| 摘要 |
A two speed gearbox comprises an input shaft, an output shaft and a reduction gear mechanism, such as an epicyclic gear mechanism, having high speed low torque and low speed high torque output drives. A dog clutch connects the high speed output drive to the output shaft when the clutch is fully engaged. A slidable coupling is rotatable with the low speed output drive and is movable between a first position in which it is disconnected from the output shaft and a second position in which it is connected to the output shaft for driving the latter. A weak spring urges the slidable coupling towards its second position and means, such as a strong compression spring, urges the clutch members of the clutch in to full engagement. A radial flange on the driven clutch member and balls held captive with the slidable coupling interact to maintain the slidable coupling in its first position against the urging force of the weak spring while the clutch members are maintained in full engagement by the compression spring. However, when the torque applied to the output shaft exceeds a predetermined value the clutch members will begin to part and the slidable coupling will engage the output shaft. When the coupling is fully engaged with the output shaft the balls and radial flange will interact to maintain the clutch members fully out of engagement.
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