Abstract: Provided is a power transmission device including a housing and a ball screw device including a nut housed in the housing. The device includes a screw shaft passing through the nut, and balls disposed between the nut and the screw shaft. The device also includes a first bearing and a second bearing that are disposed to be adjacent to each other in a center axis direction parallel with a center axis of the nut between the housing and the nut; and a preload applying member constituted of an elastic body and configured to apply preloads to the first bearing and the second bearing. The first bearing and the second bearing respectively include outer rings that are fitted to the housing and separated from each other in the center axis direction, and the first bearing and the second bearing are disposed to be a face-to-face combination.

Abstract: A power transmission device including a housing and a ball screw device including a nut, a screw shaft, and a plurality of balls. The device includes a pulley device including a driving pulley configured to be driven by receiving power transmitted from a power source, a driven pulley fixed to the nut, and a belt wound around outer peripheral surfaces of the driving pulley and the driven pulley. The device also includes a first bearing and a second bearing disposed between the housing and the nut in a center axis direction parallel with a center axis of the nut; and a preload applying member configured to apply preloads to the first bearing and the second bearing. The first bearing and the second bearing are respectively disposed on both sides of the driven pulley to be a face-to-face combination, and each of the first bearing and the second bearing includes an outer ring engaged with the housing.

Abstract: It is an object of the present invention to provide a thrust ball bearing which has a large load capacity, can realize thinned wall, and can further withstand a radial load. A pair of raceways (21, 22) include double rows of raceway grooves (23A, 23B) provided along a radial direction on surfaces facing each other. The retainer (40) includes claw-shaped protrusions (42) that protrude from peripheral edges of openings of pockets (41) in a convex manner and are arranged to face each other only in a circumferential direction of the retainer. A maximum width W of the claw-shaped protrusions (42) in the radial direction is smaller than a maximum width L of the raceway grooves (23) in the radial direction.