Abstract:
A rotor for an electric motor which includes permanent magnets is formed so that the possibility of demagnetization of the permanent magnets is reduced. The rotor has at least one permanent magnet embedded in a magnetically conductive rotor core, and at least one flux path in the rotor core, for a magnetic flux caused by a magnetic stator field generated by a stator of the electric motor. The rotor core is realized, with respect to at least one of the flux paths, with a magnetically conductive shunt that bridges at least one of the permanent magnets for the magnetic flux that is caused by the stator field.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the priority, under 35 U.S.C. §119, of German patent application DE 10 2016 207 800.3, filed May 4, 2016; the prior application is herewith incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    The invention relates to a rotor for an electric motor. The invention additionally relates to an electric motor. Furthermore, the invention relates to a device for driving a vehicle, and to a vehicle. 
         [0003]    Rotors for electric motors are disclosed in patent application publication No. US 2010/0171386 A1 (see, German published DE 11 2008 001 333 T5) and in commonly assigned German published patent application DE 10 2012 010 993 A1. Those rotors have a plurality of embedded permanent magnets, of which, when viewed in an end-face view of the rotor, at least two permanent magnets are each oriented in such a way that one end is radially closer to a circumference of the rotor than an opposite end. The foregoing publications are herewith incorporated by reference. 
         [0004]    Such rotors are a constituent part of motors having internally mounted permanent magnets. These motors can deliver a comparatively high torque, or a comparatively high efficiency, and are therefore used in preference, for example as drive motors, for hybrid vehicles and electric vehicles, in which a high drive power must be output. A magnetic stator field generated in the stator of the motor acts, as an inverse magnetic field (opposing field), on these permanent magnets. If such an opposing field is too great, this can result in an irreversible demagnetization of the magnets, and consequently in a failure of the motor. 
         [0005]    Hitherto, it has been sought to set a high coercive field strength of the permanent magnets against the generated opposing field. This is achieved by alloying the permanent magnets with rare-earth elements such as, for example, dysprosium (Dy) and/or neodymium (Nd) and/or terbium (Tb). The temperature resistance of the permanent magnets is also thereby increased. However, such rare-earth elements are very expensive. 
         [0006]    In order to reduce costs, it is proposed in US 2010/0171386 A1 to divide the permanent magnets into a plurality of magnetic regions that have differing coercive field strengths. In this case, the region having the greatest coercive field strength, i.e. having the highest proportion of rare earths, is positioned such that it is exposed to the greatest opposing field load. In the case of the regions having a lesser opposing field load, the proportion of rare earths is reduced accordingly. In this way, the expensive rare earth elements are thus only used to a greater extent where they are actually needed. 
         [0007]    According to the above-mentioned DE 10 2012 010 993 A1, a further cost reduction is to be achieved in that, when viewed in an end-face view of the rotor, the end of the permanent magnets that is radially closer to the circumference of the rotor is wider than the opposite end of the permanent magnets. 
         [0008]    In the case of the prior art arrangements, the opposing field always permeates the permanent magnets in the rotor, such that there continues to be the possibility of demagnetization of the permanent magnets. 
       SUMMARY OF THE INVENTION 
       [0009]    It is accordingly an object of the invention to provide a rotor for an electric motor which overcomes the above-mentioned and other disadvantages of the heretofore-known devices and methods of this general type and which further decreases the possibility of demagnetization of the permanent magnets in a rotor of an electric motor. 
         [0010]    With the foregoing and other objects in view there is provided, in accordance with the invention, a rotor for an electric motor, the rotor comprising: 
         [0011]    a magnetically conductive rotor core and at least one permanent magnet embedded in the rotor core, the rotor core having at least one flux path defined therein for conducting a magnetic flux caused by a magnetic stator field generated by a stator of the electric motor; 
         [0012]    at least one magnetically conductive shunt formed in the rotor core for the at least one flux path, the at least one magnetically conductive shunt bridging the at least one permanent magnet for the magnetic flux caused by the stator field. 
         [0013]    In other words, the objects of the invention are achieved by a rotor for an electric motor, comprising at least one permanent magnet embedded in a magnetically conductive rotor core, and at least one flux path, realized in the rotor core, for a magnetic flux caused by a magnetic stator field generated by a stator of the electric motor, wherein the rotor core is realized, with respect to at least one of the at least one flux paths, with at least one magnetically conductive shunt that bridges at least one of the at least one permanent magnets for the magnetic flux that is caused by the stator field. 
