Rotation transmission mechanism, bicycle provided with rotation transmission mechanism, and elastically-deformable body used in rotation transmission mechanism

A rotation transmission mechanism comprising:

• an internal rotation member into which a rotation shaft is inserted;
• and
• an external rotation member rotatably arranged with respect to the internal rotation member,
• wherein the internal rotation member comprises:
• a disk-shaped internal rotation member main body having a rotation shaft insertion hole;
• and one or a plurality of outer-peripheral projected portions which are formed integrally with the internal rotation member main body or fixed to the internal rotation member main body and protrude toward an outer-peripheral side of the internal rotation member main body,
• wherein the external rotation member comprises:
• a circular ring rotatably arranged with respect to the internal rotation member and at an outside of the outer-peripheral projected portions of the internal rotation member;
• and one or a plurality of inner-peripheral projected portions which are formed integrally with the circular ring or fixed to the circular ring so as to protrude toward an inner-peripheral side of the circular ring and are alternately arranged with respect to the outer-peripheral projected portions of the internal rotation member,
• wherein the outer-peripheral projected portions have a forward-movement surface that is located at a position displaced from a center of the outer-peripheral projected portion in a forward movement direction in which the rotation transmission mechanism rotates by forward movement,
• wherein an elastically-deformable portion is disposed between the forward-movement surface and the inner-peripheral projected portion facing the forward-movement surface in the forward movement direction,
• wherein a space is partially formed in the elastically-deformable portion, and
• wherein when the internal rotation member rotates relative to the external rotation member, the elastically-deformable portion is sandwiched between the outer-peripheral projected portion and the inner-peripheral projected portion and is thereby elastically deformed.