Hydraulic actuator for operating an engine cylinder valve

Information

  • Patent Grant
  • 6782852
  • Patent Number
    6,782,852
  • Date Filed
    Monday, October 7, 2002
    22 years ago
  • Date Issued
    Tuesday, August 31, 2004
    20 years ago
Abstract
A hydraulic actuator operates either an intake or an exhaust valve for an engine cylinder. A driver piston is adapted to be operably connected to open and close the engine cylinder valve. An electrically driven operator produces movement of a valve spool which controls flow of fluid to and from the driver piston. A feedback mechanism is coupled to the valve spool and responds to movement of the driver piston by moving the valve spool into a position at which fluid flows neither to nor from the driver piston. The feedback mechanism ensures that the stroke of the hydraulic actuator is proportional to the magnitude of the electric current applied to the operator regardless of variation of the fluid pressure applied to the driver piston.
Description




CROSS-REFERENCE TO RELATED APPLICATIONS




Not Applicable




STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT




Not Applicable




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to hydraulic actuators, and more particularly to hydraulic actuators for operating an intake or exhaust valve for a cylinder of an internal combustion engine.




2. Description of the Related Art




Internal combustion engines have a plurality of cylinders containing pistons that are connected to a crankshaft. Each cylinder has two or more valves to control the air flow into the cylinder and the flow of exhaust gases from the cylinder. Traditionally the cylinder valves were controlled by a cam shaft which in turn was mechanically connected to rotate with the engine crankshaft. Gears, chains, or belts coupled the crankshaft to the cam shaft so that the two would rotate in unison. It is important that the valves open and close at the proper times during the combustion cycle within each cylinder. Heretofore, that timing relationship was fixed by the mechanical coupling between the crankshaft and the cam shaft.




The setting of the cam shaft timing often was a compromise which produced the best overall operation at all engine operating speeds and conditions. However, it was recognized that optimum engine performance could be obtained if the valve timing was varied as a function of engine speed, engine load and other factors.




The trend in motor vehicles is toward the increased use of electronics and microcomputer control systems. This is especially true with respect to controlling the engine, where many mechanical components have been replaced by electrically operated devices controlled by a microcomputer. With this trend, it became possible to determine the optimum engine valve timing based on the operating conditions occurring at any given point and time. That optimum timing then can be used to activate electrically controlled mechanisms which open and close the intake and exhaust valves for each cylinder.




A typical mechanism for this function employs a separate hydraulic actuator to operate the respective intake valve or exhaust valve. A piston, attached to the stem of the cylinder valve, is driven by hydraulic fluid to move the cylinder valve. The existing lubricating oil for the engine frequently is used as the hydraulic fluid and a separate pump supplies that oil at a greater pressure than the conventional oil pump. A solenoid valve, operated by the engine computer, controls the flow of the hydraulic fluid to and from the piston for the cylinder valve. Thus the solenoid actuator does not directly drive the engine valve, but instead operates a valve member to control relatively high pressure fluid that produces movement of the engine valve. This allows a smaller solenoid actuator to be used than where the solenoid alone would have to supply the force that moves the cylinder valve.




SUMMARY OF THE INVENTION




A hydraulic actuator for operating an engine cylinder valve includes a driver piston to move the engine cylinder valve into open and closed states. A hydraulic valve is in fluid communication with the driver piston, a first conduit carrying fluid at a first pressure, and a second conduit carrying fluid at a second pressure that is less than the first pressure. For example, the second conduit may be connected to a fluid reservoir for the engine. The hydraulic valve has a valve spool which in a first position enables fluid to flow between the first conduit and the driver piston to open the engine cylinder valve, and in a second position enables fluid to flow between the second conduit and the driver piston to close the engine cylinder valve.




An operator, such as an electrically driven solenoid, is operably coupled to produce movement of the valve spool into the first and second positions. A feedback mechanism is coupled to the valve spool, The feedback mechanism responds to movement of the driver piston by moving the valve spool into a third position at which neither the first conduit nor the second conduit is in fluid communication with the driver piston. The feedback mechanism ensures that the stroke of the hydraulic actuator is proportional to the magnitude of the electric current applied to the operator regardless of variation of the pressure in the first conduit.