         [0014]    According to the invention, in this way the permanent magnet, or the permanent magnets, of the rotor of the electric motor are disposed outside of the flux paths provided in the rotor core for the magnetic flux that is caused in the rotor core by the magnetic field caused by the stator, i.e. the stator field. A permanent magnet embedded in the rotor core in the case forms, within the rotor core, a region of low magnetic conductivity, around which the magnetic flux resulting from the stator field is guided by one or more magnetically conductive shunts, i.e. the permanent magnet is bridged by the magnetically conductive shunt or shunts for the magnetic flux caused by the stator. Consequently, the stator field cannot act, as an opposing field, such that it has a demagnetizing effect on the permanent magnet or permanent magnets. The latter can therefore be realized with a lesser coercive field strength than would be required to prevent demagnetization of the permanent magnet or permanent magnets if the latter were to become permeated by the opposing field. 
         [0015]    Advantageously, the at least one magnetically conductive shunt simultaneously forms a magnetic conductor for the magnetic flux of the permanent magnet; in particular, the at least one magnetically conductive shunt is directly adjacent to at least one magnetic pole—magnetic north pole and/or south pole—of the permanent magnet. 
         [0016]    The invention thus makes it possible to use permanent magnets having a further reduced proportion of rare earths, corresponding to the reduction of the required coercive field strength. In a marginal case it is even possible to dispense entirely with the addition of rare-earth elements in the material of the permanent magnets; it is thereby possible to achieve a further reduction in cost for the production of the permanent magnets. 
         [0017]    In accordance with an added feature of the invention, a direction of magnetization of at least one of the at least one permanent magnets is oriented substantially (i.e., either exactly or at least almost) orthogonally to the direction of the magnetic flux, caused by the stator field, in at least one flux path adjacent to the at least one of the at least one permanent magnets, in particular in at least one shunt of this flux path. In other words, the direction of the magnetic flux caused by the stator field, for which the said flux path is realized, is at least substantially orthogonal to the direction of magnetization of the respective permanent magnet. Consequently, the stator field does not act as an opposing filed for the permanent magnet, and demagnetization is prevented in an effective manner. 
         [0018]    It should be noted at this point that a motor having a stator and a rotor is known from U.S. Pat. No. 9,273,691 B2 and its counterpart German published patent application DE 10 2012 021 109 A1 (these publications are herewith incorporated by reference). That stator comprises an armature core having a plurality of teeth that extend radially inward, and a segment conductor wire that is wound around each tooth of the armature core. The rotor comprises first and second rotor cores, a ring magnet as a field magnet, and a connecting magnet as an integrated auxiliary magnet. 
         [0019]    The first rotor core comprises a disk-type first core base, and a plurality of first hook-type magnet poles, which are disposed at equal distances on a peripheral portion of the first core base. In this case, each of the first hook-type magnet poles projects outward in the radial direction of the rotor, and comprises a first elongated portion, which extends along an axial direction of the rotor. The second rotor core comprises a disk-type second core base, and a plurality of second hook-shaped magnet poles, which are disposed at equal distances on a peripheral portion of the second core base. In this case, each of the second hook-type magnet poles projects outward in the radial direction, and comprises a second elongated portion, which extends along the axial direction. The first and second hook-type magnet poles are disposed alternately along a circumferential direction of the rotor in a state in which the first and the second core base are mutually opposite in the axial direction. 
         [0020]    The field magnet is disposed between the first and the second core base in the axial direction, and is magnetized along the axial direction such that the first hook-type poles act first poles—here: north poles—and the second hook-type poles act as second poles—here: south poles. A neodymium magnet may be used as a field magnet. 
         [0021]    The auxiliary magnet comprises at least two or more inter-pole magnet portions, which are realized so as to be integral with connecting portions, wherein each of the inter-pole magnet portions is disposed in a cavity between respectively one of the first hook-type poles and respectively one of the second hook-type poles, and is magnetized in the circumferential direction. It is explicitly described that the auxiliary magnet is realized from first and second inter-pole magnet portions, which are disposed between the first hook-type poles and the second hook-type poles, and connecting portions, which connect axial end portions of these inter-pole magnet portions. The connecting portions are disposed alternately at the first end side and at the other end side of the rotor, in each cavity between the hook-type poles. In this case, a zigzag shape is produced along the hook-type poles by the inter-pole magnet portions and the connecting portions. The first and the second inter-pole magnet portions are magnetized in the circumferential direction in such a manner that parts thereof, which face toward the first and second hook-type poles, have the same polarities. 
         [0022]    In the case of this configuration, the directions of the magnetizations, both of the field magnets and of the auxiliary magnet, are oriented orthogonally to the direction of a magnetic field, generated by the stator, coming out of the teeth of the armature core. However, no measures are described to avoid the situation in which the magnetic field generated by the stator, as an opposing field, permeates the magnets—the field magnet and also the auxiliary magnet—and thereby causes demagnetization, both of the field magnet and of the auxiliary magnet. 
         [0023]    In the case of a further preferred embodiment of the rotor according to the invention, a plurality of permanent magnets and a plurality of magnetically conductive shunts are provided, wherein at least some of the permanent magnets and at least some of the magnetically conductive shunts are arranged in a grouped combination to form respectively one permanent magnet group. 
