Abstract:
In a unipolar transverse flux machine, to attain a modular structure favorable in terms of production, the stator and the rotor each have the same number of identical stator modules and rotor modules. Each stator module includes an annular coil, disposed coaxially to the rotor shaft, and U-shaped stator yokes fitting over the annular coil. To achieve a high static torque, each rotor module comprises two rotor rings with external toothing, and the rotor rings surround two radially oppositely magnetized permanent magnet rings, which in turn are seated on a common flux-conducting element, which is formed for instance by the rotor shaft produced from ferromagnetic material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a 35 USC 371 application of PCT/DE 02/02825 filed on Aug. 1, 2002. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention is directed to an improved unipolar transverse flux machine. 
   2. Brief Description of the Prior Art 
   A known unipolar transverse flux machine is disclosed in European Patent Disclosure EP 0 544 200 A1 and refaced to in that publication as a hybrid synchronous machine with transverse magnetic flux. In this machine, the toothing of each rotor ring has one row of teeth extending along the outer circumference of the rotor ring, remote from the rotor axis, and another set of teeth extending along the inner circumference of the rotor ring, oriented toward the rotor axis, both rows having the same tooth pitch. The rows of teeth on each rotor ring are offset from one another by one tooth pitch. The yoke spacing on the stator corresponds to the tooth pitch of an inner or outer row of teeth, so that an outer tooth of one rotor ring and an inner tooth of the other rotor ring are always located simultaneously under one stator yoke. The two rotor modules, each comprising two rotor rings and one permanent-magnetic member for generating a radial magnetic flux in opposite directions in the rotor rings, are firmly fastened, on the sides remote from one another in the axial direction of the rotor, to a rotor body that is braced on the housing via rotary bearings. Each permanent-magnetic member is formed by a permanent magnet ring fastened between the rotor rings, which is magnetized unipolarly in the direction of the rotor axis. The stator yokes of each stator module that are received by the housing are U-shaped, and with their yoke legs oriented parallel to the rotor axis they fit over the inner and outer rows of teeth of the two rotor rings of the rotor modules. In each stator module, the circular annular coil, disposed concentrically to the rotor axis, passes through the stator yokes at the base of the yoke; that is, it is located in the region between the annular face of the outer rotor ring, pointing away from the rotor body, and the crosspiece of the stator yokes. 
   Transverse flux machines with permanent magnet excitation are known from the literature, such as Michael Bork,  Entwicklung und Optimierung einer fertigungsgerechten Transversalflussmaschine, Diss,  82 , RWTH Aachen [Development and Optimization of a Transverse Flux Machine Suitable for Production, Dissertation No. 82, Rheinland-Westfalen Technical University in Aachen], Shaker Verlag, Aachen, 1997, page 8 ff. The circularly wound stator winding is surrounded by U-shaped yokes of soft iron, which are disposed at twice the pole spacing in the direction of rotation. The open ends of these U-shaped yokes are aimed at the air gap between the stator and the rotor and form the poles of the stator. Facing them, tiny permanent magnet plates are disposed such that the two tiny plates that face the poles of a stator yoke have opposite polarity. For short-circuiting the permanent magnets, which upon rotor rotation are sometimes located between the poles of the stator and have no ferromagnetic short circuit, short-circuit elements are disposed in the stator. They prevent the flux of the permanent magnets from scattering via the yoke legs and the annular coil and lessening the effectiveness of the stator flux concatenation from attenuation of the stator flux. Thus the short-circuit elements lead to a marked enhancement of the performance of the machine. 
