Hydraulic control system with cross function regeneration

1. In a hydraulic system that includes a plurality of hydraulic functions connected to a supply conduit carrying pressurized fluid from a source and to a return conduit connected to a tank, each hydraulic function comprising a hydraulic actuator with a first port and a second port that are coupled by a valve assembly to the supply conduit and to the return conduit, a method for controlling one hydraulic function comprising:

receiving a command designating desired motion of the hydraulic actuator;

sensing a hydraulic load acting on the hydraulic actuator;

deriving a pressure value denoting a pressure present in the hydraulic system; and

in response to the command, the hydraulic load and the pressure value, operating the valve assembly in a metering mode in which fluid from the return conduit flows into the hydraulic actuator and fluid flows from the hydraulic actuator into the supply conduit.

2. The method as recited in claim 1 wherein deriving a pressure value comprises determining pressure of fluid in at least one of the supply conduit and the return conduit.

3. The method as recited in claim 1 wherein deriving a pressure value comprises sensing pressure in the supply conduit and sensing pressure in the return conduit.

4. The method as recited in claim 1 wherein:

the hydraulic actuator comprises cylinder with a piston that defines a rod chamber and a head chamber in the cylinder; and

the metering mode comprises one of:

(a) extending the piston from the cylinder by operating the valve assembly to connect the head chamber to the return conduit and the rod chamber to the supply conduit thereby sending fluid from the rod chamber into the supply conduit, and

(b) retracting the piston into the cylinder by operating the valve assembly to connect the rod chamber to the return conduit and the head chamber to the supply conduit thereby sending fluid from the head chamber into the supply conduit.

5. The method as recited in claim 4 wherein sensing a hydraulic load comprises sensing pressure of fluid in at least one of the rod chamber and the head chamber.

6. The method as recited in claim 4 wherein extending the piston from the cylinder occurs when pressure in the supply conduit is less than pressure in the rod chamber.

7. The method as recited in claim 4 wherein extending the piston from the cylinder is performed when the hydraulic load L acting on the piston satisfies the expression L≦R*Pr−Ps−K, where R is the ratio of a surface area of the piston in the head chamber to a surface area of the piston in the rod chamber, Ps is pressure in the supply conduit, Pr is pressure in the return conduit, and K is a value representing losses in the hydraulic system.

8. The method as recited in claim 4 wherein retracting the piston into the cylinder is performed when pressure in the supply conduit is less than pressure in the head chamber.

9. The method as recited in claim 4 wherein retracting the piston into the cylinder is performed when the hydraulic load L acting on the piston satisfies the expression L≧R*Ps−Pr+K, where R is the ratio of a surface area of the piston in the head chamber to a surface area of the piston in the rod chamber, Ps is pressure in the supply conduit, Pr is pressure in the return conduit, and K is a value representing losses in the hydraulic system.

10. The method as recited in claim 4 wherein:

the valve assembly comprises a first valve coupling the head chamber to a supply conduit carrying pressurized fluid from a source, a second valve coupling the rod chamber to the supply conduit, a third valve coupling the head chamber to a return conduit connected to a tank, and a fourth valve coupling the rod chamber to the return conduit; and further comprising;

extending the piston from the cylinder is performed by opening the second valve and third valve; and

retracting the piston into the cylinder is performed by opening the first valve and fourth valve.

11. In a hydraulic system that includes a plurality of hydraulic functions connected to a supply conduit carrying pressurized fluid from a source and to a return conduit connected to a tank, at least one hydraulic function comprising a cylinder with a piston that defines a rod chamber and a head chamber in the cylinder, a first valve coupling the head chamber to the supply conduit, a second valve coupling the rod chamber to the supply conduit, a third valve coupling the head chamber to the return conduit, and a fourth valve coupling the rod chamber to the return conduit, a method for operating the at least one hydraulic function comprising:

receiving a command designating desired motion of the piston;

determining a hydraulic load acting on the cylinder;

indicating a first pressure present in the supply conduit;

indicating a second pressure present in the return conduit;

in response to the command, the hydraulic load, the first pressure and the second pressure, selecting a metering mode from among a Standard Powered Retraction (Piston Extend) mode, a Standard Powered Extension (Piston Extend) mode, a Standard Powered Extension (Piston Retract) mode, and a Standard Powered Retraction (Piston Retract) mode; and

in response to the metering mode selected, opening two of the first, second, third and fourth valves as defined in the following table:

Metering Mode

Valves Opened

Standard Powered Retraction (Piston Extend)

second and third valves

Low Side Regeneration Extension

third and fourth valves

High Side Regeneration Extension

first and second valves

Standard Powered Extension (Piston Extend)

first and fourth valves.

Standard Powered Extension (Piston Retract)

first and fourth valves

High Side Regeneration Retraction

first and second valves

Low Side Regeneration Retraction

third and fourth valves

Standard Powered Retraction (Piston Retract)

second and third valves.

12. The method as recited in claim 11 wherein selecting a metering mode also can choose from among a Low Side Regeneration Extension mode, a High Side Regeneration Extension mode, a High Side Regeneration Retraction mode, and a Low Side Regeneration Retraction mode.

