Abstract:
A double excitation, rotating electrical machine mounted on a shaft includes a rotor whereof the magnetic circuit carries at least one excitation element and a stator whereof the magnetic circuit carries a stator coil. The at least one excitation element includes at least a ring-shaped magnet associated with at least two disks each provided with radial teeth evenly distributed at their periphery and at least a ring-shaped part provided with slots in each of which is engaged contactless, one tooth of at least one toothed disk, and the stator magnetic circuit includes an even number, not less than two, of ring-shaped elements of magnetic circuit, at least an excitation stator coil being arranged between at least two neighboring elements among the magnetic circuit elements.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to rotating electrical machines and more particularly to synchronous machines such as alternators for motor vehicles, traction engines or other machines. 
     Among the known machines, mention may be made of machines with excitation by windings mounted in the rotor, machines with excitation by magnets mounted in the rotor and machines with double excitation by both windings and magnets mounted in the rotor. 
     Such machines are especially described in Patent Application FR 97/03429 filed on Mar. 20, 1997 by the Applicant. 
     Although giving acceptable results, the known double-excitation machines are relatively bulky because of the presence of brushes and slip rings. 
     SUMMARY OF THE INVENTION 
     The invention therefore aims to create a rotating electrical machine of the double-excitation type which, whilst still having good performance characteristics, is less bulky than the known machines of the same type. 
     The subject of the invention is therefore a rotating electrical machine comprising, mounted on a shaft, a rotor whose magnetic circuit carries at least one excitation element and a stator whose magnetic circuit carries a stator winding, characterized in that the at least one said excitation element of the rotor comprises at least one annular magnet associated with at least two discs each provided with radial teeth uniformly distributed around their periphery and at least one annular piece provided with slots in each of which a tooth of at least one toothed disc is engaged without any contact, and in that the magnetic circuit of the stator includes an even number, at least equal to two, of annular magnetic-circuit elements, at least one stator excitation winding being arranged between at least two adjacent elements among the said magnetic-circuit elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be more clearly understood with the aid of the description which follows, given solely by way of example and with reference to the appended drawings, in which: 
     FIG. 1 is a cross-sectional partial schematic view of an elementary double-excitation rotating electrical machine according to the invention; 
     FIG. 2 is a cross-sectional partial schematic view of a variant of the elementary machine in FIG. 1; 
     FIG. 3 is a cross-sectional partial schematic view of complete double-excitation electrical machine produced frog the elementary machine in FIG. 1; 
     FIG. 4 is a cross-sectional partial view of a double-excitation electrical machine resulting from the juxtaposition of several elementary machines of FIG. 1; 
     FIG. 5 is a cross-sectional partial schematic view of a double-excitation machine of a particular type; 
     FIG. 6 is a cross section on the line  6 — 6  of the machine in FIG. 5 without its stator; 
     FIG. 7 is a cross-sectional partial view of a double-excitation machine with an offset stator excitation winding in the rotor; and 
     FIG. 8 is a cross-sectional partial schematic view of a double-excitation electrical machine according to the invention resulting from the juxtaposition of a machine of FIG.  7  and of machines similar to that of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The electrical machine shown in FIG. 1 is a machine comprising, mounted on a shaft  1  made of non-magnetic material, a rotor  2  whose magnetic circuit includes toothed discs  3  provided with radial teeth  4  uniformly distributed around their periphery. 
     The radial teeth  4  of one plate  3  are offset with respect to the radial teeth of the other plate so that a tooth of one plate lies opposite a gap between the teeth of the other plate. 
     An annular piece  5  provided with slots  6  uniformly spaced around its periphery, which in the present example are made in the form of axial slots emerging at the opposite ends of the annular piece, is mounted coaxially with respect to the shaft  1 . The teeth  4  of the toothed discs  3  are engaged in corresponding slots  6  in the annular piece  5  without any contact with the walls of the said slots. The annular piece  5  is fastened to the shaft  1  by any suitable mechanical means (not shown). 
     Placed between the toothed discs  3  is an annular excitation magnet  7 . 
     Moreover, in the example shown in FIG. 1, magnets  8  are placed in the gaps between the teeth  4  of the toothed discs  3  and the walls of the corresponding slots  6  of the annular piece  5 . 
     However, the gaps between the teeth  4  may also be devoid of such magnets. 
     The rotor  2  is surrounded by a stator  10  comprising a laminated magnetic circuit formed from two magnetic-circuit elements  11  joined together by an external annular yoke  12  and on which an armature winding  13  is mounted. An excitation winding  14  is placed between the magnetic-circuit elements  11 . 
     The electrical machine shown in FIG. 2 is in every way similar to that of FIG. 1 apart from the fact that it has a shaft  15  made of a magnetic material and from the fact that the toothed discs  3  each have a central bore  16  ensuring that they are magnetically separated from the shaft  15 . 
     Advantageously, a ring of insulating material  17  is placed in each central bore  16 . 
