| 摘要 |
PROBLEM TO BE SOLVED: To prevent falling down of soil from a backet by providing a delay means to delay operation of a control valve to a position corresponding to operation position of an operation lever when the operation lever is operated to the elevation side of a boom. SOLUTION: When a first boom is operated to the elevation side or decending side, the detection values of sensors 36, 37, 38 on the angles of upward/ downward direction and right/left direction of a boom and the angle of forward/ rearward direction of an am are input to a controller 40. For example, when the boom is operated to the elevation side by operating the right operation lever 9 to the rear operation side, each of first and second set angles is computed. Ten, the upward/downward angle of the boom exceeds the first set agnle, the pilot pressure of a pilot valve 31a is operated to decrease the pressure by means of a pressure control valve 41 based on the difference between both the angles, and operation of the boom to the elevation side is decelerationwise operated. Furtheremore, when the upward/downward angle reaches the second set angle, the pilot pressure of the pilot valve 31a is unloaded by means of the pressure control valve 41, and operation of the boom to the elevation side is stopped. Accordingly, the purpose is attained.
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