Bidirectional torque limiter

A bidirectional torque limiter comprising:

• an inner race;
• a first coil spring formed of a wound wire mounted on the inner race so as to be in contact with an outer peripheral surface of the inner race,
• a tubular intermediate race into which the inner race mounted with the first coil spring is to be inserted,
• a second coil spring formed of a wound wire mounted on the intermediate race so as to be in contact with an outer peripheral surface of the intermediate race, and
• a tubular outer race into which the intermediate race mounted with the second coil spring is to be inserted;
• wherein the inner race, the intermediate race and the outer race have a common central axis;
• the first coil spring has a first hook portion to be fixed to the intermediate race in a manner incapable of rotating relatively, so that the first coil spring is incapable of rotating with respect to the intermediate race;
• the second coil spring has a second hook portion to be fixed to the outer race in a manner incapable of rotating relatively, so that the second coil spring is incapable of rotating with respect to the outer race;
• a direction to loosen the clamping force of the first coil spring by circumferentially pushing the first hook portion is opposite to a direction to loosen the clamping force of the second coil spring by circumferentially pushing the second hook portion when viewed from an axial direction;
• and
• in a case where a rotation torque about the central axis to rotate the inner race in one direction with respect to the outer race is applied and when the rotation torque is larger than a first predetermined value, the inner race rotates with respect to the intermediate race by overcoming the frictional force between the first coil spring and the inner race;
• and in a case where a rotation torque about the central axis to rotate the inner race in an opposite direction with respect to the outer race is applied and when the rotation torque is larger than a second predetermined value, the intermediate race rotates with respect to the outer race by overcoming the frictional force between the second coil spring and the intermediate race.