To obtain a downsized lightweight structure which can facilitate assembling work, can certainly prevent a clatter sound generated at a moment when the rotational direction of an electric motor is converted, and also can more certainly prevent uncomfortable feeling at steering from being imparted to a driver.
A spline hole 13 is formed at the base end of a worm shaft 6, and the first and second spline shafts 15 and 16a are provided at the top of an output shaft 12 of the electric motor. The first spline shaft 15 is formed of a rigid body and rotates in synchronization with the output shaft 12, and the second spline shaft 16a is externally fitted to a male spline-like support shaft 23 having an elastic material-made sleeve 19a at the top of the output shaft 12a. In the second spline shaft 16a composed of the sleeve 19a, thicknesses T1 and T2 of respective second male spline teeth 22a in a circumferential direction are changed according to axial positions.
Takashi Daejeon
Masaki Muto
Kinzo Koyama