Patent Publication Number: US-7721696-B2

Title: Cam follower for a valve drive of an internal combustion engine

Description:
This application is a non-provisional application of provisional application Ser. No. 60/833,673 filed Jul. 27, 2006. 

   FIELD OF THE INVENTION 
   The invention relates to a cam follower for a valve drive of an internal combustion engine, having a roller, which is rotatably mounted on a journal, as a cam thrust face, which journal runs with its outer casing in a respective bore of a first and second guide wall of the cam follower, between which guide walls the roller is held, wherein the journal is held in the bores by means of travel limitations. 
   BACKGROUND OF THE INVENTION 
   A cam follower of said type can be gathered from U.S. Pat. No. 5,385,124 which is considered as generic. The journal is secured axially by means of two securing rings which run in annular grooves of bores in the guide walls. The formation of the two annular grooves for the securing rings is complex. It is also observed that the assembly of the journal, with the snapping-in of the two securing rings, is unnecessarily complex. 
   GB 2 233 418 A (FIG. 2) discloses a cam follower whose journal is calked at both ends. Said calked connection can become loosened during operation, for example in the event of unfavorable tolerancing. It is otherwise clear that undesired influencing of the bore region of the respective guide wall can occur as a result of the material displacement which has taken place during the calking. In addition, calking of said type requires increased checking expenditure at the quality control stage. 
   OBJECT OF THE INVENTION 
   It is therefore an object of the invention to create a cam follower of the above-described type, in which the stated disadvantages are eliminated. 
   ACHIEVEMENT OF THE OBJECT 
   According to the invention, said object is achieved by means of the novel features of claim  1 , with expedient physical embodiments of the invention being the subject matter of the subclaims, which can also contain individually patentable measures. 
   Accordingly, in simple terms, an axial travel limitation of the journal is provided in only one direction by means of a securing ring which is provided at the end side on the outer casing of said journal, whereas an axial travel limitation in the other direction of said journal is formed by means of an annular collar which runs between two stepped diameter regions of the journal. 
   Here, it is particularly expedient if, as is proposed in a physical embodiment of the invention, the journal is guided with a clearance fit with respect to the bores and with slight axial play between the travel limitations. 
   A “floating” bearing arrangement of the journal in relation to the bores is therefore provided. By means of the collar, there is a “hard” abutment of the journal against a lateral surface of one of the guide walls. Another abutment can be formed by means of a corresponding inner annular face of the proposed securing ring. It is therefore clear to a person skilled in the art that the journal fixing according to the proposed invention permits a small axial travel and also a rotational movement of the journal relative to the bores. The stepped-diameter journal can be mass-produced easily in manufacturing terms. 
   It is also possible, instead of the proposed securing ring, to provide further separate elements, such as for example split pins or other radially projecting components. 
   In a refinement of the invention, it is proposed to guide the roller on the journal either by means of a rolling bearing arrangement which is known per se, or to provide a plain bearing in this region. 
   Considered as a cam follower is for example a beam-like component, such as a tilt lever, oscillating arm or rocker arm, or else a roller tappet. All components can be present in switchable or non-switchable form, and can likewise be designed such that they can be acted on only indirectly in the valve drive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail on the basis of the drawing. 
       FIG. 1  shows a schematic plan view of a beam-like cam follower having a first variant of a fastening of its journal, and 
       FIG. 2  shows an alternative variant to  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1  shows a plan view of a cam follower  1  which is embodied as a rocker arm or oscillating arm, wherein the bearing region of said cam follower  1  is not illustrated here for clarity. 
   That end of the cam follower  1  which is illustrated at the left-hand side acts, by means of its underside, on a gas exchange valve. Here, the cam follower  1  has two opposing guide walls  7 ,  8 , in the cutout of which is held a roller  3  as a direct cam thrust face. The roller  3  runs, in  FIGS. 1 ,  2 , on a journal  2  via a rolling bearing  18  such as a needle bearing arrangement. 
   The journal  2  is designed with stepped thickness, and is composed of a first section  9  and a second section  10 , wherein the first section  9  has a greater diameter than the second section  10 . As can be seen, the first section  9  is illustrated in  FIG. 1  as an annular projection  13 . The latter bears against an outer lateral surface  14  of the first guide wall  7 . 
   The two bores  5 ,  6  in the guide walls  7 ,  8  ( FIG. 1 ) have an identical diameter. Axially behind the second guide wall  8 , a securing ring/circlip  12  runs in an annular groove  15 . An axial travel limitation of the journal  2  in its other direction is therefore provided by means of contact of said securing ring  12  against an outer lateral surface  16  of the second guide wall  8 . As illustrated, the journal  12  is guided in the bores  5 ,  6  with slight axial play (see spacing of the securing ring  12  to the outer lateral surface  16  of the second guide wall  8 ). In addition, the journal  2  is held so as to be rotationally moveable relative to the bores  5 ,  6 , so that, for both solutions, it is possible to refer to a “floating” bearing arrangement. 
     FIG. 2  shows a similar embodiment to  FIG. 1 . However, the bores  5 ,  6  in the guide walls  7 ,  8  have a different diameter. Here, the first bore  5  is larger than the second bore  6 . The journal  2  extends with its first section  9  through the bore  5 , and, by means of the collar  11 , faces an inner lateral surface  17  of the second guide wall  8 . The second section  10  of the journal  2 , with a smaller diameter, runs in the second bore  6 . The design of the securing ring  12  is the same as in  FIG. 1 . 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Cam follower 
         2  Journal 
         3  Roller 
         4  Outer casing 
         5  First bore 
         6  Second bore 
         7  First guide wall 
         8  Second guide wall 
         9  First section 
         10  Second section 
         11  Collar 
         12  Securing ring 
         13  Projection 
         14  Outer lateral surface 
         15  Annular groove 
         16  Outer lateral surface 
         17  Inner lateral surface 
         18  Rolling bearing