Patent ID: 7393281

Claim:
A power transmission device comprising: a pulley rotatably attached to a casing; a hub arranged at a forward end portion of a rotary shaft protruding outside from the casing, and rotated integrally with the rotary shaft, wherein the hub includes a torque limiter for shutting off an excessively high torque transmission between the pulley and the rotary shaft; an elastic member for torque transmission, interposed between the pulley and the hub, and held by both the pulley and the hub, wherein the hub and the rotary shaft are connected to each other by engagement of a female screw portion, which is formed on an inner circumferential face of the hub, with a male screw portion which is formed on an outer circumferential face of the forward end portion of the rotary shaft, the power transmission device further comprising a seal means for sealing a portion between the hub and the rotary shaft, the seal means being arranged in the front of the screw engaging portion or in the front and the rear of the screw engaging portion, wherein the seal means is a cap that closes an opening of a large outer diameter portion of the torque limiter; an outer circumferential face of the cap is a sealing face that seals an inner circumferential face of the large outer diameter portion of the torque limiter; the torque limiter portion and the rotary shaft are connected to each other by the engagement of the male and female screw portions; and when the torque limiter is loaded with an excessively high torque, the torque limiter is broken by an excessive axial force that is generated by the engagement of the screw portions.