Patent Publication Number: US-6668775-B2

Title: Lock-pin cartridge for a two-step finger follower rocker arm

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 10/121,720, filed Apr. 12, 2002, now U.S. Pat. No. 6,615,782. 
    
    
     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 pre-assembled lock-pin cartridge for a two-step finger follower type rocker arm having a slider member disposed in a finger follower body for sliding motion in the direction of lift between high and low positions, the cartridge having a locking pin operative in an orthogonal bore in the finger follower body for latching and unlatching the slider member and 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. 
     It is a principal object of the present invention to provide a simplified variable valve lift apparatus wherein maufacturing assembly is simplified and cost is reduced by incorporation of a pre-assembled lock-pin cartridge. 
     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 includes an elongate, rigid follower body having a socket at a first end for engaging a conventional hydraulic lash adjuster as a pivot means, and having an arcuate pad at a second and opposite end for engaging a valve stem or lifter means. A passage through the follower body in the direction of actuation by an engine cam lobe is slidingly receivable of a slider member for variably engaging a central cam lobe, preferably a high-lift lobe. A transverse bore in the follower body intersects the passage. A slotted passage is provided in the slider member, and an elongate pin extends through the bore in the body and through the slotted passage in the slider member such that the length of travel of the slider member in the passage is at least the length of the slotted passage therein. Outboard of the follower body, the pin is provided on either side of the body with first and second identical lateral roller followers, preferably rotatably mounted in bearings on the pin, for variably engaging first and second lateral cam lobes, preferably low-lift lobes, flanking the central cam lobe. A lost-motion spring urges the slider member into contact with the central lobe, and the hydraulic lash adjuster urges the lateral rollers into contact with the lateral lobes when the slider member is unlatched. A transverse locking pin can selectively engage and lock the slider member to the follower body such that the follower follows the motion of the central cam lobe. When the locking pin is disengaged from the slider member, the member slides within the follower body, allowing the lateral rollers to engage and follow the lateral lobes. Means are provided for limiting the rotational movement of the slider member in the body passage. Preferably, the central lobe is a high-lift lobe and the lateral lobes are low-lift lobes. Preferably, the locking pin is provided as a pre-assembled cartridge unit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is an isometric view from the front of a two-step finger follower rocker arm assembly in accordance with the invention; 
     FIG. 2 is an exploded isometric view of the rocker arm assembly shown in FIG. 1; 
     FIG. 3 is an isometric view from above of the rocker arm assembly shown in FIG. 1, the slider member being omitted for illustration; 
     FIG. 4 is an elevational cross-sectional view of the rocker arm assembly shown in FIG. 1, installed schematically in an internal combustion engine and having the associated valve closed, the locking pin unlocked, and the slider member on the base circle portion of the central cam lobe; 
     FIG. 5 is an elevational cross-sectional view like that shown in FIG. 4, showing the locking pin still unlocked, the lateral roller followers on the nose of the lateral cam lobes, and the valve opened to a low-lift position; 
     FIG. 6 is an elevational cross-sectional view like that shown in FIG. 4, showing the locking pin in locked position in the slider member, the nose of the central cam lobe on the slider member, and the valve opened to a high-lift position; 
     FIG. 7 is an elevational cross-sectional view of a first embodiment of a locking pin assembly in accordance with the invention; 
     FIG. 8 is an elevational cross-sectional view of a second embodiment of a locking pin assembly, showing a cartridge pin subassembly having a piston extension for mechanical actuation of the locking pin; 
     FIG. 9 is a view like that shown in FIG. 8, showing a cartridge pin subassembly without the piston extension, as would be configured for hydraulic actuation of the locking pin; 
     FIG. 10 is an elevational cross-sectional view of a two-step finger follower in accordance with the invention, including the cartridge pin subasssembly shown in FIG. 8, the pin and slider member being in the unlocked position; 
     FIG. 11 is an elevational cross-sectional view like that shown in FIG. 10, showing the pin and slider member in the locked position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 through 6, a two-step finger follower rocker arm assembly  10  in accordance with the invention includes a follower body  12  having a first end  14  having means for receiving the head of a hydraulic lash adjuster  16  for pivotably mounting assembly  10  in an engine  18 . The receiving means is preferably a spherical socket  20 , as shown in FIGS. 4-6. A second and opposite end  22  of follower body  12  is provided with a pad  24 , preferably arcuate, for interfacing with and actuating a valve stem  26 . Body  12  is provided with a passage  28  therethrough between socket  20  and pad  24 , passage  28  being generally cylindrical for slidably receiving a partially-cylindrical mating portion  30  of a slider member  32  having a longitudinal slot  33  therein. Body  12  is further provided with a first bore  34  transverse of passage  28 , ending in bosses  36  for receiving roller bearings  38  for rotatably supporting a shaft  40  extending through bore  34  and slot  33  to slidably retain slider member  32  in passage  28 . Each roller bearing  38  includes an inner face  39 . First and second lateral follower rollers  42   a,b  are mounted on opposite ends, respectively, of shaft  40 . 
