Abstract:
An electrical machine is described, having a stationary main element as stator and a rotating main element as rotor, of which one main element having a magnetic yoke and poles, of a predefined number of poles, projecting radially from the former, is made of SMC material and carries a pole winding on each pole. To achieve cost-effective manufacturing of the main element, the main element is assembled from at least two modules that are axially adjacent, rigidly connected to one another, and produced from SMC material, each module having a yoke part, closed in on itself, of the magnetic yoke having an equal number of divisions of poles attached thereto in one piece, which corresponds to a fraction of the number of poles determined by the number of modules.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an electrical machine having a stationary main element as stator and a rotating main element as rotor, of which one is produced from SMC material. 
   BACKGROUND INFORMATION 
   Magnetic conductive members of stators or rotors of electrical machines will, in the near future, be increasingly made of SMC material (soft magnetic powder iron composite), and will replace laminated core assemblies or laminated cores, since, from a manufacturing technology point of view, they are much more simple to produce. The SMC material is pressed into the desired shape using a pressing mold, and is then heat treated at a relatively low temperature, so that the necessary insulating layers between the powder particles are not destroyed. 
   In one known multipolar stator made of SMC material for an internal-rotor machine (PCT International Publication No. 99/50949) the outer-lying magnetic yoke is composed of a number of yoke segments corresponding to the number of poles of the stator poles. Each yoke segment carries in one piece a stator pole having a pole core and a pole shoe bordering the pole core at the latter&#39;s remote end. Each yoke segment along with pole core and pole shoe is produced from SMC material by pressing and heat treating. The pole cores are rounded off at their axial ends or have an oval profile, so that, as a result of the removal of sharp edges at the pole cores, only a thin insulating layer has to be applied, onto which the pole winding may then be wound. The individual pole windings of the stator winding are wound directly onto the pole cores, using the usual machine-based winding technology. After winding the pole windings, the individual yoke segments are set next to one another in the circumferential direction and are fixedly connected to one another. 
   In the case of another known stator made of an SMC material for an internal-rotor motor (PCT International Publication No. 00/69047), the ring-shaped magnetic yoke on the one hand, and the stator pole having pole core and pole shoe on the other hand, are made separately of SMC material in the desired shape. After sliding the pole windings, prefabricated as ring coils, onto the pole cores, the stator poles are set into prepared recesses in the magnetic yoke with form locking, with the ends of the pole cores that are at a distance from the pole shoe, and are fastened there. 
   SUMMARY OF THE INVENTION 
   The electrical machines according to the present invention have the advantage that the main element of the electrical machine, made of SMC material, e.g. the rotor of a commutator motor or the stator of a brushless DC motor or synchronous motor, an asynchronous motor, a switched reluctance motor or a synchronous reluctance motor is composed only of extremely few modules which, from a manufacturing technology point of view, may favorably be pressed from SMC material. The modules are preferably pressed from an SMC powder having a density of 7.3 g/cm 3  or greater, in order to achieve the required magnetic properties, and are subsequently exposed for about 30 minutes to a temperature of ca. 500° C., in order also to be given acceptable mechanical properties. In this context, the main element may be executed having all the usual number of poles. 
   In contrast to the composition undertaken in the circumferential direction, of the yoke segments pressed from SMC material in the related art, axially assembling only two or three modules is non-problematical from a manufacturing technology point of view, since, in contrast to what is done in the related art, no centrifugal forces act on the connecting locations between the assembled parts. Fixing the modules to one another may, for example, be undertaken by simple adhesion or mechanical clamping. The subdivision of the main element into two or three or more modules, each having only one part of the overall number of poles, makes possible the winding of the individual poles using the pole windings developed as individual coils in the usual winding technique on customary winding machines, since the pole gaps in the poles in each module are sufficiently large for guiding through the winding finger that guides the winding wire, because of the absence of the poles assigned in each case to the other modules. Because of the low number of modules for forming the main element, which may partially even be executed identically, both manufacturing costs for the modules themselves and assembly costs for the main element are clearly reduced, so that the main element may be manufactured in a clearly more cost-effective manner as compared to known rotors or stators made of SMC material. The main element made of SMC material is implemented equally well for internal-rotor and external rotor machines. 
