Abstract:
The invention relates to an electrical machine with at least eight exciter poles in the stator and with a commutator rotor, comprising numerous pole teeth, differing from the number of exciter poles and the pole teeth thereof carrying at least one coil each and being connected with commutator laminates being in contact with each other in pairs vie contact bridges, wherein the number of laminates is a plurality of the pole teeth. To reduce the magnetic and electric ripple of the machine the number of the commutator laminates are a plurality of half of the pole pair number of the exciter poles, but not a plurality of the whole pole pair number, wherein the pole pair number has to be an even number.

Description:
TECHNICAL FIELD 
       [0001]    The invention concerns an electrical machine, preferably a direct current motor according to the category of claim  1 . 
       BACKGROUND 
       [0002]    It is advantageous to choose high pole numbers for direct current motors with high torque and low engine speed. Additionally the use of a single-tooth winding allows a high performance or torque concentration. In order to achieve small torque ripple, the number of teeth should preferably be chosen in such a way that the least common multiple (KGV) of pole number and teeth number is as high as possible, so that many different magnetic breakaway positions develop between the teeth and poles per rotation. Thus a KGV of 88 results at for example an electrical direct current motor with eight exciter poles and a commutator rotor with eleven teeth. In order to keep the installation space and the manufacturing effort low for the electrical machine, the number of commutator laminates has to chosen as low as possible. 
         [0003]    It is known from WO02/21665 A2 to use a plurality of the pole number for the number of the commutator laminates. It is also known to connect the commutator laminates in default distances with each other by contact bridges in order to reduce the number of brushes for example to two carbon brushes. Such familiar solutions have nevertheless the disadvantage of a relatively high number of commutator laminates with a corresponding installation space and manufacturing effort. 
         [0004]    As long as the number of commutator laminates is a plurality of the pole pair number and the slot number, the same orders of the power and torque variations are induced that are caused by magnetic reluctance and electric commutation. This causes in particular an increased noise emission. 
       SUMMARY 
       [0005]    The present solution intends to reduce the number of commutator laminates by more than the familiar measure at a torque ripple of the electrical machine that is as small as possible. 
         [0006]    Thus a maximum ripple reduction is established at electrical machines with the featured characteristics of claim  1  in an advantageous way by a useful combination of pole number, teeth number and laminate number. A further advantage is that by a compact constructing commutator the installation space and the manufacturing effort can be kept low for the machine. Moreover a reduced noise emission is achieved. 
         [0007]    Advantageous embodiments and improvements of the characteristics that are stated in the main claim are established by the mentioned characteristics in the sub-claims. 
         [0008]    Thus a better commutation of the coils is provided thereby that the commutator has two plus and two minus brushes, which are each offset to each other by half a laminate width more than the plurality of the whole laminate width. Thereby it is ensured that a current commutation under the two plus or minus brushes always takes place as a counter act, which is not the case at the familiar solutions with a brush offset by a whole plurality of the laminates width. 
         [0009]    Thereby different solutions result depending on the number of laminates. Thus at an even number of laminates of the commutator the two plus brushes and the two minus brushes are each advantageously offset to each other by a double pole pitch of the exciter coil and at an uneven number of laminates the two plus brushes and the two minus brushes of the commutator are offset to each other by 180°. Furthermore an optimal current commutation is achieved at the electrical machine thereby that one of the minus brushes is offset to one of the plus brushes by a triple pole pitch (in direction of rotation of the machine). A further commutation optimization takes place thereby that the laminates of the commutator that have each been offset by four pole pitches to each other are connected by contact bridges to each other. 
         [0010]    A very comfortable manufacturing of the coils and the contact bridges by automatic coiling machines is achieved thereby that the coils of the pole teeth and the contact bridges of the commutator are winded by a winding wire. Such electrical machines can preferably be used in varied applications in motor vehicles. An electrical machine with a commutator rotor consisting of eight pole teeth or slots as well as 22 laminates and an eight-pole exciter is here suggested among others as a preferred embodiment for a wiper direct drive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The invention is further explained in the following by the figures. It is shown in: 
           [0012]      FIG. 1  is a schematic illustration of the front view of the electrical machine according to the invention as a first embodiment; 
           [0013]      FIG. 2  is a winding chart for the coils and contact bridges of the machine that have to created by automatic coiling machines; 
           [0014]      FIG. 3   a  is a schematic illustration of an execution of the machine from  FIG. 1  with the first three coils and contact bridges of the commutator rotor; 
           [0015]      FIGS. 3   b - 3   d  show a further schematic illustration for producing the rotor winding according to the winding chart in  FIG. 2  for the coils and the contact brushes  4  to  6 ,  7  to  9  and  10  to  11 ; 
           [0016]      FIG. 4  is a schematic illustration of an eight-pole machine with 9 teeth and 18 laminates as a further embodiment; 
           [0017]      FIG. 5  is a related winding chart; 
           [0018]      FIG. 6  is a schematic illustration of the execution of the machine from  FIG. 4  with the two first coils and contact bridges according to the winding chart in  FIG. 5 , 
           [0019]      FIG. 7  is a schematic illustration of a twelve-pole electrical machine with 11 teeth and 33 laminates in a third embodiment and 
           [0020]      FIG. 8  is the corresponding winding chart; and 
           [0021]      FIG. 9  is the corresponding execution of the machine from  FIG. 7  with the first three coils that have been created according to the winding chart in  FIG. 8  and 6 contact bridges. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  schematically shows the front view of a permanently magnetically activated eight-pole direct current motor as electrical machine that is labeled with  10  for a first embodiment. Such machines are preferably used for actuators, fanners, windshield wipers and similar in motor vehicles and have to work reliably at high workloads for the entire operational life span of the motor vehicle. Further requirements are power and torque variations as low as possible and low noise emissions. The direct current motor  10  has an eight-pole stator  11 , which interacts over a working air gap  12  with a commutator rotor  13  that is called rotor in the following. The rotor  13  consists of a laminated core  14 , which is attached to a double-sided rotor shaft  15 . At the scope of the laminated core  14  are 11 evenly spread pole teeth Z are arranged, in between which slots N are provided for the intake of overall 11 coils S of a rotor winding  17 . The coils S are thereby created as single-tooth coils each on one pole tooth Z by automatic coiling machines. They are thereby wired up in a special way with a commutator  16  that is put on top of the rotor shaft  15  on the front side of the laminated core  14 . The commutator has 22 laminates L that are evenly spread over the scope and that interact with two fixed plus carbon brushes B+ and two fixed minus carbon brushes B−. They are each offset by 90° to each other and are supplied with direct current for operating the electrical machine. The 11 pole teeth Z of the rotor  13  interact thereby with 8 exciter poles of the stator  11 . In order to establish a torque ripple of the electrical machine that is as small as possible, the number of pole teeth differs from the number of exciter poles. Besides the number of laminates L is here twice as high as the number of pole teeth. 
         [0023]    For an optimal magnetic reluctance and electric commutation of the machine it is furthermore required that the number of commutator laminates L is a plurality of half of the pole pair number of the exciter poles P, but not a plurality of the whole pole pair number. Furthermore the pole pair number has to be an even number. These conditions apply to the direct current motor  10  according to  FIG. 1  with a pole pair number p=4 and a laminate number of 22. The commutation of the machine is furthermore thereby optimized, in that the two plus brushes B+ as well as the two minus brushes B− are offset to each other by half of a laminate width more than a plurality of the whole laminate width b. Thereby it is ensured that always when one of the plus brushes or minus brushes stands in the middle of a laminates L, the other plus brush or minus brush each bridge over two adjacent laminates L. For an optimal magnetic reluctance it is furthermore required at an even number of laminates of the commutator  16 , that the two plus brushes B+ as well as the two minus brushes B− are each offset to each other by a double pole pitch Pt of the exciter poles P. This results at an eight-pole direct current motor  10  according to  FIG. 1  in a brush offset of 90° each. It is furthermore required for an optimal commutation that one of the minus brushes B− is offset to one of the plus brushes B+ by a triple pole pitch Pt in the direction of the rotation of the arrow D of the machine. 
         [0024]      FIG. 2  shows a winding chart, with which the 11 coils of the direct current motor  10  are created and wired up with the 22 laminates L of the commutator  16  as well as with the contact bridges K. The winding chart is thereby processed by an automatic coiling machine, in which the coils S of the pole teeth Z and the contact bridges K are each alternately wired by a winding wire. 
         [0025]      FIG. 3   a  to  3   d  show executions of the direct current motor  10  from  FIG. 1  in a schematic illustration, with which the production of the coils S and the contact bridges K is illustrated in four sections according to the winding chart from  FIG. 2  and described below. The eight-pole stator  11  with the poles P 1  to  8 , the eleven pole teeth Z 1  to  11 , the slots N 1  to  11  and the commutator  16  with the laminates L 1  to  22  can be noticed there. 
         [0026]      FIG. 3   a  shows a first section for producing the rotor winding  17  with the coils S 1  to S 3  and the contact bridges K 1  to K 3 . The winding start  18   a  is arbitrary and is here assigned to laminate L 1 . Furthermore the also arbitrary assignment of the commutator laminates L to the pole teeth Z is selected here in such a way that the first pole tooth Z 1  lies exactly on the height of the laminates gap between laminate L 1  and L 22  of the commutator  16 . This position shall now have the angle position of φ=0° according to  FIG. 3   a.  Besides the first north pole P 1  of the stator  11  stands in the middle over pole tooth Z 1  in this position. While the first plus brush B+ bridges over laminates L 22  and L 1 , the second plus brush B+ is offset by a double pole pitch 2 Pt, which means 90° in the direction of the rotation D, and stands in the middle of laminate L 6 . The first minus brush B− is arranged offset to the first plus brush B+ by a triple pole pitch 3 Pt, corresponding to an angle of 135° in the direction of the rotation D, and stands on laminate L 9 . The second minus brush B− is offset to it by 90° again and stands on laminates L 14  and L 15 . The brush offset of the plus brushes as well as the minus brushes amount therefore each to five and a half times the laminate width (5.5 b). 
         [0027]    The automatic coiling machine processes the winding chart according to  FIG. 2  line by line, whereby coils S 1  to S 11  and the contact brushes K 1  to  11  are winded one by one and are each contacted with their assigned laminates L of the commutator  16 . 
         [0028]    For a better overview the slots N and the laminates L are numbered consecutively in  FIG. 3   a  to  3   d.  The coils that are illustrated twice in the executions are each shown dotted on the right side of  FIGS. 3   a  to  3   d.    
         [0029]    Thereby it is proceeded as follows: 
         [0030]    Beginning with coil S 1  the winding wire  18  is initially attached to laminate L 1  according to  FIG. 3   a,  then the beginning of coil S 1  is put through slot N 6 , thereupon 88 windings are winded around pole tooth Z 7 , in order to attach the coil end through slot N 7  at laminate L 2  thereafter. Subsequently the first contact bridge K 1  is placed from laminate L 2  to laminate L 13  without interrupting the winding wire. Thence the start of the coil S 2  is put through slot N 1 , the coil is winded with 88 windings around tooth Z 2  and the end is lead through the slot N 2  to laminate L 14 . Subsequently the contact bridge K 2  is placed from here to laminate L 3 . Thence the start of coil S 3  is put through slot N 7 , the coil winded around tooth Z 8  and the end placed through slot N 8  to laminate L 4 . From here the winding wire is transferred over to  FIG. 3   b.    
         [0031]    According to  FIG. 3   b  the contact bridge K 3  follows now from laminate L 4  to laminate L 15 . It can be thereby noticed that the contact bridges K each connect the laminates L of the commutator  16  that are offset to each other by 180°, which corresponds with a fourfold pole pitch 4 Pt. Subsequently the start of coil S 4  is put from laminate L 15  through slot N 2 , the coil winded around tooth Z 3  with 88 windings and the end put through slot N 3  onto laminate L 16 . Now the contact bridge K 4  follows from laminate L 16  to laminate L 5 . Thence the start of coil S 5  is put through slot N 8 , the coil winded around tooth Z 9  and the coil end put through slot N 9  onto laminate L 6 . Now the contact bridge K 5  follows from laminate L 6  to laminate L 17 . Subsequently the start of coil S 6  is put from laminate L 17  through slot N 3 , the coil winded around tooth Z 4  and the end put through slot N 4  onto laminate L 18 . Thence the winding wire  18  is transferred to  FIG. 3   c.    
         [0032]    According to  FIG. 3   c  the contact bridge K 6  follows now from laminate L 18  to laminate L 7 . Subsequently the start of coil S 7  is put from laminate L 7  through slot N 9 , the coil winded around tooth Z 10  and the end put through slot N 10  onto laminate L 8 . Thereupon the contact bridge K 7  follows from laminate L 8  to laminate L 19 . Thence the start of coil S 8  is put through slot N 4 , the coil winded around tooth Z 5  and the end put through slot N 5  onto laminate L 20 . Thereupon the contact bridge K 8  follows from laminate L 20  to laminate L 9 . Thence the start of coil S 9  is put through slot N 10 , the coil winded around tooth Z 11  with 88 windings and the coil end put through slot N 11  onto laminate L 10 . The winding wire  18  is transferred to  FIG. 3   d  from here. 
         [0033]    According to  FIG. 3   d  the contact bridge K 9  follows now from laminate L 10  to laminate L 21 . Subsequently the start of coil S 10  is put from laminate L 21  through slot N 5 , the coil winded around tooth Z 6  with 88 windings and the end put through slot N 6  onto laminate L 22 . Thereupon the contact bridge K 10  follows from laminate L 22  to laminate L 11 . Thence the start of coil S 11  is put through slot N 11 , the coil winded around tooth Z 1  and the end put through slot N 1  onto laminate L 12 . At the end the contact bridge K 11  is placed from laminate L 12  to laminate L 1 . The winding wire  18  is here finally separated and creates the end  18   b  of the rotor winding  17 . 
         [0034]      FIG. 4  shows a direct current motor  20  in a second embodiment, whose stator  11  again provides eight poles P. But the commutator rotor  13  is here supplied with only nine slots N or pole teeth Z, which each carry a coil S. The commutator  16  is here supplied with eighteen laminates L and is supplied with direct current over two plus brushes B+ and two minus brushes B−. 
         [0035]      FIG. 5  shows a winding chart for the rotor winding  17  of the direct current motor  20  according to  FIG. 4 . 
         [0036]      FIG. 6  again shows an execution of the direct current motor  20  from  FIG. 4  in a schematic illustration, with which the production and wiring of the coils S and the contact bridges K for the first four winding sections of the winding chart from  FIG. 5  are further explained in the following. The two plus brushes B+ and the two minus brushes B− are thereby offset to each other by 90° to each other like in the first embodiment, which corresponds with a double pole pitch 2 Pt at an eight-pole stator  11 . The first minus brush B− is here also offset towards the first plus brush B+ by 135° or by three pole pitches. 
         [0037]    It can be noticed from the winding chart according to  FIG. 5  that the nine coils S and the contact bridges K have to be created by a continuing winding wire  18 . It is thereby acted as follows: 
         [0038]    Starting out with coil S 1  the winding wire  18  is initially attached with the beginning  18   a  to laminate L 1  according to  FIG. 6 , then the beginning of coil S 1  is put through slot N 5 , thereupon 88 windings are winded around pole tooth Z 6 , in order to attach the coil end through slot N 6  at laminate L 2  thereafter. Subsequently the first contact bridge K 1  is placed from laminate L 2  to laminate L 11  without interrupting the winding wire. Thence the start of the coil S 2  is put through slot N 1 , the coil S 2  is winded around tooth Z 2  and the end is lead through the slot N 2  to laminate L 12 . Subsequently the contact bridge K 2  is placed from here to laminate L 3 . Thence the winding wire in the execution according to  FIG. 6  is lead out on the right side to coil S 3 . Like in the first embodiment of  FIG. 3   a  to  FIG. 3   d  the winding chart according to  FIG. 5  is also processed step by step in the second embodiment, until the winding wire finally gets back to laminate L 1  with the last contact bridge K 10  and is separated there. 
