Patent Publication Number: US-6708656-B1

Title: Engine valve actuator

Description:
TECHNICAL FIELD 
     The present disclosure is directed to an engine valve actuator and, more particularly, the present disclosure is directed to an anti-lash mechanism for an engine valve actuator. 
     BACKGROUND 
     Many vehicles, such as, for example, automobiles, on highway trucks, or off highway trucks, typically include an internal combustion engine that provides power for the vehicle. A typical internal combustion engine includes a series of intake and exhaust valves that control the flow of gases to and from the combustion chambers of the engine. The engine may also include a valve actuation system, such as, for example, a cam driven valve actuation system to control the actuation timing of the engine valves. 
     The overall performance of the internal combustion engine may be improved by using a series of auxiliary valve actuators, such as, for example, hydraulically powered actuators, that actuate the engine valves to selectively implement variations on the conventional, cam-driven valve timing. For example, the auxiliary valve actuators may be used to actuate the exhaust valves of the engine to implement an “engine braking” cycle. In an engine braking cycle, the auxiliary valve actuators open the exhaust valves of the engine when a piston associated with each combustion chamber is at or near a top-dead-center position of a compression stroke. This opening of the exhaust valves allows the air compressed by the piston in the combustion chamber during the compression stroke to escape from the combustion chamber through an exhaust passageway. In this manner, the pistons of the engine are selectively used as air compressors to absorb power instead of generating power in response to the combustion of fuel. 
     Because the auxiliary valve actuators are used only when the engine is experiencing selected operating conditions, the auxiliary valve actuators should avoid interfering with the operation of the cam driven valve actuation system when the engine is experiencing other operating conditions. The performance of the engine may be negatively impacted if, for example, the auxiliary valve actuators inadvertently opened the exhaust valves during the intake stroke of the pistons. This type of interference may occur if the auxiliary valve actuators do not account for changes in the size of engine components due to thermal expansion. 
     To prevent any such interference, the auxiliary valve actuators are typically separated from the exhaust valve assembly by a certain distance, which is commonly referred to as a “lash.” The lash is a distance that separates the auxiliary valve actuators from the engine valve assembly. The lash may prevent inadvertent or unintentional opening of the engine valves by the auxiliary valve actuators when changes in temperature of the engine cause a change in size of the engine components. 
     However, the auxiliary valve actuators must take up the lash before engaging the engine valves to open the engine valves. This may result in the auxiliary valve actuators requiring additional fluid and/or additional time to open an associated engine valve. To obtain the best engine performance, the actuation timing of the engine valves should be controlled precisely. Accordingly, the system that controls the auxiliary valve actuators must account for the lash in each actuation of the associated engine valves. 
     An auxiliary valve actuator may include an anti-lash mechanism. For example, as illustrated in U.S. Pat. No. 4,898,128 to Meneely, an auxiliary valve actuator may include a relatively low force spring that biases the valve actuator into contact with the valve assembly. In this manner, the lash is removed and the auxiliary valve actuator remains in contact with the associated valve without impacting the performance of the engine under normal operating conditions. However, adding additional components to the auxiliary valve actuator increases the overall cost of the auxiliary actuator and may result in additional maintenance. 
     The engine valve actuator of the present disclosure solves one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure is directed to an engine valve actuator for an internal combustion engine that includes a housing having an opening. An adjustment member is disposed in the housing and defines a chamber. A piston is disposed in the opening of the housing and has a protrusion adapted to be received in the chamber of the adjustment member. The piston has a first position where the protrusion of the piston is disposed in the chamber and a portion of the piston contacts a corresponding portion of the adjustment member and a second position where the portion of the piston is separated from the corresponding portion of the adjustment member. A fluid passageway is adapted to provide pressurized fluid to the opening. The pressurized fluid acts on the piston to move the piston towards the second position to thereby allow pressurized fluid to enter the chamber to prevent the piston from returning to the first position. A push rod is operatively engaged with the piston and is adapted to engage and open the engine valve. 
