Abstract:
The invention relates to a method for producing a shaft ( 22 ), and an apparatus containing such a shaft ( 22 ), in particular an armature shaft ( 22 ) of an electric motor-driven drive ( 12 ) that is brought to a nominal dimension ( 44 ). The shaft ( 22 ) is reshaped by means of material displacement ( 46 ) at least one point until the nominal dimension ( 44 ) is reached.

Description:
CROSS REFERENCE TO RELATED DOCUMENTS 
     This application is a 371 of PCT/DE01/00497, filed Feb. 9, 2001, which claims the benefit of German Patent Applications: No. 100 09 053.2, filed Feb. 28, 2000 and No. 100 30 353.6, filed Jun. 21. 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a method for producing a shaft, and an apparatus containing such a shaft. 
     An apparatus was made known in the German utility-model patent GM 297 02 525.2 that is used, for example, to move window panes, sunroofs, or seats. In order to prevent an undesired axial end play of the armature shaft, it is proposed there that a damper rubber be pressed into a recess of the housing on at least one of its faces. The armature shaft presses a stop disk against this damping rubber. By means of the firmly locking into position and the elastic properties of the damping rubber, the armature shaft remains firmly fixed in place despite ageing processes and signs of wear. Additionally, the armature shaft can be installed very easily and cost-effectively together with the damping rubber. However, the elimination of the axial end play of the armature by means of such a damping rubber limits the maximally permissible tolerance in the production of the armature shaft. Narrower tolerances lead to higher production costs, however, which are undesired in a mass production of the armature shaft. 
     SUMMARY OF THE INVENTION 
     The method according to the invention has the advantage that the favorable offset of end play with the damping rubber can continue to be used even when the shaft is fabricated not very exact to length in production. By introducing an additional working step, the manufacturing-related length of the shaft subject to tolerance can be decoupled from the elimination of the end play of the shaft. This also makes a very cost-effective and simple manufacture of the endless screw on the armature shaft possible. The end play is suppressed even more reliably as compared with earlier means for attaining the object of the invention, because the tolerance stack-ups are markedly lower after the material displacement than before. The useful We of the armature shaft is increased as a result and clicking noises produced when the direction of rotation changes are reliably prevented. 
     If the material displacement takes place near an end of the shaft, the stability of the shaft across the entire length is largely maintained. Additionally, the material displacement at this point does not take up any additional space. If the material displacement is carried out by means of burnishing, this is a cost-effective, exact and easy-to-use process. Burnishing brings about a continuous elongation of the shaft that can be well-controlled. The burnishing results in an even constriction, which also has a very advantageous effect on the stability of the shaft. It is also possible to achieve the material displacement simply by means of squeezing, however. Such a working step is less expensive than burnishing, but it does not entirely achieve the same dimensional accuracy. 
     If the length of the shaft is measured during the material displacement, the nominal dimension of the shaft can be achieved rapidly and exactly in one working cycle. 
     It proves to be particularly favorable when the shaft is installed in the pole well of the electric motor before the material displacement is started. The tolerances that are stacking up are eliminated as a result. Moreover, the armature shaft then lies in “its” bearings, so that the dimensional accuracy and the position of the material displacement can be coordinated with the eventual site of application, particularly when burnishing the material displacement. 
     It is advantageous to measure the length of the part of the installed shaft extending over the pole well, because the shaft can then be produced to the nominal dimension in the installed state. As a result, the tolerance stack-up of the end play can be markedly reduced. 
     A further alternative is to measure the set value for the end play during material displacement with the shaft in the installed state. This has the advantage that the measured value of greatest interest—the end play—can be measured directly and it can be adjusted exactly to the set value by means of the material displacement. With this method, all manufacturing and fitting tolerances are completely eliminated. 
     Efficient process engineering is a further advantage of material displacement by means of burnishing. The endless screw of the armature shaft can be produced and the material displacement can be carried out using just one tool. Even if one tool each is used for the burnishing of the endless screw and the burnishing of the material displacement, one complete working step is spared, because the shaft need be chucked only once for this process. This makes rapid and cost-effective production possible. 
     The apparatus according to the invention having the features of the independent claim 9 has the advantage that a high-quality product with narrow tolerances is created despite initially great production tolerances of the shaft after installation. 
     The material displacement located at the end of the shaft and the semicircular cross-sectional area of the circumferential groove have an advantageous effect on the preservation of stability of the shaft. It is advantageous that the shaft diameter can be reduced up to one-half of the original value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of an apparatus according to the invention is presented in the diagram, and it is explained in greater detail in the subsequent description. FIG. 1 shows a sectional drawing of an apparatus, and FIG. 2 shows an enlarged section of the shaft according to II in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An adjusting drive  10  is shown in FIG. 1 that comprises a motor  12  and a multisectional housing  16  enclosing a gear  14 . The motor  12  is electrically commutated and comprises an armature  18 , a commutator  20 , and an armature shaft  22  supported in bearings in multiple locations that extends into the region of the gear  14 . An endless screw  26  that communicates with a worm gear  24  is rolled onto the armature shaft  22 . This is supported at the faces  28  and  30  of the armature shaft  22  via stop disks  32  and  34  and at the housing  16  or a part of the housing  16  via a damping means  36 . 
