Patent Publication Number: US-6338320-B1

Title: Hydraulically-assisted engine valve actuator

Description:
RELATED APPLICATIONS 
     The present application is a continuation-in-part application of U.S. patent application Ser. No. 09/152,497, filed Sept. 9, 1998 now U.S. Pat. No. 6,044,815. 
    
    
     TECHNICAL FIELD 
     The present invention relates to internal combustion engines. More particularly, the present invention relates to engine valve actuation. 
     BACKGROUND OF THE INVENTION 
     It is desirable that a hydraulically-assisted engine valve actuator provide for flexible engine valve operation under a wide band of engine operating conditions. The hydraulically-assisted engine valve actuator should provide for variable valve timing of closing and opening and variable lift as desired in order to achieve the greatest engine efficiencies. Presently, hydraulic fluid is supplied to hydraulically actuated valves through tubes commonly called rails. Valve motion profiles in current hydraulic actuation designs depend on a pre-established constant value of oil pressure at the supply rails because rail pressures cannot be adjusted fast enough to modulate valve profiles. The constant rail pressure values result in constant valve profiles regardless of engine rpm. 
     Present hydraulic actuation schemes add complexity to the engine design. Some hydraulic actuation designs rely on additional hydraulic supply rails at constant pressure levels. Further, hydraulic actuation that relies on on/off solenoid (spool or poppet) valve operations require engine valve position sensors for reliable timing of the solenoids and for safe operation. The plurality of sensors required, further adds to the engine complexity. 
     A hydraulically-assisted engine valve actuator should provide for uniform valve actuation over a wide range of hydraulic fluid temperatures. Present hydraulic actuation schemes typically rely on mechanical damping mechanisms for seating in order to prevent the valve from seating too rapidly. Such mechanisms are typically very dependent on oil temperature, leading to nonuniform valve actuation characteristics. 
     There is further a need to ensure the opening of an engine exhaust valve, especially under conditions of very high compression forces in the combustion chamber of the engine. Such conditions occur, for example, during compression braking of the engine. Where hydraulic actuation is utilized for such exhaust valve opening, it is important to minimize the volume of hydraulic actuation fluid that is necessary to effect the valve opening. 
     SUMMARY OF THE INVENTION 
     The hydraulically-assisted engine valve actuator of the present invention allows for flexible engine valve operation: variable valve timing of the closing and the opening and variable valve lift. Further, the mechanical components needed to effect the hydraulic actuation are relatively simple, thereby minimizing the additional engine components required. No sensors or mechanical damping mechanisms are needed. Additionally, the hydraulic actuation of the present invention is designed to provide for uniform actuation over a wide range of hydraulic fluid temperatures and viscosities. 
     The foregoing advantages of the present invention are effected by the use of fine needle control. The fine needle control provides for modulation of engine valve profiles: varying engine profiles at varying engine speeds, varying the shape of the profiles at a given rpm. The present invention further allows aggressive valve openings and closings which translates into better volumetric efficiency of the engine. 
     The hydraulically-assisted engine valve actuator of the present invention is not sensitive to pressure variation in the high-pressure rail, that is, the modulation of engine valve motion is capable of tolerating a substantial variation of pressure (above a predetermined threshold pressure) in the high-pressure rail. 
     The low-pressure line in an embodiment of the present invention is shared with the existing lubricating oil supply. In an embodiment of the present invention, only a high-pressure supply line is required. Spent hydraulic actuation fluid is vented to the engine oil pan or reservoir. In the case of engines with a fuel injection system incorporating a high-pressure rail, the same high pressure fluid supply is used for valve actuation in order to further minimize the added components to the engine. 
     In the case of the present invention, the output, i.e. the engine valve position, very closely follows the input to the hydraulic actuator. Therefore, the device of the present invention does not require the added complexity of requiring a sensor to measure engine valve position for feedback control. Accurate control of valve seating is attained by accurate control of the needle at the end of the stroke. 
     The present invention further provides very good cold temperature operating performance despite the hydraulic actuating fluid preferably being lubricating oil. The proportional flow areas of the hydraulic fluid passages are not so small as to compromise performance under variable operating temperatures. This is especially important in cold temperature operation since the viscosity of hydraulic fluid, particularly lubricating oil, is significantly higher when the engine is cold than after the engine has warmed up. 
     In one embodiment, the invention incorporates a power piston to assist in opening the exhaust valve of the engine. The power piston operates with each cycle of the engine valve and does not require a separate valve that is dedicated to control of the power piston, as is the case with known power pistons. Additionally, the stroke of the power piston is limited to that necessary to only crack open the exhaust valve. Once the exhaust valve is cracked open, the compressive forces in the combustion chamber are relieved and the servo piston alone can complete the full opening of the exhaust valve without the assistance of the power piston. By limiting the stroke of the power piston, the volume of high pressure actuating fluid necessary to activate the power piston is minimized. 
