Abstract:
A finger follower assembly ( 30 ) for variably activating a valve of an internal combustion engine having a camshaft with at least one lobe ( 40 ). The finger follower assembly includes a follower body ( 54 ), a shaft ( 78 ), a cam follower ( 56 ), and a latching mechanism ( 58 ). The cam follower is supported by the shaft and is configured for engagement with the at least one lobe. The cam follower is configured to pilot on the camshaft to maintain an alignment of the cam follower with respect to the at least one lobe. The latching mechanism selectively latches and unlatches the cam follower to the follower body to provide first valve lift capability and a second valve lift capability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 60/718,120, filed Sep. 16, 2005, the entire contents of which are hereby incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines, and more particularly to finger follower type rocker arms for changing between high and low valve lifts. 
         [0003]    Variable valve activation (VVA) mechanisms for internal combustion engines are known. It is known to lower the lift of one or more valves of a multiple-cylinder engine, especially intake valves, during periods of light engine load. Such deactivation can improve fuel efficiency. 
         [0004]    Various approaches have been disclosed for changing the lift of valves in a running engine. One approach is to provide an intermediary cam follower arrangement which is rotatable about the engine camshaft and is capable of changing both the valve lift and timing. In such an approach, the camshaft typically includes both high-lift and low-lift lobes for each such valve. Such an arrangement can be complicated and costly to manufacture and difficult to install during engine assembly. 
         [0005]    Another known approach is to provide a deactivation mechanism in the hydraulic lash adjuster (HLA) upon which a cam follower rocker arm pivots. Such an arrangement is advantageous in that it can provide variable lift from a single cam lobe by making the HLA either competent or incompetent to transfer the motion of the cam eccentric to the valve stem. A shortcoming of providing deactivation at the HLA end of a rocker arm is that, because the cam lobe actuates the rocker near its longitudinal center point, the variation in lift produced at the valve-actuating end can be only about one-half of the extent of travel of the HLA deactivation mechanism. 
         [0006]    Still another known approach is to provide a deactivation mechanism in the valve-actuating end of a rocker arm cam follower (opposite from the HLA pivot end) which locks and unlocks the valve actuator portion from the follower body. Unlike the HLA deactivation approach, this approach typically requires both high-lift and low-lift cam lobes to provide variable lift. 
         [0007]    Another known approach is to provide a rocker arm cam follower with a finger body having a first cam follower positioned within the finger body and a secondary cam follower. In some designs, the first cam follower is selectively moveable relative to the finger body and in other designs the secondary cam followers are selectively moveable relative to the finger body. The moveable members generally are axially moveable or pivot about a secondary axis which adds complexity to the design or fails to provide smooth motion. 
       SUMMARY OF THE INVENTION 
       [0008]    In one embodiment the invention provides a finger follower assembly for variably activating a valve of an internal combustion engine having a camshaft with at least one lobe. The finger follower assembly includes a follower body, a shaft, a cam follower and a latching mechanism. The follower body has a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the follower body between the first and second end portions. The shaft is coupled to the follower body and transverses the aperture. The cam follower is supported at least partially within the aperture by the shaft and is configured for engagement with the at least one lobe. The cam follower is configured to pilot on the camshaft to maintain an alignment of the cam follower with respect to the at least one lobe. The latching mechanism selectively latches and unlatches the cam follower to the follower body to provide a first valve lift capability and a second valve lift capability. 
         [0009]    In another embodiment the invention provides the follower body having a first end portion configured to couple to the engine, a second end portion configured to couple to the valve of the engine, and an aperture formed in the first end portion. The latching mechanism includes a base portion, a piston movable relative to the base portion between an extended position and a retracted position, and a biasing member. The biasing member is coupled between the base portion and the piston to bias the piston toward the retracted position, and the base portion, the piston, and the biasing member are at least partially located within the aperture. 
