Patent Publication Number: US-2020295610-A1

Title: Rotor for an Axial Flux Motor, a Radial Flux Motor, and a Transversal Flux Motor

Description:
The invention relates to a rotor for an electric drive, in particular for an axial flux motor (AFM), a radial flux motor and a transversal flux motor. In particular, different rotors are intended to be proposed for the individual types of electric drives. 
     Electric drives may be used as a generator and as an electric machine. Electric drives generally comprise a stator and a rotor which are arranged coaxially with respect to each other. The rotor is in this instance referred to as the carrier of permanent magnets, whilst the stator has a coil arrangement. 
     The rotor or the stator may be connected to a shaft which is driven by means of the electric drive (operation as an electric machine) or which transmits a rotational movement to the axial flux motor (generator operation). The basic structure of this electric drive may be presumed to be known. In this instance, the specific structure of a rotor is described. 
     In an axial flux motor, the rotor and stator are in particular arranged one behind the other in the axial direction. In this instance, differently magnetized magnets are arranged alternately in the peripheral direction on the rotor. The magnetic field lines of an axial flux motor extend substantially parallel with the rotation axis in an axial direction, the magnetic field is thus orientated substantially parallel with the rotation axis. 
     An electric axial flux machine is known, for example, from DE 10 2009 021 703 B4. 
     In a radial flux motor, the rotor and stator are arranged in particular in a radial direction one behind the other (that is to say, for example, rotor internally and stator externally or vice versa). In this instance, differently magnetized magnets are arranged in a peripheral direction alternately on the rotor. The magnetic field lines of a radial flux motor extend substantially transversely relative to the rotation axis in a radial direction, the magnetic field is thus orientated substantially transversely relative to the rotation axis. 
     Transversal flux motors generally comprise a stator and a rotor. The rotor and stator are in particular arranged in a radial direction one behind the other (that is to say, for example, rotor internally and stator externally or vice versa). In this instance, differently magnetized magnets are arranged alternately in the peripheral direction on the rotor. The magnetic field lines of a transversal flux motor extend substantially parallel with the rotation axis in an axial direction, the magnetic field is thus orientated substantially parallel with the rotation axis. The magnetic flux also extends in this instance three-dimensionally in a radial direction and in a peripheral direction. 
     The structure of a claw-pole stator of a transversal flux motor is explained below by way of example. Two claw-pole stators are arranged beside each other in the axial direction, wherein they contact each other over the end faces thereof. Each claw-pole stator has a large number of poles which extend from a base face in the axial direction. The first poles of the first claw-pole stator and second poles of the second claw-pole stator are arranged alternately in the peripheral direction and adjacent to each other so as to overlap each other in the axial direction, but spaced apart from each other. The poles may be arranged on the inner peripheral face or on the outer peripheral face. The claw-pole stators then contact each other via the end faces on the outer peripheral face or on the inner peripheral face. In the intermediate space of the claw-pole stators, in the axial direction between the end faces and in the radial direction between the mutually contacting end faces and the poles, a coil may be arranged so as to extend in the peripheral direction between the claw-pole stators. 
     An electric machine with cores of soft magnetic composite (SMC) is known from WO 2016/066714 A1. The permanent magnets used therein in the rotor are magnetized in a direction parallel with the rotation axis, that is to say, in the axial direction, that is to say, the flux lines of the magnetic field are discharged in an axial direction from the respective permanent magnets. 
     The coil arrangement of a stator has cores, for example, of SMC, which are surrounded by current-carrying windings. Each core may be an element which is arranged in order to be magnetized when a current is conducted through current-carrying windings around the core. The current-carrying windings may be formed as coils. Each coil may have an inner diameter which is substantially equal to an outer diameter of each core. 
     SMC is in particular formed by iron powder particles which are electrically insulated from each other. Iron losses in SMC particles in an electrical alternating field are generally low. In this respect, it therefore appears to be desirable to use SMC in electric machines at least partially in place of the most frequently used steel lamination (steel sheets or electric steel). In order to form a component from SMC, the particles are compressed and hardened. The SMC material is in this instance not sintered. Instead, there is carried out a tempering to below a melting temperature, which is, however, sufficient for the material to permanently keep the intended geometry. 