In one embodiment of the hydraulic actuator, the feedback mechanism comprises a feedback piston which moves in response to fluid pressure produced by movement of the drive piston. A feedback spring extends between the valve spool and the feedback piston. In another embodiment, the drive piston slides within a common bore with the valve spool and the feedback mechanism comprises a feedback spring which extends between the valve spool and the drive piston.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a cross sectional view of an engine cylinder valve actuator according to the present invention in which the cylinder valve is closed;





FIG. 2

is a cross sectional view of the actuator while the engine cylinder valve is opening;





FIG. 3

is a cross sectional view of the actuator in a dwell state when the engine cylinder valve is being held open;





FIG. 4

is a cross sectional view of a second actuator according to the present invention is a state in which the cylinder valve is closed;





FIG. 5

is a cross sectional view of the second actuator while the engine cylinder valve is opening; and





FIG. 6

is a cross sectional view of the second actuator in a dwell state while the engine cylinder valve is being held open.











DETAILED DESCRIPTION OF THE INVENTION




With reference to

FIG. 1

, the cylinder head


12


of an internal combustion engine has a first bore


28


into which extends the stem


20


of an engine cylinder valve


22


. A coil type valve spring


24


is disposed concentrically around the valve stem


20


with one end engaging a surface on the cylinder head


12


and another end engaging a retaining ring


26


affixed to the valve stem. The valve spring


24


biases the engine cylinder valve


22


into the illustrated closed state against a seat formed in the intake or exhaust passage


21


through the cylinder head.




The engine cylinder valve


22


is operated by a hydraulic actuator


10


comprising a hydraulic valve


16


which is opened and closed by a solenoid operator


14


to apply pressurized engine oil to a driver piston


18


. The driver piston


18


slides reciprocally within the first bore


28


which forms a drive chamber


30


on a side of the driver piston that is remote from the valve stem


20


. The driver piston


18


abuts the cylinder valve stem


20


. A head of the driver piston defines a sensor chamber


34


within the first bore


28


on the opposite side of the piston head


32


from the drive chamber


30


.




The cylinder head


12


has a second bore


29


. A piston conduit


31


connects the drive chamber


30


of the first bore


28


to the second bore


29


and a feedback conduit


33


extends from the sensor chamber


34


to the second bore. A high pressure conduit


13


, a low pressure conduit


17


and a tank conduit


15


also extend through the cylinder head


12


and into the second bore


29


. The low pressure conduit


17


is connected to the output of the standard oil pump which supplies oil for lubricating the engine components. The high pressure conduit


13


is connected to another pump and receives engine oil at a relatively high pressure as compared to the pressure produced by the standard oil pump. The tank passage


15


extends to the oil reservoir of the engine. Although the exemplary hydraulic engine valve actuator


10


is integrated into bores in the cylinder head


12


, a separate enclosure may be provided for the entire actuator or for the solenoid operator


14


and the hydraulic valve


16


components. In the latter case, the cylinder head and that enclosure would combine to form the housing of the hydraulic engine valve actuator.




The solenoid operator


14


and the hydraulic valve


16


are combined into an assembly that is inserted into the second bore


29


in the cylinder head


12


. The solenoid operator


14


is of a conventional design comprising an electromagnetic coil


40


wound around an annular bobbin


42


of a non-magnetic material, such as a plastic. A armature


44


is movably received within the central opening of the bobbin


42


and is affixed to an armature shaft


46


. An armature spring


48


biases the armature shaft


46


toward the hydraulic valve


16


.




The hydraulic valve


16


comprises a cylindrical spool


50


which slides within a circular bore


53


in a valve sleeve


51


. The valve sleeve


51


is received within the second bore


29


of the cylinder head


12


and is attached to the solenoid operator


14


. A high pressure port


60


in the valve sleeve


51


provides a passage between the bore


53


and the high pressure conduit


13


in the cylinder head


12


. A tank port


62


in the valve sleeve


51


provides a passage between the bore


53


and the tank conduit


15


. The valve sleeve


51


also has a piston port


64


that provides a path between the sleeve bore


53


and the piston conduit


31


leading to the drive chamber


30


. The valve spool


50


has an annular notch


52


in its outer surface and has an aperture


54


extending longitudinally between opposite ends. One end of the spool


50


engages the inner end of the armature shaft


46


and the other end abuts a feedback spring


56


which biases the spool against the armature shaft. The feedback spring


56


also abuts a feedback piston


58


that is slidably held within the bore


53


of the valve sleeve


51


by a retaining ring


59


.





