Patent Publication Number: US-6668779-B2

Title: Two-step finger follower rocker arm assembly

Description:
RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS 
     The present application claims the benefit of U.S. Provisional Application, Ser. No. 60/378,852, filed May 8, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates to mechanisms for altering the actuation of valves in internal combustion engines; more particularly, to finger follower type rocker arms having means for changing between high and low or no valve lifts; and most particularly, to a two-step finger follower type rocker arm assembly, having a fixed central cam follower and a pair of pivotable lateral cam followers disposed on the finger follower body, and having locking means for latching and unlatching the lateral cam followers from the finger follower body to shift between high lift and low lift modes. 
     BACKGROUND OF THE INVENTION 
     Variable valve activation (VVA) mechanisms for internal combustion engines are well known. It is known to be desirable to lower the lift, or even to provide no lift at all, of one or more valves of a multiple-cylinder engine, especially intake valves, during periods of light engine load. Such deactivation can substantially improve fuel efficiency. 
     Various approaches have been disclosed for changing the lift of valves in a running engine. One known 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, the cam shaft typically having 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 onto a camshaft during engine assembly. 
     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. 
     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. 
     U.S. Pat. No. 5,655,488 issued Aug. 12, 1997, discloses a system including an inner rocker arm in engagement with a valve and with a first cam, an outer rocker arm in engagement with a second cam, and a latch member which is insertable between the rocker arms. A significant drawback of the disclosed apparatus is that the latching mechanism is a relatively large box-like member which “essentially surrounds” the outer rocker arms, thereby increasing undesirably the mass and inertia of the rocker assembly. Another drawback is that its outer rocker arms are inter-connected and move in unison thereby increasing the mass and inertia of the moving members. 
     It is a principal object of the present invention to provide a simplified variable valve lift apparatus. 
     It is a further object of the invention to provide an increased range of motion between a high lift and a low lift position of an engine valve. 
     SUMMARY OF THE INVENTION 
     Briefly described, a two-step finger follower rocker arm assembly in accordance with the invention is configured to cooperate with an engine camshaft having both high-lift and low-lift cam lobes. For each valve of the valve train equipped with the present rocker arm assembly, a central low-lift cam lobe is accompanied by at least one high-lift lobe and preferably is flanked symmetrically by a pair of lateral high-lift lobes. 
     The present rocker arm assembly includes an elongate, rigid follower body that has a socket at a first end for engaging a conventional hydraulic lash adjuster as a pivot means, and that has an arcuate pad at a second and opposite end for engaging a valve stem or lifter means. A central well or passage through the follower body contains means, preferably in the form of a fixed slider or roller, for following the central low-lift cam lobe to provide low-lift of the valve when engaged therewith. Outboard of the follower body and pivotably mounted thereupon are first and second lateral high-lift followers, including sliders or rollers, for following the lateral high-lift lobes to provide high-lift of the valve. A latch block disposed on the body is slidable by piston and spring means between first and second positions to alternatively latch and unlatch the high-lift followers. In latched position, the rocker arm assembly acts in high-lift mode; in unlatched position, in low-lift mode. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is an exploded isometric view from a first direction of a first embodiment of a two-step finger follower rocker arm assembly in accordance with the invention; 
     FIG. 1 a  is a view like that shown in FIG. 1 showing a second embodiment of a central follower means; 
     FIG. 2 is an isometric view of the rocker arm assembly shown in FIG. 1 after assembly and taken from a second direction, showing lateral followers in unlatched position, the assembly being in low-lift mode; 
     FIG. 3 is an isometric view like that shown in FIG. 2, showing the followers in latched position, the assembly being in high-lift mode; 
     FIG. 4 is an elevational cross-sectional view of a second embodiment of a rocker arm assembly similar to the assembly shown in FIGS. 1 through 3 but including a guide pin for alignment of the latch block during actuation thereof, installed schematically in an internal combustion engine; 
     FIG. 5 is an exploded isometric view from the first direction of the second embodiment shown in FIG. 4; 
     FIG. 6 is an isometric view of the rocker arm assembly shown in FIG. 5 after assembly; and 
     FIG. 7 is an isometric view of a second embodiment of a lateral follower. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A two-step finger follower rocker arm assembly in accordance with the invention is configured to cooperate with an engine camshaft having both high-lift and low-lift cam lobes. For each valve of the valve train equipped with the present rocker arm assembly, a low-lift cam lobe is accompanied by at least one high-lift lobe. In the description below, the rocker arm assembly is configured to cooperate with a cam arrangement wherein a central low-lift lobe is flanked symmetrically by a pair of lateral high-lift lobes. 
     Referring to FIGS. 1 through 4, a first embodiment  10  of a two-step finger follower rocker arm assembly used in internal combustion engine  17  in accordance with the invention includes a longitudinal follower body  12  having spherical socket  14  at a first end  16  for pivotably mounting onto an engine pivot means such as a conventional hydraulic lash adjuster (HLA)  18 . At a second end  20  of body  12  is an arcuate pad  22  for engaging and actuating a valve stem  24  or other valve-actuation linkage such as a lifter. An upper surface  21  of body  12  is provided with means for following a central low-lift cam lobe  23  of camshaft  27 . Such means may comprise a conventional slider surface (not shown), but is preferably a vertically transverse well or passage  26  in body  12  containing a conventional roller bearing assembly  28  comprising an outer race  30  and roller or needle bearings  32 . Bearing assembly  28  is rotatably supported in well  26  by a first cross-shaft  34  fixedly disposed in first bores  36  in body  12  along first axis  38 . 
