| 摘要 |
A safety coupling for preventing backspin at excessive speeds of a torque transmitting drive powering a drive string which stores reactive torque due to torsional stress. The safety coupling includes a rotatable driving member to be coupled with a torque producing power source, a rotatable driven member to be coupled with the drive string for axial rotation therewith. The driven member is movable relative to the driving member between an engaged position wherein the driving and driven members are coupled by a torque transfer structure to provide a positive driving connection between the torque transmitting drive and the shaft, and a disengaged position wherein the driving and driven members are freely rotatable relative to each other so that back-spin of the torque transmitting drive is prevented. The driven member is biased into the disengaged position and forced into the engaged position only during forward rotation of the shaft. To start rotation of the shaft, the coupling further includes an auxiliary coupling component which transfers a selected torque between the driving and driven members for start-up of the shaft from standstill and to force the driven member into the engaged position. However, the amount of torque transmitted by the auxiliary coupling component is less than the torque required for build-up of sufficient reactive torsion to create a potentially hazardous back-spin. Thus, the auxiliary coupling component is disengaged before potentially dangerous levels of reactive torsion are stored in the shaft, which prevents potentially hazardous back-spin, should the main coupling components of driving and driven member and torque transfer structure fail. The coupling substantially prevents damage to the torque transmitting drive upon excessive back-spin of the drive string and reduces the risk of injury to personnel working in the vicinity of a drive string storing elastic torsion. The coupling is preferably part of a safety arrangement including the coupling, a brake for slowing back-spin of the shaft created upon interruption of power to the shaft, and a common control member for controlling both the operation of the coupling and the brake.
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