         [0039]      FIG. 7  shows a direct current motor  30  in a third embodiment, whose twelve-pole stator  31  has twelve permanent magnets  32  that are evenly spread at the scope. They create eight poles with alternating polarity, which interact with a rotor  33 , which provides eleven slots N and pole teeth Z, on which each a coil S is wired. The eleven coils S are connected to a commutator  36 , which provides thirty-three laminates L at its scope. The commutator laminates L interact with two plus brushes B+ and two minus brushes B− as electrical supply of the machine. The difference between this and the first two embodiments is that the commutator  36  has an uneven number of laminates L here. It is thereby possible to offset the two plus brushes B+ and the two minus brushes B− each by 180° to each other for an optimal commutation. The minus brushes B− are each offset by 90° to the plus brushes B+. 
         [0040]      FIG. 8  shows a winding chart, with which the eleven coils S and 22 contact bridges K can be created with an automatic coiling machine. Differing form the previous embodiments after each coil two contact bridges K are created one after the other before the next coil follows. All coils S and contact bridges K can be wired here with a winding wire. 
         [0041]      FIG. 9  shows the twelve-pole stator  31  with the rotor  33  and its commutator  36  in an execution of the direct current motor  30 . With the winding chart from  FIG. 8  the production and arrangement of the first three coils S and the first six contact bridges K is explained further with the aid of  FIG. 9  in the following. Thereby the following step sequence arises: 
         [0042]    Initially the winding wire  18  is attached at laminate L 1  at the point  18   a,  then the beginning of coil S 1  is put through slot N 4 , thereafter 88 windings are winded around pole tooth Z 5 , in order to attach the coil end thereupon through slot N 5  at laminate L 24 . Subsequently the first contact bridge K 1  is placed from laminate L 24  to laminate L 2  without interrupting the winding wire and at the same time the second contact bridge K 2  is lead up to laminate L 13 . Thence the start of the coil S 2  is put through slot N 8 , the coil is winded around tooth Z 9  and the end is lead through the slot N 9  to laminate L 3 . From here the contact bridge K 3  is placed to laminate L 14  and contact bridge K 4  to laminate L 25 . Thence the beginning of coil S 3  is put through slot N 1 , the coil winded around pole tooth Z 2  and the end put through slot N 2  to laminate L 15 . Thereafter contact bridge K 5  follows to laminate L 26  and contact bridge K 6  to laminate L 4 . From laminate L 4  the winding wire is lead out on the right side of the execution according to  FIG. 9  to coil S 4 , whereby this winding step as well as all further winding steps that can be taken from the chart according to  FIG. 8  are processed by an automatic coiling machine like it was explained in the first embodiment, until the winding wire finally gets back to laminate L 1  with the last contact bridge K 22  and is separated there. 
         [0043]    At electrical machines, whose number of laminates is a plurality of the pole teeth number, the superior solution idea for reducing ripples of the magnetic reluctance and the electric commutation is that the number of the commutator laminates L is still a plurality of half of the pole pair number of the exciter poles in any case, but not a plurality of the whole pole pair number p, whereby the pole pair number has to be an even number. This solution idea is therefore not limited to the illustrated embodiments. Therefore further alternatives arise only for the rotor of the eight-pole electrical machine for example with thirteen slots/pole teeth and twenty-six commutator laminates or fifteen slots/pole teeth and thirty commutator laminates. Accordingly many alternatives also arise at four-pole, twelve-pole and sixteen-pole electrical machines. 
         [0044]    A further superior characteristic of the embodiments is that the commutator provides two plus brushes B+ and two minus brushes B−, whereby the plus brushes as well as the minus brushes are offset to each other by half of the laminate width more than a plurality of the whole laminate width b. Thereby a low current ripple is achieved at the commutation of the machine by never commutating the current under both plus brushes and minus brushes from one laminate to an adjacent laminate at the same time. In doing so it is further achieved that the frequency of the magnetic ripple (pole pair number z teeth number) deviates from the frequency of the current ripple. This means low power and torque variations as well as low noise emissions.