Abstract:
A cam follower having a clamp disposed on at least one end thereof. The follower includes two opposing sidewalls interconnected by a lower pallet. A roller is rotatably mounted to and disposed between the sidewalls via needled or journal bearings or other rotatable connection known in the art. A clamp is disposed about an end of the follower to induce compression force in the pallet and possibly act as the valve guide walls. The clamp increases the stiffness of the follower and induces compressive stress in the pallet area thereby increasing fatigue life. The clamp could also increase the length of the valve guide walls for better stability during engine assembly.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to a cam follower and particularly to a roller follower having a clamp to induce a compression force in a lower pallet portion and/or possibly act as valve guide walls. 
     2. Description of the Related Art 
     Roller followers for opening valves in an over head camshaft in an internal combustion engine arrangement are known in the art. FIG. 1 depicts one such known device. The follower of FIG. 1 includes a substantially one-piece U-shaped body having two upstanding sidewalls interconnected by a bottom wall or pallet. A first end of the follower is adapted to receive an end of a lifter post or tappet on which the roller follower can pivot. A second end of the roller follower receives the upper end of a valve stem arrangement. A middle portion of the bottom wall or pallet is cut out to accommodate a roller rotatably disposed between the sidewalls for engaging an overhead cam. The valve stem extends upward from the cylinder head through a coiled compression spring. As the cam rotates, the cam engages the roller to cause the follower to pivot about the lifter/tappet thereby opening and closing the valve as the stem is displaced. 
     However, the roller follower devices of the prior art are susceptible to fatigue failure at the ends and particularly at the end of the roller follower adjacent the interface with the valve stem. 
     It is the object of the present invention to improve upon the cam follower designs of the related art and to provide a follower with a clamp to induce a compressive force on the lower pallet thereby increasing fatigue life and stiffness of the follower. Additionally, the side walls of the clamp may extend past the pallet to act as valve guide walls to improve stability during engine operation. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to cam follower having a clamp disposed on at least one end. A one-piece stamped follower includes two opposing sidewalls interconnected by a lower pallet. A roller is rotatably mounted to and disposed between the sidewalls via needled or journal bearings or other rotatable connection known in the art. A clamp is disposed about an end of the follower to induce compression force in the pallet. The clamp increases the stiffness of the follower and induces compression forces in the pallet thereby increasing fatigue life and allows for long valve guide walls to help the roller finger follower from tipping over during engine assembly operations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 . is a partial cross sectional view of a valve actuating mechanism of an overhead cam driven internal combustion engine with a cam follower according to the prior art. 
     FIG. 2 is an isolated partial cross sectional view of the cam follower of FIG.  1 . 
     FIG. 3 is an isolated side view of the cam follower and clamp according to the present invention. 
     FIG. 4 is a sectional view taken along lines  4 — 4  of FIG. 3 without the roller. 
     FIG. 5 is an isolated side view of the cam follower according to an alternate embodiment of the present invention. 
     FIG. 6A is a sectional view taken along lines  6 — 6  of FIG. 5 without the roller. 
     FIG. 6B is a sectional view of an alternate form of the cam follower of FIG.  6 A. 
     FIG. 6C is a sectional view of an additional alternate form of the cam follower of FIG.  6 A. 
     FIG. 7 is an elevated perspective view of the cam follower and clamp of FIG. 3 without the roller. 
     FIG. 8 is an elevated perspective view of the cam follower and clamp of FIG. 5 without the roller. 
     FIG. 9A is a sectional view of an alternate embodiment of the present invention. 
     FIG. 9B is an exploded sectional view of the embodiment of FIG.  9 A. 
     FIG. 10 is a top view of an alternate follower to which the clamp of the present invention may be employed. 
     FIG. 11 is a front view of the follower of FIG.  10 . 
     FIG. 12 is a front view of an alternate clamp to be employed with the follower of FIG.  10 . 
     FIG. 13 is a front view of an alternate embodiment of the present invention. 
     FIG. 14 a  is a front exploded view of an alternate embodiment of the present invention. 
     FIG. 14 b  a front view of the assembled embodiment of FIG. 14 a.   