FIG. 1

illustrates the engine cylinder valve


22


in the closed state with the solenoid operator


14


de-energized. In this state, the stronger force provided by the feedback spring


56


, as compared to the force from the armature spring


48


, pushes the spool


50


into a position which blocks the high pressure port


60


and any significant flow of oil from the high pressure conduit


13


. It should be understood that in this closed state some leakage of the oil through the valve will still occur. This position of the spool


50


also opens a fluid path from the drive chamber


30


through the piston conduit


31


and the valve sleeve bore


53


into the tank conduit


15


. Since the tank conduit is at substantially atmospheric pressure, any pressure within the drive chamber


30


is relieved which enables the valve spring


24


to force the engine cylinder valve


22


against the seat formed in the intake or exhaust passage


21


, thereby closing the cylinder valve.




Referring to

FIG. 2

, when the solenoid operator


14


is activated by application of electric current to the solenoid coil


40


, the armature


44


and the attached armature shaft


46


are forced in a direction toward the valve spool


50


. The force that the armature shaft


46


applies is directly related to the magnitude of the electric current applied to the solenoid coil


40


. Thus the oil flow and the resultant rate at which the engine cylinder valve opens and closes can be varied as desired by controlling the rate of change of the electric current. The force of the solenoid operator


14


overcomes the force provided by the feedback spring


56


, thereby moving the spool


50


into a position in which the annular notch


52


provides a fluid path between the high pressure conduit


13


and the piston conduit


31


. This action applies high pressure oil into the drive chamber


30


which drives the driver piston


18


to push against the valve stem


20


. As a result, the engine cylinder valve


22


is forced away from the seat in the cylinder head


12


, thereby opening the intake or exhaust passage


21


.




The aperture


54


through the valve spool


50


provides a passage between the sections of the sleeve bore


53


on opposite sides of the valve spool. This passage facilitates movement of the valve spool


50


as engine oil can flow through that aperture


54


from one side of the valve spool to the other, thereby eliminating any resistance to the sliding of the spool within the sleeve bore


53


or pressure imbalance.




With reference to

FIG. 3

, the sensor chamber


34


, feedback conduit


33


, feedback chamber


70


, feedback piston


58


, and the feedback spring


56


comprise a feedback mechanism which ensures that the stroke of the hydraulic actuator


10


is proportional to the magnitude of the electric current applied to the solenoid operator


14


regardless of variation of the pressure in the high pressure conduit


13


. As the driver piston


18


moves downward opening the engine cylinder valve


22


, the sensor chamber


34


diminishes in volume as evident from a comparison to the de-energized actuator in FIG.


1


. This movement of the driver piston


18


forces the oil that was previously in the sensor chamber


34


through the feedback conduit


33


and into a feedback chamber


70


at the innermost portion of the second bore


29


. A first check valve


72


within the low pressure conduit


17


prevents fluid flow from the feedback chamber


70


. As a consequence, the pressure within the feedback chamber


70


increases which forces the feedback piston


58


of the hydraulic valve


16


farther into the valve sleeve


51


. The movement of the feedback piston


58


compresses the feedback piston


56


, thereby exerting a greater force on the spool


50


counteracting the force exerted in the opposite direction by the solenoid operator


14


and armature spring


48


. The pressure within the feedback chamber


70


, in this state, is such that the force exerted by the feedback spring


50


counterbalances the force produced by the solenoid operator


14


so that the land at one end of the spool


50


extends across and closes the piston port


64


of the hydraulic valve


16


. As a consequence, the pressure is held within the drive chamber


30


, thereby maintaining the open condition of the engine cylinder valve


22


. The magnitude of the feedback force is directly related to the magnitude of the electric current fed to the solenoid operator


14


and correspondingly to the oil pressure in the drive chamber


30


. That is, the greater the oil pressure in the drive chamber


30


, the farther the driver piston


32


moves thus further compressing the oil in the feedback circuit, i.e. conduit


33


and chambers


34


and


70


. Thus the counterbalancing occurs independently of variation of the electric current or of the pressure level in the high pressure conduit


13


. The cylinder valve speed can be controlled by ramping the current at a controlled rate.




