Abstract:
A two-step roller finger follower including an elongate body having side walls defining coaxially disposed shaft orifices, a pallet end and a socket end interconnecting with the side walls to define a slider arm aperture, and a latch channel. The socket end is mountable to an hydraulic lash adjuster, and the pallet end is matable with a valve stem. A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and has a first end pivotably mounted to the pallet end of the body and the second end forming a slider tip for engaging an activation/deactivation latch. The latch is slidably disposed in the latch channel, and the latch has a nose section for selectively engaging the slider tip. A spool-shaped roller having first and second roller elements fixedly attached to the shaft is rotatably disposed in the shaft orifices, the roller being adapted to follow the surface motion of low-lift cam lobes. Preferably, the shaft is journalled in roller or needle bearings which extend between and through the first and second shaft orifices, being thus exposed to normal copious oil flow through the RFF.

Description:
RELATIONSHIP TO OTHER APPLICATIONS AND PATENTS 
     This application claims the benefit of U.S. Provisional Application, Serial No. 60/359,744, filed Feb. 26, 2002. 
    
    
     TECHNICAL FIELD 
     The present invention relates to roller finger followers used in overhead cam type internal combustion engines, and more particularly to a roller finger follower wherein a spool-shaped roller set is used. 
     BACKGROUND OF THE INVENTION 
     Roller Finger Followers (RFF) are widely used in overhead cam internal combustion engines to sequentially open and close the cylinder intake and exhaust valves. In a typical application, the RFF serves to transfer and translate rotary motion of a cam shaft lobe into a pivotal motion of the RFF to thereby open and close an associated valve. 
     It is known that, for a portion of the duty cycle of a typical multiple-cylinder engine, the performance load can be met by a functionally smaller engine having fewer firing cylinders, and that at low-demand times fuel efficiency can be improved if one or more cylinders of a larger engine can be withdrawn from firing service. It is also known that 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 high lift position to admit more fuel. It is known in the art to accomplish this by de-activating a portion of the valve train associated with pre-selected cylinders in any of various ways. One way is by providing a special two-step RFF having an activatable/deactivatable central slider arm which may be positioned for contact with a high lift lobe of the cam shaft. Such a two-step RFF typically is also configured with rollers disposed at each side of the slider arm for contact with low lift lobes of the cam shaft. Thus, the two-step RFF causes low lift of the associated valve when the slider arm of the RFF is in a deactivated position, and high lift of the associated valve when the slider arm of the RFF is in an activated position to engage the high lift lobe of the cam shaft. 
     A two-step RFF known in the art comprises a generally elongate body having a pallet end in contact with an axially movable valve stem and an opposing socket end in contact with a stationary pivot such as, for example, a hydraulic lash adjuster (HLA). A moveable and therefore deactivatable high lift slider is positioned central to the RFF body. Rollers are rotatably mounted on each side of the slider on a non-rotatable shaft fixed to the body. The rollers ride on narrow bearings, as for example needle bearings. End washers are used to rotatably fix the rollers and bearings to the shaft and to restrain the rollers and bearings from moving laterally on the shaft. 
     The width of the bearings in the background art is limited to the width of the rollers themselves. Further, because the bearings are disposed outside the body side walls, the bearings are substantially shielded from flow of lubricating oil within the RFF body. 
     It is a principal object of the present invention to provide an improved roller bearing arrangement for better durability without substantially increasing the overall width of the RFF. 
     It is also an object of the invention to provide a simplified RFF having fewer components. 
     While this invention is described in the context of a two-step deactivation RFF, it should be understood that the bearing improvements may be applied to the rollers of single-step RFFs as well. 
