Patent Publication Number: US-8522643-B2

Title: Cam follower

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of DE 10 2010 033 120.1 filed Aug. 3, 2010, which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a cam follower for a high-pressure fuel pump or for a valve drive in each case of an internal combustion engine with quantity or quality regulation, having a cam roller which is accommodated in a pocket of the cam follower, which cam roller is mounted by means of its bore on a pin which is seated at the ends in receptacles of opposite walls of the pocket, the cam roller running with its end sides directly in front of said walls. 
     A cam follower of said type emerges from DE 10 2005 047 234 A1. Said cam follower is designed as a cup-shaped tappet and serves to exert a periodic loading on a pump piston of a fuel pump. A further cam follower is described in DE 103 54 683 A1. Said cam follower takes the form of a rocker arm and is used for exerting a loading on a gas exchange valve in a valve drive. 
     In each case one roller mounted on a pin serves as a cam opposing member. Said roller runs via its end sides, which are planar with the exception of a structurally necessary chamfer in the transition region to the bore and to an outer surface of the cam roller, against flat walls of the pocket. On account of tolerances and/or the unfavorable summing thereof, an edge region of the end side to the outer surface of the cam roller may come into contact, during operation, with the corresponding wall of the pocket. In addition to the wear in the region of direct contact, the cam roller is braked, which results in slippage in the bearing and at the cam contact area. It is attempted in the prior art to counteract the undesirably high wear by means of very high production accuracy, applied coatings and/or improved lubrication. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a cam follower of the type described in the introduction which, however, does not have the stated wear problems. 
     According to the invention, said object is achieved in that each end side of the cam roller takes substantially the form of an outer surface of a spherical zone, wherein each wall is of smooth-walled, straight design at least in the region of its nm-on piece at the respective end side of the cam roller. 
     An alternative design to this is the subject matter of the further independent claim  3 , according to which each end side of the cam roller is planar, and wherein the run-on piece of said end sides on the wall is formed as a spherical section bulged inward in the direction of the cam roller. 
     If appropriate, it is also possible for both end sides to simultaneously take the form of spherical sections bulged toward one another, or similar designs. 
     Owing to this solution which can be realized very cheaply in production terms, the stated wear problems are eliminated and the service life of the cam follower is increased. The additional wear protection measures described in the introduction are not required but may be applied as before. If appropriate, the tolerancing accuracy may be reduced. 
     If the cam roller assumes an undesired oblique position, a much “less severe” contact region arises. So-called “edge loads” are eliminated by the measures according to the invention. On account of the planar or flattened radially inner section, high-wear edge contact at the transition region in the bore is simultaneously prevented. 
     It goes without saying that chamfers [bevels or rounded portions] are still provided at the transition regions from the end side to the bore and to the outer surface, because these are structurally necessary. 
     A further subclaim relates to simple measures for mounting the cam roller on the pin. Either a rolling bearing, such as a needle-roller bearing, or a plain bearing is used. The cam contact area may be lubricated by means of targeted spraying of oil and/or by means of oil mist. The pin may be fastened by being caulked, riveted, pressed in, etc. Depending on the application, it is also conceivable and provided for said pin to be mounted in a floating fashion. 
     It is also proposed, in the case of a design of the cam follower as a cup-shaped tappet or roller tappet (push rod loading), that the receptacles for the pins be provided in longitudinal flattened portions which are recessed from the cylindrical skirt, such that a flat, inner abutment surface for the end of the pin is generated in a simple manner. If appropriate, said flattened portion may however also be generated retroactively, for example by cutting. 
     Alternatively, the cam follower may also take the form of a lever such as a rocker arm, oscillating arm or tilt lever, between the side walls of which the cam roller is installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained on the basis of the drawing, in which: 
         FIGS. 1-4  show a cam follower for a high-pressure fuel pump, designed in this case as a roller tappet, in two side views and two sectional views; 
         FIG. 5  shows a three-dimensional view of a cam follower for a valve drive, designed in this case as a rocker arm; 
         FIG. 6  shows a greatly enlarged partial section in the region of the mounting of the pin in the wall of the cam follower; 
         FIG. 6A  shows a further embodiment of the present invention in a view corresponding to that of  FIG. 6 ; and 
         FIG. 7  shows a partial section similar to that mentioned above, but with a solution according to the prior art. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-4  show a cam follower  1 , designed as a cup-shaped tappet, for a high-pressure fuel pump of an internal combustion engine. The cam follower  1  is composed of a hollow cylindrical skirt  14 , from the drive-side edge  13  of which extends a pocket  2 . A cam roller  3  is accommodated in said pocket. Said cam roller has a bore  4  with a rolling bearing  12  by means of which the cam roller  3  runs on a pin  5 . The pin  5  is seated at the ends in receptacles  6  of opposite walls  7  of the pocket  2 . The walls  7  are formed as diametrically opposite recessed longitudinal flattened portions  18 . The cam roller  3  runs with its end sides  8  directly in front of and/or against the walls  7 . 
     As can be most clearly seen in this context from  FIG. 6 , each end side  8  of the cam roller  3  is formed as an outer surface of a spherical zone. In other words, said end side  8  is of crowned or domed design. At the same time, each wall  7  has a smooth-walled, plain profile in the region of its run-on piece  11 , i.e., the portion of the wall  7  on which the cam roller  3  can run. A section  10 , which directly adjoins an annular edge  9  in the bore  4 , of the respective end side  8  of the cam roller  3  is, however, of planar design. 
     If the cam roller  3  runs “obliquely” with one of its end sides  8  against the opposite wall  7 , then the contact region in the edge section of the end side  8  to the outer casing  17  is made much “less severe”. The wear problems described in the introduction are no longer to be expected. At the same time, a sharp-edged transition region of the end side  8  to the bore  4  is avoided as a result of the fact that the end side  8  is initially of planar form radially at the inside. 
       FIG. 5  shows a further variant of a cam follower  1  designed according to the invention. Here, said cam follower takes the form of a lever  15  (rocker arm), between the walls  7  of which is held the cam roller  3  which is mounted on the pin  5 . The lever  15  has a downwardly open U-shaped profile, wherein said lever may also have an upwardly open U-shaped profile or an H-shaped profile. The lever  15  may also be composed of solid material. 
       FIG. 6A  shows a further embodiment in which each end side  8 ′ of the cam roller  3 ′ is planar and the run-on piece  11 ′ of the end sides of the wall  7 ′ is formed as a spherical section. The section  10 ′ is flattened and is disposed radially outward from the annular edge  9 ′ of the bore  4 ′ of the cam roller  3 ′. 
     Finally,  FIG. 7  is representative of solutions realized previously in cam follower design, having end sides  8 , which are planar with the exception of chamfers, on the respective cam roller  3 , which end sides run against smooth-walled, straight walls  7 . The illustration shows an oblique position of the cam roller  3  which, in the relatively sharp-edged transition region of the end side  8  thereof to the outer surface  17 , runs with high wear against the wall  7 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1 ) Cam Follower 
           2 ) Pocket 
           3 ) Cam Roller 
           4 ) Bore 
           5 ) Pin 
           6 ) Receptacle 
           7 ) Wall 
           8 ) End Side 
           9 ) Annular Edge 
           10 ) Section 
           11 ) Run-on Piece (Wall) 
           12 ) Rolling Bearing 
           13 ) Edge 
           14 ) Skirt 
           15 ) Lever 
           16 ) Tappet 
           17 ) Outer Surface 
           18 ) Longitudinal Flattened Portion