Patent ID: 6974014

Claim:
A rotary coupling comprising: 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, wherein 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 one of the fixed part and the drivable part and, in a second condition, the coupling members are juxtaposed to a secondary annular contact surface of the driving part; wherein 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; wherein said arrangement is such that, when the coupling members are in said first condition, 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, application of a second torque on the coupling members causes the coupling members to engage the secondary annular contact surface; and wherein each coupling member is a truncated cylinder, the major part of which is cylindrical with a cylinder axis parallel to a rotational axis of the coupling, the truncated cylinder being truncated parallel to said cylinder axis to define a wedging surface which faces the adjacent primary and secondary annular contact surfaces, when the coupling members are in the first and second conditions, respectively.