     Slider member  32  further includes an actuating portion  44  having an arcuate outer surface  46  for engaging a central cam lobe  48  of an engine camshaft  47 . Portion  44  extends toward first and second ends  14 , 22  of  12  to define, respectively, a latching surface  49  and a spring seat  50 . Portion  44  extends away from outer surface  46  to define flats  51   a, b  in cylindrical mating portion  30 . When slider member  32  is received in passage  28  of body  12 , each inner face  39  of roller bearings  38  is located in close proximity of flats  51   a, b  thereby limiting the rotational movement of slider member  32  in passage  28 . Second end  22  of body  12  is provided with a well  52  for receiving a lost-motion spring  54  disposed between end  22  and spring seat  50  (spring  54  is shown in FIG. 10 but omitted from the other drawings for clarity). Thus, pin  55 , guided close fittedly by the inside diameter of spring  54 , in conjunction with the close proximity of roller bearing inner faces  39  to slider member flats  51   a, b,  serve to limit undesirable rotation of slider member  32 . 
     First end  14  is further provided with a latching mechanism  56  for engaging and locking slider member  32  at its most outward extreme of motion in passage  28 . Mechanism  56  comprises a stepped second bore  58  in body  12  and having an axis  60  intersecting passage  28 , preferably orthogonally, bore  58  being preferably cylindrical. 
     Referring to FIGS. 4 through 7, a first embodiment  57  of latching means in mechanism  56  includes a piston  62 , biased outwards in bore  58  by a return spring  64  and extending toward slider member  32  to support a latch member  66  which may slide along a slide surface  68  in body  12 . Bore  58  is closed by a plug  70 , forming a hydraulic chamber  72  in communication via passage  74  with socket  20 . Pressurized oil may be supplied to chamber  72  in known fashion from HLA  16 , upon command from an engine control module (not shown), to cause piston  62  to become hydraulically biased toward slider member  32 . When such biasing occurs, to overcome the counter-bias of return spring  64 , outer surface  46  being engaged on the base circle portion  76  of central cam lobe  48 , latch member  66  is urged axially into latching and locking engagement with latching surface  49 . As shown in FIG. 6, when cam lobe  48  rotates to engage nose portion  78  with surface  46 , valve stem  26  is actuated from a zero lift position  80  to a high lift position  82 . 
     Still referring to FIGS. 4 through 6, central cam lobe  48  is flanked by first and second identical lateral cam lobes  84  (only one visible in FIGS. 4-6) for selectively engaging first and second lateral follower rollers  42   a,b,  respectively. When the engine control module determines, in known fashion from various engine operating parameters, that a low-lift condition is desired, oil pressure is no longer supplied to chamber  72 , allowing return spring  64  to again bias piston  62  and associated latch member  66  away from slider member  32 . When cam lobe  48  rotates to place surface  46  on base circle portion  76  again, piston  62  unlatches latch member  66  and slider member  32  is again free to slide in passage  28 . When the camshaft again rotates to place nose  78  on surface  46 , member  32  is depressed into body  12 , allowing noses  86  on lateral cam lobes  84  to be engaged by rollers  42   a,b,  as shown in FIG. 5, thus displacing valve stem  26  from zero lift position  80  to a low-lift position  88 . As long as oil pressure is withheld from chamber  72 , latching mechanism  56  remains disengaged from slider member  32 , and assembly  10  functions as a low-lift rocker. 
     As shown in FIGS. 3 and 7, latch member  66  includes flatted bottom surface  67  for slidable engagement with flatted portion  69  of slider surface  68 . Thus, when latch member  66  is in position to lock slider member  32 , the downward force exerted on the slider member is supported vertically by latch member  66  and slider surface  68  and is not translated torsionally through piston  62 . 
     Of course, it will be seen by those of skill in the art that the dimensions of the lateral cam lobes and lateral follower rollers may be configured to provide any desired degree of lift to valve stem  26  in a range between positions  80  and  88 . 
     Referring to FIGS. 8 through 11, a second embodiment  90  is shown for a latching mechanism  56  in accordance with the invention. Embodiment  90  comprises a latching cartridge  92  which may be inserted into bore  58  and which is preferably and conveniently pre-assembled as a subassembly, thereby greatly simplifying the overall assembly of follower  10 . Cartridge  92  includes a body  94 , preferably tubular and closed at outer end  96  and sized to be press-fitted into bore  58 , thereby eliminating the need for plug  70 . Preferably, body  94  is constricted  98  to separate piston  62 ′ from end  96 , thereby providing a hydraulic chamber  72 ′ within the cartridge. Constriction  98  is perforated  100  to allow hydraulic communication with passage  74  and socket  20 . Body  94  is partially closed at inner end  102  to retain return spring  64 ′ and provide guidance for piston  62 ′ in driving latch member  66 ′ into (FIG. 11) and out of (FIG. 10) engagement with latching surface  49 . 
     Referring to FIG. 8, a variation  92 ′ of cartridge  92  is provided with a piston extension  104  slidably extending through outer end  96  for engagement by mechanical or electromechanical actuation means (not shown), for example, a conventional solenoid actuator, in place of the previously-discussed hydraulic actuation. 
     Cartridges  92  and  92 ′ are useful in all types of variable valve actuation rocker arms, not just those discussed above, wherein lock pin mechanisms are used to latch and unlatch components of a rocker arm mechanism to vary the lift of associated valves. Cartridges in accordance with the invention contain the entire locking mechanism in a single assembly, which reduces the precision required in a receiving bore in a rocker arm mechanism. The entire cartridge may be pre-assembled before insertion into the arm assembly, thereby simplifying rocker arm assembly. 
     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.