Abstract:
The present invention provides a valve actuation system for an internal combustion engine. The valve actuation system of the present invention may provide an increased range of auto-ignition operation by providing a valve re-opening mechanism to provide products of combustion into the cylinder to increase the thermal efficiency and stability of the auto-ignition combustion process. The present invention allows the poppet valve re-opening timing, lift and duration to be tailored to specific engine architecture and operating conditions. Additionally, the present invention provides a method of re-opening a poppet valve of an internal combustion engine.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/674,213, filed Apr. 22, 2005, which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a valve actuation system for an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Dilute combustion of gasoline in an internal combustion engine, using either air or recirculated exhaust gas, can enhance the thermal efficiency and decrease the production of oxides of Nitrogen (NOx). However, there is a limit to which an internal combustion engine may operate with a dilute mixture due to misfire and combustion instability resulting from a slow burn rate of the dilute mixture. Known methods to extend the dilution tolerance limit include: 1) improving the ignitability of the mixture by enhancing ignition and mixture preparation, 2) increasing the flame speed by introducing charge motion and turbulence, and 3) operating the engine in a controlled auto-ignition combustion mode. 
     The controlled auto-ignition process may be referred to as Homogeneous Charge Compression Ignition (HCCI). In this process, a charge mixture of combusted gases, air, and fuel is created and auto-ignition is initiated simultaneously from multiple ignition sites within the compressed charge mixture, thereby resulting in stable power output and high thermal efficiency. Since the combustion is highly dilute and uniformly distributed throughout the charge mixture, the temperature of the burnt gas is typically lower than that of a traditional spark ignited engine with a propagating flame front and a diesel engine with an attached diffusion flame. The reduced temperature of the burnt gas may result in reduced NOx emissions when operating in the HCCI mode. 
     Four stroke gasoline internal combustion engines may operate in a controlled auto-ignition combustion mode by employing various valve opening and closing strategies. By altering the operating characteristics of the exhaust valves and/or the intake valves, a high proportion of residual burnt gases or products of combustion may be retained within the cylinder of the internal combustion engine to provide favorable conditions to auto-ignite a highly dilute charge mixture. The range of engine speed and load over which controlled auto-ignition combustion can occur may be expanded by employing various valve operating strategies, thereby obviating the need to increase the compression ratio of the spark ignited internal combustion engine. 
     One such valve operating strategy is exhaust re-compression. In this mode of operation, the exhaust valve is closed earlier in the exhaust stroke than in a typical four-stroke internal combustion engine. Correspondingly, the intake valve is opened later than in a typical four stroke internal combustion engine. The early exhaust valve closing and late intake valve opening provides a negative valve overlap period where products of combustion become trapped within the engine&#39;s cylinder. These trapped products of combustion will mix with the inducted fuel and air charge mixture during the intake stroke of the engine, thereby promoting the auto-ignition process. 
     Another valve strategy is exhaust re-breathing. In this mode, the exhaust valve is opened for a first period to allow combusted gasses to be expelled from the combustion chamber. Subsequently, the exhaust valve opens for a second period to allow products of combustion previously exhausted from the cylinder to be drawn back into the cylinder. By opening the exhaust valve twice during each four-stroke cycle of the internal combustion engine, the requisite conditions are created within the combustion chamber to support stable auto-ignition combustion. 
     Yet another valve strategy is a hybrid between exhaust re-compression and exhaust re-breathing. In this mode, the exhaust re-compression mode may be used when the engine is operating at a low engine load. For higher engine loads, the exhaust re-breathing strategy may be used. Additionally, by varying the exhaust valve lift and intake valve phasing, the spark-ignited engine may operate in a non-throttled load control mode (NTLC). In this mode, the intake valve phasing will vary the engine load by controlling the amount of air inducted into the cylinder. At the highest loads, the engine may operate in a traditional spark ignited fashion to enable maximum power density. 
     To enable the above-mentioned exhaust re-breathing valve strategy, the internal combustion engine may employ cam phasers, a two-step cam system, and a valve re-opening system. 
     SUMMARY OF THE INVENTION 
     The present invention is an engine valve actuation system with valve re-opening capability. The system of the present invention does not require a separate high-pressure source of fluid and is flexible in terms of re-opening lift, timing, and duration. The system of the present invention may be applied to either the intake or the exhaust valves and may be applied to either a conventional single lobe cam driven system or a two-step cam driven system. Additionally, the present invention provides a method of re-opening a valve of an internal combustion engine. 
     Accordingly, provided is a valve actuation system for a poppet valve, which is selectively movable between a closed position and an open position. The valve actuation system includes a reservoir operable to contain a fluid and a first hydraulic device that is in selective fluid communication with the reservoir. Also included is a second hydraulic device, which operates to bias the poppet valve toward the open position from the closed position. The second hydraulic device is in selective fluid communication with the reservoir and the first hydraulic device. An accumulator is in selective fluid communication with the first hydraulic device and the second hydraulic device. The first hydraulic device operates to communicate the fluid to the accumulator for at least a portion of the movement of the poppet valve from the closed position to the open position. The accumulator is operable to communicate the fluid to the second hydraulic device to bias the poppet valve toward the open position from the closed position. 
