Abstract:
The invention relates to a synchronous machine with hybridenergisation, in particular a generator for supplying the electrical system of a motor vehicle, comprising a laminated stator ( 16 ) with a multiphase stator winding ( 18 ) and a laminated rotor ( 20 ) with an energizer winding ( 29 ), which together with permanent magnets ( 24,25 ) around the rotor periphery, provides the energisation for the machine. According to the invention, favorable electrical and magnetic properties and an improvement in manufacturing conditions of the machine can be achieved, wherein the grooves ( 40 ) for the energiser windings ( 29 ) are disproportionately enlarged in relation to the groove base ( 44 ) and are preferably bell-shaped.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/061,178, filed Jun. 14, 2011, which is a U.S. 371 National Phase filing of PCT/EP2009/060463, filed Aug. 13, 2009, which claims priority to German Application No. 10 2009 002 739.4, filed Apr. 30, 2009 and German Application No. 10 2008 041 606.1, filed Aug. 27, 2009. The entire contents of all the foregoing are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention is based on an electric machine, such as is described in the older German patent application DE 10 2007 025 971.0. Such a hybrid-excited synchronous machine is suitable, in particular, for supplying the power supply of motor vehicles, wherein said synchronous machine is used in a multi-phase stator winding system in the generator mode with regulated induced voltage, and the poles of the rotor are excited on a permanently magnetic and/or electric basis. 
       SUMMARY OF THE INVENTION 
       [0003]    The electric machine according to the invention has the advantage that as a result of the proposed shaping of the rotor grooves the exciter winding can be embodied without difficulty with a high filling factor and with a short average turn length with a low electrical resistance. Furthermore, the proposed groove geometry makes it possible to optimize the configuration of the rotor in a particularly advantageous way in order to achieve a low electrical and magnetic resistance, in particular when permanent magnets are arranged on the rotor circumference in order to bring about additional permanent magnetic excitation. In addition, it is possible without difficulty to carry out automatic winding of the groove. Furthermore, in this way the rotor winding can very easily be divided into component coils, which can then advantageously be arranged symmetrically on either side of the rotor shaft. This minimizes the imbalance of the rotor. 
         [0004]    It is expedient here if the rotor grooves at the groove base rise on both sides toward the groove center, in particular are curved in a circular shape toward the groove opening and are embodied so as to be concentric with respect to the passage opening in the rotor shaft. On the one hand, this facilitates the winding process since the individual runs of the exciter winding enter into all the regions of the groove with low lateral guidance by virtue of the groove cross section which drops away toward the groove corners, and permit a high filling factor. At the same time, the turn length and therefore the electrical resistance of the exciter winding are minimized. 
         [0005]    The lateral groove walls are preferably curved toward the groove center, with the result that the grooves are given overall a substantially bell-shaped cross section. In this context, the iron cross section of the rotor along the groove edges can also be adapted in a particularly effective way to the respective size of the magnetic flux, and the magnetic resistance between the core of the rotor and the poles can be reduced. 
         [0006]    In particular, in the case of two-pole basic rotor electrical excitation the advantages which can be achieved by means of the proposed shaping of the grooves are particularly striking In this case, the rotor has, at its circumference, only two grooves in which an exciter winding composed of two substantially identical component coils which are arranged symmetrically with respect to the rotor shaft can be accommodated in a particularly advantageous way. Given suitable shaping and dimensioning of the grooves as is emphasized in the subclaims, very favorable conditions are obtained both in terms of fabrication technology and in terms of the electrical and magnetic resistance. 
         [0007]    Insulating foils which are introduced into the rotor grooves as electric insulation are secured in a very reliable and enduring fashion by virtue of the fact that the insulating foils are suitably secured to the inner sides of the poles in the region of the groove openings, in particular are fixed in slits on the inner side of the poles. In this context it is expedient if the slits for securing the insulating foils are embodied as undercuts in the poles, preferably as a prolongation of the lateral groove walls. The insulating foils are expediently composed of stiff insulating paper. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Exemplary embodiments of the invention are illustrated in the drawings which are explained in more detail in the following description. 
