Patent Publication Number: US-2004050349-A1

Title: Variable force engine valve actuator

Description:
TECHNICAL FIELD  
       [0001] The present disclosure is directed to an engine valve actuator and more particularly to a variable force engine valve actuator.  
       BACKGROUND  
       [0002] An internal combustion engine typically includes a series of valves. These valves are configured to control the intake and exhaust of gases to and from the combustion chambers of the engine. A typical engine will include at least one intake valve and at least one exhaust valve for each chamber in the engine. The opening of each of valve is timed to occur at a certain point in the operating cycle of the engine. For example, an intake valve may be opened when a piston is moving towards a bottom dead center position within a cylinder to allow fresh air to enter the combustion chamber. An exhaust valve may be opened when the piston is moving towards a top dead center position in the cylinder to expel the exhaust gas from the combustion chamber.  
       [0003] The actuation, or opening and closing, of the engine valves may be controlled in a number of ways. For example, each engine valve may be operatively engaged with a cam follower that engages a cam on a cam shaft that is operatively connected to the engine crankshaft. A rotation of the crankshaft causes a corresponding rotation in the cam shaft. As the camshaft rotates, the cam moves the cam follower to actuate the engine valve. Because the rotation of the crankshaft also controls the motion of the piston, this arrangement may be used to coordinate the actuation of each engine valve with the desired movement of the respective piston.  
       [0004] This configuration does not, however, provide a high degree of flexibility in the timing of valve actuation. It has been found that engine efficiency may be improved by varying the timing of the valve actuation based on the operating conditions of the vehicle. With the cam and cam follower configuration, the engine valves will be actuated at the same point in the crankshaft rotation regardless of the vehicle operating conditions. Thus, these types of systems are relatively inflexible and may not be capable of maximizing the efficiency of an engine.  
       [0005] Another approach involves actuating the engine valves independently of the crankshaft rotation. This may be accomplished, for example, with a hydraulic system. As shown in U.S. Pat. No. 6,263,842, a hydraulically-driven piston may be used to actuate an engine valve. In this approach, each engine valve includes a piston that is connected to the engine valve and is actuated by the introduction of pressurized fluid. The valve actuation may, therefore, be controlled independently of the crankshaft rotation and may provide additional flexibility in the valve timing.  
       [0006] To obtain improvements in engine efficiency, the engine valves may need to be actuated when the gas within the combustion chamber is under pressure from an engine piston. A hydraulically actuated valve will need to exert a force significant enough to open the valve under these conditions. This may require either a highly pressurized fluid or a piston with a large surface area. An additional pump may be required to provide the highly pressurized fluid. A piston with a large surface area will require a substantial amount of pressurized fluid each time the valve is actuated, which may decrease the amount of fluid available to other systems within the vehicle.  
       [0007] In addition, a hydraulically actuated valve may not be able to control the amount of movement, i.e. “lift,” during valve actuation. In a situation where the valve is actuated when the piston is advancing within the combustion chamber, the valve lift may need to be limited to prevent a collision between the piston and the valve. Such a collision may damage the valve and prevent the valve from properly sealing the gas passageway. This damage may disrupt the operation of the engine.  
       [0008] The engine valve actuator of the present invention solves one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0009] One aspect of the present invention is directed to an engine valve actuator that includes a first piston and a second piston moveably received within the first piston. An actuator body is provided that has a bore defining a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A valve element is operatively connected to the second piston to move in response to movement of the second piston.  
       [0010] In another aspect, the present invention is directed to a method of actuating a valve. A first piston having an opening is provided. A second piston is disposed within the opening. The second piston is operatively connected to a valve element. An actuator body having a bore configured to receive the first and second pistons is provided. The bore defines a first stop and a second stop. The first stop is configured to engage the first piston to limit movement of the first piston at a first preselected distance of travel. The second stop is configured to engage the second piston to limit movement of the second piston at a second preselected distance. A pressurized fluid is directed against the first and second pistons to thereby move the valve element.  
       [0011] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0012] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the principles of the invention. In the drawings:  
     [0013]FIG. 1 a  is a cross-sectional diagrammatic view of an engine valve actuator in accordance with an exemplary embodiment of the present invention;  
     [0014]FIG. 1 b  is a top view of an engine valve actuator in accordance with an exemplary embodiment of the present invention;  
     [0015]FIG. 2 is a cross-sectional diagrammatic view of an engine valve actuator in accordance with another exemplary embodiment of the present invention; and  
     [0016]FIG. 3 is a schematic representation of an engine system having an engine valve actuator in accordance with an exemplary embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0017] An exemplary embodiment of an engine valve actuator is illustrated in FIG. 1 a  and is designated generally by reference number  10 . As shown, engine valve actuator  10  includes an actuator body  12  having a first surface  13 . Actuator body  12  is configured to be attached to a cylinder head  28  of an engine  11 . Engine  11  may be any type of internal combustion engine, such as, for example, a diesel engine, a gasoline engine, or a natural gas engine.  
