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公开(公告)号：US4945723A
公开(公告)日：1990-08-07
申请号：US213179
申请日：1988-06-29
申请人： Eiki Izumi , Toichi Hirata , Yusaku Nozawa , Masahiko Shimotori
发明人： Eiki Izumi , Toichi Hirata , Yusaku Nozawa , Masahiko Shimotori
CPC分类号： F15B13/0405 , E02F9/2225 , E02F9/2232 , Y10T137/87193
摘要： A hydraulic drive system has first and second flow control valves. Each of the control valves has a main valve of the seat valve type with a valve body for controlling communication between an inlet port and an outlet port which are both connected to a main circuit. Each further have a variable restrictor capable of changing an opening degree thereof in response to displacements of the valve body, and a back pressure chamber communcating with the inlet port through the variable restrictor and producing a control pressure to urge the valve body in the valve-closing direction. A pilot valve is connected to a pilot circuit which is connected between the back pressure chamber and the outlet port of the main valve; and an auxiliary valve is connected to the pilot circuit for controlling a differential pressure between the inlet pressure and the outlet pressure of the pilot valve. The auxiliary valve is controlled such that the differential pressure between the inlet pressure and the outlet pressure of the pilot valve has a relationship expressed by a certain equation including constants .alpha., .beta. and .gamma., with respect to a differential pressure between the delivery pressure of a hydraulic pump and the maximum load pressure of the first and second hydraulic actuators, a differential pressure between that maximum load pressure and the self-load pressure of each of the hydraulic actuators, and the self-load pressure, wherein the constants .alpha., .beta. and .gamma. are set to respective predetermined values.
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