| 摘要 |
PROBLEM TO BE SOLVED: To lower a work machine to an operation target position in a state wherein stop impact is prevented. SOLUTION: A feed/delivery oil passage 40 of a hydraulic cylinder 30 is switched among an oil delivery state, an oil feed state and a feed/delivery stop state by a cylinder side opening and closing valve 42 and a tank side opening and closing valve 47. A lifting valve 60 is provided in an operation oil passage 50 connected to the cylinder side opening and closing valve 42 and the tank side opening and closing valve 47. The lifting valve 60 switches the feed/delivery oil passage 40 and operates the hydraulic cylinder 30 by operating the operation oil passage 50 and controlling a back pressure of the cylinder side opening and closing valve 42 and the tank side opening and closing valve 47. A deceleration operation state is provided between the lowering state and the stop state of the lifting valve 60. Regarding the deceleration operation state of the lifting valve 60, a check valve 70 is operated by a tilt outer peripheral part 65d of a spool 65, and the operation oil passage 50 is throttled, and the feed/delivery oil passage 40 is gradually switched from the oil delivery state to the feed/delivery stop state by the cylinder side opening and closing valve 42. COPYRIGHT: (C)2007,JPO&INPIT
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