Abstract:
The invention relates to an electric machine, in particular an alternator for motor vehicles, comprising a stator and a claw-pole rotor ( 15 ) that co-operates with the latter. The claw-poles of the rotor have claw-pole fingers ( 34 ) which are uniformly distributed around the periphery, axially intermesh in alternate directions at a distance from one another and comprise a pole core and an excitation winding. Permanent magnets are arranged between the claw-pole fingers ( 34 ) and are held in a retaining ring ( 42 ) with a zigzag configuration. To mount the retaining ring ( 42 ) in as simple a manner as possible between the claw-pole fingers ( 34 ), a longitudinal slit ( 38 ) is provided on each longitudinal side ( 37 ) of the claw-pole fingers ( 34 ). The retaining ring ( 42 ) engages in said slit by means of one respective longitudinal side of its axial sections ( 43 ).

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to an electric machine, in particular a three-phase generator for motor vehicles according to the preamble of claim 1, and a method for producing a machine of this nature according to the preamble of claim 6.  
           [0002]    An electric machine of this nature is made known in DE 199 39 808 A1. According to said publication, the permanent magnets in the open spaces between the intermeshing claw-pole fingers are inserted into a retaining ring that absorbs the centrifugal forces acting on the permanent magnets produced when the machine operates. The retaining ring is welded together with the adjacent claw-pole fingers on both sides of its axial sections.  
           [0003]    Using a “windingless rotor” as an example, a means of attaining the object of the invention described hereinabove has the advantage that welding the retaining ring results in a permanent connection being formed between the free claw pole conductive element and the claw pole plate situated on the rotor shaft, allowing the connection ring used heretofore to be eliminated. Since, in the case of “slip-ring rotors”, both claw poles are usually mounted on the rotor shaft, a fixed connection is not required there.  
           [0004]    Rather, it has the disadvantage that a special working step performed at an additional processing station is required to make the welded connections between the retaining ring and claw-pole fingers.  
           [0005]    The goal of the present means of attaining the object of the invention is to permit the simplest possible installation of the retaining ring between the claw-pole fingers.  
         ADVANTAGES OF THE INVENTION  
         [0006]    Compared to the prior art, the electric machine according to the invention having the characterizing features of claim 1 has the advantage that the reconfiguration of the claw-pole fingers enables the creation of nothing more than a positive connection between the permanent magnets and the retaining ring, instead of a fixed connection. As such, the costly need to produce welded connections is eliminated, and the centrifugal forces acting on the retaining ring are still reliably absorbed by the claw poles.  
           [0007]    A further advantage is the fact that, due to the zigzag configuration of the retaining ring, the holders for the permanent magnets no longer extend into the winding space for the excitation winding, which means that an excitation winding having a larger cross-section and, therefore, greater excitation power can now be housed in the claw-pole rotor.  
           [0008]    Compared to the prior art, the method according to the invention for producing an electric machine according to the characterizing features of claim 6 has the advantage that the retaining ring and permanent magnets can be installed fully automatically between the claw poles of the rotor on the existing assembly line for producing a claw-pole rotor without permanent magnets at an additional assembly station inserted there.  
           [0009]    Advantageous further developments and embodiments of the invention result from the remaining features listed in the dependent claims.  
           [0010]    As an additional means for restricting the elastic pressing-upward of the claw-pole fingers by the centrifugal forces within narrow limits, the longitudinal slits on the lateral flanks of the claw-pole fingers are interconnected via an end-face slit on the tip of the claw-pole fingers, into which said end-face slit a bead integrally molded on the connection section of the retaining ring engages. Furthermore, to increase the bending stiffness of the axial sections of the retaining ring, it is advantageous to equip each of them with a radially outwardly directed longitudinal hollow. Simple production of the retaining ring can be attained by punching and stamping the retaining ring out of a piece of non-magnetic sheet metal. In the simplest manner possible, a punched-out sheet metal strip is used that is bent and stamped in the shape of an open retaining ring.  
