Pumps – Condition responsive control of drive transmission or pump... – Having condition responsive pumped fluid control
Patent
1997-02-27
1998-11-24
Freay, Charles G.
Pumps
Condition responsive control of drive transmission or pump...
Having condition responsive pumped fluid control
4172221, 60445, F04B 4900
Patent
active
058398856
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for controlling the capacity of a variable capacity hydraulic pump, that can be used in a hydraulic circuit for a working machine actuator of a hydraulic shovel or the like.
BACKGROUND ART
As an apparatus for controlling the capacity (i. e. the amount of discharge per rotation) of a variable capacity hydraulic pump (hereinafter simply referred to as a variable hydraulic pump), there has hitherto be known an apparatus that is designed to maintain the driving torque (i. e. the capacity x the pump discharge pressure) constant by controlling the capacity in accordance with the pump discharge pressure.
On the other hand, as a hydraulic circuit for a working machine actuator in a construction machine such as a power shovel, there has been known a hydraulic circuit of pressure compensation type in which the discharge pressure fluid of a single variable hydraulic pump is supplied via a plurality of operating valves into a like plurality of actuators, there is provided a pressure compensating valve and, with this pressure compensating valve set according to a highest load pressure, the discharge pressure fluid of the single variable hydraulic pump is supplied, distributively in terms of the flow rates of the fluid, simultaneously to the actuators of different loads.
In such a hydraulic circuit of pressure compensation type, the capacity of a variable hydraulic pump is so controlled according to different load pressures that for a low load pressure the capacity may be decreased to lower the pump discharge pressure and then to reduced the energy loss and for a high load pressure the capacity may be increased to heighten the pump discharge pressure.
For the known apparatus, as mentioned above, for controlling the capacity so as to maintain the driving torque constant and at the same time so as to maintain a differential pressure between the pump discharge pressure and the load pressure constant, one that is illustrated in FIG. 1 of the accompanying drawings hereof will be typical.
More specifically, in a hydraulic circuit in which the discharge path 2 of a variable capacity hydraulic pump 1 (hereinafter referred to as a variably hydraulic pump) is connected via an operating valve 3 to an actuator 4, there is provided a capacity control cylinder device 6 in which a capacity control member, e. g., a swash plate 5, of the variable hydraulic pump 1 is operated to increase and decrease the capacity and which has a large diameter chamber 7, a small diameter chamber 10 and a capacity control piston 6a that is displaced by a differential pressure between the said two chambers, and the pump discharge pressure is supplied from a pump pressure introduction passage 14 into a large diameter chamber 7 controlledly via a first control valve 8 and a second control valve 9 and is also supplied directly into the said small diameter chamber 10 from the said pump pressure introduction passage 14.
The above mentioned first control valve 8 is adapted to be thrusted towards a supply position A under a pressure within a pressure receiving section 11 and to be thrusted towards a drain position B by a spring 12 that is provided at the opposite side to the said pressure receiving section 11. The said pressure receiving section 11 is configured to communicate with the said pump pressure introduction passage 14 via a first fluid passage 13. The said spring 12 is held in contact with a feedback lever 15. And, the said first control valve 8 at its position A is adapted to deliver the pump discharge pressure from an inlet port 16 to an outlet port 17 and at its position B is configured to establish a communication of the said outlet port 17 with a tank port 18 and also to block the said inlet port 16.
The said second control valve 9 is adapted to be thrusted towards a first position C under a pressure within a first pressure receiving section 19 and to be thrusted towards a second position D under a pressure within a second pressure receiving section 20 that is provided at the opposit
REFERENCES:
patent: 4710106 (1987-12-01), Iwata et al.
patent: 4976106 (1990-12-01), Noerskau et al.
patent: 5344288 (1994-09-01), Oda
Ishizaki Naoki
Morino Kenji
Oda Yosuke
Freay Charles G.
Komatsu Ltd.
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