Patent Publication Number: US-10320273-B2

Title: Method for manufacturing a brush-commutated direct-current motor

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
     This application is a National Phase Patent Application of International Patent Application Number PCT/EP2015/068517, filed on Aug. 12, 2015, which claims priority of German Patent Application Number 10 2014 215 976.8, filed on Aug. 12, 2014. The contents of which are both included herein by reference. 
     BACKGROUND 
     This invention relates to a method for manufacturing a brush-commutated direct-current motor and a brush-commutated direct-current motor. 
     A brush-commutated direct-current motor comprises a stator with a plurality of exciter poles and a rotor rotatable relative to the stator about an axis of rotation. The rotor has a plurality of pole teeth and grooves arranged between the pole teeth, which separate the pole teeth from each other along a circumferential direction around the axis of rotation. On the pole teeth coil windings are arranged, which in operation of the brush-commutated direct-current motor are energized via a commutator arranged on the rotor and in this way produce an electromotive force on the rotor by interacting with the exciter poles of the stator. The commutator comprises a plurality of lamellae to which the coil windings of the rotor are connected via connecting arms. 
     In the manufacture of brush-commutated direct-current motors it can be provided to mount a plurality of coil windings on each pole tooth, in order to thereby reduce the wire thickness required for the manufacture of the coil windings. When merely one coil winding would be arranged on each pole tooth, the same would require a wire of comparatively large wire thickness, which renders processing of the wire for winding around the pole teeth comparatively difficult. By mounting several coil windings on each pole tooth, the wire thickness of the wire used can be reduced, so that the manufacturing process in general turns out to be easier. 
     As described in FR 2 841 399 A, a first winding cycle and a second winding cycle, in each of which a coil winding is arranged on each pole tooth, conventionally are carried out in an identical way. 
     Because the coil windings on the pole teeth are wound in different winding cycles, coil windings which differ in their position however are obtained on each pole tooth. A succeeding coil winding of a later winding cycle now is wound onto a coil winding from a preceding winding cycle, which leads to the fact that the wire length of the outer coil winding wound at a later time is larger and thus in operation parallel branches of coil windings are obtained, which can differ in their electrical resistance—due to the different wire length. This can lead to asymmetries in the commutation current. 
     In addition, hybrid winding arrangements nowadays are known, in which the coil windings arranged on a pole tooth are not connected with the same lamellae, but are connected to different lamellae. For example, from U.S. Pat. No. 7,821,170 B2 and EP 1 489 724 B1 brush-commutated direct-current motors are known, in which on each pole tooth a first coil winding is mounted in a first winding direction and a second coil winding is mounted in an opposite, second winding direction. Because in such winding arrangements the connecting arms with which the different coil windings of a pole tooth are connected to the respectively associated lamellae possibly intersect, laying of the connecting arms towards the associated lamellae possibly may not be easy to do—in particular with a view to the available installation space. 
     SUMMARY 
     It is an object of the present invention to provide a method for manufacturing a brush-commutated direct-current motor and a brush-commutated direct-current motor, which provide for a manufacture of the direct-current motor in a simple way making use of the available installation space and a good operating behavior of the motor. 
     This object is solved by a method with features as described herein. 
     Accordingly it is provided that on each pole tooth a first coil winding wound around the pole tooth in a first winding direction and a second coil winding wound around the pole tooth in a second winding direction opposite to the first winding direction are arranged, wherein
         in a first winding cycle the first coil windings are wound on a first part of the pole teeth and the second coil windings are wound on a second part of the pole teeth, and   in a second winding cycle the second coil windings are wound on the first part of the pole teeth and the first coil windings are wound on the second part of the pole teeth.       

