초록 ▼

A hydraulic system for a work machine is disclosed. The hydraulic system has a reservoir configured to hold a supply of fluid and a source configured to pressurize the fluid. The hydraulic system also has a fluid actuator, a first valve, and a second valve. The first valve is configured to selective

A hydraulic system for a work machine is disclosed. The hydraulic system has a reservoir configured to hold a supply of fluid and a source configured to pressurize the fluid. The hydraulic system also has a fluid actuator, a first valve, and a second valve. The first valve is configured to selectively fluidly communicate the source with the fluid actuator to facilitate movement of the fluid actuator in a first direction. The second valve is configured to selectively fluidly communicate the fluid actuator with the reservoir to facilitate movement of the fluid actuator in the first direction. The hydraulic system further has a proportional pressure compensating valve configured to control a pressure of a fluid directed between the fluid actuator and the reservoir.

대표청구항 ▼

What is claimed is: 1. A hydraulic system, comprising: a reservoir configured to hold a supply of fluid; a source configured to pressurize the fluid; a fluid actuator; a first valve configured to selectively fluidly communicate the source with the fluid actuator to facilitate movement of the fluid

What is claimed is: 1. A hydraulic system, comprising: a reservoir configured to hold a supply of fluid; a source configured to pressurize the fluid; a fluid actuator; a first valve configured to selectively fluidly communicate the source with the fluid actuator to facilitate movement of the fluid actuator in a first direction; a second valve configured to selectively fluidly communicate the fluid actuator with the reservoir to facilitate movement of the fluid actuator in the first direction; a third valve configured to selectively fluidly communicate the fluid actuator with the reservoir to facilitate movement of the fluid actuator in a second direction; a shuttle valve disposed between the second and third valves and movable between a first position where pressurized fluid from the second valve is passed through the shuttle valve, to a second position where pressurized fluid from the third valve is passed through the shuttle valve; and a proportional pressure compensating valve configured to control a pressure of the fluid directed between the fluid actuator and the reservoir. 2. The hydraulic system of claim 1, wherein the proportional pressure compensating valve includes a valve element movable toward a flow blocking position in response to a pressure of the fluid flowing through the second valve exceeding a predetermined pressure, thereby slowing the movement of the hydraulic actuator. 3. The hydraulic system of claim 1, wherein the hydraulic actuator is a motor. 4. The hydraulic system of claim 1, further including: a fourth valve configured to selectively fluidly communicate the source with the fluid actuator to facilitate movement of the fluid actuator in the second direction. 5. The hydraulic system of claim 4, wherein each of the first, second, third, and fourth valves are solenoid-actuated control valves. 6. The hydraulic system of claim 4, further including a first fluid passageway disposed between the fluid actuator and the first and third valves; and a second fluid passageway disposed between the fluid actuator and the second and fourth valves. 7. The hydraulic system of claim 6, further including a first check valve disposed within the first fluid passageway and spring-biased to selectively prevent fluid flow from the fluid actuator to the first and third valves during movement of the fluid actuator in the first direction; and a second check valve disposed within the second fluid passageway and configured to selectively prevent fluid flow from the fluid actuator to the second and fourth valves during movement of the fluid actuator in the second direction. 8. The hydraulic system of claim 7, further including: a first signal passageway configured to communicate the first fluid passageway and the second check valve; and a second signal passageway configured to communicate the second fluid passageway and the first check valve. 9. The hydraulic system of claim 4, further including a first fluid passageway disposed between the reservoir and the second and third valves, wherein the second and third valves are connected to the first fluid passageway in parallel and the proportional pressure compensating valve is disposed between the first fluid passageway and the reservoir. 10. The hydraulic system of claim 9, further including a first signal passageway, wherein the proportional pressure compensating valve includes a valve element movable between a flow passing position and a flow blocking position, and the first signal passageway is configured to direct fluid from between the proportional pressure compensating valve and the first fluid passageway to the proportional pressure compensating valve to bias the valve element toward one of the flow passing position and the flow blocking position. 11. The hydraulic system of claim 10, wherein the proportional pressure compensating valve includes a spring configured to bias the valve element toward one of the flow passing and flow blocking positions. 12. The hydraulic system of claim 4, further including: a second signal passageway disposed upstream of the second and third valves, the second and third valves being in fluid communication with the second signal passageway, the shuttle valve being disposed within the second signal passageway. 13. The hydraulic system of claim 12, wherein the shuttle valve is movable in response to a fluid pressure. 14. The hydraulic system of claim 12, further including a third signal passageway configured to direct pressurized fluid from one of the second and third valves via the shuttle valve to the proportional pressure compensating valve to bias the proportional pressure compensating valve element toward the other of the flow passing and flow blocking position. 15. The hydraulic system of claim 1, wherein the first valve and the second valve are independently operable. 16. A method of operating a hydraulic circuit, comprising: pressurizing a fluid; directing the pressurized fluid to a fluid actuator via a first valve to facilitate movement of the fluid actuator in a first direction; draining fluid from the fluid actuator via a second valve to facilitate movement of the fluid actuator in the first direction; draining fluid from the fluid actuator via a third valve to facilitate movement in a second direction; controlling a pressure of the fluid drained from the actuator with a proportional pressure compensating; and selectively preventing fluid flow from the fluid actuator to the first and third valves in response to a pressure differential across the fluid actuator exceeding a predetermined value during movement of the fluid actuator in the first direction. 