Abstract:
A rotor for a rotating electric machine includes a plurality of pole teeth supporting an excitation winding, grooves respectively formed between the pole teeth, and wedges provided in the grooves, each wedge having a concave shape with a bulge oriented towards the inside of the rotor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. National Stage Application of International Application No. PCT/EP2013/051235 filed Jan. 23, 2013, which designates the United States of America, and claims priority to DE Application No. 20 2012 000 842.0 filed Jan. 26, 2012 and DE Application No. 20 2012 003 120.1 filed Feb. 16, 2012, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a rotor for a rotating electric machine, in particular for an electric motor or a generator. In addition, a method for manufacturing such a rotor is disclosed. 
       BACKGROUND 
       [0003]    Electric motors are increasingly installed in modern motor vehicles. Said electric motors are used in this context, in particular, as drive motors which are fully integrated in the drive train or, for example, as starter generators or axle-mounted motors in hybrid applications. In this context, partially externally excited synchronous machines are used which have a rotor composed of a laminated core provided with an exciter winding. In such rotors, grooves are formed between the wound pole teeth. 
         [0004]    During operation, high centrifugal forces, which can pull the exciter winding out of the grooves, occur both in the case of internal rotors as well as in the case of external rotors. The centrifugal forces are dependent on the rotational speed and on the weight of the groove-internal components. In particular in the case of revving up machines the winding is therefore additionally secured after assembly. For this purpose, various bonding agents are known which are used as impregnating resins or casting compounds. 
         [0005]    In addition, groove stoppers or groove wedges can be used in order to prevent the winding dropping out of the groove. Such groove wedges are known, for example, from document DE 28 17 951 A1. In the case of rotors which are configured for electric motors with a high rotational speed (10,000 revolutions per minute and more) it would be appropriate to secure the groove-internal components, in particular the exciter winding, even more effectively against centrifugal forces which occur during operation. 
       SUMMARY 
       [0006]    One embodiment provides a rotor for a rotating electric machine, which comprises a number of pole teeth which support an exciter winding; grooves are formed between each of the pole teeth; and groove wedges are provided in the grooves, wherein the groove wedges have a concave shape with a bulge which is directed toward the interior of the rotor. 
         [0007]    In a further embodiment, the groove wedges have a constant curvature radius. 
         [0008]    In a further embodiment, the groove wedges are clamped tight in a dimensionally stable fashion on their longitudinal sides in the pole teeth. 
         [0009]    In a further embodiment, the groove wedges have a seal on their longitudinal side. 
         [0010]    In a further embodiment, a sealing plug is provided between at least one end of the groove wedges and adjoining rotor components. 
         [0011]    In a further embodiment, the sealing plug has flexible lamellas. 
         [0012]    In a further embodiment, the exciter winding is surrounded by a casting compound or an impregnating compound. 
         [0013]    Another embodiment provides an electric motor having a rotor as disclosed above. 
         [0014]    Another embodiment provides a motor vehicle having an electric motor having a rotor as disclosed above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    Example embodiments of the invention are discussed below with reference to the drawings, in which: 
           [0016]      FIG. 1  is a schematic view of a cross section through an electric motor according to one embodiment; 
           [0017]      FIG. 2  is a schematic view of a perspective view of the electric motor according to  figure 1 ; 
           [0018]      FIG. 3  is a schematic view of the use of a sealing cushion during the casting of the rotor; 
           [0019]      FIG. 4  is a schematic view of a perspective view and of a cross section through the rotor; 
           [0020]      FIG. 5  is a schematic view of a cross section through the groove wedge, and 
           [0021]      FIG. 6  is a schematic view of a longitudinal section through the rotor. 
       
    
    
     DETAILED DESCRIPTION  
       [0022]    Embodiments of the disclosure a rotor for a rotating electric machine whose exciter winding is fixed with respect to centrifugal forces in such a way that the rotor can also be used for high rotational speeds. 
         [0023]    According to one embodiment, a rotor is specified for a rotating electric machine, which rotor has a number of pole teeth which support an exciter winding. Grooves are formed between each of the pole teeth, and groove wedges are provided in the grooves. The groove wedges have a concave shape with a bulge which is directed toward the interior of the rotor. 
