Abstract:
The present invention essentially relates to an electric machine ( 1.1 ) with homopolar double excitation, comprising a rotor particularly consisting of a central portion ( 51 ) made of a solid magnetic material and a laminated annular portion ( 53 ) located at the periphery of the solid portion. In addition, the rotor comprises permanent magnets ( 54 ), the magnetisation thereof being radially oriented relative to the axis ( 33 ) of the rotor ( 31 ), and separated from one another such that the double excitation flow generated by the field coils ( 38, 39 ) can enter the rotor ( 31, 67 ) via the flanges ( 48, 49 ) of the rotor, and come back out via the spaces between the magnets ( 54 ), or vice-versa.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is the US national stage under 35 U.S.C. §371 of International Application No. PCT/FR2009/052152 which claims the priority of French application 0857636 filed on Nov. 10, 2008. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a rotating electric machine with homopolar double excitation. The goal of the invention is in particular to facilitate the passage of the double excitation flux inside the electric machine. 
         [0003]    The invention finds a particularly advantageous, but not exclusive, application in synchronous electric machines intended to be used with electric or hybrid vehicles combining the use of a combustion engine and an electric machine. 
         [0004]    Rotating electrical machines with double excitation are disclosed in the French patent application number FR-2846483. 
         [0005]    As shown in  FIG. 1  herein, such machines  1  have a stator  3  and a rotor  5  separated from each other by a functional air gap  6 . 
         [0006]    More precisely, stator  3  comprises an annular lamellar magnetic core  7  provided with a stator coil  8  and annular coils  9 ,  10  generating a double excitation flux. Core  7  and stator coils  9 ,  10  are arranged in a solid magnetic ring  11  in contact with the exterior surface of core  7 . This ring  11  comprises at each extremity a rim  13 ,  14  facing the rotor  5 . 
         [0007]    Rotor  5  contains a body  15  comprising permanent magnets  18  with tangentially oriented magnetization (perpendicular to the rotor radius) and separated from each other by teeth  19  ( FIG. 2 ) composed of lamellar plates which channel the flux generated by magnets  18  and direct it to the air gap  6 . 
         [0008]    Rotor  5  further comprises annular flanges  21 ,  22  positioned on both opposite sides of body  15 , each having peripheral portions defining, with the radial extremity rims  13  and  14  of the stator ring  11 , air gaps for return of the magnetic flux. The flanges  21  and  22  are connected to teeth  19  in an alternating manner. Each tooth  19  comprises an extremity facing towards flange  21  and an extremity facing towards flange  22 . 
         [0009]    With such an arrangement the excitation coils  9 ,  10  can modulate the flux of magnets  18  by creating a flux, called double excitation flux, which circulates through paths  24  and  25  passing through stator ring  11 , a radial extremity rim  13 ,  14 , a flange  21 ,  22 , the laminations  19  of the rotor, first in an axial direction along the active length D of the machine, then in a radial direction, then through the magnetic core  7  of the stator, closing the loop with ring  11 . 
         [0010]    Given that the excitation coils  9 ,  10  have an annular shape and that rotor  5  is made of lamellar material, the reluctance seen by the double excitation flux is high, which penalizes the yield of the machine  1 . In order to minimize this reluctance, it was first contemplated to replace this lamellar rotor  5  by a solid rotor, but the core losses would then be excessive. Therefore, it seemed advantageous to combine in the rotor, according to the invention, a lamellar circuit in the periphery (to minimize the losses) and another solid circuit (to facilitate the passage of flux). 
         [0011]    However, in the case of a rotor with tangential magnetization, the practical execution of the invention is difficult, in particular because of reasons of mechanical strength, construction complexity, or small improvement in flux circulation. 
         [0012]    We also know double excitation electric machines with radial magnets, like those described in U.S. Pat. No. 5,682,073 to Mizuno, using a single excitation coil positioned in the middle of the stator. In this case, it is possible to create a lamellar and solid rotor as in the invention. However, if the rotor according to the Mizuno patent is combined with the stator according to French application no FR-2846483, the obtained electric machine will not function correctly because there would be a magnetic short circuit penalizing the correct circulation of the flux in the machine. 
       BRIEF SUMMARY 
       [0013]    Briefly, an electrical machine structure is provided that facilitates the circulation of the flux along the length D of the machine and minimizes the core losses generated at the periphery of the rotor. 