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     To facilitate the understanding of the present invention, the prior art follower device will be described. FIG. 1 depicts a valve-actuating device incorporating a roller follower  1  of the prior art. A cam follower  1  is pivotally supported on a lifter post/tappet  3  and extends to engage a valve stem  5  of an internal combustion engine. A camshaft  7  is provided to pivot the cam follower  1  to displace the valve stem  5  between an open and closed position. The cam follower  1  is provided with a roller  9  to provide a rolling interface  11  between the camshaft  7  and the follower  1 . As the camshaft  7  rotates, the cam follower  1  is forced to pivot downward about the lifter post/tappet  3  and force the valve stem  5  down to an open position. A coiled compression spring  4  is disposed about the valve stem  5  to bias the valve stem upward to a closed position. The camshaft  7  continuously rotates to open and close the valve stem  5  in a reciprocating manner. The lifter post/tappet  3  may be adjustable or hydraulically yielding to provide zero lash adjustment. Such arrangements are well known in the art. 
     FIG. 2 is an isolated view of the cam follower  1  of FIG.  1 . The cam follower  1  has a main body including a pair of spaced apart sidewalls  2  interconnected by a lower wall  6 . The main body extends from a first end  10  and is adapted to be pivotally supported on the lifter post  3 . The first end  10  has a recess to receive the upper end of the lifter post/tappet  3 . The second end  8  preferably has a groove or elongated recess to receive and engage the upper end of the valve stem  5 . An intermediate portion of the lower wall  6  has a cut out  14  to accommodate the roller  9  rotatably disposed between and mounted to the sidewalls  2 . The roller  9  is rotatably mounted to the sidewalls  2  to engage the camshaft  7  and thus cause the pivotal movement of the follower  1  which in turn causes the reciprocating movement of the valve stem  5 . The roller  9  may be mounted about an axle extending between the sidewalls  2 . In such an arrangement bearings such as needle bearings or journal bearings (not shown) are disposed between the roller  9  and axle to facilitate rotation there between. As can be seen in FIG. 2, the roller  7  extends through the cut out  14  or opening and below the lower wall  6  of the main body. However, the present invention is not limited to such an embodiment. The lower wall may be substantially solid and possibly form an oil belly to facilitate lubrication of the roller  9 . The roller  9  further extends upward beyond the upper portion of the sidewalls  2  to enable engagement with the camshaft  7 . 
     The present invention improves upon the prior art roller follower  1  as described above. The cam follower  101  of the present invention is employed as in the aforementioned description of the prior art. That is, the cam follower  101  of the present invention is disposed in an overhead cam shaft internal combustion engine pivotally supported by a tappet to reciprocatingly open and close the valve stem. Therefore, only the specific structure of the cam follower  101  as it differs from the prior art will now be explained. However, it is to be understood that the cam follower  101  of the present invention may be employed in other valve actuating mechanisms than the aforementioned description. 
     The roller follower  101  of the present invention includes a clamp  120  disposed about one end of the follower  101  to induce a compression force to the lower pallet  106 . As can bee seen from FIG. 4, the cam follower  101  is made of a substantially U-shaped main body having two opposed sidewalls  102  interconnected by a pallet  106  disposed at a lower portion. The lower pallet  106  preferably has a groove  106   a  formed along a bottom surface thereof for engagement with the upper end of the valve stem. As shown in FIG. 3 a roller is disposed between and rotatably mounted to the sidewalls  102  as is known in the art. 
     As can be seen in FIGS. 3 &amp; 4, the clamp  120  is made of an inverted substantially U-shaped channel member pressed over the end  108  of the follower  101 . The clamp  120  is dimensioned to provide a compression force through the lower portion of the cam follower  1  and through the pallet  106  as indicated by the arrows in each of FIG.  4 . Fatigue failure is associated with tensile forces. Therefore, by inducing a compression force through the lower pallet  106 , increased fatigue life is achieved. Furthermore, the clamp  120  arrangement provides for an overall stiffer follower device. The clamp  120  is preferably a one-piece stamped member formed of the same metal used to form the main body of the cam follower  101 . However, other materials, such as strong plastics may be employed so long as compressive forces are induced in the lower pallet  106 . 
