Abstract:
In a method for manufacturing a bar winding for the stator of an electric machine, in particular of a claw pole alternator for motor vehicles, resistance welding is used to form mechanically and electrically reliable and permanent connections in the winding overhang of the stator even with winding configurations that include four or more superposed conductor segments, and even with the very small amount of working space that remains for the necessary connections, using a minimum of production-related outlay. With a design, in particular, of four radially superposed conductor segments in the winding overhang, particularly advantageous configurations result in terms of the placement of the bar ends and in terms of the design of the welding electrodes.

Description:
CROSS-REFERENCE 
     The invention described and claimed hereinbelow is also described in PCT/EP2007/001147, filed on Apr. 10, 2007 and DE 10 2006 019 312.1, filed on Apr. 26, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d). 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a method for manufacturing a bar winding for the stator of an electric machine, in particular of a claw pole alternator for motor vehicles, as made known basically in DE 40 31 276 A. This publication discloses a method for manufacturing a stator for electric machines, the bar winding of which is made of four superposed winding bars that lie in slots in pairs, which are pre-bent in the manner of hairpins, and which are inserted into the core slots with a separation corresponding to the pitch between poles. The ends of the winding bars are interlaced on both sides of the core, and they are joined galvanically in pairs on one side of the core via welding or soldering. The publication does not make any detailed statements regarding the method used to join the ends of the winding bars. 
     SUMMARY OF THE INVENTION 
     In contrast to the related art, the inventive method makes it possible—by using the method of resistance welding, which is basically known—to create mechanically and electrically reliable and permanent connections in the winding overhang of the stator even with winding configurations that include four or more superposed conductor segments, and even with the very small amount of working space that remains for the necessary connections, using a minimum of production-related outlay. With a design, in particular, of four radially superposed conductor segments in the winding overhang, particularly advantageous configurations result in terms of the placement of the bar ends and in terms of the design of the welding electrodes. 
     According to a very simple and advantageous method, the electrical connections of two radially superposed conductor pairs in the winding overhang may be created simultaneously or in succession using the electrodes by contacting one conductor segment of each pair radially and at least one conductor segment axially by an electrode, and by redirecting the welding current by 90° in this process. 
     Advantageously, the outwardly lying conductor segments of two conductor pairs to be connected are each contacted by a separate, radially operating electrode, and the two center conductor segments are contacted by a single, axially operating electrode. This mode of operation is particularly advantageous when the ends of the inwardly lying conductor segments of two conductor pairs extend further out of the core of the stator than do the outer conductor segments, because the inwardly lying conductor segments are then more easily accessible, and because it makes it possible to use a lower-wear electrode with a larger cross section. This mode of operation also makes it possible, without any mechanical reworking, to melt off—using the electrode—ends of the inner conductor segments that extend out of the core of the stator by different extents, in order to make them the same length, and to then contact them. 
     A particularly advantageous embodiment of the inventive method results when the ends of the inwardly lying conductor segments of two conductor pairs extend further out of the stator core than do the outer conductor segments, and when all conductor segments are contacted radially by the electrodes in the welding process. This method of operation offers the advantage in particular that, during the welding process, no axial forces act on the conductor segments, and the radial forces may be absorbed around the full circumference of the welding electrodes without the need for additional mechanical securing measures. 
     The inventive method may also be used, advantageously, with a configuration that includes more than four, e.g., six conductor segments in the winding overhang, which are radially superposed and are interconnected in pairs, by axially contacting the ends of all conductor pairs by the electrodes in the welding process. It is also possible, however, to contact the outwardly lying conductor segments of the outer conductor pairs to be connected using one radially operating electrode, in which case, the radially operating electrodes absorb the forces acting in the radial direction during the welding process. As a result, only the axially acting forces need to be absorbed using a separate clamping device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the present invention are presented in the drawing and are described in greater detail in the description below. 
