Pilot operated spool valve
A spool valve assembly includes a spool that is moveable by differential pressure across the spool.
1. A spool valve assembly for controlling fluid flow comprising:
a body defining:
a chamber having first and second ends
a spool input port for fluid communication into the chamber;
a spool output port for fluid communication out of the chamber;
a reference inlet port for fluid communication into the chamber and
a reference outlet port for fluid communication out of the chamber; and
a spool having first and second ends disposed in the chamber for sliding movement between a first position which allows fluid flow from the spool input port to the spool output port and a second position which restricts fluid flow from the spool input port to the spool output port, the spool being positioned by differential pressure across the spool between a first volume of fluid, at a command pressure, disposed between the first spool end and the first end of the chamber and a second volume of fluid, at a reference pressure, disposed between the second spool end and the second end of the chamber, the reference inlet port and the reference outlet port both being in selective fluid communication with the second volume of fluid, one of the reference inlet port and the reference outlet port having a first flow capacity when the spool is in the first position and the one of the reference inlet port and the reference outlet port having a second flow capacity when the spool is in the second position, such that the reference pressure is changed by changing the position of the spool.
2. The spool valve assembly of claim 1 wherein the body includes a spool valve sleeve, supporting the spool.
3. The spool valve assembly of claim 1 , further comprising:
a command port adapted to receive a command pressure signal;
the reference inlet port being adapted to be connected to a source of fluid at a first pressure;
the reference outlet port being adapted to be connected to a region of fluid at a second pressure, less than the first pressure; and
the first end of the spool cooperating with the body to define the first volume of fluid to have a variable size between the first end of the spool and the first end of the chamber, the first volume being in continuous fluid communication with the command port,
the second end of the spool cooperating with the body to define the second volume of fluid to have a variable size between the second end of the spool and the second end of the chamber, the spool being movable between the first position, adjacent the first end of the chamber, and the second position, adjacent the second end of the chamber while substantially preventing fluid leakage through the chamber between the first volume of fluid and the second volume of fluid, the spool permitting fluid communication between the spool input port and the spool output port when the spool is in the first position, the spool blocking fluid communication between the spool input port and the spool output port when the spool is in the second position, the spool progressively decreasing fluid communication between the reference outlet port and the first volume of fluid and progressively increasing fluid communication between the reference inlet port and the first volume of fluid as the spool is moved from the first position thereof toward the second position thereof to cause pressure to rise in the second volume of fluid as the spool is moved from the first position toward the second position thereof, the spool being moved by a difference in pressures between the first volume of fluid and the second volume of fluid.
4. The spool valve assembly of claim 3 , further comprising a pilot microvalve which is selectively actuated to send a pressure command to the first volume of fluid, wherein a cross-sectional flow area of a port of the spool valve changes in proportion to the actuation of the pilot microvalve.
5. The spool valve assembly of claim 3 , wherein the body comprises:
a valve housing; and
a sleeve disposed in the valve housing, within the chamber, the spool input port and the spool output port being formed in the sleeve.
6. The spool valve assembly of claim 1 , further comprising a pilot microvalve which is selectively actuated to send a pressure command to the first volume of fluid, wherein a cross-sectional flow area of a port of the spool valve changes in proportion to the actuation of the pilot microvalve.
7. The spool valve assembly of claim 6 , further comprising a longitudinal fluid bore defined in the spool, the bore providing fluid communication a location in a fluid flow path between the reference inlet port and the reference outlet port to provide the selective fluid communication between the reference inlet port and the second volume, and to provide the selective fluid communication between the reference outlet port and the second volume, such that the reference pressure in the second volume changes in response to changes in the position of the spool.
8. The spool valve assembly of claim 7 , further comprising:
a first region of the spool, intermediate the first end and the second end of the spool, that cooperates with the spool input port and the spool output port to varying fluid flow between the spool input port and the spool output port; and
a groove formed in an outer surface of the spool at a location between the first region of the spool and the first end of the spool, the groove being in fluid communication with the longitudinal fluid bore.
9. The spool valve assembly of claim 8 , wherein the pilot valve is a microvalve.
10. The spool valve assembly of claim 6 , wherein the pilot valve is an open center 3-way valve.
11. The spool valve assembly of claim 10 , further comprising a longitudinal fluid bore defined in the spool, the bore providing fluid communication a location in a fluid flow path between the reference inlet port and the reference outlet port to provide the selective fluid communication between the reference inlet port and the second volume, and to provide the selective fluid communication between the reference outlet port and the second volume, such that the reference pressure in the second volume changes in response to changes in the position of the spool.
12. The spool valve assembly of claim 11 , further comprising:
a first region of the spool, intermediate the first end and the second end of the spool, that cooperates with the spool input port and the spool output port to varying fluid flow between the spool input port and the spool output port; and
a groove formed in an outer surface of the spool at a location between the first region of the spool and the first end of the spool, the groove being in fluid communication with the longitudinal fluid bore.
