Patent Publication Number: US-2009236928-A1

Title: Electrical  machine

Description:
PRIOR ART 
     The invention relates to an electrical machine, in particular a DC machine, according to the preamble to claim  1 . 
     WO 2005/076442 A has disclosed an electric motor with a symmetrically arranged armature winding. The symmetrically arranged armature winding is composed of a first coil that is wound between two arbitrary armature slots and is electrically connected to adjacent commutator plates. A second coil is wound between two armature slots, which are situated centrosymmetrically to the two armature slots of the first coil in relation to the center point of the armature shaft, and is wound in the opposite direction. In the motor, the number of armature slots is equal to the number of commutator plates. The motor has one brush each for high and low speeds and also has a shared brush. The first and second coils are arranged so that they are situated in a position symmetrical to an axis that passes through the center point of the brush for high speeds and the center point of the rotary shaft when the brush for high speeds comes into contact with the adjacent commutator plate and thus short-circuits the first coil with the second coil. 
     DISCLOSURE OF THE INVENTION 
     The electrical machine according to the invention, with the defining characteristics of claim  1 , has an improved noise reduction and an improved electromagnetic compatibility (EMC). This is achieved by virtue of the fact that the electrical machine according to the invention has an armature winding composed of armature coils, at least one armature coil being composed of two partial coils that are arranged symmetrically in relation to the rotation axis of the armature. This means that the armature coils are embodied so that the two partial coils of each pair are arranged symmetrically to each other in relation to the rotation axis of the armature. According to the invention, the number of commutator plates is an integral multiple of the number of armature slots. In particular, the number of commutator plates is at least twice as great as the number of armature slots. It is preferable for the number of commutator plates to be twice as great as the number of armature slots. The number of plates, however, can also be, for example, three times the number of armature slots. In addition, the commutator preferably has an even number of commutator plates. 
     According to the invention, the two partial coils are arranged symmetrically to each other so that when current is supplied to the partial coils, essentially no radial forces act on the armature in a magnetic field. The two partial coils can be commutated simultaneously, for example by being connected to adjacent commutator plates. The resulting radial forces are compensated for in a particularly favorable fashion in that the two partial coils are arranged essentially parallel to each other geometrically and spaced the same distance apart from the rotation axis of the armature. The radial forces can also be compensated for particularly well in that the two partial coils have the same number of windings. It is furthermore possible to compensate for radial forces in a particularly fashion in that the two partial coils are wound in opposite winding directions from each other. The two partial coils arranged symmetrically to each other are referred to below as a partial coil pair. In particular, this is a two-poled electrical winding. 
     The two symmetrically arranged partial coils are preferably wound in the fashion of a fractional pitch winding, but can also be wound in the fashion of a full-pitch diametrical winding. 
     With a multiple number of commutator plates, a corresponding multiple number of partial coils is wound into each armature slot. Thus, for example, with twice the number of plates, two partial coils (each being a partial coil of a partial coil pair) are wound into one armature slot and with three times the number of plates, three partial coils (likewise each being a partial coil of a partial coil pair) are wound into one armature slot. This means that one armature slot contains two or three partial coils of two or three partial coil pairs. With a given slot area, this can, for example, be achieved by means of a correspondingly lower number of windings per partial coil or by means of a smaller coil wire cross section, the former being accompanied by a change in the speed and the latter being accompanied by a change in the output. 
     The two partial coils of a partial coil pair can be electrically connected to each other either in series or in parallel. With the series connection, the two partial coils have two ends that are each electrically connected to a respective commutator plate. If twice the number of commutator plates are provided, then the two ends of the two series-connected partial coils are each electrically connected to a respective commutator plate that is spaced one plate away from the other. Thus, for example, the first end of a first partial coil pair is connected to a first commutator plate and the second end of the first partial coil pair is connected to the plate spaced one plate away from the first, i.e. the third commutator plate. The second commutator plate situated between them is connected to the first end of a second partial coil pair and the second end of the second partial coil pair is in turn connected to the plate spaced one plate away it, i.e., the fourth commutator plate in this case. This connection of the two ends of a series-connected partial coil pair continues in corresponding fashion until all of the armature slots are occupied by symmetrically arranged partial coils. If three times the number of commutator plates are provided, then the two ends of the series-connected partial coils are each electrically connected in an analogous fashion to the respective commutator plate that is the third plate in relation to the other. This means that, for example, the first end of a first partial coil pair is connected to a first commutator plate and the second end of the first partial coil pair is connected to the fourth commutator plate. The first end of a second partial coil pair is thus connected to the second commutator plate and the second end of the second partial coil pair is connected to the fifth commutator plate. In addition, the first end of a third partial coil pair is connected to the third commutator plate and the second end of the third partial coil pair is connected to the sixth commutator plate. 
