Patent ID: 8196698
Filing Date: 2012-06-12
Classification: B62D

Abstract:
1. A motor-driven power steering apparatus comprising; a rack shaft accommodated movably within a rack case, being moved by a steering force applied to a steering wheel, and also being moved by a driving force of a motor to assist the steering force, an input shaft coupled to a steering wheel, being rotatably supported in a steering gear box, being coupled to a pinion shaft via a torsion bar within the steering gear box, and tooth of the pinion shaft engaged with tooth of the rack shaft, a torque sensor provided around the torsion bar within the steering gear box, a target current computing means calculating a target current on the basis of a steering torque detected by the torque sensor, to control the motor to assist the steering force in accordance with the target current; a board temperature detecting apparatus provided on a control board, detecting a board temperature of the control board; a motor current detecting means detecting an armature current of the motor; a fault diagnosing means diagnosing a fault of the board temperature detecting apparatus on the basis of the armature current detected by the motor current detecting means and the board temperature detected by the board temperature detecting apparatus; a target current suppressing means suppressing the target current at a time when the fault diagnosing means diagnoses that the board temperature detecting apparatus is out of order, and a CPU provided on the control board; wherein the board temperature detecting apparatus is provided within a housing of the rack case, and exists in a common space formed by a torque sensor accommodating portion of the steering gear box and a motor case and the housing of the rack case, the board temperature detected by the board temperature detecting apparatus is output to the CPU as an ambient atmosphere temperature of the common space, and using this output, the CPU supplies a temperature compensation of the torque sensor and a temperature compensation of a generating torque of the motor, and preventing thermal damage of the control board.