| 摘要 |
A hydraulic driving unit is provided with a directional control valve 23 and directional control valve 24 for controlling a boom cylinder 6 and arm cylinder 7 , both of which are driven by pressure oil delivered from a main hydraulic pump, respectively, a boom control device 25 for selectively controlling the directional control valve 23 and an arm control device 26 for selectively controlling the directional control valve 24 , and is mounted on a hydraulic excavator. To permit effective use of pressure oil in a rod chamber 6 a of the boom cylinder 6 when a bottom pressure of the arm cylinder 7 has become high while performing a combined operation such that pressure oil is being supplied to bottom chambers 6 a, 7 a of the boom cylinder 6 and arm cylinder 7 , the hydraulic driving unit is provided with a communication controlling means for bringing the rod chamber 6 b of the boom cylinder 6 and the bottom chamber 7 a of the arm cylinder 7 into communication with each other when the bottom pressure of the arm cylinder 7 has increased to a high pressure equal to or higher than a predetermined pressure.
|
