Abstract:
A value actuator assembly for an engine includes a movable engine valve a movable spool valve and dual feedback channels with flow regulated by a pair of orifices. The valve actuator assembly also includes a driving channel interconnecting the spool valve and the engine valve. The feedback channels interconnecting the engine valve and the spool valve. First and second feedback channels communicate between the second and third fluid chambers and fourth and fifth fluid chambers of the spool valve. Orifices restrict fluid flow through the feedback channels as needed to actuate the spool valve and thereby improve valve controllability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Patent Application No. 60/587,321 filed Jul. 13, 2004. 
    
    
     TECHNICAL FIELD 
     This invention relates to engine valvetrains and, more particularly, to an electrohydraulic valve actuator assembly for an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Valve actuator assemblies for camless valvetrains of internal combustion engines have been proposed in the art. Such actuators often result high energy consumption, low repeatability from cycle to cycle and cylinder to cylinder and high seating velocity-induced noise. Some valve actuator assemblies do not provide full capability of variable lift. They may also be of relatively high cost and have large packaging size. 
     It is desirable to provide an engine valve actuator assembly that improves controllability. It is also desirable to provide a valve actuator assembly having increased flexibility and full capacity for variable lift. Further, it is desirable to provide a valve actuator assembly that reduces energy consumption and provides satisfactory seating velocity. Therefore, there is a need in the art to provide a valve actuator assembly for an engine that meets these desires. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new camless engine valve actuator assembly that has internal feedback for improved controllability. 
     The valve actuator assembly includes a movable engine valve, a movable spool valve, a driving channel interconnecting the spool valve and the engine valve and dual feedback channels having a pair of flow regulating orifices. The feedback channels interconnect the engine valve and the spool valve. 
     The spool valve controls fluid flow to the driving channel to position the engine valve. The orifices regulate feedback fluid pressure to the spool valve to provide internal feedback for valve controllability and flow control. 
     An advantage of the present invention is that the valve actuator assembly has dual hydraulic feedback for precise motion. Another advantage is that the valve actuator assembly provides improved valvetrain stability without sacrificing dynamic performance. The valve actuator assembly also enables improved engine performance and fuel economy and lower engine emissions by improved valve control. The valve actuator assembly minimizes energy consumption by optimized flow control, a simple spool valve and efficient valve control to minimize throttling of the fluid flow. The spool valve and the first and second orifices create dual feedback to provide both precise valve lift control and soft valve landing. Another advantage of the valve actuator assembly of the present invention is that it is of relatively small size and easy to package in an engine. Another advantage of the present invention is that it has relatively less contents and therefore lower cost. 
     These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic view of a valve actuator assembly, according to the present invention, illustrated in operational relationship with an engine of a vehicle; 
         FIG. 2  is a cross-sectional view of the valve actuator assembly of  FIG. 1  in an engine valve closed position; 
         FIG. 3  is a similar view of the valve actuator assembly of  FIG. 1  in an engine valve opening position; 
         FIG. 4  is a similar view of the valve actuator assembly of  FIG. 1  in an engine valve opened position; 
         FIG. 5  is a similar view of the valve actuator assembly of  FIG. 1  in an engine valve closing position; and 
         FIG. 6  is a similar view of the valve actuator assembly of  FIG. 1  in an engine valve closed position. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to  FIGS. 1 and 2  of the drawings in detail, numeral  10  generally indicates an electrohydraulic valve actuator assembly mounted on a cylinder head  12  including at least one opening  16  in communication with an internal combustion chamber, not shown, of the engine. The cylinder head  12  also includes a movable engine valve  18  for each opening  16 . The engine valve  18  has a valve stem  20  and a valve head  22  at one end of the valve stem. The engine valve  18  is movable between open and closed positions within its respective opening  16 . It should be understood that the engine valve  18  may be either an intake or an exhaust valve. 
     The valve actuator assembly  10  further includes a valve housing  24  disposed adjacent the cylinder head  12 . The valve housing  24  has a main or first fluid chamber  26  therein. A first piston  28  is connected to or in contact with the valve stem  20  of the engine valve  18 . The piston  28  is disposed in the first fluid chamber  26  of the valve housing  24  and forms a second fluid chamber  30  therein. An engine valve spring  32  is disposed about the valve stem  20  and contacts the cylinder head  12  to bias the engine valve  18  toward the closed position so that the valve head  22  closes the opening  16 , as shown in  FIG. 2 . 