     [0018] Engine  11  includes an engine block  32  that defines a series of combustion chambers  34  (one of which is illustrated in FIG. 1 a ). Cylinder head  28  defines a series of passageways  30  (one of which is illustrated in FIG. 1 a ) that lead to and from each combustion chamber  34 . The series of passageways are configured to conduct inlet gas to the combustion chamber and to release exhaust gas from the combustion chamber. For the purposes of the present disclosure, the illustrated passageway  30  may be considered as an exhaust passageway.  
     [0019] As illustrated in FIG. 1 a , actuator body  12  defines a bore  14  that has a first stop  16  and a second stop  18 . In the illustrated exemplary embodiment, first stop  16  and second stop  18  are formed in bore  14  as concentric shoulders that have different diameters and are axially spaced apart within bore  14 . In other words, first stop  16  and second stop  18  may be generally circular steps that are located at different distances from first surface  13  of actuator body  12 . Various alternative configurations of first and second stop  16  and  18  may be readily apparent to one skilled in the art and are considered to be within the scope of the present invention.  
     [0020] As also shown in FIG. 1 a , a first piston  20  and a second piston  22  are disposed within bore  14 . First piston  20  may be generally circular and have a first surface  42  and a second surface  46 . First piston  20  may also include an opening  38  that is centrally disposed within first piston  20 .  
     [0021] First piston  20  is disposed within bore  14  for reciprocating movement in the directions indicated by arrows  60  and  62 . The movement of first piston  20  in the direction indicated by arrow  60  is limited by first stop  16 . First piston  20  may move between a first position (as illustrated in FIG. 1 a ) until first surface  42  of first piston  20  engages first stop  16 . The travel distance of first piston  20  is illustrated as distance d 1  in FIG. 1 a . First piston  20  may include a sealing mechanism (not shown) that is configured to create a seal with the surface of bore  14 .  
     [0022] Second piston  22  is disposed within opening  38  of first piston  20 . As illustrated in FIG. 1 b , both of first and second pistons  20  and  22  may have a generally circular shape. Second piston  22  may include a sealing mechanism (not shown) that is configured to create a seal with first piston  20 .  
     [0023] First and second pistons  20  and  22  are configured to allow for joint movement of both first and second pistons  20  and  22  relative to bore  14  and for individual movement of second piston  22  relative to first piston  20 . In the exemplary embodiment illustrated in FIG. 1 a , second piston  22  includes a shoulder  40  that is configured to engage first surface  42  of first piston  20 . When first piston  20  moves in the direction of arrow  60 , first surface  42  of first piston  20  will engage shoulder  40  of second piston so that first and second pistons  20  and  22  move together. Second piston  22  may, however, move in the direction of arrow  60  independently of first piston  20 . Alternative configurations of first and second pistons  20  and  22  that provide the described joint and individual movement may be readily apparent to one skilled in the art and are considered to be within the scope of the present invention.  
     [0024] As also illustrated in FIG. 1 a , second piston  22  includes a contact surface  46  that is configured to engage second stop  18 . When second piston  22  is moving in the direction of arrow  60 , second stop  18  will engage contact surface  46  to limit the movement of second piston  22 . The travel distance of second piston  22  is indicated as d 2  in FIG. 1 a.    
     [0025] As further illustrated in FIG. 1 a , a valve element  26  is connected to second piston  22  with a shaft  24 . It should be noted that valve element  26 , second piston  22 , and shaft  24  may be constructed as a single unit or may be constructed as separate components that are assembled together. Valve element  26  is configured to engage a valve seat  31  in passageway  30 . Valve element  26  may be any device used in an engine to selectively block an intake or exhaust passageway.  
     [0026] A spring  54  is disposed between cylinder head  28  and shaft  24  and acts to bias valve element  26  into engagement with valve seat  31  to block passageway  30 . A locking ring  58  and a washer  56  may be connected to shaft  24 . One end of spring  54  acts on washer  56  to bias shaft  24  in the direction of arrow  62  to thereby engage valve element  26  with valve seat  31 .  
     [0027] As also shown in FIG. 1 a , actuator body  12  defines a chamber  50 , a fluid inlet  52 , and a fluid outlet  53 . Chamber  50  is configured to receive pressurized fluid through fluid inlet  52 . When the pressurized fluid is introduced to chamber  50 , the pressurized fluid will exert a force on second surface  44  of first piston  20  and a second surface  48  of second piston  22 . The force exerted by the fluid will overcome the opposing force of spring  54  and chamber pressure to move or “lift” valve element  26  away from valve seat  31  to thereby open passageway  30  with combustion chamber  34 .  
