Abstract:
A slip ring module ( 76 ) for a rotor ( 40 ) of an electrical machine ( 10 ), in particular, an alternator is disclosed, comprising at least one first slip ring ( 79 ) with at least one first connecting conductor ( 103 ) held in sections of an insulation material ( 101 ) for the slip ring module ( 76 ), in electrically conducting connection with at least one first slip ring ( 79 ) and with an end ( 115 ) of the connection conductor ( 103 ), facing away from the first slip ring ( 79 ), provided for connection to an excitation coil ( 61 ). The invention is characterised in that the slip ring module ( 76 ) has a further formed conductor ( 139 ) forming a direct electrical connection from the first connection conductor ( 103 ) to a surface ( 142 ) of the slip ring module ( 76 ). An electric machine is also provided, in particular, an alternator for motor vehicles, comprising a rotor ( 40 ), supporting an excitation coil ( 61 ), said slip ring module ( 76 ) providing the power supply to the excitation coil ( 61 ). Furthermore, a method for production of a slip ring module ( 76 ) for an electric machine, in particular, an alternator, is disclosed, wherein, in one step, at least one connector conductor ( 103 ) is bonded to an electrically insulating holder ( 100 ), in particular, by means of a injection moulding process and, in another step, the connection conductor is directly connected to an electrically conductible conductor ( 139 ) made from a composite material, the composite material comprising electrically conducting and electrically non-conducting regions.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a slip ring assembly for a rotor of an electric machine, an electric machine with a slip ring assembly, and a method for producing a slip ring assembly. Known slip ring assemblies of this type are normally comprised of two slip rings, which are supported by a holder made of insulating material. The two slip rings are each connected to an electrical connecting conductor, via whose ends one end can be fastened to an excitation coil of the rotor. One such slip ring assembly is known for example from Unexamined German Application DE 38 38 436 A1. 
     However, when using these and similar types of slip ring assemblies, previously unknown problems with rotary current generators, for which these types of slip ring assemblies are intended, have cropped up in connection with drive materials modified by vehicle manufacturers; in particular new materials for multi-V belts. 
     One phenomenon in this case is that, during rotational movement of the rotor, high electrostatic voltages build up, which discharge suddenly when an undefined limit is exceeded and which can thereby damage or even destroy the electronic components such as the regulator for the excitation coil. This voltage generation functions in accordance with the known “Van de Graaf generator.” 
     Various efforts have already been made to solve this problem. Thus, Unexamined German Application DE 101 18 004 A1 discloses a system in which the electrostatic voltage is dissipated from the electromagnetic iron part via the negative slip ring to the electrical ground of the electric machine, for example, via a conductive coating of the holder made of insulating material. The disadvantage of the attainments disclosed there is that smooth functioning of the excitation coil after assembly and after connection to the slip ring assembly is no longer reliable or cannot even been tested anymore. The consequence of this is that rotors that are untested or untestable in this respect are not recognized under some circumstances as damaged, and therefore are processed further in the cost-intensive manufacturing process even though they are long since defective goods. 
     SUMMARY OF THE INVENTION 
     The advantage of the slip ring assembly in accordance is that because of the additional molded conductor, which forms a direct electrical connection from the first connecting conductor to a surface of the slip ring assembly, a high-voltage test of the excitation coil of the rotor can be conducted. This high-voltage test is used both during fabrication as well as after testing to check the winding for short circuits to the so-called rotor ground, i.e., to the magnetic parts of the rotor. 
     If one provides for the additional molded conductor to be positioned on the at least one first connecting conductor as a separate component, the advantage of the associated prefabrication is that a concrete precisely dimensioned component can be prefabricated that has no essential tolerance fluctuations, and therefore this separate component forms a reliable and precise electrical connection from the first connecting conductor to a surface of the slip ring assembly. If the additional molded conductor is embodied by molding on the at least one first connecting conductor, the spraying on of this additional molded conductor also permits the creation of an exact precise additional molded conductor that is high-quality and precise. 
     If the additional molded conductor has a material section, which forms an undercut and engages in an undercut of the connecting conductor, a secure radial position is achieved in particular in the embodiment as a separate component. 
     So that the additional molded conductor does not cause any short circuits of the excitation coil, it is envisaged that this additional molded conductor has a conductivity of 1E5 Ωcm to approx. 1E12 Ωcm. This makes sufficiently high currents to avoid the electrostatic discharge possible. At the same time, the effect on the excitation current is reasonably minimal. 
