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 This is especially true with respect to controlling the engine, where many mechanical components have been replaced by electrically operated devices controlled by a microcomputer.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&#39;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.