         [0010]    In yet another embodiment the invention provides the latching mechanism having an engagement surface and the cam follower having an engagement surface configured to engage the engagement surface of the latching mechanism. At least one of the engagement surfaces is at least partially convex. 
         [0011]    In yet another embodiment the invention provides the latching mechanism at least partially defining a fluid chamber, and the finger follower assembly further including a vent passageway formed in the first end portion of the follower body and providing selective fluid communication between the fluid chamber and an outer surface of the follower body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  is a perspective view of a camshaft and a finger follower assembly embodying the present invention. 
           [0013]      FIG. 2  is an exploded view of the finger follower assembly of  FIG. 1 . 
           [0014]      FIG. 3  is a cross section view of the finger follower assembly of  FIG. 1  taken along lines  3 - 3  of  FIG. 14 . 
           [0015]      FIG. 4  is a cross section view of the finger follower assembly of  FIG. 1  taken along lines  4 - 4  of  FIG. 14  illustrating a piston of the finger follower assembly in a retracted position. 
           [0016]      FIGS. 5-6  are perspective views of a lateral cam follower of the finger follower assembly of  FIG. 1 . 
           [0017]      FIG. 7  is an end view of the lateral cam follower of  FIG. 5 . 
           [0018]      FIG. 8  is a side view of the lateral cam follower of  FIG. 5 . 
           [0019]      FIG. 9  is a cross section view of the finger follower assembly of  FIG. 1  taken along lines  9 - 9  of  FIG. 14  illustrating the piston between the retracted position and an extended position. 
           [0020]      FIG. 10  is a perspective view of a latching mechanism of the finger follower assembly of  FIG. 1  illustrating the piston in the retracted position. 
           [0021]      FIG. 11  is a bottom view of the latching mechanism of  FIG. 10 . 
           [0022]      FIG. 12  is a perspective view of the latching mechanism of  FIG. 10  illustrating the piston in the extended position. 
           [0023]      FIG. 13  is a bottom view of the latching mechanism of  FIG. 12 . 
           [0024]      FIG. 14  is a perspective view of the finger follower assembly of  FIG. 1  illustrating the piston in the retracted position. 
           [0025]      FIG. 15  is a cross section view of the finger follower assembly of  FIG. 14  taken along lines  15 - 15  of  FIG. 14 . 
           [0026]      FIG. 16  is a cross section view of the finger follower assembly of  FIG. 14  taken along lines  16 - 16  of  FIG. 14 . 
           [0027]      FIG. 17  is a perspective view of the finger follower assembly of  FIG. 1  illustrating the piston in the extended position. 
           [0028]      FIG. 18  is a cross section view of the finger follower assembly of  FIG. 17  taken along lines  18 - 18  of  FIG. 17 . 
           [0029]      FIG. 19  is a cross section view of the finger follower assembly of  FIG. 17  taken along lines  19 - 19  of  FIG. 17 . 
           [0030]      FIG. 20  is a perspective view of the finger follower assembly of  FIG. 1  illustrating the piston in the extended position and the lateral cam follower in a downward position. 
           [0031]      FIG. 21  is a cross section view of the finger follower assembly of  FIG. 20  taken along lines  21 - 21  of  FIG. 20 . 
           [0032]      FIG. 22  is a cross section view of the finger follower assembly of  FIG. 20  taken along lines  22 - 22  of  FIG. 20 . 
           [0033]      FIG. 23  is a perspective view of an alternative construction of the finger follower assembly of  FIG. 1 . 
           [0034]      FIGS. 24-32  are cross section views of the finger follower assembly of  FIG. 23  taken along lines  23 - 23  through  32 - 32 , respectively, of  FIG. 23 . 
       
    
    
       [0035]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In addition, the invention will be described with reference to the accompanying drawing figures wherein like numbers represent like elements throughout. Certain terminology, for example, “top”, “bottom”, “right”, “left”, “front”, “frontward”, “forward”, “back”, “rear”, “rearward”, “upwardly” and “downwardly” is used in the following description for relative descriptive clarity only and is not intended to be limiting. 