     The rotor of the electric drive (that is to say, the axial flux electric drive, of the radial flux motor and the transversal flux motor) may have permanent magnets or also soft-magnetic elements, for example, in recesses. Thus, using permanent magnets as an electric drive (in particular an axial flux electric motor, a radial flux electric motor or a transversal flux electric motor), a permanently excited synchronous or brushless direct-current motor (BLDC for short) can be formed, whilst, for example, using soft magnetic elements, a reluctance motor can be provided as an electric motor of the axial, radial or transversal type. 
     There is a constant requirement to increase the power capacity of electric machines. 
     Based on this, an object of the present invention is to at least partially solve the problems set out with respect to the prior art. In particular, a rotor for an electric drive (for an axial flux motor, a radial flux motor and a transversal flux motor) which has a higher level of efficiency is intended to be proposed. 
     In order to solve this problem, a rotor according to the features of claim  1  is proposed. The dependent claims relate to advantageous developments. The features set out individually in the claims can be combined with each other in a technologically advantageous manner and can be supplemented by explanatory facts from the description and details from the Figures, wherein additional embodiments of the invention are set out. 
     A contribution is made to this by a rotor for an electric drive, in particular for an axial flux motor, a radial flux motor and/or a transversal flux motor, having a rotation axis which extends in an axial direction, wherein the rotor extends in an annular manner and has in a peripheral direction a large number of permanent magnets (the term also includes in this instance in particular soft magnetic elements). The permanent magnets are preferably differently magnetized alternately in the peripheral direction (first permanent magnets with a first magnetization and second permanent magnets with a second magnetization). The magnetization of the permanent magnets is orientated in each case in a peripheral direction, wherein the permanent magnets are arranged spaced apart from each other in the peripheral direction, wherein at least one soft magnetic composite is arranged as a first material between the permanent magnets. 
     In this instance, it is in particular proposed that the permanent magnets are not magnetized in an axial direction, but instead in a peripheral direction. That is to say, the (or a majority of the) flux lines of the magnetic field of a (each) permanent magnet are discharged (substantially) in a peripheral direction from the respective permanent magnet. 
     A first material which can serve to concentrate the flux lines (increase the flux density, reduction of the eddy current flux losses) is arranged between the permanent magnets. 
     The flux lines of the magnetic field which are discharged in a peripheral direction from the permanent magnets are in particular directed through the first material which is adjacent in a peripheral direction toward the adjacent magnet. 
     Particularly between the permanent magnets, an iron-containing material is further arranged as a second material. 
     Preferably, the second material is a sintered iron-containing material or an electric steel material. 
     In particular as a result of the combination of the first material and second material, iron losses as a result of electric eddy current losses which occur on the surfaces of the first material and/or the second material can be prevented or reduced. 
     Preferably, for the axial flux motor, the first material and the second material are arranged in layers and in this instance one behind the other in the axial direction. In particular, therefore, in the axial direction, firstly one material and then the other material are arranged. 
     In particular, for the radial flux motor and/or a transversal flux motor, the first material and the second material are arranged in layers and in this instance arranged one behind the other in a radial direction. In particular, therefore, in the radial direction, firstly one material and then the other material are arranged. 
     With the arrangement of the rotor on a stator in order to form an electric machine, the first material is arranged in particular in the direction toward the stator. 
     In particular for the radial flux motor and/or the transversal flux motor, the first material in the radial direction is arranged adjacent to a stator of the radial flux motor and the transversal flux motor. In particular, the second material is arranged with spacing with respect to the stator. In particular, the first material is arranged between the second material and the stator. 
     In particular, the first material and the second material have together in the axial direction an overall height for the axial flux motor, wherein the first material extends over a first height which is at least 10%, in particular at least 20%, preferably at least 40% of the overall height. 
     Preferably, the first material has a first height which is a maximum of 9 0 %, in particular a maximum of 80%, of the overall height. 
     In particular, the first material and the second material together have in the radial direction an overall height for the radial flux motor and/or the transversal flux motor, wherein the first material extends over a first height which is at least  10 %, in particular at least 20%, preferably at least 40%, of the overall height. 
     Preferably, the first material has a first height which is a maximum of 90%, in particular a maximum of 80%, of the overall height. 
     In particular, the permanent magnets for the axial flux motor have in the axial direction an extent which (substantially) corresponds to the overall height. In particular, the permanent magnets for the radial flux motor and/or the transverse flux motor have in the radial direction an extent which (substantially) corresponds to the overall height. 
