| 摘要 |
PROBLEM TO BE SOLVED: To prevent excessive rotation in a relief region and to reduce the consumption of drive power by detecting the drain flow of a relief valve setting the discharge pressure of an electric pump, and feedback-controlling the revolving speed of the electric pump so that the detected drain flow becomes the prescribed value set in advance. SOLUTION: A drain passage 5 is branched from a hydraulic passage 4 connecting the discharge port of a pump 3 and a load in an electric pump 1 constituted of an electric motor 2 and a pump 3. A relief valve 6 is provided in the middle of the drain passage 5, and a flow sensor 8 is arranged on the downstream side of the relief valve 6. The revolving speed of the electric motor 2 is controlled by a revolving speed control device 9 based on the detection signal from the flow sensor 8. When the discharge pressure of the pump 3 exceeds the set pressure of the relief valve 6, the revolving speed of the electric motor 2 is controlled so that the drain flow becomes a target value, thereby the electric pump 1 can be operated with the minimum drive power. |