         [0024]    Advantageously in this case, each permanent magnet group, respectively, is realized in such a manner and in order to be used like a single permanent magnet in a conventional rotor, e.g. instead of the permanent magnets having the reference Mb in FIG. 10( a ) of the above-mentioned publication US 2010/0171386 A1, or the permanent magnets having the references Mc1, Mc2 and Mc3 in FIG. 11( a ) of the publication. Although the individual permanent magnet groups, of which, in this example, respectively one is used to replace respectively one of the permanent magnets Mb, Mc1, Mc2 and Mc3, are thus disposed entirely in the rotor flux paths there for the magnetic flux caused by the stator, owing to the design according to the invention the individual permanent magnets of the permanent magnet groups are nevertheless not permeated by this flux; instead, this flux is routed through the at least one shunt of each permanent magnet group. Advantageously in this case, the permanent magnet groups, with the configuration of the rotor core being otherwise unchanged—apart from the structure of the rotor core in the area immediately surrounding the permanent magnets—can replace the conventional permanent magnets in the conventional arrangements that are permeated by the stator field, whereby advantages of these arrangements, i.e. rotor configurations, can be assumed directly. Within the individual permanent magnet groups, the magnetically conductive shunts for the magnetic flux caused in the rotor core by the stator preferably simultaneously form magnetic conductors for the magnetic flux of the permanent magnets of the respective permanent magnet group. 
         [0025]    According to a further preferred embodiment of the rotor according to the invention, the permanent magnets arranged in combination to form respectively one permanent magnet group are ranged almost rectilinearly in succession, wherein, in particular, the permanent magnets within this row have a direction of magnetization that in each case is reversed from one of the permanent magnets to the next, preferably a direction of magnetization that in each case is reversed by at least almost 180°. This ranging in a rectilinear row favors the creation of an oblong-rectangle cross-sectional structure of the permanent magnet group—in particular as viewed in a cross section through the rotor core in a radially oriented cross-sectional plane—and consequently simple replacement of conventional permanent magnets by a permanent magnet group according to the invention in the realization of the rotor core. 
         [0026]    In a further preferred design of the rotor according to the invention, permanent magnets, in particular respectively one of the permanent magnets, and magnetically conductive shunts, in particular respectively one of the magnetically conductive shunts, are disposed alternately in respectively one of the permanent magnet groups; preferably, the permanent magnets and magnetically conductive shunts are disposed alternately in succession along the at least almost rectilinear row. There is thus provided, for each of the permanent magnets, on each of the two sides in the direction of the row, a respective shunt, via which, on the one hand, the flux from the stator is routed; on the other hand, the two shunts adjacent to respectively one of the permanent magnets route the flux of the permanent magnet. This produces a particularly advantageous configuration for the aforementioned intended purpose. 
         [0027]    In accordance with an additional feature of the invention, at least one recess is formed in the rotor core, forming a magnet pocket for accommodating the at least one embedded permanent magnet, preferably respectively one of the at least one magnet pockets for respectively one of the at least one permanent magnets, wherein each of the at least one magnet pockets is realized with respectively at least one magnetically non-conductive spatial region that, with respect to a direction of magnetization of the at least one permanent magnet when this at least one permanent magnet is in a proper mounting position in the at least one magnet pocket, is disposed at the side of this permanent magnet. 
         [0028]    In particular, walls of the individual magnet pockets are closely adjacent to magnet poles of the permanent magnets accommodated therein, so as to ensure good conduction of the magnetic flux of the permanent magnets into the rotor core. The walls of the magnet pockets in this case are formed by the magnetically conductive shunts, and are preferably integral with the rotor core. At the same time, the magnetically non-conductive spatial regions disposed, at least one per permanent magnet, at the side of the individual permanent magnets—realizing a type of magnetically non-conductive “protective spaces” at the side of the permanent magnets—on the one hand prevent the permanent magnet from being permeated, transversely through the permanent magnets, i.e. orthogonally in relation to the direction of magnetization of the permanent magnets, by the flux generated by the stator. On the other hand, these magnetically non-conductive spatial regions serve to avoid magnetic short circuits for the flux of the permanent magnets. 
         [0029]    According to a preferred development of the rotor according to the invention, at least one of the at least one magnet pockets is realized with, in particular, hook-type shapes for guiding and/or holding the at least one permanent magnet in the magnet pocket and for mechanical support and/or load relief in the rotor core via the at least one permanent magnet. In particular, these hook-type shapes are formed onto the magnetically conductive shunts and project into the magnetically non-conductive spatial regions. This achieves the effect that the hook-type shapes prevent the permanent magnets from slipping into the magnetically non-conductive spatial regions, such that the magnetically non-conductive spatial regions can be realized as recesses filled with gas and/or fluid and/or, preferably, air, thereby saving costs and weight. Advantageously, the hook-type shapes encompass the individual permanent magnets and support them in the radial direction of the rotor, or in a direction in which force components of centrifugal forces act on them when the rotor is in operation. As a result, not only are the permanent magnets protected against the influence of the centrifugal forces in the rotor core, but it also becomes possible to relieve the load of the centrifugal forces in the rotor core via the shunts and the permanent magnets; in particular, portions of the rotor core that are disposed radially outside of a mounting position of a permanent magnet and/or of a permanent magnet group are supported, via the shunts and the permanent magnets, against the action of the centrifugal forces. This increases the mechanical strength of the rotor. 