         [0014]    To this end, the rotor is comprised of a central part made of solid magnetic material and an annular part made of lamellar material situated in the periphery of the solid part. Furthermore, the rotor contains permanent magnets with radially oriented magnetization relative to the axis of the rotor and separated from each other in such a manner that the double excitation flux generated by the excitation coils can enter the rotor through the flanges of the rotor and exit through the spaces between magnets, or vice versa. 
         [0015]    The claimed invention relates therefore to a rotating electric machine with homopolar double excitation, characterized in that it comprises: 
         [0016]    a stator comprising a central core and two excitation coils positioned on both sides of the core generating a double excitation flux, and 
         [0017]    a rotor comprising:
       a central solid part with isotropic magnetic behavior facilitating the circulation of double excitation flux according to the rotor axis,   an annular part of lamellar material installed around the central solid part, and   permanent magnets with radially oriented magnetization relative to the rotor axis, these magnets have the same polarization, and two consecutive or adjacent magnets are separated by a magnetic space to allow for the circulation of the double excitation flux in the rotor between magnets.       
 
         [0021]    According to an embodiment, each permanent magnet occupies approximately half of the polar pitch. 
         [0022]    According to an embodiment, the permanent magnets are installed in the periphery of the rotor to maximize the passage section of the double excitation flux in the solid central part. 
         [0023]    According to an embodiment, the permanent magnets are built in the interior of the annular part. 
         [0024]    According to an embodiment, the permanent magnets are mounted in the periphery of the annular part. 
         [0025]    According to an embodiment, the geometrical orientation of the magnets is longitudinal relative to the axis of the rotor. 
         [0026]    According to an embodiment, the permanent magnets are each formed by an assembly of U-shaped magnets. 
         [0027]    According to an embodiment, the stator further comprises a stator coil wound around an annular magnetic core, and at least one magnetic ring in contact with the exterior surface of the annular magnetic core, said the magnetic ring comprises in each extremity a radial extremity rim. 
         [0028]    According to an embodiment, the rotor further comprises two annular flanges of magnetic material arranged on both sides of the central part and coaxially according to the rotor axis, these flanges each comprise an axial peripheral portion defining with the radial extremity rims of the ring return air gaps for the magnetic flux. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The electrical machine will be better understood by reading the following description and by examining the accompanying figures. These figures are provided as non-limiting illustrations of the invention. They show: 
           [0030]      FIG. 1  (already described) is a truncated perspective view of an electric machine with double excitation according to the state of the art; 
           [0031]      FIG. 2  (already described) is a perspective view of the machine of  FIG. 1  with one of the flanges removed to show the direction of the rotor core laminations; 
           [0032]      FIG. 3  is a truncated perspective view of an electric machine with homopolar double excitation according to the claimed invention; 
           [0033]      FIG. 4  is a truncated perspective view of the machine of  FIG. 3  showing the double excitation flux generated by the excitation coils of the stator; 
           [0034]      FIG. 5  is a graphic representation of the flux variation of the machine according to  FIGS. 3 and 4  as a function of the electric angle for different electrical supply currents of the excitation coils; 
           [0035]      FIGS. 6   a  and  b  are schematic views of varying positions of the permanent magnets of the rotor. 
       
    
    
       [0036]    Identical elements retain the same reference from one figure to another. 
       DETAILED DESCRIPTION 
       [0037]      FIGS. 3 and 4  show a rotating electric machine  1 . 1  with homopolar double excitation comprising a stator  29  and a rotor  31  with an axis  33 . The stator  29  and this rotor  31  are separated by a functional air gap  34 . 
         [0038]    The stator  29  comprises an annular core  35  made of magnetic laminations, on both sides of which are arranged annular excitation coils  38 ,  39 . The currents circulate through these excitation coils  38 ,  39  in opposite directions. 
         [0039]    A stator coil  41 , surrounded by the excitation coils  38 ,  39 , is wound in a conventional manner around core  35  which presents for this purpose an interior surface formed by teeth  42 . 
         [0040]    The assembly of core  35  and coils  38 ,  39  is housed in an exterior magnetic ring  44  which is in contact with an exterior surface of the magnetic core  35 . This solid ring  44  comprises lateral extremity rims  45 ,  46  facing towards rotor  31 . 
         [0041]    The rotor  31  comprises two annular flanges  48 ,  49  of solid magnetic material arranged coaxially with the axis  33 . These flanges  48 ,  49  each comprise an axial peripheral portion defining, with the radial extremity rims  45  and  46  of ring  44 , return air gaps for the magnetic flux. 
