Abstract:
A reluctance rotor of a dynamoelectric rotary machine has an even number of poles constructed of a material having structural magnetic anisotropy. The magnetic anisotropy of the material is characterized by a first magnetic resistance, a magnetic permeability of μr&gt;20 and a saturation polarization of &gt;1T in a first spatial direction, and by a second magnetic resistance which is greater than the first magnetic resistance with a magnetic permeability of μr&lt;1.6 in spatial directions perpendicular to the first spatial direction.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of European Patent Application, Serial No. 13180733.1, filed Aug. 16, 2013, pursuant to 35 U.S.C. 119(a)-(d), the disclosure of which is incorporated herein by reference in its entirety as if fully set forth herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a rotor of a dynamoelectric rotary machine and the dynamoelectric rotary machine itself, wherein the rotor has directionally different inductances. 
         [0003]    The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention. 
         [0004]    Thus, for example, in previous electrical machine manufacture, reluctance rotors have been constructed using magnetically soft material and combined with air gaps in the rotor laminations in order to obtain directionally different magnetic resistances. Different inductances are therefore produced in a d-axis and a q-axis, thus causing tangential forces on the rotor surfaces. 
         [0005]    In the case of permanently excited machines having magnets inside the rotor, air gaps are selectively provided in the rotor&#39;s magnetically soft laminations in order to reduce the q-inductances. 
         [0006]    Disadvantageously, however, the production costs for such a rotor are comparatively high. The efficiency of dynamoelectric rotary machines of this type is comparatively low. 
         [0007]    It would therefore be desirable and advantageous to obviate prior art shortcomings and to create a rotor, in particular a reluctance rotor, of simple construction which has the same electrical and dynamic characteristics as permanently excited synchronous motors. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect of the present invention, a reluctance rotor of a dynamoelectric rotary machine has an even number of poles, wherein the pole material of the reluctance rotor exhibits structural magnetic anisotropy, having in one spatial direction a comparatively low magnetic resistance, a magnetic permeability of μr&gt;20 and a saturation polarization of &gt;1T and, in the other two spatial directions perpendicular thereto, a comparatively high magnetic resistance with a magnetic permeability of μr&lt;1.6. 
         [0009]    According to another aspect of the present invention, a permanently excited rotor by means of essentially radially disposed ferrite magnets which are separated from one another by a material exhibiting structural magnetic anisotropy, having in one spatial direction a comparatively low magnetic resistance, a magnetic permeability of μr&gt;20 and a saturation polarization of &gt;1T and, in the other two spatial directions perpendicular thereto, a comparatively high magnetic resistance with a magnetic permeability of μr&lt;1.6. 
         [0010]    According to another aspect of the present invention, a dynamoelectric rotary machine has a rotor of the aforedescribed type and a stator with a system of windings generating a magnetic field that interacts electromagnetically with the rotor during the operation of the dynamoelectric rotary machine. 
         [0011]    The materials of the reluctance rotor exhibit structural magnetic anisotropy. In one spatial direction, the material has a low magnetic resistance μr&gt;20 and a saturation polarization of B&gt;1T. In the two other spatial directions perpendicular thereto, the material behaves similarly to air and has a μr&lt;1.6. In these two other spatial directions, the magnetic resistance is comparatively high. 
         [0012]    This design provides a similar efficiency to that of permanently excited synchronous machines. This material having structural magnetic anisotropy is not a case of full-fledged permanent magnets constituting separate excitation of the rotor, rather the structural anisotropy causes the magnetic flux produced by the stator to be guided with low magnetic resistance in one spatial direction—which can also be varied section by section. 
         [0013]    The production costs are lower because no full-fledged permanent magnets have to be manufactured, in particular magnetized. 
         [0014]    This material exhibiting structural magnetic anisotropy has only a comparatively low coercive field strength. 
         [0015]    Advantageously, neodymium-iron-boron having a low coercive field strength &lt;10 kA/m is mainly used in the embodiment according to the invention. 
         [0016]    The use of these materials with dynamoelectric machines results in new design features. The flux can now be directed, resulting in low leakage and increasing the efficiency of the dynamoelectric machine particularly compared to conventional reluctance machines. Rotor inductances are directionally influenced or rather set as early as the rotor construction phase, so that two-, four-, six-, eight- or multi-pole rotors are produced. 
         [0017]    In another embodiment of the invention, the structural magnetic anisotropy reduces the shunt-inductances in permanently excited machines having interior magnets, e.g. ferrite magnets that are arranged radially. This results in a comparatively higher linearity of the current/torque characteristic of the dynamoelectric machine. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0018]    Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
           [0019]      FIG. 1  shows a basic representation of the magnetic properties of the material, 
           [0020]      FIG. 2  shows a two-pole reluctance rotor, 
           [0021]      FIG. 3  shows a four-pole reluctance rotor, 
           [0022]      FIG. 4  shows a stator and a rotor of a permanently excited machine having interior magnets, 
           [0023]      FIG. 5  shows a reluctance machine in cross-section, 
           [0024]      FIG. 6  shows a stator and a rotor of a permanently excited machine having interior magnets with basically represented field pattern, and 
           [0025]      FIG. 7  shows a reluctance machine in cross-section with basically represented field pattern. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0026]    Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
         [0027]    Turning now to the drawing, and in particular to  FIG. 1 , there are shown the magnetic properties of the employed neodymium-iron-boron based material which exhibits structural magnetic anisotropy. The magnetic flux density B is here plotted against the magnetic field strength H. “1” denotes the curve with μr&gt;20 and low magnetic resistance. “2” denotes the other spatial directions having a comparatively high magnetic resistance. 