This state of the hydraulic actuator


10


is maintained until the electric current applied to the coil


40


of the solenoid operator


14


is removed, thereby de-energizing the actuator


10


. When this occurs, the electromagnetic force on the armature


44


is removed and the force exerted by the feedback spring


56


moves the spool


50


toward the solenoid operator


14


into the position illustrated in FIG.


1


. In this position of the spool


50


, a passage is created through the hydraulic valve


16


from the drive chamber


30


to the tank conduit


15


relieving the pressure within the drive chamber. With the release of that pressure from acting on the piston


18


, the valve spring


24


returns the engine cylinder valve


22


to the closed position.




Wear of the valve and seat surfaces and the build-up of carbon deposits on those surface cause the position of the valve stem


20


to shift with respect to the actuator


10


. That position shift effects the size of the sensor chamber


34


in the closed state, and thus the pressure supplied to the feedback chamber


70


when the cylinder valve is opened. This variation can adversely effect the operation of the feedback mechanism. In addition, should air become entrapped in the feedback circuit, the compressible nature of air also will adversely effect the force provided by the feedback piston


58


.




As a consequence, the present engine cylinder valve actuator


10


incorporates a compensation mechanism for the feedback circuit. During the de-energized state shown in

FIG. 1

, the drive chamber


30


is connected by the hydraulic valve


16


to the tank conduit


15


which is at substantially atmospheric pressure. As a consequence, the first check valve


72


opens, admitting that oil from the low pressure conduit


17


into the feedback chamber


70


and then through the feedback conduit


33


into the sensor chamber


34


. The pressure within chamber


34


causes a second check valve


74


to open, enabling the oil to flow into the drive chamber


30


and continue through the hydraulic valve


16


to the tank conduit


15


. This flow flushes any air from the feedback circuit and the actuator chamber and fills the feedback circuit with oil, thereby compensating for volume changes due to variation of the cylinder valve position over time. An orifice


75


adjacent the second check valve


74


restricts this flow to a small level so that the lubrication of the engine is not substantially affected.




When the hydraulic valve


16


is again activated by applying high pressure oil from conduit


13


into the drive chamber


30


, the second check valve


74


closes because the drive chamber is at a higher pressure than the sensor chamber


34


. This traps the existing oil within the feedback circuit as the driver piston


32


causes the pressure in the feedback circuit to increase above that in the pressure conduit


17


, thereby closing the first check valve


72


.




With reference to

FIG. 4

, a second version of a hydraulic engine valve actuator


100


has a solenoid operator


102


, a hydraulic valve


104


and a driver piston


106


aligned with the longitudinal axis of the cylinder valve stem


108


. The cylinder valve stem


108


is biased by a valve spring


109


. The hydraulic engine valve actuator


100


is mounted to the valve cover


110


of the engine. However, unlike conventional valve covers, this valve cover


110


includes a high pressure oil conduit


112


and a low pressure oil conduit


114


which carries engine oil from the conventional oil pump.




The solenoid operator


102


is identical to that described previously with respect to the embodiment in FIG.


1


. Specifically, the solenoid operator


102


has an electromagnetic coil


116


, which when energized produces a magnetic field that causes movement of an armature


118


that is fixedly attached to an armature shaft


120


. An armature spring


122


biases the armature shaft


120


toward the hydraulic valve


104


, whereas the magnetic field moves the armature shaft away from the hydraulic valve.




The hydraulic valve


104


has a valve sleeve


124


which is attached to the housing of the solenoid actuator


102


to form a unitized structure. The valve sleeve


124


projects through the valve cover


110


. The valve sleeve


124


has an internal circular bore


126


, that is connected by a first port


128


to the high pressure conduit


112


and by a second port


130


to the low pressure conduit


114


.




A cylindrical valve spool


132


is slidably received within the bore


126


of the valve sleeve


124


. The valve spool


132


has an aperture


134


extending from end to end, thereby providing a fluid passage between chambers


136


and


138


formed within the bore


126


on opposite sides of the valve spool. An annular notch


140


extends around the outer circumferential surface of the valve spool


132


and an aperture


142


provides a passage from the bottom of the notch


140


to the end-to-end aperture


134


.




