Abstract:
A sliding bearing ( 10 ) having a bearing body ( 11 ) which receives a shaft ( 1 ) in a guide bore ( 26 ) and is fabricated by a noncutting production process, wherein the bearing body ( 11 ) serves for at least indirect arrangement in a preferably fixedly arranged element ( 2 ), in particular a housing. According to the invention, it is provided that the bearing body ( 11 ) is provided on its outer circumference with a receptacle ( 14 ) for an elastic bearing element ( 12 ) for bearing against the fixed element ( 2 ).

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a sliding bearing. The invention also relates to a process for producing a sliding bearing and to the use of a sliding bearing. 
     For cost reasons, sintered bearings are usually employed in relatively small electric motors as are used, for example, as a comfort drive in motor vehicles as a seat adjustment drive or as a power-window drive. These bearings are produced by axial pressing of the material. However, radial undercuts (radial grooves) cannot be produced by this production process. Such sintered bearings are embodied as spherical or cylindrical sliding bearings. Here, in the case of spherical sliding bearings, the self-alignment of the bearing with respect to a housing is decisively influenced by the frictional engagement of additional components, resulting in a relatively high degree of scatter under similar conditions. Furthermore, the additional components (spring plates) in combination with the assembly and testing steps make the known spherical sliding bearings relatively expensive to produce. In the case of cylindrical sliding bearings, no self-alignment takes place at all, with the result that there is a relatively high risk of service life-reducing, so-called edge running. Furthermore, when the cylindrical sliding bearing is pressed in a force-fitting manner into a housing, the tolerances and cylinder shape defects of the housing are transferred to the bearing bore. Moreover, as a result of additional effects caused by different thermal expansions between the housing, the bearing and the shaft, a relatively large bearing play is required. This can result in undamped contact between the bearing and the housing, promoting the transmission of structure-borne noise. As seen overall, conventional bearings therefore have some negative properties which can only be avoided through a relatively high outlay on manufacturing, with correspondingly associated relatively high production costs. 
     SUMMARY OF THE INVENTION 
     Taking the illustrated prior art as a starting point, the object of the invention is to develop a sliding bearing such that, with relatively low production costs, it particularly allows an arrangement in a housing in which the transmission of structure-borne noise is avoided and tolerances between the bearing and the housing can be compensated for in a relatively simple manner. Here, the invention is based on the idea of forming the sliding bearing substantially only from two parts, namely the bearing body for receiving the shaft, and an elastic bearing element which is received on an outer lateral surface of the bearing body in a receptacle and produces contact with respect to the housing. Here, the elastic design of the bearing element achieves a constantly secure and noise-damping bearing of the sliding bearing against the housing, it being possible at the same time for component tolerances to be compensated for in a relatively simple and effective manner through the elasticity of the bearing element. 
     Advantageous developments of the sliding bearing according to the invention are specified in the subclaims. The scope encompasses all combinations of at least two features disclosed in the claims, the description and/or the figures. 
     With particular preference it is provided that the receptacle is designed as a radially encircling, groove-shaped receptacle. In a further embodiment of the invention, this means that the elastic bearing element can be designed as a standardized component, in particular as an O-ring or square ring. Consequently, the production costs of the sliding bearing can be reduced and high degrees of accuracy are achieved by means of the standardized component. 
     In one structural design of the sliding bearing in which the latter can be produced in a relatively simple manner by axial pressing, it is provided that the lateral surface has, in the longitudinal direction of the bearing body and on both sides of the receptacle, respective guide ribs which form the receptacle by way of mutually facing bevels, wherein the guide ribs arranged on both sides of the receptacle have an angle-of-rotation offset with respect to one another. 
     The bearing body of the sliding bearing can be produced with a wide variety of materials suitable for axial pressing. Provision can be made here in particular for the bearing body to consist of sintered metal, graphite, (which has naturally good lubricating properties), ceramic, plastic (here both thermosets and thermoplastics) or hard metal. 
     The invention also comprises a process for producing a sliding bearing according to the invention. Provision is made here for the bearing body to be produced by axial pressing by means of a tool, wherein, in order to form the guide bore (for the shaft), a first part of the tool is designed as a cylindrical mandrel toward which parts designed as a bottom die and as a top die are moved from two different directions of the longitudinal axis of the mandrel in order, by means of pressure, to form the material situated between the parts into the bearing body. 
     In a particularly preferred variant, it is proposed here that the parts of the tool serving as the bottom die and top die have a crown-like design. 
     To form the receptacle of the elastic bearing element, it is proposed here that tooth-like projections of the crown-like bottom die and top die are moved toward one another to form the receptacle, wherein the projections engage in one another over part of their length. 
