| 摘要 |
<p>PROBLEM TO BE SOLVED: To permit a rod side oil chamber and oil tank to instantaneously communicate with each other by making a pipe conduit connect with the rod side oil chamber from a control valve, inputting a pilot pressure detection signal and main signal in a controller, and powering an electromagnetic switching valve. SOLUTION: A pilot secondary pressure signal from each pilot valve 19F, 18R at the arm pushing operation side and arm pulling operation side and main signal from a hydraulic pump are inputted in a controller 37. In the center of the neutral position (n) of an operation lever 18 is in the angular zone of a minimum falling down side, the pilot secondary pressure at the arm pushing operation side is brought in a lowered conduit near zero. In addition, from a point of time near a release set pressure of the main pressure, secondary pressure derivative initiation condition is detected by a pressure sensor 36, and the signal is inputted in the controller 37 so as to electrify the solenoid 28. In this case, during switching operation of the electromagnetic switching valve 27, a rod side oil chamber 23 communicates with an oil tank 16. In this operation, a closed inner pressure in the minimum falling down angular zone is drawn out so that abrupt falling of the arm 11 can be prevented.</p> |
