Abstract:
A method for producing a rotor assembly for a rotating electrical machine, especially an alternator, the rotor assembly including two rotors defining between themselves at least one inter-rotor space suitable for accommodating at least one magnet structure, which includes at least one index mark. The magnet structure is positioned against at least two of the rotors, using the index mark to identify a direction of orientation of the magnetization of the magnet structure.

Description:
FIELD OF THE INVENTION 
     The invention in particular relates to a method for producing a rotor assembly for a rotating electrical machine, especially an alternator. 
     BACKGROUND OF THE INVENTION 
     French Patent FR 2 793 085 describes an alternator for a motor vehicle, comprising a stator and a rotor. The rotor assembly comprises a winding and two rotors each equipped with a plurality of claws. The rotors define between themselves, on a level with the claws, inter-rotor spaces each able to accommodate a permanent magnet structure, in particular made of rare earth. The direction of magnetization of these magnet structures must be alternating from one inter-rotor space to the next. For this purpose, these magnet structures are arranged in two distinct groups, according to their direction of magnetization. However these two groups cannot be distinguished visually. Thus when the magnet structures are assembled in the inter-rotor spaces of the rotor, special care must be taken to select the magnet structures with the correct direction of orientation. 
     U.S. Pat. No. 7,095,154 describes an alternator rotor assembly comprising permanent magnets held in inter-rotor spaces by means of support elements. Each magnet is positioned in a non-centric way in the corresponding inter-rotor space. 
     SUMMARY OF THE INVENTION 
     The invention is aimed in particular at simplifying the method for producing a rotor assembly while avoiding risks of error in assembling the magnet structures. 
     The object of the invention is thus a method for producing a rotor assembly for a rotating electrical machine, especially an alternator, the rotor assembly comprising two rotors defining between themselves at least one inter-rotor space suitable for accommodating at least one magnet structure, which comprises at least one index mark, the method comprising the following step:
         positioning the magnet structure against at least one of the rotors, using the index mark to identify a direction of orientation of the magnetization of the magnet structure.       

     The presence of index marks according to the invention enables the risk, when assembling the magnet structures on the rotor by orientating them along an incorrect direction of magnetization, to be reduced or even eliminated. 
     These index marks also make it possible to quickly check if all the magnet structures are correctly positioned in the inter-rotor spaces. 
     As the case may be the magnet structures can be placed on the rotor all the right way or all the wrong way, and the collector is placed, at the closing of the electrical circuit of the machine, in an adequate configuration depending on the position of the magnet structures observed. 
     The invention is particularly suited to a method carried out manually. 
     It is also possible to check the electromagnetic circuit of the electrical machine at the end of assembly. 
     In an exemplary embodiment of the invention, the magnet structure is positioned against one of the rotors, before they are assembled. 
     Alternatively, the magnet structure is inserted in an inter-rotor space after the two rotors have been assembled. 
     Preferably, the index mark of the magnet structure is visible with the naked eye, enabling a person to identify an orientation of magnetization of the magnet structure for example. 
     As the case may be, in order to magnetize the magnet structures, these are positioned in parallel, along the same direction, when they pass through a magnetizing device. 
     With the invention it is thus possible to avoid having to magnetize the magnet structures along two different directions and therefore creating two groups of magnets, which simplifies the method. 
     Moreover by handling magnet structures all with the same orientation of magnetization with respect to the index mark, it is possible to avoid confusion in the various production stages of the rotor assembly. A single magnet structure reference can be used. 
     Alternatively it is possible, in order to magnetize the magnet structures, to position these in parallel, along an alternating direction, when they pass through a magnetizing device. In this case two magnet structure references can be used. 
     In an exemplary embodiment of the invention, the rotor assembly comprises a plurality of inter-rotor spaces, each able to accommodate at least one magnet structure, and the method comprises the following step:
         starting with a set of magnet structures all having north and south poles directed the same way with respect to the corresponding index mark, selecting and positioning a plurality of magnet structures on at least one of the rotors in the successive inter-rotor spaces, orientated alternating from one inter-rotor space to the other.       