     In particular, the permanent magnets extend in a radial direction at least partially (in particular completely) further outward than the first material (and where applicable than the second material). 
     In particular, the permanent magnets extend in a radial direction at least partially (in particular completely) further inward than the first material (and where applicable than the second material). 
     Furthermore, an electric drive is proposed in the form of an axial flux motor, a radial flux motor or a transversal flux motor, at least comprising a stator and the rotor which has already been described, wherein the stator has a large number of cores which are surrounded by coils. 
     In particular, the stator has a soft magnetic composite. 
     The number of cores (or coils) may be different from the number of permanent magnets. 
     The embodiments relating to the rotor apply equally to the electric drive (or to the axial flux motor, the radial flux motor and the transversal flux motor) and vice versa. 
     By way of precaution, it should be noted that the numerals used here (“first”, “second” . . . ) serve primarily (only) to differentiate a plurality of identical objects or variables, that is to say, they in particular do not necessarily predetermine any dependency and/or sequence of these objects or variables. If a dependency and/or a sequence should be required, this is set out explicitly here or it becomes self-evident for the person skilled in the art when studying the specifically described embodiment. 
    
    
     
       The invention and the technical background are explained in greater detail below with reference to the Figures. It should be noted that the invention is not intended to be limited by the embodiments set out. In particular, as long as not explicitly set out otherwise, it is also possible to extract part-aspects of the content explained in the Figures and to combine them with other components and knowledge from the present description and/or Figures. In particular, it should be noted that the Figures and in particular the size relationships set out are only schematic. The same reference numerals refer to the same objects so that where applicable explanations from other Figures can be used in addition. In the drawings: 
         FIG. 1 : is a perspective view of a first construction variant of an axial flux motor; 
         FIG. 2 : is a perspective view of the rotor of the axial flux motor according to  FIG. 1 ; 
         FIG. 3 : is a side view of the rotor according to  FIG. 2 ; 
         FIG. 4 : shows the rotor according to  FIGS. 2 and 3  in a view along the rotation axis; and 
         FIG. 5 : is a graph in which eddy current losses and the torque which can be produced are illustrated in accordance with a distribution of the first material and second material; 
         FIG. 6 : is a first perspective view of a second construction variant of an axial flux motor; 
         FIG. 7 : is a second perspective view of the axial flux motor from  FIG. 6 ; 
         FIG. 8 : shows a path of the magnetic flux in a radial flux motor and a transversal flux motor and a temporally varying magnetic field at one time; 
         FIG. 9 : is a side view of a radial flux motor from  FIG. 8  along the rotation axis; 
         FIG. 10 : is a perspective view of the radial flux motor according to  FIG. 9 ; 
         FIG. 11 : shows a cut-out of a transversal flux motor as a side view along the rotation axis; 
         FIG. 12 : is a first perspective view of the cut-out according to  FIG. 11 ; 
         FIG. 13 : is a second perspective view of the cut-out according to  FIGS. 11 and 12 . 
     
    
    
       FIG. 1  is a perspective view of a first construction variant of an axial flux motor  2  having a rotation axis  4 . The axial flux motor  2  comprises a stator  14  and a rotor  1 , wherein the stator  14  has a large number of cores  15  which are surrounded by coils  16 . The cores  15  are produced at least partially from the first material  8 . 
       FIG. 2  is a perspective view of the rotor  1  of the axial flux motor  2  according to  FIG. 1 .  FIG. 3  is a side view of the rotor  1  according to  FIG. 2 .  FIG. 4  shows the rotor  1  according to  FIGS. 2 and 3  in a view along the rotation axis  4 .  FIGS. 2 to 4  are described together below. 
     The rotor  1  has a rotation axis  4  which extends in an axial direction  3 , wherein the rotor  1  extends in an annular manner and has in a peripheral direction  5  a large number of first permanent magnets  6  (having a first magnetization) and second permanent magnets  7  (having a second magnetization which is different from the first magnetization). The permanent magnets  6 ,  7  are differently magnetized alternately in the peripheral direction  5 . The magnetization of the permanent magnets  6 ,  7  is in each case orientated in a peripheral direction  5 , that is to say, the direction of the flux lines  17  (when leaving or entering the permanent magnets) is orientated in the peripheral direction  5 . The permanent magnets  6 ,  7  are arranged spaced apart from each other in the peripheral direction  5 , wherein a soft magnetic composite is arranged between the permanent magnets  6 ,  7  as a first material  8 . 