           [0009]    In the drawings: 
           [0010]      FIG. 1  shows a longitudinal section through an alternating current generator for motor vehicles having a hybrid-excited rotor in an alternating pole arrangement, 
           [0011]      FIG. 2  shows a laminated rotor section for a machine with two-pole electrical excitation, having a total of fourteen poles with six permanently magnetically excited poles, 
           [0012]      FIG. 3  shows a perspective illustration of an inventive machine with two-pole electrical excitation and having two component coils which are arranged symmetrically with respect to the rotor shaft, with the end plate removed, and 
           [0013]      FIG. 4  shows a component section through the rotor of the alternating current generator according to the invention with an illustration of the groove insulation. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]      FIG. 1  illustrates a section through an electric machine  10  in the embodiment as an alternating current generator for motor vehicles. Said alternating current generator has 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 , with a circular-ring-shaped laminated stator packet  17 , in whose grooves  19  which are open toward the inside and extend axially a stator winding  18  is inserted. The annular stator  16  surrounds, with its radially inwardly directed surface, a rotor  20  which is embodied as a hybrid-excited rotor. The stator  16  interacts here over a working air gap with the rotor  20  which is rotatably mounted in the stator  16 . 
         [0015]    The rotor  20  has, in a predefined sequence over its circumference, a plurality of north poles N and south poles S which are formed by permanent magnets  24 ,  25  and by the exciter winding  29 . In this context, the pole number of the rotor  20  can be changed as a function of the strength and direction of an exciter current Ie in the exciter winding  29  and by the number of permanent magnets used. 
         [0016]    The rotor  20  has a magnetically permeable body which is embodied as a lamination packet  21 . The laminated rotor packet is laminated in the axial direction with lamination thickness between 0.1 mm and 2.0 mm. Below 0.1 mm, the resistance of the lamination packet  21  to centrifugal forces is too small. Above 2.0 mm, the reduction in the eddy current losses on the outer surface of the rotor  20  is no longer sufficient, with the result that the permanent magnets  24 ,  25  which are installed can be damaged or demagnetized. 
         [0017]    The axial length of the laminated rotor packet  21  preferably corresponds to the axial length of the circular-ring-shaped laminated stator packet  17 , or is longer or shorter than the laminated stator packet  17  for a tolerant compensation of up to 2 mm, and is preferably held together by weld seams. Instead of welds it is possible to use rivets or buttoned connections. 
         [0018]    The exciter winding  29  is embodied by way of example as a diameter coil in the case of the two-pole variant, and it is located in grooves  40  which are punched out of the lamination packet  21 . The exciter winding  29  can be wound, for example, as a flyer winding (double flyer) directly into the laminated rotor packet  21 . Furthermore, areas  41  into which permanent magnets  24 ,  25  can be inserted are hollowed out in the laminated rotor packet. 
         [0019]    According to the invention, the magnets  24 ,  25  are preferably inserted into punched out areas  41  in the laminated rotor packet. This makes it possible to take up the centrifugal forces which occur during operation, and as a result to ensure that the magnets are reliably held on the rotor. A material with a remanent induction of greater 1 T proves particularly advantageous as the magnet material. In particular permanent magnets made of rare earth material have these magnetic properties. The magnets are installed here in the rotor in such a way that they generate a substantially radial field. This field then enters the laminated stator packet from the rotor across the air gap and induces a voltage in the windings of the stator as the rotor rotates. 