       DETAILED DESCRIPTION  
       [0036]      FIG. 1  illustrates a finger follower rocker assembly  30  for use with an internal combustion engine having a camshaft assembly  32 . The camshaft assembly  32  includes a camshaft  34  that rotates about an axis  36 . The illustrated camshaft assembly  32  includes a plurality of cam assemblies  38  that are coupled to the camshaft  34  for rotation with the camshaft  34 . Each of the cam assemblies  38  includes a central cam lobe  40 , a first lateral cam lobe  42  and a second lateral cam lobe  44 . The first and second lateral lobes  42  and  44  are adjacent the central lobe  40 . Each of the cam lobes  40 ,  42 ,  44  includes a perimeter surface  46  and side walls  48  that are generally normal to the perimeter surface  46 . In the illustrated construction, the central cam lobe  40  has a larger profile or outer dimension than the lateral cam lobes  42  and  44  such that the central cam lobe  40  includes side wall portions  48  that extend beyond the perimeter surfaces  46  of the lateral cam lobes  42  and  44 . In the illustrated construction, the internal combustion engine further includes a lash adjuster  50  and an engine valve  52 . 
         [0037]    Referring to  FIGS. 2 and 4 , the finger follower assembly  30  includes a follower body  54 , a follower assembly  56 , and a latching mechanism  58 . The follower body  54  includes a first end portion  60  and a second end portion  62 . The first end portion  60  includes a concave socket  64  and a bore  66 . The concave socket  64  couples to an engine through the lash adjuster  50  ( FIG. 1 ). As best seen in  FIG. 4 , the bore  66  partially receives the latching mechanism  58 . The illustrated bore  66  is generally cylindrical and defines an inner dimension D 1  that is generally constant. The second end portion  62  is coupled to the valve  52  ( FIG. 1 ). 
         [0038]    Referring to  FIGS. 2 and 3 , the follower body  54  further includes opposed side walls  68  that extend between the end portions  60 ,  62 . The illustrated side walls  68  partially define an aperture  70  between the first and second end portions  60 ,  62 . The side walls  68  include an inner surface  72  that defines an inner width W 1  of the aperture  70  and an outer surface  74  that defines an outer width W 2  of the follower body  54 . The side walls  68  each further include an aperture  76 . The apertures  76  of the side walls  68  are aligned such that apertures  68  receive a shaft  78  having a shaft axis  79 . 
         [0039]    Referring to  FIGS. 2 and 4 , the follower assembly  56  includes a lateral cam follower  80  and a central cam follower  82 . The central cam follower  82  includes an inner cylindrical race  84  and an outer cylindrical race  86  with rolling elements  88  positioned therebetween such that the outer cylindrical race  86  is rotatable about the shaft axis  79 . In the illustrated construction, the inner cylindrical race  84  is coupled to the shaft  78  using a loose fit such that the inner cylindrical race  84  is movable along the shaft axis  79  and around the shaft axis  79 , the purpose of which will be discussed below. 
         [0040]    Referring to FIGS.  3  and  5 - 8 , the lateral follower  80  has a body portion  90  with a through bore  92  that receives the shaft  78  to couple the lateral follower  80  to the follower body  54 . The lateral follower  80  pivots or rotates about the shaft  78  and is movable along the shaft  78  in a direction parallel to the shaft axis  79 . 
         [0041]    Referring to  FIGS. 8 and 9 , the body portion  90  of the lateral follower  80  further includes an actuator receiving aperture  94 . The actuator receiving aperture  94  is partially defined by a downwardly facing surface  96 . As best seen in  FIG. 9 , the downwardly facing surface  96  of the lateral follower  80  is at least partially convex (e.g., radiused, logarithmic profile, etc.) such that the surface  96  defines a crowned profile when viewed in the cross section illustrated in  FIG. 9 , the purpose of which will be discussed below. 