     A solenoid valve may operate to selectively communicate fluid between the first hydraulic device, the accumulator, the second hydraulic device, and the reservoir. A camshaft may be provided having base circle portion and a lobe portion and a rocker arm, such as a roller finger follower, may be disposed between the camshaft and the poppet valve. The camshaft rotatably engages the rocker arm and operates to selectively open the poppet valve as the camshaft rotates from the base circle portion to the lobe portion. An electronic control unit may operate to provide control to the solenoid valve. The second hydraulic device may be mounted with respect to an end of the rocker arm opposite the poppet valve and the first hydraulic device may be mounted with respect to the rocker arm between the poppet valve and the second hydraulic device. 
     A method of re-opening a poppet valve that is selectively movable between a closed position and an open position by a rocker arm engaged with a rotatable camshaft, having a base circle portion and a lobe portion is also provided. The method includes communicating a fluid from a first hydraulic device, in selective communication with a reservoir containing the fluid, to an accumulator for at least a portion of the rotation of the lobe portion of the camshaft into engagement with the rocker arm to facilitate the opening of the poppet valve. The method also includes blocking communication of the fluid between the first hydraulic device and the accumulator after a predetermined time. The method further includes communicating at least a portion of the fluid within the first hydraulic device and a second hydraulic device to the reservoir. The second hydraulic device is operable to engage the rocker arm to bias the poppet valve toward the open position from the closed position. Subsequently, the method includes communicating the fluid from the accumulator to the second hydraulic device to facilitate the re-opening of the poppet valve. The method may also include communicating the fluid from the second hydraulic device to the reservoir to facilitate the closing of the poppet valve subsequent to the re-opening. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagrammatic representation of a valve actuation system consistent with the present invention; and 
         FIG. 2  is a schematic diagrammatic representation of the states of operation of a solenoid valve contained within the valve actuation system shown in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly  FIG. 1 , the reference numeral  10  generally designates a valve actuation system in accordance with the present invention in the context of an internal combustion engine. The valve actuation system  10  includes a camshaft  12 , a rocker arm  14  such as a roller finger follower, a valve assembly  16 , an accumulator  18 , a solenoid valve  20 , a reservoir  22  containing a volume of fluid  23 , and two hydraulic devices  24  and  26 . 
     The camshaft  12  includes a lobe portion  28  and a base circle portion  30 . The camshaft  12  rotatably engages a roller element  32  of the rocker arm  14 . The rocker arm  14  has a first arm portion  34  and a second arm portion  36 , each disposed on either side of the roller element  32 . 
     The valve assembly  16  includes a poppet valve  38  biased by a valve spring  40  coaxially disposed about the stem of the poppet valve  38 . The poppet valve  38  is reciprocally movable within a cylinder head  42  and operates to selectively open and close a port  44  defined by the cylinder head  42 . The first arm portion  34  of the rocker arm  14  operates to bias the poppet valve  38  into an open position when the camshaft  12  rotates to engage the roller element  32  with the lobe portion  28 , while the valve spring  40  operates to bias the poppet valve  38  into a closed position. Although  FIG. 1  only shows one valve, the present invention may be applied to a multi-valve engine while remaining within the scope of that which is claimed. 
     The hydraulic device  24  contains a piston  46  slidably disposed within a bore  48  defined by a body  50 . The piston  46  and bore  48  cooperate with an end plate  52  to define a variable volume cavity  54 . The hydraulic device  24  exerts a reaction force on the second arm portion  36  of the rocker arm  14 , thereby defining a pivot point. The hydraulic device  26  contains a piston  56  slidably disposed within a bore  58  defined by a body  60 . The piston  56  and bore  58  cooperate with an end plate  62  to define a variable volume cavity  64 . The piston  56  of the hydraulic device  26  is sufficiently configured to engage the first arm portion  34  of the rocker arm  14 . 
     The accumulator  18  contains a piston  66  slidably disposed within a bore  68  defined by a body  70 . A spring  72  is disposed between the piston  66  and an end plate  74  and operates to bias the piston  66  within the bore  68 . The piston  66  and bore  68  cooperate with an end plate  76  to define a variable volume cavity  78 . 
     The solenoid valve  20 , in the preferred embodiment, is a solenoid actuated spool valve. Such spool valves and their operation are known to those skilled in the art of hydraulic controls. An electronic control unit  79  provides control signals to the solenoid valve  20 . The electronic control unit  79  may include a pre-programmable digital computer as is well known in the art of electronic controls. The solenoid valve  20  is in selective fluid communication with the hydraulic devices  24  and  26  through hydraulic ports  80  and  82  respectively. The solenoid valve  20  is in selective fluid communication with the accumulator  18  through a hydraulic port  84 . Additionally, the solenoid valve  20  is in selective fluid communication with a reservoir  22  through a hydraulic port  86 . The reservoir  22  operates to selectively supply the fluid  23  to, and receive the fluid  23  from the valve actuation system  10 . 