     Furthermore, in the present embodiment, the gaps between the teeth  4  of the toothed discs  3  and the walls of the slots  6  of the annular piece  5  are devoid of magnets. 
     The electrical machine shown in FIG. 3 has a shaft  21  made of non-magnetic material carrying a rotor  22  which includes two end plates  23  between which two toothed discs  24  are placed, the said toothed discs  24  being provided with radial teeth  25  placed at regular angular intervals, the teeth of one of the discs being angularly offset with respect to the teeth of the other disc. 
     Mounted on the end plates  23  is an annular piece  26  provided with slots  27  which, in the present example, are axial slots and in which the teeth  25  of the toothed discs  24  are engaged without any contact. 
     Excitation magnets  28 ,  29  are placed, on the one hand, between the toothed discs  24  and, on the other hand, between each toothed disc and the corresponding end plate  23 . 
     The excitation magnet  28  placed between the toothed discs  24  and the excitation magnets  29  placed between each toothed disc and its corresponding end plate  23  are of reverse polarities. 
     The rotor thus formed is surrounded by a stator  30  comprising a magnetic circuit formed from two magnetic-circuit elements  31  each placed opposite a corresponding toothed disc  24  and on which a stator winding  32  is mounted. 
     The magnetic-circuit elements  31  are joined together by a yoke  33 . Placed between the magnetic-circuit elements  31  is an excitation winding  34 . 
     The electrical machine shown in FIG. 4 results from the juxtaposition of several elementary machines such as that shown in FIG.  1 . 
     It has a common shaft  41  made of non-magnetic material which carries a rotor  42  formed from two end plates  43  and of toothed discs  44   a  to  44   n , n being an even number at least equal to two. 
     Each of the toothed discs  44   a  to  44   n  has teeth  45   a  to  45   n  offset one with respect to another. 
     The end plates  43  and the toothed discs  44   a  to  44   n  have bores  46  and  47   a  to  47   n  through which the non-magnetic shaft  41  passes. An advantageous embodiment consists in producing this annular piece by assembling n coaxial elementary annular pieces. Mounted on the end plates  43  is an annular piece  48  perforated by slots  49   a  to  49   n  uniformly distributed around its periphery and offset one with respect to another. The teeth  45   a  to  45   n  of the toothed discs  44   a  to  44   n  are engaged in the corresponding slots  49   a  to  49   n  without any contact with the latter. 
     Placed in the gaps provided between the end plates  43  and the toothed discs  44   a  to  44   n , defining with the shaft  41  and the perforated piece  48  forming a sleeve joined to the end plates, on the one hand, two end chambers  51  located between the first end plate  43  and the adjacent toothed disc  44   a  and between the second end plate  43  and the adjacent toothed disc  44   n  and, on the other hand, chambers  52   a  to  52   n− 1 located between the toothed discs  44   a  to  44   n , are annular magnets  53  and  54   a  to  54   n− 1, respectively. 
     The arrangement of these annular magnets is such that the polarities of the two adjacent magnets are of opposite sign or polarity. 
     The excitation magnets  53  located in the end chambers  51  have a thickness equal to half that of the magnets  54   a  to  54   n− 1 located in the chambers  52   a  to  52   n− 1 defined between the successive toothed discs  44   a  to  44   n.    
     The rotor that has just been described is mounted in a stator  55  having as many magnetic-circuit elements  55   a  to  55   n  as the rotor has toothed discs  44   a  to  44   n . A common armature stator winding  56  is mounted on these magnetic-circuit elements. 
     Spaced between two successive adjacent magnetic-circuit elements is a corresponding excitation winding  57   a  to  57   n− 1. 
     The electrical machine shown in FIG. 5 has a shaft  60  made of magnetic material on which is mounted a rotor  61  comprising two toothed discs  62  whose radial teeth  63  are uniformly distributed around the periphery of each disc, the teeth of one of the discs being offset with respect to those of the other. 
     The shaft  60  furthermore carries an annular piece  64  provided with slots such as the slot  65  which, in the present embodiment, consist of axial slots and in which the teeth  63  of the toothed discs  62  are engaged without any contact. 
     The annular piece  64  is linked to the shaft  61  by a disc-shaped central core  66 . 
     The toothed discs  62  each have, surrounding the shaft  60 , a bore  68  in which annular magnets  69  are placed. 
     Magnets  70  are also placed between the core  66  and each of the toothed discs  62 , while, as shown in FIG. 6, the gaps between the teeth  63  of each of the toothed discs  62  and the walls of the slots  65  in the annular piece  64  are furnished with magnets  72 . 
     The gaps between the teeth  63  of the toothed pieces  62  and the walls of the notches  65  in each annular piece  64  may also be devoid of such magnets. 
     The rotor that has just been described is surrounded by a stator  74  which has a magnetic circuit formed from two laminated annular magnetic-circuit elements  75  joined together by an external yoke  76  and carrying an armature winding  77 . 