     Further, the mechanical components that are required for valve actuation by the present invention do not significantly increase the engine complexity, i.e., very few modifications to an existing cylinder head are needed in order to incorporate the valve actuator assembly of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view in section of the hydraulically-assisted engine valve actuator of the present invention coupled to an engine valve; 
     FIGS. 2 a - 2   b  depict the valve opening cycle. Specifically, FIG. 2 a  is a side elevational view in section of the valve actuator with the actuator and the valve in the closed retracted configuration; 
     FIG. 2 b  is a side elevational view in section of the valve actuator with the actuator needle commencing translation to the right and the valve in the closed retracted configuration; 
     FIG. 2 c  is a side elevational view in section of the valve actuator with the actuator needle in a rightward position and the valve approaching the open extended configuration; 
     FIG. 2 d  is a side elevational view in section of the valve actuator with the actuator needle and valve stopped in the open extended configuration; 
     FIGS. 3 a - 3   b  depict the valve closing cycle. Specifically, FIG. 3 a  is a side elevational view in section of the valve actuator with the actuator needle and the valve in the open extended configuration; 
     FIG. 3 b  is a side elevational view in section of the valve actuator with the actuator needle and the valve in the open extended configuration, the actuator needle having translated to the left exposing the extender chamber to low pressure hydraulic fluid; 
     FIG. 3 c  is a side elevational view in section of the valve actuator with the valve in transition between the open extended configuration and the closed retracted configuration, the actuator needle having translated to the left exposing the extender chamber to low pressure hydraulic fluid; 
     FIG. 3 d  is a side elevational view in section of the valve actuator with the actuator needle and valve in the closed retracted configuration; 
     FIGS. 4 a - 4   b  depict various actuator and valve parameters on a common time base, the valve being actuated by the valve actuator of the present invention. Specifically, FIG. 4 a  is a graph of actuator and valve displacement over time; 
     FIG. 4 b  is a graph of the flow of high pressure hydraulic fluid to the actuator over time; 
     FIG. 4 c  is a graph of force on the actuator piston and the valve spring force over time; 
     FIG. 4 d  is a graph of actuator pressure in the extender and retractor chambers over time; 
     FIGS. 5 a - 5   b  are hydraulic schematics depicting the valve opening cycle and the valve closing cycle in sequence. Specifically, FIG. 5 a  is a side elevational view in section of the valve actuator with the actuator and valve in the closed retracted configuration just prior to the valve downstroke; 
     FIG. 5 b  is a side elevational view in section of the valve actuator with the actuator needle commencing translation to the downward and the valve in the closed retracted configuration; 
     FIG. 5 c  is a side elevational view in section of the valve actuator with the actuator needle in a downward position and the valve approaching the open extended configuration; 
     FIG. 5 d  is a side elevational view in section of the valve actuator with the actuator needle and the valve stopped in the open extended configuration; 
     FIG. 5 e  is a side elevational view in section of the valve actuator with the actuator needle commencing upward retraction and the valve in the open extended configuration; 
     FIG. 5 f  is a side elevational view in section of the valve actuator with the actuator needle and valve in the open extended configuration, the actuator needle having retracted upward exposing the extender chamber to low pressure hydraulic fluid and the valve in the closed retracted configuration; 
     FIG. 6 is a sectional view of an embodiment of an intake valve actuator; 
     FIG. 6 a  is an enlarged depiction of the portion of FIG. 6 in the circle  6   a ; 
     FIG. 7 is a sectional view of an embodiment of an exhaust valve actuator; and 
     FIG. 7 a  is an enlarged depiction of the portion of FIG. 7 in the circle  7   a.   
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The hydraulically assisted engine valve actuator of the present invention is shown generally at  10  in FIGS. 1-5 f . In FIG. 1, actuator  10  is depicted coupled to an engine head  12 . 
     The engine head  12  has a valve  14  translatably disposed therein. The valve  14  opens and closes an intake/exhaust passageway  16 . Intake/exhaust passageway  16  is either an intake passageway or an exhaust passageway depending on whether the valve  14  is an intake valve or an exhaust valve. For the purposes of the present invention depicted in FIGS. 1-5 f , valve  14  can be either an intake or an exhaust valve. 
     In the depiction of FIG. 1, valve  14  is in the closed configuration seated on valve seat  18 . An elongate cylindrical valve stem  20  is translatably borne within a valve guide  22 . A valve seal  24  mounted on the engine head  12  prevents fluids from escaping around the valve stem  20 . 
     A coil valve spring  26  is disposed concentric with the valve stem  20  and has a first end bearing on the engine head  12 . The second end of the valve spring  26  is retained within a valve rotator  28 . The valve spring  26  is preferably maintained in a state of compression between the valve rotator  28  and the engine head  12  when the valve  14  is either in the open or closed configurations, compression of valve spring  26  being greatest when the valve  14  is open. A valve keeper  30  has a portion thereof disposed within a keeper groove  32  formed circumferential to the valve stem  20 . The valve keeper  30  holds the valve rotator  28  in engagement with the valve stem  20 . 
     The hydraulic actuator  10  of the present invention includes three major components: actuator casing  40 , actuator piston  42 , and needle  44 . 
     Referring to FIG. 2 a , the actuator casing  40  is preferably formed of three components: a centrally disposed casing body  46 , a casing cap  48 , and a casing insert  50 . Referring again to FIG. 1, the casing body  46  of the actuator casing  40  has a cylinder bore  52  defined concentric with the longitudinal axis of the actuator casing  40 . A low pressure (LP) fluid passageway  54  is defined between the casing body  46  and the casing insert  50 . LP fluid passageway  54  extends from the exterior of the actuator casing  40  to intersect the cylinder bore  52 . 
     A piston bore  58   a ,  58   b  is defined concentric with the longitudinal axis of the actuator casing  40  and the casing body  46  and casing insert  50 , respectively. The piston bore  58   a ,  58   b  is generally cylindrical, having a diameter that is substantially less than the diameter of the cylinder bore  52 . A high pressure (HP) fluid passageway  56  is defined between the casing body  46  and the casing cap  48 . HP fluid passageway  56  intersects the piston bore  58   a.    
     A needle bore  60  is defined in the casing cap  48  of the actuator casing  40 . An O-ring seal groove  62  is defined circumferential to the needle bore  60 . 
     The actuator piston  42  has a cylindrical piston body  64  and a piston head  66 . The piston body  64  has a generally elongate cylindrical shape. The piston body  64  is operably coupled at a first end to the end of the valve stem  20  of the valve  14 . A needle bore  72  is defined in the second end of the piston body  64 . The needle bore  72  extends approximately half the longitudinal dimension of the piston body  64 . The needle bore  72  is concentric with the longitudinal axis of the actuator piston  42 . The piston body  64  is slideably disposed within the piston bore  58   a ,  58   b.    
