Abstract:
A variable valve actuation assembly for actuation of an engine intake valve between low-lift and high-lift modes. The VVA assembly includes a special rocker assembly having a pivotable central high-lift cam follower and two peripheral low-lift cam followers; a camshaft having low-lift and high-lift lobes engageable with the respective cam followers; a primary latching assembly including a slidable primary latching pin in the rocker assembly for engaging and disengaging the high-lift follower; a solenoid for causing the primary latching pin to be engaged and disengaged; and a secondary latching mechanism between the solenoid and the primary latching pin to automatically limit engagement and disengagement of the primary latching pin to times in the duty cycle of the camshaft (during lift events) when ejections of the primary latching pin are not possible.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to internal combustion engines; more particularly, to devices for controlling the variable actuation of intake valves in an internal combustion engine; and most particularly, to a variable valve actuation assembly for controllably actuating and deactuating a rocker assembly responsive to a triple-lobed cam in an internal combustion engine between high valve lift and low valve lift modes.  
         BACKGROUND OF THE INVENTION  
         [0002]    Internal combustion engines are well known. In an overhead valve engine, the valves may be actuated directly by camshafts disposed on the head itself, or the camshaft(s) may be disposed within the engine block and may actuate the valves via a valve train which may include valve lifters, pushrods, and rocker arms.  
           [0003]    It is known that for a portion of the duty cycle of a typical multiple-cylinder engine, especially at times of low torque demand, valves may be opened to only a low lift position to conserve fuel; and that at times of high torque demand, the valves may be opened wider to a higher lift position to admit more fuel. It is known in the art to accomplish this by providing a special rocker assembly having a switching or latching pin which may be actuated and/or deactuated electromechanically. The rocker assembly includes both fixed peripheral low-lift cam followers that cause low lift of the valve when the pin is disengaged, and a pivotable central high lift cam follower that causes high lift of the valve when the latching pin is engaged into the high lift follower.  
           [0004]    Various methods for actuating this type of latching pin are known. For example, see the disclosures of U.S. Pat. Nos. 5,619,958; 5,623,848; and 5,697,333. All of these methods employ individual solenoids, acting through bellcranks or similar structures, as part of an actuation system.  
           [0005]    A significant problem for these devices is how to balance the physical size of the solenoid against the force required to actuate the mechanism. The solenoid desirably has rapid response, small size, sufficient stroke and pull-in force, low power requirement, and low sensitivity to voltage and temperature variations; whereas, large size, high pull-in force, and high power are typically required to energize prior art mechanisms.  
           [0006]    One approach, disclosed in the above-referenced patents, is to reduce the solenoid force required by using the rotational motion of the rocker assembly inherent in its duty cycle to supply a portion of the actuating force. Typically, the motion of the rocker assembly permits the solenoid to “pull in” to a low air gap wherein high actuating forces can be generated. The solenoid essentially locks itself in the engaged position during a valve lift event (lift portion of the duty cycle), and some other compliant element in the device, such as a bellcrank, resiliently deflects as the rocker returns to the base circle portion of the cam at the conclusion of the lift event. Once the rocker reaches the base circle, the energy stored in the compliant element causes the locking pin to become engaged with the high-lift follower, shifting the rocker assembly to high-lift mode. This configuration requires the holding force of the solenoid in the actuated position to be greater than the force exerted against it by the compliant element; otherwise, the motion of the rocker assembly will overcome the solenoid and increase the magnetic air gap within the solenoid to a point at which the solenoid force becomes too small to actuate the pin, and the rocker then does not shift to high-lift mode.  
           [0007]    Another prior art approach, disclosed in U.S. Pat. No. 5,623,897, decouples the force generated by the compliant element from the locking force of the solenoid. One end of the compliant element is “grounded” to the cylinder head, and the solenoid moves the opposite end of the compliant element into a position wherein it may engage the rotational displacement of the rocker assembly. The solenoid simply has to hold the compliant element in that position; it is not required to resist the internal force carried by the compressed compliant element.  
           [0008]    The prior art configurations as disclosed have several shortcomings.  