           [0011]    Although the inventive features can be used particularly advantageously with collector rings, they can also be realized on “windingless rotors”, provided that the fixed claw-pole connection is created there using additional means or measures. In that case, the conductive element forms one of the two claw poles.  
           [0012]    In the production of the electric machine according to the invention, axial longitudinal slits for accommodating the axial sections of the retaining ring are recessed in the lateral flanks of the claw-pole fingers in a process step in preparation for assembly of the retaining ring. At an additional assembly station, the retaining ring with a zigzag configuration is first inserted into the longitudinal slits in the claw-pole fingers of the first claw pole by means of one longitudinal side of its axial sections. To accomplish this, the first claw pole is mounted on a tool holder that has a magnetic ring enclosing the claw-pole fingers and the retaining ring from the outside, which said magnetic ring is partially magnetized in the region of the axial sections of the retaining ring. To install the permanent magnets, they are advantageously first inserted in an annular arrangement in axial holes of a round magazine. The round magazine is then positioned over the exposed, end-face connection section of the retaining ring in such a manner that the axial holes with the permanent magnets come to rest in pairs between the connection sections of the retaining ring. Using an annular plunger having fingers matched with the holes in the round magazine that is located above the round magazine, the permanent magnets are pushed axially out of the holes into the space between the claw-pole fingers until the permanent magnets rest against each of the lateral flanks of a claw-pole finger. As they are pushed further, the permanent magnets glide along the side of the lateral flanks of the claw-pole fingers, thereby assuming an inclined position, where they are held by the magnetic ring by means of its partial magnetization. After the plunger and the round magazine are removed, the permanent magnets are set into their final position on the axial sections of the retaining ring by means of a shaped plunger having a claw pole-shaped contour plunging axially into the magnetic ring of the tool holder, where they are held by the magnetic ring. The first subassembly which is preassembled in this fashion is joined, together with the tool holder and the magnetic ring, with the rotor shaft, the pole core, the excitation winding, and the second claw-pole, and the first claw-pole is placed on the rotor shaft with an interference fit. The second claw-pole is placed on the rotor shaft with a sliding fit, then positioned by the first claw-pole and the retaining ring, and, finally, caulked with the rotor shaft. 
       
    
    
     SUMMARY OF THE DRAWINGS  
       [0013]    An exemplary embodiment of the invention is presented in the drawings and described in greater detail.  
         [0014]    [0014]FIG. 1 is a longitudinal sectional view of a three-phase generator for motor vehicles configured according to the invention,  
         [0015]    [0015]FIG. 2 is a spacial representation of a first claw-pole of the alternator in FIG. 1,  
         [0016]    [0016]FIG. 3 is a spacial representation of a retaining ring for the permanent magnets,  
         [0017]    [0017]FIG. 4 is a spacial representation of the first claw pole with installed retaining ring,  
         [0018]    [0018]FIG. 5 is a spacial representation of an assembly station for inserting the permanent magnets,  
         [0019]    [0019]FIG. 6 shows the assembly station in FIG. 5 with a shaped plunger for positioning the permanent magnets,  
         [0020]    [0020]FIG. 7 shows the assembly station in FIG. 6 with the first claw pole, the retaining ring, and the permanent magnets positioned therein as the first subassembly,  
         [0021]    [0021]FIG. 8 is a partial view of the assembly station in FIG. 7 with the second subassembly comprising rotor shaft, pole ring and excitation winding inserted in the first claw pole, and with the second claw pole before assembly, and  
         [0022]    [0022]FIG. 9 shows the assembled claw-pole rotor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 1 is a longitudinal sectional view of a three-phase generator for motor vehicles, the housing of which is composed substantially of two end shields  10  and  11  that are held together by screws  12 , and between which the laminated stack  13  of a stator  14  is clamped. A claw-pole rotor  15  is located inside the stator bore, the excitation winding  16  of which is wound on a pole core  17 . A hub  18  is developed on the left drive side of the generator in the end shield  10 , in which said hub a roller bearing  19  is located to support the drive-end part of a rotor shaft  20 . The right part of the rotor shaft  20  is supported in a roller bearing  21  having a weaker configuration, which said roller bearing is located together with a collector-ring housing  22  in a hub  23  of the end shield  11 . A positive heat sink  24  and a negative heat sink  25  of a rectifier, together with a protective cap  26 , are mounted on the front side of the rear end shield  11 . A first and second claw pole  27 ,  28  are pressed onto or caulked on the rotor shaft  20  on the front side of the pole core  17 . Two collector rings  29 ,  30  are secured in an insulated manner to the rear shaft end to supply electricity to the excitation winding  16 . Said collector rings interact with the brushes of a brush holder  31  secured on the rear end shield  11 .  