     If the additional molded conductor is arranged between the first slip ring and the end of the connecting conductor facing away from the first slip ring, it is thus possible in a mounted state to contact the molded conductor with an inner ring of a roller bearing, and thus dissipate the electrostatic charge from the magnetic parts via its shaft, the inner ring of the bearing, the molded conductor and connecting conductor. This arrangement takes into consideration the normal arrangements of compact generators (double-flow rotors) as disclosed in the prior art cited at the outset. If the first slip ring is arranged between the end of the connecting conductor facing away from the first slip ring and the additional molded conductor, then this arrangement corresponds to another variation of designs of compact generators, in which the slips rings are arranged between the supporting bearing or the roller bearing and the magnetic part of the rotor. In this case as well, dissipating the charge via the molded conductor on an inner ring of the roller bearing is possible. 
     If the additional molded conductor has a higher specific electric resistance than the connecting conductor, but a smaller specific electrical resistance than the insulating material, a clear path or route is produced for dissipating the electrostatic charge. 
     If a polymer composite material, which is preferably a mixture of polymer insulating material and conductive material, is selected as the material for the molded conductor, a molded conductor is obtained that can be manufactured using an injection molding process, and as a result it can be relatively freely designed in terms of its shape. As a result, it is quite possible in particular to adapt to local circumstances. In addition, there is the possibility of spraying this molded conductor on the insulating material of the slip ring assembly, which is comprised for example of similar materials, whereby a mechanical connection of the molded conductor to the embedded or adhering insulating material is quite possible. Slipping or detaching of the molded conductor before assembly on the electric machine is therefore ruled out. 
     If the molded conductor grips around the connecting conductor in an essentially U-shaped manner or the entire cross section of the connecting conductor, then an especially large-area connection of the molded conductor to the connecting conductor is obtained. A clamping in claws or frictionally engaged or positively engaged connection between the connecting conductor and the molded conductor is therefore quite possible. The molded conductor can therefore adhere especially well to the connecting conductor. Another embodiment of the invention provides for the first connecting conductor to be covered by the additional molded conductor in an axial section, and for the first connecting conductor to be at least partially surrounded there by insulating material of the slip ring assembly, wherein a width of the insulating material in the circumferential direction is greater than a width of the additional molded conductor in the circumferential direction. This measure makes specific cooperation with the electric machine possible. Because of the different widths, the angular position of the slip ring assembly is secured at the shaft end or on the rotor, on the one hand. The width of insulating material is responsible for this. As a result of the fact that the width of the additional molded conductor is smaller in the circumferential direction, however, than the width of the insulating material, contacting of the molded conductor in the circumferential direction in the area of the shaft or the rotor is ruled out. As a result, no electrical connection can be established to begin with between the additional molded conductor and the iron or magnetic parts of the rotor. This makes functional testing of the excitation winding possible after connecting said excitation winding to the slip ring assembly since the molded conductor is not able to cause a short circuit. 
     If the additional molded conductor defines, at its axial position and its angular position, a greater radius of the slip ring assembly with respect to an axis of the slip rings than said slip ring assembly has at another angular position of the same axial position, then a good electrical contact can be established between the metallic roller bearing inner ring and the molded conductor when said inner ring of the roller bearing is in a slid-on position. 
     In addition, an electric machine is envisaged that supports the slip ring assembly in accordance with the invention, and is used to supply power to the excitation coil and to dissipate the static electricity. Such a combination makes a reliable and very precisely reproducible dissipation of the static electricity possible. An especially space saving arrangement of the additional conductor is possible if the rotor has a shaft end on the slip ring side and the shaft end has a slot featuring slot walls, which slot extends in the axial direction and in which the at least one connecting conductor is arranged. 
     If the molded conductor contacts the shaft end only indirectly or if the current path goes from the first connecting conductor to the ground of the machine from the shaft and its essentially cylindrical outer side or a seat of the roller bearing on the inner ring of the roller bearing and from there to the additional molded conductor, then this arrangement makes the already mentioned testing of the excitation coil possible without the slid-on bearing. 
     A distance between the molded conductor and the slot walls makes indirect contacting of the molded conductor with the shaft end possible in an indirect manner. 
     In order to form an especially good contact between the roller bearing inner ring and the molded conductor, provisions are made for the mounted roller bearing to compress the molded conductor and for the resulting compression to enable an electric contact between the molded conductor and the roller bearing ring. 
     A method in accordance with the invention for producing a slip ring assembly envisages, in one step, that at least one connecting conductor is connected to an electrically insulating holder, in particular by means of an extrusion coating process, and, in another step, for this same connecting conductor to be directly connected to an electrically conductive conductor made of a composite material, wherein the composite material has electrically conductive and non-electrically conductive portions. 
     This method allows the dissipation of static electricity, which discharges via a narrowly delimited path. An especially compact design with simultaneous protection of the connecting conductor from corrosive attacks is produced if the connection is surrounded over a section in the direction of its longitudinal extension both, i.e., in the direction that is defined by the distance between the slip rings and the connections for the excitation winding, both by the electrically insulating holder as well as by the electrically conductive holder so that a common sheath is formed, wherein the insulating holder and the electrically conductive conductor complement one another to form the common sheath. 
     A particularly compact and reliable design of the slip ring assembly is produced if the electrically insulating holder is fabricated by extrusion coating of at least the one connecting conductor with subsequent solidification and preferably also the electrically conductive conductor, which is supposed to guarantee the electrostatic dissipation, is sprayed around surface sections of the connecting conductor. 
     It is envisaged that the electrically conductive conductor made of the composite material also be sprayed on the connecting conductor and that it preferably completely complement a recess of the insulating material, which was sprayed on the connecting conductor in a previous step. An overall impervious sheath is obtained and attacks from media that could lead to corrosion of the connecting conductor are practically impossible. Reliability is high. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings schematically depict exemplary embodiments of an inventive slip ring arrangement, an electric machine, as well as a method for producing a slip ring arrangement. The drawings show: 
         FIG. 1A  rotary current generator of a type as previously used since the beginning of the 1990s, 
         FIG. 2  A spatial view of a conventional slip ring assembly as it is used in a generator according to  FIG. 1 , 
         FIG. 3  A spatial view of a slip ring assembly in accordance with the invention in a first exemplary embodiment, 
         FIG. 4  The slip ring assembly after a first injection molding process. 
         FIG. 5  The molded conductor independent of the slip ring assembly, 
         FIG. 6  The slip ring assembly in a state mounted on the shaft whereby the molded conductor is shown in a top view, 
         FIG. 7  Various possible cross-sectional shapes of a crosspiece with an additional conductor molded or positioned thereon, 
         FIG. 8  A cross section through two connecting conductors of the slip ring assembly, 
         FIG. 9  Another exemplary embodiment of a molded conductor, 
         FIG. 10  Another exemplary embodiment of a slip ring assembly, whereby in this case the slip rings are arranged between the molded conductor and one end of the connecting line facing away from the first slip ring. 
         FIG. 11A  longitudinal section through the mounted slip ring assembly, 
         FIG. 12  A top view of the mounted slip ring assembly and a mounted roller bearing, 
         FIG. 13  A spatial representation of a portion of the connecting conductor with a molded conductor for another exemplary embodiment of a slip ring assembly, 
         FIG. 14  A cross section through the connecting conductor and the molded conductor from  FIG. 13 , 
         FIG. 15  A slip ring assembly with the connecting conductor and the molded conductor according to  FIG. 13 , 
         FIG. 16  A cross section through the special crosspiece of the slip ring assembly from  FIG. 15 , 
         FIG. 17  A schematic representation of an electric machine with a rotor. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an electric machine  10 , designed as a rotary current generator for motor vehicles. This electric machine  10  is comprised of a housing  13 , which is embodied as two pieces. This housing  13  features a drive-side end shield  16  and a so-called brush-side end shield  19 . A stator  25  is held between these two housing parts  16  and  19  by means of housing screws  22 . This stator  25  is comprised of a stator core  28  into whose grooves (not shown here) a stator winder  31  is inserted. A drive-side winding head  34  and a brush-side winding head  37  of this stator winding  31  can be seen. A rotor  40  is arranged within the stator core  28 . This rotor  40  is positioned via a shaft  43  both in the drive end shield  16  as well as in the brush-side end shield  19  by means of two bearings, namely a drive-side bearing  46  and a reverse bearing  49 . The magnetic parts of the rotor  40  are positioned between the two bearings  46  and  49 . A pole body  58  is positioned between a first magnet wheel half  52  and a second magnet wheel half  55 . An excitation winding  61  is positioned around the pole bodies  58 . The magnetic wheel half  52 , the pole body  58 , the excitation winding  61  and the magnet wheel half  55  are supported by the shaft  43 . A first fan  64  is fastened on the side of the magnet wheel half  52  facing away from the excitation winding  61  and a second fan  67  is fastened on the corresponding counter side on the other magnet wheel half  55 . Both fans are used to suction air from the axial direction and blow it through openings in the winding heads  34  and  37  and discharge it after warming through openings arranged on the radial outside (not shown here) to the environment. 
     A belt pulley  73  is fastened on the drive-side end  70  of the shaft  43  by means of a screw nut. This belt pulley is used to rotate the rotor by means of a belt  74 . A slip ring assembly  76  is fastened on the brush-side end of the shaft  43 . This slip ring assembly is used to energize the excitation winding  61  by means of two slip rings  79  (negative slip ring) and  81  (plus slip ring). 
     For this purpose, additional connecting elements are provided: a first connecting line  84  between the negative slip ring  79  and a second connecting line  87  as a connection between the positive slip ring  81  and the other end of the excitation winding  61 . To energize the excitation winding  61 , brushes (not designated in more detail here), which are loaded with excitation current by a regulator  90 , glide on the cited slip rings  79  and  81 . In addition, a normal rectifier  93  is present, which is covered with a protective cap  96 . 
       FIG. 2  shows a spatial representation of a slip ring assembly  76  as it is used in the previously described generator. This slip ring assembly supports the already mentioned slip ring assemblies  79  and  81 . Both slip rings  79  and  81  are held by a holder  100 . The holder  100  is a complex entity, which is created by means of an injection molding process and is molded from an insulating material  101 . This holder  100  bears two connecting conductors  103  and  106  concealed in its interior. The connecting conductor  103  connects the first slip ring  79  via a crosspiece  109  to a contact tag  112  embodied to be a single piece with the connecting conductor  103  and represents an end  115  facing away from the first slip ring  79 . The connecting conductor  106  connects the second slip ring  81  via the crosspiece  118  to a contact tag  121  that is also embodied to be a single piece and also represents an end  124  of the connecting conductor  106  facing away from the slip ring  81 . The connecting conductor  106  just like the connecting conductor  103  is arranged within the holder  100 . The connecting conductor  106  passes through the slip ring  79 . The slip rings  79  and  81  form an outer delimitation for the holder  100 . Provided radially within the slip rings  79  and  81  is an opening  127 , which is embodied hollow cylindrically. Later in a mounted state, this opening  127  is occupied by a shaft-side pin. This basically hollow cylindrical section between the end-side opening  127  and the transition of the holder  100  to the two crosspieces  109  and  118  is delimited by a protuberance  130 , which is positioned approximately annularly around the rotational axis  133 . A ring section  136  is adjacent to the end of the crosspiece  109  or  118  facing away from the protuberance  130 , and said ring section stabilizes the position of the ends  115  in that these ends  115  and  124  or sections of this connecting conductor  103  or  106  are embedded in this ring section  136 . 
     The holder  100  includes both the portion of the holder part  100  that is arranged within the slip rings  79  and  81  as well as the area around the protuberance  130 , the insulation of the crosspieces  109  and  118  and the ring section  136 . 
     It is easy to see that the slip ring assembly shown in  FIG. 3  is very similar to the slip ring assembly depicted in  FIG. 2 . The difference is the different designs of the crosspiece  109 , a section of the protuberance  130  and a portion of the remaining holder  100 . 
     Thus, large parts of the holder  100  and its insulation of the crosspieces  118  and  109  are composed of the insulating material  101 . The crosspiece  109  with the adjacent area of the protuberance  130  and a small section of the annular cylindrical area of the holder  100  is replaced with another material. According to this exemplary embodiment, this material is also an injection moldable material, which is designated here as a polymer composite material. This polymer composite material is a mixture of a polymer insulating material, such as PA  66 , and a conductive material, e.g., graphite or metal components that were originally present in form of a powder. In this case, this material forms a molded conductor  139 , which forms a direct electrical connection from the first connecting conductor  103  embedded in the crosspiece  109  to a surface  142  of the slip ring assembly  76 . The surface  142  in this exemplary embodiment is formed by the molded conductor  139  or the material partially injected around the connecting conductor  103 . “Molded” conductor  139  means that the shape of the conductor  139  as a whole originates from the use of a mold, and its surface shape or contour is produced by the contour-generating manufacturing mold. 
     As a result, a slip ring assembly  76  for a rotor  40  of an electric machine  10 , in particular a rotary current generator, is provided, wherein this slip ring assembly  76  has at least one first slip ring  79 . At least one first connecting conductor  103  is held, preferably embedded, in sections in the insulating material  101  of the slip ring assembly  76  and said connecting conductor is electrically conductively connected to the at least one first slip ring  79 . This first connecting conductor  103  has an end  115  facing away from the first slip ring  79 , which is provided for an electrical connection to an excitation coil  61 . The slip ring of the component  76  has another molded conductor  139 , which forms a direct electrical connection from the first connecting conductor  103  to a surface  142  of the slip ring assembly  76 . 
     It is envisaged that the additional molded conductor  139  be sprayed on the at least one connecting conductor  103  via an injection molding process and therefore be molded on said connecting conductor  103 . The molded conductor should generally have, i.e., not just for this exemplary embodiment, a conductivity of 1E5 Ωcm to 1E12 Ωcm. This conductivity relates in this case to the material strength, which relates to between the connecting conductor  103  and the surface  142 . It is envisaged for the smooth functioning of the molded conductor  139  that said conductor have a higher specific electrical resistance than the connecting conductor  103 , but a smaller specific electric resistance than the insulating material  101 . The connecting conductor  103  in this case is the connecting conductor, which is surrounded by the molded conductor  139  at least in sections. 
     The additional molded conductor  139  is arranged between the first slip ring  79  and the end  115  of the connecting conductor  103  facing away from the first slip ring  79 . This position of the molded conductor  139  is situated preferably at a position provided for the seat of the bearing  49 . 
       FIG. 4  shows the slip ring assembly  76  before its completion. As already mentioned, the slip ring assembly  76  in accordance with a first exemplary embodiment is supposed to be manufactured by two injection molding process steps. Thus, a first process step whose result is depicted in  FIG. 4  provides that the two slip rings  79  and  81  as well as the connecting conductors  103  and  106  attached or electrically connected to the two slip rings are partially extrusion coated with the insulating material  101  in such way that the outer sides of the slip rings  79  and  81  are left exposed, the inner sides of slip rings are covered with insulating material  101  and the connecting crosspiece  118  is completely sheathed in insulating material  101 . In addition, the ring section  136  is also cast on in this process step. In the case of the crosspiece  109 , the status after this first process step is such that the connecting conductor  103  in this case is free to the radial outside and therefore not covered with insulating material  101  at this location. A recess  148  is thus left free. This figure also shows that the connecting conductor  103  has an opening  145 , which will later fulfill a function. 
     The molded conductor  139  by itself can be seen in  FIG. 5 . This section complements the arrangement from  FIG. 4  in an injection molding mold such that the slip ring assembly according to  FIG. 3  is produced. 
     As indicated in  FIG. 4 , the first connecting conductor  103  is covered by the additional molded conductor  139  in an axial section  148 . The connecting conductor  103  in this case is also at least partially surrounded by insulating material  101  of the slip ring assembly  76  as is evident in  FIG. 4 . It is envisaged in this case that a width B iso  of the insulating material  101  in the circumferential direction su is greater than a width b L  of the additional molded conductor  139  in the circumferential direction su; also see  FIGS. 6 and 7   a.    
       FIGS. 7   a  through  7   e  depict various embodiments of a crosspiece  109 . Thus,  FIG. 7   a  shows the preferred embodiment as depicted in accordance with the section diagramed in  FIG. 3 . Clear to see in this case is the connecting conductor  103  that is embedded in the insulating material  101 , which is freely accessible on its upper side after the first injection process. After this first injection process, the molded conductor  139  is sprayed on, in this case in such a way that the additional molded conductor  139  essentially grips around the connecting conductor  103  in a U-shaped manner. The exemplary embodiment in accordance with  FIG. 7   b  shows a molded conductor  139 , which is just as wide as the insulating material  101  or the non-conductive insulation of the crosspiece  109 .  FIG. 7   c  depicts a connecting conductor  103 , which is covered by a molded conductor  139 , whose width is just as great as that of the connecting conductor  103 . The molded conductor  139  in  FIG. 7   d  is wider than the connecting conductor  103 .  FIG. 7   e  shows a connecting conductor  103  with an opening  145  forming an undercut. The additional molded conductor  139  grips behind this opening  145  or the undercut with a section of its material so that as a result the additional molded conductor  139  is secured in its position to the radial outside. 
     If one observes the slip ring assembly  76  in a section through the two crosspieces  118  or  109 , (see  FIG. 8 ), then one will recognize with reference to the described opening  127 , whose longitudinal axis covers itself with a rotational axis of the rotor  40 , that the outer radii of the crosspieces are different. In this concrete case, this means that the outer radius r Iso , of the crosspiece  118 , i.e., of the crosspiece that does not support the molded conductor  139 , is smaller than radius r L  of the molded conductor  139 . This means that the additional molded conductor  139  defines, at its axial position and its angular position, a greater radius r L  of the slip ring assembly  76  than said slip ring assembly has at another angular position (here in this case at the position of crosspiece  118 ) of the same axial position. 
       FIG. 9  shows another exemplary embodiment of a molded conductor  139 . Thus, it is envisaged for example, as an alternative to a molded conductor  139  sprayed on the holder  100 , to use an otherwise pre-molded conductor  139 . This pre-molded conductor  139  can be placed for example on the first connecting conductor  103  of the semi-finished slip ring assembly  76 , as indicated in  FIG. 4 . This type of pre-molded conductor  139  can of course also be designed as described in  FIGS. 7   a  to  7   d . In addition, this pre-molded conductor  139  could also be pre-molded in such a way that projections on this conductor  139  could engage in an undercut or an opening  145  (attainment according to  FIG. 7   e ). But even the conditions that are formulated in the description regarding  FIG. 8  can of course also be fulfilled by a pre-molded conductor  139 . 
       FIG. 10  depicts another exemplary embodiment of a slip ring assembly  76 . In contrast to the previously depicted embodiments, in this case the position of the slip rings is switched with the position of the molded conductor  139 . This embodiment takes designs for electric machines into account, particularly rotary current generators, whose roller bearing  49  is not arranged near to the magnetic parts of the rotor  40 , but at a more distant or the most distant end of the shaft  43 . 
       FIG. 11  shows a longitudinal section through the slip ring assembly  76 . In addition, in this case the bearing  49  is mounted on the slip ring assembly  76 . The slip ring assembly  76 , and especially the molded conductor  139  are dimensioned in such a way (also see  FIG. 8 ) that a roller bearing  49  mounted on the slip ring assembly  76  compresses the molded conductor  139  in the radial direction. This produces a good quality electrical contact point between the molded conductor  139  and a roller bearing ring  150 . 
       FIG. 12  shows a top view of the molded conductor  139 . The molded conductor sits with its crosspiece  109  in a slot  153  extending in the axial direction of the shaft  43 . This slot  153  in the shaft end  156  has slot walls  159  and  160 , which are arranged parallel to one another and opposite from one another. The connecting conductor  103  arranged in the crosspiece  109  is arranged in the slot  153 . 
       FIG. 13  shows a spatial representation of a portion of the connecting conductor  103  with a molded conductor  139  for another exemplary embodiment of a slip ring assembly  76 , which has far-reaching commonality with the other exemplary embodiments. The connecting conductor  103  has an angular shape so that the section of the connecting conductor  103  arranged in the crosspiece  109  and the end section  115  enclose an angle. At this angular or “knee” point, the connecting conductor  103  is sheathed in a mold by the molded conductor  139  in a first extrusion coating process. The molded conductor  139  grips around the connecting conductor  103 , in this case around its entire cross section. This sheathing of the connecting conductor  103  by the conductive material is easy to see in  FIG. 14  in a cross section though the connecting conductor  103  and the molded conductor  139 . 
     According to the slip ring assembly  76  depicted in  FIG. 15 , it is envisaged that the molded conductor  139  appear in the area of the crosspiece  109  so that as with the preceding exemplary embodiments (also see  FIG. 11 ) an inner ring  150  of a positioned roller bearing  49  can contact the molded conductor  139 . In this case, similar to the depiction of  FIG. 7   d , the insulating material  101  forms a contact obstacle to the shaft  43 . In this regard also see  FIG. 16  with a cross-sectional depiction through the special crosspiece  109  of the slip ring assembly  76  from  FIG. 15 . This molded conductor  139  could also directly contact the shaft  43  in an alternative exemplary embodiment. 
     As already mentioned with respect to the previously discussed exemplary embodiments, the molded conductor  139  could also be molded separately from the connecting conductor  103 . Such a preform can then for example be placed or mounted around the connecting conductor  103 . Then a holder  100  could be sprayed around this molded conductor  139  in a molding process. 
       FIG. 17  shows a schematic representation of an electric machine  10  with a rotor  40 . The rotor  40  supports a slip ring assembly  76 , which energizes the excitation winding  61 . 
     As already explained in connection with  FIGS. 6 and 7   a , the molded conductor  139  in a particular embodiment has a lower width in the circumferential direction than the insulating material or than the crosspiece width B Iso . Because the radially internally oriented side or inner cylindrical surface of the inner ring  150  of the bearing  49  contacts the shaft  53 , the electrostatic charge can be transmitted from the shaft  43  to the inner ring  150 . From there the current flows from the inner ring to the molded conductor  139  and from there, in turn, to the connecting conductor  103 , which is connected to the slip ring  79 . It is clear, as a result, that the shaft end  43  supporting the roller bearing  49  is an electrical connection between the molded conductor  139  and the slip ring  79 . The slip ring  79  is in turn connected via its brushes and the regulator to the ambient ground so that the electrostatic electricity can be dissipated thusly. It follows from this that the molded conductor  139  contacts the shaft end  43  only indirectly. As  FIG. 12  shows, there is a distance  162  or  163  between the molded conductor  139  and the slot walls  159  and  160 . 
     The production process will be described in the following. As described previously, for example with regard to  FIG. 4 , in one step, at least one connecting conductor  103  is connected to the electrically insulating holder  100 . This connection step is preferably conducted by an extrusion coating process in a closed casting mold. According to a preferred embodiment, in another step, the same connecting conductor  103  is connected directly to an electrically conductive conductor  139  made of a composite material. The composite material in this case has electrically conductive and non-electrically conductive portions. In this case it is not important whether the molded conductor  139  is first sprayed on the connecting conductor  103  or after extrusion coating of the holder  100 . 
     Alternatively, provisions can also be made for the semi-finished part of the connecting conductor  103  with the slip ring  79  or the connecting conductor  106  with slip ring  81  to be inserted into in an already pre-fabricated holder  100 . 
     As depicted in  FIGS. 7   a  through  7   e  in connection with  FIG. 4 , it is envisaged that the connecting conductor  103  be surrounded over section  148  in the direction of its longitudinal extension, i.e., in the direction in which the two slip rings  79  and  81  are spaced apart, by both the electrically insulating holder  100  as well as by the electrically insulating conductor  139  made of the composite material. A common sheath is formed in the process, wherein the insulating holder  100  and the electrically conductive conductor  139  complement one another to form the common sheath  170 , see  FIG. 7 . The electrically conductive conductor  139  is preferably sprayed around a surface section of the connecting conductor  103 . 
     The variation presented in  FIG. 9  envisages that the electrically conductive conductor  139  be prefabricated from the composite material and is added as such a component to the connecting conductor  103 . 
     According to the preferred embodiment, it is envisaged that the electrically insulating holder  100  be fabricated by extrusion coating of at least the one connecting conductor  103  and subsequent solidification. On its outer side the holder  100  supports at least one slip ring  79 , which electrically contacts the connecting conductor  103 . According to the depiction in  FIG. 4 , when spraying on the holder  100 , a longitudinal section  148  of the connecting conductor  103  is left free of insulating material  101  (formation of a recess) and an end section of the connecting conductor  103  also remains free and is used for connecting to an excitation winding  61 . In this case, the electrically conductive conductor  139  is sprayed on the connecting conductor  103  preferably from the already mentioned composite material and in the process preferably completely complements a recess  144  of the insulating material  101 . 
     In the case that testing the excitation coil  61  after assembly on the rotor  40  is considered unnecessary, providing the molded conductor  139  as a complete sheath around the connecting conductor  103  is also envisaged. The molded conductor  139  can also be arranged merely on the inner side of the conductor  103  and thus be a direct connection in the slot  153 . 
     The molded conductor  139  should represent a resistance of 10 kΩ to 10 MΩ between the shaft  43  and the slip ring  79 . Functioning is assured within these limits: on the one hand, enough charge per time unit is bled off so that no static voltages can build up, on the other hand, the resistance is great enough to make smooth functioning of the excitation winding  61  possible.