     In another aspect, the present disclosure is directed to a method of an engine valve of an internal combustion engine. Pressurized fluid is provided to a housing defining an opening and including a chamber. The pressurized fluid is directed to the opening of the housing and against a piston having a protrusion engaged with the chamber. The pressurized fluid acts on the piston to move the piston from a first position where a portion of the piston engages a corresponding portion of the housing. The movement of the piston cause the engine valve to move to an open position and allows fluid to flow into the chamber. The engine valve is returned to a closed position. The movement of the engine valve acts to move the piston within the housing. The fluid in the chamber prevents the piston from returning to the first position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of an engine valve actuator in accordance with an exemplary embodiment of the present invention, illustrating a piston in a first position; 
     FIG. 2 is a pictorial view of a piston in accordance with an exemplary embodiment of the present invention; 
     FIG. 3 is a partial cross-sectional view of an engine valve actuator in accordance with an exemplary embodiment of the present invention, illustrating a piston in a second position; and 
     FIG. 4 is a partial cross-sectional view of an engine valve actuator in accordance with an exemplary embodiment of the present invention, illustrating a piston between the first and second positions. 
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of an engine valve actuator  12  for an internal combustion engine  10  is illustrated in FIG.  1 . Engine  10  includes an engine block  16  having a cylinder  17  that defines a combustion chamber  20 . A cylinder head  18  may be engaged with engine block  16  to cover cylinder  17 . 
     As also shown, a piston  14  may be disposed within cylinder  17 . Piston  14  is adapted to reciprocate between a bottom-dead-center position and a top-dead-center position within cylinder  17 . Piston  14  may be connected to a crankshaft (not shown) such that a rotation of the crankshaft causes piston  14  to reciprocate between the bottom-dead-center position and the top-dead-center position in cylinder  17 . In addition, a reciprocating movement of piston  14  between the bottom-dead-center position and the top-dead-center position within cylinder  17  will cause a corresponding rotation of the crankshaft. 
     Engine  10  may, for example, operate in a conventional four stroke diesel cycle. In a four stroke diesel cycle, piston  14  moves through an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. One skilled in the art will recognize that engine  10  may operate in other known operating cycles, such as, for example, an Otto cycle. 
     As also illustrated in FIG. 1, cylinder head  18  defines an opening  21  that leads to a passageway  22 . For the purposes of the present disclosure, opening  21  and passageway  22  will be referred to as an exhaust opening and an exhaust passageway. One skilled in the art will recognize, however, that opening  21  and passageway  22  may also be an intake opening and an intake passageway. 
     Cylinder head  18  may define one or more additional exhaust openings as well as one or more intake openings and passageways that lead to and/or from combustion chamber  20 . Exhaust passageway  22  may connect combustion chamber  20  with an exhaust manifold (not shown). An intake passageway may connect combustion chamber  20  with an intake manifold (not shown). 
     An engine valve  24  may be disposed in exhaust opening  22 . For the purposes of the present disclosure, engine valve  24  will be referred to as an exhaust valve. One skilled in the art will recognize, however, that engine valve  24  may also be an intake valve. 
     Exhaust valve  24  may include a valve stem  26  and a valve element  25 . Exhaust valve  24  may be moved between a first position and a second position. In the first position, exhaust valve  24  blocks exhaust opening  21  to prevent a flow of fluid from combustion chamber  20  to exhaust passageway  22 . In the second position, exhaust valve  24  allows fluid to flow from combustion chamber  20  to exhaust passageway  22 . 
     A valve actuation system (not shown) may be provided to actuate exhaust valve  24 . As one skilled in the art will recognize, the valve actuation system may be a cam-driven system, a hydraulically driven system, an electrically driven system, or a combination thereof. The valve actuation system may be adapted to exert a force on valve stem  26  to thereby move exhaust valve  24  from the first position to the second position. A valve return spring  28  may be engaged with valve stem  26  to return exhaust valve  24  to the first position when the force exerted by the valve actuation system is removed. 
     The valve actuation system may be adapted to coordinate the opening of exhaust valve  24  with the movement of piston  14 . For example, the valve actuation system may open exhaust valve  24  when piston  14  is moving through an exhaust stroke. In this manner, exhaust gases created during the combustion of fuel in combustion chamber  20  may be exhausted to exhaust passageway  22 . 
     Engine  10  may also include a fuel injection system (not shown). The fuel injection system may deliver, for example, diesel fuel, gasoline, or natural gas to combustion chamber  20 . The fuel injection system may be configured to inject a certain quantity of fuel into combustion chamber  20  at a certain point in the operating cycle of engine  10 . For example, the fuel injection system may inject a quantity of diesel fuel into combustion chamber  20  as piston  14  moves from a top-dead-center position towards a bottom-dead-center position during an intake stroke. 