         [0024]    The claw poles  27  and  28  are produced out of pole plates by means of cold forming. Each of them is composed of a pole disk  32  with a hole  33  stamped in the center, and axially angled claw-pole fingers  34  distributed evenly around the circumference. The claw-pole fingers  34  of the two claw poles  27  and  28  intermesh in alternate directions at a distance from one another, and they enclose the excitation winding  16 . To increase the excitation power of the claw-pole rotor  15 , a permanent magnet  35  is located between each of the claw-pole fingers  34  and housed in a holder  36  in such a manner that is is supported against the centrifugal forces acting on it when the machine operates.  
         [0025]    [0025]FIG. 2 shows an enlarged spacial representation of the first claw pole  27  of the claw-pole rotor  15 . Said figure shows that each of the claw-pole fingers  34  has a longitudinal slit  38  created by means of chip removal on its lateral flank  37 , which said longitudinal slit extends from the claw-pole base  39  to the claw-pole tip  40  in freely emerging fashion. The longitudinal slits  38  on the two lateral flanks  37  of each claw-pole finger  34  are interconnected on the claw-pole tip  40  of the claw-pole fingers  34  by means of an end-face slit  41 .  
         [0026]    [0026]FIG. 3 shows the holder  36  for the permanent magnets  35  in the form of a zigzag-configured retaining ring  42  produced out of non-magnetic material that comprises alternating axial sections  43  and connection sections  44 , which said connection sections simultaneously function as axial stops for the permanent magnets  35 . The retaining ring  42  has been punched, bent and stamped out of a piece of sheet metal. As an alternative, it can also be punched, bent and stamped as an open retaining ring out of a sheet metal strip, whereby the beginning and end of the sheet metal strip are preferably located in the center of an axial section  43 . Each of the axial sections  43  of the retaining ring  42  is equipped with a radially outwardly arched longitudinal hollow  45  to increase its bending stiffness. The connection sections  44  are configured—as shown in FIG. 3 a —as bars  46  with a sheet metal cross-section that is rectangular, radially bent-upward, and frame-shaped, as shown along the line A-A in FIG. 3. This provides the connection sections  44  with a high amount of bending stiffness against the centrifugal forces that occur there. It is greater than the bending stiffness of the axial sections  43  in terms of the centrifugal forces that occur there.  
         [0027]    [0027]FIG. 4 shows an enlarged spacial representation of the first claw-pole  27  in FIG. 2 with the retaining ring  42  in FIG. 3 pushed onto its claw-pole fingers  34 . Said FIG. 4 shows that each of the axial sections  43  rests against a lateral flank  37  of the claw-pole fingers  34  by means of its one longitudinal side by engaging in the longitudinal slit  38  of the claw-pole fingers  34  recessed there, and the connection sections  44  of the retaining ring  42  connect two adjacent axial sections  43  with each other on each of the pole tips  40  of the claw-pole fingers  34 . Combined with FIG. 3, it is furthermore obvious in FIG. 4 that the bars  46  of the connection sections  44  are molded on over nearly their entire width and angled radially inwardly on each of the end faces of the adjacent axial sections  43 . This provides the retaining ring  42  with a high amount of stiffness against the centrifugal forces that act on it. Furthermore, the connection sections  44  form an axial stop when the retaining ring  42  is pushed onto the claw-pole fingers  34  of the claw pole  27 . In this position, furthermore, a bead  47  integrally molded on the connection sections  44  of the retaining ring  42  engages in the slit  41  on the pole tip  40  of the claw-pole fingers  34 .  
