Abstract:
A method of manufacturing a rotor for rotating electrical machines, notably an alternator, the rotor including two magnet wheels defining between them at least one interpole space arranged to receive at least one magnet. At least one angular indexing mark is produced on at least one of the magnet wheels. At least one groove partially delimiting the interpole space is formed, by machining, on the magnet wheel while maintaining the magnet wheel in an angular position dependent on the angular indexing mark.

Description:
FIELD OF THE INVENTION 
     The invention concerns in particular a method of manufacturing a rotor for a rotating electrical machine, in particular an alternator. 
     BACKGROUND OF THE INVENTION 
     The patent FR 2 793 085 describes an automobile vehicle alternator comprising a stator and a rotor mounted on a shaft. The rotor includes a coil and two pole wheels each provided with a plurality of claws. Interpole spaces that can receive rare earth permanent magnets are defined between the claws of the wheels. The method of manufacturing the rotor includes the step of machining grooves in the claws, once the pole wheels have been assembled, by means of one pass of a tool. This method has a number of drawbacks. For example, as the coil is assembled between the pole wheels before machining the grooves, lubricant is not used during machining, which leads to faster wear of the tool and/or slower machining. Moreover, because of the limitations imposed on the machining tool used, the interpole space between the grooves cannot be made as narrow as required. Finally, swarf produced by the machining can be introduced into the rotor. 
     SUMMARY OF THE INVENTION 
     The invention aims in particular to remedy the aforementioned drawbacks. 
     Thus the invention consists in a method of manufacturing a rotor for a rotating electrical machine, in particular an alternator, the rotor including two pole wheels defining between them at least one interpole space adapted to receive at least one magnet, the method including, before assembly of the two pole wheels, the following steps:
         producing on at least one of the pole wheels at least one angular indexing mark, and   forming by machining on the pole wheel at least one groove partially delimiting the interpole space with the pole wheel secured in an angular position depending on the angular indexing mark.       

     Thanks to the invention, machining being carried out before assembling the pole wheels, the type of tool used to machine the groove (which can be a standard tool) can be chosen so as to be able to form a groove, and therefore an interpole space, of small size, thus enabling small magnets to be inserted into the interpole spaces. 
     It is equally possible to avoid the risk of cutting the wires of the coil that exists if machining is carried out after assembly and to have larger winding windows. 
     The risk of introducing swarf into the rotor can also be reduced. 
     It is further possible to modify the width of the machined groove without changing the machining tool, by varying the displacement of the tool during machining. 
     Moreover, as the grooves are machined before assembling the different components of the rotor, in particular a coil, it is possible to use a lubricant when machining the grooves. 
     What is more, machining can be effected for the most part upstream of the final rotor assembly line, for example by a supplier. 
     It is possible to have a single machining station for a number of assembly lines, if required. 
     The angular indexing marks of the invention, which serve as angular references, enable the corresponding pole wheel to be positioned precisely during machining. As the pole wheels can be assembled using the angular indexing marks as angular references, the relative disposition of the pole wheels can be precise, which ensures that the interpole spaces are themselves precise, so as to be able to insert magnets into them correctly. 
     In one embodiment of the invention the method includes, before assembling the two pole wheels, the step of adjusting the diameter of at least one of the pole wheels by machining a circumferential face of the pole wheel with the pole wheel secured in an angular position depending on the angular indexing mark. 
     The method can include the following step:
         producing a bore in the pole wheel with the pole wheel secured in an angular position depending on the indexing mark so as to form an interior passage adapted to receive a shaft of the rotating electrical machine.       

     The invention produces an interior passage at a precise position identified by the angular indexing mark or marks. 
     The method preferably includes the following step:
         assembling the pole wheels positioned angularly relative to each other by means of indexing marks produced on the pole wheels.       

     As the grooves delimiting the interpole spaces are machined with the pole wheels positioned relative to the indexing marks and the pole wheels are assembled taking the indexing marks as references, the grooves, which define functional surfaces, are positioned precisely relative to each other, which ensures that the interpole spaces have precise dimensions so that the permanent magnets can be inserted in them correctly. 
     In one embodiment of the invention, the pole wheel is secured in the predetermined angular position by at least one locating rod cooperating with at least one of the indexing marks of the pole wheel. 
     The locating rod can belong for example to a machine on which the pole wheel is machined or a machine on which two pole wheels are assembled. 
     The locating rods are for example retractable rods that can be engaged with the indexing marks of the pole wheels and retracted to be disengaged from those marks. 
     The locating rod or rods can be adapted to be moved parallel to or perpendicular to a longitudinal axis of the pole wheel, depending on the embodiment. 
     In one embodiment of the invention, the pole wheel includes at least two consecutive claws and the indexing mark is formed between two consecutive claws of the pole wheel. 
     For example, the indexing mark can be formed at an equal angular distance from the two claws. Alternatively, the indexing mark can be formed closer to one of the claws. 
     If required, the indexing mark can be formed on a lateral face of the pole wheel, the indexing mark having in particular a hollow shape, for example being a notch. This notch has a substantially circular arc shaped cross section, for example. The indexing mark can for example extend between two opposite plane faces of the pole wheel. 
     If necessary, the pole wheel can include two angular indexing marks, in particular diametrally opposed. Alternatively, the indexing marks can be disposed one relative to the other at an angular distance less than 180°. 
     It is equally possible to have on one pole wheel an angular indexing mark between the claws of each consecutive pair, which marks can then serve as polarizers. 
     The angular indexing mark is advantageously formed by removing material, in particular by machining. 
     In one embodiment of the invention, the method includes a step of calibrating the pole wheel and the angular indexing mark is produced by machining during or after calibrating the pole wheel. This calibration step adjusts the dimensions of the pole wheel, for example by cold pressing in a mold. 
     The angular indexing mark can advantageously be produced before machining the groove partially defining the interpole space. 
     In another embodiment of the invention, when the pole wheel is produced by molding, the indexing mark can be produced as part of molding the pole wheel. A step can be provided for removing any flash from the indexing mark after extraction of the pole wheel from the mold. 
     The rotor preferable includes a coil and at least one interpole magnet, and the method includes the following step:
         after assembling the two pole wheels, the coil and the interpole magnet, impregnating at least the coil and the interpole magnet with a varnish.       

