Abstract:
An armature shaft for an electrical machine having a plurality of notches, extending along the circumference of the armature shaft essentially parallel to the longitudinal direction of the armature shaft, which notches form a notching heap. At least the notching heaps form acute angles whereby the imbalance of the armature directly after the shafts have been press-fitted into the lamination packet is reduced markedly. Moreover, the structure-borne sound of the motors is reduced compared to motors with stamped-out armature packets.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is based on an armature shaft for an electrical machine having a plurality of notches, which extend along the circumference of the armature shaft essentially parallel to the longitudinal direction and form a notching heap. 
   2. Description of the Prior Art 
   In packet-making by means of notches, two notches each extending longitudinally are made in the armature shaft with a two-piece, U-shaped tool. The notching creates a heap or ridge of displaced material, which increases the outer diameter of the armature shaft in the notched region. As a result, the armature shaft can be firmly press-fitted into the bore in the packet. The notching heap joins each lamination in the packet solidly to the armature shaft. Moreover, because the notching heap slightly penetrates the laminations, a positive engagement is achieved which markedly increases the torques of the packet. The axial displacement force of the packet, however, is usually slight, above all at the end laminations, and these laminations must therefore as a rule also be ring-calked. By means of notches, an extremely stable connection is created, which meets the most stringent demands in terms of the quality of the balancing and low-vibration operation. Thus very low-noise motors can be produced. However, complicated technical production prerequisites must be met, if the method is to be used at all with long, thin shafts. 
   In production, bore tolerances, for instance, selected must be close. The heaps of the notches must likewise have close tolerances; otherwise, the press-fitting forces exceed the buckling force of the shaft. Because of the close tolerances, introducing the shaft is difficult. A high rejection rate must be expected, because of cold welding of shaft material to the packet sheet metal. Especially long packets, with a length of about 50 mm, for instance, have a particularly pronounced tendency to cold welding because of the long press-fitting distances. Because of the relatively high press-fitting forces, excessively great errors of concentricity often occur at the shaft upon press-fitting and must then be corrected manually or by machine in a further operation. Packet-making by press-fitting a notched shaft is indeed the appropriate method for producing low-noise motors that are relatively impact-resistant. However, they require considerable effort and expense technically. Rejections from buckling of the shaft after seizing are highly likely in the press-fitting process. 
   Notches with a notching heap are in contrast to knurling, in which no notching heaps are created, or only indentations are created because of compaction of the material. This makes knurling unsuitable for an armature shaft to which an armature packet is to be secured. 
   OBJECT AND SUMMARY OF THE INVENTION 
   The object of the invention is to markedly minimize the high rejection rates in packet-making with a notched, long and thin shaft (for instance, 150 mm long with a 4 mm diameter) and a greater packet length. Moreover, the high structure-borne sound values of small motors, especially small power window motors, are to be reduced markedly. 
   By means of the armature shaft of the invention for an electrical machine the advantage has been attained that the imbalance of the armature directly after the shafts are press-fitted into the lamination packet is reduced markedly. Moreover, the structure-borne sound of motors is reduced by 8 dBR compared to motors with stamped-out armature packets. For this purpose, an armature shaft for an electrical machine is provided that has a plurality of notches, which extend along the circumference of the armature shaft essentially parallel to its longitudinal direction and form a notching heap; the notches and the notching heaps form acute angles relative to one another. 
   The acute angle can be formed such that adjacent notching heaps each form an angle of 1° to 5°, as a result of which each lamination is securely held. 
   The acute angle can furthermore be formed by providing that the depth of the notches on one end is greater than on the other end, and that the height of the notching heap on one end is greater than the other end, so that the bottom of the notch and the spine of the notch form the acute angle. The result is a conical course along the shaft, which has a positive effect on the press-fitting process. Preferably, the notch base has a slope of 0.01 mm over 50 mm of length. 
   The acute angle can also be formed by providing that only the tail ends of the notches are arrowhead-shaped, creating a chamfer on the notching heap that prevents chips from forming in the press-fitting process, because chips in the interstice between the shaft and the notch are the primary cause of seizing. 
   The armature shaft with the notches can be produced more precisely and in only one operation if the notching heaps extend on only one side of the notches. In this respect it is also advantageous that the notching heaps of adjacent notches are oriented toward or away from one another, which additionally makes easier visual monitoring possible. 