     The piston head  66  is a generally cylindrical shape. The diameter of the piston head  66  is substantially greater than the diameter of the piston body  64 . The piston head  66  is disposed within the cylinder bore  52  defined within the actuator casing  40 . As depicted in FIG. 1, the piston head  66  divides the cylinder bore  52  into a left variable volume extender chamber  68  and a right variable volume retractor chamber  70 . The piston body  64  is translatable within the piston bore  58   a ,  58   b , and the piston head  66  is translatable therewith within the cylinder bore  52 . Such translation in the cylinder bore  52  acts to simultaneously change the volume of the extender chamber  68  and the retractor chamber  70 , increasing the volume of one chamber while decreasing the volume of the other chamber. 
     A plurality of fluted passageways  74  extend through the piston body  64  to accommodate the flow of hydraulic fluid from the LP fluid passageway  54  to the extender chamber  68  (depending on the position of the needle  44 ) and to the retractor chamber  70 . A plurality of fluted passageways  76  extend through the piston body  64  to accommodate the flow of hydraulic fluid from the HP fluid passageway  56  to the extender chamber  68 . 
     The third component of the hydraulic actuator  10  is the needle  44 . The needle  44  is a generally elongate cylindrical rod. The needle  44  is disposed at least partially in the needle bore  72  defined in the piston body  64 . The needle  44  extends through the needle bore  60  defined in the casing cap  48  of the actuator casing  40 . An O-ring  65  disposed in the O-ring seal groove  62  effects a fluid seal between the needle  44  and the needle bore  60 . The needle  44  is slideably translatably disposed within both the needle bore  60  and the needle bore  72 . 
     The needle  44  extends beyond the casing cap  48  and is operably coupled to a needle positioning mechanism  80 . In the depiction of FIG. 1, needle positioning mechanism  80  is a solenoid. Needle positioning mechanism  80  may also be the lobe of a cam or a stepper motor or other suitable positioner as desired. 
     The inward directed end of the needle  44  is shaped to form a spool valve including a first end groove  82 . Groove  82  has a diameter that is substantially less than the inside diameter of the needle bore  72 , thereby defining an annular fluid passageway between the first end groove  82  and the needle bore  72 . A second groove  84  is defined at approximately the center point along the longitudinal axis of the needle  44 . The second groove  84  also has a diameter that is substantially less than the diameter of needle bore  72 , thereby defining an annular fluid passageway between the second groove  84  and the needle bore  72 . 
     Operation of Invention 
     In operation, the hydraulically assisted engine valve actuator  10  relies on low and high pressure fluid. A source of low pressure hydraulic fluid, such as engine lubricating oil, under pressure as the oil is circulated through the engine for lubricating purposes, is operably coupled to the LP fluid passageway  54 . A source of high pressure fluid, such as engine oil under pressure as necessary to operate some engine fuel injectors. This source may be operably coupled to the HP fluid passageway  56 . Such a high pressure source is described in connection with a hydraulically-actuated, electronically-controlled unit fuel injector system in U.S. Pat. Nos. 5,191,867 and 5,392,749 which are incorporated by reference herein. Translational movement of the needle  44  responsive to input from the needle positioning mechanism  80  distributes hydraulic fluid into and out of the extender chamber  68  and the retractor chamber  70  defined by the position of the piston head  66  of the actuator piston  42  to act on the piston head  66  in such a way (described in detail in the following section) that the actuator piston  42  (and the valve  14  position) very closely follow the translational movement of the needle  44 . 
     The actuator piston  42  acts directly on the engine valve  14 , the engine valve  14  being biased to the closed position by the valve spring  26 . The valve spring  26  always exerts a leftward directed force on the actuating piston  42 , as depicted in FIGS. 1-3 d . The actuator piston  42  has sufficient rightward directed force, when motivated by high pressure hydraulic fluid, to overcome the opposing bias of the spring  26  and the opposing force of any combustion forces acting on the engine valve  14  in order to open the valve  14 . 
     Translational motion of the needle  44  is not opposed by the spring  26  or the combustion forces and therefore requires only a minimal force exerted by the needle positioning mechanism  80  to effect translation. The needle  44  may be effectively controlled to describe a prescribed valve  14  opening/closing profile. In a preferred embodiment, the actuating force necessary to translate the needle  44  is less than 12 pounds and more preferably is substantially about 6 pounds. The translational position of the needle  44  controls the position of the engine valve  14 . Positioning the valve  14  requires a much larger force input than the force input needed to position the needle  44 . This much larger force input is available by means of the high pressure hydraulic fluid acting in the extender chamber  68  acting on the actuator piston  42 . In this regard, the actuator  10  is a servo follower system. Control is maintained of the needle  44  by the needle positioning system  80 . The needle  44  acts as a servo pilot with the actuator piston  42  being the servo main stage and following the needle  44 . The force needed to actuate needle  44  is relatively very small compared to the forces that follow the needle  44 . This greatly reduces the mass and complexity of the components needed to effect actuation of the valve  14 . 
     FIGS. 2 a - 2   d  depict the opening stroke of the valve  14 , sequentially progressing from the closed position in FIG. 2 a  to the open position in FIG. 2 d . In FIG. 2 a , the engine valve  14  is initially resting against the valve seat  18  through action of the bias exerted by the valve spring  26 . The needle  44  and actuator piston  42  are fully retracted to the leftmost position. Low-pressure fluid enters the LP fluid passageway  54  and flows through the fluted passageways  74  to fill the retractor chamber  70  and then flows through the fluid passageway defined by the first end groove  82  to flood the extender chamber  68  of the actuator piston  42 . With low pressure hydraulic fluid acting on both sides  69 ,  71  of the piston head  66 , the actuator piston  42  is in a state of hydraulic equilibrium. No hydraulically generated force is acting to counter the force of the spring  26 . 