   According to one advantageous specific embodiment, the poles at each yoke part are situated offset by equal circumferential angles to one another, the yoke parts preferably having equal axial widths, and at least two of the modules being designed identically. Because of these measures, the piece number of the modules that may be manufactured using one pressing mold may be doubled, which reduces the production costs. In each case, two modules having axes rotated by 180° to each other are assembled for the main element. For motors of greater power, which require a main element having greater axial dimension, the main element is composed of several, such as three modules. Because of that, the yoke parts of the individual modules have a small axial width or depth, which is advantageous for the pressing procedure. Because of the poles subdivided into several modules, bigger pole gaps are created in the individual modules, which brings along advantages in the mechanical winding of the poles. 
   According to one advantageous specific embodiment of the present invention, each pole has a pole core and a pole shoe that is situated at the former&#39;s end that is distant from the yoke part, and is thus in one piece. The pole cores have an axial core width corresponding to the axial width of the yoke part, and the pole shoes are designed in such a way that their boundary edges that extend in the circumferential direction are in alignment with one another when the modules are put together. Using this manner of construction, one may advantageously implement an external-rotor motor, and preferably, indeed, using only two modules. In this context, the pole shoes are aligned in the axial direction asymmetrically to the pole cores, so that on one side they axially protrude beyond the yoke part, and, when the modules are put together, their protruding region is inserted into the other modules. 
   According to one advantageous specific embodiment of the present invention, each pole has a pole core and a pole shoe that is situated at the former&#39;s end that is distant from the yoke part, and is thus in one piece with it. The axial width of the pole core is greater than the axial width of the yoke part, and the yoke parts have notches on their end face facing the other module respectively, for the form locking partial accommodation of the pole cores in the region where they protrude beyond the yoke part of the adjoining module. The pole shoes, again, are aligned to the pole cores in such a way that their matching edges extending in the circumferential direction are in alignment. Because of this method of construction, a stator of an external-rotor machine or a rotor of an internal-rotor machine may be implemented using three modules whose yoke parts have a clearly smaller axial width. The cross section of the pole cores and the surfaces of the pole shoes, and thus the magnetic relationships remain unchanged from the two-module embodiment. The pole shoes of the two outer modules, as seen in the axial direction, are again aligned asymmetrically to the pole shoes, while the pole shoes of the middle module is situated symmetrically to the pole cores. The protruding regions of the pole shoes beyond the yoke parts, in the case of assembled modules, are then inserted in each case into the adjacent module. 
   According to one advantageous specific embodiment of the present invention, in each module the poles extend beyond at least one end face of the yoke part in the axial direction so far that, with the modules assembled, the poles extend over the axial width of the magnetic yoke, preferably their axial lengths being equal to the axial length of the permanent magnet segments, for reasons of stray field reduction. 
   In the case of a main element assembled from two modules, in this context, the poles extend beyond the yoke part on one side, and are inserted, using their protruding region, into the yoke part of the other module. In a three-module composition of the main element, as in the case of the two-module embodiment, the poles of the two outer modules extend beyond the respective yoke part on one side, while, in the case of the middle module, the poles symmetrically protrude on both sides of the yoke part. Because of this method of construction, preferably the stator of an internal-rotor motor may manifest itself advantageously. The poles may be executed with or without pole shoes, additional mechanical means having to be provided for holding the pole winding on the pole cores, in the case of lacking pole shoes, thus, for example, according to one advantageous specific embodiment of the present invention, a concave arching at least one axial end face of the pole cores, into which, then, a pole winding prefabricated as a ring coil is inserted and swiveled onto the pole core, and in this context, becomes axially clamped. In the case where pole cores are closed off using pole shoes which protrude on the edge beyond the pole cores, these additional holding means are omitted, and the pole winding is wound directly onto the pole cores. The usual winding techniques may be used for this, since the distance between the poles in each module is large enough to make possible guiding through the winding FINGER that guides the winding wire. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a perspective view of an external-rotor motor. 