         [0028]    Existing production lines can be used to produce the three-phase generator according to FIG. 1. Due to the novel method of holding the permanent magnets in the claw-pole rotor  15  according to the invention, the production of the stator  14  and the two end shields  10  and  11  remains unchanged. With regard for the claw-pole rotor  15  as well, its individual parts, e.g., rotor shaft  20 , pole core  17 , excitation winding  16 , claw poles  27  and  28 , and the complete collector ring arrangement can be produced first in unchanged fashion. The novel aspects, on the other hand, are the arrangement and holder  36  of the permanent magnets  35  and their installation between the claw-pole fingers  34  when the claw-pole rotor  15  is assembled. To accomplish this, as shown in FIG. 2, the axial longitudinal slits  38  for accommodating the axial sections  43  of the retaining ring  42  are created first of all in the lateral flanks  37  of the claw-pole fingers  34  of the two claw poles  27  and  28 . Furthermore, to hold the permanent magnets  35 , the retaining ring  42  composed of non-magnetic material is die-cut out as shown in FIG. 3 with the axial sections  43  and the connection sections  44  out of a piece of sheet metal and then bent and stamped in the shape shown in FIG. 3. The retaining ring  42  is then pushed, first of all, in the axial direction onto the claw-pole fingers  34  of the first claw pole  27  by pushing one longitudinal side each of its axial sections  43  as shown in FIG. 4 into the longitudinal slits  38  in the claw-pole fingers  34  until the rear connection sections  44  rest against the pole tips  40  of the claw-pole fingers  34 .  
         [0029]    As shown in FIG. 5, the first claw pole  27  with the retaining ring  42  is now mounted on a tool holder  50 , whereby a magnetic ring  51  is mounted on the tool holder  50 , said magnetic ring enclosing the claw pole  27  with its claw-pole fingers  34  and the retaining ring  42  from the outside, thereby surrounding said parts. The magnetic ring  51  is partially magnetized in the region of the axial sections  43  of the retaining ring  42 . The only difference between the tool holder  50  and the prior art is the addition of the magnetic ring  51 .  
         [0030]    Novel features, on the other hand, are the devices shown in FIGS. 5 and 6 for inserting and positioning the permanent magnets  35  in the retaining ring  42 . To accomplish this, round magazines  52  are first loaded with the permanent magnets  35  at another location by placing said permanent magnets in appropriately-sized axial holes  53  of the round magazine  52 . The round magazines loaded in this fashion can be delivered on pallets. To produce the claw-pole rotor  15 , then, one round magazine  52  each is taken from a not-shown pallet of this nature and positioned over the tool holder  50  as shown in FIG. 5. The axial holes  53  with the permanent magnets  35  are held in their axial position in an annular configuration using vacuum by means of a valve housing  54  located above it and to be moved axially, using the known pick-and-place technique. The round magazine  52  is positioned on the valve housing  54  by means of pins  55  in the valve housing  54  that engage in axial holes  56  in the round magazine  52 . An annular plunger  57  is located above the valve housing  54 , which said annular plunger is axially displaceable as well and comprises axially projecting fingers  58  on its underside which are also arranged in the shape of a ring and that are matched with the axial holes  53  in the round magazine  52 . The round magazine  52 , valve housing  54  and plunger  57  are now moved toward the tool holder  50  and positioned on the exposed, end-face connection sections  44  in such a manner that the axial holes  53  with the permanent magnets  35  come to rest in pairs between the connection sections  44 . The set of permanent magnets  35  located in the round magazine  52  is then pushed axially by the fingers  58  of the annular punch  57  out of the holes  53  into the space between the claw-pole fingers  34  until the permanent magnets  35  rest against each of the lateral flanks  37  of a claw-pole finger  34 . When the permanent magnets  35  are pushed further by the fingers  58  of the plunger  57 , the permanent magnets finally glide along each of the lateral flanks  37  of a claw-pole finger  34  and assume an inclined position. Due to the partial magnetization of the magnetic ring  51 , the permanent magnets  35  are held in this position at first, so that the round magazine  52  with the valve housing  54  and the plunger  57  can be removed.  
