Power transmission device

A power transmission device comprising:

• an annular fixed part including an inner peripheral surface;
• an output shaft including an outer peripheral surface facing the inner peripheral surface and a recessed surface recessed radially inward from the outer peripheral surface;
• an input shaft including a pressing portion accommodated in the recessed surface;
• a pair of first rolling elements that are accommodated in the recessed surface and are arranged on opposite sides in a circumferential direction with respect to the pressing portion;
• and
• a pair of second rolling elements each of which has a smaller diameter than a diameter of each first rolling element and is arranged between the corresponding first rolling element and the pressing portion, wherein
• the recessed surface includes:
• a bottom surface extending in the circumferential direction and facing the inner peripheral surface in a radial direction;
• and
• a pair of pressed surfaces extending radially outward from opposite circumferential ends of the bottom surface,
• the bottom surface includes:
• a pair of cam surfaces each having the corresponding first rolling element arranged on a radially outer side;
• and
• a pair of guide surfaces each having the corresponding second rolling element arranged on a radially outer side,
• a distance between each cam surface and the inner peripheral surface gradually increases with proximity to the corresponding pressed surface,
• a distance between a portion of each cam surface closer to the corresponding guide surface and the inner peripheral surface is smaller than a diameter of each first rolling element,
• a distance between a portion of each cam surface closer to the corresponding pressed surface and the inner peripheral surface is larger than the diameter of each first rolling element,
• the second rolling element is sandwiched between the first rolling element, the guide surface, and the pressing portion, and
• the pressing portion pushes the second rolling element between the first rolling element and the guide surface when the pressing portion moves circumferentially outward from a state in which the pressing portion is disposed at a center portion of the recessed surface in the circumferential direction.