Abstract:
The invention relates to an electrical machine ( 10 ), especially a three-phase generator for vehicles. The electrical machine ( 10 ) comprises a stator ( 16 ) and a rotor ( 20 ). The rotor ( 20 ) comprises a first and a second claw pole ( 22, 23 ) from which claw pole fingers ( 24 ) respectively extend in the axial direction from claw pole roots ( 60 ). A centring point ( 74 ) for a tool is located on a rear radius ( 72 ) of the claw pole roots ( 60 ).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    EP 0 783 700 B1 relates to a rotor arrangement for an electric machine. A rotor for an electric machine is disclosed, which rotor comprises a coil core, having a center point, wherein a rotational axis runs through the center point. The rotor comprises radially outwardly protruding first and second walls as well as a wire which is wound around a coil core, between the first and second walls, which wire constitutes the winding. Said wire comprises at least one tab which protrudes radially from the center point, pointing from the first wall of the coil core, wherein each tab is formed bent down onto the field winding in the assembled rotor. A notch is formed in the radially outer end of each tab. 
         [0002]    U.S. Pat. No. 5,229,672 presents an electric machine which is embodied as a generator and which has a rotor. The electric machine is embodied as a claw pole generator, wherein the claw poles of two claw pole boards engage one in the other. For balancing, notches or drillholes, with which the generator is balanced after completion, are provided arranged distributed with respect to one another along the circumferential direction of the rotor. 
         [0003]    FR 2 789 240 A1 relates to a generator for applications in motor vehicles. This generator is also a claw pole generator in which individual claw poles which are formed on claw pole boards engage one on the other. A balancing drillhole is arranged in the region of the claw pole roots which constitute a junction between a plate part of the claw pole board and the individual claw poles which are oriented bent through 90° with respect to said claw pole board. 
         [0004]    During the fine balancing of components of an electric machine, for example a generator for use in motor vehicle applications, the rotor must be balanced. This is preferably carried out on the cold-shaped claw poles in the region of the claw pole roots on the back radius by providing fine balance drillholes. The fine balance drillholes constitute a locally concentrated removal of material, as a result of which the rotor of the generator, in particular of a claw pole generator, can be balanced after the mounting. Fine balancing of the rotor of this embodiment of electric machines is thus significant since the rotor in claw pole generators rotates with rotational speeds of the order or magnitude of 18 000 min −1  and higher. The greater the precision with which the balance drillholes, i.e. the fine balance drillholes, can be provided, the greater the quietness of the running of the electric machine which can be achieved. Furthermore, a very long service life of the roller bearings with which the rotor is mounted in the housing, i.e. the stator part of the claw pole generator, can be achieved by extremely precise balancing of the rotor of the claw pole generator. 
         [0005]    The provision of fine balance drillholes in the region of the claw pole root on the back radius often leads to misalignment of the drill since drilling occurs at the apex point of the radius of the claw pole root in order to generate removal of material precisely at this point. This can lead to damage to the fan which has already been mounted on the shaft of the rotor or to breaking of the drills. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention is based on the object of simplifying the manufacture of balance drillholes on the rotor of an electric machine which is operated at a high rotational speed. 
         [0007]    According to the solution proposed by the invention, a center is preferably provided on the back radius of the claw pole root, which center both prevents misalignment of the drill and permits greater flexibility in the fabrication in terms of relatively steep drilling angles. This center can be embodied, for example during the fabrication of the claw pole or the claw pole board, as a depression on the back radius of the claw pole root, that is to say for example in the form of a centering point, in the form of a sphere or with various other geometries, for example as a square funnel or the like. This depression, which is fabricated on the back radius of the claw pole board, on the one hand ensures a precise position of the fine balance drillhole and, on the other hand, avoids damage to a fan which is already attached to the premounted rotor, since the misalignment of the drillhole is then ruled out. The back radius, provided with a center, of the claw pole root permits relatively steep drilling angles, which, on the one hand, permits greater flexibility in terms of the location of the removal of material for balancing the rotor, and, on the other hand, facilitates the mounting and last but not least can decisively improve the quality of the fine balancing. 
