Patent Publication Number: US-7721695-B2

Title: Connection element for the secure fixing of a lever-type cam follower

Description:
FIELD OF THE INVENTION 
   The invention relates to a connecting element, composed of flat material, for captively retaining a lever-like cam follower, which serves for actuating a gas-exchange valve of an internal combustion engine, on a support element which has a spherical end which merges in a stepless fashion or without an undercut from a cylindrical section and on which the cam follower is mounted, by means of a spherical-cap-shaped formation, so as to be pivotably movable in the direction of the gas-exchange valve about a centre of rotation. Here, the connecting element engages around the cylindrical section with elastically deformable projections, which proceed from central webs, parallel to the pivot axis of the cam follower in such a way that the connecting element is connected to the cylindrical section merely in a frictionally-engaging manner. 
   BACKGROUND OF THE INVENTION 
   Connecting elements of said type permit, in a known way, the generation of a module which contains for example a rocker arm as a cam follower and a support element With a module of said type, the risk of potential incorrect assembly in the cylinder head of the internal combustion engine is minimized. Said incorrect assembly could inter alia consist in that the rocker arm is mounted in the valve drive rotated through 180°. In this case, the contact partners the ball head of the support element and spherical cap of the rocker arm, and the valve shank end and corresponding mating surface on the rocker arm, would be interchanged. This would result at least in valve drive malfunction, and in the worst case, even in serious engine damage. 
   In contrast to connecting elements which engage in a form-fitting manner into an annular groove below the ball head, connecting elements which act in a frictionally-engaging manner can advantageously be used in cases in which the annular groove cannot or cannot economically be produced as an undercut. Further demands on a connecting element of said type are not only that a separation of rocker arm and support element by transport influences is reliably prevented, but also that the rocker arm and the support element remain aligned with respect to one another, corresponding to the operational state, by means of the connecting element even during the assembly of the module into the internal combustion engine. In this respect, the connecting element also performs the task of largely preventing the rocker arm from tilting about its longitudinal axis by means of suitable lateral support on the support element in order to ensure correct transverse alignment of the rocker arm on the camshaft which is to be installed. A tilting of the rocker arm about its longitudinal axis is referred to below as a tilting movement in contrast to its pivoting movement in the direction of the gas-exchange valve. 
   The prior art has already proposed connecting elements which are connected to the support element in a frictionally-engaging instead of form-fitting manner. U.S. Pat. No. 6,047,675 A, which is considered as being generic, discloses a connecting element which is composed of flat material and which is connected in a frictionally-engaging manner to a support element which has no undercut in the region of the spherical end. Said connecting element has projections which are aligned towards the cylindrical section below the spherical end and which engage around the support element in such a way that a tilting movement of the rocker arm which is mounted on the support element is largely prevented, while the pivoting movement of said rocker arm in the actuating direction of the gas-exchange valve is permitted. 
   The connecting element proposed in the cited document nevertheless has some significant disadvantages. For example, the projections of said connecting element are of flat design and extend merely in a plane parallel to the pivot axis of the rocker arm. This firstly has the result that a lever arm, which promotes the correct transverse alignment of the rocker arm on the support element, between the contact points of the projections and the centre of rotation of the rocker arm is disadvantageously small. Secondly, on account of the not only flat but also short projections, as a result of their limited material elasticity, it is necessary for the splaying of the projections, which is required for the assembly of the connecting element, to be imparted largely by means of elastic deformation of the webs from which the projections proceed. However, there is the risk here of an undesired warping of the webs, for example in the form of corrugation, torsion or twisting. Such deformation of the connecting element can likewise lead, on account of projections being offset in terms of height, to misalignment of the rocker arm. In connection with said short lever arm, there is additionally an increased risk of the connecting element slipping in the tilting direction of the rocker arm. 
   Said disadvantageous effect can be further intensified taking into consideration the component tolerances. The cause for this is likewise to be considered the planar, short and consequently comparatively rigid projections, so that both a production-related change in spacing of the projections relative to one another and also a fluctuating diameter of the cylindrical section as a result of additional deformation of the web sections from which the projections proceed must be compensated. 
