Micromachined Device and Control Method

Abstract

A microvalve device is disclosed for controlling fluid flow in a fluid circuit. The microvalve device comprises a body having a bore formed therein. A pilot-operated main valve spool supported by the body is movably disposed in the bore for opening and closing ports formed in the body. A pilot microvalve is operable for controlling movement of the pilot-operated main valve. The pilot microvalve may include a movable valve element that controls the cross-sectional area of two variable orifices in series. When the pilot microvalve is at rest, one orifice is closed and the other is open. Upon actuating the pilot microvalve, the closed orifice may begin to open and the open orifice may begin to close. Pressure between the orifices is used as a command pressure, which is utilized to position the pressure control valve to control load pressure. A method of operating a microvalve device is also disclosed.

1 . A device, comprising:
 a pilot-operated valve operating in response to a command pressure to supply fluid at a load pressure to a load, which load pressure is substantially equal to the command pressure during steady state flow conditions; and   a pilot microvalve generating the command pressure in a fluid conduit communicating with the pilot-operated valve, such that the command pressure can be varied between 0% and 100% of a supply pressure, which supply pressure is the pressure of a pressurized fluid supplied to the pilot microvalve, the pilot microvalve comprising:   a first fluid conduit receiving the pressurized fluid at the supply pressure and communicating with a region of relatively low pressure at a return pressure;   a first variable orifice disposed in the first fluid conduit;   a second variable orifice disposed in series arrangement with the first variable orifice in the first fluid conduit, the command pressure being developed in the first fluid conduit between the first variable orifice and the second variable orifice; and   a second fluid conduit in fluid communication with the first fluid conduit between the first variable orifice and the second variable orifice, the second fluid conduit being the fluid conduit communicating command pressure to the pilot-operated valve,   the command pressure supplied from the pilot microvalve to the pilot-operated valve being a function of supply pressure supplied to the pilot microvalve, and the cross sectional areas of the first variable orifice and the second variable orifice, according to the equation:   
       
         
           
             
               
                 P 
                 2 
               
               = 
               
                 
                   
                     P 
                     1 
                   
                   · 
                   
                     A 
                     1 
                     2 
                   
                 
                 
                   
                     A 
                     1 
                     2 
                   
                   + 
                   
                     A 
                     2 
                     2 
                   
                 
               
             
           
         
         where 
         P 2  is the command pressure supplied from the pilot microvalve to the pilot-operated valve; 
         P 1  is the supply pressure; 
         A 1  is the cross sectional area of the first variable orifice; and 
         A 2  is the cross sectional area of the second variable orifice. 
       
     
     
         2 . (canceled) 
     
     
         3 . The device of  claim 1 , further comprising:
 a damping orifice disposed in the second fluid conduit for dampening variations in the command pressure.   
     
     
         4 . The device of  claim 1 , further comprising a filter disposed in the second fluid conduit. 
     
     
         5 . The device of  claim 1 , further comprising:
 a manifold disposed between the pilot microvalve and the pilot-operated valve, the manifold defining a portion of the second fluid conduit; and   an o-ring disposed between the manifold and the pilot-operated valve, the o-ring forming a portion of the pressure boundary of the second fluid conduit.   
     
     
         6 . The device of  claim 5 , further comprising a filter disposed between the pilot-operated valve and the manifold such that fluid flowing through the second fluid conduit is directed through the filter. 
     
     
         7 . The device of  claim 1 , the pilot-operated valve comprising:
 a body defining a longitudinal bore therein, a supply passageway providing fluid communication for fluid from a source of pressurized fluid to the longitudinal bore, a return passageway providing fluid communication from the longitudinal bore to an area of lower pressure, and a load passageway providing fluid communication from the longitudinal bore to the load; and   a spool disposed for sliding movement in the bore,
 the spool having a first end, the first end of the spool and the body cooperating to define a command chamber in the bore, the command chamber being in fluid communication with the second fluid conduit conveying the command pressure, 
 the spool having a second end opposite the first end, the second end of the spool being subjected to the load pressure, 
 the spool defining an annular valve groove extending about an outer surface of the spool, 
 the spool defining a spool passageway providing fluid communication between the second end of the spool and the valve groove, 
 the spool being positionable to a first position where the valve groove and the spool passageway cooperate to define a flow path between the supply passageway and the load passageway, the spool being positionable to a second position where the valve groove and the spool passageway cooperate to define a flow path between the load passageway and the return passageway. 
   
     
     
         8 . The device of  claim 20 , wherein the pressure space comprises an annular second groove extending about the outer surface of the spool in an axial location between the valve groove and the first end of the spool, the spool passageway being in fluid communication with the second groove to supply load pressure from the second end of the spool to the second groove. 
     
     
         9 . The device of  claim 7 , wherein the spool is positionable to a third position where the valve groove is not in fluid communication with the supply passageway, and where the valve groove is not in fluid communication with the return passageway. 
     
     
         10 . The device of  claim 1 , further comprising:
 a body for the pilot-operated valve, the body defining:
 a first port, 
 a second port, and 
 a longitudinal bore; and 
   a spool movable in the longitudinal bore in response to the command pressure, the spool being movable between a first position permitting fluid communication between the first port and the second port and a second position preventing fluid communication between the first port and the second port.   
     