         [0024]    Such a rotor is also suitable for high rotational speeds of 10,000 revolutions per minute and more. A groove wedge which is shaped in such a way secures the groove-internal components particularly well since the centrifugal forces can be conducted away better with a concavely curved groove wedge. 
         [0025]    In one embodiment, the groove wedges have a constant curvature radius. They therefore form an arc in cross section. 
         [0026]    In one embodiment, the groove wedges are clamped tight in a dimensionally stable fashion in the pole teeth. For this purpose, recesses are provided as securing means in the pole teeth, which recesses can be shaped in accordance with the shape of the groove wedges and hold the edge sections of the groove wedges. Recesses which are shaped in this way follow the shape of the groove wedges and support the effect of the concave groove wedge shape. 
         [0027]    In order to provide the seal during the casting, the boundary face between the groove wedges and the pole teeth can have a seal, for example in the form of a silicone or adhesive bead. Such a sealing bead can be applied either to the groove wedges or into the recesses in the pole teeth before or during the assembly of the groove wedges. Said sealing bead seals the groove wedges over their entire longitudinal sides. 
         [0028]    A seal in the form of a sealing plug can also be provided between at least one end of the groove wedges and adjoining rotor components. In this context, the sealing plug can have flexible lamellas. 
         [0029]    In one embodiment, the exciter winding is surrounded with a casting compound. For this purpose, after the assembly of the rotor, after the windings have been applied and groove wedges have been mounted the electrically insulating casting compound, for example a casting resin or epoxy resin such as araldite or a plastic, is introduced into the cavities inside the grooves of the rotor and cures. In one embodiment, the cavities inside the grooves are filled essentially completely with a casting compound. 
         [0030]    In such rotors, the groove-internal components, in particular the exciter winding, are particularly well secured against centrifugal forces which occur during operation. 
         [0031]    Alternatively, the exciter winding can also be surrounded with an impregnating compound, for example an impregnating resin. During impregnation, the rotor is dipped into the impregnating compound and subsequently dried. In this context, all the groove components are bonded together and the rest of the impregnating compound drips off. The rotor grooves are typically not completely filled in this context. 
         [0032]    According to one embodiment, an electric motor having the rotor described is specified. The electric motor can be embodied, in particular, as an externally excited synchronous machine. It can be embodied either as an internal rotor or as an external rotor. 
         [0033]    Since the groove-internal components are effectively secured against centrifugal forces which occur, the electric motor can be configured for rotational speeds of 10,000 revolutions per minute and more. 
         [0034]    Such electric motors are suitable for use in a motor vehicle. They can be used either as drive motors which are fully integrated in the drive train or, for example, as starter generators, wheel hub motors or axle-mounted motors. According to one aspect of the invention, a motor vehicle is therefore specified having a drive which has the described electric motor. The motor vehicle can be embodied here as an electric vehicle or hybrid vehicle. 
         [0035]    Other embodiments provide a method for manufacturing the rotor is specified, wherein the method comprises the following method steps:
       providing a rotor laminated core with exciter windings and groove wedges which cover the grooves;   fitting sealing cushions onto the outer sides of the groove wedges, wherein the sealing cushions cover the outer sides of the groove wedges completely;   introducing the rotor into a casting tool;   casting the rotor; and   taking the rotor out of the casting tool and removing the sealing cushions.       
 
         [0041]    The use of the sealing cushions makes it possible to effectively prevent the casting compound from escaping from the interface between the pole teeth and the groove wedge. The casting compound is therefore also prevented from reaching the surface of the groove wedges. For a particularly good sealing effect, sealing cushions composed of an elastic material, for example a temperature-resistant silicone, can be used, which sealing cushions are compressed when they are placed into the casting tool. 
         [0042]    Advantageous refinements of the rotor presented above are also to be considered advantageous refinements of the electric motor or of the motor vehicle insofar as they can also be transferred to the electric motor or to the motor vehicle. 
         [0043]      FIG. 1  is a schematic view of a cross section through an electric motor  1  having a rotor  2  which is embodied as a laminated core, and a stator  3  which surrounds the rotor  2 . 
         [0044]    The rotor  2  has a number of pole teeth  4  which are separated from one another by grooves  7 . The pole teeth  4  support exciter windings  5  which are electrically insulated with respect to the pole teeth  4 , for example by means of a groove insulating paper  6 . It is also possible to use some other type of insulation, for example encapsulation by injection molding with a plastic. 