         [0020]    The rotor  20  is mounted in the respective end plates  13 . 1  and  13 . 2 , respectively, in such a way that it can rotate by means of a shaft  27  and a roller bearing  28  on each side of the rotor. Said rotor  20  has two axial end faces, to each of which a fan  30  is attached. These fans are substantially composed of a plate-shaped or disk-shaped section from which fan blades extend in a known fashion. The fans  30  serve to permit air to be exchanged between the outside and the interior of the electric machine  10  via openings  48  in the end plates  13 . 1  and  13 . 2 . For this purpose, openings  48  are provided at the axial ends of the end plates  13 . 1  and  13 . 2 , and cooling air is sucked into the interior of the electric machine  10  by means of the fans  30  via said openings  48 . This cooling air is accelerated radially outward by the rotation of the fans  30 , with the result that said air can pass through the cooling-air-permeable winding heads  50  on the drive side and the cooling-air-permeable winding heads  51  on the electronics side. This effect cools the winding heads  50 ,  51 . After the cooling air has passed through the winding heads  50 ,  51 , or flowed around the winding heads, the cooling air takes a radial path toward the outside through openings (not illustrated). 
         [0021]    A protective cap  47 , which protects various components against ambient influences, is located on the right-side in  FIG. 1 . This protective cap  47  closes off a slip ring assembly  49  which supplies the exciter winding  29  with exciter current. Arranged around this slip ring assembly  49  is a heat sink  53 , which acts here as a positive heat sink and on which positive diodes  59  are mounted. The end plate  13 . 2  acts as what is referred to as a negative heat sink. The connecting plate  56 , which connects negative diodes  58  and positive diodes  59  attached to the end plate  13 . 2  to one another in the form of a bridge circuit  69 , is arranged between the end plate  13 . 2  and the heat sink  53 . 
         [0022]      FIG. 2  shows a laminated rotor section of an electric machine  10  which has a total of  14  poles and has two-pole basic electrical excitation, distributed over four north poles  32  and four south poles  34 , as well as having six poles  24  and  25  which are permanently magnetically excited. In the case of electrical excitation, which generates north poles  32  in the upper half of the illustration and the south poles  34  in the lower half, the permanent magnets are respectively magnetized in opposite directions, with the result that they form south poles  25  at the circumference of the rotor  20  in the upper half, and north poles  24  in the lower half. The permanent magnets  24  and  25  are held in pockets  43  which are punched out from the laminated rotor packet  21  between the electrically excited poles  32 ,  34 . The permanent magnets are securely held in the pockets, in particular against the strong centrifugal forces during the operation of the machine. 
         [0023]    In order to obtain a high power density of the machine, preferably rare earth magnets are used as permanent magnets  24  and  25 . When there are relatively small demands made of the power density of the machine, it is instead also possible to use ferrite magnets as permanent magnets. In terms of the pole number of the machine, alternatives are possible, and in the case of two-pole electrical excitation it is, in particular, also possible to equip the machine alternately with four or eight permanent magnets between electrically excited poles, as a result of which the overall pole number of the machine correspondingly changes. 
         [0024]    The laminated rotor section illustrated in  FIG. 2  has two bell-shaped grooves  40  which are disproportionately enlarged in relation to the groove base  44  to a width B which is larger than the diameter d of the rotor shaft  27 , or of an opening  45  for the rotor shaft to pass through. The largest width B of the grooves  40  is oriented according to the rotor diameter D and is at maximum 40% of the rotor diameter. This configuration of the grooves makes it easily possible to divide the exciter winding into two component coils which can be arranged symmetrically in the winding heads  50 ,  51 , distributed evenly on both sides of the rotor shaft  27  with a minimized winding head length and correspondingly reduced electrical resistance. A range of between 20% and 45% of the rotor diameter D has proven advantageous here as the minimum distance a between two exciter grooves  40  in the rotor core  26 . With such dimensioning of the rotor iron at this narrow point, a sufficient cross section for the magnetic flow is ensured. 
         [0025]    The grooves  40  of the rotor  20  are also configured in such a way that the groove base  44  rises on both sides toward the groove center, preferably with a circular curvature, with the result that the groove base  44  extends concentrically with respect to the passage opening  46  for the rotor shaft  27 . The radius R of the groove base is to be in the range between twice and four times the radius d/2 of the rotor shaft  27  here in order also to ensure a constant and sufficient magnetic cross section in the rotor core  26 . 