   In a unipolar transverse flux machine of the type defined at the outset, it has already been proposed (in German Patent Disclosure DE 100 39 466) that the toothing of the rotor rings be provided solely on the outer circumference of the rotor rings, facing away from the rotor axis, and that the stator yokes in the stator module be disposed such that one yoke leg of the stator yokes faces one rotor ring, while the other yoke leg of the stator yokes faces the other rotor ring, each with radial gap spacing. Between successive stator yokes in the direction of rotation of the rotor, a respective short-circuit element is disposed, which extends axially past both rotor rings and faces each of them with the same radial gap spacing. The permanent-magnetic member for generating a magnetic flux extending radially in opposite directions in the rotor rings is formed by a permanent magnet ring, which is fastened between the two rotor rings and is unipolarly magnetized in the axial direction of the rotor. A unipolar transverse flux machine of this kind has the advantage of simple modular construction, with which any desired number of branches of the machine can be achieved by adding or subtracting identically embodied stator modules and rotor modules, or in other words can be constructed in modular fashion. As the number of modular units, each composed of one stator module and one rotor module, increases, the concentricity of the machine is improved, and an initially indexing-like behavior of the machine changes over to continuous concentricity without ripples in the course of the moment. Since the total moment of the machine is the sum of the proportional moments of the module units, the total moment of the machine can be adapted easily to existing requirements. 
   SUMMARY AND ADVANTAGES OF THE INVENTION 
   The unipolar transverse flux machine of the invention has the advantage of greater static torque, with the same magnet volume of the permanent-magnetic member. With unchanged dimensions and the same design of the unipolar transverse flux machine, compared to the last unipolar transverse flux machine described in the previous paragraph, the average torque is thus increased. 
   By means of the provisions described, advantageous refinements of and improvements to the unipolar transverse flux machine are possible. 
   In an advantageous embodiment of the invention, the flux-conducting element joining the two permanent magnet rings to one another is formed by a hollow cylinder of ferromagnetic material, which is seated on the rotor shaft in a manner fixed against relative rotation and receives the two permanent magnet rings in a manner fixed against relative rotation. The rotor shaft is made from magnetically nonconductive material. 
   In a preferred embodiment of the invention, the flux-conducting element is formed directly by the rotor shaft itself, to which the two permanent magnet rings are attached. By the elimination of the separate flux-conducting element, the expense for components is reduced, but in that case there is the necessity of making the rotor shaft of ferromagnetic material. 
   In an advantageous embodiment of the invention, in a multi-branched version of the unipolar transverse flux machine, that is, in which a plurality of stator modules are seated on the ferromagnetic rotor shaft, the rotor shaft is subdivided into shaft portions, each extending across one rotor module, and solid disks of magnetically nonconductive material are disposed between the shaft portions. Shaft portions comprising solid disks result in a torsion-proof shaft. By means of these magnetically insulating solid disks, the rotor modules of the individual modular units or branches of the unipolar transverse flux machine are magnetically decoupled, so that no mutual magnetic influence can occur. 
   The same effect is attained in a multi-branched version of the unipolar transverse flux machine with a ferromagnetic rotor shaft, if in an alternative embodiment of the invention the axial spacings between the rotor modules are made greater than the axial width of the rotor modules. The optimum for the axial spacings is achieved when the magnetic influence between the rotor modules becomes negligibly slight. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in further detail herein below, with reference to the drawings, in which: 
       FIG. 1  is a detail, in perspective, of a two-branch, 32-pole unipolar transverse flux machine, shown partly schematically; 
       FIG. 2 , a perspective elevation view of a fragment of a unipolar transverse flux machine that is modified compared to  FIG. 1 ; and 
       FIG. 3 , a graph showing the course of the torque in the unipolar transverse flux machine of  FIG. 1  or  FIG. 2 , in comparison to a known machine. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The unipolar transverse flux machine shown in perspective in  FIG. 1 , partly cut away, has a machine housing  10  with a stator  11  retained on it as well as a rotor  12  revolving in the stator  11 ; the rotor is seated in a manner fixed against relative rotation on a rotor shaft  13  supported in the machine housing  10 . The rotor  12  has a plurality of rotor modules  15 , and the stator  11  has an equal number of stator modules  14 . The rotor modules  15  are mounted axially one after the other directly on the rotor shaft  13  in a manner fixed against relative rotation, and the stator modules  14  are secured to the machine housing  10  axially one after another in radial alignment with the associated rotor module  15 . The number of modular units each including one stator module  14  and one rotor module  15  is determined by the selected number of branches of the unipolar transverse flux machine, which in the exemplary embodiment of  FIG. 1  has two branches and accordingly has two modular units. However, it can also be single-branched or with three or more branches. The stator modules  14  and rotor modules  15  and thus the individual modular units are embodied identically, so that the unipolar transverse flux machine has a modular design, and by adding or subtracting modular units, it is no problem to make adaptations to existing requirements with regard to power and torque. 