     The valve actuator assembly  10  further includes a third fluid chamber  34  axially spaced from the first fluid chamber  26  and defined by the housing  24 . A second piston  36 , connected to the first piston  28 , is disposed in the third fluid chamber  34 . 
     The valve actuator assembly  10  also includes a spool valve  38  fluidly connected to the first fluid chamber  26  of the valve housing  24 . The spool valve  38  is of a three position three-way type. The spool valve  38  has a high pressure port  40  fluidly connected by an intermediate channel  42  to a fluid pump  44  and a low pressure port  46  fluidly connected by second intermediate channel  48  to a fluid tank  49 . If desired, the fluid pump  44  may be fluidly connected to the fluid tank  49  or a separate fluid tank. 
     The spool valve  38  further includes a third port  50  fluidly connected by a driving channel  52  to the first fluid chamber  26 . The spool valve  38  also has a fourth port  54  fluidly connecting a fourth chamber  56  to the second fluid chamber  30  of the valve housing  24  via a first feedback channel  58  and a fifth port  60  fluidly connecting a fifth chamber  62  via a second feedback channel  64  to the third fluid chamber  34 . The spool valve  38  is operable to control fluid flow to and from the first fluid chamber  26 . 
     The spool valve  38  also includes an actuator  68  at one end of the spool valve  38  adjacent the fifth chamber  62 . The actuator  68  is of a linear type, such as a solenoid, electrically connected to a source of electrical power, such as a controller  70 . The spool valve  38  further includes a spool valve spring  72  disposed in the fourth chamber  56  to bias the spool valve toward the actuator  68 . The controller  70  energizes and de-energizes the actuator  68  to move the first spool valve  38 . 
     The spool valve spring  72  is operative to bias the spool valve  38  toward the actuator  68  when fluid pressures in the fourth and fifth chambers  56  and  62  are equal. However, a pressure differential between the fourth or the fifth chambers  56  and  62  may be able to overcome the force of the spool valve spring  72 . 
     The valve actuator assembly  10  further includes a first orifice  74  fluidly connected to the second fluid chamber  30  of the valve housing  24 . The orifice  74  has first and second ports  86 ,  88 . The first port  86  is fluidly connected by the first feedback channel  58  to the second fluid chamber  30 . The second port  88  is fluidly connected to a fluid tank  90  by a low pressure line  92 . It should be appreciated that the fluid tank  90  is able to maintain certain level of back pressure. 
     The valve actuator assembly  10  further includes a second orifice  94  fluidly connected to the third fluid chamber  34  of the valve housing  24 . The orifice  94  has first and second ports  96 ,  98 . The first port  96  is fluidly connected by the second feedback channel  64  to the third fluid chamber  34 . The second port  98  is fluidly connected to the fluid tank  90  by a low pressure line  100 . If desired, the low pressure line  100  may be fluidly connected to a separate fluid tank, not shown. 
     It should be appreciated, that the size and flow rates of the orifices  74  and  94  will vary depending on the application. One skilled in the art may determine the optimal sizes of the orifices  74 ,  94  using the following equation,
 
Q=KA√{overscore (ΔP)}, where:
         Q equals the flow rate;   K is a constant;   A is the area of the orifice; and   ΔP is the pressure drop across the orifice.
 
The orifices  74  and  94  must be sized to allow adequate fluid flow to and from the second and third chambers  30  and  34  during engine valve  18  actuation to allow the engine valve to properly open and close. However, the amount of fluid flow through the orifices  74  and  94  should be limited to create sufficient backpressures in the first and second feedback channels  58  and  64  to actuate the spool valve  38  and thereby control the opening and closing velocities of the engine valve  18 .
       

     In operation, as illustrated by  FIG. 2 , the engine valve  18  is shown in the closed position. In this position, the controller  70  de-energizes the actuator  68 . This allows the spool valve spring  72  to move the spool valve  38  toward the actuator, closing the high pressure port  40  and opening the low pressure port  46 . This communicates the first chamber  26  with the fluid tank  49  via the low pressure port  46  and allows the engine valve spring  32  to keep the engine valve  18  closed with the valve head  22  closing the opening  16 . 