         [0031]    [0031]FIG. 6 shows the tool holder  50  with the magnetic ring  51  and the set of permanent magnets  35  in the aforementioned inclined position. It is obvious in this figure as well that the permanent magnets  35  are designed in the shape of bars and have a trapezoidal cross-section that increases in size as it extends outward. In order to bring the permanent magnets  35  into their final position underneath the axial sections  43  of the retaining ring  42 , a shaped plunger  59 —as shown in FIG. 6—is now brought into position over the tool holder  50  with the magnetic ring  51 . Said shaped plunger plunges axially with a claw-shaped contour  60  into the magnetic ring  51 , and each of its claw tips  61  is guided between the paired, inclined permanent magnets  35 . Finally, the permanent magnets  35  are set in their final position, where they are held when the shaped plunger  59  is then removed from the magnetic ring  51 .  
         [0032]    [0032]FIG. 7 shows the tool holder  50  with the magnetic ring  51  and with the permanent magnets  35  located in their final position, each one on the inside of an axial section  43  of the retaining ring  42 . The first claw pole  27 , together with the retaining ring  42  and the permanent magnets  35 , forms a first subassembly.  
         [0033]    In another production step, the rotor shaft  20  is preassembled in known fashion with the pole core  17  and the excitation winding  16  to form a second subassembly. As shown in FIG. 8, the first preassembled subassembly on the tool holder  50 , together with the magnetic ring  51 , is now joined with the aforementioned second subassembly. The first claw pole  27  is placed on a knurled section of the rotor shaft  20  and fixed in position. FIG. 8 also shows that the excitation winding is enclosed by a paper insulation  62  that is fixed in position by a binding  63 , and on the top front side of which the wire ends  64  of the excitation winding are guided out for connection to the collector ring arrangement  47 . To produce the claw-pole rotor  15 , the second claw pole  28  is now placed axially on the exposed end of the rotor shaft in a further working step. The claw-pole fingers  34  of said claw-pole rotor engage between the claw-pole fingers  34  of the first claw pole  27  in the gaps between the axial sections  43  of the retaining ring  42 . The longitudinal sides of the axial sections  43  of the retaining ring  42  that are still free are then pushed into the longitudinal slits  38  in the claw-pole fingers  34  of the second claw pole  28 . The second claw pole  28  is positioned by means of its sliding fit in the circumferential direction on the rotor shaft  20  by means of the first claw pole  27  and the retaining ring  42 . After it is positioned on the rotor shaft  20 , it is finally fixed in position by means of caulking. In a further working step, the collector ring arrangement  47  can now be placed on the top end of the rotor shaft  20 , as usual.  
         [0034]    [0034]FIG. 9 shows the fully-assembled claw-pole rotor  15  with the retaining ring  42  configured according to the invention, each of the axial sections  43  of which is located between two adjacent claw-pole fingers  34 , and that rest in a longitudinal slit of a lateral flank  37  of the claw-pole fingers  34  by means of their longitudinal sides. The permanent magnets are enclosed and held from the outside by the lateral flanks  37  of the claw-pole fingers  34  and by the connection sections  44  on the side, and by the axial sections  43  of the retaining ring  42 . They are further fixed in position between the claw-pole fingers  34  by means of a common dipping impregnation procedure. Additionally, before the rotor is assembled with the stator, they are magnetized with alternating polarity in the circumferential direction of the rotor by magnetic fields applied to the claw-pole fingers  34  from the outside.