     Fatigue failure of the cam follower  1  and lower portion  6  is often associated with the end  108  adjacent the valve stem. Therefore, it is preferred to employ the clamp member  120  adjacent the end  108  of the cam follower that engages the upper end of the valve stem. Of course, the clamp member  120  may be employed at the opposite end  110  or a clamp member provided at both ends to enhance the overall stiffness of the cam follower. 
     FIGS.  5 - 6 A&amp;B&amp;C represent an alternate embodiment of the present invention. In the alternate embodiment, clamp member  220  simply includes an additional extension  222  extending inward and underneath the pallet  206  terminating adjacent the groove  206   a . However as can be seen in FIGS.  6 B,  6 C the necessity of groove  206   a  can be eliminated by utilizing the extensions  222  as the guide walls. The extension  222  increases the height of the clamp  220  and provides increased guidance for engagement with the upper end of the valve stem. Such an arrangement also increases the stability of the cam follower  202  valve stem interface that is particularly beneficial during assembly of the cylinder head components. As shown in FIG. 6 c  the extensions  222 ′ may extend beyond the side walls  202  to form opposing valve guide walls. 
     The main body of the follower  101 , 201  is preferably stamped from a single sheet of steel to form a one-piece body which is then heat treated. However cast or net formed followers may similarly be employed. The clamp  120 , 220  may be similarly stamped. 
     As depicted in each of FIGS. 3-8, the cam follower  101 , 201  of the preferred embodiment comprises an upward extending U-shaped member and the clamp  120 , 220  is a downward extending U-shaped member disposed over the cam follower  101 , 201 . However, it is to be understood that the cross section of the main body of the cam follower could be an inverted U-shaped member or H-shaped member. The clamp member would then be suitably shaped to induce compression through the connecting pallet member  106 , 206 . 
     FIGS. 7-8 simply represent an elevated perspective view of the cam follower and clamp device of the embodiments of FIGS.  3 , 4  and  5 , 6 A respectively. The arrows indicate the induced compression forces through the lower pallet  106 , 206 . 
     FIGS. 9A&amp;9B represent an alternative method of securing the clamp  320  to the follower  301 . In this embodiment, a dimple or detent  330  is formed on each side wall  302 . The clamp  320  is then simply fitted over the follower and crimped or otherwise deformed to engage the dimple to retain the clamp to the pallet. In an alternate embodiment, the clamp  320  may be pre-deformed and installed on the follower in a snap fit fashion. In yet another embodiment, the side walls of the follower and inner surface of the clamp may be formed with corresponding barbed like retention members to facilitate a snap fit fashion. In such an instance either the side walls or the inner surface of the clamp may be formed with a plurality of corresponding projections and recesses as will be appreciated within the art. The side walls of the clamp  320  may also be extended to act as valve guide walls to improve stability during engine assembly and operation. 
     Although the present invention has been fully described in connection with the preferred embodiment thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the present invention as defined by the appended claims. For example, the present invention is not limited to the fold up type follower depicted in FIGS. 1-9. The present invention may similarly be adapted and dimensioned to accommodate other types of followers, Specifically, FIGS. 10-11 represent an alternative follower  401 . As shown in FIG. 12 an inverted U-clip  420  has tabs  422  that snap over the follower  401  of FIGS. 10-11 to facilitate a simple installation. Further embodiments of the present invention are shown in FIGS.  13  and  14 A- 14 B. 
     FIG. 13 depicts a U-shaped clamp  520  which is spot welded at points  599  to the side walls  502  of the cam follower  501 , The side walls of the clamp  520  extend past the pallet  506  to provide improved stability during installation of the valve assembly or engine operation. FIGS. 14A-14 b  show a similar arrangement wherein the clamp  620  is secured to the sidewalls of cam follower  601  having a preformed coined recess  698  formed in the sidewall to accommodate a lance  699  formed in the clamp  620 . FIGS. 14A depicts an exploded view of the clamp  620  and cam follower  601  in a pre-assembled state. FIG. 14B depicts the clamp  620  and cam follower  601  in an assembled stated, The clamp  620  is simply forced over the cam follower  601  in a snap fit fashion.