       FIG. 2  shows an exploded view of the external-rotor motor in  FIG. 1 . 
       FIG. 3  shows an exploded view of an external-rotor motor according to a further exemplary embodiment. 
       FIG. 4  shows a perspective view of a stator of an internal-rotor motor. 
       FIG. 5  shows a representation in perspective of a module of the stator in  FIG. 4 . 
       FIG. 6  shows a representation in perspective of a module of a stator for an internal-rotor motor according to a second exemplary embodiment. 
       FIG. 7  shows an exploded representation of a stator for an internal-rotor motor according to a third exemplary embodiment. 
       FIG. 8  shows a view of the stator in the direction of arrow VIII in  FIG. 7 . 
       FIG. 9  shows a section along line IX-IX in  FIG. 8 . 
       FIG. 10  shows a representation in perspective of a module of a stator for an internal-rotor motor according to a fourth exemplary embodiment. 
       FIG. 11  shows a view of the module in the direction of arrow XI in  FIG. 10 . 
       FIG. 12  shows a section along line XII-XII in  FIG. 11 . 
       FIG. 13  shows an exploded representation of a stator for an internal-rotor motor according to a fifth exemplary embodiment. 
       FIG. 14  shows a representation in perspective of a module of a stator for an internal-rotor motor according to a sixth exemplary embodiment. 
       FIG. 15  shows a representation in perspective of the module in  FIG. 14  having only one pole shoe and having a mounted pole winding. 
       FIG. 16  shows the same representation as in  FIG. 15 , to demonstrate the mounting of the pole winding. 
       FIG. 17  shows an exploded representation of a stator for an internal-rotor motor according to a seventh exemplary embodiment. 
   

   DETAILED DESCRIPTION 
     FIGS. 1 and 2  show a brushless, eight pole external-rotor DC motor having a stator  11  and a rotor  12  that concentrically surrounds stator  11  in a perspective or an exploded representation. Stator  11  and rotor  12  represent the so-called main elements of the motor. Rotor  12  has the usual construction and has a solid or laminated outer ring  13 , that bears eight permanent magnet segments  14  on its inner surface facing stator  11 , which are situated offset by equal circumferential angles, and are polarized alternately in opposite direction. Stator  11  has a ring-shaped magnetic yoke  15  and twelve teeth or poles  16  in total, which project radially outwards from magnetic yoke  15 , and are situated offset by equal circumferential angles with respect to one another at magnetic yoke  15 , and in one piece with it. 
   Each pole  16  has a pole core  161  and a pole shoe  162 , which is situated in one piece with pole core  161  at the end of pole core  161  facing away from the yoke. Pole shoes  162  have an axial length corresponding to the axial width of permanent magnet segments  14 , and protrude on all sides beyond pole cores  161 , which, on the one hand, has the effect of a flux concentration in pole cores  161 , and, on the other hand, is used for supporting a pole winding wound on pole core  161 . All poles  16  are covered by a pole winding not shown in  FIGS. 1 and 2 , which is designed as a concentrated ring coil. 
   As may be seen in the exploded representation of the motor in  FIG. 2 , stator  11  is composed of two axially adjoining modules  17 ,  18  that are rigidly connected to each other. Each module  17 ,  18  has a ring-shaped yoke part  151 ,  152 , closed on itself, of magnetic yoke  15 , having in each case six of the in total twelve poles  16 . Corresponding to the division of poles  16  into the two yoke parts  151 ,  152 , at each yoke part  151  or  152 , poles  16 , in turn, are offset by equal circumferential angles to one another, the angle of staggering being twice as great as the angle of staggering between poles  16  in stator  11  in  FIG. 1 . Pole shoes  162  of poles  16  are aligned asymmetrically to pole cores  161 , and axially protrude beyond the one end face of yoke part  151  or  152 . Modules  17 ,  18  are made of SMC material (soft magnetic powder iron composite), SMC iron powder being pressed in a press form into the shape of modules  17 ,  18  that are to be seen in  FIG. 2 , and is subsequently exposed for 30 min to a temperature of ca. 500° C. Since the two modules  17 ,  18  have identical shapes, they may be produced using the same mold, so that there results a large quantity of modules  17 ,  18  that is favorable for manufacturing. Now, a pole winding is wound on all poles  16 , because of doubly enlarged distance between adjacent poles  16 , the usual winding techniques on the usual winding machines may be used without a problem 
   Modules  17 ,  18 , thus wound, are axially assembled using module axes that are rotated by 180° with respect to each other, namely, in such a way that pole shoes  162  penetrate at poles  16  of the one module  17  into the gaps present between pole shoes  162  of the other module  18 , and vice versa. In this context, because of the development of pole shoes  162  already mentioned, the bordering edges of pole shoes  162  that extend in the circumferential direction are aligned. The two modules  17 ,  18  are rigidly connected to each other, e.g. by adhesion or clamping the adjoining, ring-shaped end faces of yoke parts  151 ,  152 . 