           [0009]    First, several of the linkages are fixed with respect to the pivot point of the rocker assembly, which typically is the ball-head of a hydraulic lash adjuster (HLA) supporting the assembly. The vertical length of the HLA may vary in the normal course of operating, and thus the pivot point may also vary in the z (vertical) direction. Further, the vertical and horizontal (x,y) locations of the pivot point must vary inherently from engine to engine as a result of stack-up of manufacturing tolerances. The prior art disclosures do not address practical or self-compensating means for accommodating tolerances in the cylinder head and cam cover.  
           [0010]    Second, mechanisms disclosed in the prior art typically employ rotating linkages which may add friction to the force required for actuation and thus increase the force requirements of the solenoid.  
           [0011]    Third, none of the disclosed mechanisms, except that shown in U.S. Pat. No. 5,623,897, fully decouples the solenoid force from the compliant element and, therefore, from the pin actuating force. In the disclosure of U.S. Pat. No. 5,623,897, a rotating rocker assembly with a large rocker ratio and large rotational inertia pivots through a relatively large angle in actuating the engine valve. These characteristics add to the force requirements of the solenoid. Further, the solenoid plunger does not act orthogonally to the rocker assembly, resulting in side-loading and friction in the solenoid bearings.  
           [0012]    Fourth, in some prior art mechanisms, the point in the rotational cycle of the cam at which the solenoid is energized must be very carefully timed to avoid a phenomenon known in the art as “ejection” wherein the mechanism attempts to engage or disengage the locking pin into or out of the high-lift follower. When the pin is only slightly engaged, it is violently ejected, which can damage the pin or the high-lift follower and which causes a very loud and objectionable noise. Accurate timing of the solenoid energizing can be complex, as the response time of the mechanism may be affected by various operating parameters, such as oil temperature and thus viscosity.  
           [0013]    It is a principal object of the present invention to provide an improved variable valve actuation (VVA) assembly wherein a secondary latching mechanism between the solenoid and the primary latching pin in the rocker assembly automatically self-times the engagement of the secondary latching mechanism such that the timing of solenoid energizing and de-energizing is not critical and ejections are prevented.  
           [0014]    It is a further object of the invention to provide an improved VVA requiring a low solenoid actuating force and short stroke.  
           [0015]    It is a still further object of the invention to provide an improved VVA wherein variation in assembly performance from the stack-up of manufacturing and operating tolerances among the components of the assembly is minimized.  
         SUMMARY OF THE INVENTION  
         [0016]    Briefly described, a variable valve actuation assembly for variably opening of an engine intake valve in either a low-lift or high-lift mode includes a special rocker assembly pivotably disposed in the engine for opening and closing the valve and having a central high-lift cam follower and two peripheral low-lift cam followers, responsive to rotation of a camshaft having low-lift and high-lift lobes engageable with the respective cam followers; a primary latching mechanism including a slidable primary latching pin in the rocker assembly for engaging and disengaging the high-lift follower; a solenoid for causing the primary latching pin to be engaged and disengaged; and a secondary latching mechanism between the solenoid and the primary latching pin to automatically limit engagement and disengagement of the primary latching pin to times in the duty cycle of the camshaft when ejections are not possible.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    These and other features and advantages of the invention will be more fully understood and appreciated from the following description of certain exemplary embodiments of the invention taken together with the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is an isometric view from above, taken from the camshaft side (camshaft omitted for clarity) showing two variable valve actuation assemblies in accordance with the invention configured for operation of adjacent intake valves of adjacent engine cylinders;  
         [0019]    [0019]FIG. 2 is an isometric view from above of the VVA assemblies shown in FIG. 1, taken from opposite the camshaft side (camshaft omitted for clarity);  
         [0020]    [0020]FIG. 3 is an isometric view similar to that shown in FIG. 1, showing the VVA assemblies installed in the head of an engine;  
         [0021]    [0021]FIG. 4 is a view similar to that shown in FIG. 1, but including a camshaft with high-lift and low-lift cams for one of the VVA assemblies;  
         [0022]    [0022]FIG. 5 is an isometric view, partially exploded, taken from the VVA side opposite the camshaft side, of secondary latching mechanisms in the VVA assemblies shown in FIGS.  1 - 4 ;  
         [0023]    [0023]FIG. 6 is an isometric view, partially in cross-section, similar to that shown in FIG. 5, showing the relationship of the solenoid mounted on an arbor on the engine and a secondary latching pin in the secondary latching mechanisms shown in FIG. 5;  
         [0024]    [0024]FIGS. 7 through 10 are cross-sectional elevational views through a VVA taken along plane  7 - 10  in FIG. 4, showing successive stages in one operating cycle of a VVA in accordance with the invention; and  
         [0025]    [0025]FIG. 11 is another view of FIG. 1 showing cam follower rollers as an alternate embodiment. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    Referring to FIGS. 1 and 2, an improved dual variable valve actuation (VVA) assembly  10  in accordance with the invention is shown for variable actuation of two separate valves  12  of internal combustion engine  13 . Assembly  10  includes two separate, substantially identical VVA mechanisms  10 ′ sharing a common arbor  14  mountable onto an engine head  94  (as shown in FIG. 3). As the two VVA assemblies are substantially mirror images of each other, the following discussion is directed to only one VVA but should be understood as being applicable to both except as noted. Each mechanism  10 ′ includes a rocker assembly  16  and a secondary latching assembly  18 . Rocker assembly  16  is pivotably mounted, preferably by a ball-and-socket joint, on a conventional hydraulic lash adjuster (HLA)  20  and is pivotably connected near a distal end  22  to the stem of a valve  12 .  
