To provide a power transmission mechanism which can eliminate a risk of unnecessary cut-off of power transmission even though a load torque generated on the driven equipment side becomes negative.
A spiral spring 47 is fitted at its outer end part 47a on a power transmission protrusion 44 on the rotor 41 side through the intermediary of a power transmission recess 49, and is retained at its inner end part 47b to a rotary shaft so as to be prevented from rotating. The spiral bearing 47 is incorporated being elastically deformed so as to urge the outer end part 47a of itself. The rotor 41 is formed thereon with a limit surface 45a which abuts against the outer surface 47a so as to limit the displacement of the outer end part 47a due to the urging force of the spiral spring 47. A releasing protrusion 53 is formed on the rotary shaft 16 side, and if the load torque becomes higher, exceeding a predetermined value, it releases the outer end part 47a from the limit surface 45a due to relative rotation between the rotor 41 and the rotary shaft 16 in order to remove the urging force of the spiral spring 47. An erroneous release inhibiting surface 44b is formed on the power transmission protrusion 44, and an erroneous release countermeasure surface 49b is formed on the inner surface of the power transmission recess 49.
URYU AKIHITO
KIMURA KAZUYA