     An iron-containing material is further arranged between the permanent magnets  6 ,  7  as a second material  9 . The first material  8  and the second material  9  are arranged in layers and in this instance in the axial direction  3  one behind the other. In the axial direction  3 , the first material  8  and then the other material  9  are arranged. 
     The first material  8  and the second material  9  together have in the axial direction  3  an overall height  10 , wherein the first material  8  extends over a first height  11 , which is approximately 50% of the overall height  10 . 
     The permanent magnets  6 ,  7  have in the axial direction  3  an extent  12  which corresponds to the overall height  10 . 
     The permanent magnets  6 ,  7  extend in a radial direction  13  both further outward and further inward than the first material  8 . 
       FIG. 5  shows a graph which illustrates eddy current losses 18 [Watt] (vertical axis) and the torque  19  which can be produced [mNm] (Milli-Newton meter) (vertical axis) in accordance with a distribution of the first material and second material (ratio  20  of the first height  11  to overall height 10 [%]; horizontal axis). 
     The first line  21  shows the path of the eddy current losses  18  in accordance with the ratio  20 . The second curve  22  shows the path of the torque  19  which can be achieved in accordance with the ratio  20 . 
       FIG. 6  is a first perspective view of a second construction variant of an axial flux motor  2 .  FIG. 7  is a second perspective view of the axial flux motor  2 . Reference may be made to the explanations relating to  FIGS. 1 to 4 . 
     In the axial flux motor  2 , the rotor  1  and stator  14  are arranged one behind the other in the axial direction  3 . In this instance, differently magnetized permanent magnets  6 ,  7  are arranged in the peripheral direction  5  alternately on the rotor  1 . The magnetic field lines of an axial flux motor  2  extend substantially parallel with the rotation axis  4  in an axial direction  3 , the magnetic field is thus orientated substantially parallel with the rotation axis  4 . 
       FIG. 8  shows a path of the magnetic flux or the magnetic field lines  25  in a radial flux motor  23  and a transversal flux motor  24  and a temporally varying magnetic field at a time. The stator  14  is illustrated without coils  16 , wherein the changing polarity of the time-variable magnetic field for a time is illustrated by the +/- symbol. The rotor  1  has a rotation axis  4  which extends in an axial direction  3 , wherein the rotor  1  extends in an annular manner and has in a peripheral direction  5  a large number of first permanent magnets  6  (with a first magnetization) and second permanent magnets  7  (with a second magnetization which differs from the first magnetization). The permanent magnets  6 ,  7  are differently magnetized alternately in the peripheral direction  5 . The magnetization of the permanent magnets  6 ,  7  is orientated in each case in the peripheral direction  5 , that is to say, the direction of the flux lines  17  (when leaving or entering the permanent magnets) is orientated in the peripheral direction  5 . The permanent magnets  6 ,  7  are arranged spaced apart from each other in the peripheral direction  5 , wherein a soft magnetic composite is arranged between the permanent magnets  6 ,  7  in the radial direction  13  externally as a first material  8  and a second material  9  is arranged in the radial direction  13  internally. 
       FIG. 9  is a side view of a radial flux motor  23  along the rotation axis  4 .  FIG. 10  is a perspective view of the radial flux motor  23  according to  FIG. 9 .  FIGS. 9 and 10  are described together below. Reference may be made to the statements relating to  FIG. 8 . 
     In a radial flux motor  23 , the rotor  1  and stator  14  are arranged one behind the other in a radial direction  13  (that is to say, in this instance the rotor  1  internally and stator  14 ). In this instance, differently magnetized permanent magnets  6 ,  7  are arranged in the peripheral direction  5  alternately on the rotor  1 . The magnetic field lines  25  of a radial flux motor  23  extend substantially transversely relative to the rotation axis  4  in a radial direction  13 , the magnetic field is thus orientated substantially transversely with respect to the rotation axis  4 . 
     For the radial flux motor  23 , the first material  8  and the second material  9  are arranged in layers and in this instance in a radial direction  13  one behind the other. Starting internally and moving outwardly in the radial direction  13 , first the second material  9  and then the first material  8  are arranged in this case. 
     In the arrangement of the rotor  1  on the stator  14 , in order to form an electric machine the first material  8  is arranged in the direction toward the stator  14 . 