         [0027]    Referring to FIGS. 1 and 2 and any of FIGS. 7 through 10, rocker assembly  12  is similar to two-stage rocker assemblies known in the art, as described above. A frame  24  has a spherical socket  26  for pivotably mating with the ball head  28  of HLA  20 . Frame  24  provides a rigid but pivotable bridge between HLA  20  and valve  12 , and is formed having a generally rectangular longitudinal aperture  30  for receiving a high-lift cam follower  32  having a surface for following a high-lift cam lobe as described below. Follower  32  is pivotably pinned at one end by pin  34  in slot  36  formed in frame  24  in communication with aperture  30 . Preferably, a first torsion spring (not shown) is disposed on pin  34  in slot  36  to bias follower  32  upwards into continual contact with its respective cam lobe. Frame  24  further is provided with two rigidly-mounted low-lift cam followers  38 , each having a surface for following a low-lift cam lobe as described below.  
         [0028]    At the proximal end  40  of rocker assembly  16 , a primary latching assembly  17  in frame  24  includes a stepped bore  42  slidably receivable of a primary latching pin  44  comprising a latching portion  46  and a trigger portion  48 . Pin  44  is urged away from high-lift follower  32  by a compression spring  50  disposed in bore  42  between frame  24  and trigger portion  48 . When follower  32  is suitably positioned (as shown in FIG. 10), portion  46  may be moved axially of bore  42  to engage portion  46  under latching nose  52  of follower  32 , thereby preventing follower  32  from rotating about pin  34 , and transforming rocker assembly  16  into high-lift mode, as described below.  
         [0029]    Referring to FIGS. 5 through 10, secondary latching assembly  18  includes a backer frame  54  having a central aperture  56  for receiving a blocker plate  58  therein. Backer frame  54  is provided with bores  60  for receiving pivot screw  62  which is threadedly received in a bore in arbor  14  to pivotably attach frame  54  to arbor  14 . A shim  64  on screw  62  spaces frame  54  a predetermined distance from arbor  14  and supports a second torsion spring  66  engaged by a first tang  68  into arbor  14  and by a second tang  70  onto frame  54  for urging frame  54  pivotably toward rocker assembly  16 . As shown in FIGS. 5 and 6, each siderail  72  of frame  54  is further provided with a stepped bore  74  for receiving a stepped secondary latching pin  76  having a flat boss  78  at one end thereof. A compression spring  80  is disposed in bore  74  around pin  76  for urging pin  76  outwards of bore  74 . Only one bore  74  is used for each frame  54 , but preferably the two bores  74  provided in each frame are mirror images of each other so that a single configuration of frame  54  may be used for either of the assemblies  18  shown in these figures.  
         [0030]    Blocker plate  58  is provided with a first bore  82  at an end thereof for receiving screw  62  to pivotably mount plate  58  between bores  60  in frame  54  such that plate  58  can swing through aperture  56 . A third torsion spring  75  is disposed on screw  62  coaxially with plate  58  and is configured conventionally to urge plate  58  rotationally of screw  62  against trigger portion  48 . Plate  58  is further provided with a medial bore  84  for receiving secondary latching pin  76  to rotationally lock plate  58  to frame  54  when so desired.  