     Referring to FIG. 2 b , the needle positioning mechanism  80  translates the needle  44  rightward. First, such translation advances the shoulder  83  of the first end groove  82  of the needle  44 , sealing the extender chamber  68  from the retractor chamber  70 . Second, as the needle  44  continues to translate rightward, the needle  44  allows the high pressure fluid supply from HP fluid passageway  56  to flow through the second groove  84  and through the fluted passageways  76 . The high pressure fluid communicates with the extender chamber  68  and bears on the extender side face  69  of the piston head  66 . Extender side face  69  forms a portion of the variable volume extender chamber  68 . It should be noted that the low pressure fluid is always acting on the retractor side face  71  of the piston head that forms a portion of the retractor chamber  70 . The high pressure oil in the extender chamber  68  drives the actuator piston  42  and engine valve  14  to the open position (FIG. 2 c ), overcoming the opposing force of the spring  26  and the opposing force of the low pressure fluid acting on the side  71  of the piston head  66  that forms a portion of the retractor chamber  70 . In a preferred embodiment, the high pressure fluid operates in a pressure range of approximately 450 psi to 3000 psi and the low pressure fluid operates at a pressure of approximately 50 psi. 
     The rate of rightward translational displacement of the needle  44  determines the area of the fluid passageway opening defined between the second groove  84  and the fluted passageways  76  to the extender chamber  68  and thereby meters the high pressure fluid from the high pressure supply at the HP fluid passageway  56  that is available to act upon the side  69  of the piston head  66  that forms a portion of the extender chamber  68 . This metering permits control of the opening profile of the valve  26 , as desired. The faster the needle  44  continues to move rightward, the less the throttling effected on the high-pressure oil and the greater the volume of the high pressure fluid supply that the needle  44  allows to communicate with the extender chamber  68  to act upon the side  69  of the piston head  66  that forms a portion of the extender chamber  68 . The high pressure fluid in the extender chamber  68  drives the actuator piston  42  and engine valve  14  to the opening position, overcoming the force of the spring  26  and the opposing force of the low pressure fluid acting on the side  71  of the piston head  66  that forms a portion of the retractor chamber  70 . 
     Conversely, the slower the displacement of the needle  44 , the less area of the fluid passageway defined by the second groove  84  that is open to the fluted passageways  76  and thence to the extender chamber  68  and the greater the throttling effect on the high pressure oil. The resulting lower high pressure oil volume in the extender chamber  68  results in less force available to overcome the force of the spring  26 , compression or combustion forces acting to close the engine valve  14 , and the opposing force of the low pressure fluid acting on the side  71  of the piston head  66  that forms a portion of the retractor chamber  70 . This in turn results in slower movement of the actuator piston  42  and results in a valve profile that is characterized by slower opening movement of the engine valve  14 . 
     Referring to FIG. 2 d , when the needle  44  is brought to a stop at its point of greatest rightward translation, the pressure in the extender chamber  68  and the inertia of the actuator piston  42  cause the actuator piston  42  and valve  14  to continue their rightward motion for a short distance until the shoulder  85  of the second groove  84  of the needle  44  seals the fluted passageway  76 , preventing further high pressure fluid from affecting the extender chamber  68  of the piston actuator  42 . A balance then ensues between the fluid trapped in the extender chamber  68  by the needle  44  and the opposing bias of the spring  26 . 
     The closing stroke of the valve  14  effected by actuator  10  is depicted sequentially in FIGS. 3 a - 3   d . Referring to FIG. 3 a , the needle  44  and actuator piston  42  are initially positioned such that the engine valve  14  is unseated at some lift (at least partially open) as a result of the last action in the open stroke referred to with reference to FIG. 2 d  above. The needle  44  seals the extender chamber  68  from both the high and low pressure oil supplies, as previously described in reference to FIG. 2 d.    
     Referring to FIG. 3 b  the needle positioning mechanism  80  retreats the needle  44 , causing leftward translation of the needle  44 . The movement of the needle  44  opens the fluid passageway defined circumferential to the first end groove  82  to fluidly connect the extender chamber  68  to the retractor chamber  70 . As previously indicated, the retractor chamber  70  is always exposed to the low pressure oil supply at LP fluid passageway  54 . The extender chamber  68  is isolated from the high pressure oil at HP fluid passageway  56  by the needle  44  proximate the second groove  84 . The second groove  84  is positioned to isolate the fluted passageways  76  from the high pressure fluid supply at passageway  54 . The high pressure fluid in the extender chamber  68  flows into the retractor chamber  70  until extender chamber  68  and the retractor chamber  70  are in a state of hydraulic pressure equilibrium. The force of the spring  26 , which is always acting on the actuator piston  42 , drives the engine valve  14  and actuator piston  42  leftward towards the closed position, as depicted in FIG. 3 c.    
     The rate at which the needle  44  retreats is determined by the needle positioning mechanism  80  and determines the area of the fluid passageway fluidly communicating between the retractor chamber  70  and the extender chamber  68 , thereby metering the high pressure fluid flow from the extender chamber  68  to the retractor chamber  70 . The force of the spring  26  acts to push the engine valve  14  and actuator piston  42  to the closed position as the high pressure fluid is discharged from the extender chamber  68 . The faster that the needle  44  is displaced leftward, the larger the area and the faster the rate at which the oil is discharged from the extender chamber  68  to the retractor chamber  70 . The oil in the extender chamber  68  must be displaced in order for the valve  14  to close. The rate of displacement of the needle  44  closely controls the rate of valve  14  closure. Control of the rate of translation of the needle  44  thereby affords close control of the profile of the closing of the valve  14 . 
     When the needle  44  is brought to a stop, as depicted in FIG. 3 d , the force of the spring  26  and of inertia act to continue the leftward motion of the actuator piston  42  towards the closed position for a small amount of travel after needle  44  stoppage. Such travel continues until the extender chamber  68  is sealed from the retractor chamber  70  by the shoulder of the first end groove  82 . A balance then ensues between the fluid pressure in the extender chamber  68  and the retractor chamber  70 . The force of the spring  26  continues to act on the actuator piston  42  and the valve  14 , maintaining the valve  14  in the seated closed position. 