     SUMMARY OF THE INVENTION 
     Briefly described, a roller finger follower for use in conjunction with a cam shaft of an internal combustion engine comprises an elongate body having first and second side members defining coaxially disposed shaft orifices. A pallet end and a socket end interconnect with the first and second side members to define a slider arm aperture and a latch pin channel. The socket end is adapted to mate with a mounting element such as an hydraulic lash adjuster, and the pallet end is adapted to mate with a valve stem, pintle, lifter, or the like. A slider arm for engaging a high-lift cam lobe is disposed in the slider arm aperture and has first and second ends, the first end of the slider arm being pivotally mounted to the pallet end of the body and the second end defining a slider tip for engaging an activation/deactivation latch. The latch is slidably and at least partially disposed in the latch pin channel, the latch pin having a nose section for selectively engaging the slider tip. A spool-shaped roller comprising a shaft and at least one roller element fixedly attached to the shaft is rotatably disposed in the shaft orifices, the roller being adapted to follow the surface motion of a low-lift cam lobe. Preferably, the shaft is journalled in roller or needle bearings which extend between and through both the first and second shaft orifices, being thus exposed to normal copious oil flow through central regions of the RFF. 
    
    
     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 of a first embodiment of an RFF in accordance with the present invention; 
     FIG. 2 is a cross-sectional view of the RFF taken through center axis A in FIG. 1; 
     FIG. 3 is a cross-sectional view of the RFF taken through center axis D in FIG. 1; 
     FIG. 4 is a side view of the lost motion spring lugs of a second embodiment; 
     FIG. 5 is a side view of the lost motion spring lugs of a third embodiment; 
     FIG. 6 is a perspective view of the RFF, cam shaft, valve and HLA; 
     FIG. 7 is a cross section view of the RFF similar to FIG. 3, but with the slider engaged; 
     FIG. 8 is a cross-sectional view taken through center axis A showing rollers of an alternate embodiment; 
     FIG. 9 a  is a perspective view showing the bearings of an alternate embodiment; 
     FIG. 9 b  is an exploded view of FIG. 9 a;    
     FIG. 9 c  is an exploded view of a variation of the embodiment shown in FIGS. 9 a  and  9   b;    
     FIG. 10 is an exploded view similar to FIG. 9 b  showing rollers of yet another embodiment; and 
     FIGS. 11 a  and  11   b  are cross sectional views taken through axis A showing forces exerted on the bearings by the rollers. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1,  2 ,  3 , and  6 , improved RFF  10  is shown. A pallet end  12  of RFF  10  engages valve stem  11  and socket end  14  of RFF  10  engages lash adjuster  13 . RFF  10  includes body assembly  15  (FIG.  3 ), slider arm assembly  18  (FIG.  3 ), spool roller assembly  20  (FIG.  2 ), lost motion springs  22  (FIGS.  1  and  3 ), and latch assembly  24  (FIG.  3 ). 
     Body assembly  15  includes elongate body  16  and roller bearings  17 . Roller bearings  17 , while shown in FIG. 1 as a needle bearing type, can be of any bearing type known in the art. Elongate body  16  includes slider arm aperture  26  bounded by body side walls  28 , 30 . Body side walls  28 , 30  define shaft orifices  32 , 34  therethrough and bearing flanges  35 . Each of shaft orifices  32 , 34  is concentric with center axis A. The diameters of shaft orifices  32 , 34  are sized to press fittedly receive roller bearings  17  which preferably are identical. Body side walls  28 , 30  further define slider arm shaft apertures  36 , 38  therethrough. Each of shaft apertures  36 , 38  is concentric with center axis B. Center axis A is substantially parallel with center axis B. Body side walls  28 , 30  proximate pallet end  12  of body  16 , further define lost motion spring lugs  40  located circumferentially around slider shaft apertures  36 , 38 . Socket end  14  of body  16  defines latch pin clearance orifice  42 , 44  and latch channel  46 . Each of latch pin clearance orifice  42 , 44  is concentric with center axis C. Latch channel  46  is concentric with center axis D. Center axis C is substantially parallel with center axes A and B; center axis D is substantially perpendicular to center axes A, B and C. Socket end  14  of body  16  further defines oil passage  48  adjacent and parallel to latch channel  46  and in communication with oil orifice  50  (FIG.  3 ). As is described more particularly later, lubricating oil received under pressure from the HLA is fed through oil passage  48  and directed at slider arm assembly  18  which will now be described. 