         [0045]    The groove  7  is also closed off from the outside by a groove wedge  8 . The groove wedge  8  is embodied from a non-magnetizable material. 
         [0046]    The groove wedge  8  has in this embodiment a material which essentially has the alloy composition Fe Rem Cr a Ni b Mn c C d Si e P f S g N h , wherein a, b, c, d, e, f, g and h are given in percent by weight and 18≦a≦19; 12≦b≦13; 0≦c≦1.4; 0≦d≦0.055; 0≦e≦0.6; 0≦f≦0.04; 0≦g≦0.008 and 0≦h≦0.1. 
         [0047]    Compared to known “Nirosta” steels this material has a particularly high proportion of chromium and nickel. As has become apparent, materials made of this steel continue to be non-magnetizable even after shaping, punching or cutting. Eddy current losses in the groove wedge  8  are therefore avoided. 
         [0048]    The groove wedge  8  has a concave shape with a bulge  11  toward the interior of the rotor  2 . The curvature radius of the groove wedge  8  is constant over its entire cross section. With its edge regions the groove wedge  8  is held and secured in recesses  10  in the pole teeth  4 . 
         [0049]    The concave shape of the groove wedge  8  conducts away centrifugal forces which occur during operation. The groove wedge  8  therefore secures the groove-internal components, in particular the exciter windings  5 , additionally in the groove  7  even in the case of high rotational speeds of the electric motor  1 . 
         [0050]      FIG. 2  shows a perspective view of the rotor  2 . In this view, the groove wedges  8  which extend between the pole teeth  4  can be seen. The groove wedges  8  extend axially, that is to say in the direction of the arrow  14  parallel to the rotational axis of the rotor  2 , over the entire length of the groove  7 . In the case of an oblique groove which is frequently used to reduce the cogging torque of electric motors, the groove wedges follow the oblique profile of the groove  7  correspondingly. 
         [0051]    The groove wedges  8  are assembled after the exciter windings  5  have been applied. They can be assembled either axially or radially. In this context, both unbent pieces of sheet metal—for example unwound from the coil and shaped during assembly—as well as parts which are already shaped before assembly are used. After assembly of the groove wedges  8 , the remaining cavities of the grooves  7  are filled with a casting compound (not shown). 
         [0052]      FIG. 3  illustrates the sealing of the rotor  2  during casting. Revving up rotors are frequently cast with a casting compound in order to stabilize the groove-internal components. Since rotor parts are to be as far as possible cast evenly without air occlusions, the rotor  2  which is already assembled is cast in a vacuum. 
         [0053]    In the region of the groove wedges  8 , a sealing cushion  15  is provided in order to prevent the casting compound from escaping, said sealing cushion  15  simulating with its shape the contour of the groove wedge  8  on the rotor side and a round shape on the casting tool side. The sealing cushion  15  can be shaped and dimensioned in such a way that it forms the seal in all directions: On its surface  16  with respect to the concave groove wedge  8 , on its surface  17  with respect to the casting tool (not shown), at its side faces  18  with respect to the pole teeth  4 . In particular, the sealing cushion  15  can have undercuts  9  with which it latches or wedges into the recess  10 . 
         [0054]    Due to the geometry and the flexibility of the sealing cushion  15 , both straight and oblique grooves  7  can be sealed in this way. 
         [0055]    The casting tool is generally an open and closed tool composed of two sealing faces which are round on the inside and which form a hollow cylinder after the closing of the tool. The rotor  2  is accommodated inside the hollow cylinder. 
         [0056]    In the embodiment shown, the sealing cushions  15  are not flush with the outside of the rotor  2  but rather protrude slightly. When the tool is closed, the sealing cushions  15  which are made of flexible materials seal off the region of the groove wedge  8  radially. As a result of the pressing when the tool is closed, the sealing cushion  15  extends in the direction of the longitudinal axis of the rotor  2 . This also results in a sealing effect in the axial direction in the region of the cover of the winding head  21 . The sealing regions (radial and axial) are also illustrated in  figure 4 . 
         [0057]    The sealing cushion  15  can also be used during impregnation in order to prevent impregnating resin from escaping from the grooves  7 . 
         [0058]      FIG. 4  shows the regions Dr which are to be sealed radially and the region D a  which is to be sealed axially, where the three rotor components rotor laminated core, groove wedge  8  and cover of the winding heads  21  meet. The sealing of these regions prevents casting compound or impregnating resin from escaping. The sealing cushions  15  are removed after the casting and can be used in further casting cycles. 
         [0059]    An alternative possibility for preventing casting compound from escaping, which can also be used in addition to the sealing cushion  15 , will now be described with reference to  FIGS. 4 to 6 . 
         [0060]    In the radial sealing region Dr a seal  19  can be provided in the recess  10 . This seal  19  can be embodied as a liquid seal or as a sealing rail and can either be introduced into the recess  10  or else applied as a sealing bead to the side faces  20  of the groove wedge  8 . For example silicone can be used for this. 
         [0061]    The region D a  which is to be sealed axially can additionally be sealed off by a sealing plug  23  which is shown in section in  figure 6 . The sealing plug  23  is manufactured from a non-magnetizable material, for example from silicone or some other material, and can already be plugged on or integrally injection-molded onto the edge region  22  of the groove wedge  8  during the manufacture thereof. Alternatively, it can also be connected to the groove wedge  8  during the assembly of the rotor  2 , either by pre-assembling both parts and subsequently joining them or by mounting the groove wedge  8  and subsequently fitting the sealing plug  23 . 
         [0062]    In the embodiment shown, the sealing plug  23  has compressible lamellas  24 . The lamellas  24  compensate the assembly tolerances and fabrication tolerances of all components in the sealing region D a . 
         [0063]    During the assembly it is possible to adopt the following: Firstly, the groove wedges  8  are mounted with the sealing plug  23 , and afterward the covers of the winding heads  21  are fitted on. In this context, the lamellas  24  of the sealing plugs  23  are pressed and therefore position themselves against the sealing contour. As a result, the region which is to be sealed is closed off. Even if the lamellas  24  are not positioned precisely against the cover of the winding head  21 , at least one labyrinth seal is formed here. If the casting compound or the impregnating resin penetrates the first lamellas  24  during the casting or impregnation, it is therefore largely held back by the labyrinth geometry. 
         [0064]    Although at least one exemplary embodiment has been shown in the preceding description, various changes and modifications can be made. The specified embodiments are merely examples and are not provided for limiting the scope of validity or the possibility of application or the configuration in any way. Instead, the preceding description provides the person skilled in the art with a plan for implementing at least an exemplary embodiment, wherein numerous changes in the function and the arrangement of elements described in an exemplary embodiment can be made without departing from the scope of protection of the appended claims and their legal equivalents. 
         [0065]    In addition, a method for manufacturing a rotor  2  which is described in the above description may include the following method steps:
       providing a rotor laminated core with exciter windings  5  and groove wedges  8  which cover the grooves  7 ;   fitting sealing cushions  15  onto the outer sides  27  of the groove wedges  8 , wherein the sealing cushions  15  cover the outer sides  27  of the groove wedges  8  completely;   introducing the rotor  2  into a casting tool;   casting the rotor  2 ; and   taking the rotor  2  out of the casting tool and removing the sealing cushions  15 .       
 
       LIST OF REFERENCE NUMERALS 
       [0071]      1  Electric motor 
         [0072]      2  Rotor 
         [0073]      3  Stator 
         [0074]      4  Pole tooth 
         [0075]      5  Exciter winding 
         [0076]      6  Groove insulating paper 
         [0077]      7  Groove 
         [0078]      8  Groove wedge 
         [0079]      9  Undercut 
         [0080]      10  Recess 
         [0081]      11  Bulge 
         [0082]      14  Arrow 
         [0083]      15  Sealing cushion 
         [0084]      16  Surface 
         [0085]      17  Surface 
         [0086]      18  Side face 
         [0087]      19  Seal 
         [0088]      20  Side face 
         [0089]      21  Cover of the winding head 
         [0090]      22  Edge region 
         [0091]      23  Sealing plug 
         [0092]      24  Lamellas 
         [0093]      25  Longitudinal side 
         [0094]      26  End 
         [0095]      27  Outer side