A section


144


of the bore


126


, in a portion of the valve sleeve


124


that projects beneath the valve cover


110


, has a larger internal diameter. The cylindrical driver piston


106


is slidably received within this larger diameter section


144


and is biased away from the valve spool


132


by a feedback spring


146


which engages both of those components. The armature spring


122


exerts a greater force on the valve spool


132


via the armature shaft


120


than the force exerted by the feedback spring


146


. An aperture


148


is locate in an end of the driver piston


106


that faces outward toward the cylinder valve stem


108


.




A lash adjuster


150


is formed within that aperture


148


. Specifically, the lash adjuster


150


comprises a lash piston


152


which slides within the driver piston aperture


148


and is biased outward by a lash spring


154


within a lash chamber


156


at the bottom of that aperture


148


. A check valve


158


is located in a passage between the chamber


156


and a recess


160


in the outer surface of the driver piston


106


. The check valve permits oil to flow only from the recess


160


into the chamber


156


, as will be described.





FIG. 4

depicts the second hydraulic engine valve actuator


100


in a de-energized state where the engine cylinder valve is closed. In this state, the valve spool


132


is biased by springs


122


and


146


into an equilibrium position where the notch


140


opens into the low pressure conduit


114


. Oil at that low pressure is conveyed through spool apertures


142


and


134


to the bore chambers


136


and


138


on the opposite sides of the valve spool


132


. Because the chambers


136


and


138


on both sides of the valve spool are at equal pressure, the application of the low pressure from conduit


114


does not produce movement of the valve spool


132


. Furthermore, the low pressure is insufficient to exert enough force on the driver piston


160


to overcome the valve spring force acting on the engine cylinder valve stem


108


and thus the cylinder valve remains closed.




With reference to

FIG. 5

, application of electric current to the solenoid coil


116


produces an electromagnetic field which causes the armature


118


and the armature shaft


120


to move away from the valve spool


132


(upward in the drawings). The force exerted on the valve spool


132


by the feedback spring


146


keeps the valve spool into engagement with the armature shaft


120


as that latter component moves. Thus, the valve spool


132


moves into a position where its notch


140


communicates with the first port


128


, thereby applying high pressure oil from conduit


112


to the valve spool's axial aperture


134


. The high pressure oil, conveyed into chamber


138


, exerts force on the driver piston


106


which responds by moving outward from the valve sleeve


124


. This motion applies force to the end of the cylinder valve stem


108


, pushing the engine cylinder valve away from its seat and opening the corresponding intake or exhaust passage (not shown).




The second hydraulic engine valve actuator


100


also includes a feedback mechanism which ensures that the stroke of the driver piston


106


is proportional to the magnitude of the electric current applied to the solenoid operator


102


regardless of pressure variation in the high pressure conduit


112


. As the driver piston


106


moves outward from the valve sleeve


124


, the feedback spring


146


expands, thereby reducing the force that it applies to the valve spool


132


. This reduces the aggregate force from the electromagnetic field and the feedback spring which counteracts the force from the armature spring


122


. As a result, the armature spring


122


pushes the armature shaft


120


and valve spool


132


toward the driver piston


106


until the feedback spring


146


is compressed sufficiently to increase the aggregate counteracting force to again equal the armature spring force. When that occurs, the valve spool


132


is in a new equilibrium position, illustrated in

FIG. 6

, where the spool notch


140


is between the first and second ports


128


and


130


. In this position, oil from neither the high pressure conduit


112


nor the low pressure conduit


114


can enter that notch


140


and flow into the interior of the valve spool


132


. In addition, the existing oil pressure remains trapped within chambers


136


and


138


of the hydraulic valve


104


. This trapped oil pressure maintains the extended position of the driver piston


106


which holds the engine cylinder valve open, as long as electric current continues to be applied to the solenoid operator


102


.




When electric current is removed from the coil


116


of the solenoid operator


102


, the armature spring


122


exerts a greater force on the armature shaft


120


than the counterforce applied by the feedback spring


146


. As a consequence, the armature shaft


120


pushes the valve spool


132


downward in the drawings, returning to the position illustrated in

FIG. 4

at which the spool notch


140


again communicates with the second port


130


. This allows the oil to flow from the hydraulic valve


104


into the low pressure conduit


114


, relieving the relatively high pressure in the sleeve bore chambers


136


and


138


. The release of that pressure also enables the spring


109


, engaging the engine cylinder valve stem


108


, to push the driver piston


106


back into valve sleeve


124


. This movement of the valve stem


108


also closes the engine cylinder valve.




