| 摘要 |
Into a housing ( 3 ) is hermetically inserted an annular piston ( 5 ), and into the annular piston ( 5 ) is hermetically inserted an output rod ( 8 ). A spring ( 14 ) located below the piston ( 5 ) moves the piston ( 5 ) upward for locking, pressurized oil in a release chamber ( 12 ) formed above the piston ( 5 ) moves the piston ( 5 ) downward for releasing. On an upper surface of the piston ( 5 ) is provided a pressing surface ( 38 ), on an inner periphery of a peripheral wall of the release chamber ( 12 ) is provided a first tapered surface ( 41 ), which narrows upward, and on an outer periphery of the output rod ( 8 ) is provided a second tapered surface ( 52 ), which narrows downward. Between the pressing surface ( 38 ), the first tapered surface ( 41 ) and the second tapered surface ( 52 ) are inserted a plurality of balls ( 55 ) circumferentially at intervals. Thereby, when the spring ( 14 ) moves the piston ( 5 ) upward for locking, a moving stroke of the output rod ( 8 ) is larger than that of the piston ( 5 ).
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