         [0008]    The provision of the center as proposed in the invention for the application of the material-removing drill can be carried out along the entire length of the back radius of the claw pole root. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be explained in more detail below on the basis of the drawing, in which: 
           [0010]      FIG. 1  shows a cross section through an electric machine which is embodied as a claw pole generator, 
           [0011]      FIG. 2  shows a schematic illustration of a claw pole with claw pole fingers, a center and fine balance drillhole, and 
           [0012]      FIG. 3  shows a plan view of one of the claw pole fingers of the claw pole board according to  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]      FIG. 1  shows a cross section through an electric machine  10 , here in the embodiment as a generator for motor vehicles. 
         [0014]    This electric machine  10  has, inter alia, a two-component housing  13  which is composed of a first end plate  13 . 1  and a second end plate  13 . 2 . The end plate  13 . 1  and the end plate  13 . 2  hold a stator  16  which is composed, on the one hand, of an essentially annular iron stator core  17 , and a stator winding  18  is inserted into the axially extending, radially inwardly directed grooves thereof 
         [0015]    The stator  16  which is of annular design surrounds, with its radially inwardly directed, grooved surface, a rotor  20  which is embodied as a claw pole rotor. The rotor  20  comprises, inter alia, two claw poles  22  and  23  on whose outer circumference claw pole fingers  24  and  25  which extend in the axial direction are respectively arranged. The two claw poles  22  and  23  are arranged in the rotor  20  in such a way that the claw pole fingers  24  and  25  thereof, which extend in the axial direction, alternate with one another on the circumference of the rotor  20 . Intermediate spaces, magnetically required as a result of this, are produced between the oppositely magnetized claw pole fingers  24  and  25 , which are referred to as claw pole intermediate spaces. The rotor  20  is rotatably mounted in the respective end plates  13 . 1  and  13 . 2  of the housing  13  by means of a shaft  27  and, in each case, one roller bearing  28  which is located on, in each case, one side of the rotor. 
         [0016]    The rotor  20  has a total of two axial end faces, on each of which a fan  30  is attached. This fan  30  is composed essentially of a plate-shaped or disk-shaped section from which fan blades protrude in a known manner. These fans  30  serve to permit air to be exchanged between the outside of the electric machine  10  and the interior of the electric machine  10  via openings  40  in the end plates  13 . 1  and  13 . 2 . For this purpose, the openings  40  are provided essentially on the axial ends of the end plates  13 . 1  and  13 . 2 , via which cooling air is sucked into the interior of the electric machine  10  by means of the fans  30 . This cooling air is accelerated radially outward through the rotation of the fans  30 , with the result that said cooling air passes through the winding overhang  45  which is permeable to cooling air. This effect cools the winding overhang  45 . After the cooling air passes through the winding overhang  45  or after it flows around this winding overhang  45 , it travels a certain distance radially toward the outside, through openings not illustrated here in  FIG. 1 . 
         [0017]    On the right-hand side of  FIG. 1  there is a protective cap  47  which protects various components against ambient influences. The protective cap  47  covers, for example, a slip ring assembly  49  which serves to supply an exciter winding  51  with exciter current. A cooling element  53 , which acts here as a positive cooling element, is arranged around this slip ring assembly  49 . The end plate  13 . 2  acts as a negative cooling element. Between the end plate  13 . 2  and the cooling element  53  there is a connecting plate  56  which serves to connect to one another negative diodes  58  arranged in the end plate  13 . 2  and positive diodes (not illustrated in the illustration according to  FIG. 1 ) in the cooling element  53 , and therefore to form a bridge circuit which is known per se. 
         [0018]    The rotor  20  is mounted as illustrated above: Firstly, the shaft  27  is made ready. Subsequent to this, the pole core and the claw poles  22  and  23  are fitted onto the shaft  27 . The component composed of the shaft  27 , pole core and claw poles  22  and  23 , which is premounted in this way, is pre-balanced in a first step. Pre-balancing drillholes  82 , which are illustrated in  FIG. 1 , and are provided essentially on an outer side  70  within the carrier part  66  of the claw poles  22  and  23  of the rotor  20 , serve for this purpose. Subsequent to this, the fans  30  are mounted and attached to the two end sides of the claw poles  22  and  23 . The attachment of the fans  30  to the end sides of the claw poles  22 ,  23  can be carried out, for example, by means of spot welding. In conjunction with this working step, the slip rings or the slip ring assembly  49  are also attached. 
         [0019]    From the illustration according to  FIG. 1 , it is apparent that due to the fan  30  fine balance drillholes can only be provided with difficulty in the region of a back radius  72  of the claw pole root  60 . 