13. The method as recited in claim 11 wherein selecting a metering mode comprises:

determining whether the piston is to be extended from or retracted into the cylinder in response to the hydraulic load L; and

choosing a given metering mode based on whether a hydraulic load/pressure relationship given in the following table is satisfied for that given metering mode

Hydraulic Load

Metering Mode

Pressure Relationship

Standard Powered Retraction (Piston Extend)

L ≦ R * Pr − Ps − K

Low Side Regeneration Extension

L ≦ R * Pr − Pr − K

High Side Regeneration Extension

L ≦ R * Ps − Ps − K

Standard Powered Extension (Piston Extend)

L ≦ R * Ps − Pr − K

Standard Powered Extension (Piston Retract)

L ≧ R * Ps − Pr + K

High Side Regeneration Retraction

L ≧ R * Ps − Ps + K

Low Side Regeneration Retraction

L ≧ R * Pr − Pr + K

Standard Powered Retraction (Piston Retract)

L ≧ R * Pr − Ps + K

where R is the ratio of a surface area of the piston in the head chamber to a surface area of the piston in the rod chamber, Ps is pressure in the supply conduit, Pr is pressure in the return conduit, and K is a value representing losses in the hydraulic system.

14. The method as recited in claim 13 wherein when the hydraulic load/pressure relationship for more than one given metering mode is satisfied selecting the first such metering mode in an order specified in the table that produces piston motion in a direction designated by the command is selected.

15. The method as recited in claim 13 further comprising:

sensing a third pressure in the head chamber;

sensing a fourth pressure in the rod chamber; and

calculating the hydraulic load L in response to the third pressure and the fourth pressure.

16. The method as recited in claim 15 wherein the hydraulic load L is determined according to the expression L=R*Pa−Pb, where R is a ratio of a surface area of the piston in the head chamber to a surface area of the piston in the rod chamber, Pa is pressure in the head chamber, Pb is pressure in the rod chamber.

17. The method as recited in claim 15 further comprising wherein the hydraulic load L is determined by sensing a force Fx acting on the piston and employing the expression L=−Fx/Ab, where Ab is a surface area of the piston in the rod chamber.

18. In a hydraulic system that includes a plurality of hydraulic functions connected to a supply conduit carrying pressurized fluid from a source and to a return conduit connected to a tank, at least one hydraulic function comprising hydraulic actuator with a first port and a second port, a first valve coupling the first port to the supply conduit, a second valve coupling the second port to the supply conduit, a third valve coupling the first port to the return conduit, and a fourth valve coupling the second port to the return conduit, a method for operating the at least one hydraulic function comprising:

receiving a command designating desired motion of the hydraulic actuator;

sensing a parameter that indicates a magnitude of a hydraulic load acting on the hydraulic actuator;

sensing pressure in the hydraulic system; and

in response to the command, the hydraulic load and the pressure, selecting a metering mode among a first metering mode in which the first and fourth valves are opened wherein fluid from the supply conduit drives the hydraulic actuator in a first direction, a second metering mode in which the second and third valves are opened wherein fluid from the supply conduit drives the hydraulic actuator in a second direction, and a third metering mode in which the first and fourth valves are opened while the hydraulic actuator is moving in the second direction wherein fluid flow from the hydraulic actuator into the supply conduit and from the return conduit to the hydraulic actuator.

19. The method as recited in claim 18 wherein selecting a metering mode also can choose from among a fourth metering mode in which the second and third valves are opened while the hydraulic actuator is moving in the first direction wherein fluid flow from the hydraulic actuator into the supply conduit and from the return conduit to the hydraulic actuator.

20. The method as recited in claim 18 wherein sensing pressure in the hydraulic system comprises sensing pressure in at least one of the supply conduit and the return conduit.

21. The method as recited in claim 18 wherein sensing a parameter comprises sensing pressure of fluid adjacent at least one of the first port and the second port.

22. The method as recited in claim 18 further comprising connecting the first valve and the second valve to the supply conduit through a reversible check valve.

23. In a hydraulic system that includes a plurality of hydraulic functions connected to a supply conduit carrying pressurized fluid from a source and to a return conduit connected to a tank, each hydraulic function comprising a piston-cylinder arrangement with a first chamber and a second chamber both coupled by a valve assembly to the supply conduit and to the return conduit, a method for operating one hydraulic function comprising:

receiving a command designating desired motion of the hydraulic actuator;

sensing a hydraulic load acting on the hydraulic actuator;

sensing a pressure value denoting a pressure present in the hydraulic system; and

in response to the command, the hydraulic load and the pressure value, operating the valve assembly to direct fluid from the first chamber into both the second chamber and the supply conduit.

24. The method as recited in claim 23 wherein operating the valve assembly produces retraction of the piston-cylinder arrangement.

25. The method as recited in claim 23 wherein sensing a pressure value comprises determining pressure of fluid in at least one of the supply conduit and the return conduit.