     Particular preference is given to the use of a sliding bearing according to the invention for mounting shafts in small electric motors. Here, such small motors can be provided in particular in motor vehicle comfort drives, in particular as power-window drives or seat adjustment drives. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages, features and details of the invention will become apparent from the following description of preferred exemplary embodiments and with reference to the drawing, in which: 
         FIG. 1  shows a longitudinal section through part of a drive motor using a sliding bearing according to the invention, 
         FIG. 2  shows a view in direction II-II of  FIG. 1 , 
         FIG. 3  shows a side view of a bearing body of a sliding bearing according to the invention, 
         FIG. 4  shows a section through a tool for producing a sliding bearing according to the invention, 
         FIG. 5  shows a top and bottom die of a tool according to  FIG. 4  in a simplified side view, 
         FIG. 6  shows a view in direction VI-VI of  FIG. 5 , an 
         FIG. 7  shows a representation to illustrate the interaction between the top die and bottom die to form a receptacle for a bearing element. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1  there is shown, in a detail view, a region of a small electric motor  100  in the region where its shaft  1  is mounted. Here, the small motor  100  is in particular, but with no restriction being implied, a constituent part of a motor vehicle comfort drive, for example a power-window drive, a seat adjustment drive or the like. 
     The small motor  100  or the motor vehicle comfort drive has a housing  2  in the interior of which the shaft  1  is positioned or mounted by means of a sliding bearing  10  according to the invention. The sliding bearing  10  has a bearing body  11  which is positioned and received in the housing  2  via an elastic bearing element  12 . Here, the bearing element  12  is designed in particular as a standardized component in the form of an O-ring or square ring which is received in a form-fitting manner in a radially encircling, groove-like receptacle  14  of the bearing body  11 , wherein a radial gap  3  is additionally formed between the bearing body  11  and the housing  2  to compensate for component tolerances and to avoid the transmission of structure-borne noise to the housing  2 . 
     As can be seen in particular by looking at  FIGS. 1 to 3  together, the sleeve-shaped bearing body  11  has on its outer circumference guide ribs  16 ,  17  which are arranged in the longitudinal direction of the bearing body  11 , i.e. axially parallel to the longitudinal axis  18  of the bearing body  11 . Here, the guide ribs  16 ,  17  are arranged on both sides of the receptacle  14  in such a way that the guide ribs  16  forming one set each have an angle-of-rotation offset with respect to the guide ribs  17  forming the other set, wherein the distance a between the individual guide ribs  16 ,  17  is in each case identical and corresponds to the width b of a guide rib  16 ,  17  ( FIG. 3 ). It can also be seen that the receptacle  14  in each case extends as far as the base  19  of the guide ribs  16 ,  17 , and the guide ribs  16 ,  17  have bevels  21 ,  22  against which the bearing element  12  comes to bear. 
     The bearing body  11  is produced by a noncutting forming process in the form of axial pressing. Here, the bearing body  11  consists in particular of sintered metal, graphite, ceramic, plastic or hard metal. 
     The production process for a bearing body  11  will now be described in greater detail with reference to  FIGS. 4 to 7 :  FIG. 4  depicts in a simplified manner a tool  25  for producing the bearing body  11 , the tool substantially comprising four parts: a cylindrical mandrel  27  arranged in the region of the guide bore  26  of the bearing body  11  or forming the guide bore  26 , a top die  28 , a bottom die  29  and a receiving body  24  which radially encloses the top die  28  and the bottom die  29 . As can be seen in particular from  FIGS. 5 and 6 , both the top die  28  and the bottom die  29  each have a crown-like design. Here, the top die  28  and the bottom die  29  each have tooth-like projections  30  which serve to form the guide ribs  16 ,  17  and to form the receptacle  14 . Furthermore, concentrically to the longitudinal axis  31  of the top die  28  and of the bottom die  29 , a respective aperture  32  is formed at the bottom  33  of the top die  28  and of the bottom die  29  and is dimensioned such that the diameter of the aperture  32  is tailored to the diameter of the mandrel  27 . As can also be seen from  FIG. 4 , the top die  28  and the bottom die  29  are moved toward one another in the direction of the arrows  35 ,  36  by means of drives (not shown) in order to produce the bearing body  11 , with the mandrel  27  protruding through the two apertures  32  of the top die  28  and the bottom die  29 . Furthermore, it can be seen from  FIG. 7  that the angle-of-rotation position between the top die  28  and the bottom die  29  is such that, during the movement of the top die  28  and bottom die  29  toward one another, the tooth-like projections  30  project into one another over a part of their length, with the regions of the projections  30  which project into one another forming the receptacle  14  when the top die  28  and bottom die  29  are subsequently moved apart. 
     To form the bearing body  11 , the material of the bearing body  11  is pressed between the top die  28 , the bottom die  29  and the mandrel  27  by axially moving the top die  28  and bottom die  29  toward one another. The manufactured bearing body  11  can be removed from the tool  25  by withdrawing the mandrel  27  and then axially moving apart the top die  28  and bottom die  29 . 
     The sliding bearing  10  described so far can be varied or modified in a variety of ways without departing from the idea of the invention. In particular, the bearing body  11  may also have different geometries. It is essential only that the bearing body  11  is produced by axial pressing, with a receptacle  14  for receiving an elastic bearing element  12  being formed during axial pressing.