Abstract:
A method for producing a shaft and a device containing such a shaft ( 22 ), in particular an armature shaft ( 22 ) of an electric motor drive ( 10 ), which shaft is held by at least one shaft bearing ( 43 ), includes forming a bearing surface ( 40 ) for guidance in a shaft bearing ( 42 ) onto the shaft ( 22 ) at at least one point by positive displacement of material.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method for producing a shaft and to a device containing such a shaft [as generically defined by the preambles to the independent claims]. 
     With German Utility Model GM 297 02 525.2, a device has become known that is used for instance for displacing windows, sliding roofs, or seats. The object of this teaching is to avoid unwanted longitudinal play of an armature shaft, by means of a rubber insulator attached to the face end. A worm is pressed onto the armature shaft and transmits the torque of the electric motor to the worm wheel. The forward end of the armature shaft is guided in a rotary bearing receiving bush. This prevents the worm from deviating radially and thereby interfering with the meshing of the worm and wheel or destroying teeth. This is especially important when strong radial forces occur between the worm and the worm wheel, especially whenever the adjusting part runs up against a stop. From a production standpoint, pressing the completed worm onto the armature shaft is a very complicated and expensive process. Directly rolling the worm onto the armature shaft, conversely, is much less expensive. Then, however, the process creates a lengthy trailing region of the worm that can be used for neither transmitting force to the worm wheel nor bearing the armature shaft. As a result, especially in applications in which there is little installation space available, the end of the armature shaft can no longer be braced, or else complicated production processes are required to achieve such a support. 
     SUMMARY OF THE INVENTION 
     The method of the invention [having the characteristics of claim  1  ] has the advantage that regardless of the production process for the worm, a bearing surface for supporting the armature shaft can be created in a very simple way. By means of cold forming, and by not using metal-cutting machining, it is possible to produce a bearing point produced economically. The transition zone from the completed worm to the bearing can be kept quite short, and the meshing of teeth is moved close to the bearing point. This makes safe and reliable adjusting operation possible, in which damage to the teeth is effectively avoided. 
     By means of the characteristics recited in the dependent claims, advantageous refinements of the method of claim  1  are possible. From a production standpoint, it is particularly important first to form on a worm over a certain region of the shaft, for instance using a rolling method. From the method standpoint, relatively lengthy trailing regions are created on the ends of the worm that can be used for neither force-transmitting toothing nor as a bearing face. Here it is especially advantageous for these trailing regions of the shaft to be reshaped into a bearing surface by means of positive displacement of material. Above all with the goal of saving installation space, it is an important criterion to make the bearing surface in the immediate vicinity of the effective tooth engagement of the worm. By means of positive displacement of material, portions in the middle region of the worm can also be very easily reshaped into a bearing surface, without creating lengthy transitional zones between the bearing surface and the worm. 
     If the worm and the bearing surface are formed on by positive displacement of material on the same machine tool, then for this operation the shaft has to be chucked only once. One complete work step is dispensed with, which makes fast and economical production possible. 
     Material reshaping by means of rollers proves to be especially favorable. For this purpose, smoothing-rolling tools that are simple to manufacture can be employed. The desired width of the bearing surface is predetermined by the width of the smoothing-rolling tool. As a result, a radial motion of the rolling cylinder to the armature shaft suffices. This makes for an extremely easy process step. 
     By means of the positive displacement of material, not only is a diameter reduction as in the metal-cutting method possible, but filling up of gaps in the material is also possible. This enables the production of a greater bearing diameter, preferably of approximately the same diameter as the original shaft. Weak points in the armature shaft from a lesser bearing diameter are thus avoided. Moreover, the surface quality of a bearing surface produced by cold forming in this way is greater. 
     It is especially advantageous to form the bearing surface onto the end of the shaft. This is where the greatest possible deflection of the armature shaft occurs, generated by the force transmission of the teeth. If the shaft is securely guided on its end by a bearing, an adequate tooth engagement is assured. In order that the shaft need not be unnecessarily long, it is especially advantageous in this arrangement that by means of positive displacement of material, a very sharp transition from the bearing surface to the effective tooth engagement is created. 
     It is also advantageous if the bearing surface is formed on with a width at least equivalent to the pitch height of an encompassing thread course of the worm. Since the material in the region of the worm teeth is compressed more strongly than in the region of the tooth gaps, the regions of the former worm teeth are harder and can thus carry greater loads. If the length of a bearing point is equivalent to at least the pitch of a set of teeth, then over the circumference of the bearing point, high surface quality with a spiral course is assured. 