   A rocker arm which is aligned correctly on the support element can finally be of significance not only for the transport and assembly of the module but also for fail-safe operation in the internal combustion engine. For example, in the event of a loss of contact between the rocker arm and the actuating cam, the action of the cam which aligns the rocker arm can be lost. Causes for a loss of contact of said type can be undesired subsidence of the most-used support elements with hydraulic valve play compensation, or lifting of the rocker arm from the cam as a result of an excessively high rotational speed of the internal combustion engine. In the phase of contact loss, a “skewed” connecting element would then force the rocker arm in the tilting direction. In this regard, rocker arms with a very narrow cam contact face are to be given particular consideration. These are used in multi-valve engines with restricted installation space or also in variable valve controllers in which a cam pack composed of a plurality of cams of different lift is movably mounted on its camshaft and is placed in engagement with the rocker arm by the cam suitable for the operating state of the internal combustion engine. The rocker arm is then at particular risk with regard to a further tilting movement or completely tilting away from the support element, since in the event of renewed contact with its cam, said rocker arm can no longer be aligned on the cam to a sufficient degree on account of the narrow cam contact face. 
   OBJECT OF THE INVENTION 
   It is therefore an object of the invention to create a connecting element of the above-specified type in which the cited disadvantages are eliminated using simple means. It should accordingly be ensured, in contrast to the connecting elements known in the prior art, firstly that the cam follower is held in a sufficiently captive manner on the support element, and secondly that the operational transverse alignment of the cam follower on the support element has an increased level of robustness. Here, robustness is to be understood to mean the stability of the required transverse alignment of the cam follower under the action of disturbance influences, which include for example the previously specified component tolerances. 
   SUMMARY OF THE INVENTION 
   Said object is achieved according to the features of Claim  1 , while advantageous refinements and embodiments can be gathered from the subclaims. Accordingly, the object is achieved in that the projections are embodied as lugs which are angled away from the central webs and which extend in a direction pointing away from the cam follower, so that as such, the projections are elastic in shape. 
   The stated disadvantages are in this way eliminated using simple means. The projections which are embodied as lugs engage around the cylindrical section at contact points which are spaced apart from the centre of rotation of the cam follower by a relatively great distance. The lever arm generated in this way is sufficiently large to promote the operational transverse alignment of the cam follower on the support element and to stabilize said transverse alignment against slipping. At the same time, on account of the projections which are inherently elastic in shape, it is ensured that the elastic deformation of the connecting element required for the frictionally-engaging connection on the cylindrical section is imparted primarily by the lugs themselves and only to an insignificant extent by the webs from which the lugs proceed. The risk of the deformation of the webs, which can lead to the misalignment of the cam follower, explained in the introduction is also minimized in that the projections which are elastic in shape are extremely well suited to compensating said component tolerances. 
   In one preferred embodiment of the invention, the central webs should belong to a closed and substantially planar annular section, which annular section bears against a first side, which faces towards the support element, of a base, which surrounds the spherical-cap-shaped formation, of the cam follower. In order to fasten the connecting element to the cam follower, the annular section has angled holding claws which are aligned in the longitudinal direction of the cam follower and which are latched with holding lugs on a second side, which faces away from the support element, of the base. By means of said embodiment, a rigid connection of the connecting element to the cam follower is obtained. The sufficiently large lever arm is then generated in that the lugs engage around the cylindrical section of the support element at contact points whose spacing, projected onto a longitudinal axis of the support element, to the centre of rotation is greater than a spacing, projected onto the longitudinal axis, of the planar annular section to the centre of rotation. 
   In addition, the cam follower should be embodied as a rocker arm which has a generally U-shaped cross section and which is produced in a non-cutting fashion from sheet metal material. A moulded part composed of cold-hammered sheet metal material is expediently also to be provided as a connecting element. A connecting element of said type is particularly simple and cost-effective to produce and can be assembled on the cam follower in a reliable manner. One particularly preferred embodiment of the invention is finally given by a combination of the features as specified in Claim  5  and explained above. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is explained in more detail on the basis of the appended drawings which illustrate an exemplary embodiment and in which: 
       FIG. 1  shows a connecting element according to the invention in the assembled state of a valve drive, with a cam follower shown in longitudinal section, 
       FIG. 2  shows the connecting element as per  FIG. 1  in an enlarged perspective illustration. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1  illustrates a detail of a valve drive  1  of an internal combustion engine in the assembled state. Illustrated is a cam follower  2  which, in a known way, is driven in the actuating direction of a gas-exchange valve  4  by means of a cam (not shown) via a rotatably mounted roller  3  which is connected to the cam follower  2 . It is of course also possible, instead of the roller  3 , for a sliding face which is rigidly connected to the cam follower  2  to be provided as a cam contact face. The cam follower  2  is formed in the exemplary embodiment as a rocker arm  5  which has a generally U-shaped cross section in the longitudinal direction and is produced in a cost-effective manner from sheet metal material in a non-cutting shaping process. A support element  6  which is mounted so as to rest in the internal combustion engine has a spherical end  7  on which the cam follower  2  is mounted, by means of a spherical-cap-shaped formation  8 , so as to be pivotably movable in the direction of the gas-exchange valve  4  about a centre of rotation  9 . 