     [0028] The force exerted by the pressurized fluid on valve element  26  is dependent upon the contact surface area of first and second pistons  20  and  22  and the pressure of the pressurized fluid. The generated force may be increased by either increasing the pressure of the fluid or by increasing the contact surface area of first and/or second pistons  20  and  22 .  
     [0029] The engagement of first surface  42  of first piston  20  with shoulder  40  of second piston  22  will cause first and second pistons  20  and  22  to move together until first piston  20  engages first stop  16 . First stop  16  prevents further movement of first piston  20  in the direction of arrow  60 . The pressurized fluid will continue to exert a force on second piston  22 , which may move within opening  38  of first piston  20  in the direction of arrow  60 .  
     [0030] The amount of movement of second piston  22  relative to first piston  20  is determined by the distance between first and second stops  16  and  18 . The further the distance between first stop  16  and second stop  18 , the greater the additional travel of second piston  22 . The location of second stop  18  will also control the amount of lift provided to valve element  26 . The maximum amount of lift provided to valve element  26  is equal to distance d 2 .  
     [0031] Both first piston  20  and second piston  22  are moved for the first portion of the lift of valve element  26 . When first piston  20  engages first stop  16 , the fluid required to continue movement of valve element  26  is decreased as only second piston  22  continues to move. Thus, the amount of fluid required to continue movement of valve element  26  is decreased in comparison to the amount of fluid require to initiate movement of first and second pistons  20  and  22 .  
     [0032] The combined contact surface area of first and second pistons  20  and  22  may provide the force required to actuate the valve when, for example, the piston is at or near a top dead center position. Referring to FIG. 1 a , when pressurized fluid is introduced to chamber  50 , the pressurized fluid will act on the surfaces of both first and second pistons  20  and  22  and will exert a first force on valve element  26 . The first force may be great enough to lift valve element  26  under any condition, including when a piston  36  is advancing in combustion chamber  34 . After first piston  20  engages first stop  16 , the pressurized fluid will act only on second piston  22  to exert a second force on valve element  26 . The second force may be great enough to continue to move valve element  26  through the remainder of the lift height.  
     [0033] Passageway  30  may be closed by releasing the pressurized fluid from chamber  50  through fluid outlet  53 . When the pressure in chamber  50  is reduced the force of spring  54  will act on shaft  24  to move first and second pistons  20  and  22  in the direction of arrow  62  until valve element  26  engages valve seat  31 .  
     [0034] Another exemplary embodiment of engine valve actuator  10  is illustrated in FIG. 2. In this alternative exemplary embodiment, actuator body  12  defines a second chamber  64  having a fluid inlet  66  and a fluid exit  68 . Second chamber  64  is configured to receive a pressurized fluid through fluid inlet  66 . Second chamber  64  is disposed adjacent first piston  20  so that a pressurized fluid introduced to second chamber  64  will exert a force on first piston  20 . In addition, chamber  50  is configured so that pressurized fluid introduced to chamber  50  will exert a force on second piston  22 .  
     [0035] The configuration illustrated in FIG. 2 may also provide for a variable force valve actuation using fluid having a constant pressure. Pressurized fluid may be introduced to one or both of chamber  50  and second chamber  64  to create different forces on valve element  26 . For example, fluid at a predetermined pressure may be introduced into chamber  50  to act on second piston  22  and exert a first force on valve element  26 . Fluid at the same pressure may also be introduced into second chamber  64  to act on first piston  20  and exert a second force on valve element  26 . In addition, the pressurized fluid may be introduced into both chamber  50  and second chamber  64  to act on both first and second pistons  20  and  22  to exert a third force on valve element  26 . This configuration allows pressurized fluid to selectively act on either first or second pistons  20  and  22  or both first and second pistons  20  and  22 . Thus, the magnitude of the force exerted on valve element  26  may be controlled by selectively directing pressurized fluid into one or both of chamber  50  and second chamber  64 .  
     [0036] The embodiment illustrated in FIG. 2 may also provide for variable lift heights of valve element  26 . A first preselected lift height may be obtained by introducing pressurized fluid into second chamber  64 . The pressurized fluid will act to move first piston  20  into engagement with first stop  16 . As no fluid is introduced into chamber  50 , second piston  22  will not move relative to first piston  20 . Thus, the lift height of valve element  26  will be equivalent to distance d 1 . Alternatively, to obtain a second preselected lift height, pressurized fluid may be introduced into chamber  50 . The pressurized fluid will act on second piston  22  to move second piston  22  into engagement with second stop  18 . Thus, the lift height of valve element  26 ,will be equivalent to distance d 2 . In this manner, different lift heights of valve element  26  may be achieved.  