         [0042]    As best seen in  FIGS. 3 and 7 , the body portion  90  of the lateral follower  80  defines a width W 3  that is less than the inner width W 1  of the aperture  70  such that there are gaps  98  between the inner surfaces  72  of the follower body walls  68  and the body portion  90  of the lateral follower  80 . While  FIG. 3  illustrates the gaps  98  with a substantially equal length L 1 , the follower body  90  is movable in a direction parallel to the shaft axis  79  such that the length L 1  of the gaps  98  can vary. 
         [0043]    Referring to  FIGS. 5-8 , the lateral follower  80  further includes first and second contact portions  100 ,  102  that extend upwardly from the body portion  90  to define a gap  104  therebetween. The contact portions  100 ,  102  each include a convex contact surface  106 ,  108  respectively, having a width W 4 , W 5 , respectively. In one construction the widths W 4  and W 5  both are approximately 8.25 mm. In other constructions, the widths W 4  and W 5  can be greater than or less than 8.25 mm. 
         [0044]    Referring to  FIG. 3 , in the illustrated construction, a ratio of the total width of the contact surfaces  106  and  108  (W 4 +W 5 ) to the outer width W 2  of the follower body  54  (i.e., (W 4 +W 5 )/W 2 ) is approximately 70%. In other constructions the ratio can be greater or less than 70%. 
         [0045]    As best seen in  FIGS. 5-7 , the first and second contact portions  100  and  102  further define lateral contact portions  110  and  112 , respectively. The lateral contact portions  110  and  112  are generally normal to the convex contact surfaces  106  and  108 , respectively, and the lateral contact portions  110  and  112  partially define the gap  104  between the contact portions  100  and  102 . 
         [0046]    Referring to  FIGS. 3 and 5 , the body portion  90  of the lateral follower  80  further defines a generally centrally located slot  114  that receives and retains the central follower  82  partially within the body portion  90  of the lateral follower  80 . 
         [0047]    The illustrated lateral follower  80  is integrally formed as a single piece, such as by casting, molding, machining and the like. In other constructions, the lateral follower  80  can be a two-piece design, such that the first and second contact portions are separate components. In such constructions, the contact portions and can be interconnected by a member such that the contact portions are coupled for co-rotation about the shaft  78  and movement along the shaft axis  79 . 
         [0048]    Referring to  FIGS. 1 and 3 , when the follower assembly  30  is assembled with the camshaft assembly  32 , the central lobe  40  of the cam assembly  38  is received in the gap  104  between the first and second contact portions  100  and  102  of the lateral follower  80 . Thus, the central lobe  40  is captured between the contact portions  100  and  102  of the lateral follower  80 . Because the central lobe  40  has a larger profile than the lateral lobes  42  and  44 , the side wall portions  48  of the central lobe  40  are available to pilot the lateral contact portions  110  and  112  of the lateral follower  80  at all rotational positions of the lateral follower  80  and the camshaft  34 . Due to manufacturing tolerances or variations and thermal expansions or contractions, the location of the cam assembly  38  can vary along the camshaft axis  36 . However, because the lateral follower  80  pilots on the central lobe  40 , the central lobe  40  can contact either of the lateral contact surfaces  110  or  112  of the lateral follower  80  to move the lateral follower  80  relative to the valve  52  and within the follower body  54  to maintain proper relative position of the lateral follower contact surfaces  106  and  108  with respect to the lateral lobes  42  and  44 . The gaps  98  between the follower body  54  and the lateral follower body  90  allow the lateral follower  80  to move in a direction parallel to the shaft axis  79  along the shaft  78 . Furthermore, because the lateral follower  80  is one piece, the entire lateral follower  80  will move in a direction parallel to axis  79  along the shaft  78 . In addition, the central follower  82 , which is retained in the slot  114  of the lateral follower  80 , will move in a direction parallel the shaft axis  79  with the lateral follower  80 . Therefore, the central follower  80  maintains proper alignment with the central lobe  40 . Such movement of the central follower  80  is facilitated by the loose fit of the inner race  84  of the central follower  82  on the shaft  78 . 