   In the exemplary embodiment, that may be seen in exploded representation in  FIG. 3 , of a likewise brushless, eight pole external-rotor DC motor, as may be seen assembled in  FIG. 1 , stator  11  is assembled from three modules  21 ,  22  and  23 . Each module  21 - 23  has, in turn, a yoke part  151 - 153 , whose axial width amounts to one-third of the axial width of magnetic yoke  15 . Each module  21 - 23  at this point has only four poles  16  having in each case a pole core  161  and a pole shoe  162 , which are situated offset by 90° in the circumferential direction with respect to one another at magnetic yoke  15 . The number of poles  16  at each module  21 - 23  is equal to a third of the total number of stator poles  16 . The axial width of pole cores  161  is maintained corresponding to poles  16  in  FIG. 2 , so that, at this point, pole cores  161  project axially over yoke parts  151 - 153 . In the two outer modules  21  and  22  in  FIG. 3 , pole cores  161  protrude on one side beyond yoke parts  151 ,  152  in the axial direction, whereas in middle module  23 , pole cores  161  extend on both parts axially slightly beyond yoke part  153 . Pole shoes  162  in the two outer modules  21 ,  22 , are, in turn, aligned asymmetrically to pole cores  161  in the axial direction. In middle module  23 , pole shoes  162  are aligned symmetrically to pole cores  161 . Yoke parts  151 ,  152  of the two outer modules  21 ,  22  have, in their one ring-shaped end face, four concave notches  24 , which are used for the form locking accommodation of protruding regions of pole cores  161  of middle module  23 . Middle module  23  has respectively four concave notches  24  in both end faces of yoke part  153 . Notches  24  are used for the form locking accommodation of pole cores  161  that protrude beyond yoke parts  151 ,  152  of the two outer modules  21 ,  22 . The pole windings again are applied by direct winding of pole cores  161  to poles  16  of the three modules  21 - 23 . All three modules  21 ,  22 ,  23  are, in turn, made of SMC material using the method described, the two outer modules  21 ,  22  being identical and being produced using the same mold. A separate mold is required for middle module  23 . The three wound modules  21 ,  22 ,  23  are axially assembled is the alignment shown in  FIG. 3 , and are rigidly connected to one another. In the composite form, the bordering edges of pole shoes  162 , that extend in the circumferential direction, are in alignment. 
   Stator  11  shown in  FIGS. 2 and 3  may also be developed having a different number of poles. In this context, basically stators having three, nine or fifteen poles are assembled from three modules, of which two are identical, and stators having six, twelve or eighteen poles are assembled from only two identical modules. A similar division is also possible in the case of an even higher number of poles. 
     FIG. 4  shows a stator for a three-phase, four pole internal-rotor DC motor. This stator  31  has a cylindrical or ring-shaped magnetic yoke  32 , and six poles  33  radially protruding inwards from it and in one piece with it. Each pole  33  has a pole core  331  and a pole shoe  332  situated at the end of pole core  331 , that is distant from the yoke, and in one piece with the former, and which protrudes somewhat on all sides beyond pole core  331 . A pole winding that is not shown here is accommodated, in turn, on each pole core  331 , as may be seen, for example in  FIGS. 15 and 16 . 
