Abstract: A portion of a steering shaft 2 capable of being advanced and retracted defines a ball screw shaft 2a of a ball screw mechanism 13. A motor rotor 10 of an electrically driven motor 8 for providing a steering assist force is externally mounted on a rotary nut 14. Mounting of the motor rotor 10 onto the rotary nut 14 is carried out so that the both can be adjustably aligned. By way of example, the rotary nut 14 has an outer peripheral surface formed with an annular protrusion 33 of a arcuate longitudinal sectional shape, having a surface thereof formed with a plurality of axially extending surface indentations 33a arranged side by side in a direction circumferentially of the rotary nut 14.

Abstract: A belt type infinite variable-speed drive using a ball screw is proposed which is compact and noise-free. The nut of the ball screw mechanism is fixed to a casing and the threaded shaft is rotatably coupled to a movable pulley member through a ball bearing so that ball circulating portions on the nut will not rotate while the movable pulley member is movable axially. Also, the ball circulating portions, which are low in the load bearing capacity, are oriented in such a direction that load hardly acts on the ball screw mechanism. This makes it possible to compactly and rationally design a belt type infinite variable-speed drive and to suppress noise due to vibration of the balls in the ball circulating portions.

Abstract: A portion of a steering shaft 2 capable of being advanced and retracted defines a ball screw shaft 2a of a ball screw mechanism 13. A motor rotor 10 of an electrically driven motor 8 for providing a steering assist force is externally mounted on a rotary nut 14. Mounting of the motor rotor 10 onto the rotary nut 14 is carried out so that the both can be adjustably aligned. By way of example, the rotary nut 14 has an outer peripheral surface formed with an annular protrusion 33 of a arcuate longitudinal sectional shape, having a surface thereof formed with a plurality of axially extending surface indentations 33a arranged side by side in a direction circumferentially of the rotary nut 14.