| 摘要 |
A rotary coupling comprises a driving part, a drivable part, a fixed part in which the driving and drivable parts are each rotatable coaxially, and a set of coupling members carried by one of the driving and drivable parts for torque-transmitting engagement with the other. The coupling members are selectively positionably arranged so that, in a first condition, the coupling members are juxtaposed to a primary annular contact surface of either the fixed part or the drivable part and, in a second condition, the coupling members are juxtaposed to a secondary annular contact surface of the driving part. Each coupling member is free to move relative to the driving and drivable parts into and out of engagement with the primary and secondary annular contact surfaces. The arrangement is such that, when the coupling members are in the first condition, the application of a first torque on the coupling members causes the coupling members to engage the primary annular contact surface and, when the coupling members are in the second condition, the application of a second torque on the coupling members causes the coupling members to engage the secondary annular contact surface.
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