     As also shown in FIG. 1, valve actuator  12  includes a housing  30 . Housing  30  has an inner surface  68  and defines a fluid passageway  32  and an opening  34 . A source of pressurized fluid  80 , which may be, for example, a variable capacity pump, may supply a flow of pressurized fluid to opening  34  through fluid passageway  32 . A control valve  78  may be disposed in fluid passageway  32  to control the rate of fluid flow through fluid passageway  32 . 
     An adjustment member  36  may be disposed in housing  30 . Adjustment member  36  defines a chamber  46  that includes a seat  40 . Adjustment member  36  includes a shoulder  66  that surrounds chamber  46 . Adjustment member  36  is positioned in housing  30  to expose chamber  46  to opening  34 . 
     Adjustment member  36  and housing  30  may be adapted to allow adjustment of the position of seat  40  and shoulder  66  relative to housing  30 . For example, an outer surface  60  of adjustment member  36  may include threads that are configured to engage corresponding threads in housing  30 . Adjustment member  36  may be rotated to thereby adjust the position of adjustment member  36  relative to housing  30 . One skilled in the art will recognize that the position of adjustment member  36  relative to housing  30  may be adjusted through other known methods and/or devices, such as, for example, a spring-loaded ball and detent mechanism. 
     A nut  61  may be engaged with the threads of adjustment member  36 . When adjustment member  36  is properly positioned with respect to housing  30 , nut  61  may be tightened to secure adjustment member  36  to housing  30 . In this manner, further movement of adjustment member  36  relative to housing  30  may be prevented. 
     Valve actuator  12  also includes a piston  38 , which may be, for example, a slave piston. As shown in FIG. 2, piston  38  includes a pressure surface  74  and an outer surface  70 . Piston  38  also includes a protrusion  48  that extends from pressure surface  74  to a face  62 . Protrusion  48  may include an outer surface  49 . One or more slots  50  may be formed in outer surface  49 . Slots  50  may be formed in protrusion  48  to start at a distance, x, from pressure surface  74  and extend to face  62 . Slots  50  may extend, for example, for approximately half of the height of protrusion  48 . 
     As shown in FIG. 1, piston  38  also includes an inner surface  42  and a contact surface  72 . Piston  38  may be slidably disposed in opening  34  of housing  30 . Outer surface  70  of piston  38  may be adapted for a close tolerance fit with opening  34 . In addition, a seal (not shown) may be disposed between outer surface  70  of piston  38  and housing  30 . Chamber  46  of adjustment member  36  is adapted to receive protrusion  48  of piston  38  with a close tolerance fit. 
     Piston  38  may be moved relative to housing  30  and adjustment member  36  between a first position and a second position. In the first position, protrusion  48  is fully disposed in chamber  46  so that a portion of piston  38  engages a portion of adjustment member  36  or housing  30 . For example, when piston  38  is in the first position, face  62  of protrusion  48  may engage seat  40  of chamber  46 . Alternatively, when piston  38  is in the first position, pressure surface  74  of piston  38  may engage shoulder  66  of adjustment member  36  or inner surface  68  of housing  30 . As shown in FIG. 3, when piston  38  is in the second position, slots  50  provide a fluid passageway  64  between opening  34  of housing  30  and chamber  46  of adjustment member  36 . As shown in FIG. 4, as piston  38  moves from the second position to the first position, slots  50  will move past shoulder  68  of adjustment member  36  to close fluid passageway  64 . 
     As shown in FIG. 1, a push rod  54  may be adapted to engage piston  38 . Push rod  54  includes a head  55  that may engage contact surface  72  of piston  38  and an end  58  that extends from housing  30 . Push rod  54  may be adapted to move relative to housing  30  in response to a corresponding movement of piston  38 . One skilled in the art will recognize that push rod  54  and piston  38  may be formed as a single piece or as separate pieces. 
     A piston return spring  52  may be disposed in housing  30 . A plate  56  having an opening  57  that is configured to slidably receive push rod  54  may be engaged with housing  30  on one side of piston return spring  52 . Piston return spring  52  may act between plate  56  and head  55  of push rod  54 . Piston return spring  52  acts to move push rod  54  and piston  38  to engage face  62  of protrusion  48  with seat  40  of chamber  46 . 
