To provide a control method of a variable displacement pump responding to bleed-off characteristics of each actuator, which uses the variable displacement pump and closed-center-type directional control valves, has good economic efficiency of a bleed-off control method, and a hydraulic circuit with good operability, and is capable of controlling an entire region of operation even during an emergency.
In the hydraulic circuit in which the actuator 1 is connected to each of the variable displacement pump 2 driven by an engine which can adjust a pump discharge amount from the outside and to a plurality of the close-center-type directional control valves, control of the variable displacement pump 2 by electric operation is performed via a solenoid proportional valve so that the closed-center-type directional control valves replace center-bypass-type directional control valves. At the time of emergency where a signal to the solenoid proportional valve cannot be obtained, the actuators 1 are operated by making the discharge pressure of the variable displacement pump a predetermined value.
COPYRIGHT: (C)2007,JPO&INPIT
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Shinichi Abe
Yuji Tsujida