         [0049]    Because the lateral follower  80  pilots in this manner on the central lobe  40 , the lateral follower  80  and central follower  82  remain aligned with the cam assembly  38  regardless of the manufacturing variations or thermal variations that may change the position of the cam assembly  38 . Such as feature allows the widths W 4  and W 5  of the contact surfaces  106  and  108  to be maximized such that the widths W 4  and W 5  of the contact surfaces  106  and  108  are generally equal to the width of the perimeter surfaces  46  of the lateral lobes  42  and  44 , respectively, and the contact surfaces  106  and  108  generally contact the lateral lobes  42  and  44 , respectively, along their entire width W 4  and W 5 . Generally, it is desirable to increase the width of the contact between the lateral lobes  42  and  44  and the contact surfaces  106  and  108  so that the lateral follower  80  is capable of carrying a larger valve lift load. Because the lateral follower  80  can move along the shaft  78  in response to a change in position of the cam assembly  38 , the lateral lobes  40  and  42  and both of the contact surfaces  106  and  108  remain aligned to facilitate contact along substantially the entire width of the contact surfaces  106  and  108 . 
         [0050]    Referring to  FIGS. 3 and 14 , a biasing member  116  is coupled to the follower body  54  and the lateral follower  80  such that the biasing member  116  biases the lateral follower  80  about the axis  79  of the shaft  78  upwardly in the direction of arrow  117  ( FIG. 14 ). In the illustrated construction, the biasing member  116  is a torsion spring. In other constructions, the biasing member can take other suitable forms. 
         [0051]    Referring to  FIG. 2 , the illustrated latching mechanism  58  includes a piston  120 , a biasing member  122 , a shaft  124 , and an end cap or base  126 . Referring to  FIG. 9 , the piston  120  is a generally cylindrical member that includes a blind bore  128 . As illustrated, the portion of the piston  120  received in the bore  66  has a generally constant outer dimension. The piston  120  further includes a locking projection  130  that extends from an end of the piston  120 . The locking projection  130  includes an upwardly facing surface  132  and a downwardly facing surface  134 . As best seen in  FIG. 9 , the upwardly facing surface  132  of the locking projection  130  is generally planar. 
         [0052]    Referring to  FIGS. 9 and 17 , the illustrated piston  120  further includes vent apertures  136  that extend through the piston  120  and provide fluid communication between piston bore  128  and the exterior of the finger follower assembly  30 . 
         [0053]    Referring to  FIGS. 9-13 , the piston  120  farther includes a slot  138  that provides fluid communication between the concave socket  64  and the bore  128  of the piston  120 . The slot  138  receives a tang or tab  140  that extends from the base  126 . When the finger follower  30  is assembled, the base  126  is generally fixed with respect to the follower body  54  and the tang  140  engages the slot  138  to limit the amount of rotational movement of the piston  120  about the shaft  124 . As best seen in  FIG. 11 , there is a gap  142  or clearance between the tang  140  and the piston  120  to provide only a limited amount of rotational movement of the piston  120  with respect to the base  126  and follower body  54 . Referring to  FIG. 9 and 11 , the gap  142  allows the piston  120  to rotate in order to align the upwardly facing surface  132  of the piston  120  and the downwardly facing surface  96  of the lateral follower  80  when the surfaces  132  and  96  engage such that the surfaces  132  and  96  are generally parallel ( FIG. 23 ). However, the slot  138  restricts rotation of the piston  120  in order to ensure that the locking projection  130  can be received in the aperture  94  of the lateral follower  80 . 