13. The spool valve assembly of claim 12 , wherein the pilot valve is a microvalve.
14. The spool valve assembly of claim 1 , further comprising:
a pilot valve having:
a pilot input port; and
a pilot output port, at least one of the cross-sectional flow area through the pilot input port and the cross-sectional flow area through the pilot output port being varied as the pilot valve is operated,
the spool cooperating with the body to define a fluid passageway from the spool input port to the spool output port,
at least one of the cross-sectional flow area through the spool input port and the cross-sectional flow area through the spool output port being varied as the spool moves,
the command pressure in the first volume of fluid being controlled by the pilot valve,
the spool moving in response to changing command pressures from the pilot valve such that a ratio of the cross-sectional flow area of the spool input port to the spool output port is maintained substantially equal to a ratio of the cross-sectional flow area of the pilot input port to the pilot output port.
15. The spool valve assembly of claim 14 , the spool valve further comprising:
the spool input port being adapted to be connected to a source of fluid at a first pressure,
the spool output port being adapted to be connected to a region of fluid at a second pressure, less than the first pressure; and
the spool being movable between a first position adjacent the first end of the chamber and a second position adjacent the second end of the chamber while substantially preventing fluid leakage through the chamber between the first volume at the command pressure and the second volume at the reference pressure, the spool permitting fluid communication between the spool input port and the spool output port when the spool is in the first position, the spool blocking fluid communication between the spool input port and the spool output port when the spool is in the second position, the spool progressively decreasing fluid communication between the reference outlet port and the second volume at the reference pressure and progressively increasing fluid communication between the reference inlet port and the second volume at the reference pressure as the spool is moved from the first position thereof toward the second position thereof to cause pressure to rise in the reference volume as the spool is moved from the first position toward the second position thereof, the spool progressively increasing fluid communication between the reference outlet port and the second volume at the reference pressure and progressively decreasing fluid communication between the reference inlet port and the second volume at the reference pressure as the spool is moved from the second position thereof toward the first position thereof to cause pressure to fall in the reference volume as the spool is moved from the second position toward the first position thereof, the spool being moved by a difference in pressures between the first volume at the command pressure and the second volume at the reference pressure.
16. The spool valve assembly of claim 15 , wherein the spool is movable to simultaneously modulate flow from the spool input port to the spool output port and modulate flow between the reference inlet port and the reference outlet port.
17. The spool valve assembly of claim 14 , wherein the pilot valve is a microvalve.
18. The spool valve assembly of claim 14 , wherein the body comprises:
a valve housing; and
a sleeve disposed in the valve housing, within the chamber, the spool input port and the spool output port being formed in the sleeve.
19. The spool valve assembly of claim 14 , wherein the pilot valve is an open center 3-way valve.
20. The spool valve assembly of claim 14 , further comprising a longitudinal fluid bore defined in the spool, the bore providing fluid communication a location in a fluid flow path between the reference inlet port and the reference outlet port to provide the selective fluid communication between the reference inlet port and the second volume, and to provide the selective fluid communication between the reference outlet port and the second volume, such that the reference pressure in the second volume changes in response to changes in the position of the spool.
21. The spool valve assembly of claim 20 , further comprising:
a first region of the spool, intermediate the first end and the second end of the spool, that cooperates with the spool input port and the spool output port to varying fluid flow between the spool input port and the spool output port; and
a groove formed in an outer surface of the spool at a location between the first region of the spool and the first end of the spool, the groove being in fluid communication with the longitudinal fluid bore.
22. The spool valve assembly of claim 21 , wherein the pilot valve is a microvalve.
23. The spool valve assembly of claim 1 , wherein the body comprises:
a valve housing; and
a sleeve disposed in the valve housing, within the chamber, the spool input port and the spool output port being formed in the sleeve.
24. The spool valve assembly of claim 1 , wherein the spool is movable to simultaneously modulate flow from the spool input port to the spool output port and modulate flow between the reference inlet port and the reference outlet port.
25. The spool valve assembly of claim 24 , further comprising a longitudinal fluid bore defined in the spool, the bore providing fluid communication a location in a fluid flow path between the reference inlet port and the reference outlet port to provide the selective fluid communication between the reference inlet port and the second volume, and to provide the selective fluid communication between the reference outlet port and the second volume, such that the reference pressure in the second volume changes in response to changes in the position of the spool.
26. The spool valve assembly of claim 25 , further comprising:
a first region of the spool, intermediate the first end and the second end of the spool, that cooperates with the spool input port and the spool output port to varying fluid flow between the spool input port and the spool output port; and
a groove formed in an outer surface of the spool at a location between the first region of the spool and the first end of the spool, the groove being in fluid communication with the longitudinal fluid bore.
27. The spool valve assembly of claim 26 , wherein the pilot valve is a microvalve.
28. The spool valve assembly of claim 1 , further comprising a longitudinal fluid bore defined in the spool, the bore providing fluid communication a location in a fluid flow path between the reference inlet port and the reference outlet port to provide the selective fluid communication between the reference inlet port and the second volume, and to provide the selective fluid communication between the reference outlet port and the second volume, such that the reference pressure in the second volume changes in response to changes in the position of the spool.
29. The spool valve assembly of claim 17 , further comprising:
a first region of the spool, intermediate the first end and the second end of the spool, that cooperates with the spool input port and the spool output port to varying fluid flow between the spool input port and the spool output port; and
a groove formed in an outer surface of the spool at a location between the first region of the spool and the first end of the spool, the groove being in fluid communication with the longitudinal fluid bore.
30. The spool valve assembly of claim 29 , wherein the groove extends circumferentially about the spool.