     FIGS. 4 a - 4   d  depict a comparison of a cam valve train engine exhaust valve  14  profile with a camless profile effected by the present invention wherein an aggressive valve opening is selected and controlled around bottom dead center. The FIGS. 4 b - 4   d  depict actuator flow rate, piston forces, and actuator pressures corresponding to motion depicted in FIG. 4 a . The FIG. 4 a  shows the engine piston motion profile, cam valve train profile of a conventional system, needle position of the present invention, and response of the piston actuator of the present invention and engine valve to the needle position input. FIG. 4 a  depicts how closely the output in the form of motion of valve  14  tracks the input in the form of needle  44  position, thus obviating the need for a sensor to track position of the valve  14 . FIG. 4 b  depicts flow rate of high pressure oil needed to effect a valve opening and closing cycle. FIG. 4 c  depicts the force of the high pressure oil acting on the actuator  42  in comparison to the opposing force of the spring  26 . FIG. 4 d  indicates that the pressure needed to keep the valve open stabilizes at about 400 psi after 0.02 seconds. Virtually any high pressure hydraulic fluid that is above the threshold of about 400 psi is adequate to cause the actuator  10  to function as designed. 
     Turning now to FIGS. 5 a - 5   f , a hydraulic schematic of the operation of an embodiment of the hydraulic actuator  10  is depicted sequentially through a downstroke of the valve  14  and an upstroke of the valve  14 . In order to effect the downstroke of the valve  14 , there are two downward motions that must be considered. First, the actuator piston  42  is coupled to the valve  14  and drives the valve  14  in the downward direction as depicted. Second, the needle  44  translates within the needle bore  72  defined in the actuator piston  42  under the influence of the needle positioning mechanism  80  to control the motion of the actuator piston  42 . 
     Prior to commencement of the downstroke of the valve  14 , the actuator piston  42  and the needle  44  are in their fully retracted and upward positions as depicted in FIG. 5 a . High pressure lubricating oil available at the high pressure fluid passageway  56  from a high pressure rail floods the chamber  90  and flows into the second groove  84 . The second groove  84  is sealed at its downwardmost end by the shoulder  86  of the needle  44  sealingly engaging the actuator piston  42 . 
     Low pressure engine lubricating oil available at the low pressure fluid passageway  54  from a low pressure rail floods the retractor chamber  70 . The low pressure engine lubricating oil is prevented from entering the extender chamber  68  by a sealing engagement of the shoulder  88  of the needle  44  with the actuator piston pin  42 . 
     The valve  14  is kept in its fully upward seated disposition, as depicted in FIG. 5 a , by the action of the low pressure engine lubricating oil acting on the retractor surface  71  of the piston head  66 , in combination with the bias exerted by the valve spring  26 . See FIG.  1 . 
     FIG. 5 b  depicts the initiation of the downstroke of the valve  14 . In FIG. 5 b , the needle  44  has translated downward relative to the actuator piston  42  under the actuating influence of the needle positioning mechanism  80 . Such downward translation backs the shoulder  86  of the needle  44  out of engagement with the actuator piston  42  to create a fluid passageway through the second groove  84  to the extender chamber  68 . High pressure engine lubricating oil flows through the second groove  84  into the extender chamber  68  and bears on the extender surface  69  of the piston head  66 . The force exerted by the high pressure engine lubricating oil is sufficient to overcome the countering force exerted by the engine pressure lubricating oil acting on the retractor surface  71  in combination with the bias exerted by the valve spring  26  and any combustion forces acting on the valve  14 . Accordingly, translation of the actuator piston  42  and the coupled valve  14  commences downward very closely trailing the translation of the needle  44 . The flow of high pressure engine lubricating oil into the extender chamber  68  is depicted by arrows A. The extender chamber  68  remains sealed from the retractor chamber  70  by the sealing action of the shoulder  88  in a sealing relationship with the piston head  66 . Low pressure oil continues to flood the retractor chamber  70 . 
     FIG. 5 c  depicts the valve  14  as the valve  14  approaches the downward, fully open, unseated position. In the depiction of FIG. 5 c , the needle  44  has translated downward its full travel. The actuator piston  42  lags slightly behind the needle  44 . Accordingly, as indicated by arrows A, high pressure engine lubricating oil continues to flood the extender chamber  68  and to act on the extender surface  69 , thereby urging the actuator piston  42  and the valve  14  in the downward direction. 
     FIG. 5 d  depicts the valve  14 , the actuator piston  42 , and the needle  44  all in their fully downward positions. As compared to FIG. 5 c , the actuator piston  42  has continued to translate downward slightly relative to the needle  44  after motion of the needle  44  has ceased. This translation results generally from the inertia of the actuator piston  42  and the valve  14 . Such translation seals the extender chamber  68  by the action of the shoulder  86  of the needle  44  again sealingly engaging the actuator piston  42 . Additionally, the shoulder  88  of the needle  44  is in sealing engagement with the actuator piston  42 , thereby isolating the retractor chamber  70  from the extender chamber  68 . In this position, there is no flow of either high pressure engine lubricating oil or low pressure engine lubricating oil. This is essentially a static position. High pressure engine lubricating oil is sealed within the extender chamber  68  creating a hydraulic lock, preventing the lower pressure engine lubricating oil that is acting on the retractor surface  71  of the piston head  66  (in combination with the bias of the valve spring  26 ) from moving the actuator piston  42  in an upward direction. Flow into or out of retractor chamber  70  ceases since all passages are sealed and there is no motion of the actuator piston  42 . 
