| 摘要 |
PURPOSE:To allow change-over from speed control to pressure control by providing a drain oil passage which is branched from the discharge circuit o a fixed displacement pump to be connected to an oil tank via an unload change-over valve, and thereby releasing the unload change-over valve when the hydraulic pressure within the discharge circuit of a variable displacement pump is equal to a set value. CONSTITUTION:In a hydraulic pump control circuit for an injection molding machine and the like wherein the machine is furnished with the discharge circuit 3a of a variable displacement pump supplying oil to an injection cylinder 10 out of the variable displacement pump 5, and with the discharge circuit 36 of a fixed displacement pump supplying oil to the injection cylinder 10 out of the fixed displacement pump 6, an unload change-over valve 13 is interposed onto a drain oil passage 3d branched from the discharge circuit 3b of the fixed displacement pump. A pilot pressure change-over valve 12 is switched by means of a control device 11 with the output signal of a pressure sensor 7 detecting the pressure of a main hydraulic circuit compared with a set pressure, pilot pressure is then applied to the unload change-over valve 13 at the II position of the valve while the unload change-over valve 13 is designated to its II position, and hydraulic pressure within the discharge circuit 3b of the fixed displacement pump is constituted to be released into an oil tank. |