   Because the notching heaps are rounded, they are not sharp, and thus the tendency to chip development is reduced. 
   Preferably, the pitch of the notches varies over the circumference in the longitudinal direction, and as a result all the sheet-metal laminations have a defined contact with the armature shaft. This is assured especially well in that a first, second, third and fourth notch are provided; that the first notch and the second notch form an angle with respect to the center axis of the armature shaft, and the angle is smaller than 90° on one end of the notches and larger than 90° on the other end; that the second notch and the third notch form an angle with respect to the center axis of the armature shaft, and the angle is smaller than 90° on one end of the notches and larger than 90° on the other end; that the third notch and the fourth notch form an angle with respect to the center axis of the armature shaft, and the angle is smaller than 90° on one end of the notches and larger than 90° on the other end; and that the larger angle is preferably about 91°, and the smaller angle is preferably about 89°. 
   An armature with an armature packet and with an armature shaft of this kind has only very little imbalance. An electrical machine with such an armature has reduced structure-borne sound. This is advantageous especially in the passenger compartment of a passenger car. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of a preferred embodiment, taken in conjunction with the drawings, in which: 
       FIG. 1  is a side view of an electrical drive unit; 
       FIG. 2  shows an armature with a partial section; 
       FIG. 3  shows the armature shaft in an end-on view; 
       FIG. 4  shows the armature shaft in a developed view; 
       FIG. 5  shows the armature shaft in a side view; 
       FIG. 6  shows a tail end of a notch marked as detail IV in  FIG. 2 ; and 
       FIG. 7  is a fragmentary sectional view of the armature shaft with a notch. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , an electrical machine or drive unit  10  is shown, which is preferably used in a motor vehicle. The drive unit  10  may be a power window raiser, a sunroof drive mechanism, a power train actuator, in particular clutch actuator, a seat adjuster, or the like. The drive unit  10  includes an electric motor  12  and may additionally include a gear  14 ; it may also be an electrical machine with brushes or a brushless electrical machine or an electronically commutated electrical machine. 
   In  FIG. 2 , the armature  16  of the electrical machine  10  is shown in a partial section showing only one half of the armature packet  18 . The armature packet  18  is produced from stamped-out packeted laminations  19 . For the sake of greater clarity, the winding is not shown. The armature packet  18  is slipped with a central bore  20  onto the armature shaft  22 . 
   As already indicated in  FIG. 2 , the armature shaft  22  has a plurality of notches  24 , extending along the circumference of the armature shaft  22  essentially parallel to its longitudinal direction. Forming the notches  24  displaces material, forming a notching heap  26  ( FIG. 7 ). As a result, the diameter is partially increased at the places where the notching heap is, creating a press fit when the armature shaft  22  is inserted. Instead of the term notching heap  26 , this can be called an accumulation of material. 
   As seen more clearly in  FIGS. 3 and 4 , a first, second, third and fourth notch  24 . 1 ,  24 . 2 ,  24 . 3  and  24 . 4  are provided. The first notch  24 . 1  and the second notch  24 . 2  form an angle  30 . 1  with respect to the center axis  28  of the armature shaft  22 . The angle  30 . 1  is smaller than 90° on one end  32  of the notches  24 . 1 ,  24 . 2  and larger than 90° on the other end  34 . The second notch  24 . 2  and the third notch  24 . 3  form an angle  30 . 2  with respect to the center axis  28  of the armature shaft  22 . The angle  30 . 2  is smaller than 90° on one end  32  of the notches  24 . 2 ,  24 . 3  and larger than 90° on the other end  34 . The third notch  24 . 3  and the fourth notch  24 . 4  form an angle  30 . 3  with respect to the center axis  28  of the armature shaft  22 . The angle  30 . 3  is smaller than 90° on one end  32  of the notches  24 . 3 ,  24 . 4  and larger than 90° on the other end  34 . For the sake of greater clarity the angles  30  in  FIGS. 3 and 4  are shown greatly exaggerated. Normally, the oblique course of the notches  24  may be only poorly apparent to the eye under some circumstances. Preferably, the smaller size of the angle  30 . 1 ,  30 . 2 ,  30 . 3  is about 89°, and the larger size is preferably about 91°, including production-dictated tolerances. The production-dictated tolerances have the effect that the angles  30 . 1 ,  30 . 2 ,  30 . 3  can range within a bandwidth of approximately 89.5° to 90.5°, and in this bandwidth, production-dictated deviations of a few angle minutes can occur. In its course, the angle ranges from 85° to 95°, and once again production-dictated deviations of a few minutes of angle or even degrees of angle can occur. In general terms, the pitch of the notches  24  varies over the circumference in the longitudinal direction of the armature shaft  22 . Naturally, a different number of notches  24  may be provided, for instance  2 ,  3 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10 ,  11 ,  12  of them, and so forth. 