     Referring to FIG. 5 e , the commencement of the upstroke of the valve  14  is depicted. In FIG. 5 e , the needle  44  has translated upward slightly under the influence of the needle positioning mechanism  80 . Such upward translation backs the shoulder  88  out of the sealing engagement with the actuator piston  42 . The shoulder  86  remains in sealing engagement with the actuator piston  42 . The translation of the needle  44  opens a fluid passageway from the extender chamber  68  through the first groove  82  and then through to the retractor chamber  70 . The pressure of the high pressure hydraulic actuating fluid (engine lubricating oil) trapped in the extender chamber  68  is dissipated into the retractor chamber  70  as indicated by the arrows B. With the dissipation of the hydraulic lock as depicted in FIG. 5 d , there is hydraulic equilibrium in chambers  68 ,  70  and the bias of the valve spring  26  is therefore free to act on the valve  14  and the actuator piston  42 . 
     Referring to FIG. 5 f , the upward bias of the valve spring  26  (depicted in FIG. 1) acting on the valve  14  forces the actuator piston  42  upward. The upward motion of the actuator piston  42  displaces substantially all the hydraulic actuating fluid from the extender chamber  68  into the retractor chamber  70 , as depicted by arrows B. As indicated in FIG. 5 f , the shoulder  88  is disengaged from the actuator piston  42  to permit the continued flowing of engine lubricating oil from the extender chamber  68  to the retractor chamber  70 . The needle  44  retracts upward with the actuator piston  42  causing the shoulder  86  to maintain a sealing engagement with the actuator piston  42 , thereby isolating the high pressure engine lubricating oil from the extender chamber  68 . This completes the upstroke of the valve  14 . 
     A further preferred embodiment of the present invention is depicted in FIGS. 6,  6   a ,  7 , and  7   a . FIGS. 6 and 6 a  depict a sectional view of the valve actuator  100  for use with any intake valve. FIGS. 7 and 7 a  depict a sectional view of a valve actuator  102  for use with an exhaust valve. There are certain components that are common to the valve actuators  100 ,  102 , like numerals being used with reference to both FIGS. 6,  6   a ,  7 , and  7   a  to depict common components. 
     Referring to FIGS. 6 and 6 a , the valve actuator  100  is utilized with an intake valve  112  disposed in a head  120  of an internal combustion engine, the internal combustion preferably operating on the diesel cycle. The valve  112  has a valve stem  114  and upper end of a valve of a spring  116  is retained by a rotator  118  secured to the valve stem  114  in a conventional manner. 
     The head  120  has an actuator bore  122  defined therein. A ring groove  124  is defined in the actuator bore  122  proximate the lower margin of the actuator bore  122 . 
     A high pressure rail  126  is defined in the head  120 . The high pressure rail  126  conveys a hydraulic medium, preferably, engine lubricating oil. A circumferential oil passage or groove  128  is defined in the actuator bore  122  and is fluidly coupled to the high pressure rail  126 . A threaded bore  130  is defined in the head  120  proximate an upper margin of the head  120 . 
     The valve actuator  100  has two major components; actuator assembly  132  and controller assembly  134 . The actuator assembly  132  has two major subcomponents; intake casing  136  and a servo piston or actuator piston  138 . 
     The intake casing  136  of the actuator assembly  132  is preferably generally cylindrical in shape and sized to be received within the actuator bore  122  of the head  120 . The intake casing  136  is retained within the actuator bore  122  by a retaining ring  140  disposed in the ring groove  124 . A spacer washer  142  is interposed between the lower margin of the intake casing  136  and the retaining ring  140 . The outer margin of the intake casing  136  has a plurality of O-ring grooves  144  defined therein. O-rings  145  disposed in the O-ring grooves  144  define a substantially fluid-tight seal between the intake casing  136  and the actuator bore  122  of the head  120 . An adapter shoulder  146  is defined at the upper margin of the intake casing  136 . 
     The intake casing  136  has a circumferential oil passageway or groove  148  defined in the outer margin of the intake casing  136 . When the intake casing  136  is disposed within the actuator bore  122 , the circumferential oil passage  148  is continuously fluidly coupled to the circumferential oil passage  128 . A plurality of radial oil passageways  150  defined in the intake casing  136  fluidly couple the circumferential oil passageway  148  to a cylinder bore  152  defined within the intake casing  136 . Cylinder bore  152  is thereby fluidly coupled to the high pressure rail  126 . A circumferential stop shoulder  154  is defined at the lower margin of the cylinder bore  152 . 
     The second subcomponent of the actuator assembly  132  is the actuator piston  138 . The actuator piston  138  has a preferably cylindrical piston body  156 . The piston body  156  is translatably disposed within the cylinder bore  152  of the intake casing  136 . A cap  158  encloses the lower portion of and defines the lower surface of the actuator piston  138 . The cap  158  abuts against the end of the valve stem  114  of the valve  112  such that translation of the actuator piston  138  results in simultaneous translation of the valve  112 . 
     An expanded circumference stop shoulder  160  is disposed on the exterior margin of the actuator piston  138  immediately above the cap  158 . The stop shoulder  160  comes into contact with the stop shoulder  154  of the intake casing  136  to limit upward travel of the actuator piston  138  in the cylinder bore  152 . 
     The actuator piston  138  is a valve spool and the exterior surface thereof includes a reduced diameter portion or groove  162  defining an annular oil passage  164  in cooperation with the surface of the cylinder bore  152 . A plurality of transverse oil passageways  165  extend inward from the oil passage  164  through the body of the piston  138  to provide selective fluid communication with an interior needle bore  168  defined within the actuator piston  138  coaxial with a longitudinal axis thereof. A high pressure throttle area  166  is defined in part by a shoulder  167  that forms the upper intersection of the transverse oil passageway  165  with the needle bore  168 . 