     Slider arm assembly  18  includes slider arm  52  and slider shaft  54 . Shaft  54  includes outer ends  55 , 56  and central portion  58 . Slider arm  52  defines slider shaft orifice  60 , slider surface  21 , slider tip  64 , and roller shaft clearance aperture  66 . The diameter of slider shaft orifice  60  is sized to press-fittedly receive central portion  58  of shaft  54 . In turn, the diameter of slider shaft apertures  36 , 38  in body  16  are sized to receive outer ends  55 , 56  of shaft  54  in a loose fit arrangement. Thus, shaft  54  is free to rotate in slider shaft apertures  36 , 38  but not free to rotate in slider shaft orifice  60 . As a result, when assembled into slider arm aperture  26 , slider arm assembly  18  is free to rotate about central axis B with relative motion only between slider shaft  54  and apertures  36 , 38  of body  16 . 
     As best shown in FIGS. 1 and 2, spool-shaped roller assembly  20  includes spaced apart roller elements  68 ,  70  and roller shaft  72 . Roller shaft  72  includes outer ends  73 , 74  and central portion  76 . Roller elements  68 ,  70  define internal diameter  78 , and outer diameter  80 . Internal diameter  78  of rollers  68 ,  70  is sized to press-fittedly receive outer ends  73 ,  74  of shaft  72 . It is understood that the roller elements could also be loosely received on outer ends  73 , 74  and, for example, be welded, bonded, or staked to the shaft, or fixedly attached to the shaft by any other means known in the art. When assembled to the shaft, the outside end surfaces of roller elements  68 ,  70  are substantially flush with end surfaces of shaft  72 . Internal diameter  82  of roller bearings  17  is sized to rotatably receive shaft  72 . Thus, roller bearings  17  are free to rotate about the shaft in an essentially friction free manner as known in the art. 
     Therefore, as best shown in FIG. 2, when assembled into body assembly  15 , roller elements  68 ,  70  and shaft  72  rotate as an integral spool-shaped unit within roller bearings  17 . Since the bearings are mounted inboard of the roller elements, the bearing width is not limited to the width of the roller elements as in the prior art. In fact, as can be readily seen in FIG. 2, width  84  of the bearings is almost three times the width  86  of rollers  68 , 70  without increasing the overall width  88  of the RFF assembly. Further, since end washers are not needed to secure the roller elements to the shaft ends as in the prior art, even wider bearings could be used without increasing the overall width of the RFF assembly. Moreover, in the prior art, where the end washers and the walls of the RFF body serve as lateral thrust surfaces for the rollers, bearing shoulders  89  or bearing flanges  35  serve as lateral thrust surface of the present invention. As is discussed more thoroughly below, the thrust surfaces of the present invention are well lubricated to reduce friction and wear. 
     Referring again to FIG. 1, lost motion springs  22  are coiled around outer ends  55 , 56  of slider shaft  54  to abuttingly engage spring stop  90  on body  16  and the underside  19  of slider surface  21 . Each of lost motion springs  22  is guided centrally about central axis B by at least one of lost motion spring lugs  40  extending from each of walls  28 , 30 . Retainer clip  92  having at least one end wrap  93  loops around at least one of spring lugs  40  to secure lost motion springs  22  laterally in place. As aternate embodiments for securing the lost motion springs in place, end hooks  94  can be formed on the ends of the spring lugs  40 ′ (FIG. 4) or lugs  40 ″ can be formed to axially diverge away from central axis B (FIG. 5) without the need for retainer spring  92 . When assembled to RFF  10 , each of lost motion springs  22  applies a bias force to slider arm assembly  18  in the counter clockwise direction (as viewed in FIG.  3 ). 