17. The method of claim 16, wherein controlling a pressure includes moving a valve element of the proportional pressure compensating valve toward a flow blocking position in response to a pressure of the fluid flowing through the second valve exceeding a predetermined pressure, thereby slowing the movement of the hydraulic actuator. 18. The method of claim 16, further including: directing the pressurized fluid to the fluid actuator via a fourth valve to facilitate movement in the second direction. 19. The method of claim 18, wherein each of the first, second, third, and fourth valves are solenoid-actuated control valves. 20. The method of claim 18, further including: selectively preventing fluid flow from the fluid actuator to the second and fourth valves in response to a pressure differential across the fluid actuator exceeding a predetermined value during movement of the fluid actuator in the second direction. 21. The method of claim 20, further including directing a flow of pressurized fluid from an inlet of the fluid actuator to a check valve located at an exit of the fluid actuator to bias the check valve away from a seat. 22. The method of claim 18, further including: directing a flow of pressurized fluid from immediately upstream of the proportional pressure compensating valve to an end of the proportional pressure compensating valve to urge a valve element of the proportional pressure compensating valve towards a flow passing position; and directing a flow of pressurized fluid from the second and third valves to an end of the proportional pressure compensating valve to urge a valve element of the proportional pressure compensating valve towards a flow blocking position. 23. The method of claim 16, wherein the first valve and the second valve are independently operable. 24. A machine, comprising: a power source; a traction device; a hydraulic motor connected to move the traction device, thereby propelling the machine; a reservoir configured to hold a supply of fluid; a source driven by the power source to pressurize the fluid; a first valve configured to selectively fluidly communicate the source with the hydraulic motor to facilitate movement of the traction device in a first direction; a second valve configured to selectively fluidly communicate the hydraulic motor with the reservoir to facilitate movement of the traction device in the first direction; a third valve configured to selectively fluidly communicate the hydraulic motor with the reservoir to facilitate movement of the traction device in a second direction; a shuttle valve disposed between the second and third valves and movable between a first position where pressurized fluid from the second valve is passed through the shuttle valve, to a second position where pressurized fluid from the third valve is passed through the shuttle valve, wherein the shuttle valve is movable in response to a fluid pressure; and a proportional pressure compensating valve configured to control a pressure of a fluid directed between the hydraulic motor and the reservoir. 25. The machine of claim 24, wherein the proportional pressure compensating valve includes a valve element movable toward a flow blocking position in response to a pressure of the fluid flowing through the second valve exceeding a predetermined pressure, thereby slowing the movement of the traction device. 26. The machine of claim 24, further including: a fourth valve configured to selectively fluidly communicate the source with the hydraulic motor to facilitate movement of the traction device in the second direction. 27. The machine of claim 26, wherein each of the first, second, third, and fourth valves are solenoid-actuated control valves. 28. The machine of claim 26, further including a first fluid passageway disposed between the hydraulic motor and the first and third valves; and a second fluid passageway disposed between the hydraulic motor and the second and fourth valves. 29. The machine of claim 28, further including a first check valve disposed within the first fluid passageway and spring-biased to selectively prevent fluid flow from the hydraulic motor to the first and third valves during movement of the hydraulic motor in the first direction; and a second check valve disposed within the second fluid passageway and configured to selectively prevent fluid flow from the hydraulic motor to the second and fourth valves during movement of the hydraulic motor in the second direction. 30. The machine of claim 29, further including: a first signal passageway configured to communicate the first fluid passageway and the second check valve; and a second signal passageway configured to communicate the second fluid passageway and the first check valve. 31. The machine of claim 26, further including a first fluid passageway disposed between the reservoir and the second and third valves, wherein the second and third valves are connected to the first fluid passageway in parallel and the proportional pressure compensating valve is disposed between the first fluid passageway and the reservoir. 32. The machine of claim 31, further including a first signal passageway, wherein the proportional pressure compensating valve includes a valve element movable between a flow passing position and a flow blocking position, and the first signal passageway is configured to direct fluid from between the proportional pressure compensating valve and the first fluid passageway to the proportional pressure compensating valve to bias the valve element toward one of the flow passing position and the flow blocking position. 33. The machine of claim 26, further including: a second signal passageway disposed upstream of the second and third valves, the second and third valves being in fluid communication with the second signal passageway, the shuttle valve being disposed within the second signal passageway. 34. The machine of claim 33, further including a third signal passageway configured to direct pressurized fluid from one of the second and third valves via the shuttle valve to the proportional pressure compensating valve to bias the proportional pressure compensating valve element toward the other of the flow passing and flow blocking position. 35. The work machine of claim 24, wherein the first valve and the second valve are independently operable.