Electric power steering apparatus

1. An electric power steering apparatus comprising an electric motor for producing a steering assist force, further comprising:

a speed reducing mechanism for decelerating a rotation of a rotatable shaft in the electric motor; and

a converting mechanism for converting an output rotation of the speed reducing mechanism into an axial movement of a steering shaft extending toward right and left sides of a vehicle,

the speed reducing mechanism comprising:

an input pulley driven by the electric motor,

an output pulley arranged with the steering shaft enclosed thereby,

a belt for connecting the input pulley and the output pulley,

a mechanism for adjusting a tension of the belt, including a tensioner having a fixed member, a movable member, a tensioner pulley supported on a first end of the movable member via a supporting shaft so as to be rotatable and engaging with the belt, wherein the moveable member is supported on a second end by a supporting bracket via a second supporting shaft with the moveable member axially extending in a direction that is substantially parallel to an extending direction of the belt,

an urging mechanism for urging the tensioner pulley through the movable member in the direction in which tension is applied to the belt through contact at a point on the moveable member between the first end and the second end, wherein a slack side of the belt is pressed toward a tension side by the tensioner pulley so that a belt wrap contact area on the input pulley expands and the tensioner pulley engages the belt at a position that is in closer proximity to the input pulley than the output pulley;

a first housing comprising a substantially Ω-shaped cross-section and a base portion, wherein a substantially cylindrical shape is formed by the first housing, the first housing supporting the input pulley and enclosing the mechanism for adjusting the tension of the belt, wherein the supporting bracket is fixed to the base portion of the Ω-shaped first housing; and

a second housing comprising a substantially Ω-shaped cross-section such that a substantially cylindrical shape is formed by the second housing, the second housing enclosing the steering shaft and the output pulley.

2. The electric power steering apparatus according to claim 1 , wherein

a pitch circle diameter of the input pulley is within a range of 12 to 30 mm, and

a center angle of the input pulley, corresponding to the belt wrap contact area on the input pulley, is within a range of 135 to 210 degrees.