         [0030]    There is also provided, in accordance with the invention, an electric motor, which includes a rotor as described and claimed. 
         [0031]    The objects of the invention are also achieved by a means for driving a vehicle, in particular a road vehicle, which comprises an electric motor of the type previously described and/or a rotor as described and claimed. 
         [0032]    Finally, there is also provided, in accordance with the invention, a vehicle, in particular a road vehicle, which comprises a traction device as described, in the form of an electric motor with the above-summarized rotor. 
         [0033]    The corresponding electric motor lends itself to inexpensive production, particularly in large-scale motor-vehicle production, with a high output being achievable at the same time. 
         [0034]    Other features which are considered as characteristic for the invention are set forth in the appended claims. 
         [0035]    Although the invention is illustrated and described herein as embodied in a rotor for an electric motor, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0036]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0037]      FIG. 1  shows, in a roughly schematic representation, a sector-shaped portion of an axial sectional view of a first example for a conventional electric motor having a conventional prior art permanent magnet; 
           [0038]      FIG. 2  shows, in a roughly schematic representation, an electric motor according to the invention having a first exemplary embodiment of a rotor according to the invention, as a modification according to the invention of the electric motor according to  FIG. 1 , likewise represented in a sector-shaped portion of an axial sectional view; 
           [0039]      FIG. 3  shows, in a roughly schematic representation, a sector-shaped portion of an axial sectional view of a second example for a conventional electric motor having two conventional permanent magnets in a so-called V arrangement; 
           [0040]      FIG. 4  shows, in a roughly schematic representation, an electric motor according to the invention having a second exemplary embodiment of a rotor according to the invention, as a modification according to the invention of the electric motor according to  FIG. 3 , likewise represented in a sector-shaped portion of an axial sectional view; 
           [0041]      FIG. 5  shows, in a roughly schematic representation, a sector-shaped portion of an axial sectional view of a third example for a conventional electric motor having two conventional permanent magnets in a so-called Q arrangement; and 
           [0042]      FIG. 6  shows, in a roughly schematic representation, a third exemplary embodiment of an electric motor according to the invention having a third exemplary embodiment of a rotor according to the invention, as a modification according to the invention of the electric motor according to  FIG. 5 , likewise represented in a sector-shaped portion of an axial sectional view. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    Referring now to the figures of the drawing in detail and first, particularly, to  FIG. 1  thereof, there is shown, identified by reference numeral  152 , a conventional electric motor, such as a motor as shown in similar form in US 2010/0171386 A1 (cf. FIGS. 8F, 10( a ) and, in particular, 14( a )), with a number of poles that is varied according to the principle. The electric motor  152  is represented, in roughly schematic form, in a sectional view along a radial plane, only a portion corresponding to one quarter of the total cross section being shown, for simplification. The electric motor  152  comprises a stator  151  and a rotor  150 , having a magnetically conductive rotor core  153  and a magnetically non-conductive rotor shaft  154 . An air gap  155  extends between the stator  151  and the rotor  150 , in the circumferential direction of a rotor core  153 , along the circumferential surface thereof, and into the plane of the drawing. 
         [0044]    A recess is formed in the rotor core  153 , extending in the axial direction of the rotor  150 , i.e. perpendicularly into the plane of the drawing. The recess has a rectangular cross section and, with a greater of its two cross-sectional dimensions, extends tangentially, i.e. in the circumferential direction, in relation to the rotor  150 . The recess forms a magnet pocket  156  and accommodates a cuboid permanent magnet  157 , which, in this simplified representation, completely fills the magnet pocket  156 . To this extent, the spatial arrangement of the permanent magnet  157  in the rotor core  153  of the electric motor  152  according to  FIG. 1  corresponds to that of the magnet Mf in FIG. 14( a ) of US 2010/0171386 A1. 
         [0045]    In  FIG. 1 , the magnetic flux, or the magnetic field, caused by a magnetization of the permanent magnet  157  is indicated, in direction and spatial propagation in the permanent magnet  157 , in the rotor core  153  and in the stator  151 , by arrows  158 . In the case of the illustrated arrangement, this magnetic flux, or this magnetic field  158 , caused by the permanent magnet  157  is directed away from the center of the rotor, i.e. away from a rotor shaft  154 , through the permanent magnet  157  and the rotor core  153 , via the air gap  155 , into the stator  151 . 
         [0046]    By contrast, the magnetic flux, or the magnetic field, caused by the stator  151  is indicated, in direction and spatial propagation in the permanent magnet  157 , in the rotor core  153  and in the stator  151 , by arrows  159 . In the case of the illustrated arrangement, this magnetic flux, or this magnetic field  159 , caused by the stator  151  is directed from the stator  151 , via the air gap  155 , into the rotor core  153 , and through the permanent magnet  157  to the center of the rotor, i.e. to the rotor shaft  154 . 
         [0047]    Thus, within the permanent magnet  157 , the magnetic fields, or magnetic fluxes, from the stator  151  and from the permanent magnet  157  are oriented counter to each other, i.e. the magnetic field  159  from the stator  151 , the stator field, forms an opposing field to the magnetic field  158  of the permanent magnet  157 . The opposing field can cause the permanent magnet  157  to become demagnetized if the magnetic field strength of the stator field is of a corresponding magnitude. 
         [0048]      FIG. 2  shows a first exemplary embodiment of an electric motor  102  according to the invention, with a first exemplary embodiment of a rotor  100  according to the invention as a modification according to the invention of the electric motor  152  which is illustrated in  FIG. 1 . Here, too, the assembly is illustrated in a highly schematic representation, in a sector-shaped portion of an axial sectional view. A stator  101  of the electric motor  102  is preferably identical in structure to the stator  151  of the electric motor  152  according to  FIG. 1  and it is also not illustrated in greater detail. The rotor  100  of the electric motor  102  is realized with a magnetically conductive rotor core  103  and a magnetically non-conductive rotor shaft  104 . An air gap  105  extends between the stator  101  and the rotor  100 , in the circumferential direction of the rotor core  103 , along the circumferential surface thereof and into the plane of the drawing. 
         [0049]    A recess  114  is formed in the rotor core  103 , extending in the axial direction of the rotor  100 , i.e. perpendicularly into the plane of the drawing. The recess  114  has a contour according to the invention. For this, within a region  106  of the sector-shaped portion of the axial sectional view of the rotor core  103  there is now disposed a permanent magnet group  107 , having a rectangular cross section, which is preferably at least almost the same as the cross section of the magnet pocket  156  according to  FIG. 1 , or which resembles the latter, and which, with a larger of its two cross-sectional dimensions, again extends tangentially, i.e. in the circumferential direction, in relation to the rotor  100 , extending in this tangential direction. 
         [0050]    The permanent magnet group  107  is realized with a linear row of permanent magnets  108  and magnetically conductive shunts  109  that is oriented in the direction of the greater of its two cross-sectional dimensions, i.e. in the tangential direction of the rotor  100 , respectively one of the permanent magnets  108  and respectively one of the magnetically conductive shunts  109  being disposed in mutual alternation in the direction of this row, beginning and ending with respectively one of the magnetically conductive shunts  109 . Each of the permanent magnets  108  is thus bordered on both sides, in the direction of the row, by respectively one of the magnetically conductive shunts  109 . In addition, the magnetizations of the permanent magnets  108  are oriented along the aforementioned tangential direction of the rotor  100 , i.e. in the direction of the said row, but rotated by 180° from respectively one of the permanent magnets  108  in the row to the next, such that, alternately along the row, respectively two magnetic north poles N and two magnetic south poles S face toward each other via respectively one of the magnetically conductive shunts  109 , and are connected in a magnetically conductive manner. In a modification, the permanent magnet group  107  may comprise magnets of differing sizes, or also a different number of magnets, e.g. also only two magnets. Also, the magnets may be positioned radially further inward or outward. 
         [0051]    The magnetically conductive shunts  109  between every two mutually facing magnetic north poles N of two permanent magnets  108  that succeed one another in the row then respectively form a common magnetic north pole of these two permanent magnets  108 , and in the example according to  FIG. 2  are respectively connected to, in particular integrally formed onto, a portion  110  of the rotor core  103  that faces radially outward, i.e. toward the air gap  105 , such that the magnetic field is directed from these common north poles N toward the air gap  105 , and thus toward the stator  101 . 
         [0052]    The magnetically conductive shunts  109  between every two mutually facing magnetic south poles S of two permanent magnets  108  that succeed one another in the row respectively form, correspondingly, a common magnetic south pole of these two permanent magnets  108 , and in the example according to  FIG. 2  are respectively connected to, in particular integrally formed onto, a portion  111  of the rotor core  103  that faces radially inward, i.e. toward the rotor shaft  104 , such that the magnetic field of the permanent magnets  108  leads from the direction of the rotor shaft  104  to these common south poles S. 
         [0053]    The spatial course of the magnetic field, or magnetic flux, caused by the permanent magnets  108  is symbolized by arrows  112 . 