     The actuator piston  138  further includes an expanded diameter needle bore  170 . The expanded diameter needle bore  170  defines in part a low pressure oil passage  172 . The low pressure oil passage  172  has an opening at the upper margin of the needle bore  168 , i.e. at the upper end  173  of the actuator piston  138 . A low pressure throttle area  174  is defined in part by a shoulder  176  created by the expansion of the needle bore  168  to expanded portion  170 . 
     Above the circumferential groove  162 , the exterior surface of the actuator piston  138  has a portion  175  disposed adjacent the cylinder bore  152  and adjacently thereabove, a reduced diameter portion  177  extending to the end  173  of the actuator piston and defining a pressure bearing surface  178  on the upper side of the portion  175 . The pressure bearing surface  178  defines a variable volume pressure chamber  180  in cooperation with the cylinder bore  152  of the intake casing  136  and the reduced diameter exterior surface  177 . 
     A spring cavity  182  is disposed at the lower margin of the needle bore  168 . The spring cavity  182  preferably has a greater diameter than the needle bore  168 . 
     The second component of the valve actuator  100  is the controller assembly  134 . The controller assembly  134  has three subcomponents; motor adapter  179 , motor  181 , and needle  183 . 
     The motor adapter  179  has a generally cup-shaped housing  184 . A housing flange  186  overlies the threaded bore  130  defined in the head  120 . A bore  188  defined in the housing flange  186  is in registry with threaded bore  130 . During assembly, a cap screw or similar fastener may be threaded into the threaded bore  130  to affix the valve actuator  100  to the head  120 . An inward directed shoulder  190  forms the lower margin of the housing  184 . The shoulder  190  bears on a ledge defined in the head  120  and on the adapter shoulder  146  of the intake casing  179  in order to secure the valve actuator  100  within the actuator bore  122  defined in the head  120 . 
     At least one relatively large oil passage  192  is defined in the housing  184 . The oil passage  192  is typically at ambient pressure. A relatively small threaded bore  194  is defined in a wall of the housing  184 . A cap screw may be threaded into the threaded bore  194  to secure the motor  181  to the motor adapter  179 . 
     The second component of the controller assembly  134  is the motor  181 . The motor  181  may be a linear motor that is a product of BEI-Kimko Magnetics, Inc. Other motors may be suitable as well. As depicted, the motor  181  has a stationary core  196 . A translatable cylindrical armature  198  is slidably disposed in a cylindrical groove  200  defined in the stationary core  196 . A spacer annulus  202  is defined in a lower portion of the armature  198 . The lower portion of the armature  198  defines in part a rather voluminous oil gallery  204  The oil gallery  204  is fluidly coupled to the oil passage  192  and is preferably at ambient conditions. 
     The third component of the controller assembly  134  is the pilot valve or needle  183 . The needle  183  has a needle body  206 . The needle body  206  is preferably a relatively short generally cylindrical rod. The needle body  206  is fixedly coupled as by screws (not shown) to the lower margin of the translatable armature  198  of the motor  181 , a spacer  208  being disposed in the spacer groove  202  of the motor  181  between the armature and the needle body. 
     The exterior surface of the upper portion of the needle body  206  defines an annular low pressure oil passage  172  in cooperation with the expanded needle bore  170 . The central portion of the needle body  206  has a reduced circumference to define a groove  210  which partially defines an annular high pressure oil passageway  211  that may be fluidly coupled to the transverse oil passageway  165  or to the low pressure passage  172  depending on the relative positions of the needle body  206  and the piston  138 . The groove  210  has an upper shoulder  212  that defines in part the low pressure throttle area  174  and a lower shoulder  214  that defines in part the high pressure throttle area  166 . 
     The lower portion of the needle body  206  has a spring retainer  216  fixedly coupled thereto to transmit the biasing force of a failure return spring  218  disposed in the spring cavity  182  defined in the actuator piston  181 .to the needle  183 . 
     In operation, to open the engine intake valve  112 , an electrical signal to the motor  181  causes the armature  198  and the needle  183  to translate downward with respect to the core  196  and the actuator piston  138 . As the lower shoulder  214  of the needle groove  210  clears the shoulder  167  of the actuator piston  138  at the high pressure throttle area  166 , high pressure actuating fluid from the high pressure rail  126  flows upward through the groove passage  211  to flood the pressure chamber  180 . The pressure of the high pressure actuating fluid acting downward on the pressure bearing surface  178  of the actuator piston  138  causes the actuator piston  138  to commence downward travel to cause the opening of the engine intake valve  112 . 
     The rate of downward translation of the needle  183  relative to the actuator piston  138  varies the amount of throttling of the high pressure actuating fluid through the high pressure throttle area  166 . Such throttling causes the actuator piston  138  to translate downward at a greater or lesser rate in response to the rate of motion of the needle  183  in order to affect the rate of opening of the valve  112 . As the actuator piston  138  translates downward, the oil passage  164  is continuously in fluid communication with the rail  126  and the pressure chamber  180  is continuously in fluid communication with the high pressure actuating oil via the groove passage  211 . 
     The needle  183  stops at its full downstroke. Inertia may carry the actuator piston  138  and the valve  112  further downward slightly after cessation of travel by the needle  183 . Such additional translation of the actuator piston  138  relative to the needle  183  will throttle and ultimately halt the flow of high pressure actuating fluid through the high pressure throttle area  166 . 
     To cause closing of the engine valve  112 , a further electrical command to the motor  181  causes retraction of the needle  183  relative to the actuator piston  138 . At the point that the upper shoulder  212  of the needle slightly passes the shoulder  176  of the actuator piston  138 , throttling of low pressure actuating fluid into the low pressure throttle area  174  commences. As the opening between the shoulders  176 ,  212  increases, high pressure oil in the pressure chamber  180  passes out through the low pressure oil passages  172  into the oil gallery  204  and out of the oil passage  192  to ambient conditions on top of the cylinder head  120 , but under the valve cover (not shown), to drain back to the oil pan or other reservoir. With the relief of pressure on the pressure bearing surface  178  of the actuator piston  138 , the valve spring  116  acts upwardly on the valve  112  and forces the valve  112  and actuator piston  138  to their initial upward and closed disposition. 