     The method can comprise the following step:
         selecting and making the magnet structure rotate by a chosen angle, in particular using the index mark as reference, in order to place it in an adequate position before positioning it against one of the rotors.       

     The above steps can be carried out manually or, alternatively, using a robot equipped with an articulated arm. 
     The object of the invention is equally a magnet structure suitable for mounting in a rotor assembly for a rotating electrical machine, especially an alternator, in particular produced by the method as defined above, characterized in that it comprises at least one index mark suitable for permitting, in particular visually, the direction of magnetization of this magnet structure to be distinguished. 
     In an exemplary embodiment of the invention, the magnet structure comprises a plate and a magnet positioned against the plate, and the index mark is created at least partially on the plate. 
     This plate is used in particular to hold the magnet and plays a role of mechanical absorber. 
     If desired, the index mark comprises at least one orifice or cut formed in the plate. 
     The index mark can comprise an excess length of the magnet in the continuation of the length of the plate, said excess length only being present on one side of the magnet structure so as to distinguish one side of the magnet from the other. 
     Alternatively, the plate can have an excess length with respect to the magnet. 
     This being the case, the index mark is formed by at least two zones having different, in particular optical, electromagnetic properties, being of different colours or reflective properties for example. 
     These two zones of different optical properties can extend in the length or width of the magnet structure. 
     The index mark, if desired, is formed by a variation in the thickness of either the plate or the permanent magnet. 
     In an exemplary embodiment of the invention, the index mark is created at least partially on the magnet. 
     The index mark may be constituted by an extraction of material, a notch for example, on the magnet or a sign printed on this magnet for example. 
     Generally the index mark, that it is formed on the magnet or the plate or both at the same time, can be created in various ways, in particular by creating a discontinuity and/or dissymmetry, for example by cutting, notching, printing of an ink visible or invisible with the naked eye, affixing, for example by bonding, a separate element such as an adhesive patch or a label, etc. . . . . 
     In an exemplary embodiment of the invention, at least one of the magnet structures has a roughly rectangular parallelepipedic shape or alternatively a trapezoidal cross section. 
     For example, the plate is fixed by adhesive on the magnet. 
     The object of the invention is equally a rotor assembly comprising two rotors and at least one magnet structure as defined above, mounted in a defined inter-rotor space between the two rotors. 
     Advantageously all the magnet structures have the same direction of magnetization with respect to the index mark. 
     Preferably, all the magnet structures of the rotor assembly are identical. 
     Advantageously the magnet structure comprises a permanent magnet extending over the whole width of the inter-rotor space. 
     The object of the invention is again a rotating electrical machine, especially an alternator of a motor vehicle, comprising a rotor assembly as mentioned above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood on reading the detailed description below of non-restrictive, exemplary embodiments of the invention, and on examining the appended drawing, wherein: 
         FIG. 1  schematically and partially illustrates in longitudinal section, an alternator conforming to an exemplary embodiment of the invention, 
         FIG. 2  schematically illustrates production stages of a rotor assembly of the alternator of  FIG. 1 , and 
         FIGS. 3 to 11  schematically and partially illustrate examples of magnet structures according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the continuation of the description, arrows “A” and “R” of  FIG. 1  indicate axial and radial directions respectively. 
       FIG. 1  shows a poly-phase rotating electrical machine  1 , in this exemplary embodiment of the invention, forming an alternator for a motor vehicle. Of course, the electrical machine  1 , if desired, may be reversible and form an alternator-starter, which can function in electric motor mode to start the combustion engine of the vehicle and in alternator mode to generate electrical energy. 
     This machine  1  comprises a casing  10  and, inside the latter, a rotor assembly  12  rotating as one with a rotary shaft  14  of axis X, called rotor shaft, and a stator  16  which surrounds rotor assembly  12 . 
     Stator  16  comprises a body  17  formed from a stack of laminations provided with notches for assembling a stator winding  18  forming coil ends on either side of the stator body  17 . 
     Rotor assembly  12  comprises two rotors  20  and  22 , each equipped with a transverse plate  24 , on the periphery of which is connected a plurality of claws  26  extending roughly along axial direction A. 