         [0026]    The bell shape of the grooves  40  is also characterized in that the lateral groove walls  39  are curved toward the groove center, with the result that in this area a sufficient iron cross section is also available for the magnetic flux to the electrically excited poles  32  and  34  which are located directly to the side of the grooves. A further characteristic variable in this area of the rotor iron is here the edge distance b to the side of the exciter grooves  40  from the adjacent edge of the permanent magnets  24  and  25  arranged there. In order to ensure a sufficient cross section between the corners of the permanent magnets  24 ,  25  and the adjacent groove edges, the lateral distance b is to be between 25% and 100% of the pole pitch τ of the electrically or permanently magnetically excited rotor pole. 
         [0027]      FIG. 3  shows a perspective illustration of a synchronizing machine according to the invention of the bearing cover  13 . 2  removed. The machine has two-pole basic electrical excitation, wherein the exciter winding  29  is divided into two substantially identical component coils  29   a  and  29   b  which engage around the rotor shaft  27  on both sides and are arranged symmetrically with respect thereto. The laminated packet  17  of the rotor  20  corresponds here to the lamination section which is shown in  FIG. 2  and has bell-shaped grooves, only the groove openings  45  of which can be seen. The winding heads of the two component coils  29   a  and  29   b  of the exciter winding engage over a base plate  63  in the fan  30 . The exciter winding  29  completely fills the grooves  40  here and is configured in such a way that the ratio of the copper mass m N  in the exciter grooves  40  with respect to the copper mass m w  of the winding heads is 0.4 to 2.5, preferably 0.5 to 1. The mass ratio of the winding parts in the grooves, or in the winding heads, corresponds to the respective wire lengths and constitutes, in the specified ratio, an advantageous compromise in terms of the shaping of the exciter winding  29  and of the stator winding  18 , wherein the given ratio of the copper mass in the grooves, or in the winding heads, is larger in the case of the stator than in the case of the rotor.  FIG. 3  shows of the stator  16  only the winding head of the stator winding  18  and its lamination packet  17 , which is seated, according to the illustration in  FIG. 1 , in the end plate  13 . 1  of the two-part housing  13 . The described and illustrated shape of the hybrid excited rotor  20  of the machine according to the invention forms here an advantageous compromise in terms of the requirements with respect to strength, guidance of flux, fabrication methods and short winding head connections. 
         [0028]      FIG. 4  shows a perspective illustration of part of the lamination packet  21  of the rotor  20  with a groove  40 , such as has already been previously described in detail in particular with respect to  FIG. 2 . Identical reference signs are used for identical parts here. 
         [0029]    The exciter winding  29  is illustrated in  FIG. 4  only as hatching. It is insulated from the laminations of the laminated rotor packet  21  by means of foil  38  which is preferably composed of insulating paper. The insulating foil  38  is supported in the region of the groove openings  45  on the inner sides  33 ,  35  of the poles  32 ,  34  and is secured there in the slits  36  which are formed as undercuts in the poles  32 ,  34  and extend as a prolongation of the lateral groove walls  39 . This method of securing the groove insulation in undercut-like slits  36  can basically also be used for other groove shapes than for the illustrated bell-shaped groove. However, in this groove shape the advantage of the proposed securing means for the groove insulation is particularly pronounced since the insulating foil has a tendency, owing to the groove shape, to move out in the region of the groove opening toward the interior of the groove, as a result of which the insertion of the exciter winding  29  could be disrupted. 
         [0030]    Furthermore, in the region of the groove openings  45  it is possible to insert groove wedges  37  which improve the insulation of the winding on the inner sides  33 ,  35  of the poles  32 ,  34 , to secure the insulating foil  38  in its position and to support the exciter winding  29  in withstanding large centrifugal forces.