   As shown in perspective in  FIG. 1 , in the two-branched version of the unipolar transverse flux machine, the two rotor modules  15 , seated axially side by side on the rotor shaft  13 , of the two modular units are oriented in alignment with one another, and the two stator modules  14 , disposed axially side by side in the machine housing  10 , of the two modular units are rotated 90° electrically from one another, which is equivalent to one-half the pole spacing; that is, in the 32-pole version of the machine, this means a three-dimensional offset angle of 5.625° in the direction of rotation. Alternatively, it is possible to orient the two stator modules  14  axially in alignment with one another and to rotate the rotor modules  15 , seated on the rotor shaft  13 , by the aforementioned angle of 90° electrically from one another. 
   If the unipolar transverse flux machine is embodied with more than two branches, or in general with m branches, where m is a whole number greater than 2, then the stator modules  14  disposed axially one after the other on the stator  11  should be shifted electrically relative to one another by an angle of 360°/m, or in other words, in a three-branched machine with three modular units, by 120° electrically. 
   Each rotor module  15  has two coaxial, toothed, ferromagnetic rotor rings  16 ,  17  and one permanent-magnetic member  18 , which generates a magnetic flux that extends radially in opposite directions in the rotor rings  16 ,  17 , as indicated in  FIG. 2  by the arrows  19 ,  20 . The permanent-magnetic member  18  comprises two permanent magnet rings  26 ,  27 , which are each surrounded on the outside by a respective rotor ring  16  and  17 , and one flux-conducting element  29 , which connects the two permanent magnet rings  26 ,  27  to one another. In the exemplary embodiment of FIG.  1 , the flux-conducting element  29  is formed by the rotor shaft  13 , which is made of ferromagnetic material and to which the two permanent magnet rings  26 ,  27  are attached, spaced apart axially from one another. Each permanent magnet ring  26 ,  27  is magnetized radially; the direction of magnetization is opposite in the two permanent magnet rings  26 ,  27 , as indicated in  FIG. 2  by the north pole N and south pole S of the two permanent magnet rings  26 ,  27 . If more than one rotor module  15  is seated on the rotor shaft  13 , or in other words if the unipolar transverse flux machine is two-branched, as in  FIG. 1 , or has more than two branches, then it is advantageous for the individual rotor modules  15  to be decoupled by means of solid disks of magnetically nonconductive material disposed in the rotor shaft  13 . In  FIG. 1 , one such magnetically insulating solid disk  30  is inserted between the portions, each carrying one rotor module  15 , of the rotor shaft  13 . Alternatively, the spacing between the rotor modules  15  seated on the one-piece rotor shaft  13  can be increased to such an extent that the magnetic influence of the individual branches on one another is negligible. 
   Each rotor ring  16 ,  17  is toothed with a constant tooth pitch on its outer circumference, facing away from the rotor shaft  13 , so that the teeth  22 , each separated from one another by a tooth gap  21 , of the resultant row of teeth have the same angular spacing from one another. The teeth  22  on the rotor ring  16  and on the rotor ring  17  are aligned axially with one another. The rotor rings  16 ,  17  with the teeth  22  integrally formed onto them are laminated and are preferably assembled from identical stamped pieces of sheet metal, which rest against one another in the axial direction. 