         [0042]    A central part  51  of solid (non-lamellar) magnetic material is arranged between the flanges  48 ,  49  and coaxially with the axis  33  of rotor  31 . Due to its solid character, the central part  51  has an isotropic magnetic behavior, which facilitates the circulation of flux along the axis  33  of the rotor generated by the double excitation. In the center of part  51  there is an opening intended for receiving a shaft (not shown) on which rotor  31  is mounted. 
         [0043]    Rotor  31  also comprises an annular part  53  of lamellar magnetic material which limits core losses. This annular part  53  is installed around part  51 . The lamellar plates  53 . 1  of part  53  are by preference oriented radially relative to the rotor axis  33 . In one embodiment, rotor  31  has a radius Re of approximately 125 mm; the annular part  53  has a thickness of approximately 16 mm, the overall length L of machine  1  is approximately 100 mm. 
         [0044]    Permanent magnets  54 , with the same polarity and generating a magnetic field radial relative to the rotor axis  33 , are installed inside rotor  31 . Here, magnets  54  extend geometrically according to the extension of machine  1 . 1  and generate a magnetic field indicated by arrows  55  going from the exterior of rotor  31  towards the center of rotor  31 . In a variant, the direction of the magnetic field of these magnets  54  is reversed and goes from the center of rotor  31  towards the exterior of rotor  31 , as shown in  FIG. 6   a.    
         [0045]    Magnets  54  are installed in the periphery of rotor  31  to maximize the passage section of the double excitation flux in the central solid part  51 . Here, the magnets  54  are built in the interior of annular part  53  which is provided with cavities for this purpose. These magnets  54  are separated from each other by a magnetic space through which the double excitation flux circulates inside rotor  31  between magnets  54 . “Magnetic space” is understood to be a space which is a good conductor of magnetic flux consisting for instance of a solid magnetic material and/or as here a lamellar magnetic material. 
         [0046]    By preference, each magnet  54  occupies approximately half of the polar pitch, one polar pitch being equal to the perimeter of the rotor  31  divided by the number of pole pairs p. As shown in  FIG. 6   a , the angular free space α 1  between two successive or adjacent magnets  54  is approximately equal to the angular space α 2  occupied by one magnet  54 , these angles α 1  and α 2  are equal to the product of the radius Re of rotor  31  and the number π divided by the number of pole pairs p of machine  1 . 1 . 
         [0047]    In a variant, magnets  54  are mounted, by gluing for instance on the periphery of the annular part  53 . In a variant, magnets  54  are installed in the hollows of slots made in the periphery of the annular part  53 . 
         [0048]    In a variant, as shown in  FIG. 6B , magnets  54  are replaced by U-shaped assemblies of permanent magnets  54 . 1 - 54 . 3 . The field created by each of these magnet assemblies is radial relative to the axis  33 . The direction of this field is either from the center of rotor  31  towards the exterior of rotor  31 , or from the exterior towards the center of rotor  31 . The U shape has the advantage of increasing the flux generated by magnets  54 ; however this increased flux is obtained to the detriment of the space reserved for the solid part  51  (therefore to the detriment of the flux circulation generated by the double excitation coils  38 ,  39 ). 
         [0049]    As indicated in  FIG. 4 , when machine  1 . 1  is running, the flux generated by double excitation coil  38  circulates through a first magnetic circuit  56  according to which the flux travels through the ring  44 , the core  35 , the functional air gap  34 , the annular part  53  between magnets  54 , the central part  51 , the flange  48 , the rim  45  to close the loop through ring  44 . The direction of the flux inside the circuit  56  is indicated by arrow  56 . 1 . 
         [0050]    The flux generated by the excitation coil  39  circulates through a second magnetic circuit  58  according to which the flux passes through the ring  44 , the central part  51 , the flange  49 , the rim  46  to close the loop through ring  44 . The direction of the flux inside circuit  58  is indicated by arrow  58 . 1 . 
         [0051]    The presence of permanent magnets  54  with magnetic permeability close to 1 (making it an element equivalent to an air gap) prevents the double excitation flux from acting on the poles where the magnets are housed. 
         [0052]      FIG. 5  shows the evolution of the total flux observed for the machine  1 . 1  expressed in milliWeber (mWb) as a function of the electric angle θ expressed in degrees. Curve  60  shows that, without the double excitation flux, the permanent magnets  54  generate an alternating flux. 
         [0053]    By supplying the excitation coils  38 ,  39  in one direction or another, the value of the flux under one pole of machine  1 . 1  will vary. When coils  38 ,  39  generate a flux which is added to the flux of permanent coils  54  (flux increase), curve  62  is obtained, while when the coils generate a flux which is deducted from the flux of the permanent magnets  54  (flux decrease), curve  64  is obtained.