Pumps – Condition responsive control of drive transmission or pump...
Patent
1995-04-13
1997-12-16
Thorpe, Timothy
Pumps
Condition responsive control of drive transmission or pump...
417218, 60452, F04B 4900
Patent
active
056977646
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 Continuation of PCT/JP93/01577 Oct. 29, 1993.
FIELD OF THE INVENTION
The present invention relates to a displacement control system for a variable displacement hydraulic pump to be employed in a hydraulic circuit of an actuator for a work implement of a constructional machine and so forth.
DESCRIPTION OF THE BACKGROUND ART
As a system for controlling a displacement (discharge amount per one cycle of revolution) of a variable displacement hydraulic pump (hereinafter referred to as variable hydraulic pump), there has been known a system for adjusting a drive torque (displacement X pump discharge pressure) of the variable hydraulic pump by controlling a displacement depending upon a pump discharge pressure.
On the other hand, as a hydraulic circuit for an actuator for a work implement of a constructional machine, such as a power shovel, there has been known a pressure compensation type hydraulic circuit, in which a discharged pressurized fluid of one variable hydraulic pump is supplied to a plurality of actuators through a plurality of operating valves, a pressure compensation valve is disposed at the midway of a pressurized fluid supply passage for each actuator, and respective pressure compensation valves are set a load pressure corresponding to the highest load pressure to simultaneously distribute the discharged pressurized fluid of one variable hydraulic pump to a plurality of actuators having mutually distinct load pressures.
In this pressure compensation type hydraulic circuit, by controlling the displacement of the variable hydraulic pump depending upon the discharge pressure, the torque required for driving a variable hydraulic pump is controlled to be constant by adjusting the displacement smaller at higher discharge pressure and by adjusting the displacement greater at low discharge pressure. When the pressure difference is large, the displacement is adjusted to be smaller and when the pressure difference is small, the displacement is adjusted to be larger to reduce energy loss.
In case of the system for controlling the displacement depending upon the pump discharge pressure and the load pressure as set forth above, it is desired to make it possible to adjust response characteristics in control of the variable hydraulic pump in order to improve operability of the work implement.
The present invention is worked out in view of the above-mentioned point. It is an object of the present invention to provide a displacement control system for a variable displacement hydraulic pump which can improve operability of a work implement by adjusting response characteristics in control of the variable displacement hydraulic pump.
DISCLOSURE OF THE INVENTION
In order to accomplish above-mentioned and other objects, as one aspect of the present invention, there is provided a displacement control system for a variable displacement hydraulic pump comprises a displacement control piston assembly having a large diameter chamber for operating a displacement control member of the variable displacement hydraulic pump selectively in a direction of smaller displacement and in a direction of larger displacement, first control valve and second control valve for selectively communicating the large diameter chamber of the displacement control piston assembly with a pump discharge line and a tank, the first control valve being placed at a supply position by the pump discharge pressure, and at a drain position by a spring associated with the displacement control piston assembly via a feedback lever, and the second control valve being placed at a first position by the pump discharge pressure for communicating the pump port and the large diameter chamber and at a second position by a load pressure for communicating the large diameter chamber to the first control valve, the flow path area is varied at the intermediate position of a fluid passage from the large diameter chamber to the pump discharge passage or to a tank.
With the construction set forth above, by variation of the cross-sectional flow
REFERENCES:
patent: 4553904 (1985-11-01), Ruseff et al.
patent: 4821514 (1989-04-01), Schmidt et al.
patent: 5201803 (1993-04-01), Goto et al.
patent: 5203678 (1993-04-01), Sugiyama et al.
Oda Yosuke
Shirai Kiyoshi
Kabushiki Kaisha Komatsu Seisakusho
Kananen Ronald P.
Korytnyk Peter G.
Thorpe Timothy
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