Motors: expansible chamber type – Plural relatively movable or rigidly interconnected working... – Condition responsive means for modifying working member...
Patent
1980-03-24
1982-10-26
Hershkovitz, Abraham
Motors: expansible chamber type
Plural relatively movable or rigidly interconnected working...
Condition responsive means for modifying working member...
91445, 91447, 91523, 1375992, 251282, F15B 1116
Patent
active
043555659
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
TECHNICAL FIELD
This invention relates generally to a fluid circuit, and more particularly relates to a fluid circuit having a load check and by-pass valve having zero leakage when associated with a fluid cylinder.
BACKGROUND ART
Construction vehicles, such as hydraulic excavators, employ work tools thereon which are normally actuated by double-acting hydraulic cylinders. For example, the cylinders may be employed to selectively actuate the boom, stick, and bucket of the excavator. The hydraulic circuit employed to selectively actuate the cylinders generally includes a load check valve to ensure that a load carried by a cylinder upon its extension and isolation, for example, will not descend abruptly upon loss of hydraulic fluid pressure in the circuit.
In certain commercial applications, the load check valve takes the form of a standard poppet valve to block the escape of fluid from the cylinder when it is maintained in an actuated condition of operation. However, such poppet valves are difficult to control in respect to closely modulating fluid flow in the circuit.
In conventional applications wherein the load check valve includes a reciprocal spool, it is well known that spools of this type do not insure leakage control at an acceptable rate during normal operation. A load check valve of this type is disclosed in U.S. Pat. No. 4,102,250 issued on July 25, 1978 to Lawrence F. Schexnayder and assigned to the assignee of this application.
The present invention is directed to overcoming one or more of the problems set forth above.
DISCLOSURE OF INVENTION
In one aspect of the present invention, a fluid circuit comprises a fluid source, an actuator, control means for selectively communicating pressurized fluid to the actuator, and check valve means, including a load check valve, having a reciprocal spool, for isolating fluid pressure in the actuator in response to selective actuation of the control means. The improved load check valve of this invention includes means for communicating equalized fluid pressure from the actuator to either end of the spool when the control means is actuated to isolate fluid pressure in the actuator.
In another aspect of this invention, a pair of actuators in the form of double-acting cylinders are each connected to a load check valve, and a control means interconnects the load check valves. The improved control means includes resolver valve means for moving to a first position to equalize the fluid pressures in the cylinders upon retraction thereof and when the level of fluid pressure in one of the cylinders exceeds the level of fluid pressure in the other one, and for moving to a second position to permit gradual reduction of the level of fluid pressure in the cylinders upon loss of fluid pressure between the load check valves.
The check valve means of this invention will prevent an abrupt dropping of a load supported by the actuator and the load check valve thereof will function to control leakage therethrough at an acceptable rate during normal operation. For example, when the actuator constitutes a double-acting hydraulic cylinder employed on a construction vehicle or the like and when the cylinder is extended and under load, the check valve means will function to continuously maintain the cylinder in its extended condition of operation without causing any appreciable decay in the pressurized fluid utilized to maintain the cylinder in such extended condition. Furthermore, the load check valve is adapted for attachment to the housing of the cylinder proper, thus avoiding the need for flexible lines interconnecting the same. The feature of providing a control means interconnected between the individual load check valves of a pair of cylinders ensures that the fluid pressures in the cylinders are equalized and that any sudden loss of fluid pressure therebetween will permit the cylinders to lower a load carried thereby, gradually.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of this invention will become apparent from the following desc
REFERENCES:
patent: 2766585 (1956-10-01), Wittren
patent: 2836196 (1958-05-01), Gunn
patent: 2959190 (1960-11-01), Barnes
patent: 3500721 (1970-03-01), Allen
patent: 3811363 (1974-05-01), Cryder
patent: 3906840 (1975-09-01), Bianchetta
patent: 3943825 (1976-03-01), Bianchetta
patent: 4000683 (1977-01-01), Schexnayder
patent: 4094228 (1978-06-01), Schexnayder
patent: 4102250 (1978-07-01), Schexnayder
patent: 4194532 (1980-03-01), Hall
patent: 4204459 (1980-05-01), Johnson
patent: 4258610 (1981-03-01), Maucher
Caterpillar Tractor Co.
Grant John W.
Hershkovitz Abraham
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