     A second cross-shaft  40  is disposed in second bores  42  in body  12  along a second axis  44  parallel to first axis  38 . Shaft  40  extends beyond body  12  to support first and second lateral high-lift cam followers  46   a , 46   b  at a first end  47  thereof. Between followers  46   a , 46   b  and body  12  are disposed lost motion springs  48   a , 48   b , respectively, which urge followers  46   a , 46   b  in a counter-clockwise direction, as seen in FIGS. 1 through 3, to maintain contact between the followers and high-lift cam lobes  25  (FIG.  4 ). Cam followers  46   a , 46   b  may be fixedly attached to shaft  40 , and shaft  40  may be provided with bearings (not shown) in known fashion such that shaft  40  is rotatable in bore  42 ; or the shaft may be fixed in the bore and the cam followers provided with bearings for rotation thereupon, to equal effect. Lateral cam followers  46   a , 46   b  are preferably provided with curved upper surfaces  50  for following high-lift lobes  25 ; however, if desired, either or both of the followers ( 46 ′) may be modified as shown in FIG. 7 to include a roller  52  disposed in a well  53  on a cross shaft  54 . In either case, the maximum width of assembly  10  is defined by the distance  11  along shaft  40  between respective first and second outer surfaces  13 , 15  (FIG. 2) of lateral followers  46   a , 46   b , which coincides with the axial direction of cam lobes  23 , 25 . 
     A longitudinal latch block  56  is formed to slide along upper surface  21  of body  12 . Block  56  has a central opening  58  in slider element  60  to accommodate bearing assembly  28  protruding through and further has a latching head  62  extending substantially orthogonally from the plane of element  60 .  30  Latching head  62  is formed having first and second latches  64   a , 64   b  extending into the rotary plane of actuation of lateral followers  46   a , 46   b , respectively, and having first and second latching surfaces  66   a , 66   b  for latchingly engaging mating latching surfaces  68   a , 68   b  on noses  70   a , 70   b  of followers  46   a , 46   b  when the latches are moved into interference with the noses, said noses being formed at respective second ends  55  of said lateral followers. 
     Latch block  56  is further provided with a yoke  72  extending orthogonally from element  60  for capturing and retaining an actuating piston assembly  74  in a recess  76  in body  12 , as shown in FIG.  4 . Recess  76  is connected via passage  78  to hollow hydraulic lash adjuster  18 , whereby pressurized oil may be supplied to piston assembly  74  as desired to urge latch block  56  along surface  21  and latching head  62  toward body  12 . At the outward extent of piston travel, latches  64   a , 64   b  are brought into interference with noses  70   a , 70   b . If lateral followers  46   a , 46   b  are depressed, as shown in FIG. 2, by being temporarily engaged with the eccentric portion  80  of high-lift lobes  25 , then the latches are temporarily biased against the noses. When lobes  25  rotate such that eccentric portions  80  of high lift lobes  25  move away from follower surfaces  50  of followers  46   a , 46   b , lost motion springs  48   a , 48   b  raise the followers into latching position and the piston bias slides latching surfaces  66   a , 66   b  of latches  64   a , 64   b  into latching relationship with latching surfaces  68   a , 68   b  of noses  70   a , 70   b  (FIG.  3 ). Body  12  preferably is provided with a shelf extension  84  (FIG.1) for supporting latching head  62 . Preferably, body  12  is further provided with an end bore  86  and latch block  56  is provided with an alignment stud  88  to align the latching head during latching movement of the latch block. Stud  88  is slidingly entered into bore  86  at all positions of travel of latching head  62 . A return spring  90  (omitted for clarity from FIG. 1 but shown in FIG. 5) is disposed in compression between latching head  62  and body  12  to unlatch the assembly when pressure is reduced from piston assembly  74 . When the lateral high-lift followers are unlatched, they continue to follow the high-lift cam lobe through lost motion. However, as eccentric portions  80  move away from surfaces  50  of followers  46   a , 46   b , travel stop pins  51  (only one shown in FIG. 3) restrict counter clockwise rotation of lateral followers  46   a , 46   b  thereby preventing follower surfaces  50  of followers  46   a , 46   b  from remaining in contact with base circle portions  82  of high lift cam lobes  25 . This momentary break from contact with surfaces  50  facilitates distribution of lubricating oil to the mating surfaces. 
     Referring to FIG. 1 a , in some applications it can be desirable to substitute a simple fixed central slider surface  28 ′ for roller assembly  28  in providing for engagement with central cam lobe  23 . 
     Referring to FIGS. 4 through 6, in an alternative embodiment of an alignment arrangement, end bore  86 ′ includes a boss  92  for centering and retaining an alignment pin  94  that extends through a mating alignment bore  96  in latching head  62 . Referring to FIG. 4, in an alternative embodiment of a latch block, latch block  56 ′ is provided in two separate and inexpensive components. A slider element  60 ′ is formed as by stamping from sheet metal and includes a first integral yoke  72 ′ for retaining piston assembly  74  and a second integral yoke  98  for retaining a separate latching head  62 ′ held in place against yoke  98  by return spring  90 . 
     In all of the various embodiments and arrangements, an important consideration is that the two lateral followers both latch with certainty. If either one fails to latch when the other does, substantial damaging torque may be applied to the assembly  10 . This can happen when the locking head is just starting to engage the lateral followers when the high-lift event begins. If there is not enough or only partial engagement, one or both of the lateral followers can slip off the locking head. This is known in the art as an “ejection.” To counteract this, preferably the noses  70   a , 70   b  of the lateral followers are radiused  75  in such a way (FIG. 6) that if one of the followers ejects, it will push the locking head back and cause the other arm to eject as well. 
     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. 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.