| 摘要 |
PCT No. PCT/JP90/00193 Sec. 371 Date Jul. 2, 1990 Sec. 102(e) Date Jul. 2, 1990 PCT Filed Feb. 19, 1990 PCT Pub. No. WO90/09528 PCT Pub. Date Aug. 23, 1990.A hydraulic circuit system comprising a hydraulic-fluid supply source, at least one hydraulic actuator operated by hydraulic fluid from the hydraulic-fluid supply source, a flow control valve for controlling the flow of the hydraulic fluid to be supplied to the actuator and a pressure control element for maintaining the differential pressure across the flow control valve at a predetermined value. The system according to the present invention comprises: first element for selectively creating, from the load pressure of the actuator and the supply pressure of the hydraulic-fluid supply source, either the pressure which is the same as the load pressure or the intermediate pressure which is higher than the load pressure but lower than the supply pressure and transmitting it as the control pressure; second element for operating said first element for instructing to select either the pressure which is the same as the load pressure or the intermediate pressure; and connection element for introducing the control pressure to the pressure control element. The pressure control element maintains the above-described differential pressure at the predetermined value when the level of the control pressure is the same as that of the load pressure, while it makes the level of the differential pressure lower than the predetermined value when the control pressure is the intermediate pressure.
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