     With the parallel connection, however, each of the two partial coils of a partial coil pair has two ends so that for each partial coil pair, four ends are connected to the commutator plates in an electrically conductive fashion. With twice the number of commutator plates, the ends of the two partial coils are connected to adjacent commutator plates in alternating fashion. This means that the second end of one partial coil is respectively connected to the commutator plate spaced one away from the other. Thus, for example, the first end of a first partial coil is connected to a first commutator plate and the second end of the first partial coil is connected to the one after the next, i.e. the third commutator plate, while the first end of the second partial coil is connected to the second commutator plate and the second end of the second partial coil is connected to the fourth commutator plate. 
     The electrical machine according to the invention has at least two brushes that rest against the commutator in sliding fashion. For example, the two brushes are situated opposite each other. In order to assure the most uniform possible flow of current during commutation, the brush width is selected so that during rotation of the commutator, the respective plates that are connected to the two partial coils are short-circuited. It is also possible, however, to select a different brush width, e.g. 1.2 times the width of a commutator plate. 
     In the electrical machine according to the invention, it is also possible for speed adjustment purposes to provide a third brush that is situated radially between the brushes that are situated opposite each other (referred to below as the first and second brushes). The third brush is thus arranged offset in relation to the first brush by a certain angle of less than 180°, e.g. 70°, in the rotation direction. In this case, in the low speed stage, the two brushes situated opposite each other, i.e. the first and second brushes, are supplied with current while the third brush is without current. In the high speed stage, the second and third brushes are supplied with current whereas the first brush is without current. The second brush therefore constitutes the shared brush, which cooperates with the first brush at low speeds and cooperates with the third brush at high speeds. 
     In another preferred embodiment, the symmetrically arranged partial coils are embodied in two layers, in the form of a double winding with a reduced, i.e. halved, coil wire cross section. This makes it possible to achieve an increased slot space factor. 
     The electrical machine according to the invention can, for example, be a two-poled DC motor for adjusting moving components in a motor vehicle, e.g. a windshield wiper motor, a power window motor, or a seat adjusting motor. 
     The invention will be explained in greater detail below in conjunction with the accompanying drawings. 
    
    
     
       DRAWINGS 
         FIG. 1  shows an electrical machine with two brushes 
         FIG. 2  shows a first embodiment of armature coils having two symmetrical partial coils with a fractional pitch winding arranged in a series circuit, 
         FIG. 3  shows a second embodiment of armature coils having two symmetrical partial coils with a fractional pitch winding arranged in a parallel circuit, 
         FIG. 4  shows a third embodiment of armature coils having two symmetrical partial coils with a full-pitch diametrical winding, and 
         FIG. 5  shows a fourth embodiment with three times the number of commutator plates. 
     
    
    
       FIG. 1  shows an electrical machine  100 , which has an armature  20 , two magnetic poles  30 , and a commutator  10  with commutator plates  11 . The armature  20  and the commutator  10  are supported in a rotationally fixed fashion on an armature shaft  22  with a rotation axis  21 . A first and second brush  14  are arranged opposite each other, resting against the commutator  10  in sliding fashion. 
       FIG. 2  schematically depicts a partial developed view of a first embodiment of armature coils, each with two symmetrical partial coils. In the embodiment shown, the commutator  10  has 24 plates  11  and the armature  20  has twelve teeth  23  and twelve armature slots  24 . The armature coil is wound in the fashion of a multiple circuit winding in the form of a fractional pitch winding. A first partial coil pair  25 ,  26  is wound as follows: the winding of a first partial coil  25  is situated in a first armature slot  24  between the twelfth and first teeth  23  and in the sixth armature slot  24  between the fifth and sixth teeth  23 . The winding of a second partial coil  26  is situated in the twelfth armature slot  24  between the eleventh and twelfth teeth  23  and in the seventh armature slot  24  between the sixth and seventh teeth  23 . The two ends of the first and second partial coils  25 ,  26  are each electrically connected to the respective commutator plate  11  spaced one apart from the other (in this case, the third and fifth plates). The two partial coils  25 ,  26  are thus connected in series. The first and sixth armature slots  24  and the seventh and twelfth armature slots  24  are respectively situated opposite each other so that the two partial coils  25 ,  26  are arranged symmetrically to each other in relation to the rotation axis  13  of the armature  20 . The partial coils  25 ,  26  run parallel to each other, with the two partial coils  25 ,  26  being wound in opposite winding directions. In the embodiment shown, the first partial coil  25  is wound first before the second partial coil  26  is wound. Alternatively, however, it is also possible for the two partial coils  25 ,  26  to be wound in alternation. 