   Each stator module  14 , concentrically surrounding one rotor module  15  with radial spacing, has an annular coil  23  disposed coaxially with the rotor shaft  13  and also has U-shaped stator yokes  24 , which fit over the annular coil  23 , and short-circuit elements  25 , which are located below the annular coil  23 . The also-laminated stator yokes  24  and short-circuit elements  25 , which are both put together from stamped sheet-metal pieces to form sheet-metal laminations, are attached to the machine housing  10  with a yoke or short-circuit element spacing corresponding to the tooth pitch on the rotor module  15 , so that they have the same angular spacing from one another as the teeth  22  of the rotor rings  16 ,  17 . The stator yokes  24  are disposed here in such a way that one yoke leg  241  is radially aligned with one rotor ring  16 , and the other yoke leg  241  is radially aligned with the other rotor ring  17  of the associated rotor module  15 , and the free end faces  244  of the yoke legs that form the pole faces are located facing the respective rotor ring  16  and  17  with radial gap spacing. In the exemplary embodiment, the end faces of the yoke legs have the same axial width as the rotor rings  16 ,  17 . However, end faces of the yoke legs that protrude axially on one or both sides past the rotor rings  16 ,  17  are advantageous. The short-circuit elements  25  are each disposed between two stator yokes  24  in the direction of rotation of the rotor  12  and are offset from the stator yokes  24  by one-half the yoke or short-circuit element spacing, or one pole spacing. The short-circuit elements  25  extend parallel to the rotor shaft  13  to beyond both rotor rings  16 ,  17  and face the rotor rings with the same radial gap spacing as the stator yokes  14  do. 
   In the exemplary embodiment of  FIG. 1 , the short-circuit elements  25  are for instance C-shaped, each with two legs radially facing a respective rotor ring  16 ,  17  and with a crosspiece joining the legs that extends parallel to the rotor shaft  13  on the inside, facing toward the rotor shaft  13 , of the circularly embodied annular coil  23 . In order to save material or to gain clearance, alternative shapes for the short-circuit elements  25  can be selected, such as rectangular or trapezoidal. Because of this embodiment of the short-circuit elements  25  and stator yokes  24 , the circular annular coil  23  passes between the stator yokes  24  at the base of the yoke legs and onward past each short-circuit element  25 . The axial width of the end faces of the legs of the short-circuit elements  25  here is equal to the axial width of the rotor rings  16 ,  17 . However, the legs of the short-circuit elements  25  can also protrude axially past the rotor rings  16 ,  17 . 
   In  FIG. 3 , a graph is shown as an example with four courses of moment over an electrical angle of 180°. Curve a shows the course of the static torque of the unipolar transverse flux machine of  FIG. 1 , and curve b shows the course of the static torque of a unipolar transverse flux machine as it occurs, given the same design, in the unipolar transverse flux machine of DE 100 39 466, in which the permanent-magnetic member  18  is formed not by two permanent magnet rings  26 ,  27  magnetized radially in opposite directions but instead by one permanent magnet ring, disposed between the rotor rings  16 ,  17  and magnetized in the axial direction of the rotor  12 . It can be seen clearly that the average torque is increased, in the machine described here. 
   Curves c and d represent the course of the resting moment of the unipolar transverse flux machine of  FIG. 1  (curve c) and of the aforementioned known unipolar transverse flux machine (curve d). Once again, an increase in the resting moment can be seen. 
   In the modified 32-pole unipolar transverse flux machine, shown only in fragmentary form in  FIG. 2 , the two permanent magnet rings  26 ,  27  are not mounted directly on the rotor shaft  13  but instead are mounted in a manner fixed against relative rotation, with equal axial spacing from one another, on a hollow cylinder  28  of ferromagnetic material, which in turn is received by the rotor shaft  13  in a manner fixed against relative rotation. Because of this hollow cylinder  28 , which forms the flux-conducting element  29  of the permanent-magnetic member  18  between the two permanent magnet rings  26 ,  27  that are magnetized radially in opposite directions, a magnetically conductive embodiment of the rotor shaft  13  can be dispensed with. In the case of a multi-branched version of the unipolar transverse flux machine, the individual rotor modules  15 , seated on the one-piece rotor shaft  13  of magnetically nonconductive material, are magnetically well decoupled and can be disposed close together, in order to attain a low axial structural depth of the unipolar transverse flux machine. 
   The foregoing relates to preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.