     For manufacturing the coil windings on the pole teeth of the rotor (at least) one first coil winding in the first winding direction and a second coil winding in the opposite, second winding direction are mounted on each pole tooth. This is effected in different winding cycles, wherein per winding cycle one coil winding is mounted on each pole tooth. In a first winding cycle first coil windings are arranged on a first part of the pole teeth and second coil windings are arranged on a second part of the pole teeth, while in a succeeding, second winding cycle second coil windings are mounted on the first part of the pole teeth and first coil windings are mounted on the second part of the pole teeth. This has the effect that for the first part of the pole teeth the first coil windings are arranged within the second coil windings, because the second coil windings are wound onto the first coil windings, but for the second part of the pole teeth the second coil windings are arranged within the first coil windings, because the first coil windings are wound onto the second coil windings. 
     Because thus for some pole teeth the first coil windings lie inside and the second coil windings lie outside and for other pole teeth the second coil windings lie inside and the first coil windings lie outside, the wire lengths differ between the first coil windings and the second coil windings not uniformly, but in a different way. In the first part of the pole teeth the wire lengths of the second coil windings, which are wound onto the first coil windings, are longer than the wire lengths of the first coil windings, while for the second part of the pole teeth the wire lengths of the first coil windings are larger than the wire lengths of the second coil windings. In this way, asymmetries in the resulting electrical branches can at least be reduced in operation of the direct-current motor, so that an at least approximately uniform height is obtained in the commutation current, because parallel branches can have an approximately symmetrical resistance distribution. 
     In an advantageous aspect, first coil windings are wound onto the one half of the pole teeth and second coil windings are wound onto the other half of the pole teeth in each winding cycle. When the number of pole teeth is an odd number, the first part for example can comprise N/2+1 of the pole teeth and the second part can comprise N/2−1 of the pole teeth, wherein N corresponds to the number of pole teeth of the rotor and is an odd integral number. Thus, in the first winding cycle N/2+1 first coil windings and N/2−1 second coil windings are wound onto the respectively associated pole teeth. 
     In one aspect, the first coil winding is connected with a first lamella via a first connecting arm and with a second lamella via a second connecting arm, wherein the first connecting arm and/or the second connecting arm of the first coil winding are laid around at least one other pole tooth towards the respectively associated lamella. This proceeds from the idea to lay a connecting arm of a coil winding not directly from the coil winding wound onto a pole tooth towards the associated lamella, but around one or more pole teeth. In particular in such coil windings in which a connection is not provided to a lamella arranged directly radially within the coil winding, but the associated lamella is offset to the coil winding in circumferential direction, laying of the connecting arm towards the lamella around one or more pole teeth can be advantageous, because in this way intersections of connecting arms of different coil windings can be avoided. Laying of the connecting arms thus can be effected in a favorable way saving installation space. 
     In a concrete configuration the first winding arm of the first coil winding is laid around exactly one pole tooth adjacent to the associated pole tooth in circumferential direction and the second winding arm of the first coil winding is laid around exactly one pole tooth adjacent to the associated pole tooth against the circumferential direction. 
     To this end, the first connecting arm of the first coil winding for example can extend through a first groove adjoining the associated pole tooth in circumferential direction, around the pole tooth adjacent to the associated pole tooth in circumferential direction, and through a second groove different from the first groove towards the associated lamella. Analogously, the second connecting arm of the first coil winding then extends through a third groove adjoining the associated pole tooth against the circumferential direction, around the pole tooth adjacent to the associated pole tooth against the circumferential direction, and through a fourth groove different from the third groove towards the associated lamella. The connecting arms of the first coil winding on a pole tooth thus—as seen along the circumferential direction—extend in different directions away from the coil winding and are laid around the pole teeth to the left and right of the pole tooth on which the coil winding is arranged. The connecting arms of the first coil winding thus are not guided directly from the pole tooth towards the associated lamellae, but are laid around the adjacent pole teeth and only then are guided towards the lamellae and connected to the same. 
     While the connecting arms of the first coil winding thus are laid around other pole teeth, the connecting arms of the second coil winding can be connected to adjacent lamellae which are arranged radially within the second coil winding and thus at least approximately are located at the same circumferential position as the coil winding. The connecting arms of the second coil winding here advantageously are connected to adjacent lamellae and intersect. 
     While the connecting arms of the second coil winding are connected to adjacent lamellae, the connecting arms of the first coil winding are connected with lamellae which are offset to these adjacent lamellae in circumferential direction. The first connecting arm is connected to a first lamella which is offset to the adjacent lamellae in circumferential direction, while the second connecting arm of the second coil winding is connected to a second lamella which is offset to the adjacent lamellae against the circumferential direction. Between the adjacent lamellae and the first lamella on the one hand and the second lamella on the other hand one or more other lamellae each can be arranged, so that both the first lamella and the second lamella are spaced from the adjacent lamellae by one or more lamellae in circumferential direction. 
     In a concrete exemplary embodiment the number of the pole teeth corresponds to an odd integral number, while the number of the lamellae corresponds to twice the number of pole teeth. For example, six exciter poles can be arranged on the stator. The number of the pole teeth for example can be 7, 9 or 11, while the number of the lamellae correspondingly is 14, 18 or 22. 
     Preferably, the coil windings are formed as so-called concentrated windings, also referred to as single-tooth windings. This means that the coil windings each are wound around exactly one pole tooth and thus are fabricated by winding a wire around a pole tooth. The coil windings for example can include one, two or three or also more windings and be fabricated of a suitable winding wire. 
     In one embodiment jumpers are provided, which serve to short individual lamellae of the commutator, in order to thereby reduce the number of the required brush pairs to 1 in the ideal case. When the number of the exciter poles is six, for example, each jumper advantageously shorts three lamellae, so that the three lamellae are at the same potential when one of the lamellae is in contact with a brush. The shorted lamellae advantageously have the same angular distance of 120° to each other, corresponding to the equation
 
α=720°/ P,  
 
wherein P corresponds to the number of exciter poles and is a multiple of 2.
 
     For shorting two lamellae, for example, the jumpers each with at least one portion extend around at least one pole tooth by each extending from a lamella through a groove between two pole teeth, around at least one pole tooth and through another groove to another lamella. This allows mounting of the jumpers on the rotor such that they extend through the grooves between the pole teeth and correspondingly are laid in the space in which the coil windings also are arranged on the pole teeth. This on the one hand provides for a reduction of the installation space, because no additional installation space must be provided for the jumpers. The jumpers easily can be laid through the grooves around one or more pole teeth, in order to shortingly connect lamellae with each other. On the other hand it thus becomes possible to fabricate the coil windings and jumpers from an individual winding wire and thus coherent, so that the coil windings and jumpers can be mounted on the rotor in a coherent working step. Separate working steps on the one hand for mounting the coil windings and on the other hand for mounting the jumpers thus can be omitted. 
     By the fact that a connecting arm or a jumper is laid around at least one pole tooth it is to be understood that the connecting arm or a jumper at least sectionally encloses at least one pole tooth. The connecting arm or the jumper however do not fully surround the pole tooth or teeth, but for example proceeding from a front side of the rotor, on which the lamellae of the commutator are arranged, are inserted into a groove, on a rear side of the rotor extend along one or more pole teeth and are guided through another groove back to the front side of the rotor, in order to be connected with an associated lamella on this front side. 
     The coil windings and the jumpers advantageously are fabricated from a continuous wire and thus can be mounted on the pole teeth of the rotor in one coherent working step by continuous winding and laying. This results in a simple manufacture which favorably can be automated by use of suitable winding machines. In particular, after mounting the coil windings no more separate working step is required, in order to mount suitable jumpers. Moreover, additional components which conventionally are required for jumpers can be omitted, so that the number of all the required components can be reduced. 
     When the coil windings and the jumpers are fabricated from a continuous wire, an arrangement in which one portion of a jumper each is arranged between two coil windings preferably is obtained on the rotor. For fabrication a coil winding is mounted on a pole tooth and with one connecting arm each is connected with a lamella, wherein proceeding from a connecting arm a portion of a jumper is laid towards another lamella and this portion of the jumper then is adjoined by a further coil winding. 
     In one aspect the continuous wire forms a first coil winding, adjoining thereto a portion of a jumper, adjoining thereto a second coil winding and adjoining thereto another portion of a jumper, which in turn is adjoined by a first coil winding. The different coil windings on the pole teeth and the portions of the jumpers thus are produced by a continuous wire and one after the other can be arranged on the pole teeth in successive winding cycles. 
     The object also is solved by a brush-commutated direct-current motor, comprising
         a stator with several exciter poles,   a rotor rotatable relative to the stator about an axis of rotation, comprising a plurality of pole teeth, grooves arranged between the pole teeth, and coil windings arranged on the pole teeth, and   a commutator which is arranged on the rotor and includes a plurality of lamellae to which the coil windings are connected.       

     It here is provided that on each pole tooth a first coil winding wound around the pole tooth in a first winding direction and a second coil winding wound around the pole tooth in a second winding direction opposite to the first winding direction are arranged, wherein
         for a first part of the pole teeth the first coil winding is wound onto the respectively associated pole tooth and the second coil winding circumferentially is wound onto the first coil winding, and   for a second part of the pole teeth the second coil winding is wound onto the respectively associated pole tooth and the first coil winding circumferentially is wound onto the second coil winding.       

     As to the advantages and advantageous aspects reference will be made to what has been explained above, which analogously can be applied to the apparatus. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The idea underlying the invention will be explained in detail below with reference to the exemplary embodiments illustrated in the Figures. 
         FIG. 1  shows a schematic view of a brush-commutated direct-current motor. 
         FIG. 2  shows a schematic, unwound representation of a brush-commutated direct-current motor. 
         FIG. 3A  shows a description of a first winding cycle of a winding scheme. 
         FIG. 3B  shows a description of a second winding cycle of the winding scheme. 
         FIG. 4A  shows a schematic representation of the winding process at the beginning of the first winding cycle of the winding scheme. 
         FIG. 4B  shows a schematic representation of the further winding process during the first winding cycle of the winding scheme. 
         FIG. 4C  shows a schematic representation of the winding process, after the first winding cycle of the winding scheme. 
         FIG. 4D  shows a schematic representation of the second winding cycle of the winding process. 
         FIG. 4E  shows a schematic representation of the winding process, after completion of the second winding cycle. 
         FIG. 5  shows a schematic representation of the winding scheme, with marked current flows. 
         FIG. 6  shows a schematic individual representation of two coil windings on two pole teeth. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a schematic view of a brush-commutated direct-current motor  1  which includes a stator  10  and a rotor  11  rotatably arranged on the stator  10  about an axis of rotation D. 
     As is known, the stator  10  includes a number of exciter poles M 1 -M 6  which are formed by permanent magnets and are uniformly distributed around the circumference of the stator  1 . The exciter poles M 1 -M 6  point towards the rotor  11  with different, alternating poles N, S such that in circumferential direction U a north pole N always is followed by a south pole S and vice versa. 
     In the illustrated exemplary embodiment the stator  10  has exactly six exciter poles M 1 -M 6 . 
     The rotor  11  is rotatably arranged on the stator  10  about the axis of rotation D and, in the illustrated exemplary embodiment, has nine pole teeth Z 1 -Z 9 , which are extended along a direction of extension E radially to the axis of rotation D, point towards the stator  10  and are separated from each other by grooves N 12 , N 23 , N 34 , N 45 , N 56 , N 67 , N 78 , N 89 , N 91  in circumferential direction around the axis of rotation D. The rotor  11  for example in a manner known per se can be designed as sheet pack of individual rotor sheets, in which the pole teeth Z 1 -Z 9  are integrally molded. 
     In the illustrated exemplary embodiment the rotor  11  has exactly nine pole teeth Z 1 -Z 9 . 
     Each pole tooth Z 1 -Z 9  carries coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  in the form of concentrated windings which each are wound around a pole tooth Z 1 -Z 9 . The coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  each are connected with lamellae L of a commutator  110  which is firmly arranged on the rotor  11  and slidingly is operatively connected with brushes B 1 , B 2  which are stationarily arranged on the stator  10  such that via the brushes B 1 , B 2  and the commutator  110  the coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  can be energized to produce an electromotive force (EMF). Via the commutator  110  a commutation of the current flowing in the coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  is effected. 
       FIG. 2  shows a schematic view of the brush-commutated direct-current motor  1 , wherein for a simplified overview the brush-commutated direct-current motor  1  is shown in an unwound way and correspondingly the exciter poles M 1 -M 6  and the pole teeth Z 1 -Z 9  as well as the commutator  110  with its individual lamellae L 1 -L 18  are not arranged along a circle, but along a straight line. 
     In the illustrated exemplary embodiment the commutator  110  includes eighteen lamellae L 1 -L 18 . 
     As shown in  FIG. 2 , two coil windings Z 1   l -Z 91 , Z 1   r -Z 9   r  are arranged on each pole tooth Z 1 -Z 9 . The coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  arranged on a pole tooth Z 1 -Z 9  here are wound onto the associated pole tooth Z 1 -Z 9  in different winding directions. Each pole tooth Z 1 -Z 9  correspondingly carries a first coil winding Z 1   l -Z 9   l  wound in a first winding direction (also referred to as left-wound coil winding) and a second coil winding Z 1   r -Z 9   r  wound in an opposite, second winding direction (referred to as right-wound coil winding). 
     At its connecting arms Zl 1 , Zl 2 , Zr 1 , Zr 2  each coil winding Z 1   l -Z 91 , Z 1   r -Z 9   r  is connected with exactly two lamellae L 1 -L 18  of the commutator  110  of the rotor  11 . For example, the right-wound coil winding Z 1   r  of the first pole tooth Z 1  is connected with the lamella L 1  via a first connecting arm Zr 1  and with the lamella L 2  adjacent to the lamella L 1  via a second connecting arm Zr 2 , while the left-wound coil winding Z 1   l  of the first pole tooth Z 1  is connected with the lamella L 17  via a first connecting arm Zl 1  and with the lamella L 4  via a second connecting arm Zl 2 . While the right-wound coil winding Z 1   r  thus is connected with adjacent lamellae L 1 , L 2 , the left-wound coil winding Z 1   l  is connected with lamellae L 17 , L 4  spaced from each other in circumferential direction U around the axis of rotation D and arranged on both sides of the pair of lamellae L 1 , L 2  connected with the right-wound coil winding Z 1   r.    
     Analogously, the remaining coil windings Z 2   l -Z 9   l , Z 2   r -Z 9   r  also are connected with lamellae L 1 -L 18 . 
     The energization of the coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  in operation of the direct-current motor  1  is effected via the brushes B 1 , B 2 , wherein in the illustrated exemplary embodiment exactly two brushes B 1 , B 2  are provided. To ensure that lamellae L 1 -L 18  offset to each other by 120° are at the same potential and to be able to omit additional brushes, jumpers K 1 -K 6  are provided, which each short three lamellae L 1 -L 18  offset to each other by 120° in circumferential direction around the axis of rotation D and thus ensure that upon contact of one of the three lamellae L 1 -L 18  with one of the brushes B 1 , B 2  the correspondingly shorted lamellae L 1 -L 18  are at the same potential. 
     In the illustrated exemplary embodiment, as can be taken from the schematic view of  FIG. 2 , the following lamellae are shorted with each other: 
     L 1 -L 7 -L 13  (jumper K 1 ), 
     L 2 -L 8 -L 14  (jumper K 2 ), 
     L 3 -L 9 -L 15  (jumper K 3 ), 
     L 4 -L 10 -L 16  (jumper K 4 ), 
     L 5 -L 11 -L 17  (jumper K 5 ), 
     L 6 -L 12 -L 18  (jumper K 6 ). 
     When in the rotor position as shown in  FIG. 5  the brush B 1  for example rests against the lamellae L 2 , L 3  and the brush B 2  rests against the lamellae L 5 , L 6  and when the brush B 1  has a positive polarity (+) and the brush B 2  has a negative polarity (−), the current flow directions indicated by arrows in  FIG. 5  are obtained at the connecting arms Zl 1 , Zl 2 , Zr 1 , Zr 2  of the coil windings Z 1   l , Z 1   r , Z 2   l , Z 2   r , Z 3   l , Z 3   r.    
     In the exemplary embodiment shown in  FIG. 2  the connecting arms Zr 1 , Zr 2  of the second, right-wound coil winding Z 1   r -Z 9   r  with adjacent lamellae L 1 -L 18  are arranged directly radially within the associated pole tooth Z 1 -Z 9 , wherein the connecting arms Zr 1 , Zr 2  intersect, as can be taken from  FIG. 2 . The first, left-wound coil windings Z 1   l -Z 9   l  with their connecting arms Zl 1 , Zl 2  on the other hand are connected with lamellae L 1 -L 18  which are arranged on both sides of the pair of lamellae L 1 , L 2 . For the first coil winding Z 1   l  and the second coil winding Z 1   r  on the first pole tooth Z 1  the first coil winding Z 1   l  for example is connected with the lamellae L 17 , L 4 , while the second coil winding Z 1   r  is connected with the lamellae L 1 , L 2 . The pair of lamellae L 1 , L 2  connected with the second coil winding Z 1   r —as seen along the circumferential direction U—thus is arranged between the lamellae L 17 , L 4 , to which the first coil winding Z 1   l  is connected, wherein the lamellae L 17 , L 4  to which the first coil winding Z 1   l  is connected each are spaced from the pair of lamellae L 1 , L 2 , to which the second coil winding Z 1   r  is connected, by exactly one lamella L 18 , L 3 . 
     While the connecting arms Zr 1 , Zr 2  of the second coil winding Z 1   r -Z 9   r  here are laid directly to the associated, adjacent lamellae L 1 -L 18 , the connecting arms Zl 1 , Zl 2  of the first coil winding Z 1   l -Z 9   l  each extend around a pole tooth Z 1 -Z 9 , which is adjacent to the pole tooth Z 1 -Z 9  on which the coil winding Z 1   l -Z 9   l  is arranged. This results in the laying as shown in  FIG. 2 , in which for the first coil winding Z 1   l  of the first pole tooth Z 1  the first connecting arm Zl 1  extends around the ninth pole tooth Z 9  adjacent to the first pole tooth Z 1  and for this purpose is laid through the groove N 91  between the first pole tooth Z 1  and the ninth pole tooth Z 9 , around the ninth pole tooth Z 9  and through the groove N 89  between the ninth pole tooth Z 9  and the eighth pole tooth Z 8  towards the associated lamella L 17 . The second connecting arm Zl 2  of the first coil winding Z 1   l  of the first pole tooth Z 1  on the other hand extends around the second pole tooth Z 2  adjacent to the first pole tooth Z 1  against the circumferential direction U and for this purpose is laid through the groove N 12  between the first pole tooth Z 1  and the second pole tooth Z 2 , around the second pole tooth Z 2  and through the groove N 23  between the second pole tooth Z 2  and the third pole tooth Z 3  towards the associated lamella L 4 . 
     Analogously, the connecting arms Zl 1 , Zl 2  of the other first coil windings Z 2   l -Z 9   l  also are laid on the other pole teeth Z 2 -Z 9 , as can be taken from  FIG. 2 . 
       FIGS. 3A, 3B  in a synopsis with  FIGS. 4A-4E  illustrate the winding process for mounting the coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  on the pole teeth Z 1 -Z 9 . The coil windings Z 1   l -Z 9   l , Z 1   r -Z 9   r  here are wound together with the jumpers K 1 -K 6  by using a continuous wire in two succeeding winding cycles, wherein per winding cycle one coil winding Z 1   l -Z 9   l , Z 1   r -Z 9   r  is mounted on each pole tooth Z 1 -Z 9 . 
     Corresponding to the first line in  FIG. 3A , the winding process starts at the lamella L 3 . The steps of the winding process according to the first four lines in  FIG. 3A  are illustrated in  FIG. 4A . 
     Proceeding from the lamella L 3  the first connecting arm Zl 1  of the first coil winding Z 3   l  of the third pole tooth Z 3  initially is laid through the groove N 12 , around the second pole tooth Z 2  and through the groove N 23  towards the third pole tooth Z 3 , in order to wind the first coil winding Z 3   l  on the third pole tooth Z 3 . Then, the second connecting arm Z 12  of the first coil winding Z 31  of the third pole tooth Z 3  is laid through the groove N 34 , around the fourth pole tooth Z 4  and through the groove N 45  towards the lamella L 8  and connected to the same (first line according to  FIG. 3A ). 
     Proceeding from the lamella L 8  a portion of the jumper K 2  between the lamella L 8  and the lamella L 14  then is laid, wherein this portion is laid around the pole teeth Z 5 , Z 6 , Z 7  (second line according to  FIG. 3A ). 
     Proceeding from the lamella L 14  the second coil winding Z 7   r  then is wound onto the seventh pole tooth Z 7 , wherein the winding direction of this second coil winding Z 7   r  differs from the first coil winding Z 3   l  of the third pole tooth Z 3 . The second coil winding Z 7   r  of the seventh pole tooth Z 7  then is connected with the lamella L 13 , wherein the connecting arms Zr 1 , Zr 2  of this coil winding Z 7   r  intersect (third line according to  FIG. 3A ). 
     Proceeding from the lamella L 13  a portion of the jumper K 1  between the lamella L 13  and the lamella L 1  then is laid, wherein this portion of the jumper K 1  extends around the pole teeth Z 7 , Z 8 , Z 9  (fourth line according to  FIG. 3A ). 
       FIG. 4B  illustrates the next four lines according to  FIG. 3A . First of all, the first coil winding Z 2   l  is wound onto the second pole tooth Z 2  (fifth line according to  FIG. 3A ), then a portion of the jumper K 6  between the lamellae L 6 , L 12  is laid (sixth line according to  FIG. 3A ), the second coil winding Z 6   r  is wound onto the sixth pole tooth Z 6  (seventh line according to  FIG. 3A ), and finally a portion of the jumper K 5  between the lamellae L 11 , L 17  is laid (eighth line according to  FIG. 3A ). 
     At the end of the first winding cycle, as it is described in  FIG. 3A , the coil arrangement according to  FIG. 4C  is obtained. For a simplified representation,  FIG. 4C  (and likewise  FIGS. 4D and 4E ) shows the jumpers K 1 -K 6  with their portions not in their laying extended around the pole teeth Z 1 -Z 9 , but schematically shows the same outside the pole teeth Z 1 -Z 9  under the lamellae L 1 -L 18 . 
     After the end of the first winding cycle exactly one coil winding is arranged on each pole tooth Z 1 -Z 9 , wherein on some pole teeth Z 1 -Z 3 , Z 8 , Z 9  first coil windings Z 1   l -Z 3   l , Z 8   l , Z 9   l  are arranged, and on other pole teeth Z 4 -Z 7  second coil windings Z 4   r -Z 7   r  are arranged. In addition, the jumpers K 1 -K 6  sectionally, but not completely are manufactured after the end of the first winding cycle. 
     Then follows the second winding cycle described in  FIG. 3B , in which the coil windings and portions of the jumpers K 1 -K 6  as shown in  FIG. 4D  are manufactured. In the second winding cycle especially those coil windings and portions of the jumpers K 1 -K 6  are manufactured which have not been manufactured in the first winding cycle. In the second winding cycle first coil windings Z 1   r -Z 3   r , Z 8   r , Z 9   r  are mounted on the pole teeth Z 1 -Z 3 , Z 8 , Z 9  and first coil windings Z 4   l -Z 7   l  are mounted on the pole teeth Z 4 -Z 7 . The portions of the jumpers K 1 -K 6  missing after the first winding cycle are supplemented. 
     After the end of both winding cycles the arrangement shown in  FIG. 4E  is obtained, in which on each pole tooth Z 1 -Z 9  exactly one first coil winding Z 1   l -Z 9   l  of a first winding direction (left-wound) and a second coil winding Z 1   r -Z 9   r  of a second winding direction (right-wound) are arranged and the jumpers K 1 -K 6  for shorting three lamellae L 1 -L 18  each are completed. 