     Latch assembly  24  includes substantially cylindrical latch  96 , contact paddle  98 , spring  100 , and latch pin  102 . Latch  96  further defines flattened nose section  104  and reduced diameter section  106 . Nose section  104  is configured to selectively engage slider tip  64  and reduced diameter section  106  is formed to facilitate the passage of oil from orifice  50  to oil passage  48  for lubricating slider surface  21  of slider arm  52 . Latch  96  is sized to slidably fit into latch channel  46 . Latch  96 , opposite nose section  104 , defines latch pin orifice  108  and slot  110  for receiving contact paddle  98 . A similarly sized orifice  112  is disposed in contact paddle  98  such that, when paddle  98  is received in latch slot  110 , orifices  108  and  112  are aligned co-axially. Bias spring  100 , configured as, for example, a coil spring, is positioned around cylindrical latch  96 , and abuttingly engages spring stop  116  in body  16  when latch assembly  24  is assembled into latch channel  46 . The other end of spring  100  engages latch pin  102  so as to bias latch assembly  24  in the outward (FIG. 3) or slider-disengaged position. The assembly of latch pin assembly  24  into body assembly  15  will now be discussed. 
     Latch pin  102  includes ends  119 , 120  and central section  122 . The diameter of latch pin  102  at central section  122  is sized to be press-fittedly received by at least one of orifices  108 , 112 . Center axis C of latch pin clearance orifices  42 ,  44  in body  16  is generally co-axial with the center axis E of orifices  108 , 112  when latch assembly  24  is positioned in RFF  10  as shown in FIG.  3 . When assembled in this fashion, central section  122  of pin  102  is inserted into orifices  108 , 112  such that ends  119 , 120  of pin  102  extend at least partially into clearance orifices  42 , 44 . Since the diameter of latch pin clearance orifices  42 , 44  is substantially larger than the diameter of latch pin  102  at pin ends  119 , 120 , the size of orifices  42 , 44  relative to the diameter of pin ends  119 , 120  control the left/right, engagement/disengagement travel of latch assembly  24 . Thus, when assembled into RFF  10 , pin  102  serves multiple purposes including (1) providing a seat for spring  100 ; (2) fixing paddle  98  to latch  96 ; (3) limiting the leftward (FIG. 3) travel of latch  96 ; and (4) limiting the rightward (FIG. 3) travel of latch  96 . 
     Referring now to FIG. 3, RFF assembly  10  is shown in the slider-disengaged mode. Latch assembly  24  is in its full rightward position. Nose section  104  of latch  96  is not in engagement with slider tip  64  of slider arm  52 . In this mode, as best described with reference to FIG. 6, the rotary motion of low lift cam lobes  132  of cam shaft  130  is translated by roller elements  68 ,  70  into a pivoting movement of RFF  10  about lash adjuster  13  thereby providing a low-lift opening of the associated valve. Since slider arm assembly  18  is disengaged from the latching mechanism, the rotary motion of high lift cam lobe  134  imparted on slider arm  52  is absorbed by lost motion springs  22  and is not translated by slider arm  52  into a pivoting movement of RFF  10 . In this mode (disengaged position), the entire cam surfaces of the low lift cams, including low lift lobes  132  and base circles  133  of the low lift cams remain in contact with roller elements  68 ,  70  through the full rotation of the cam shaft. Further, because of the action of lost motion springs  22  on slider arm assembly  18 , the entire surface of the high lift cam, including high lift lobe  134  and base circle  135  of high lift cam, remains in contact with slider surface  21  to maintain a film of oil between the cam surface and the slider surface. Note in FIG. 3 that roller shaft clearance aperture  66  in slider arm  52  is sized to provide sufficient clearance to roller shaft  72  to permit full travel of slider arm assembly  18  as described above. 