         [0028]      FIG. 2  shows a reluctance rotor  3  having two poles  6  separated from one another by a pole gap  5 . The low magnetic resistance path is denoted by “ 7 ”. The poles  6  are here bonded to a shaft  4  and the pole gap  5 . Additionally, or instead, this overall arrangement can also be fixed in the circumferential direction by a banding  8 . 
         [0029]      FIG. 3  shows a reluctance rotor  3  having four poles  6  separated from one another by pole gaps  5 . The low magnetic resistance path is denoted by “ 7 ”. The poles  6  are here bonded to a shaft  4  and the pole gaps  5 . Additionally, or instead, this overall arrangement can also be fixed in the circumferential direction by a banding  8 . 
         [0030]    The pole gaps  5  of this reluctance rotor  3  are preferably made of non-magnetic material. 
         [0031]      FIG. 4  shows a cross-section through a dynamoelectric rotary machine  9  having a stator and a system of windings  11  disposed in grooves  10  of the stator. The grooves  10  point toward an air gap  15  of the dynamoelectric rotary machine  9 . The rotor of this machine  9  has radially disposed ferrite magnets  13  whose field lines run tangentially within the ferrite magnets  13  (see  FIG. 6 ). Viewed in the circumferential direction, the ferrite magnets  13  are separated from one another by segments  14 . In this embodiment, the segments  14  are disposed in the circumferential direction between the ferrite magnets  13  and retain the latter by at least partially tangentially covering or rather engaging around the ferrite magnets  13  in the region of the air gap  15 . The covers  20  are also suitable for flux guidance in the region of the air gap  15 . The segments  14  are made of the structurally anisotropic material in order to assist, by means of the structural magnetic anisotropy, the magnetic excitation of the rotor produced by the ferrite magnets  13 . 
         [0032]      FIG. 5  shows another dynamoelectric machine  9  having a reluctance rotor comprising four poles  6  which are present as exterior segments. Between the energized windings  11  of the stator and the reluctance rotor  3 , electromagnetic interactions occur which cause the reluctance motor to turn, producing a torque. The electromagnetic interaction is preferably determined by the sections of the poles  6  facing the air gap  15 . In this embodiment, the shaft  4  is therefore surrounded by a stainless-steel sleeve  16  to which the poles  6  are fixed. The poles  6  of structurally anisotropic material are positioned on said stainless-steel sleeve by an interference fit or by bonding—e.g. adhesively—to the stainless-steel sleeve  16 . 
         [0033]    The poles  6  can similarly be positioned on or adjacent to a hollow shaft in which, for example, gearing units or control elements of a motor are at least partly disposed. 
         [0034]    The poles  6  of structurally anisotropic material are each implemented in one piece. In another embodiment, the poles  6  each consist of a plurality of sections. The boundary planes of the adjacent sections of a pole  6  are disposed axially parallel or perpendicular to the axis. 
         [0035]      FIG. 6  shows a dynamoelectric rotary machine  9  according to  FIG. 4 , wherein a basic field line pattern in the stator lamination, the rotor segments  14  and the ferrite magnets  13  is illustrated. In the segments  14  between the ferrite magnets  13 , because of the provided structural magnetic anisotropy of the material of the segments  14 , the field lines run virtually radially and parallel, having the preferred direction denoted by “7”, as there the lowest magnetic resistance is present due to the material. The field lines within the ferrite magnets  13  run tangentially. As a result of the optimized field line pattern, a comparatively higher utilization of the dynamoelectric rotary machine  9  is achieved. 
         [0036]    In  FIG. 6  only the shaft  4  is hatched and the system of windings  11  is graphically distinguished by a checkered pattern. The lines in the stator lamination, the lines in the ferrite magnets  13  and the radial lines in the segments  14  represent magnetic field lines. 
         [0037]      FIG. 7  shows a dynamoelectric rotary machine  9  according to  FIG. 5 , wherein a basic magnetic field line pattern in the stator lamination and in the rotor poles  6  disposed on the stainless-steel sleeve  16  is illustrated. The field lines in the poles  6  run virtually tangentially to the axis  21  or rather, in this embodiment, parallel to the respective edge of the stainless-steel sleeve  16  on which the poles  6  are disposed. 
         [0038]    In  FIG. 7  only the shaft  4  and the stainless-steel sleeve  16  is hatched and the system of windings  11  is graphically distinguished by a checkered pattern. The lines in the stator lamination and the lines in the poles  6  having their preferred direction “7” represent magnetic field lines. 
         [0039]    Because of their utilization or rather their operating characteristics, dynamoelectric rotary machines  9  incorporating the above described rotors behave like permanently excited synchronous machines having rare-earth magnets. 
         [0040]    Such dynamoelectric rotary machines  9  incorporating the above described rotors are suitable for machine tool drives and for drives in automotive applications such as rail vehicles, E-bikes and E-cars. 
         [0041]    While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of, the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
         [0042]    What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: