Abstract:
The invention relates to an electrical machine ( 10 ), and to a method for producing such an electrical machine, especially for adjusting mobile parts in a motor vehicle. Said machine comprises a rotor ( 20 ) on which a bipolar electrical winding ( 25 ) having a plurality of coils ( 26 ) is arranged. Said coils ( 26 ) are configured to give two symmetrical coil sections ( 27 ) each which are disposed symmetrical to each other relative to the axis of rotation ( 23 ) of the rotor ( 20 ), both coil sections ( 27 ) being simultaneously commutable.

Description:
CROSS REFERENCE 
   The invention described and claimed hereinbelow is also described in German Patent Applications DE 10 2005 015 139.6 filed on Mar. 31, 2005 and DE 10 2005 035 411.4 filed on Jul. 28, 2005. This German Patent Application 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 relates to an electric machine with a tool-poled electric winding. 
   U.S. Reissue 27,893 disclosed an armature winding in an electric machine in which two coils are situated approximately in geometrically parallel fashion on a laminated armature core. Such an arrangement of the two coils is produced with a winding machine on which two coils can be wound at the same time by means of two flyers. These virtually parallel coils, however, are supplied with current independently of each other so that when the coils are supplied with current during operation, radial force components are exerted on the armature, which generate undesirable motor noise. 
   SUMMARY OF THE INVENTION 
   The two-poled electric machine according to the invention and its manufacturing method, with the defining characteristics of the independent claims, have the advantage that the simultaneous commutation of the two symmetrically situated coil sections compensates for the radial force components of the two coil sections when they are supplied with current. Such a symmetrical arrangement of the two coil sections in relation to the rotation axis makes it possible with a simultaneous flow of current through the coil sections, to achieve a smoother motor operation, which significantly reduces the motor noise. 
   Advantageous modifications and improvements of the defining characteristics disclosed in claim  1  ensue from the defining characteristics disclosed in the dependent claims. The interfering radial force components can be compensated for with particular ease because the two coil sections are situated approximately parallel to each other geometrically, are spaced the same distance apart from the rotation axis, and have the same number of windings. 
   If the two coils sections are wound in the opposite winding direction from each other on the armature core, then when the coil sections are supplied with current, the respective radial force components of the coil sections are situated in precise opposition to each other. This provides optimum compensation for these radial forces. 
   In a preferred embodiment, the two coil sections are electrically connected in series so that they can be wound one after another in continuous fashion with a single wire. 
   In this case, the coil sections connected to each other in series have a total of two ends that can each be directly connected to a respective lamination of the commutator—in particular laminations situated adjacent to each other. 
   In an alternative embodiment, the two coil sections are electrically connected in parallel, which permits the two coil sections to be wound at the same time as each other, for example. 
   In the parallel-connected coil sections, the respective ends of the first coil section and the two ends of the second coil section are electrically connected to the same two laminations so that the two coil sections can be commutated simultaneously. 
   The arrangement of the two coil sections symmetrically to each other on the armature core is optimized in such a way that with the simultaneous flow of current through the two coil sections, the radially acting forces are compensated for to the greatest extent possible. 
   According to the invention, the commutator has an even number of laminations, for example eight or ten laminations; the two brushes, preferably contact the laminations offset from each other by approximately 180°. Each pair of coil sections is connected to a pair of laminations. 
   In order to assure the most uniform possible flow of current during commutation, the brushes are embodied so that as the commutator rotates, they each overlap two adjacent laminations so as to short circuit them. This makes it possible to significantly reduce brush sparking. 
   It is advantageous to embody the coil sections in the form of a double winding equipped with two approximately parallel coil wires with a reduced cross section. This makes it possible to achieve a higher space factor of the grooves and therefore to increase the output of the electric motor without increasing production time. 
   The manufacturing method according to the invention for a two-poled electric machine with two coil sections situated symmetrically to each other can be used to easily manufacture a reduced-noise electric drive motor of the kind used, for example, in adjusting applications in motor vehicles. This does not require any appreciable increase in complexity compared to conventional winding methods, thus making it possible, in a cost-neutral fashion, to achieve a significant increase in the quality of the electric machine by reducing the amount of noise it generates. 
