Power plants – Pressure fluid source and motor – Having condition responsive control in a system of distinct...
Patent
1993-10-04
1995-03-07
Look, Edward K.
Power plants
Pressure fluid source and motor
Having condition responsive control in a system of distinct...
60452, 60468, 91517, F16D 3102
Patent
active
053946979
ABSTRACT:
An unloading valve is connected to a hydraulic pump, the unloading valve being opened when a differential pressure between a delivery pressure of the hydraulic pump and a maximum load pressure exceeds a predetermined value, for discharging a part of a flow rate of a hydraulic fluid delivered from the hydraulic pump to a reservoir. A fixed restriction for generating a control pressure corresponding to the flow rate of the hydraulic fluid discharged through the unloading valve is connected downstream of the unloading valve. A control device for the hydraulic pump is constructed to reduce the delivery rate of the hydraulic pump as the control pressure generated by the fixed restriction is raised, and increase the pump delivery rate as the control pressure is lowered. An adjusting valve is connected to the hydraulic pump in parallel to the unloading valve at a position upstream of the fixed restriction, and this adjusting valve is controlled such that an opening area of the adjusting valve is large when an input amount of a control lever is small, and the opening area is reduced as the input amount of the control lever increases. Thus, LS control through the unloading valve and bleed-off control through the adjusting valve are selectively performed depending on the input amount of the control lever, so that flow rate control can be implemented by utilizing characteristics of both the control modes.
REFERENCES:
patent: 4694647 (1987-09-01), Yoshida
patent: 4884402 (1989-12-01), Strenzke et al.
patent: 4977928 (1990-12-01), Smith et al.
Hitachi Construction Machinery Co. Ltd.
Look Edward K.
Nguyen Hoang
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