Abstract:
Method for frictionally connecting the front surfaces of two machine components ( 1′, 2″; 2′, 3″; 3′, 4″ ) for transmitting high torques or transverse forces, wherein elevations ( 20 ) are provided on one ( 1′, 2′, 3′ ) of the surfaces ( 1′, 2″; 2′, 3″; 3′, 4″ ) to be connected, which are harder than the material of the other surface.

Description:
[0001]     This application claims Paris Convention priority of DE 10 2005 062 522.3 filed Dec. 19, 2005 the complete disclosure of which is hereby incorporated by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     The invention concerns a method for frictionally connecting the front surfaces of two machine components for transmitting high torques or transverse forces, and a structural component which is formed from these machine components and produced in accordance with this method.  
         [0003]     Frictional connections of two machine component surfaces are used in many fields of mechanical engineering for transmitting transverse forces or torques. The force that can be transmitted is thereby substantially produced by the surface pressure and the resulting friction between the connected surfaces. Such connections are important mainly in drive technology, e.g. for driving auxiliary units. The power that can be transmitted is often limited by the force that can be transmitted through contact between the two abutting surfaces.  
         [0004]     Such connections are mostly realized through force/friction fit in the form of shaft/hub connections. Depending on the geometry of the active surfaces, these are front, conical or cylindrical compression joints and associated friction fit combinations (flanges, clamping elements, screw heads). All of these connections are based on surface contact. The generated frictional force depends on different factors, e.g. on the type of joint, the surface roughness and the surface compression which preferably acts perpendicularly to the surfaces.  
         [0005]     Hard particles are conventionally introduced between the two surfaces to be connected in order to increase friction. A micro-positive locking is produced in the area where the hard particles penetrate into the material of the softer surfaces to be connected. The increase in friction results from the resistance of the material of the surfaces relative to grooves due to the hard particles. Such connections are disclosed e.g. in DE 31 49 596 A1, DE 101 48 831, DE 18 16 854 A1 and DE 23 46 275 C2. Resilient-elastic foils (diamond foils) are also conventionally used into which particles of hard material (diamond) are embedded (EP 0 961 038 B1, EP 1 564 418 A1). They are disposed between the surfaces to be connected.  
         [0006]     The production of these foils, in particular, of the diamond particles embedded in the foil, is expensive. The method for producing such connections and the constructive considerations are complex.  
         [0007]     It is therefore the underlying purpose of the invention to create a method for producing frictional connections between the front surfaces of two machine elements for transmitting high torques, which is considerably simpler than conventional methods and also produces structural components of two machine elements for transmitting high torques, which can be produced in a considerably easier and less expensive fashion than up to now.  
       SUMMARY OF THE INVENTION  
       [0008]     In accordance with the invention, this is achieved by the features of the independent claims. The invention moreover concerns advantageous further developments thereof.  
         [0009]     The inventive method is extremely simple, since there are conventional methods for producing depressions (micro-shaped pockets) and thereby also elevations, surrounding them, in metallic surfaces through suitable laser radiation systems, although the elevations are subsequently removed again through honing. The micropockets that remain in the surfaces improve the tribological properties, i.e. reduce friction (compare DE 20 2005 011 772 U, DE 20 2005 005 905 U, EP 0 565 742 B1; DE 43 16 012 C2, DE 295 06 005 U; EP 1 275 864 B1, and compare also U. Klink and G. Flores, Laser-Strukturieren von Zylinderlaufbahnen, 9. Internationales Feinbearbeitungskolloquium, 12. to 14. 10.1999, Braunschweig; Vulkan-Verlag, Essen (1999), ISBN 3-8027-8644-0; T. Abeln and U. Klink, Laserstrukturieren zur Verbesserung der tribologischen Eigenschaften von Oberflächen, in: Dausinger, F. et al., Stuttgarter Lasertage, 2001, pages 61 to 64). This technology for laser structuring supplements the present description in view of the applied devices and is hereby incorporated by reference.  
         [0010]     It has turned out that the simple method in accordance with the invention transmits much higher torques than conventional devices for a given pressure surface and contact pressure. It is thereby also possible to transmit transverse forces between flat, non-rotating and non-rotationally symmetric surfaces. The inventive content and quality of the method therefore greatly exceed the conventional improvement of the adhesive force of bearing shells in connecting rod eyes, as is disclosed in EP 1 420 177.  