   Various exemplary embodiments of an electric machine according to the invention are shown in the drawings and will be explained in detail in the description that follows. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic cross section through an electric machine, 
       FIG. 2  is a schematic representation of the current branches in the coils, 
       FIG. 3  is a cross section through the armature winding according to the prior part, 
       FIG. 4  is a schematic armature cross section, with the coil sections connected in series, 
       FIG. 5  is a schematic armature cross section, with the coil sections connected in parallel, 
       FIG. 6  is a cross section through an armature winding according to the invention, 
       FIGS. 7 through 11  show various winding schemes for a commutator with ten laminations, 
       FIG. 12  is a schematic cross section to illustrate the commutator rotation, and 
       FIGS. 13 and 14  show winding schemes for a commutator with eight laminations. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  schematically depicts a cross section through an electric machine  10  that is embodied in the form of a two-poled dc motor  12  in the exemplary embodiment. A housing  14  contains a stator  16 , which is equipped with two permanent magnets  18  and cooperates with a rotor  20  that is supported so that it can rotate in the housing  14 . The rotor  20  has a rotor shaft  22  and a laminated armature core  24  on which coils  26  are wound in the form of chords. The armature shaft  22  also supports a commutator  28  that can be electrically commutated via brushes  30 . In the exemplary embodiment, the two brushes  30  are situated offset from each other by approximately 180° and are embodied in such a way that as the commutator  28  rotates in relation to the brushes  30 , at the transition from one commutator lamination  32  to an adjacent commutator lamination  32 , the brushes  30  short circuit the two laminations. The two brushes  30  are labeled with a plus and a minus that symbolize the flow of current and represent the electrical connections of the coils  26  shown in  FIGS. 3 and 6 . The commutator  28  has an even number of laminations  32  that are labeled with the reference numerals  0  through  9  (i.e. there are ten of them). The laminations  32  are electrically insulated from one another. 
     FIG. 2  schematically depicts the flow of current when the brushes  30  overlap the laminations  32  as shown in  FIG. 1 . The short circuiting of two commutator laminations  32  generates a current I 1  through a coil  26 , for example under the plus brush  30 , between the two adjacent laminations  32  ( 9  and  0 ). Between the plus brush  30  and the minus brush  30 , there is a current branch I 2 , which in another coil  26  between the laminations  32  ( 0  and  4 ), a current I 3  between two adjacent laminations  32  ( 4  and  5 ) and in turn a current branch I 4  between the minus brush  30  and the plus brush  30  (laminations  5  and  9 ). 
     FIG. 3  shows the current flow according to  FIG. 2  in a schematic cross section through the armature core  24 , with a chorded loop winding according to the prior part. In accordance with the ten laminations  32  of the commutator  28 , the armature core  24  has ten grooves  34  into which a total of ten coils are wound. Each groove  34  is thus provided with two phase windings  29  of different coils  26 . The differences in the brush voltage drop between the plus brush  30  and the minus brush  30  and the asymmetry in the positioning of the brushes  30  due to production tolerances result in unequal current levels in the opposing grooves  34 , not only in I 1  and I 3 , but also in I 2  and I 4 . For example, the current I 1  travels in one chord-like coil  26 ′, whose windings are depicted with the two circuits +I 1  and −I 1 . At the same time, in the short circuit situation depicted in  FIG. 2 , the current I 3  flows in the coil  26 ″, depicted with the circuits +I 3  and −I 3 . It is clear in  FIG. 3  that in the prior art, the current level is unequal in the respectively opposing grooves  34  in which the currents I 1  and I 3  flow, which inequality exerts radial forces  36  on the rotor  20 . 
     FIG. 4  is a schematic cross section through an armature core  24  in which a coil  26  is wound according to the invention in the form of two coil sections  27  in different grooves  34 . The two coil sections  27  are situated in virtually parallel planes  38  that are spaced the same distance apart from the armature shaft  22 , i.e. from the rotation axis  23 , and are symmetrical to it (chorded winding). The two coil sections  27  are electrically connected in series with each other so that starting from the first lamination  32 , the current first flows through the first coil section  27 , then through the second coil section  27 , and then to a second lamination  32 . If the brushes  30  supply these two laminations  32  with current, then the respective radial forces  36  of the two symmetrical coil sections  27  compensate for each other. For the sake of clarity,  FIG. 4  schematically depicts only two laminations and one pair of coil sections  27 . In the actual layout, several pairs of coil sections  27  are each connected to a respective pair of laminations  32 . The coil  26  shown in  FIG. 4 , which is comprised of two coil sections  27 , could, for example, be associated with the current flow I 1  between the laminations  32  ( 9  and  0 ) from  FIG. 2  and  FIG. 1 . 
   In the embodiment according to  FIG. 5 , the two coil sections  27  are once again situated symmetrically in relation to the rotation axis  23 . The two coil sections  27  are each wound in respective groove pairs  34 , producing a geometrically parallel arrangement of coil sections  27  spaced approximately the same distance apart from the rotation axis  23 . In such chorded windings, the windings  54  do not pass through the rotation axis  23 . But in this embodiment, the two coil sections  27  are electrically connected in parallel so that the respective ends  42  of the first coil section  41  and the two ends  44  of the second coil section  43  are respectively connected to the two laminations  32  ( 9  and  0 ) in the same fashion. With these parallel-connected coil sections  27 , too, a pair of coil sections  27  is commutated simultaneously by the two laminations  32 . According to a preferred embodiment of the invention, the two coil sections  27  in both the series circuit and the parallel circuit are wound in opposite winding directions from each other, i.e. when the armature winding  25  is being wound, after the rotation of the rotor  20  by approx. 180°, the second coil section  27  is wound in the opposite direction in relation to the winding machine. 