         [0054]    The stator  101 , on the other hand, causes a magnetic field—stator field—or a magnetic field, that in  FIG. 2  is symbolized by arrows  113 . This magnetic field  113  forms a magnetic field that is directed contrary to the magnetic field, in the stator  101 , air gap  105  and rotor  100 , that is caused by the permanent magnets  108 , i.e. an opposing field. The opposing field  113  goes from the radially outwardly facing portion  110  of the rotor core  103 , i.e. toward the air gap  105 , via the magnetically conductive shunts  109 , to the radially inwardly facing portion  111  of the rotor core  103 , i.e. toward the rotor shaft  104 , without going through the permanent magnets  108 , i.e. it goes through the magnetically conductive shunts  109 , around the permanent magnets  108 . An influence of the opposing field  113  upon the permanent magnets  108  is thereby prevented, or at least reduced to such an extent that demagnetization of the permanent magnets  108  is thereby prevented. 
         [0055]    The recess  114  extending in the rotor core  103 , in the axial direction of the rotor  100 , i.e. perpendicularly into the plane of the drawing, extends along the radial cross-sectional plane in the rotor core  103  in a zigzag shape within the region  106  that has a rectangular cross section, and in so doing forms, firstly, air gaps  115  at end faces of the magnetically conductive shunts  109  of the permanent magnet group  107  that are oriented substantially radially, i.e. in a direction orthogonal to the tangential direction of the rotor  100 , secondly, magnet pockets  116  for accommodating the permanent magnets  108  of the permanent magnet group  107 , here, advantageously, respectively one magnet pocket  116  for respectively one permanent magnet  108 , and, thirdly, for each magnet pocket  116  respectively two magnetically non-conductive spatial regions  117 , which, with respect to the direction of magnetization of the permanent magnets  108  in their proper mounting position in the magnet pocket  116 , are disposed on both sides of this permanent magnet  108  and serve to guide flux at the side of the permanent magnets  108 . Following the zigzag-type extent of the recess  114 , succeeding one another in this sequence are an air gap  115 , a magnetically non-conductive spatial region  117 , a magnet pocket  116 , a magnetically non-conductive spatial region  117 , an air gap  115 , a magnetically non-conductive spatial region  117 , a magnet pocket  116 , a magnetically non-conductive spatial region  117 , an air gap  115 , etc., ending with an air gap  115 . The walls of the magnet pockets  116  in this case are formed by the magnetically conductive shunts  109 . The magnetically non-conductive spatial regions  117  cause both the stator field and the magnetic field of the permanent magnets  108 , or the associated magnetic fluxes, to be guided at a distance from the sides of the permanent magnets  108 . 
         [0056]    The magnet pockets  116  are bounded against the magnetically non-conductive spatial regions by hook-type shapes  118 , which are formed on, preferably integrally formed onto, the end faces of the magnetically conductive shunts  109 , bound these end faces on both sides in the tangential direction of the rotor  100 , and serve to guide and/or hold the permanent magnets  108  accommodated in the magnet pockets  116 . For this purpose, each of the permanent magnets  108  is accommodated between respectively two of the hook-type shapes  118  of each two adjacent, oppositely directed magnetically conductive shunts  109 , one of these magnetically conductive shunts  109  being connected to the radially outwardly facing portion  110  of the rotor core  103 , i.e. toward the air gap  105 , and the other of these magnetically conductive shunts  109  being connected to the radially inwardly facing portion  111  of the rotor core  103 , i.e. toward the rotor shaft  104 . In this way, not only are the permanent magnets  108  held in the magnet pockets  116  by form closure and force closure, but the radially outwardly facing portion  110  of the rotor core  103 , i.e. toward the air gap  105 , is also mechanically supported, in particular against centrifugal forces during operation, via the permanent magnets  108 , on the radially inwardly facing portion  111  of the rotor core  103 , i.e. toward the rotor shaft, and the mechanical strength of the rotor  100  is thus increased. 
         [0057]    Adjoining the recess  114  at both of its ends—as viewed in the tangential direction of the rotor  100 —at narrow ends of the region  106 , and thus adjoining the permanent magnet group  107 , there are lateral, triangular air spaces  119 , extending in the axial direction of the rotor  100 , each one of which is respectively connected to one of the air gaps  115  in which the recess  114  terminates. These lateral, triangular air spaces  119  deflect and bundle the stator field through, or onto, the permanent magnet group  107 . A mechanical weakening of the rotor core  103  caused by these lateral, triangular air spaces  119  is compensated by the load relief via the permanent magnets and the shunts  109 . In addition, these lateral, triangular air spaces  119  deflect, or bundle, the magnetic field of the permanent magnets  108  of the permanent magnet group  107 , in particular of the first and the last of the permanent magnets  108  in the linear row of permanent magnets  108  of the permanent magnet group  107 , and form, or bound, the first and the last of the shunts  109  of the permanent magnet group  107 . In a modification, the air spaces  119  may also have different contours, e.g. that of a semicircle. 
