A selectable one-way clutch includes: a pocket plate; struts; a notch plate having a plurality of notches; and a selector plate that has a plurality of window holes. The strut includes a protrusion formed at a center thereof in a radial direction of the selectable one-way clutch. The selector plate has a cutout groove extending from an inner surface of the window hole along a formation direction of the protrusion. When the selectable one-way clutch is disengaged, the cutout groove is fitted on the protrusion, and the strut and the selector plate overlap each other in a rotational axis direction of the selectable one-way clutch.

A power transmission system includes a rotating shaft, a power transmission component, a pressing member, and a wave spring. The rotating shaft is rotatable about a rotating axis. The power transmission component includes a frictional engagement portion that includes a plurality of friction members alternately stacked in an axial direction along the rotating axis. The pressing member has a contact portion and is disposed to be movable in the axial direction to press the frictional engagement portion such that the plurality of friction members engage with each other. The wave spring is to press the pressing member at the contact portion in the axial direction away from the frictional engagement portion. The contact portion of the pressing member has a reduced friction between the contact portion and the wave spring along a circumference of the wave spring.

A rotational coupling includes input and output hubs disposed about a rotational axis and an attachment ring disposed about the axis on one side of the input hub opposite the output hub. A flexible, multi-coil body such as a cable is disposed radially outwardly of the input and output hubs and couples the hubs together for rotation upon rotation of the input hub in one rotational direction. The body has ends coupled to the output hub and attachment ring. A torque limiter includes a torque transmission plate configured to rotate with the input hub and an armature plate fixed against rotation. The torque transmission plate and armature plate are configured to move axially together along the axis of rotation. An electromagnet disposed on one side of the torque limiter opposite the input hub attracts the plates in a second axial direction away from the attachment ring when energized.

A power transmitting apparatus has a clutch member and a pressure member. The cam surfaces of the pressure-contact assist cam face each other. The cam surfaces of the back torque limiter cam face each other. A receiving portion for a clutch spring (10) on the pressure member (5) side has a receiving member (11) separate from the pressure member (5). A first cam surface (C1) and a second cam surface (C2), constituting the back torque limiter cam, are, respectively, formed on the receiving member (11) and the clutch member (4). A third cam surface (C3) and a fourth cam surface (C4), constituting the pressure-contact assist cam, are, respectively, formed on the pressure member (5) and the clutch member (4).

A compact clutch which comprises a driven shaft on which the following are mounted: a gear wheel; a driving bush; a driven bush; a coil spring; a first collar with cam surfaces; and a second collar with cam surfaces. The clutch is characterized in that the gear wheel and the bushes are constrained to the driven shaft in the axial direction by means of two stop rings; in that the driven bush is constrained to the driven shaft in the circumferential direction by means of at least one tongue; and in that the tongue ensures engagement between the driven bush and the driven shaft in the circumferential direction, while in the axial direction the driven bush may slide with respect to the driven shaft.