     FIG. 6  is a schematic cross section through the armature core  24 , in which the respective coils  26  are embodied as two coil sections  27  arranged symmetrically to each other, but this time with four phase windings  29  situated in each groove  34 . This becomes particularly clear when one compares the coil arrangement according to the invention in  FIG. 6  to the coil arrangement according to the prior art in  FIG. 3 . Each coil from  FIG. 3  is placed in two symmetrically situated coil sections  27 ′,  27 ″, where with a series connection of the coil sections  27 ′ and  27 ″, the total number of windings  54  of the two coil sections  27 ′,  27 ″ is identical to the number of windings  54  of the coil  26  according to  FIG. 3 . But in the present instance, the current load is identical in the opposing grooves  34  in which the currents I 1  and I 3  flow. As a result, the currents +I 3 , −I 1 , +I 2 , −I 4 , of the groove  34 ′ compensate for the currents −I 3 , +I 1 , −I 2 , +I 4  of the opposing groove  34 ″. This largely eliminates interfering radial forces  36 . 
   With a parallel connection of the coil sections  27 ′ and  27 ″, the total number of windings  54  doubles in relation to that in the series-connected coil sections  27 ; the wire cross sections of the coil wires  48  are correspondingly halved, thus yielding the same current load. This corresponds to a double winding in which the two coil sections  27  are not, however, wound into the same grooves  34 , but are instead wound in the form of two symmetrically situated coil sections  27  spaced the same distance apart from the rotation axis  23 . The winding scheme for this double winding is shown in  FIGS. 11 and 14 . 
     FIGS. 7 through 11  show different variants for a winding with symmetrical coil sections  27 ; the winding scheme in  FIG. 7  will be explained by way of example below. At the bottom edge of the drawing, the ten laminations  32  of the commutator are depicted in the form of small boxes; the drawing shows two developed rotations of the commutator  28 . Situated above them, the grooves  34  of the armature core  24  are schematically depicted, likewise in the form of two developed rotations. In the lower half of the drawing, a pair of coil sections  27  is schematically depicted, which corresponds to the second row of the table above. Starting from the lamination  1  (right), the coil wire  48  is first placed in the groove  1  and then in the groove  5 , thus forming a coil section  27  with seven windings  54  (wdg). After the seventh complete winding  54 , the coil wire  48  once again lies in the groove  1  in order to then travel leftward to the groove  6  in order to form the second coil section  27 . Between groove  6  and groove  10 , the second coil section  27  is wound with eight windings; then one more winding is wound onto the first coil section  27  between groove  10  and groove  5  in order for the coil wire  48  to then contact the lamination  2  (left). This results in a symmetrical arrangement of two coil sections  27 , each with the same number of windings  54 . The respective coil sections  27  are wound according to this scheme, row by row according to the table above so that a total of ten pairs of coil sections  27  are situated between two adjacent laminations. 
   Thus  FIGS. 7 through 10  show different variations, each with ten coil section pairs  27  between two respective laminations  32 . The coil wire  48  in these instances has, for example, a wire diameter of 0.5 mm. In  FIG. 11 , the coil sections  27  are situated as a double winding in a first and second layer; in this case the wire diameter is 2×0.355 mm, for example. 
     FIG. 12  schematically depicts the rotation of the commutator  28  in relation to the armature core  24 . In it, a rotation angle  50  is defined that extends from the center of the groove  34  to the center of a slot  52  between two laminations  32 . In the exemplary embodiments according to  FIGS. 7 through 11 , this angle  50  of the commutator rotation is approximately 0°. In the exemplary embodiments according to  FIGS. 13 and 14 , this angle  50  is 209°, for example. 
   According to  FIGS. 13 and 14 , the commutator  28  has, for example, eight laminations  32  and correspondingly has eight grooves  34  in the armature core  24 . 
   In  FIG. 13 , according to the eight lines of the table at the top, two symmetrical coil sections  27  are each placed eight times between two laminations  32 . The number of the individual windings  54  (wdg) and the coil wire diameter can be adapted to the respective application. In a fashion analogous to  FIG. 11 ,  FIG. 14  once again shows a double winding in which the total number of windings (wdg) of the two coil sections is increased in comparison to  FIG. 13 , for which purpose the wire diameter is reduced (for example from 0.425 to 2×0.3 mm). 
   It should be noted with regard to the exemplary embodiments of the specification shown in all of the figures that there are a multitude of possibilities for combining the individual defining characteristics with one another. It is thus possible, for example, to vary the number of laminations  32  and grooves  34  as well as their concrete layout. Furthermore, the large number of winding schemes demonstrated should not in any way be taken to represent a limitation with regard to the winding of symmetrical coil sections  27 ; there are, instead, various possible transitions from one coil section  27  to the other. The exemplary embodiments according to  FIGS. 7 through 14  describe both the concrete layout of the various electrical machines  10  and also their manufacturing method. In particular, the figures demonstrate the method for winding symmetrical coil sections  27  according to the present invention.