         [0058]      FIG. 3  shows, in a roughly schematic representation, a sector-shaped portion—here, in the form of one quarter of a circle—of an axial sectional view of a second example for a conventional electric motor  252  having two conventional permanent magnets  257  in a so-called V arrangement. The conventional electric motor  252  comprises a stator  251 , and a rotor  250 , which is realized with a magnetically conductive rotor core  253  and a magnetically non-conductive rotor shaft  254 . An air gap  255  extends between the rotor  250  and the stator  251 . The permanent magnets  257  are accommodated in magnet pockets  256 , which are formed in the rotor core  253 . Apart from the arrangement and number of the permanent magnets  257  and magnet pockets  256 , the structure of the electric motor  252  corresponds to that of the electric motor  152  according to  FIG. 1 , and thus largely to that of DE 11 2008 001 333 T5, in particular FIGS. 2 therein—permanent magnets therein having the references 21—, 8A, 8E, 9( a )—permanent magnets Ma1, Ma2 therein—and 13( a )—permanent magnets Me1, Me2 therein—with associated description of known design. In this case, the permanent magnets in a V arrangement may enclose differing angles. Also represented schematically in  FIG. 3 , by arrows  258 , is a direction of magnetization of the permanent magnets  257  in their mounting position in the rotor core  253 , and the magnetic north poles N are denoted by N, the magnetic south poles being denoted by S. 
         [0059]    Represented in  FIG. 4 , as a modification according to the invention of the conventional electric motor  252  from  FIG. 3 , is a second exemplary embodiment of an electric motor according to the invention, denoted by the reference  202 , with a second exemplary embodiment of a rotor  200  according to the invention and a stator  201 , represented in the same view as that according to  FIG. 3 . As compared with  FIG. 3 , in  FIG. 4  the conventional magnet pockets  256  and permanent magnets  257 , in regions  206 , of rectangular cross section, preferably corresponding to the dimensions and extents, or positions, of these magnet pockets  256  and permanent magnets  257 , have been replaced by permanent magnet groups  207 , which correspond in their structure to that of the permanent magnet group  107  according to  FIG. 2 , except for the fact that, here, on the one hand, four instead of six permanent magnets  208  are provided, alternately with magnetically conductive shunts  209 , in a linear row, and that, on the other hand, a recess  214  in the rotor core  203 , which extends in the axial direction of the rotor  200 , i.e. perpendicularly into the plane of the drawing, and which accommodates the permanent magnet group  207 , or the permanent magnets  208 , now goes into lateral, rectangular air spaces  219 , which adjoin the recess  214  on both sides, at narrow ends of the region  206 . Optionally, a different number of permanent magnets  208  may also be provided here, e.g. six permanent magnets  208 . 
         [0060]    As in  FIG. 2 , the magnetically conductive shunts  209  are realized to hold the permanent magnets  208  with hook-type shapes  218 , and the recess  214 , in a manner resembling that of the recess  114  according to  FIG. 2 , comprises air gaps  215 , alternately along a zigzag-type extent, at end faces of the magnetically conductive shunts  209  in the permanent magnet group  207 , these end faces here, owing to the angle of the V arrangement of the permanent magnet groups  207 , facing substantially in the circumferential direction of the rotor  200 , magnet pockets for accommodating the permanent magnets  208 , and magnetically non-conductive spatial regions  217  for the magnet pockets  216 , which are disposed laterally with respect to a direction of magnetization  212  of the permanent magnets  208 . The magnetic field courses in the rotor  200  are not represented in detail. 
         [0061]    In the case of the rotor  200  also, a radially outwardly facing portion  210  of the rotor core  203 , i.e. toward the air gap  205 , is supported against a radially inwardly facing portion  211  of the rotor core  203 , i.e. toward the rotor shaft  204 , via the hook-type shapes  218  and the permanent magnets  208 , and the stability of the rotor  200  against centrifugal forces is thus increased. 
         [0062]      FIG. 5  shows, in roughly schematic form, a sector-shaped portion of an axial sectional view of a third example for a conventional electric motor  352  having two conventional permanent magnets in a so-called Q arrangement. Unlike the V arrangement according to  FIG. 3 , in the case of the Q arrangement axes that intersect the magnet pockets centrally have been shifted into the center of the rotor shaft, which corresponds to the rotor shaft  254  according to  FIG. 3 . Apart from the position of the magnet pockets, which otherwise correspond to the magnet pockets  256  according to  FIG. 3 , in the rotor core  353 , thereby slightly modified in comparison with the electric motor  252  according to  FIG. 3 , and thus also modified rotor  350 , the electric motor  352  is structurally the same as the electric motor  252  according to  FIG. 3 . 