         FIG. 1  shows a perspective view of a stator with a bar winding with the ends of the conductor segments, which have been pre-shaped for the welding process, 
         FIG. 2  shows a partial cross section through the stator core with radially extending slots, each of which contains four superposed conductor segments, 
         FIG. 3   a  is a schematic cross-sectional view with four conductor segments in the winding overhang of the stator, which are superposed and have been welded together in pairs, 
         FIG. 3   b  shows a schematic illustration of a wave winding with a welded connection of a conductor pair, 
         FIG. 4  shows a design with four conductor segments—which are of equal length, are superposed, and are to be connected in pairs—in the winding overhang, 
         FIG. 5  shows a design with four conductor segments—which are radially superposed and are to be connected in pairs—in the winding overhang, the two middle segments extending out of the stator core further than do the outer segments, 
         FIG. 6  shows a design according to  FIG. 5  with only radial contacting of the ends of the conductor segments, and 
         FIG. 7  shows a design with six conductor segments—which superposed and are connected in pairs—in a slot and in the winding overhang. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a perspective, schematic view of a stator  16  of an electric machine of the type used, e.g., in a claw pole alternator for motor vehicles. Poles  32  and slots  34  are shown on the inner surface of stator  16 . Each slot  34  contains four radially superposed conductor segments  36 . The conductor segments are bent in the shape of hairpins in a known manner on the underside of stator  16 , and they are interlaced across one pole pitch. Their free ends  42 , which are of equal length, extend out of the top side of stator  16 —also having been interlaced across one pole pitch—out of slots  34 , and they are located in four concentric rows. After the electric machine has been assembled, free ends  42  are located in drive-side winding overhang  45  of the stator, while hairpin-shaped redirections  44  extend out of opposite winding overhang  46  of stator  16 , which is oriented toward its connection side after the electric machine has been assembled. This design has the advantage that more space for the welded connections is available in drive-side winding overhang  45 . Machine axis is labeled with reference numeral  27 . 
       FIG. 2  shows an enlarged illustration of a cross-section through core  17  of stator  16 . Four conductor segments  36  are radially superposed in each slot  34 . The conductor segments are insulated—on each of their surfaces by a lacquer insulation  38 , and altogether by insulation inlays  39 —against core  17  of stator  16 . Conductor segments  36  of stator winding  18  designed as a bar winding are inserted by axially inserting conductor segments  36  into slots  34 . 
       FIG. 3  shows, in illustration a, a schematicized, partial cross sectional view through core  17  of stator  16 , out of which free ends  42  of stator winding  18  extend. Ends  42  of stator winding  18  are stripped of lacquer insulation  38  in front region  43 , so that the welding current may flow unhindered in this region in the radial and axial directions and fuse a welding area  40 . A distance d is left between ends  42  of conductor segments  36  that are not to be welded, into which a strip-type insulation  48  may also be inserted, e.g., a strip of plastic or ceramic. 
       FIG. 3   b  shows hairpin-shaped reversal  44  between conductor segments  36  in the region of winding overhang  46  facing away from the drive side, the spread of conductor segments  36  by one pole pitch, and the offset of free ends  42  toward welding areas  40 . The inventive welding of ends  42 , the various possible designs of welding electrodes, and the placement of ends  42  in welding area  40  will be discussed in greater detail with reference to the figures below. 
       FIG. 4  shows a design with four conductor segments  36 —which are radially superposed and are welded together in pairs—in a drive-side winding overhang  45 , the stripped ends  43  of which extend out of core  17  of stator  16  to equal extents and terminate in winding overhang  45  at the same level. Individual conductor segments  36  are labeled as I, II, III and IV. Conductor segments I and II, and III and IV are welded together in region  40 . An insulation  48  is inserted between conductor segments II and III. Conductor segment I is contacted radially by negative welding electrode −E 1 , and conductor segment II is contacted axially on its end face by positive electrode +E 1 . Welding current I from electrode −E 1  initially flows through conductor segment I, then it reverses its direction of flow, into an axial direction toward positive electrode +E 1 . In this manner, conductor segments I and II to be welded together, and, in the same manner, conductor segments III and IV, may be easily contacted using welding electrodes that are sufficiently sturdy and therefore permanent, and that have the service lives required in production. At the same time, the clamping forces for positioning and stabilizing conductor segments  36  during the welding process are absorbed from the outside in the radial direction by the −E 1  electrodes, and they are absorbed from the winding overhang-side in the axial direction, as indicated by arrows  50  and  52 . The contact pressures produced during welding must be absorbed—from stator  18  and the inner side of the winding overhang outward—by additional mechanical devices, which are not shown, as indicated by arrows  54  and  56 . The spacial orientation of the configuration shown in  FIG. 4  is also indicated in  FIGS. 5 through 7  via central axis  27  of the machine. 