     The first partial coil  25 ′ of a second partial coil pair  25 ′,  26 ′ is likewise situated in the first and sixth armature slots  24  while the second partial coil  26 ′ of the second partial coil pair  25 ′,  26 ′ is situated in the twelfth and seventh armature slots  24 . The two ends in turn are each connected to a respective commutator plate  11  spaced one apart from the other, the first end of the second partial coil pair in this case being connected to the fourth commutator plate  11  and the second end being connected to the sixth commutator plate  11 . Correspondingly, the other armature slots  24  are also each occupied by two respective first partial coils  25  or second partial coils  26  of two partial coil pairs  25 ,  26 , the two ends of one partial coil pair  25 ,  26  each being connected to a respective commutator plate  11  spaced one apart from the other (e.g. the third and fifth plates and the fourth and sixth plates, respectively). This means that the four ends of two partial coil pairs  25 ,  26  and  25 ′,  26 ′, which are situated in the same armature slots  24 , are each connected to a respective commutator plate  11  in alternating fashion. 
       FIG. 3  schematically depicts a partial developed view of a second embodiment of armature coils, each with two respective symmetrical partial coils  25 ,  26  and  25 ′,  26 ′ of two partial coil pairs. In the embodiment shown, the commutator  10  once again has 24 plates  11  and the armature  20  has twelve teeth  23  and twelve armature slots  24 . The armature coil is likewise wound in the fashion of a multiple circuit winding in the form of a fractional pitch winding. The winding of a first partial coil  25  of a first partial coil pair  25 ,  26  is situated in the second armature slot  24  between the first and second teeth  23  and in the seventh armature slot  24  between the sixth and seventh teeth  23 . The winding of a second partial coil  26  of the first partial coil pair  25 ,  26  is situated in the first armature slot  24  between the twelfth and first teeth  23  and in the eighth armature slot  24  between the seventh and eighth teeth  23 . The two partial coils  25 ,  26  are connected in parallel in that the two ends of each partial coil  25 ,  26  are each electrically connected to the respective commutator plate  11  spaced one apart from the other. This means that in  FIG. 3 , the first end of the first partial coil  25  is connected to the sixth plate  11  and the second end of the first partial coil  25  is connected to the eighth plate  11  while the first end of the second partial coil  26  is connected to the seventh plate  11  and the second end of the second partial coil  26  is connected to the ninth plate  1 . The four ends of the partial coil pair  25 ,  26  are thus connected to adjacent commutator plates  11  in alternating fashion. The first partial coil  25 ′ of a second partial coil pair  25 ′,  26 ′ is situated in the same armature slots  24  as the first partial coil  25  of the first partial coil pair  25 ,  26 , but the coil ends according to  FIG. 3  are electrically connected to the seventh and ninth commutator plates  11 . The second partial coil  26 ′ of the second partial coil pair  25 ′,  26 ′ is thus wound into the same armature slots  24  as the second partial coil  26  of the first partial coil pair  25 ,  26 . Its first and second ends are respectively connected to the sixth and eighth commutator plates  11 . 
       FIG. 4  schematically depicts a partial developed view of a first embodiment of armature coils that each have two respective symmetrical partial coils. In the embodiment shown, the commutator  10  has 24 plates  11  and the armature  20  has twelve teeth  23  and twelve armature slots  24 . The armature coil is wound in the fashion of a multiple circuit winding in the form of a full-pitch diametrical winding. A first partial coil pair  25 ,  26  is wound as follows: the winding of a first partial coil  25  is situated in a first armature slot  24  between the twelfth and first teeth  23  and in the seventh armature slot  24  between the sixth and seventh teeth  23 . The winding of a second partial coil  26  is likewise situated in the first armature slot  24  between the twelfth and first teeth  23  and in the seventh armature slot  24  between the sixth and seventh teeth  23 . The to ends of the first and second partial coils  25 ,  26  are each electrically connected to the respective commutator plate  11  spaced one apart from the other (in this case, the sixth and eighth plates). The two partial coils  25 ,  26  are thus connected in series. In the embodiment shown, the first partial coil  25  is wound first before the second partial coil  26  is wound. Alternatively however, it is also possible for the two partial coils  25 ,  26  to be wound in alternation. 