     A controller  76  may be connected to control valve  78 . Controller  76  may be an electronic control module that includes a microprocessor and memory. As is known to those skilled in the art, the memory may be connected to the microprocessor and may store an instruction set and variables. Associated with the microprocessor and part of the electronic control module may be various other known circuits such as, for example, power supply circuitry, signal conditioning circuitry, and solenoid driver circuitry, among others. 
     As one skilled in the art will recognize, controller  76  may be programmed to control one or more aspect of the operation of engine  10 . For example, controller  76  may be programmed to control the position of control valve  78 , the operation of source of pressurized fluid  80 , and the operation of the fuel injection system (not shown). 
     INDUSTRIAL APPLICABILITY 
     Engine  10  may be operated to provide power to propel a vehicle, such as, for example, an automobile, an on highway truck, or an off highway truck. Engine  10  may be operated in a conventional four stroke diesel cycle. For the purposes of the present disclosure, the operation of a single cylinder  17  of engine  10  will be described. 
     During a conventional operation cycle of engine  10 , piston  14  moves from a top-dead-center position towards a bottom-dead-center position in an intake stroke. As piston  14  moves through the intake stroke, the engine valve actuation system opens an intake valve (not shown) associated with combustion chamber  20 . The opening of the intake valve allows intake air to flow from an intake manifold (not shown) into combustion chamber  20 . The intake air may be at ambient pressure or the intake air may be pressurized such as, for example, by a turbocharger. 
     A fuel injection system injects a quantity of fuel during the intake stroke of piston  14 . The fuel may be injected directly into combustion chamber  20  or into the intake manifold. The fuel mixes with the intake air to form a combustible mixture. 
     Piston  14  then moves from the bottom-dead-center position towards the top-dead-center position of a combustion stroke. The movement of piston  14  within combustion chamber  20  compresses the air and fuel mixture. Engine  10  may be adapted so that piston  14  compresses the air and fuel mixture to reach the critical, or combustion, pressure when piston  14  is at or near the top-dead-center position of the compression stroke. 
     When the fuel and air mixture reaches the ignition pressure, the fuel ignites and the mixture is combusted. The combustion of the fuel and air mixture drives piston  14  towards the bottom-dead-center position in a combustion stroke. The driving power of the fuel combustion is translated into an output rotation of a crankshaft (not shown) that is used to propel the vehicle. 
     Piston  14  then returns from the bottom-dead-center position to the top-dead-center position in an exhaust stroke. During the exhaust stroke, the engine valve actuation system moves exhaust valve  24  towards the second position to create a fluid passageway from combustion chamber  20  to exhaust passageway  22 . The movement of piston  14  towards the top-dead-center position forces combustion exhaust from combustion chamber  20  into exhaust passageway  22 . The operating cycle of piston  14  may then begin again with another intake stroke. 
     When a vehicle operator provides an instruction to decelerate the vehicle, such as, for example, by depressing a brake pedal, the engine may operate in an “engine braking” mode. Controller  76  may instruct the fuel delivery system to cease delivery of fuel to combustion chambers  20 . The controller may also operate control valve  78  to activate valve actuator  12  to assist in the deceleration of the vehicle. 
     In the “engine braking” mode, controller  76  opens control valve  78  to allow pressurized fluid to flow from source of pressurized fluid  80  through fluid passageway  32  into opening  34 . The pressurized fluid exerts a force on pressure surface  74  of piston  38 , which causes piston  38  to move from the first position, as illustrated in FIG. 1, towards the second position, as illustrated in FIG.  3 . This movement of piston  38  causes a corresponding movement of push rod  54 . In addition, this movement of piston  38  opens fluid passageway  64  to allow fluid to flow from opening  34  through slots  50  and into chamber  46 . 
     As push rod  54  moves relative to housing  30 , end  58  of push rod  54  will move through distance x (referring to FIG. 1) to engage exhaust valve  24 . Push rod  54  may directly engage valve stem  26 . Alternatively, push rod  54  may engage another portion of exhaust valve  24  or an operative portion of the valve actuation system such as, for example, a bridge connecting a pair of exhaust valves  24  for combustion chamber  20 . 