       FIG. 5  also shows a design with four conductor segments—which are radially superposed and are welded together in pairs—in drive-side winding overhang  45 , the two middle segments II and III extending out of the core  17  further than do outer segments I and IV. Conductor segments I and IV are contacted from the outside in the radial direction by electrode −E 1 , and from the inside by electrode −E 2 . Conductor segments II and IV are contacted by one electrode +E in the axial direction on the end face of conductor segments  36 . Welding current I initially flows from negative electrodes −E 1  and −E 2  in the radial direction through conductor segments I and IV, and it is redirected in region  40  of the weld points into the axial direction toward positive welding electrode +E. The two conductor pairs I and II, and III and IV may be welded simultaneously. Any uneven axial lengths of the two conductor segments II and III may be compensated for by positive electrode +E by using the electrode to melt off a longer conductor segment, as indicated with segment III, before conductor segments II and III are contacted and welded connections  40  are created. With this design, the mechanical arresting forces need only be absorbed during the welding process in the region of core  17 , as indicated by arrow  54 . The remaining positioning and arresting forces  50 ,  52  and  56  are absorbed by the electrodes themselves without the use of any additional design-related measures. 
     The procedure of contacting conductor segments II and III using a single electrode +E, as shown in  FIG. 5 , may also be used with the design according to  FIG. 4  to contact middle conductor segments II and III. In this case, negative electrode −E 1  could be moved toward conductor segment IV, or an additional electrode −E 2  could be used with this design to contact conductor segment IV. 
     With the design depicted in  FIG. 4 , any differences in length between conductor segments  36  may then also be compensated for via melting, and/or the welding process may be carried out for both conductor pairs in one working step. 
       FIG. 6  shows the same configuration of conductor segments  36  as in  FIG. 5 . To contact ends  43  when welding pairs of conductor segments I and II, and conductor segments III and IV, however, four separate electrodes −E 1 /+E 1  and −E 2 /+E 2  are only used radially. Welding current I is redirected twice, from a radial direction, to an axial direction, and then back to a radial direction, with all conductor segments being easily accessible. The arresting forces for the conductor segments, which only occur in the radial direction, are absorbed exclusively by the welding electrodes, as indicated by arrows  50 . 1  and  50 . 2 , and  56 . 1  and  56 . 2 . With this configuration, no axial forces are applied to conductor segments  36 . 
       FIG. 7  shows a design with six radially superposed conductor segments I through VI in drive-side winding overhang  45 . Conductor segments I through VI are interconnected in pairs in the region of weld points  40  by inserting insulation  48  at their free and stripped ends  43 . Different possibilities are shown schematically for positioning welding electrodes −E and +E. Outer conductor segments I and VI are preferably contacted by radially applied welding electrodes −E. Likewise, these conductor segments I and VI may also be contacted axially, as shown for the remaining conductor segments II, III, IV, and V. A further alternative, which is not shown, would also be, e.g., to extend conductor segments IV and V axially, and to contact them radially or axially, as indicated in  FIGS. 5 and 6 . When radially-located welding electrodes −E are used, they may absorb radial arresting forces  50  and  56  during the welding process. When axially contacting some or all conductor segments, the necessary positioning and arresting forces must be absorbed from the side of core  17 , as indicated by arrow  54 , using suitable clamping means for core  17 . 
     Electric machines, in particular claw pole alternators for motor vehicles, with a stator winding  18  with a bar or plug-in winding design, have very good ventilation of winding overhangs  45  and  46 , and they produce relatively little noise, even at high rotational speeds. With the measures provided, considerable manufacturing-related advantages result with the manufacture of stators  16  of this type, since the welding processes are greatly simplified and improved, thereby even making it possible to use the resistance-welding method—which is very advantageous—with many applications. In addition, mechanical arresting and positioning means may be eliminated to a large extent or entirely, and the electrodes—which are subject to a great deal of wear—are designed to be sturdy and, therefore, long-lived when the design is selected according to the present invention such that the direction of current flow and the direction of the force to be applied in the welding process are separated from each other, at least partially. Via the axial offset of the location of conductor segments  36 , additional space is created for the configuration and accessibility of the welding electrodes. 
     Via the possibility of using robust and large welding electrodes, it also becomes easier to supply higher welding currents I, which results in shorter contacting times and less warming. As a result, the insulation of conductor segments  36  is less at risk to the effects of heat. In the welding region, contacts between adjacent conductor segments may be reliably prevented by using additional inlays of insulation elements  48 , which are removed after welding. As a result, faulty contactings between conductor segments  36  do not occur in the welding zone. In addition, insulations  48  may transfer force in the region of the central conductor segments by manufacturing them using a suitable material, e.g., a suitable plastic or ceramic.