     Each claw  26  has an overall trapezoidal shape when observed along radial direction R, as can be seen in particular on  FIG. 2 . 
     Claws  26  of one rotor with claws  26  of the other rotor form inter-rotor spaces  28 , each suitable for accommodating a magnet structure  30 . 
     A field winding  34  is created between the plates  24  of the rotors  20  and  22 . 
     Each rotor  20 ;  22  comprises a borehole forming an internal passage  38  for accommodating the shaft  14 . 
     The rotors  20  and  22  are made of steel for example. 
     The shaft  14  on its front end bears a pulley  40  belonging to a device for transmitting movement by means of at least one belt (not illustrated) between alternator  1  and the combustion engine of the motor vehicle, and at its rear end collecting rings  42  connected by wires (not illustrated) to the field winding  34  of rotor assembly  12 . 
     Brushes of a brush holder  44  illustrated in a very diagrammatic way are positioned in such a way as to rub on the collecting rings so as to feed electric current to winding  34 . 
     When the shaft  14  rotates and field winding  34  is activated by a power supply, the inductive rotor assembly  12  creates an induced AC current in stator  16 . 
     Casing  10 , in the example considered, consists of two parts, that is to say a front bearing  46  and a rear bearing  48  supporting brush holder  44 . 
     Bearings  46  and  48  each contain a ball-bearing  50  and  52  respectively for the rotating support of the shaft  14 . 
     Alternator  1  also comprises means for its cooling. 
     For example, as illustrated on  FIG. 1 , bearings  46  and  48  are ventilated to allow the alternator to be cooled by air circulation. 
     Rotor assembly  12 , in the example described at least at one of its axial ends, comprises a fan designed to provide air circulation. A first fan  54  is arranged on the front transverse face of rotor assembly  12  and a second ventilation unit  56  is arranged on the rear face of rotor assembly  12  for example. Each fan  54  and  56  is equipped with a plurality of blades  58  and  60 . 
     In the exemplary embodiment described, each rotor  20 ;  22  comprises six claws  26  so as to define a rotor assembly  12  with inter-rotor spaces  28 . 
     Alternatively, rotor assembly  12  can comprise 2, 4, 6, 8 or 10 inter-rotor spaces  28 , according to the type of electrical machine desired. 
     In particular with reference to  FIG. 2 , various production stages of rotor assembly  12  will now be described, particularly in connection with the assembly of the magnet structures  30  in inter-rotor spaces  28 . 
     Each magnet structure  30  comprises a permanent magnet  70 , for example made of rare earth, and a plate  71  made of non-magnetic material, for example composite material containing glass fibres. 
     In the example considered, illustrated on  FIG. 3 , the permanent magnet  70  has a roughly rectangular parallelepipedic shape. 
     This shape of the magnet is rotation invariant with an angle of 180° so that it is impossible to visually distinguish a side face  72  of north polarity and an opposite side face  73  of south polarity after magnet  70  has been magnetized. 
     In the method illustrated on  FIG. 2 , the magnet structures  30  have passed through a magnetizing device  80  designed to magnetize magnets  70  of structures  30  using a magnetic field illustrated by arrow B. 
     After this step each magnet  70  has north and south polarities, respectively, on its opposite faces  72  and  73 . 
     The magnet structures  30  pass through device  80  batch-wise, being aligned in parallel. 
     In the example described, plate  71  has a rectangular shape and entirely covers a face of the permanent magnet  70 , this plate  71  being fixed on magnet  70  before passing through the magnetizing device  80 . 
     In order to allow visual distinction between faces  72  (north) and  73  (south) of magnet  70 , and thus recognition of the direction of magnetization of this magnet  70 , each magnet structure  30  comprises an index mark  75 . 
     In the example illustrated with reference to  FIG. 3 , the index mark  75  comprises an orifice  76  formed in plate  71 , nearer to one axial end  77  than the other end  78 . 
