초록 ▼

A hydraulic circuit for lifting and lowering a load is disclosed. The hydraulic circuit may include a hydraulic pump, a fluid reservoir, a load-sense valve, and a hydraulic actuator having a first chamber and a second chamber. The hydraulic circuit may also include a first control valve assembly hav

A hydraulic circuit for lifting and lowering a load is disclosed. The hydraulic circuit may include a hydraulic pump, a fluid reservoir, a load-sense valve, and a hydraulic actuator having a first chamber and a second chamber. The hydraulic circuit may also include a first control valve assembly having first and second lowering positions, the valve being disposed between the hydraulic pump and the hydraulic actuator. A second control valve assembly may also be provided that is disposed between the first control valve assembly and the first chamber of the hydraulic actuator. In one embodiment, the second control valve assembly has a first position and a second position. In one embodiment, the load can be selectively lowered by the hydraulic circuit without use of the hydraulic pump when the first control valve assembly is in the first lowering position and the second control valve assembly is in the second position.

대표청구항 ▼

1. A hydraulic circuit for lifting and lowering a load, the hydraulic circuit comprising: (a) a hydraulic pump, a fluid reservoir, and a hydraulic actuator having a first chamber and a second chamber;(b) a first control valve assembly disposed between the hydraulic pump and the hydraulic actuator; a

1. A hydraulic circuit for lifting and lowering a load, the hydraulic circuit comprising: (a) a hydraulic pump, a fluid reservoir, and a hydraulic actuator having a first chamber and a second chamber;(b) a first control valve assembly disposed between the hydraulic pump and the hydraulic actuator; and(c) a second control valve assembly disposed between the first control valve assembly and the first chamber of the hydraulic actuator, the second control valve assembly having: i. a first position in which hydraulic fluid is blocked from exiting the first chamber, but is allowed to flow into the first chamber;ii. a second position in which hydraulic fluid is allowed to enter or exit the first chamber of the hydraulic actuator;(d) the first control valve assembly being movable to a first lowering position wherein the second control valve assembly is in fluid communication with the fluid reservoir through the first control valve assembly, and a second lowering position including: i. the second control valve assembly being in fluid communication with the fluid reservoir through the first control valve assembly and ii. the second chamber of the hydraulic actuator being placed in fluid communication with the hydraulic pump through the first control valve assembly;(e) wherein the load can be selectively lowered by the hydraulic circuit with gravity alone when the first control valve assembly is in the first lowering position and the second control valve assembly is in the second position without requiring the hydraulic pump to provide output pressure, output fluid flow, or both output pressure and output fluid flow; and(f) an electronic control system configured to operate the first control valve assembly and the second control valve assembly, wherein the control system includes a first chamber pressure sensor located between the first chamber of the hydraulic actuator and the second control valve assembly, wherein the control system includes a load-sense valve for measuring a load-sense pressure, wherein the control system is configured to selectively command the first valve assembly between the first and second lowering positions based upon the relationship between the load-sense pressure and the first chamber pressure. 2. The hydraulic circuit of claim 1, wherein the load can be selectively lowered by the hydraulic circuit with power from the hydraulic pump when the first control valve assembly is in the second lowering position and the second control valve assembly is in the second position. 3. The hydraulic circuit of claim 1, further comprising: (a) a first anti-cavitation valve in fluid communication with the fluid reservoir and the second control valve assembly, the first anti-cavitation valve allowing for hydraulic fluid to flow from the fluid reservoir to the hydraulic actuator first chamber at a preselected hydraulic pressure. 4. The hydraulic circuit of claim 3, further comprising: (a) a second anti-cavitation valve in fluid communication with the fluid reservoir and the hydraulic actuator second chamber, the second anti-cavitation valve allowing for hydraulic fluid to flow from the fluid reservoir to the hydraulic actuator second chamber at a preselected hydraulic pressure. 5. The hydraulic circuit of claim 1, wherein fluid from the second chamber of the hydraulic actuator is blocked from flowing through the first control valve assembly when the first control valve assembly is in the first lowering position. 6. A method of operating a hydraulic circuit comprising: (a) providing a first control valve assembly in fluid communication with a hydraulic actuator and a hydraulic pump, the first control valve assembly having a first lowering position and a second lowering position;(b) providing a second control valve assembly disposed between the first control valve assembly and the hydraulic actuator;(c) receiving a user indication that a load lowering operation is desired; and(d) determining whether a pressure in the hydraulic actuator is greater than a load-sense pressure associated with the first control valve assembly by a pressure margin value; i. where the pressure in the hydraulic actuator is greater than the load-sense pressure by the pressure margin value: 1. actuating the first control valve assembly to the first lowering position and proportionally controlling the second control valve assembly to maintain a pressure differential set point such that the load is selectively lowered by gravity alone without requiring the hydraulic pump to provide output pressure, output fluid flow, or both output pressure and output fluid flow;ii. where the pressure in the hydraulic actuator is lower than the load-sense pressure by the pressure margin value 1. actuating the first control valve assembly to the second lowering position and controlling the second control valve assembly to maintain a pressure at the hydraulic actuator such that the load can be lowered with power from the hydraulic pump. 7. The method of operating a hydraulic circuit of claim 6, wherein: (a) the step of proportionally controlling the second control valve assembly to maintain a pressure differential set point includes taking into account a comparison between the hydraulic actuator pressure and a third pressure value that is equal to a measured fluid pressure between the second control valve assembly and the first control valve assembly; and(b) the step of controlling the second control valve assembly to maintain a pressure at the hydraulic actuator includes taking into account a comparison between the hydraulic actuator pressure and the third pressure value. 8. The hydraulic circuit of claim 6, further including the steps of: (a) providing a first anti-cavitation valve in fluid communication with the fluid reservoir and the second control valve assembly; and(b) allowing for hydraulic fluid to flow through the first anti-cavitation valve from the fluid reservoir to the hydraulic actuator first chamber at a preselected hydraulic pressure. 9. The hydraulic circuit of claim 8, further including the steps of: (a) providing a second anti-cavitation valve in fluid communication with the fluid reservoir and the hydraulic actuator second chamber,(b) allowing for hydraulic fluid to flow through the second anti-cavitation valve from the fluid reservoir to the hydraulic actuator second chamber at a preselected hydraulic pressure.