     For a simplified representation the first coil windings Z 1   l -Z 9   l  and the second coil windings Z 1   r -Z 9   r  are shown uniformly. Because in the first winding cycle the first coil windings Z 1   l -Z 3   l , Z 8   l , Z 9   l  have been mounted on the pole teeth Z 1 -Z 3 , Z 8 , Z 9  and the second coil windings Z 4   r -Z 7   r  have been mounted on the pole teeth Z 4 -Z 7 , the same however lie on the inside, while in the second winding cycle the first coil windings Z 4   l -Z 7   l  and the second coil windings Z 1   r -Z 3   r -Z 8   r , Z 9   r  are wound onto the coil windings mounted already on the respective pole tooth Z 1 -Z 9  and thus lie radially on the outside—with respect to the direction of extension E of each pole tooth Z 1 -Z 9 . 
     Because the connecting arms Zl 1 , Zl 2  of the first coil windings Z 1   l -Z 9   l  are laid around pole teeth Z 1 -Z 9  which are spaced from the pole tooth Z 1 -Z 9  each carrying the coil winding Z 1   l -Z 9   l , an advantageous laying of the connecting arms Zl 1 , Zl 2  of the first coil windings Z 1   l -Z 9   l  is obtained. In particular, intersections of these connecting arms Zl 1 , Zl 2  with the connecting arms Zr 1 , Zr 2  of the second coil windings Z 1   r -Z 9   r  are avoided, as is clearly shown in  FIG. 4E  and can be taken from the enlarged representation of  FIG. 6 . 
     The fact that in the different winding cycles first coil windings Z 1   l -Z 9   l  are mounted on some pole teeth and second coil windings Z 1   r -Z 9   r  are mounted on other pole teeth Z 1 -Z 9  results in that for some pole teeth Z 1 -Z 9  the first coil windings Z 1   l -Z 9   l  and for the other pole teeth Z 1 -Z 9  the second coil windings Z 1   r -Z 9   r  lie on the inside. This results in the fact that for some pole teeth Z 1 -Z 9  the wire lengths of the first coil windings Z 1   l -Z 9   l  and for other pole teeth Z 1 -Z 9  the wire lengths of the second coil windings Z 1   r -Z 9   r  are longer. In operation of the direct-current motor parallel branches with at least approximately symmetrical resistance distributions are obtained, which leads to a more uniform commutation current. 
     In principle, the first winding cycle and the second winding cycle can be wound from a single continuous wire. However, it also is conceivable and possible to manufacture the first winding cycle from a first continuous wire and the second winding cycle from a second continuous wire or even use individual wires for individual winding steps per winding cycle. 
     The idea underlying the invention is not limited to the exemplary embodiments described above, but in principle can also be realized in completely different embodiments. 
     In particular, the brush-commutated direct-current motor in principle also can include other numbers of pole teeth and lamellae. In general, the number of pole teeth can correspond to an odd number, with the number of lamellae corresponding to twice the number of pole teeth. For example, the number of pole teeth also can be seven or eleven, and the number of lamellae correspondingly can be 14 or 22. 
     In principle it also is conceivable to omit jumpers. In this case, for example, three brush pairs with a total of six brushes can be used, which effect a parallel energization of the coil windings. 
     LIST OF REFERENCE NUMERALS 
       1  brush-commutated direct-current motor 
       10  stator 
       11  rotor 
       110  commutator 
     B 1 , B 2  brush 
     D axis of rotation 
     K 1 -K 6  jumper 
     L, L 1 -L 8  lamella 
     M 1 -M 6  exciter pole 
     N north pole 
     N 12 -N 91  groove 
     S south pole 
     U circumferential direction 
     Z 1   l -Z 9   l , Z 1   r -Z 9   r  concentrated coil winding 
     Zl 1 , Zl 2 , Zr 1 , Zr 2  connecting arm 
     Z, Z 1 -Z 9  pole tooth