     For the radial flux motor  23 , the first material  8  is arranged in the radial direction  13  adjacent to the stator  14  of the radial flux motor  23 . The second material  9  is arranged with spacing from the stator  14 . The first material  8  is arranged between the second material  9  and the stator  14 . 
     For the radial flux motor  23 , the first material  8  and the second material  9  have together in the radial direction  13  an overall height  10 , wherein the first material  8  extends over a first height  11 . 
       FIG. 11  shows a cut-out of a transversal flux motor  24  as a side view about the rotation axis  4 .  FIG. 12  shows the cut-out according to  FIG. 11  as a first perspective view.  FIG. 13  shows the cut-out according to  FIGS. 11 and 12  as a second perspective view.  FIGS. 11 to 13  are described together below. 
     Transversal flux motors  24  generally comprise a stator  14  and a rotor  1 . The rotor  1  and stator  14  are arranged one behind the other in a radial direction  13  (that is to say, in this instance the rotor  1  internally and stator  14  externally). In this instance, differently magnetized permanent magnets  6 ,  7  are arranged alternately in the peripheral direction  5  on the rotor  1 . The magnetic field lines  25  of a transversal flux motor  24  extend substantially parallel with the rotation axis  4  in an axial direction  3 , the magnetic field is thus orientated substantially parallel with the rotation axis  4 . The magnetic flux also extends in this instance three-dimensionally in the radial direction  13  and in the peripheral direction  5 . 
     For a claw-pole stator  14 , two claw-pole stators  14  are arranged beside each other in the axial direction  3 , wherein they contact each other via the end faces  25  (end faces  25  indicated in  FIG. 12 ) or are already constructed in one piece (see  FIG. 13 ). Each claw-pole stator  14  has a large number of poles  27 ,  28  which extend from a base face  29  in the axial direction  3 . The first pole  27  of the first claw-pole stator  14  and second poles  28  of the second claw-pole stator  14  are arranged alternately in the peripheral direction  5  and in each case adjacent to each other and so as to overlap each other in the axial direction  3 , but spaced apart from each other. The poles  27 ,  28  are arranged on the inner peripheral face  30 . The claw-pole stators  14  contact each other via the end faces  25  on the outer peripheral face  31  (see  FIG. 12  or are constructed in one piece, see  FIG. 13 ). A coil  16  is arranged so as to extend in the peripheral direction  5  between the claw-pole stators  14  in the intermediate space of the claw-pole stators  14  in the axial direction  3  between the end faces  25  and in the radial direction  13  between the mutually contacting end faces  25  and the poles  27 ,  28 . 
     For the transversal flux motor  24 , the first material  8  and the second material  9  are arranged in layers and in this instance in a radial direction  13  one behind the other. In this instance, therefore, starting from the inner side and moving in the radial direction  13  externally, first the second material  9  and then the first material  8  are arranged. 
     When the rotor  1  is arranged on the stator  14 , in order to form an electric machine the first material  8  is arranged in the direction toward the stator  14 . 
     For the transversal flux motor  24 , the first material  8  is arranged in the radial direction  13  adjacent to the stator  14  of the transversal flux motor  24 . The second material  9  is arranged with spacing from the stator  14 . The first material  8  is arranged between the second material  9  and the stator  14 . 
     For the transversal flux motor  24 , the first material  8  and the second material  9  have together in the radial direction  13  an overall height  10 , wherein the first material  8  extends over a first height  11 . 
     LIST OF REFERENCE SIGNS 
     
         
           1  Rotor 
           2  Axial flux motor 
           3  Axial direction 
           4  Rotation axis 
           5  Peripheral direction 
           6  First permanent magnet 
           7  Second permanent magnet 
           8  First material 
           9  Second material 
           10  Overall height 
           11  First height 
           12  Extent 
           13  Radial direction 
           14  Stator 
           15  Core 
           16  Coil 
           17  Direction of the flux lines 
           18  Eddy current loss [Watt] 
           19  Torque [mNm] 
           20  Ratio of first height/overall height [%] 
           21  First line 
           22  Second line 
           23  Radial flux motor 
           24  Transversal flux motor 
           25  Magnetic field line 
           26  End face 
           27  First pole 
           28  Second pole 
           29  Base face 
           30  Inner peripheral face 
           31  Outer peripheral face