         [0054]    Referring to  FIG. 9 , the shaft  124  includes a first end portion  148  and a second end portion  150 . The second end portion  150  includes a recess  152  that receives a clip  154  to couple the base  126  to the shaft  124 . The first end portion  148  includes an enlarged end portion or shoulder  156  that acts as a stop for the biasing member  122 . The illustrated biasing member  122  is a tapered coil spring. The biasing member  122  includes a first end  157   a  and a second end  157   b  and the biasing member  122  is tapered such that the outer dimension of the coil spring is smaller at the first end  157   a  and larger at the second end  157   b . The first end  157   a  of the biasing member  122  acts against the enlarged end portion  156  of the shaft  124  and the second end  157   b  of the biasing member  122  acts against a washer member  158  that is between the second end  157   b  of the biasing member  122  and a clip  160  that is received in a recess  162  formed in the piston  120 . The biasing member  122  biases the piston  120  toward the retracted or unlatched position shown in  FIG. 16 . 
         [0055]    Referring to  FIG. 9 ,  13 , and  14 , the illustrated latching mechanism  58  is a generally fully self contained latching mechanism that is received in the bore  66  formed in the first end portion  60  of the follower body  54 . The illustrated latching mechanism  58  has a relatively low mass moment of inertia because of the compact nature of the latching member  58 . The low mass moment of inertia of the finger follower  30  is also facilitated by the latch mechanism  58  being located relatively close to spherical socket  64 , which is the location where the finger follower  30  pivots. 
         [0056]    As best seen in  FIGS. 14 and 15 , when the latching mechanism  58  is assembled with the follower body  54 , the biasing member  116  of the lateral follower  80  is able to contact the engagement portion  130  of the piston  120 . Therefore, regardless of the axial location of the lateral follower  80  with respect to the shaft  78  or whether the piston  120  is in the retracted or extended position, the biasing member  116  does not block the piston  120  from moving into to the aperture  94  of the lateral follower  80 . 
         [0057]    Referring to  FIG. 1 , during operation of the engine, the camshaft  34  rotates about the camshaft axis  36  and oil is supplied from a pressurized source to the finger follower assembly  30  through the lash adjuster  50 . 
         [0058]    Referring to FIG.  1  and  14 - 16 , oil enters the finger follower assembly from the lash adjuster  50  and passes through an aperture  144  between the socket  64  and the bore  66 , and then passes through the slot  138  in the piston  120 . When low lift of the engine valve  52  is desired, the oil supplied to the finger follower  30  is at a relatively low pressure. Therefore, the biasing member  122 , which has a natural tendency to expand in the illustrated construction, retains the piston  120  in the unlatched or retracted position ( FIGS. 15-17 ). 
         [0059]    With the piston  120  in the unlatched position, the high lift or lateral lobes  42  and  44  will contact surfaces  106  and  108  of the lateral follower  80  and cause a pivoting force on the lateral follower  80 . In the unlocked condition, the lateral follower  80  simply pivots about the shaft axis  79  without imparting any significant force on the finger body  54 . The lateral follower  80  is biased toward the lateral lobes  42  and  44  by the biasing member  116  and therefore the contact surfaces  106  and  108  generally remain in contact with the lateral lobes  42  and  44 . Meanwhile, the central or low lift lobe  40  contacts the central follower  82  to cause the outer race  86  to rotate about the shaft  78 . The lift of the valve  52  is controlled by the low lift lobe  40  through the central follower  82 . 
         [0060]    Referring to  FIG. 9 , the loose fit of the inner race  84  on the shaft  78  enables relative rotational and axial movement of the inner race  84  with respect to the shaft  78 . Relative rotational motion of the inner race  84  with respect to the shaft  78  allows the inner race  84  to precess with respect to the shaft  78 . Precessing of the inner race  84  extends the life of the central follower  82  because the number of fatigue cycles at any given portion of the inner race  84  is reduced. 
         [0061]    Referring to FIGS.  1  and  17 - 19 , when high lift of the engine valve  52  is desired, the oil supplied from the lash adjuster  50  increases. Once the oil pressure is at a sufficient pressure to compress the biasing member  122 , the piston  120  moves from the retracted or unlatched position ( FIG. 16 ) to the extended or latched position ( FIG. 19 ). 