     Thus, in order to position the magnet structures  30  on one of the rotors  20 ;  22 , with the magnetization of magnets  70  oriented alternating from one inter-rotor space to the next, it is possible to use the index mark  75  to visually identify a direction of orientation of the magnetization of structure  30 . 
     For example, so that a first magnet structure  30  can be positioned in the first inter-rotor space  28 , the latter is orientated so that the index mark  75  is radially on the inside and, so that a second magnet structure  30  can be positioned in the second inter-rotor space  28 , this structure  30  is rotated to position it with the index mark situated on the outside (see  FIG. 2 ). 
     The invention thus enables errors in the orientation of magnetization structures  30  to be avoided, which is particularly advantageous if these structures  30  are assembled manually, the operator being assisted by the magnetization mark in orientating structures  30 . 
     It should be noted that the magnet structures  30  are fixed on one of the rotors  20 ;  22  before this rotor is assembled with the other rotor. 
     These magnet structures  30  are joined to the rotor by magnetization, before being enclosed between the two rotors  20  and  22 . 
     In the example which has just been described, plate  71  entirely covers a magnet face  70 . 
     Alternatively, as illustrated on  FIG. 4 , magnet  70  has an excess length  78  with respect to plate  71  in the longitudinal direction, at an axial end  77 . 
     This excess length thus forms an index mark  75  within the meaning of the invention, being used to identify a direction of orientation of the magnetization of the magnet structure  30 . 
     Plate  71  can thus be intact, with no orifice, which in particular allows its production to be simplified as regards the cutting operations. 
     Alternatively, as illustrated on  FIG. 5 , the magnet structure  30  in addition to excess length  78 , has an orifice  76  in order to distinguish the sides of structure  30  in a redundant manner. 
     In the example illustrated on  FIG. 6 , plate  71  has a length equal to that of magnet  70 , with cuts  85  on one axial side so as to form an index mark  75 . 
     These cuts  85  have a triangular shape for example. 
     Of course, these cuts can have any other suitable shape. 
     For example, plate  71  can have a single rounded cut formed in the middle of an edge of plate  71 . 
     In the example illustrated on  FIG. 7 , plate  71  comprises a portion of reduced thickness  87 , extending on one axial side of magnet  70 . 
     This portion  87  forms an index mark  75  within the meaning of the invention. 
     In the examples which have just been described, the index mark  75  is formed by shapes and/or dimensions of plate  71 . 
     Of course should the index mark be created by other means, this would not depart from the scope and spirit of the invention. 
     As illustrated on  FIG. 8 , the index mark  75  is formed by at least two zones having different optical properties, in particular being of different colours or reflective properties. 
     In the example considered, plate  71  comprises two, for example rectangular zones  88  and  89 , of different surface areas, and having different colours. 
     These zones  88  and  89  extend along a width of the magnet structure. 
     Alternatively, as illustrated on  FIG. 9 , zones  88  and  89  of identical surface area extend along a length of the structure. 
     For example, the north side (N) can be associated with a first colour of zone  89  and the south side (S) with a second colour, different from the first colour, of zone  88 . 
     When the structures are assembled on a rotor, it is possible to position the magnet structures so that all the sides of the same colour are on the rotor. 
     The index mark  75 , if desired, can be created on magnet  70 , and not on plate  71 . 
     The magnet structure  30  of  FIG. 10  comprises a magnet  70  and a plate  71  entirely covering a face of this magnet  70 . 
     An index mark  75  is formed on an axial end face  91  by way of a notch  90 . 
     This notch  90  has a rectilinear shape for example. 
     Alternatively, any other suitable shape of notch  90  can be considered. 
     For example, the notch can be circular. 
     Of course, the invention is not limited to the exemplary embodiments which have just been described. 
     For example, symmetrically on its two opposite axial ends, magnet  70  can be of a shape with rounded corners. 
     Plate  71 , if desired, can cover at least two faces of magnet  70 . 
     For example, as illustrated on  FIG. 11 , plate  71  has a portion  95  folded at right angles and covering a radial face of the permanent magnet  70 . This face can be a front or rear face of the magnet. 
     This portion  95  is used to define an index mark  75  within the meaning of the invention.