Power transmission mechanism

A power transmission mechanism characterized by:

• a first rotary body, wherein the first rotary body has an engaging projection;
• a second rotary body, which is located coaxial with the first rotary body, wherein the second rotary body has an engaging recess;
• the engaging projection engaging with the engaging recess to connect the first and second rotary bodies to each other such that power transmission is permitted;
• at least one of the engaging projection and the engaging recess being configured to change its position with respect to the first and second rotary bodies;
• and
• an elastic member, wherein, during the power transmission between the first and second rotary bodies, the elastic member permits at least one of the engaging projection and the engaging recess to change its position, thereby enabling the rotary bodies to rotate relative to each other in a predetermined angular range;
• wherein, during the power transmission between the first and second rotary bodies, the engaging projection normally abuts against a sliding surface of the engaging recess at a neutral position, and the contact position of the sliding surface of the engaging recess and the engaging projection separates from the neutral position in accordance with the increase of the transmission torque between the rotary bodies;
• and
• wherein, as the contact position separates from the neutral position, the inclination angle of the sliding surface of the engaging recess with respect to the circumferential direction of the rotary bodies gradually increases.