         [0020]    In the present context, the claw pole root  60  is understood to be that region of a claw pole  22  or  23  from which the claw pole fingers  24 ,  25  which extend essentially in the axial direction protrude on an inner side of the claw poles  22  and  23 . The claw pole root  60  characterizes the junction region within which there is a 90° orientation  62  (cf. illustration in  FIG. 2 ), and the claw pole fingers  24 ,  25  of a carrier part of the claw pole  22 ,  23  which is embodied essentially in the shape of a plate are formed in such a way that they are bent through said 90° orientation  62 . 
         [0021]    The illustration according to  FIG. 2  clearly shows this region, which is denoted by reference signal  60 . The claw pole root  60  is that region which forms the junction between the carrier part  66  (illustrated in  FIG. 2 ) and the individual claw pole fingers  25 , which protrude beyond an inner side  68  of the claw pole  23 . This claw pole root  60  is defined by a back radius  72 . As proposed according to the invention, a centering means  74  for a material-removing tool, which is generally a drill, is provided on this back radius  72 . The centering means  74  can be located at any desired position along the back radius  72 . The centering means  74  can be embodied as a depression, as a crown, as a centering point or else in the form of a sphere. Depending on the degree of aperture of a depression which is embodied, for example, in the form of a funnel and which serves as a centering means, a corresponding drilling angle region  78  for the material-removing tool, in particular a drill, is formed. The solution proposed according to the invention permits, by way of the relatively large drilling angle region  78 , a fine balance drillhole  76  (also illustrated in  FIG. 2 ) to be located in an optimum way in terms of the entry angle into the claw pole root  60 . For the precise balancing of the rotor  20 , which comprises a first claw pole  22  and a second claw pole  23  according to the illustration in  FIG. 1 , it is significant that not only the position of the fine balance drillhole  76  on the back radius  72  but also the profile thereof into the material of the claw pole  23  can be influenced with the result that balancing of the claw poles  22  and  23  which comes close to the ideal balancing result can be achieved. The centering means which is proposed according to the invention and which can be positioned at any desired location along the back radius  72  on the one hand ensures that the material-removing tool, generally a drill, does not become misaligned and, on the other hand, as explained already in conjunction with  FIG. 1 , damage to the fans  30  or the blades thereof during the manufacture of the balance drillhole  76  is avoided in the region of the claw pole root  60 . 
         [0022]    From the illustration according to  FIG. 2  it is also apparent that a depth of the fine balance drillhole  76  on the back radius  72  of the claw pole root  60  is characterized by reference symbol  80 . The depth  80  of the fine balance drillhole  76  determines the extent of the resulting material removal and is dependent on the degree of fine balance which is necessary on the respective pre-mounted assembly, comprising the shaft  27 , the pole core and at least the two claw poles  22 ,  23 , in order to ensure a qualitatively outstanding balancing result. 
         [0023]    From the illustration according to  FIG. 2  it is apparent that an opening  64 —generally this is a drillhole—is formed symmetrically in the claw pole  23 . The shaft  27  extends through this opening  64 , cf. the illustration according to  FIG. 1 , said shaft  27  holding not only the further claw pole  22  but also the pole core and the slip ring assembly, cf. reference symbol  49 . 
         [0024]    In the illustration according to  FIG. 2 , an inner side of the claw pole  23  with reference symbol  68  is shown, the claw pole fingers  25  extending from said inner side in the axial direction parallel to the axis of symmetry of the claw pole  23 . The fan  30  (illustrated in  FIG. 1 ), which has been omitted from the illustration according to  FIG. 2 , is mounted on an outer side  70  of the claw pole  23  according to the illustration in  FIG. 2 . 
         [0025]    From the illustration in  FIG. 2  it is apparent that the claw pole roots  60  slide over between the carrier part  66  of the claw pole  23  and the individual claw pole fingers  25  through at least an angular range between 90° and 120°. In this range of the claw pole roots the back radius  72  is produced, on which back radius  72  the centering means  74  can be positioned at any desired position, viewed in the axial direction, depending on requirements. 
         [0026]    Finally, the illustration according to  FIG. 3  shows a plan view of the centering means  74  on the back radius  72  of the claw pole root  60 . From the plan view according to  FIG. 3  it is apparent that the centering means  74  illustrated there is positioned offset slightly with respect to the center point of the back radius  72 .