         [0031]    Frame  54  is further provided with an actuating extension  77  for engaging with the bearing surface  79  of rocker proximal end  40 . Preferably, the bearing surface  81  of extension  77  is included in a plane including the pivot axis  83  of backer frame  54  and bearing surface  79  is a cylindrical arc centered on the center of arcuate pad  85  which interfaces with the stem of valve  12 . As rocker assembly  16  oscillates about HLA head  28  during actuation thereof, surface  79  rotates and slides along surface  81  at a constant radius, and therefore the position of backer frame  52  is unaffected by such action. Further, these geometric relationships make the VVA mechanism virtually insensitive to normal manufacturing, assembly, and operating variations in the size and position of these components.  
         [0032]    Arbor  14  is provided with a well  87  for receiving a solenoid  86  having an armature plunger  88  extending toward boss  78  on pin  76  in a direction orthogonal to plane  7 - 10  (FIG. 4), which is the actuation plane of assembly  10 ′, and parallel to the axis of rotation of the camshaft. When solenoid  86  is energized, pin  76  is urged toward blocker plate  58  in attempt to enter into bore  84  to lock plate  58  to frame  54 . Such entry is permitted under conditions as described below, wherein bore  74  becomes axially aligned with bore  84 . Where entry is not permitted immediately upon energizing of the solenoid, the energized solenoid acts as a cocked electromechanical spring and will insert pin  76  into bore  84  at the earliest opportunity during the camshaft duty cycle, as described below.  
         [0033]    Referring to FIGS. 3 and 4, a camshaft  90  is carried in bearing mounts  92  formed in engine head  94  which positions cam lobes for actuation of valves  12  via rocker assembly  16 . In FIG. 4, the camshaft and cam lobes are shown for only one valve, but it should be understood that identical lobes are provided for each valve having an associated VVA mechanism. Camshaft  90  is provided with a central high-lift lobe  96 , which is followed by central high-lift follower  32 , and a pair of identical peripheral low-lift lobes  98  flanking lobe  96 , which are followed by peripheral low-lift followers  38 .  
         [0034]    The conversion of a VVA assembly  10 ′ from low-lift mode (default mode) to high-lift mode is shown sequentially in FIGS. 7 through 10. Beginning with FIG. 7, in default low-lift mode, primary latching pin  44  is disengaged from high-lift follower  32 . Valve  12  is closed. Low-lift cam lobe  98  is engaged on its base circle portion  100  with low-lift follower  38 , and high-lift cam lobe  96  is engaged on its base circle portion  102  with high-lift follower  32 . Solenoid  86  is de-energized and therefore secondary latching pin  76  is disengaged from blocker plate  58  which is pivoted out of alignment by contact with trigger portion  48  at contact point  112 . Thus compression spring  50  which urges primary latching pin  44  out of engagement must be stronger than, and overcome, third torsion spring  75 . To begin the change from low-lift mode to high lift mode, solenoid  86  may be energized at any time during the camshaft duty cycle. Plunger  88  of the solenoid forcibly engages boss  78  (not visible in FIGS.  7 - 10 ) but secondary latching pin  76  cannot yet enter bore  84  because of axial misalignment. Secondary latching pin  76  is thus cocked by the energized solenoid to enter bore  84  in the blocker plate to lock the blocker plate to the backer frame  54  as soon as bore  84  becomes coaxially aligned with the pin.  
