Fluid handling – Self-proportioning or correlating systems – Self-proportioning flow systems
Patent
1980-03-12
1982-07-06
Spiegel, H. Jay
Fluid handling
Self-proportioning or correlating systems
Self-proportioning flow systems
137118, 137117, 91 46, 91516, 91517, 91529, G05D 1113
Patent
active
043377874
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a hydraulic circuit which controllably provides first and second preselected fluid pressure levels in the circuit to operate associated elements each requiring one of the pressure levels. More particularly, the invention relates to a hydraulic valve to automatically provide a first pressure level condition for operation of only a first means and controllably provide both first and second pressure level conditions for subsequent operation of a second means and the first means.
BACKGROUND ART
In the use of engines such as in work vehicles, starting, particularly in cold weather can be a problem. Where the engine has an associated clutch, starting can be facilitated by disengaging the clutch during start-up in order to reduce load on the engine. A clutch which is hydraulically actuated, for example, is actuated at a preset fluid pressure level supplied by a hydraulic pump usually driven by the engine itself. When the engine is shut-down, fluid can remain in the hydraulic circuit which keeps the clutch engaged or, during starting operations, turning over the engine will actuate the hydraulic pump which can supply fluid at a sufficient pressure level to engage the clutch and load the engine before the engine is fully engaged or during its warm-up period.
In some systems, it may not be possible to disengage the hydraulic pump before start-up because that pump is also used to supply other hydraulic systems, such as the drive bearings, associated with an engine driven pump. When this is the case, it is desirable to limit the maximum pressure level of hydraulic fluid from the pump to below that required for actuation of the clutch but maintain a sufficient level for other demands. It is also desirable to maintain this condition in the system for varying periods to allow for a sufficient warm-up period for the engine and to automatically disengage the clutch upon shut-down of the engine and without an external signal, such as by the operator, to prepare the engine or work vehicle for the next start-up.
The present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF INVENTION
In one aspect of the present invention, a hydraulic circuit has fluid supply means for delivering a pressurized fluid flow and first and second means operating at first and second preselected pressure levels, respectively. A main valve element has an inlet annulus positioned in fluid communication with the fluid supply means. The valve element is movable between a first position at which the inlet annulus is blocked from fluid communication with the first means and a second position at which the inlet annulus is in fluid communication with both the first and second means. Pilot means automatically communicates the inlet annulus with the first means at the first position of the valve element and initiates a condition demanding pressurized fluid flow at about the first preselected pressure level in response to a reduced fluid flow from the supply means. The pilot means also controllably initiate a condition demanding pressurized fluid flow at about the second preselected pressure level in response to a preselected input signal.
In another aspect of the present invention, a hydraulic circuit has fluid supply means for delivering a pressurized fluid flow and first and second fluid pathways which operate at first and second preselected fluid pressure levels, respectively. Means is provided for selectively, controllably directing fluid flow from the fluid supply means through the first and second fluid pathways. The means is movable toward a first position at which fluid flow is delivered through the first fluid pathway at about the first preselected pressure level in response to a reduced fluid flow and movable toward a second position at which fluid flow is delivered at about the first and second preselected pressure levels through the first and second fluid pathways, respectively, in response to a preselected input signal.
In still another aspect of the pr
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patent: 3005463 (1961-10-01), Van Meter
patent: 3353495 (1967-11-01), Bianchetta
patent: 3456560 (1969-07-01), Brannon
patent: 3488953 (1970-01-01), Haussler
patent: 3709065 (1973-01-01), Starling
patent: 4057073 (1977-11-01), Adams
patent: 4098285 (1978-07-01), Karing
patent: 4192337 (1980-03-01), Alderson et al.
patent: 4206689 (1980-06-01), Peterson
Caterpillar Tractor Co.
Heming William B.
Spiegel H. Jay
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