         [0063]      FIG. 6  shows a third exemplary embodiment of an electric motor  302  according to the invention, with a third exemplary embodiment of a rotor  300  according to the invention as a modification according to the invention of the electric motor  352  according to  FIG. 5 , in a representation corresponding to the preceding figures. In accordance with the extensive correspondence of the electric motors  252  and  352 , the electric motor  302  also differs from the electric motor  202  only in the position of the permanent magnet groups  207 , otherwise taken without change from  FIG. 4 , in the rotor core, now denoted by  303 , of the rotor  300  of the electric motor  302 , such that the same features and advantages are applicable to the electric motor  302  as for the electric motor  202  according to  FIG. 4 . 
         [0064]    The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 
         [0065]      100  rotor of  102   
         [0066]      101  stator of  102   
         [0067]      102  electric motor ( FIG. 2 ) 
         [0068]      103  rotor core of  100   
         [0069]      104  rotor shaft of  100   
         [0070]      105  air gap between  100  and  101   
         [0071]      106  region in  103  of  100  having rectangular cross section, in which  107  extends 
         [0072]      107  permanent magnet group in  103  of  100   
         [0073]      108  permanent magnet of  107   
         [0074]      109  magnetically conductive shunt of  107   
         [0075]      110  portion of  103  facing radially outward, i.e. toward  105   
         [0076]      111  portion of  103  facing radially inward, i.e. toward  104   
         [0077]      112  arrows: spatial course of the magnetic field (flux), caused by  108   
         [0078]      113  arrows: magnetic field—stator field—or magnetic flux/opposing field caused by  101   
         [0079]      114  recess in  103  extending in axial direction of  100 , i.e. perpendicularly into the plane of the drawing, accommodates  107  and  108   
         [0080]      115  air gap at end faces of  109  in  107  that are oriented substantially radially, i.e. in a direction orthogonal to the tangential direction of  100   
         [0081]      116  magnet pocket for accommodating  108   
         [0082]      117  magnetically non-conductive spatial regions for  116 , which is disposed laterally with respect to the direction of magnetization of  108   
         [0083]      118  hook-type shape on  109   
         [0084]      119  lateral, triangular air space adjoining  114   
         [0085]      150  rotor of  152   
         [0086]      151  stator of  152   
         [0087]      152  electric motor ( FIG. 1 ) 
         [0088]      153  rotor core of  150   
         [0089]      154  rotor shaft of  150   
         [0090]      155  air gap between  150  and  151   
         [0091]      156  magnet pocket in  153  for  157   
         [0092]      157  permanent magnet in  156   
         [0093]      158  arrows: magnetic flux (magnetic field) caused by magnetization of  157   
         [0094]      159  arrows: magnetic flux, or magnetic field, caused by  151 —stator field 
         [0095]      200  rotor of  202   
         [0096]      201  stator of  202   
         [0097]      202  electric motor ( FIG. 4 ) 
         [0098]      203  rotor core of  200   
         [0099]      204  rotor shaft of  200   
         [0100]      205  air gap between  200  and  201   
         [0101]      206  region in  203  of  200  having rectangular cross section, in which  207  extends 
         [0102]      207  permanent magnet group in  203  of  200   
         [0103]      208  permanent magnet of  207   
         [0104]      209  magnetically conductive shunt of  207   
         [0105]      210  portion of  203  facing radially outward, i.e. toward  205   
         [0106]      211  portion of  230  facing radially inward, i.e. toward  204   
         [0107]      212  direction of magnetization of  208   
         [0108]      214  recess in  203  extending in axial direction of  200 , i.e. perpendicularly into the plane of the drawing, which accommodates  207  and  208   
         [0109]      215  air gaps at end faces of  209  in  207 , which, due to V arrangement of  207 , face substantially in the circumferential direction of  200   
         [0110]      216  magnet pocket for accommodating  208   
         [0111]      217  magnetically non-conductive spatial region for  216 , which is disposed laterally with respect to  212  of  208   
         [0112]      218  hook-type shape on end face of  209   
         [0113]      219  lateral, rectangular air space, adjoining  214   
         [0114]      250  rotor of  252   
         [0115]      251  stator of  252   
         [0116]      252  electric motor ( FIG. 3 ) 
         [0117]      253  rotor core of  250   
         [0118]      254  rotor shaft of  250   
         [0119]      255  air gap of  252  between  250  and  251   
         [0120]      256  magnet pocket in  253  for  257   
         [0121]      257  permanent magnet in  256   
         [0122]      258  arrow: direction of magnetization of  257   
         [0123]      300  rotor of  302   
         [0124]      302  electric motor ( FIG. 6 ) 
         [0125]      303  rotor core of  300   
         [0126]      350  rotor of  352   
         [0127]      352  electric motor ( FIG. 5 ) 
         [0128]      353  rotor core of  350   
         [0129]    N magnetic north pole of  108 ,  257   
         [0130]    S magnetic south pole of  108 ,  257