| 摘要 |
<p>[PROBLEM] To provide a hydraulic drive system for a hydraulic excavator, which makes it possible to efficiently perform grading work by using residual energy of pressure oil in a hydraulic circuit although no attention has been paid to the residual energy in conventional technologies. [SOLUTION] A hydraulic drive system for a hydraulic excavator is provided with a boom cylinder 1 and arm cylinder 2, a main hydraulic pump 4 for feeding pressure oil to both the cylinders 1,2, a directional control valve 7 for a boom and directional control valve 8 for an arm to control flows of pressure oil to be fed to the boom cylinder 1 and arm cylinder 2, respectively, and a reservoir line 8c connecting the directional control valve 8 for the arm with a working oil reservoir 6. A flow-rate control valve 15 capable of selectively closing the reservoir line 8c is arranged and, when a rod-side hydraulic pressure of the arm cylinder 2 has increased to a preset value or greater while grading work is performed by a combined operation of boom raising and arm crowding, the reservoir line 8c is closed by the flow-rate control valve 15 to prevent drainage of rod-side pressure oil from the arm cylinder 2 to the working oil reservoir 8c and to feed the rod-side pressure oil to a bottom side of the boom cylinder 1.</p> |