         [0011]     One embodiment of the invention and its advantageous further developments are described below with reference to the enclosed drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]      FIG. 1  shows a connection between a crankshaft and a pulley produced in accordance with the inventive method;  
         [0013]      FIG. 2  shows the detail designated with II in  FIG. 1  in an enlarged scale;  
         [0014]      FIG. 3  shows the front surface  1 ′ of the crankshaft  1  in accordance with  FIG. 2 , also in an enlarged scale;  
         [0015]      FIG. 4  shows a top view of the front surfaces  1 ′ in the direction of arrows IV-IV in  FIG. 3 ;  
         [0016]      FIG. 5  shows the connection between the front surface  1 ′ of the crankshaft  1  and the front surface  2 ″ of the front surface  2  on an enlarged scale in correspondence with  FIG. 3 ;  
         [0017]      FIG. 6  shows further geometries for arranging the elevations on a front surface. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]      FIGS. 1 and 2  show the connection of the end of a crankshaft  1  (first machine component), two pinions  2  and  3  and a pulley  4  (further machine components) to a structural component. The front surface  1 ′ of the crankshaft  1 , the front surface  2 ′ of the pinion  2  and the front surface  3 ′ of the pinion  3  have elevations  20  ( FIGS. 2 and 3 ). When the crankshaft  1 , the pinions  2 ,  3  and the pulley  4  are tightened perpendicularly to the above-mentioned surfaces using a hexagon socket screw  15  which extends through a bore  16  in the axial projection of the pulley  4  and engages in a thread  17  in the crankshaft  1  ( FIG. 1 ), the hardened elevations  20  dig into the smooth, non-hardened front surface  2 ″ of the pinion  2 , the smooth, non-hardened front surface  3 ″ of the pinion  3 , and the smooth, non-hardened front surface  4 ″ of the pulley  4  and thereby form a micro-positive locking in each case, which accepts transmission of torques which are considerably larger than those realized by pressing smooth surfaces against each other with the same force.  
         [0019]     The hardened elevations  20  are mounted e.g. to the front surface  1 ′ through laser structuring in  FIG. 3 , i.e. through high-energy, focused laser beams which are directed onto the surface to be processed, using e.g. a YAG laser (yttrium aluminium garnet laser) (compare e.g. the schematic representation of such a laser in Popraw, R., Lasertechnik für die Fertigung, Spinger-Verlag Berlin/Heidelberg 2005, page 232′ and the above-mentioned references to patent literature). A surface  1 ′ may be exposed to a laser of his type to produce e.g. elongated pockets  21  (see  FIGS. 3 and 4 ). Such structures may be introduced in different patterns, e.g. also with dots. In this case, the pockets  22  are round. These round or elongated pockets may, in turn, be mounted linearly (e.g. as grooves  23 ) or in circles in different geometries ( FIG. 6 ).  
         [0020]     When the elevations  20  are introduced by laser radiation, the elevations are produced by point-focus melting of the material of the surfaces that warps at the edges, subsequently solidifies and hardens through cooling. The high concentration of energy at the focus of the laser beam melts and hardens the elevations of the material in the otherwise softer and smooth surface.  
         [0021]     In consequence thereof, when pressing these molten and hardened elevations  20  of the surfaces  1 ′,  2 ′,  3 ′ against each other ( FIG. 1 ), they dig into the smooth, non-hardened, softer surfaces  2 ″,  3 ″,  4 ″ that serve as a partner for forming structural components, thereby forming a connection that is resistant to torques and transverse forces, respectively. This connection may be released again.  
         [0022]     The invention extends beyond the above-described preferred embodiment. It comprises not only elevations which are produced through laser structuring, i.e. in principle through point-focus melting and hardening for digging into a softer surface. The elevations may also be introduced through an electron beam or mechanically. It is important that they are harder than the “soft” surface of the respectively other machine component.  
       LIST OF REFERENCE NUMERALS  
       [0000]    
       
           1  crankshaft  
           1 ′ front surface of  1  provided with elevations  20   
           2  pinion  
           2 ′ front surface of  2  provided with elevations  20   
           2 ″ smooth front surface of  2   
           3  pinion  
           3 ′ front surface of  3  provided with elevations  
           3 ″ smooth front surface of  3   
           4  pulley  
           4 ″ front surface of  4  provided with elevations  20   
           15  hexagon socket screw  
           16  bores  
           17  thread  
           20  elevations in  1 ′,  2 ′,  3 ′ 
           21  elongated pockets  
           22  round pockets  
           23  grooves