     [0037] As illustrated in FIG. 3, engine valve actuator  10  may be connected to a fluid rail  74 . Fluid rail  74  may be connected to any pressurized fluid system included in a vehicle. For example, fluid rail  74  may be part of the engine lubrication system, the fuel injection system, or a hydraulic lift system.  
     [0038] As shown, a source of pressurized fluid  70  draws fluid from a tank  72  and provides pressurized fluid to fluid rail  74 . The flow of pressurized fluid to engine valve actuator  10  is governed by a first inlet valve  76  and, for the exemplary embodiment illustrated in FIG. 2, a second inlet valve  80 . In addition, a first outlet valve  78  and, for the exemplary embodiment illustrated in FIG. 2, a second outlet valve  82  control the flow of fluid from engine valve actuator  10  to tank  72 .  
     [0039] First and second pistons  20  and  22  may be configured based on the pressure of the fluid within fluid rail  74 . For example, if the pressure of the fluid within fluid rail  74  is expected to be relatively low, first and second pistons  20  and  22  may have a large contact surface area. Alternatively, if the pressure of the fluid within fluid rail  74  is expected to be higher, the contact surface area of first and second pistons  20  and  22  may be reduced.  
     [0040] Engine valve actuator  10  may be used to independently actuate valve element  26 . Alternatively, as shown in FIG. 3, engine valve actuator  10  may be used to supplement a cam and cam follower system. As shown, a cam  86  may be affixed to a cam shaft  84 , which is, in turn, connected to the engine crankshaft. A cam follower  88  is disposed between cam  86  and a lever  90 . Lever  90  is configured to pivot about a pivot point  92 . Lever  90  is connected to shaft  24 .  
     [0041] When cam shaft  84  rotates, cam  86  will also rotate, thereby causing cam follower  88  to move in a reciprocal fashion. As cam follower  88  moves up, lever  90  will pivot about pivot point  92  and move shaft  24  of engine valve actuator  10 . The movement of shaft  24  causes valve element  26  to lift and open the passageway to the combustion chamber.  
     [0042] If it is desired to open the passageway to the combustion chamber at a time other than the standard timing governed by the crankshaft rotation, pressurized fluid may be introduced to chamber  50  and/or second chamber  64 . In this manner, the engine valve of the present invention may be coupled with a conventional cam and cam follower arrangement.  
     Industrial Applicability  
     [0043] As will be apparent from the foregoing description, the present disclosure provides a variable force engine valve actuator  10 . The disclosed engine valve actuator  10  creates a variable force to lift a valve element  26  based on the input of pressurized fluid. In addition, the engine valve actuator  10  may provide for variable lift heights of the valve element  26 . Thus, the present disclosure provides a valve actuation system that has a high degree of flexibility in valve timing that allows for precise movement of the valve element  26 . These benefits are accomplished without the addition of significant costly modifications and/or parts.  
     [0044] The disclosed engine valve actuator  10  may be implemented into any type of internal combustion engine  11 . Incorporation of the disclosed engine valve actuator  10  into an internal combustion engine  11  may allow for an increase in the efficiency of the engine  11 . As will be recognized by one skilled in the art, the efficiency of an engine  11  may be improved by actuating one of more of the engine valves  26  at different points in the operating cycle of the engine  11  based on the vehicle operating conditions.  
     [0045] However, achieving these efficiency gains may require that an engine valve  26  be actuated when the respective combustion chamber  34  is under compression. For example, a properly timed valve actuation during the braking, or slowing, process of the vehicle may improve the efficiency of the engine  11 . This efficiency gain may be realized by actuating an engine exhaust valve at the end of the compression stroke of the engine  11  to exhaust the compressed gas instead of inducing combustion. This results in the engine  11  expending energy to compress the gas in the combustion chamber  34 , instead of generating energy during combustion. Thus, the compression of the gas in the combustion chamber  34  may be used to help slow the vehicle. One skilled in the art may recognize additional opportunities, such as, for example, the Miller cycle, where engine efficiency gains may be realized by actuating the engine valves at various points during the operation cycle of an internal combustion engine.  
     [0046] The disclosed engine valve actuator  10  may generate an initial actuation force that is great enough to overcome the force of the compression within the combustion chamber  34 . Once the valve has moved through a first portion of the lift distance, the force on the valve element  26 , and the pressurized fluid requirements of the engine valve actuator  10 , may be reduced. This provides the flexibility required to actuate the valve under a variety of engine operating conditions. Thus, incorporation of the engine valve actuator  10  into an internal combustion engine may allow the performance of the engine to be optimized.  
     [0047] It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed engine valve actuator. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the engine valve actuator disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.