Pumps – Condition responsive control of drive transmission or pump... – Adjustable cam or linkage
Patent
1981-12-21
1985-11-19
Look, Edward K.
Pumps
Condition responsive control of drive transmission or pump...
Adjustable cam or linkage
60452, 417222, F04B 126
Patent
active
045539049
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention is directed to a pump control for a variable displacement pump and more particularly to a mechanism for maintaining a standby pressure that is responsive to fluid pressure and greater than the difference between the load and discharge pressures.
2. Background Art
In many pump controls known today, a standby pressure is achieved by providing a spring having the needed force to move a control member for directing a control signal to an actuating member of the pump to increase the output of the pump in proportion to the force of the spring. The spring must have a length of compression to accommodate the full range of load pressures. The required force capacity and length of compression of the spring makes the spring bulky consequently, requiring a large space for the total pump control. The large, bulky spring has a tendency to fail or lose its force capacity due to its length of compression.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the invention, a pump control assembly for changing the displacement of a variable displacement pump has an actuating mechanism to change the pump's displacement and a valve member having first and second ends. The valve member is movable between a first position, an infinitely variable intermediate position and a second position. At the first position, a pump discharge pressure is in communication with the actuating mechanism while at the intermediate position, the pump discharge pressure is controllably modulated to deliver a control signal to the actuating member. At the second position, the pump discharge is blocked from communication with the actuating mechanism and the actuating mechanism is in communication with a tank. The first end of the valve member is in continuous fluid communication with the pump discharge pressure for biasing the valve member toward one of the first and second positions. A signal representative of a load from a control valve in an actuated position communicates with the second end of the valve member for biasing the valve member toward the other of the first and second positions in conjunction with a spring. At the intermediate position, the valve member controllably delivers the control pressure to the actuating mechanism to maintain a constant differential pressure between the discharge pressure and the load pressure. A means is provided for controllably delivering a predetermined pressure signal to the second end of the valve member in response to the load signal being below the predetermined pressure signal so that the valve member controllably delivers a predetermined control pressure to the actuating mechanism.
This invention solves the problems encountered with using a large spring in a pump control to obtain a standby pressure greater than the difference in pressure between the load and discharge pressures. The mechanism of this invention replaces the large spring with a second valve member that provides a predetermined pressure which acts on one end of the first valve member in conjunction with a small spring to provide the needed force for the desired standby pressure. The components of the second valve are small and require limited movement which adds reliability to the pump control.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial schematic and diagrammatic representation of an embodiment of the present invention; and
FIG. 2 is a graphical illustration of a pump discharge pressure verses load pressure characteristics of the variable displacement pump utilizing the subject invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring now to FIG. 1, a fluid system is generally indicated by reference numeral 10. The fluid system 10 includes a variable displacement pump 11 connected to a tank or reservoir 12 and a control valve 13 and a cylinder 14 respectively connected to the pump 11 by a conduit 15.
The fluid system 10 further includes a pump control assembly 16 mounted to the pum
REFERENCES:
patent: 3350881 (1967-11-01), D'Amato
patent: 3406850 (1968-10-01), Hancox
patent: 4074529 (1978-02-01), Budzich
patent: 4124333 (1978-11-01), Liesener
patent: 4330991 (1982-05-01), Budzich
patent: 4420935 (1983-12-01), Kobald
Ruseff Walter Z.
Schimpf James E.
Burrows J. W.
Caterpillar Tractor Co.
Look Edward K.
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