Motor-driven steering assist apparatus

1. A motor-driven steering assist apparatus interposed between a steering wheel and a wheel side steering member for assisting steering force which a driver applies to the steering wheel on the basis of a generating torque of an electric motor comprising:

a single unit body, covered by three separate housing elements, having an input shaft to which the steering wheel is connected, an output shaft to which the wheel side steering member is connected, a torque sensor provided between the input shaft and the output shaft, an electric motor driven in correspondence to a detected torque of the torque sensor, and a gear train which transmits a rotation of the electric motor to the output shaft built-in,

the first separate housing element supports an upper end portion of the input shaft and the torque sensor,

the second separate housing element, disposed entirely longitudinally between the first and third separate housings elements, supports an upper end portion of the output shaft, the electric motor and the gear train,

the third separate housing element supports a lower end portion of the output shaft and also provides an external attachment structure for transference of tensile and compressive forces between a vehicle body side bracket and the third separate housing element,

wherein at least one attaching portion of the attachment structure to the vehicle body side bracket is provided on a lower surface of the third separate housing external to the three separate housing elements as seen from an axial direction of the output shaft, that is the lower surface just below in the axial direction in respect of a connection portion with the second housing, at a plurality of positions in the periphery of a bearing receiving portion for the output shaft provided in the third housing.

2. A motor-driven steering assist apparatus as claimed in claim 1 , wherein the attaching portion is received within a profile of the second housing as seen from the axial direction of the output shaft.

3. A motor-driven steering assist apparatus as claimed in claim 1 , the attaching portion comprising an attaching boss provided adjacent the connection portion of the second housing and the third housing at a plurality of positions in a peripheral direction in the periphery of the bearing receiving portion for the output shaft, on the lower surface of the third housing.

4. A motor-driven steering assist apparatus as claimed in claim 1 , the attaching portion comprising an attaching boss provided in a lower surface of the third housing, at a plurality of positions in a peripheral direction in the periphery of a bearing receiving portion for the output shaft provided in the third housing, and the attaching boss is fastened to a vehicle side bracket in the status that an end surface of the attaching boss is seated upon the vehicle side bracket, and a center portion including the oil seal receiving portion of the third housing, and the output shaft, are arranged in the center hole of the vehicle body side.