     FIG. 7 shows RFF  10  in the slider-engaged mode. In this mode, the rotary motion of high lift cam lobes  134  of cam shaft  150  of internal combustion engine  131  is translated by slider arm assembly  18  into a pivoting movement of RFF  10  about lash adjuster  13  thereby providing a high-lift opening of the associated valve. Referring to FIGS. 6 and 7, since the slider is engaged, the rotary motion of high lift cam lobe  134  is not absorbed by lost motion springs  22  and is therefore transferred by slider arm  52  to a pivoting movement of RFF  10 . In this mode (engaged position), while the lobed portions  132  of the low lift cams do not contact roller elements  68 ,  70 , base circle portions  133  of the low lift cams do. Thus, when in the slider-engaged position, for each revolution of cam shaft  130 , base circle  133  of the low lift cams first engage the roller elements, then disengage the roller elements when the high lift cam lobe  134  comes in contact with engaged slider arm  52 . This high frequency cyclic load placed on the spool-shaped roller by the low lift cams can increase wear on the roller element surfaces. Lightener holes  69  extending laterally through the roller elements serve to reduce the rotational mass of the roller elements to reduce inertia and wear. 
     Roller elements  68 ′,  70 ′ of an alternate embodiment having an “I-beam” shaped cross section are shown in FIG. 8, comprising a web  140 , hub  142 , and rim  144 . Like the lightening holes, the I-beam shaped cross section serves to reduce the rotational mass of the rollers to reduce inertia and wear. As shown in FIG. 8, roller elements  68 ′, and  70 ′ may also have lightening holes  69  to offer a further mass reduction. 
     RFF  10  as described herein uses split bearings  17  in the preferred embodiment. Bearings  17  are shown in FIG. 1 as needle bearings. In an alternate embodiment, rather than split bearings, RFF  10 ′ uses a full width set of needle bearings. As shown in FIGS. 9 a  and  9   b , the outer and inner diameters of long needle bearing set  150  are sized diametrically to fit into bearing orifices  152 , 154  and to fit around the diameter of shaft  156  so that, when spool roller assembly  160  and bearing set  150  are installed in elongate body  162 , the spool roller assembly is free to rotate about center axis A in an essentially friction free manner as known in the art. Width  164  of long needle bearing set  150  is substantially the same or slightly less than width  166  of body  162 . Thus, bearing flanges, as shown as numeral  35  in FIG. 1, provide lateral thrust surfaces to the rollers. In this embodiment, long needle bearing set  150  is supported by the thicknesses of body walls  28 , 30 . However, it is understood that bottom surface  168  (shown in FIG. 9 a ) of elongate body  162  can be formed to provide central support to long needle bearing set  150 . 
     In yet another embodiment (FIG.  8 ), the long needle bearing set can be replaced by bearing sleeve  170  that is either press fitted into shaft orifices  32 , 34  or loose fitted into orifices  32 , 34  to provide a low friction contact between roller shaft  72  and elongate body  162 . When press-fitted, bearing sleeve  170  offers additional stiffness to elongate body  162  to resist bending from the forces applied to the RFF by the rotating cam shaft. 
     In yet a further embodiment, the long needle bearing set as shown in FIGS. 9 a  and  9   b  can be modified to include outer tube  146  (FIG. 9 c ). In this embodiment, the outer diameter of tube  146  is sized to be press fit into bearing orifices  152 , 154  while the inner diameter of tube  146  is sized to receive the outer diameter of long needle bearing set  150 . In turn, the outer diameter of shaft  156  is sized to fit inside the inner diameter of bearing set  150  so that, once all of the components are assembled in this manner, the spool roller assembly is free to rotate about center axis A, relative to body  162 , in an essentially friction free manner as known in the art. The widths of tube  146  and long bearing set  150  are substantially the same or slightly less than width of body  162  so that bearing flanges  35 , as shown in FIG. 1, provide lateral thrust surfaces to the rollers. In this embodiment, tube  146  provides central support to bearing set  150  and rigidity to body  162 . 