   Stator  31 , in turn, is composed of two axially adjoining modules  34 ,  35 , that are rigidly connected to each other. Each module  34  and  35  has a yoke part  321  and  322 , respectively, of magnetic yoke  32  that is closed in on itself, whose axial width is half as great as that of magnetic yoke  32 . A half the poles  33  of stator  31  is situated at each yoke part  321 ,  322 , which, again, are situated offset by equal circumferential angles to one another. 
     FIG. 5  shows in perspective the one module  34  of stator  31 , with its yoke part  321  and its three poles  33  that are situated offset by 120° with respect to one another. The other module  35  is developed identically. Both modules  34 ,  35  are produced from SMC material in the same mold. As may be seen in  FIG. 5 , in each module  34 ,  35 , poles  33  axially project so far beyond an end face of yoke part  321  and  322  that, in assembled modules  34 ,  35 , they extend over the axial width of magnetic yoke  32 . Since the axial length of magnetic yoke  32  is selected to be somewhat greater than the axial length of poles  33 , the axial ends of poles  33  are somewhat set back compared to the outer edges of magnetic yoke  32 . The axial length of pole shoes  332  would, in turn, correspond to the axial length of the permanent magnet segments of a rotor. After winding poles  33  using the individual pole windings, the two modules  34 ,  35  are axially assembled using module axes rotated by 180° with respect to each other, poles  33  penetrating the pole gaps of the respective other module  35 ,  34  using their region that protrudes on one side beyond yoke parts  321 ,  322 . The adjoining, ring-shaped end faces of yoke parts  321 ,  322  are adhered together or are rigidly connected to each other in another way. 
   Stator  31  shown in exploded representation in  FIG. 17  for an internal-rotor motor differs from the motor described for  FIGS. 4 and 5  in that it carries in total nine poles  33  on magnetic yoke  32 , and is composed of in total three modules  34 - 36 , of which the two outer modules  34 ,  35  are developed identically and correspond in their design to module  34  described in  FIG. 5 . Middle module  36  has a yoke part  323  which has the same axial width as yoke parts  321 ,  322  of the two outer modules  34 ,  35 . On yoke part  323 , same as on the two outer modules  34 ,  35 , there are three poles  33  that are situated, offset by 120° in the circumferential direction, that are developed as one piece with yoke part  323 . Poles  33 , whose axial length is slightly shorter than the sum of the axial widths of yoke parts  321 - 323  of modules  34 - 36 , protrude on both sides beyond yoke part  323 , and, in fact, symmetrically. Middle module  36  is also made of SMC material, a separate mold being required, however, in this instance. Modules  34 - 36 , that are provided with pole windings, are axially assembled in the alignment shown in  FIG. 17 , and yoke parts  321 - 323  are rigidly connected to one another, such as by adhesion or clamping. 
   What was said about stators  11  according to  FIGS. 2 and 3  also applies to stators  31  in  FIG. 4 and 17 , namely, that they are able to be designed to have a different number of poles and a different number of modules. Here too, it is basically true that a stator having six, twelve or eighteen poles  33  is assembled preferably from only two identical modules  34 ,  35 , whereas a stator having three, nine or fifteen poles  33  is in each case assembled from three modules  34 ,  35 ,  36 , two or three modules being identical. Here too, higher numbers of poles are possible. 
     FIG. 6  shows a module  34  of a stator  31 , which is modified, compared to module  34  in  FIG. 5 , in so far as yoke part  321  has axially extending cutouts  37  and axially extending projections  38 . Corresponding to the number of poles  33 , there are three cutouts  37  and three projections  38 , the projections  38  completely covering the axial protruding regions of pole cores  331  beyond yoke part  321 , and ending approximately flush with them. Cutouts  37  on the one hand, and projections  38  on the other hand, are correspondingly offset to one another by a circumferential angle of 120°. Cutouts  37  are shaped in such a way that projections  38  may be inserted into them in a form locking manner. Two identical modules  34  are axially fit together to form stator  31  by having axes rotated with respect to each other by 180°, projections  38  of the one module  34  are inserted into cutouts  37  of the other module in a form locking manner. By this alternative separation of magnetic yoke  32  into the two identical yoke parts  321 , and by thereby obtained projections  38  on yoke part  321 , which in the circumferential direction protrude a little beyond pole cores  331 , it is avoided that, after winding of module  34  with the pole windings, during modules  34  being fit together, the pole windings slip off partially from pole cores  331  and disturb the fitting procedure, as may occur in modules  34  that were shown and described in  FIG. 5 . 