With continuing reference to

FIG. 4

, the lash adjuster


150


compensates for the effects of wear and carbon deposits on the engine cylinder valve. As noted previously, when this occurs the position of the end of the valve stem


108


in the closed state changes with respect to the actuator


100


. The lash adjuster


150


varies the gap between the driver piston


106


and the lash piston


150


to compensate for that change of the valve stem position over time. It should be understood that operation of the hydraulic valve


104


applies relatively high pressure oil to the chamber


138


adjacent the driver piston


106


. Some of this oil leaks out between the driver piston


106


and the inner diameter of the bore


126


in the valve sleeve


124


and into the enclosed region underneath the valve cover


110


. Some of the leaking oil fills the recess


160


in the outer surface of the driver piston


106


.




If the deposits on the cylinder valve or the mating valve seat cause the valve stem


108


to move downward over time, that movement results in the lash piston


152


moving outward from the driver piston


106


due to the force of the lash spring


154


. This movement expands the volume of the lash chamber


156


, thereby creating a partial vacuum which draws oil from the recess


160


through check valve


158


to fill the lash chamber


56


. Thereafter, when the actuator


100


is energized and the driver piston


106


is pushed downward to activate the cylinder valve, the check valve


158


prevents oil from exiting the lash cylinder chamber


156


.




The foregoing description was primarily directed to preferred embodiments of the invention. Although some attention was given to various alternatives within the scope of the invention, it is anticipated that one skilled in the art will likely realize additional alternatives that are now apparent from disclosure of embodiments of the invention. Accordingly, the scope of the invention should be determined from the following claims and not limited by the above disclosure.