     The device according to the invention having the characteristics of independent claim  8  has the advantage that a high-quality bearing surface is created with a very short transition zone to the force-transmitting worm region. 
     If the bearing surface is embodied at the end of the shaft in the form of a support journal, then it can be guided very effectively in a rotary bearing receiving bush. This prevents the worm from deviating radially. This makes a safe adjustment operation possible. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       One exemplary embodiment of a device of the invention is shown in the drawing and explained in further detail in the ensuing description. 
         FIG. 1  shows a device in section; and 
         FIG. 2  shows an enlarged detail of the shaft marked II in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIG. 1 , an adjusting drive  10  is shown, with a motor  12  and a multi-part housing  16  surrounding a gear  14 . The motor  12  is commutated electrically and has an armature  18 , a commutator  20 , and an armature shaft  22 , supported at multiple points, which extends into the region of the gear  14 . A worm  26  is mounted on the armature shaft  22  and communicates with a worm wheel  24  via a set of teeth  25 . On the face ends  28  and  30  of the armature shaft  22 , this shaft is braced longitudinally on the housing  16 , or part of the housing  16 , via stop disks  32  and  34 , and via a rubber insulator  36 . A bearing surface  40  is formed onto one end  38  of the armature shaft  22  by means of positive displacement of material. This bearing surface  40  is guided in a shaft bearing  42 , to prevent the armature shaft  22  from escaping from the teeth  25 . 
       FIG. 2 , showing an enlargement of the end  38  of the armature shaft  22 , schematically illustrates the production process of the bearing surface  40 . First, the worm  26  is rolled onto the armature shaft  22 . For production reasons, this creates a trailing region on the end of the worm  26 , in the course of which region the outer diameter  46  of the worm, in the region of the force-transmitting teeth  25 , decreases to the original diameter  48  of the end of the armature shaft  22 . This is illustrated in  FIG. 2  by an envelope curve  50  (in dashed lines). In this trailing region  44 , a bearing surface  40  is now formed on by means of rolling. To that end, two rotating smoothing-rolling tools  52  are moved radially toward the armature shaft  22 . In the simplest case, the smoothing-rolling tools  52  comprise circular disks of a certain thickness  53 , which is equivalent to the width  54  of the formed-on bearing surface  40 . As the smoothing-rolling tools  52  are advanced radially (represented by arrows  55  in  FIG. 2 ), worm teeth  56  are pressed into tooth gaps  58 , until a smooth bearing surface is created, whose diameter  48  is approximately equivalent to that of the original shaft  22 . The shaft profile after the bearing surface  40  has been formed on is shown in  FIG. 2  as a dot-dashed line  57 . The advancement of the rolling tools  52  can, however, also be ended earlier, so that the worm teeth  56  are only partially deformed. This does not create a smooth bearing surface  40 . If the width  54  of the bearing surface  40  is greater than the pitch height  60  of an encompassing thread course of the worm  26 , however, a radially symmetrical shaping of the bearing surface  40  is nevertheless assured. 
     Alternatively, smoothing-rolling tools  52  that are not circular can be used. If the rolling disk is supported eccentrically or embodied spirally, then its advancement radially to the armature shaft  26  can be omitted. It is also possible to narrower smooth-running tools  52  and to achieve the desired width  54  via an axial advancement. Regardless of the special embodiment of the rolling tools, the rolling of the worm  26  and of the bearing surface  40  can be done in the same chucking position of the armature shaft  22 . 
     In a further variation of the exemplary embodiment, the worm  26  is formed on by some other method than rolling. For instance, this can be a metal-cutting method, or the worm can be pressed as a separate component onto the shaft. Regardless of how the worm  26  is produced, in this version as well it is possible for a bearing surface  40  to be formed onto the armature shaft  22  at any arbitrary point by means of positive displacement of material in a simple way, as long as the material properties of the material used allow this. 
     In  FIG. 1 , the bearing surface  40  is form onto the end  38  of the armature shaft  22  by means of positive displacement of material. Here the bearing surface  40  forms a support journal  62 , which is guided in a very simple way by a rotary bearing receiving bush  64 . This slide bearing is very economical to produce and easy to install. In an alternative version, the bearing surface  40  is formed on in the region of the worm  26 , between the teeth  25  and the commutator  20 . The bearing is more complicated to produce then. In addition, the end  38  of the armature shaft  22  can for instance be braced only on one end, to prevent the armature shaft  22  from deviating at its end  38 . To that end, once again a bearing surface is formed onto the end  38  of the armature shaft  22 .