   In the stator shown in  FIG. 7  in exploded representation, in  FIG. 8  in a top view and in  FIG. 9  in section, for a three-phase internal-rotor motor, the two modules  34  and  35  are basically developed as in  FIG. 6 . The two yoke parts  321  and  322  again have cutouts  37  and projections  38 , the axial depth of cutouts  37 , however, being dimensioned smaller than in module  34  in  FIG. 6 . Projections  38 , which are inserted in a form locking manner into cutouts  37  when modules  34 ,  35  are assembled, are correspondingly shorter. In order to counter the above mentioned problem of the sliding off of the pole windings from pole cores  331 , the radial core height of pole cores  331  in its end sections that still extend beyond projections  38  is steadily tapered, the slanting surface  39  created thereby extending from the core end at the yoke part end to the core end at the pole shoe end. The tapering of the end sections of pole cores  331  extending beyond projections  38 , and the slanting surfaces  39  created thereby are particularly easy to see in the sectional representation in  FIG. 9 . The advantage of this constructive embodiment is that yoke parts  321 ,  322  have a greater axial crosspiece width at the foot of cutout  37 , and therefore modules  34 ,  35  are more favorably designed for manufacture by pressing. 
   In module  34  shown in  FIG. 10 , an axial offset separation of the yoke parts is omitted, and the identically formed modules  34  are assembled in a planar manner, using their parallel ring-shaped end faces. The axial width of yoke part  321  is the same in each module  34 . In order to counter the problem mentioned, of the sliding off of the pole winding in the protruding region of poles  33  beyond yoke part  321 , pole cores  331  in this protruding region are again steadily reduced in their radial core height. Since this protruding region forms half the axial length of poles  33 , slanting surface  39  thus created is substantially flatter than in the embodiment of module  34  or  35  in  FIG. 7-9 . 
   If stator  31  shown in  FIG. 17  is assembled from the three modules  34 - 36 , which are developed as shown in  FIG. 17 , and, in these modules, the regions of poles  33  protruding beyond yoke parts  321 - 323  are developed to have tapering radial core height, as shown in  FIG. 10-12 , then, deviating from outer modules  34 ,  35 , in middle module  36 , poles  33  in both protruding regions protruding symmetrically beyond yoke part  323  are provided with the described slanting surfaces  39  created by the tapering of the pole cores. 
     FIG. 13  shows a stator  31  which, compared to the stator described in conjunction with  FIG. 4 , is modified only to the extent that poles  33  are designed without pole shoes  332 . For winding this stator  31 , the pole windings are developed as prefabricated ring coils, like the one shown in  FIGS. 15 and 16 . The ring coils are pushed onto pole cores  331  and secured from sliding off using suitable mechanical means. As for the rest, we refer to the description of stator  31  as in  FIG. 4 , the same components being marked in  FIG. 13  by the same reference symbols as in  FIG. 4 . 
   In module  34  shown in  FIG. 14-16  for such a stator  31 , an example is shown for the means for the mechanical localization of pole winding  40  on pole shoe-less poles  33 . Each pole core  331  of poles  33  has at its one axial end, which axially protrudes beyond yoke part  321 , a concave arching  41 , in which pole winding  40  is held.  FIGS. 15 and 16  show in the light of a pole winding  40  how it is mounted. Pole winding  40 , that was prefabricated as a ring coil, is set into the arching  41 , and is then swiveled in arrow direction  42  in  FIG. 16  over pole core  331 , an axial clamping force being created which fixes pole winding  40 , using force locking, on the other axial end of pole core  331  that is not provided with an arching  41 . A certain clamping effect may also be achieved at the long sides of pole cores  331 . As for the rest, module  34  shown in  FIG. 14  is equivalent to module  34  shown in  FIG. 13 .