     The continued movement of piston  38  and push rod  54  after end  58  engages exhaust valve  24  causes exhaust valve  24  to move from the first position towards the second position to allow a flow of fluid from combustion chamber  20  to exhaust passageway  22 . Controller  76  may control the opening of control valve  78  so that exhaust valve  24  opens when piston  14  is at or near the top-dead-center position of the compression stroke. As will be apparent to one skilled in the art, exhaust valve  24  may be opened at another point in the operating cycle of the engine to implement another variation on conventional engine valve timing. 
     When exhaust valve  24  is opened at the end of a compression stroke, the air compressed by piston  14  escapes from combustion chamber  20  through exhaust passageway  22 . The act of compressing air will act to oppose the motion of the crankshaft. Because the air compression does not result in fuel combustion, the piston is not driven through a combustion stroke. Thus, valve actuator  12  causes engine  10  to operate as an air compressor that absorbs the kinetic energy of the moving vehicle by opposing the rotation of the crankshaft. Valve actuator  12  will, therefore, assist in the slowing of the moving vehicle. 
     To release engine valve actuator  12  and allow engine valve  24  to close, controller  76  may close control valve  78  and allow fluid to drain from opening  34 . As the fluid drains from opening  34 , the force exerted on pressure surface  74  of piston  38  decreases. Eventually, the force of valve return spring  28  and piston return spring  52  will allow engine valve  24  to move towards the first position and block exhaust opening  21   
     Piston return spring  52  will continue to act on piston  38 . Protrusion  48  may remain in at least partial engagement with chamber  46  to guide piston  38  as it moves relative to housing  30 . As protrusion  48  moves relative to chamber  46 , the fluid in chamber  46  flows through slots  50  and fluid passageway  64  to return to opening  34 . When, however, slots  50  pass shoulder  66  of adjustment member  36  (as illustrated in FIG.  4 ), fluid passageway  64  is effectively closed. When this occurs, the fluid remaining in chamber  46  is trapped. The fluid trapped in chamber  46  prevents further movement of piston  38  relative to housing  30  and adjustment member  36 . Push rod  54  will stop at a position that is closer to engine valve  24  than if piston  38  returned to the first position. 
     When piston  14  next approaches the top-dead-center position of the compression stroke, the distance that piston  38  needs to move to open engine valve  24  is reduced by the distance, x. Thus, when controller  76  opens control valve  78 , less fluid and less time is required to move piston  38  and push rod  54  to open engine valve  24 . In this manner, the response time of engine valve actuator  12  to the introduction of pressurized fluid to housing  30  may be improved. 
     When engine  10  is no longer experiencing the engine braking conditions, controller  76  will close control valve  78  and allow fluid to drain from opening  34 . The fluid trapped in chamber  46  will leak between protrusion  48  and adjustment member  36 . This will allow piston  38  to return to the first position, where pressure surface  74  of piston  38  engages shoulder  66  of adjustment member  36  or face  62  of protrusion  48  engages seat  40  of chamber  46 . 
     The starting position of piston  38  and push rod  54  relative to engine valve  24  may be adjusted by re-positioning adjustment member  36  relative to housing  30 . By adjusting the threads on outer surface  60  of adjustment member  36  to move adjustment member  36  towards exhaust valve  24 , the distance, x, separating push rod  54  from engine valve  24  may be decreased. By adjusting the threads on the outer surface  60  of adjustment member  36  to move adjustment member  36  away from exhaust valve  24 , the distance, x, separating push rod  54  from engine valve  24  may be increased. 
     While the engine valve actuator of the present disclosure has been described in relation to an engine braking condition, one skilled in the art will recognize that the described engine valve actuator may be used to implement other variations on a conventional valve actuation timing when the engine is experiencing other operating conditions. For example, the described engine valve actuator may cooperate with an intake valve to implement a “late intake” type Miller cycle when the engine is experiencing certain operating conditions, such as, for example, steady state conditions. 
     As will be apparent from the foregoing description, the present disclosure provides an engine valve actuator that removes the lash between the engine valve actuator and the associated engine valve. This reduces the amount of travel distance that the valve actuator must travel to open the associated engine valve. Accordingly, the amount of time and fluid required to open the engine valve is reduced. This may improve control over the timing of the engine valve actuation and thereby lead to enhanced performance of the internal combustion engine. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the engine valve actuator of the present invention without departing from the scope of the disclosure. Other embodiments of the engine valve actuator will be apparent to those skilled in the art from consideration of the specification and practice of the valve actuator disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.