         [0062]      FIG. 9  illustrates the piston  120  in a partially extended position. The tapered biasing member  122  facilitates travel of the oil, generally indicated by the arrows  170 , around the biasing member  122  in order to allow the pressurized oil to extend the piston  120 . 
         [0063]    Referring to FIGS.  1  and  17 - 19 , in the extended position the locking projection  130  of the piston  120  extends into the aperture  94  of the lateral follower  80  thereby interconnecting the lateral follower  80  and the follower body  54 . Thus, as the lateral or high lift lobes  42  and  44  contact the lateral follower  80  the finger follower assembly  30  pivots on the lash adjuster  50  to provide relatively high lift of the engine valve  52 . Meanwhile, a limited amount of oil is allowed to escape from the bore  126  of the piston  120  through the vent apertures  136  to provide lubrication for the lateral follower  80 , the central follower  82 , and the cams  40 ,  42 , and  44 . 
         [0064]    Referring to  FIGS. 9 ,  19 , and  22 , when the locking projection  130  is received within the aperture  94  of the lateral follower  80  there is clearance between the locking projection  130  and the lateral follower  80  to allow the locking projection  130  to be received within the aperture  94  without resistance. Therefore, when the lateral lobes  42  and  44  push downwardly on the lateral follower  80 , the lateral follower  80  rotates from the position of  FIG. 19  to the position of  FIG. 22 , where the convex downwardly facing engagement surface  96  ( FIG. 9 ) of the lateral follower  80  contacts the planar upwardly facing engagement surface  132  of the piston  120 . The convex curvature of the downwardly facing surface  96  minimizes the stress concentrations created between the engagement surfaces  96 ,  132  when the lateral follower  80  is forced into contact with the piston  120 , regardless of manufacturing variation that would cause the surfaces  96 ,  132  to contact in slightly different orientations. 
         [0065]    Referring to  FIGS. 9 and 16 , when the oil pressure is decreased to a pre-determined level, the spring  122  begins to expand to move the piston  120  back to the retracted or unlatch position ( FIG. 16 ). Excess oil within the bore  128  of the piston  120  vents through the vent apertures  136  or through other passageways created between the latching mechanism  58  and the follower body  54 . With the piston  120  in the retracted position, the lateral follower  80  pivots with respect to the follower body  54  and the engine valve  52  is returned to low lift operation. 
         [0066]      FIGS. 23-32  illustrate an alternative construction of the finger follower assembly  30  of  FIGS. 1-22 . The finger follower assembly  230  of  FIGS. 23-32  is substantially the same as the finger follower assembly  30  of  FIG. 1-22  and like components have been given like reference numbers plus  200  and only the general differences will be discussed below. 
         [0067]    The illustrated latching mechanism  258  is of a slightly different construction from the latching mechanism  58  described above. The biasing member  322  is of a different configuration having a generally cylindrical coil diameter instead of the tapered diameter of the biasing member  122 . Additionally, hooked ends  322   a  and  322   b  engage respective pins  379   a  and  379   b  that are coupled to the end cap  326  and the piston  320 , respectively. 
         [0068]    Referring to  FIGS. 26 and 27 , the finger follower assembly  230  includes a fluid venting system  380 . The fluid venting system  380  includes a vent passageway  382 , a secondary passageway  384 , and a tertiary passageway  386  formed in the follower body  254 . 
         [0069]    The vent passageway  382  is in fluid communication with a fluid chamber  381  defined by the end cap or base  326 , the bore  328  of the piston  320 , and the bore  266  of the follower body  254  depending on the location of the piston  320 . A plug  388  is located within the vent passageway  382  to substantially prevent fluid communication through the vent passageway  382  past the plug  388 . 
         [0070]    The secondary passageway  384  is adjacent the vent passageway  382 . As best seen in  FIG. 27 , the secondary passageway  384  extends to the concave socket  264  such that the secondary passageway  384  is in fluid communication with the source of pressurized fluid supplied from the lash adjuster  50  of  FIG. 1 . 