   In order to captively retain the rocker arm  5  on the support element  6 , a connecting element  10  is provided which is explained in more detail below taking into consideration  FIG. 2 . The connecting element  10 , as a moulded part produced in a non-cutting fashion, is composed of cold-hammered sheet metal material and has a closed annular section  11  which bears against a first side  12 , which faces towards the support element  6 , of a base  13 , which surrounds the spherical-cap-shaped formation  8 , of the rocker arm  5 . Holding claws  14 ,  15  which are angled away at 90° and which are aligned in the longitudinal direction of the rocker arm  5  proceed from the annular section  11 , which holding claws  14 ,  15  are latched with holding lugs  16  on a second side  17 , which faces away from the support element  6 , of the base  13 . The connecting element  10  is in this way fixed to the rocker arm  5 , with additional angles  18  being provided on the holding claw  14 , which assist precise longitudinal alignment of the connecting element  10  with respect to the rocker arm  5 . The annular section  11  comprises central webs  19 , from which angled projections  21 , which are embodied as lugs  20 , proceed in a direction pointing away from the rocker arm  5 . 
   The spherical end  7  merges in a stepless manner and without an undercut into a cylindrical section  22  which the lugs  20  engage around parallel to the pivot axis, which runs through the centre of rotation  9 , of the rocker arm  5 . For this purpose, in the non-assembled state of the connecting element  10 , the clear spacing of the lugs  20  to one another is smaller than the diameter of the cylindrical section  22 . When the connecting element  10  is pulled over the spherical end  7  onto the cylindrical section  22 , the lugs  20  deform elastically and connect the support element  6  in a frictionally-engaging manner to the connecting element  10  which is fixed to the rocker arm  5 . In this way, a module  23  composed of the rockier arm  5 , the support element  6  and the connecting element  10  is formed, which module  23 , in the non-assembled state of the valve drive  1 , captively retains the rocker arm  5  on the support element  6 . In addition, it is ensured in said state that the rocker arm  5  is aligned with respect to the support element  6  at least so as not to tilt to a great extent. An alignment of said type is promoted by the connecting element  10  and for example stabilized against slipping in that a lever arm  24 , projected onto the longitudinal axis of the support element  6 , between contact points  25  of the lugs  20  and the centre of rotation  9  of the rocker arm  5  is sufficiently large. For comparison,  FIG. 1  shows a considerably smaller lever arm  26  as would be given by non-angled projections as per the cited prior art. 
   It can also be clearly seen from  FIG. 2  that the lugs  20  are, as such, elastic in shape. This means that the elastic deformation required for pulling the connecting element  10  onto the cylindrical section  22  of the support element  6  is absorbed largely by the lugs  20  and only to a small extent by the webs  19  or by the annular section  11 . Accordingly, the risk of corrugation, twisting, torsion or similar deformation of the webs  19  or of the annular section  11  with lugs  20  which correspondingly engage, in a manner offset in terms of height, on the cylindrical section  22 , is minimized, and a resulting misalignment of the rocker arm  5  on the support element  6  is largely prevented. 
   In the illustrated exemplary embodiment, the lugs  20  are designed such that, adjacent to a transition radius, they are planar and angled by in each case 90° with respect to the central webs, and accordingly run parallel. Conically tapering and/or multiply-curved or completely curved lugs are also possible as alternative embodiments. 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Valve drive 
         2  Cam follower 
         3  Roller 
         4  Gas-exchange valve 
         5  Rocker arm 
         6  Support element 
         7  Spherical end 
         8  Spherical-cap-shaped formation 
         9  Centre of rotation 
         10  Connecting element 
         11  Annular section 
         12  First side 
         13  Base 
         14  Holding claw 
         15  Holding claw 
         16  Holding lug 
         17  Second side 
         18  Angle 
         19  Web 
         20  Lug 
         21  Projection 
         22  Cylindrical section 
         23  Module 
         24  Lever arm 
         25  Contact point 
         26  Lever arm