| 摘要 |
<p>PURPOSE: To make the smoothly finishing of a grading surface achievable by feeding an oil sump at the bottom side of a cylinder with oil at a time when an arm is operated to be drawn to this side and simultaneously making a part of return oil (most of return oil go back to an oil tank though) regeneratively converge on an oil passage at the arm cylinder bottom side through a backward cut-off oil passage with a one-way throttle part of a subspool valve. CONSTITUTION: When an arm 2C is drawn into to this side as lowering a boom 1C, secondary pressure derived out of a pilot valve 22 acts on a pilot port 23 through a concuit line 25, selecting it to a subspool valve 9. Further a selector valve 8 is selected to H. At this time, pressure oil out of a pump 12 is fed to a bottom side oil sump 31. At the same time, most of return oil goes back to an oil tank 14 by way of a throttle part 18. However, a part of the return oil regeneratively converges on an oil passage 29 at the H. Accordingly, back pressure acts on an oil sump 32 and rigidity of a cylinder 6C is improved, while a sufficient flow rate is fed to the oil sump 31, holding the extent of digging force. With this constitution, any stick slip phenomenon is prevented from occurring, and thus a smooth surface is shapable.</p> |