   Because of the described course of the notches  24  and notching heaps  26 , acute angles are formed, which make it easier to fit the armature shaft  22  into the bore  20  and improve the hold of the armature packet  18  on the shaft. The acute angle formed by the respective adjacent notches  24  and notching heaps  26  at the circumference of the armature shaft  22  is preferably within a range from 1° to 5°. 
   In  FIG. 3 , four notch edges  36  of a notching tool are also shown symbolically, along with two arrows  38 ,  39 , pointing toward one another, that indicate the direction from which the edges  36  are pressed against the armature shaft  22 . In this way, as  FIG. 7  shows, the result is that the notching heaps  26  extend on only one side of the notches  24 . It can also be seen from  FIG. 7  that the notching heaps  26  are rounded. This can be done by rounding of the edges  36 . The result is moreover an apparatus for producing the notches  24  of the armature shaft  22 , and this apparatus has four notch edges  36  which can be moved in only two directions  38 ,  39  along the armature shaft  22  and create notches  24  in the shaft  22  that are essentially offset from one another by 90°. As a result, the apparatus is simple in design yet makes it possible to produce the notches  24  and notching heaps  26  within close tolerances. 
   In the developed view of  FIG. 4 , dashed lines indicate the notching heaps  26  when the edges  36 , as shown in  FIG. 3 , are pressed against the armature shaft  22 . Dotted lines also indicate notching heaps  26  that result when the edges are rotated by 90° about the center axis  28  and pressed against the armature shaft  22 . The direct result is that the notching heaps  26  of adjacent notches  24  are either oriented toward one another or away from one another. 
   In the production of the notches  24  and notching heaps  26 , the tool edges  36  do not press in a direct line toward the center axis  28  but rather at an angle of about 45°, resulting in the formation, described above, of the notching heaps  26  on only one side of the notch  24 . 
   In  FIG. 5 , a further possible way of forming an acute angle is shown. The depth  40  of the notches  24  is greater on one end  32  than on the other end  34 . As a result, the height  42  of the notching heap  26  is greater on the end  34  than on the end  32 . Since the depth  40  corresponds to the height  42 , both are shown together in the overview of  FIG. 5 . As a result, the notch base  44  and the notch spine  46  ( FIG. 7 ) form the acute angle. It suffices if only the notch spine  46  increases in height, since the result is a partial conicity of the shaft. However, production is simpler as a result of the notches  24 . Preferably, the notch base  44  has a gradient and the notch spine  46  a slope of about 0.01 mm over 50 mm of the length  48  of the notch, including production-dictated deviations of a few percent. 
   A further possible way of forming an acute angle is also shown in  FIG. 6 . Here, the tail ends  50  at the ends  32 ,  34  of the notches  24  are arrowhead-shaped. As a result, chamfers are formed at the tail ends  50  of the notch spines  46 . Because chip formation is avoided, production is once again made easier. This characteristic may also be provided for an armature shaft  22  for electrical machines  10  with a plurality of notches, extending over the circumference of the armature shaft  22  essentially parallel to its longitudinal direction, that form a notching heap  26 , and in which the tail ends at the ends of the notch spines form a chamfer. 
   After the notches  24  and notching heaps  26  have been produced, the shaft  22  is press-fitted into the armature packet  18  in the inward press-fitting directions  52  represented by arrows in  FIGS. 4 and 5 . In the process, the height of the notching heaps  26  increases counter to the inward press-fitting direction  52 . 
   The armature shaft  22  is preferably hardened on only its outer or end regions, where it will later also be supported. In the region of the notches  24 , however, it is unhardened. 
   The provisions for forming the acute angles could be performed separately, since they have advantages separately. Combining them, however, gives the best results in terms of feasibility and in terms of the structure-borne sound of the finished motors. 
   The foregoing relates to a preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.