         [0071]    Referring to  FIG. 26 , a vent piston  390  is located within the secondary passageway  384 . The vent piston  390  is biased in the direction of the arrow  392  by a biasing member  394  that acts against a plug  396 . 
         [0072]    In the illustrated construction, the tertiary passageway  386  is generally normal to the vent passageway  382  and the secondary passageway  384 . The tertiary passageway  386  provides fluid communication between the vent passageway  382 , the secondary passageway  384 , and the outside of the finger follower  230 . 
         [0073]      FIGS. 26 and 27  illustrate the piston  320  in the recessed or unlatched position such that the finger follower  230  is operating in the low valve lift mode of operation. As best seen in  FIG. 26 , the oil pressure is insufficient to move the vent piston  390  against the bias of the biasing member  394 . 
         [0074]    As illustrated in  FIGS. 28 and 29 , as the oil pressure and oil flow from the lash adjuster  50  of  FIG. 1  increases, the piston  320  begins to extend from the bore  266 . In addition, the increased oil flow and pressure, generally indicated by the arrow  395 , moves the vent piston  390  against the force of the biasing member  394  until the vent piston  390  contacts the plug  388 . As the vent piston  390  moves from the position of  FIG. 26  to the position of  FIG. 28  air or fluid between the plug  396  and the vent piston  390  is allowed to escape through an aperture  397  defined by the plug  396 . With the vent piston  390  in the position illustrated  FIG. 28 , fluid communication is inhibited through the vent passageway  382  and the secondary passageway  384  due to the blockage created by the vent piston  390 . 
         [0075]    As illustrated in  FIGS. 30 and 31 , when the piston  320  moves to the fully extended position (i.e., high valve lift mode), the piston  320  uncovers the vent passageway  382  and oil flows into the vent passageway  382 , generally indicated by the arrow  398 . However, as best seen in  FIG. 30 , the vent piston  390  substantially prevents escape of oil from the vent passageway  382  through the tertiary passageway  386 . Therefore, adequate oil pressure is maintained within the fluid chamber  381  to maintain the piston  320  in the extended or latched position, which allows the finger follower assembly  230  to operate the engine valve  52  ( FIG. 1 ) in the high lift mode. 
         [0076]    Referring to  FIG. 23 and 25 , during both the high lift and low lift modes of operation (i.e., piston  320  extended and retracted, respectfully) oil is allowed to escape from the fluid chamber  381  through the vent apertures  336  to provide lubrication to the lateral follower  280 , central follower  282 , and the cam lobes. During the high lift mode, the oil is supplied by the lash adjuster  50  ( FIG. 1 ) at a sufficient quantity and pressure such that the oil that escapes through the vent apertures  336  does not substantially reduce the oil pressure in the fluid chamber  381  such that the piston biasing member  322  retracts the piston  320 . 
         [0077]    Referring to  FIGS. 32 and 33 , when the finger follower assembly  230  returns to the low lift mode of operation, the oil pressure in the fluid chamber  381  decreases because of the lower pressure supplied by the lash adjuster  50  ( FIG. 1 ). As the oil pressure decreases, the vent plug biasing member  394  overcomes the pressure of the oil to move the vent piston  390  back to the position illustrated in  FIG. 32 . Therefore, oil within the vent passageway  382  and the fluid chamber  381  flows, as generally indicated by the arrow  398 , from the vent passageway  382  through the tertiary passageway  386  to the exterior of the finger follower assembly  320 . Therefore, oil is quickly evacuated from the fluid chamber  381 , allowing the piston biasing member  322  to return the piston  320  to the retracted position more rapidly than if the finger follower assembly included only the vent passageways  336  ( FIG. 23 ). In an alternative embodiment, the vent apertures  336  can be eliminated and the finger follower assembly and cam assembly can be lubricated using oil from other passageways created in the finger follower assembly. 
         [0078]    Various features and advantages are set forth in the following claims.