| 摘要 |
PROBLEM TO BE SOLVED: To reduce a seating shock by making falling speed of a body generally uniform even if viscosity of hoist cylinder return fluid changes. SOLUTION: This device is provided with a hoist cylinder 9 rising and falling a body 6, a hoist valve 13 supplying outlet pressure of a hydraulic pump 11 to the hoist cylinder 9, an electromagnetic proportioning pressure control valve 30 controlling a pilot pressure of the hoist valve 13, a potentiometer 53 outputting a signal according to rising and falling movement of the body 6, and a controller 48. When the controller 48 detects that it is before the body seats, the controller 48 optimizes a current value of the electromagnetic proportioning pressure control valve 30 and reduces output pressure to reduce a meter out area of the hoist valve 13 and a falling speed. After that, the controller 48 detects the falling speed of the body. When the falling speed is different from a set falling speed, the current amount of the electromagnetic proportioning pressure valve 30 is corrected to control the meter out area of the hoist valve 13 for correction of the falling speed. The body falling speed, thereby can be controlled generally uniform to reduce the seating shock regardless of viscosity change of hoist cylinder return fluid.
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