Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1988-06-29
1990-08-07
Garrett, Robert E.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60464, 13759614, 91517, 91518, 91531, F15B 1116
Patent
active
049457233
ABSTRACT:
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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Hirata Toichi
Izumi Eiki
Nozawa Yusaku
Shimotori Masahiko
Garrett Robert E.
Hitachi Construction Machinery Co. Ltd.
Kapsalas George
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