric motor driving unit; wherein said relay unit is controlled in its operation in accordance with the kind of the failure detected by said the failure detection unit; and a straight-ahead driving detection unit that detects that said vehicle is in a straight-ahead driving state; wherein said relay unit operates to continue the driving control of said auxiliary steering angle superposition mechanism when a non-rotation failure of said electric motor is detected by said failure detection unit, and in addition, stop the driving of said electric motor and at the same time short-circuit the opposite terminals of said electric motor when it is detected by said straight-ahead driving detection unit that the vehicle is in a straight-ahead driving state.