     An excitation winding  78  is furthermore provided between the magnetic-circuit elements  75 . 
     The machine shown in FIG. 7 has a non-magnetic shaft  81  which carries a rotor  82  formed from a toothed double disc  83  mounted on the shaft  81  and provided with radial teeth  84   a ,  84   b  made on each of the elements  83   a ,  83   b  of the toothed double disc which thus define two toothed discs. The teeth  84   b  are angularly offset with respect to the teeth  84   a.    
     Mounted on either side of the toothed double disc  83  are end plates  85  provided with teeth which between them define axial slots  86  in which the radial teeth  84   a  and  84   b  of the toothed double disc  83  are engaged without any contact. 
     The end plates  85  provided with axial teeth defining annular pieces similar to those of the embodiments described previously. 
     Placed between the end plates  85  and the opposite ends of the toothed double disc  83  are annular excitation magnets  87 . 
     Furthermore, magnets  88  are placed in the spaces left free between the teeth  86  of the end plates  85  and the teeth  84   a ,  84   b  of the toothed double disc  83 . 
     The magnets  88  may also be omitted. 
     The rotor thus formed is surrounded by a stator  90  comprising a magnetic circuit formed from two laminated magnetic-circuit elements  91  each placed opposite one of the elements  83   a ,  83   b  of the toothed double disc  83  and joined together on the outside by a yoke  92 . 
     An excitation winding  93  is placed between the two magnetic-circuit elements  91 . 
     Made in the toothed double disc  83  of the rotor  82  is a groove  94  in which a second stator excitation winding  95  is placed. 
     According to a variant, the machine shown in FIG. 7 may have only one excitation winding such as the winding  93  located between the magnetic-circuit elements  91  of the stator, or else a single excitation winding such as the winding  95  placed in the annular groove  94  of the toothed double disc  83 . 
     The electrical machine shown in FIG. 8 results from the juxtaposition of a double-excitation electrical machine of the type shown in FIG.  7  and of an elementary machine such as that described with reference to FIG.  3 . 
     It has a shaft  101  made of non-magnetic material which carries a rotor  102  comprising end plates  103  provided with teeth defining, between them, axial slots  104  which are uniformly distributed around their periphery and facing each other in order to form two perforated annular pieces or cages. 
     Placed between the end plates  103  made of magnetic material are intermediate toothed discs formed by a central toothed double disc  105 , an element  105   a  of which has radial teeth  106   a  and a second element  105   b  of which has radial teeth  106   b . The teeth  106   a ,  106   b  of the first and second elements  105   a ,  105   b  of the toothed double disc  105  are uniformly distributed around the periphery of the double disc and angularly offset one with respect to another. 
     On either side of the toothed double disc  105 , the elements  105   a ,  105   b  of which form intermediate toothed discs, the rotor  102  has a first toothed disc  107  provided with radial teeth  108  and a second toothed disc  109  provided with radial teeth  110 . The teeth  108  and  110  of the toothed discs  107  and  109  are uniformly distributed around the periphery of the corresponding discs and angularly offset. 
     Engaged respectively in the axial slots  104  of the end plates  103  are the teeth  106   a  of one of the elements  105   a  of the toothed double disc  105  and the teeth  108  of the adjacent first toothed disc  107 , on the one hand, and the teeth  106   b  of the other element  105   b  of the toothed double disc  105  and the second teeth  110  of the corresponding toothed disc  109 , on the other hand. 
     Magnets  115  are placed in the spaces left free between the teeth  106   a  and  106   b  of the elements  105   a  and  105   b  of the toothed double disc and the slots  104  of the end plates  103 . 
     Annular excitation magnets  112 ,  114  are inserted, on the one hand, between the end plates  103  and the first and second toothed discs  107 ,  109  and, on the other hand, between the latter and the toothed double disc  105 . 
     The rotor thus formed is surrounded by a stator  116  comprising a magnetic circuit formed from four magnetic-circuit elements  116   a ,  116   b ,  116   c ,  116   d  and on which an armature stator winding  117  is mounted. Each of the annular circuit elements  116   a  to  116   d  is placed opposite the radial teeth of a toothed disc  107 ,  109  and opposite each of the elements  105   a ,  105   b  of the toothed double disc  105 . 
     The magnetic-circuit elements  116   b ,  116   c  which are placed opposite the two elements  105   a ,  105   b  of the toothed double disc  105  are joined together by an external yoke  118 . A stator excitation winding  119  is placed between the elements of the magnetic circuit  116   b  and  116   c.    
     Moreover, another stator winding  120  is placed in an annular slot  121  made in the magnetic circuit of the rotor between the two elements  105   a ,  105   b  of the toothed double disc  105 . 
     Because of the arrangement of this stator excitation winding inside a groove made in the body of the rotor, the machine described with reference to FIG. 8 is less bulky than that of known double-excitation machines. What is more together with the machine in FIG. 7, it is the least bulky of the machines according to the invention.