     The housing  16  comprises a recess  38  in the region of the face  28  of the armature shaft  22 , into which a damping rubber  40  is pressed as damping means  36 . The damping rubber  40  comprises a firmly specified elastic region  42 . The conception according to the invention therefore consists of the fact that the tolerances of the armature shaft  22  and the housing parts  16 , together with the assembly tolerances, may not exceed the dimension of the elastic region  42  (refer to FIG.  2 ), in order to effectively prevent play in the armature shaft. Instead of the damping rubber  40 , other damping means  36  such as spring elements or rigid stops are feasible as well. 
     In order to adhere to such a narrow tolerance, according to the invention, the shaft  22  is brought to a nominal dimension  44  by means of material displacement  46  after the endless screw  26  is rolled on. The tolerance of this nominal dimension  44  is markedly smaller than the elastic region  42  of the damping rubber  40 . The material displacement  46  is realized by constricting the shaft  22 , by way of which the shaft  22  increases. The material displacement  46  is applied to one end region  29  between the endless screw  26  and the face  28  in a region where the shaft  22  is not radially supported in bearings. 
     Methods of material displacement  46  are also feasible in which the shaft  22  is swaged, which would result in a shortening of the shaft  22 . Theoretically, there are a plurality of points on the shaft  22  where a material displacement would not disturb the structure. In order to maintain the overall stability of the shaft  22 , however, it presents itself to displace material on the ends  29 ,  31  of the shaft  22  in the region toward their faces  28 ,  30 . 
     A simple method for material displacement  46  is given by the burnishing of the shaft  22  on its end  29 . This method is to be preferred over others because a burnishing device  54  must be held in front anyway in order to produce the endless screw  26  on the armature shaft  22 . The burnishing for material displacement  46  can thereby be carried out in one working step, i.e., simultaneously with the burnishing of the endless screw  26 , or one directly after the other during one chucking on the burnishing machine  54 . 
     The length of the shaft  22  is measured simultaneously during the material displacement  46 . The shaft  22  is deformed until the length measurement of the armature shaft  22  shows the nominal dimension  44 . The nominal dimension  44  is thereby based on the entire length of the armature shaft  22  between its two faces  28 ,  30 . 
     In a second exemplary embodiment, the armature shaft  22  is installed in a part of the housing  16 —in a pole well housing  13  in this case—before its length is changed. The part of the armature shaft  22  extending over the pole well  13  is thereby measured simultaneously during its material displacement  46 . In this case, the nominal dimension  44 ′ (FIG. 1) is only based on the part of the armature shaft  22  extending out over the pole well  13 . The tolerances of the field frame  13  can thereby be eliminated as well. 
     In a further exemplary embodiment, the length of the armature  22  is not measured as a nominal dimension  44 , but rather, the axial end play  44 ″ (indicated in FIG. 2 with a dotted line) of the shaft  22  is measured directly in its installed state. After the armature shaft  22  is completely installed and the housing  16  is fully assembled, the material displacement  46  of the armature shaft  22  is thereby carried out via one or more openings in the housing  16 . The armature axial end play  44 ″ is measured by means of an electric voltage or the current drawn by the electric motor that is applied to the electric motor  12 . If the end play is great, the motor  12  reaches its final speed already at relatively low amperage. If the length of the armature shaft  22  is now extended during the current measurement in this case, the armature shaft  22  presses axially against the damping rubber  40  at any time. As soon as the shaft  22  touches the damping rubber  40 , a certain braking torque is produced that can be measured via an increase in current or a decrease in speed of the motor  12 . If the current and/or the speed reach certain values, this is an indication that the end play has been eliminated or stopped in predetermined fashion. 
     FIG. 2 shows the material displacement  46  on the end  29  of the armature shaft  22  in detail. The material displacement  46  is shaped in the form of a ring groove, i.e., encircling the entire shaft. Such a groove  48  is easy to produce by means of burnishing. The cross-sectional area  50  of the groove  48  is semicircular, i.e., the more the shaft  22  must be elongated, the deeper a segment of a circle is pressed into the shaft. It must be ensured that the cross-section  50  of the shaft  22  is not reduced to too great of an extent at the point of material displacement  46 . A reduction of the shaft diameter  52  to 50% of the original value is regarded as the limit value. 
     In further exemplary embodiments, the cross-sectional area  50  of the ring-shaped groove  48  has a form other than a semicircular form. This is the case, for example, when the burnishing tool  54  is not shaped radially, but rather takes on another, random shape. Possible shapes of the cross-sectional area  50  are a trapezoid  50 ′ or a rectangle  50 ″ (dotted lines in FIG.  2 ). With such a profile, more material is displaced along one side of the trapezoid or rectangle from the beginning onward during burnishing, while little material is displaced at the beginning with a semicircular profile of the groove  48 . 
     It is also feasible that the groove  48  is not ring-shaped around the entire circumference of the shaft  22 , but rather comprises one or more notches distributed around the circumference, for example. Such a method creates difficulties, however, with regard for a precise nominal dimension  44  of the shaft  44 , or it can produce unbalanced states. The selection of the exact point of material displacement  46  is variable between the face  28  and the start of the endless screw  26  on the motor shaft  22 .