Claims
  • 1. A hydraulic actuator for operating an engine cylinder valve comprises:a driver piston to move the engine cylinder valve into open and closed states; a hydraulic valve in fluid communication with the driver piston, a first conduit carrying fluid at a first pressure, and a second conduit carrying fluid at a second pressure that is less than the first pressure; the hydraulic valve having a valve spool which in a first position enables fluid flow between the first conduit and the driver piston to open the engine cylinder valve and in a second position enables fluid flow between the second conduit and the driver piston to allow the engine cylinder valve to close; an operator operably coupled to produce movement of the valve spool into the first position and the second position; and a feedback mechanism coupled to the valve spool and responsive to movement of the driver piston by moving the valve spool into a third position at which neither the first conduit nor the second conduit is in fluid communication with the driver piston.
  • 2. The hydraulic actuator as recited in claim 1 wherein the feedback mechanism comprises a feedback spring which applies a bias force to the valve spool which bias force varies in response to movement of the driver piston.
  • 3. The hydraulic actuator as recited in claim 2 wherein the feedback spring extends between the valve spool and the driver piston.
  • 4. The hydraulic actuator as recited in claim 2 wherein the feedback mechanism further comprises a feedback piston which moves in response to a pressure created by movement of the driver piston; and the feedback spring extends between the valve spool and the feedback piston.
  • 5. The hydraulic actuator as recited in claim 1 wherein the hydraulic valve comprises a sleeve with a bore there through within which the valve spool and the driver piston are slidably received, wherein the first conduit and the second conduit communicate with the bore.
  • 6. The hydraulic actuator as recited in claim 5 wherein the feedback mechanism comprises a feedback spring extending between the valve spool and the driver piston.
  • 7. The hydraulic actuator as recited in claim 5:wherein the driver piston has an exterior surface with a notch therein, an aperture in one end, and a check valve coupling the notch to the aperture; and further comprises a lash piston received in the aperture in the driver piston and a spring biasing the lash piston outward from the driver piston.
  • 8. A hydraulic actuator for operating a cylinder valve of an engine comprises:a housing having a first bore and a second bore with a piston conduit and a feedback conduit both between the first bore and the second bore, wherein the second bore is in fluid communication a first conduit containing fluid at a first pressure, and a second conduit containing fluid at a second pressure that is less than the first pressure; a driver piston for operative connection to the engine cylinder valve, the driver piston slidably received within the first bore thereby forming a drive chamber into which the piston conduit communicates and forming a sensor chamber into which the feedback conduit communicates; a valve spool movably received within the second bore, and having a first position in which the first conduit is connected to the piston conduit and a second position in which the second conduit is connected to the piston conduit; a feedback piston received in the second bore and moving therein in response to fluid conveyed from the sensor chamber through the feedback conduit and into the second bore; a feedback spring extending between the valve spool and the feedback piston; and an electrically driven operator operably coupled to produce movement of the valve spool into the first position and the second position.
  • 9. The hydraulic actuator as recited in claim 8 further comprising:a first check valve which allows flow of a fluid only in a direction from a source into a section of the second bore into which the feedback conduit communicates; and a second check valve which allows flow of a fluid only in a direction from the sensor chamber into the drive chamber.
  • 10. The hydraulic actuator as recited in claim 8 wherein the second conduit is connected to a fluid reservoir of the engine.
  • 11. The hydraulic actuator as recited in claim 8 wherein expansion of the drive chamber reduces the sensor chamber.
  • 12. A hydraulic actuator for operating a cylinder valve of an engine comprises:a sleeve with a bore there through wherein the bore is in communication with a first conduit containing fluid at a first pressure and with a second conduit containing fluid at a second pressure that is less than the first pressure; a driver piston slidably received in an end of the bore in the sleeve to move the engine cylinder valve into open and closed states; a valve spool slidably received in the bore of the sleeve and forming a chamber in the bore between the valve spool and the driver piston, the valve spool having a first position which allows fluid flow between the first conduit and the chamber and a second position which allows fluid flow between the second conduit and the chamber; a spring in the chamber and biasing the valve spool away from the driver piston; and an operator operably coupled to control movement of the valve spool into the first position and the second position.
  • 13. The hydraulic actuator as recited in claim 12 wherein the second conduit is connected to a fluid reservoir of the engine.
  • 14. The hydraulic actuator as recited in claim 12 wherein the valve spool comprises a first aperture which provides a fluid passage between chambers in the bore on opposites sides of the valve spool, and a second aperture providing a fluid passage between the first aperture and a side surface of the valve spool.
  • 15. The hydraulic actuator as recited in claim 12 wherein the valve spool has two end sections and a side wall between the end sections, a notch extends into the side wall, a first aperture extends between the end sections providing a fluid passage between chambers in the bore on opposites sides of the valve spool, and a second aperture extends between the notch and the first aperture.
  • 16. The hydraulic actuator as recited in claim 12:wherein the driver piston has an exterior surface with a notch therein, an aperture in one end, and a check valve coupling the notch to the aperture; and further comprising a lash piston received in the aperture in the driver piston, and a spring biasing the lash piston outward from the driver piston.
  • 17. A hydraulic actuator for operating a component on a vehicle, said hydraulic actuator comprising:a driver piston that moves the component between first and second states; a hydraulic valve in fluid communication with the driver piston, a first conduit carrying fluid at a first pressure, and a second conduit carrying fluid at a second pressure that is less than the first pressure; the hydraulic valve having a valve spool which in a first position enables fluid flow between the first conduit and the driver piston to move the component into the first state and in a second position enables fluid flow between the second conduit and the driver piston to move the component into the second state; an operator operably coupled to produce movement of the valve spool into the first position and the second position; and a feedback mechanism comprising a feedback spring engaging the valve spool and in response to movement of the driver piston, the feedback spring moves the valve spool into a third position at which neither the first conduit nor the second conduit is in fluid communication with the driver piston.
  • 18. The hydraulic actuator as recited in claim 17 wherein the feedback spring extends between the valve spool and the driver piston.
  • 19. The hydraulic actuator as recited in claim 17 wherein the feedback mechanism further comprises a feedback piston which moves in response to a pressure created by movement of the driver piston, and the feedback spring extends between the valve spool and the feedback piston, wherein the feedback piston.
  • 20. The hydraulic actuator as recited in claim 17 wherein the hydraulic valve comprises a sleeve with a bore there through within which the valve spool and the driver piston are slidably received, wherein the first conduit and the second conduit communicate with the bore.
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