Robustly stable servo-controlled metering poppet valve

1. A valve assembly comprising:

a poppet valve assembly including a poppet valve member and a fluid passage extending between a first port and a second port, and the fluid passage including a valve seat, and the poppet valve assembly having a control chamber disposed therein; and

the poppet valve member includes a control hydraulic surface exposed to hydraulic pressure inside the control chamber, and the poppet valve member being movable to a position in contact with the valve seat, and the poppet valve member having a plurality of positions with different flow areas across the valve seat; and

a pilot valve assembly fluidly connected to the poppet valve assembly, and having a first configuration wherein the first port is fluidly connected to the control chamber, and having a second configuration wherein the second port is fluidly connected to the control chamber, and having a third configuration wherein the control chamber is fluidly isolated from the first port and the second port.

2. A valve assembly as in claim 1 wherein the second port is fluidly isolated when the pilot valve assembly is in the first configuration, and the first port is fluidly isolated when the pilot valve assembly is in the second configuration.

3. A valve assembly as in claim 1 including a means for detecting a pressure difference between the first port and the second port.

4. A valve assembly as in claim 3 wherein the means for detecting a pressure difference between the first port and the second port includes a first pressure sensor sensitive to the pressure of the first port, and a second pressure sensor sensitive to the pressure of the second port.

5. A valve assembly as in claim 1 wherein the pilot valve assembly includes a pilot valve member operably coupled to an actuator, and the pilot valve assembly is biased to be in the first configuration.

6. A valve assembly as in claim 1 that includes a position sensor attached to the poppet valve assembly, and the position sensor is operably coupled to sense a displacement of the poppet valve member relative to the valve seat.

7. A valve assembly as in claim 6 wherein the position sensor includes a linear variable displacement transducer.

8. A valve assembly as in claim 1 wherein the poppet-valve assembly is a first poppet valve assembly and the pilot valve assembly is a first pilot valve assembly; and

the valve assembly includes a second, third and fourth poppet valve assembly coupled to a second, third and fourth pilot valve assembly, respectively.

9. A valve assembly as in claim 8 wherein the first port is a pump port, the second port is a drain port, and the valve assembly includes a rod port and a head port.

10. A machine comprising:

a chassis; and

a valve assembly including a poppet valve assembly, a head port, a rod port, a pump port, and a drain port, attached to the chassis; and

a hydraulic cylinder fluidly connected to the head port and the rod port; and

the poppet valve assembly includes a poppet valve member with a control hydraulic surface exposed to fluid pressure in a control chamber and movable to a plurality of positions with different flow areas across the valve seat; and

means, including a pilot valve assembly, for stopping the poppet valve member at each of the plurality of positions at least in part by fluidly isolating the control chamber.

11. A machine as in claim 10 wherein the machine is a work machine, and the hydraulic cylinder is operably coupled to an implement of the work machine.

12. A machine as in claim 11 including an electronic controller with means for determining control signals for the pilot valve assembly at least in part as a function of a pressure difference on opposite sides of the valve seat, in operable control of the pilot valve assembly.

13. A machine as in claim 12 wherein the pilot valve assembly includes an actuator operably coupled to move a pilot valve member; and

the pilot valve member can be moved to a first, second and third position; and

the pilot valve member is operable to fluidly connect the control chamber to one of the head port, the rod port, the pump port and the drain port in a first configuration, and connect the control chamber to a different one of the head port, the rod port, the pump port and the drain port in a second configuration and fluidly isolate the control chamber from the head port, the rod port, the pump port and the drain port in a third configuration.

14. A machine as in claim 11 including an electronic controller operably coupled to a position sensor attached to the poppet valve assembly, and the position sensor is operably coupled to sense a displacement of the poppet valve member relative to the valve seat.

15. A machine as in claim 11 and including a first cylinder hydraulically connected to a first poppet valve assembly that is electronically controlled by the electronic controller; and

the work machine also including a second cylinder hydraulically connected to a second poppet valve assembly that is electronically controlled by the electronic controller.

16. A method of operating a valve assembly comprising the steps of:

moving a poppet valve member with respect to a valve seat at least in part by exposing a control hydraulic surface of the poppet valve member to hydraulic pressure in a control chamber; and

stopping the poppet valve member at a position away from the valve seat at least in part by fluidly isolating the control chamber.

17. A method of operating a valve assembly as in claim 16 wherein the step of moving the poppet valve member with respect to the valve seat includes fluidly connecting the control chamber to a port.

18. A method of operating a valve assembly as in claim 16 including a step of selecting the position of the poppet valve member based at least in part on a pressure differential on opposite sides of a valve seat.

19. A method of operating a valve assembly as in claim 18 including a step of determining the pressure differential at least in part by sensing pressure in a first port and sensing pressure in a second port.

20. A method of operating a valve assembly as in claim 18 including a step of determining the position of the poppet valve member with respect to the valve seat.