     A first partial coil  25 ′ and the second partial coil  26 ′ of a second partial coil pair  25 ′,  26 ′ are likewise situated in the first and seventh armature slots  24 . The two ends are in turn each connected to a respective commutator plate  11  spaced one apart from the other, the first end of the second partial coil pair  25 ′,  26 ′ being connected to the seventh commutator plate  11  and the second end being connected to the ninth commutator plate  11 . Correspondingly, the other armature slots  24  are also each occupied by two respective first partial coils  25  or second partial coils  26  of two partial coil pairs  25 ,  26 , the two ends of one partial coil pair  25 ,  26  each being connected to the respective commutator plate  11  spaced one apart from the other (e.g. the third and fifth plates and the fourth and sixth plates, respectively). This means that the four ends of two partial coil pairs  25 ,  26  and  25 ′,  26 ′, which are situated in the same armature slots  24 , are each connected to a respective commutator plate  11  in alternating fashion. 
     In the embodiment according to  FIG. 5 , a schematic depiction is given of a partial developed view of armature coils, each with two symmetrical partial coils, in which the commutator  10  has 24 plates  11  and the armature  20  has eight teeth  23  and eight armature slots  24 . The number of commutator plates  11  is thus three times the number of armature slots  24 . The armature coil is wound in the fashion of a multiple circuit winding in the form of a fractional pitch winding. A first partial coil pair  25 ,  26  is wound as follows: the winding of a first partial coil  25  is situated in a first armature slot  24  between the eighth and first teeth  23  and in the fourth armature slot  24  between the third and fourth teeth  23 . The winding of a second partial coil  26  is situated in the eighth armature slot  24  between the seventh and eighth teeth  23  and in the fifth armature slot  24  between the fourth and fifth teeth  23 . The two ends of the first and second partial coils  25 ,  26  are each electrically connected to the respective third commutator plate  11  from the other (the third and sixth plates in this case). The two partial coils  25 ,  26  are thus connected in series. In a manner analogous to the one in the embodiment shown in  FIG. 2 , the armature slots  24  into which the first partial coil  25  is wound and the armature slots  24  into which the second partial coil  26  is wound are situated opposite each other. The two partial coils  25 ,  26  are situated symmetrically to each other in relation to the rotation axis  13  of the armature  20  in that they run parallel to each other and the two partial coils  25 ,  26  are wound in opposite winding directions. In the embodiment shown, the first partial coil  25  is wound first before the second partial coil  26  is wound. Alternatively, however, it is also possible for the two partial coils  25 ,  26  to be wound in alternation. 
     A first partial coil  25 ′ of a second partial coil pair  25 ′,  26 ′ is likewise situated in the first and fourth armature slots  24 , while the second partial coil  26 ′ of the second partial coil pair  25 ′,  26 ′ is likewise situated in the eighth and fifth armature slots  24 . The two ends in turn are each connected to the respective third commutator plate  11  from the other, the first end of the second partial coil pair  25 ′,  26 ′ here being connected to the fourth commutator plate  11  and the second end being connected to the seventh commutator plate  11 . 
     A first partial coil  25 ′ of a third partial coil pair  25 ″,  26 ″ is likewise situated in the first and fourth armature slots  24 , while the second partial coil  26 ′ of the third partial coil pair  25 ″,  26 ″ is likewise situated in the eighth and fifth armature slots  24 . The two ends in turn are each connected to the respective third commutator plate  11  from the other, the first end of the third partial coil pair  25 ″,  26 ″ in this case being connected to the fifth commutator plate  11  and the second end being connected to the eighth commutator plate  11 . 
     Correspondingly, the additional armature slots  24  are also each occupied by three respective first partial coils  25 ,  25 ′,  25 ″ or second partial coils  26 ,  26 ′,  26 ″ of three partial coil pairs  25 ,  26 ,  25 ′,  26 ″, and  25 ″,  26 ″, with the two ends of a partial coil pair  25 ,  26 ,  25 ′,  26 ″, or  25 ″,  26 ″ being connected to the respective commutator plate  11  after the next (e.g. the third and sixth, the fourth and seventh, and the fifth and eighth). This means that the four ends of two partial coil pairs  25 ,  26  and  25 ′,  26 ′ that are situated in the same armature slots  24  are each connected to a respective commutator plate  11  in alternating fashion. 
       FIGS. 2 ,  3 ,  4 , and  5  each show a respective embodiment of a series circuit and a parallel circuit of the two partial coils  25 ,  26 . Using the principle demonstrated here of the winding of two symmetrically arranged partial coils  25 ,  26 , it is possible to implement numerous other winding schemes.