     The valve actuation system  10  of the present invention operates in four modes: charge, store, re-open, and return. To charge the valve actuation system  10 , the camshaft  12  rotates such that the lobe portion  28  engages the roller element  32  thereby displacing the rocker arm  14  downwardly from the position as shown in  FIG. 1 . At this time, the solenoid valve  20  is operating in STATE  1 , shown in  FIG. 2 . The first arm portion  34  of the rocker arm  14  will bias the piston  56  downward within the bore  58 . This movement forces the fluid  23  contained within the variable volume cavity  64  to flow into the variable volume cavity  78  of the accumulator  18  by way of the solenoid valve  20 . As the fluid  23  fills the variable volume cavity  78 , the piston  66  is biased against the spring  72 . This “charging” of the valve actuation system  10  will continue until the camshaft  12  rotates to a point of peak valve lift, i.e. the apex of the lobe  28 . Additionally, the STATE  1  of the solenoid valve  20  will allow the fluid  23  contained within the variable volume cavity  54  to exhaust to the reservoir  22 . 
     Once peak lift of the poppet valve  38  has been attained, i.e. the camshaft  12  has rotated past the apex of the lobe portion  28 , the storage mode commences. The spring  72  biases the piston  66  upwardly within the bore  68 , thereby displacing the fluid  23  contained within the variable volume cavity  78  into the variable volume chamber  64  via the solenoid valve  20  in STATE  1 . Subsequently, the electronic control unit  79  commands the solenoid valve  20  to switch from STATE  1  to STATE  2 , both shown in  FIG. 2 . At this point, the fluid  23  contained within the variable volume cavity  78  is trapped. The fluid  23  within the reservoir  22  backfills the variable volume cavity  64  via the solenoid valve  20  as the piston  56  moves upwardly in concert with the first arm portion  34  of the rocker arm  14 . STATE  2  of the solenoid valve  20  will allow the fluid  23  contained within the variable volume cavity  54  to exhaust to the reservoir  22  as the piston  46  moves downwardly in concert with the second arm portion  36  of the rocker arm  14 . 
     The rocker arm  14  returns to the unbiased position wherein poppet valve  38  is closed as the camshaft  12  rotates to the base circle portion  30 , as shown in  FIG. 1 . When poppet valve  38  re-opening is desired, the electronic control unit  79  commands the solenoid valve  20  from STATE  2  to STATE  3 , both shown in  FIG. 2 . At this point, the spring  72  biases the piston  66  thereby displacing the fluid  23  contained within the variable volume cavity  78  into the variable volume cavity  54  by way of the solenoid valve  20 . As the fluid  23  fills the variable volume cavity  54 , the piston  46  is biased against the second arm portion  36  of the rocker arm  14 . The rocker arm  14  pivots against or about the camshaft  12 , acting as a fulcrum, and the arm portion  34  biases the poppet valve  38  against the bias of the valve spring  40 . When the force exerted by the arm portion  34  is of sufficient magnitude to overcome the spring force of the valve spring  40 , the poppet valve  38  will open. The amount of lift provided to the poppet valve  38  during the re-opening process is dependent upon the amount of the fluid  23  trapped within the variable volume cavity  78 . This is determined by the timing, which is typically preprogrammed into the electronic control unit  79 , to switch the solenoid valve  20  from STATE  1  to STATE  2  as described hereinabove. Additionally in STATE  3 , the solenoid valve  20  allows the fluid  23  contained within the variable volume cavity  64  to exhaust to the reservoir  22  by way of ports  82  and  86 . 
     At the desired return time, the electronic control unit  79  commands the solenoid valve  20  to switch from STATE  3  to STATE  2 , shown in  FIG. 2 . The position of the solenoid valve  20  in STATE  2  enables the fluid  23  within the variable volume cavity  54  to exhaust to the variable volume cavity  64  and the reservoir  22 . The valve spring  40  will bias the poppet valve  38  into the closed position, as shown in  FIG. 1 . Subsequently, the electronic control unit  79  commands the solenoid valve  20  to return to STATE  1 , as shown in  FIG. 2 . The valve actuation system  10  is now in a favorable condition to repeat the process described hereinabove and will continue the process for each subsequent cycle until commanded otherwise by the electronic control unit  79 . 
     The present invention seeks to improve system cost and energy consumption without requiring an additional and separate high-pressure fluid source. The present invention may reduce packaging requirements since the fluid cavities and passages can be arranged with greater flexibility than mechanical linkages. Additionally, the present invention may reduce system cost by controlling the re-opening lift provided to the poppet valve  38  by the switching of the solenoid valve  20 , via the electronic control unit, without requiring a valve position sensor. The re-opening lift of the present invention is not substantially affected by pressure variations. The present invention also enables the re-opening timing, lift, and duration to be tailored to the specific engine architecture and operating conditions, which may allow the engine to operate more efficiently. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.