A belt type infinite variable-speed drive using a ball-screw mechanism is compact and noise-free. A nut of the ball-screw mechanism is fixed to a casing and a 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 load bearing capacity, are oriented in such a direction that a 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 balls in the ball circulating portions.
In a V-belt continuously variable transmission (CVT), a sheave drive mechanism includes a movable tube coupled to a movable sheave half of a primary sheave so as to be rotatable with respect thereto and axially movable together therewith, a fixed tube disposed internally of and coaxially with the movable tube, and a ball screw mechanism provided between the fixed tube and the movable tube. The sheave drive mechanism further includes an outer peripheral wall arranged to cover the area from a fixed end of the fixed tube to the outer periphery of the movable tube, an oil seal provided between the movable tube and the outer peripheral wall to seal an internal space for enclosing the working surface of the ball screw mechanism, and a communication path for communication between the internal space and the outside of the outer peripheral wall. The V-belt (CVT) has a smooth feed operation of the ball screw mechanism in the sheave drive mechanism and has a high durability attained by waterproofing.