     
         11 - 14 . (canceled) 
     
     
         15 . A method of operating a microvalve device in the form of a pressure control valve having a pilot-operated main valve supplying pressure to a load port in a main valve body and a pilot microvalve with an first orifice having a first variable cross sectional area A 1  and a second orifice having a second variable cross sectional area A 2 , the pilot microvalve developing a control pressure between the first orifice and the second orifice, which control pressure is supplied by the pilot microvalve to the main valve for use in controlling the operation of the main valve, the method comprising
 a) supplying a fluid at a pressure P 1  to the upstream one of the first orifice A 1  and the second orifice A 2  of the pilot microvalve;   b) supplying a control signal to the pilot microvalve to set the cross sectional areas A 1  of the first orifice and the cross sectional areas A 2  of the second orifice;   c) supplying a command pressure P 2  from the microvalve to the main valve as a function of the pressure P 1  supplied to the pilot microvalve and the cross sectional areas A 1  and A 2  of the orifices according to the equation   
       
         
           
             
               
                 
                   P 
                   2 
                 
                 = 
                 
                   
                     
                       P 
                       1 
                     
                     · 
                     
                       A 
                       1 
                       2 
                     
                   
                   
                     
                       A 
                       1 
                       2 
                     
                     + 
                     
                       A 
                       2 
                       2 
                     
                   
                 
               
               ; 
             
           
         
       
       and
 d) repositioning the main valve so that pressure supplied to the load port of the main valve body is a function of the command pressure P 2  supplied from the pilot microvalve. 
 
     
     
         16 . A microvalve device, comprising:
 a pilot-operated valve including:
 a body defining a longitudinal bore therein, the body further defining
 a supply port in fluid communication with the longitudinal bore at a first axial position, 
 a load port in fluid communication with the longitudinal bore at a second axial position, and 
 a return port in fluid communication with the longitudinal bore at a third axial position; 
 
 a spool disposed for movement in said longitudinal bore in response to a command pressure,
 the spool having a first end having an axial end face and a second end having an axial end face, 
 the axial end face of the first end being in fluid communication with a command chamber, 
 the axial end face of the second end being in fluid communication with a load chamber, 
 the spool cooperating with the body to define a pressure space at a location axially spaced from the first end, 
 a load passageway providing fluid communication between the load chamber and the pressure space, 
 the spool being movable to a first position in which the load port and the load chamber are in fluid communication with the supply port, 
 the spool being movable to a second position in which the load port and the load chamber are in fluid communication with the return port, 
 the spool being movable to a third position which is one of a closed center condition and an open center condition,
 the load port and the load chamber being isolated from both the supply port and the return port in the closed center condition, 
 the load port and the load chamber being in fluid communication with both the supply port and the return port in the open center condition, 
 
 the pressure space being axially disposed not further from the command chamber in any of the first, second, and third positions than the one of the supply port and the return port that is the closest axially to the command chamber; and 
 
   a pilot microvalve connected to the pilot-operated valve to supply the command pressure to the command chamber to control the movement of the spool in the longitudinal bore of the pilot-operated valve.   
     
     
         17 . The microvalve device of  claim 16 , wherein the load passageway is defined through a portion of the spool to provide fluid communication between the load chamber and the pressure space. 
     
     
         18 . The microvalve device of  claim 17 , wherein the pressure space is a groove formed in an external surface of the spool. 
     
     
         19 . The microvalve device of  claim 16 , wherein the pressure space is a groove formed in the body. 
     
     
         20 . The device of  claim 7 , the pilot-operated valve being provided with a pressure space supplied with fluid at load pressure such that leakage from the command chamber is minimized or eliminated. 
     
     
         21 . The device of  claim 20 , wherein
 the pressure space comprises a second groove formed in the body which extends circumferentially about the spool; and   the pilot operated valve further comprises a passageway defined in one of the body and the spool that supplies fluid at load pressure to the second groove.   
     
     
         22 . A spool valve comprising:
 a body defining:
 a longitudinal bore; 
 a supply port in fluid in communication with the longitudinal bore and adapted to contain fluid at a supply pressure; and 
 a load port in fluid communication with the longitudinal bore and adapted to contain fluid at a load pressure; 
   a spool disposed in the longitudinal bore;
 the spool and the body cooperating to define a command chamber at a first end of the spool, which command chamber is adapted to receive fluid at a command pressure supplied to the body, 
 the spool being movable between a first position permitting fluid communication between the supply port and the load port and a second position preventing fluid communication between the supply port and the load port; and 
   a pressure space supplied with fluid at load pressure and disposed such that leakage from the command chamber is minimized or eliminated.   
     
     
         23 . The spool valve of  claim 22 , the spool further comprising:
 a first groove defined in the outer surface of the spool through which fluid flows from the supply port to the load port when the spool is in the first position; and   a second groove defined in the outer surface of the spool between the first end of the spool and the first groove, the second groove being supplied with fluid at load pressure to form the pressure space.   
     
     
         24 . The spool valve of  claim 23 , wherein
 the spool and the body cooperate to define a load chamber at a second end of the spool opposite the first, which load chamber is in continuous fluid communication with the load port, and   the spool defines a passageway therein that supplies the second groove with fluid at load pressure from the load chamber.   
     
     
         25 . The spool valve of  claim 22 , further comprising:
 a first groove defined in the outer surface of the spool through which fluid flows from the supply port to the load port when the spool is in the first position; and   a second groove defined in the body extending circumferentially about the spool, and disposed such in all positions of the spool, the second groove is disposed between the first end of the spool and the first groove, the second groove being supplied with fluid at load pressure to form the pressure space.