         [0035]    Referring to FIG. 8, a low-lift event is shown in progress. The camshaft has rotated the cam lobes counterclockwise such that eccentric portion  104  of low-lift lobe  98  is engaged with low-lift follower  38 , thereby rotating rocker assembly  16  clockwise about HLA head  28  and opening valve  12  with low lift. Eccentric portion  106  of high-lift lobe  96  is similarly engaged with high-lift follower  32 , but because follower  32  is disengaged from primary latching pin  44  the follower simply pivots on pin  34  without lift effect on valve  12 . Note that bearing surface  108  on trigger  48  is preferably cylindrically arcuate and bearing surface  110  on blocker plate  58  is preferably flat. Comparing the contact point  112  between these two surfaces in FIG. 7 and FIG. 8, it is seen that the surface  108  moves along surface  110  in a combination sliding and rolling motion in response to the clockwise rotation of rocker assembly  16 . The angle of surface  110  with respect to pivot point  83  is such that the relationship of blocker plate  58  to backer frame  54  does not vary with tolerance variations in the cylinder head, an importance advance in the art conferred by an assembly in accordance with the invention. Further, because the change in contact point between the bearing surfaces is eccentric with respect to the pivot point of the rocker assembly, blocker plate  58  is permitted to pivot counterclockwise slightly about pivot axis  83 , bring bore  84  into alignment with pin  76 , which then enters bore  84  at the urging of the previously energized solenoid. Because the pin is small and of low mass, and because bore  84  is aligned with pin  76  by the natural motion of rocker assembly  16  imparted by the engine, solenoid  86  may be very small and relatively weak, thus overcoming the disadvantages of prior art VVA mechanisms as described above. This is an important advantage of a VVA assembly in accordance with the invention.  
         [0036]    Referring to FIG. 9, as the low-lift event progresses, the cam lobes have rotated further counterclockwise such that the followers are in contact with the lobes at the point of merger between the eccentric portions  104 , 106  and the base circle portions  100 , 102  of the lobes  98 , 96 . Valve  12  has been closed by the action of a conventional valve spring (not shown), causing rocker assembly  16  to rotate counterclockwise back to its rest position, as shown previously in FIG. 7. However, blocker plate  58  is not free to also return to its former position because it is now locked to backer frame  54 , as was seen in FIG. 8. Further, latching portion  46  of primary latching pin  44  is still in slight interference with latching nose  52 . Therefore, the locked unit of backer frame and blocker plate is pivoted clockwise about axis  83  against second torsion spring  66 , cocking the primary and secondary latching mechanisms for engagement of primary latching pin  44  with latching nose  52  at the earliest opportunity.  
         [0037]    Referring to FIG. 10, the low-lift event is completed and rocker assembly  16  is locked in high-lift mode by primary locking pin  44 . The cam lobes have rotated slightly farther than as shown in FIG. 9, onto their respective base circle portions, and high-lift follower  32  has pivoted farther clockwise about pivot pin  34 , bringing latching nose  52  into latching alignment with latching portion  46 . Second torsion spring  66  is stronger than compression spring  50  and immediately urges primary latching pin  44  into engagement with latching nose  52 , compressing spring  50  and completing the conversion of the rocker assembly from low-lift mode to high-lift mode. During the next revolution of the camshaft, the high-lift eccentric of lobe  96  will cause rocker assembly  16  to rotate through a greater angle than in the previous duty cycle, thereby opening valve  12  wider (higher lift) than in its previous opening.  
         [0038]    Both primary latching pin  44  and secondary latching pin  76  will remain engaged as long as solenoid  86  is energized; the assembly will thus remain in high-lift mode. To shift back to low-lift (default) mode, the solenoid may be de-energized at any point. It will be seen that there is no shear force on secondary pin  76  while either a low-lift or high-lift event is in progress (eccentric lobe portions are engaged). Thus pin  76  is free to engage or disengage with bore  84  at any such time. De-energizing the solenoid during the high-lift event permits compression spring  80  to eject pin  76  from bore  84 ; however, primary latching pin  44  remains engaged with latching nose  52  because of shear force therebetween. When the lobes return to their base circles and such shear force is removed, compressed spring  50  immediately urges primary latching pin out of engagement with nose  52 . Blocker plate  85  is free to pivot away, and the assembly is returned to the default low-lift mode shown in FIG. 7.  
         [0039]    It is an important advantage of a VVA assembly in accordance with the invention that the engagement of the primary latching pin with the high-lift follower necessarily occurs at the beginning of the base circle lobe engagement, at a point of no shear force between the pin and the follower. Thus, ejections of the primary latching pin, as are well known in the prior art, are rendered impossible. Further, because the secondary latching pin engages the blocker arm only when they are axially aligned, which occurs only during the lift portion of a low-lift duty cycle, the solenoid need be only strong enough to displace the secondary pin axially a short distance.  
         [0040]    While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. For example, high-lift and low-lift cam followers  32 , 38  are shown as sliders herein but some or all of the followers may instead be provided as rollers rotatably mounted to frame  24  within the scope of the invention. For example, in FIG. 11, roller  38 ′ is shown instead of slider  38 . Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.