     To open the engine valve  18 , as illustrated in  FIG. 3 , the controller  70  energizes the actuator  68  to drive the spool valve  38  against the spool valve spring  72  closing the low pressure port  46  and opening the high pressure port  40 . This allows high pressure fluid to flow from the pump  44  through the spool valve  38  into the first chamber  26 . The fluid pressure acts against the first piston  28  to overcome the force of the engine valve spring  32  and open the engine valve  18 . 
     As the engine valve  18  opens, the first piston  28  displaces fluid from the second chamber  30  into the first feedback channel  58 . The release of fluid from the first feedback channel  58  to the fluid tank  90  is regulated by the first orifice  74 . This controls the opening velocity of the engine valve  18  by restricting fluid flow through the first orifice  74  to increase the fluid pressure within the first feedback channel  58  and the fourth chamber  56  of the spool valve  38 . The increased fluid pressure within the fourth chamber  56  drives the spool valve  38  upward against the actuator  68  and into the fifth fluid chamber  62 , thereby limiting or temporarily cutting off the connection between the driving channel  52  and the intermediate channel  42 . This reduces fluid pressure supplied to the first chamber  26  and slows the opening velocity of the engine valve  18 . As the opening velocity of the engine valve  18  is reduced, the amount of displaced fluid from the second chamber  30  to the first feedback channel  58  is reduced, thereby reducing fluid pressure within the fourth chamber  56 . Thus, allowing the actuator  68  to drive the spool valve  38  downward into the fourth chamber  56  and increase fluid flow between the intermediate channel  42  and the driving channel  52 . 
     To stop the engine valve  18  at a predetermined lift position, as shown in  FIG. 4 , the controller  70  energizes the actuator  68  to move the spool valve  38  to a neutral position that closes communication between the high and low pressure ports  40 ,  46  from the third port  50  of the spool valve  38  to seal the first fluid chamber and thereby maintain the position of the first piston  28 . It should be understood, the lift height of the engine valve  18  is determined by the timing of the closing of the spool valve  38 . 
     To close the engine valve  18 , the controller  70  de-energizes the actuator  68 . The spool valve spring  72  returns the spool valve  38  to a position which communicates the first chamber  26  with the second intermediate channel  48  and the fluid tank  49 . This allows the high pressure fluid in the first chamber  26  to exhaust into the fluid tank  49 . The engine valve spring  32  then drives the engine valve  18  upward, as illustrated in  FIG. 5 . The second fluid chamber and the third fluid chamber  30  and  34  are connected with the tank  90  so that, as the engine valve  18  returns to the closed position, low pressure fluid refills the second fluid chamber from the third fluid chamber and to the tank  90 . 
     The second orifice  94  provides a “soft landing” as the engine valve  18  returns to the closed position by limiting fluid flow between the third fluid chamber  34  and the tank  90 . Particularly, as the upward moving engine valve  18  displaces fluid from the third chamber  34  to the second feedback channel  64 , the second orifice  94  creates backpressure to increase fluid pressure within feedback channel and the fifth chamber  62  of the spool valve  38 . The fluid pressure in the fifth chamber  62  drives the spool valve  38  downward against the spool valve spring  72  until the spool valve it cuts off or reduces flow through the connection between the driving channel  52  and the intermediate channel  48 , as illustrated in  FIG. 6 . During this time, fluid within the second feedback channel  64  continues to flow through the second orifice  94  maintaining a fluid backpressure within the second feedback channel and the fifth chamber  62 . This allows the spool valve spring  72  to return the spool valve to its initial position and the engine valve spring  32  to return the engine valve  18  to the closed position at a controlled velocity. 
     The valve actuator assembly  10  has better controllability by utilizing the hydraulic feedback channels  58  and  64  and the orifices  74  and  94  are used to restrict flow through the feedback channels. The better controllability enables the valve actuator assembly  10  to provide better performance. The valve actuator assembly  10  of the present invention precisely controls the motion of the spool valve  38  though the feedback channels  58  and  64  so that it avoids unnecessary throttling of the low pressure flow and high pressure flow, thereby providing energy consumption benefits. 
     While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.