     In the event that electronic control of the motor  181  were lost, the failure return spring  218  biases the needle  183  in a upward disposition, thereby spilling the high pressure actuating oil in the pressure chamber  180  to ambient via the low pressure oil passage  172 , oil gallery  204  and oil passage  192 , thereby permitting closing of the valve  112  by the valve spring  116 . 
     The configuration of the present invention that is adapted for use with an exhaust valve is depicted in FIGS. 7 and 7 a . As indicated above, a concern which arises when using the invention to actuate an exhaust valve is being able to overcome the substantial compressive forces in the cylinder that act to keep the exhaust valve  113  closed. This is especially true during compressive breaking (commonly known as Jake-breaking) of a vehicle. The valve actuator of the present invention adapted for use with an exhaust valve  113  is shown generally at  102  in the figures. The valve actuator  102  includes substantially all of the components previously described with reference to the valve actuator  100 . In addition to the components of the valve actuator  100 , the valve actuator  102  incorporates a power piston  250 . The power piston  250  is disposed radially with respect to the actuator piston  138 . 
     The power piston  250  includes a power piston body  252 . The power piston body  252  is translatably disposed within a cylinder bore  152   a  defined within the exhaust casing  136   a . The wall thickness of the exhaust casing  136   a  is reduced as compared to the intake casing  136 , described above, to define a cylinder bore  152   a  that is greater in diameter than the cylinder bore  152  defined in the intake casing  136 . The inner margin of the power piston body  252  defines a cylinder bore  254 . The cylinder bore  254  has substantially the same dimensions as the cylinder bore  152  defined in the intake casing  136  of the intake valve actuator  100 . The actuator piston  138  is translatably disposed within the cylinder bore  254 . Thus, the power piston  250  is free to translate relative to the exhaust casing  136   a  and the actuator piston  138  is free to translate relative to the power piston  250  and the needle  183  is free to translate relative to the actuator piston  138 . 
     The power piston body  252  has an upper margin that defines a slightly domed pressure bearing surface  256 . The domed pressure bearing surface  256  defines in part an expanded volume pressure chamber  180   a . A bore aperture  258  is defined at the upper margin of the cylinder bore  254 . In the retracted disposition of FIG. 7, the pressure bearing surface  178  of the actuator piston  138  and the domed pressure bearing surface  256  of the power piston  250  may be nearly flush with one another. 
     Moving downward on the power piston  250 , an oil passage  260  is defined through the piston body  252 . At its inner margin, oil passage  260  is in flow communication with the spool oil passage  164  defined by the annular groove  162  of the actuator piston  138 . At its outer margin, oil passage  260  is in fluid communication with an annular oil passage  264  defined by annulus  262  disposed in the power piston body  252  and with the passageway  150  defined in the exhaust casing  136   a.    
     The power piston body  252  presents a lower margin  266 . In the retracted disposition of FIGS. 7 and 7 a , the lower margin  266  is spaced apart a slight distance from the washer  142 . The washer  142  acts as a stop limiting the downward travel of the power piston  250 . A stop shoulder  268  is presented inward and slightly upward of the lower margin  266 . The stop shoulder  268  acts to limit the upward travel of the actuator piston  138 . 
     During normal operation, typical pressures of the high pressure actuating fluid in the rail  126  are between 500 and 1,000 psi. Such pressures are sufficient to overcome normal cylinder gas pressures. However, the pressure in the rail  126  may be commanded to increase to as much as 4,000 psi, thus enabling the valve  112  to overcome much higher pressures that may be experienced, for example, during compression braking. The power piston  250  of the present invention is always operational, translating downward and upward over its very limited range of motion for each opening and closing cycle of the exhaust valve  113 . 
     In operation, the valve actuator  102  commences translation identically to that described above with reference to the valve actuator  100 . The initial downward translation of the needle  183  causes the high pressure actuating fluid to flood the expanded volume pressure chamber  180   a . The pressure in the expanded volume pressure chamber  180   a  generates a force acting downward on both the pressure bearing surface  178  of the actuator piston  138  and the domed pressure bearing surface  256  of the power piston  250 . The force generated by the high pressure actuating fluid substantially simultaneously causes the downward translation of the actuator piston  138  and also the power piston  250 . The power piston  250  force is only needed to crack open the exhaust valve  113  against the very high compression forces due to cylinder firing that may be acting to hold the valve  113  in the closed disposition. Once the valve  113  is cracked open just a slight amount, the high compression forces in the combustion chamber escape and the downward thrust of the actuator piston  138  is adequate to continue the opening process of the exhaust valve  113 . Accordingly, the downward stroke of the power piston  250  is limited to a very short distance as indicated by the very small distance between the lower margin  266  of the power piston body  252  and the washer  142 . When the power piston  250  comes into contact with the washer  142 , the downward stroke of the power piston  250  is arrested while the actuator piston  138  continues its downward stroke translating relative to the now-stopped power piston  250 . An advantage of limiting the stroke of the power piston  250  is that it significantly reduces the volume of high pressure actuating fluid necessary to effect an opening stroke of the exhaust valve  113 . Minimizing this volume is an important consideration when designing the auxiliary components necessary to supply the high pressure rail  126 . 
     The closing stroke of the exhaust valve  113  is effected in substantially the same manner as that previously described for the intake valve actuator  100 . As the actuator piston  138  commences its upward travel, the stop shoulder  160  of the actuator piston  138  comes into contact with the stop shoulder  268  of the power piston  250 . When such contact is made, the actuator piston  138  continues its upward travel under influence of the valve spring  116 , carrying with it the power piston  250 . 
     Variations within the spirit and scope of the invention described are equally comprehended by the foregoing description.