     Lubrication to RFF  10  and its components is improved by the present invention. As discussed above, lubricating oil is fed directly to slider surface  21  by oil passage  48  in elongate body  16 . Oil passage  48  is in fluid communication with orifice  50  which receives lubricating oil, under pressure, from the HLA. Lubricating oil flows through orifice  50 , around cylindrical latch  96  and within latch channel  46 , into oil passage  48  which is in fluid communication with channel  46 . Opening  51  (FIG. 3) extending from passage  48  directs a stream of oil at slider surface  21  and the outer surfaces of rollers  68 , 70 . Lubricating oil from slider surface  21  drips down into slider arm aperture  26  where it pools around shaft  72  and flows directly into roller bearings  17 . 
     In an alternate embodiment, in place of lightener holes  69 , air foil blades  172  are disposed through roller elements  68 ″, 70 ″ (FIG. 10) that serve both to reduce the rotational mass of the roller elements as discussed above, and to pull in and direct lubricating oil toward bearings  17 , from the surrounding environment. Thus, every frictional surface within RFF  10  is positively and copiously engulfed in lubricating oil. Regarding the alternate embodiment wherein long needle bearing set  150  is used (FIG. 9 b ), roller shaft  156  further defines spiral oiler groove  158  in its surface. Lubricating oil drips into slider arm aperture  26  as described above and is pulled through the long needle bearings toward shaft  156  by the rotation of the needle bearings in use. Spiral oiler groove  158  serves to transport lubricating oil across the surface of shaft  156  and toward roller elements  68 , 70 . 
     Regarding the alternate embodiment wherein bearing sleeve  170  is used (FIG. 8) or where tube  146  is used in conjunction with long needle bearing set  150  (FIG. 9 c ), oiler aperture  171  extends through the wall of sleeve  170  or through the wall of tube  146  to fluidly communicate slider arm aperture  26  with the surface of shaft  156  and oiler groove  158 . Thus, ample lubricating oil is positively fed inside sleeve  170  to lubricate it, the surface of shaft  156  and roller elements  68 ,  70 . 
     In yet a further alternate embodiment, the inside surface of sleeve  170  defines the spiral oiler groove  174 . In the same way as described above, lubricating oil is transported by the groove across the surface of the roller shaft toward roller elements  68 ,  70 . 
     In the background art, lubricating oil is not directed toward slider surface  21  by an integrated oil passage similar to passage  48 . Moreover, because the roller elements and roller bearings are mounted to roller shafts outside the roller body, the walls of the roller body detrimentally shield the bearings and rollers from being lubricated from oil pooled inside the body. 
     Referring to FIG. 11 a , the load forces directed toward shaft  72  and split bearings  17  of the present invention are shown. As can be seen, downward force  180  from the low lift cam lobe induces counter clockwise bending moment  182  on the shaft near the outermost edge of bearing  17 . Edge loading is high at this point which may cause unfavorable wear to the shaft/bearing edge juncture. A portion of RFF  10 ″ of an alternate embodiment is shown in FIG. 11 b . Spool roller assembly  190  includes roller shaft  192  and roller elements  194 , 196 . Bearing  17  and the portion of body  16  shown are substantially identical to equivalent components of RFF  10 . Downward force  198  from the low lift cam lobe induces counter clockwise bending moment  199  on the shaft near the outermost edge of bearing  17 . In addition, because of hub  200  being offset from contact surface  201  of roller elements  194 , 196 , downward force  198  induces a clockwise bending moment  202  on the outboard end of shaft  192 . The counter directional moments caused by the offset hub serve to reduce the magnitude of the resulting edge loading at the shaft/bearing edge juncture and thus reduce friction and unfavorable wear at the juncture.