     The invention enables the coil and the interpole magnets to be impregnated in only one step, which reduces the cost of production. 
     The rotor can include front and rear fan elements, notably provided with blades, the method being characterized in that it includes, after assembling the two pole wheels and fixing the fan elements to the pole wheels, a step of impregnating the rotor with a varnish. 
     In this way the ventilation elements can be protected from corrosion by the varnish. 
     The invention also consists in a pole wheel for rotating electrical machine rotors, characterized in that it includes an angular indexing mark, in particular produced by removing material. 
     For example, the angular indexing mark can include a notch formed between two consecutive claws of the pole wheel. 
     The notch is advantageously produced by machining the pole wheel. 
     In one embodiment of the invention, the wheel includes at least one claw on which is formed at least one groove adapted to form, after assembly with another pole wheel, an interpole space in which at least one magnet is inserted. 
     The invention further consists in a rotor including two pole wheels as defined hereinabove. 
     The invention further consists in a rotating electrical machine, in particular an automobile vehicle alternator, including a stator and a rotor as defined hereinabove. 
     The invention further consists in a method of manufacturing a rotor of a rotating electrical machine, in particular an alternator, the rotor including two pole wheels, the method including the following steps:
         producing on each pole wheel at least one angular indexing mark,   assembling the pole wheels with them disposed angularly relative to each other using the indexing marks as angular references.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood by reading the following detailed description of non-limiting embodiments of the invention and examining the appended drawings, in which: 
         FIG. 1  is a partial diagrammatic representation in longitudinal section of an alternator conforming to one embodiment of the invention, 
         FIG. 2  is a block diagram illustrating steps in the manufacture of the pole wheels and their assembly to form the  FIG. 1  alternator, 
         FIG. 3  is a block diagram illustrating steps in the manufacture of the rotor of the  FIG. 1  alternator, 
         FIG. 4  is a partial diagrammatic representation of a pole wheel of the rotor for the  FIG. 1  alternator as seen from the side, 
         FIG. 5  is a partial diagrammatic representation of the pole wheel from  FIG. 4  as seen from below, 
         FIG. 6  is a partial diagrammatic representation in section of the  FIG. 4  pole wheel, 
         FIGS. 7 to 9  are partial diagrammatic representations of different steps in the assembly of the two pole wheels of the  FIG. 1  alternator, and 
         FIG. 10  is a partial diagrammatic representation in section taken along the line X-X of a detail of the rotor of the  FIG. 1  machine. 
     
    
    
     The axial and radial directions referred to in the remainder of the description are indicated by the arrows “A” and “R”, respectively, in  FIG. 1 . 
     DETAILED DESCRIPTION 
     There is represented in  FIG. 1  a polyphase rotating electrical machine  1  which in the present embodiment of the invention takes the form of an automobile vehicle alternator. If required, the electrical machine  1  can be reversible and form an alternator-starter that can operate in electric motor mode, in particular to start the internal combustion engine of the vehicle. 
     This machine  1  includes a casing  10  and, inside the latter, a rotor  12  constrained to rotate with a central shaft  14 , called the rotor shaft, about its axis X, and a stator  16  that surrounds the rotor  12  and that includes a laminated body with cut-outs for mounting a stator coil  18  forming a bun-shaped assembly on either side of the stator  16 , i.e. at each axial end thereof. 
     The rotor  12  includes two pole wheels  20  and  22  each provided with a transverse flange  24  to a periphery of which is connected a plurality of claws  26  extending substantially in the axial direction A so as to form recesses  27  between each of the two consecutive claws  26  of the pole wheel. The claws  26  of each of the pole wheels  20 ,  22  are spaced apart in a circumferential direction, as illustrated in  FIG. 5 . 
     The claws  26  have a trapezoidal overall shape when viewed in a radial direction R, as can be seen in  FIG. 6  for example. 
     The claws  26  of one pole wheel form with the claws  26  of the other pole wheel interpole spaces  28  adapted to receive one or more permanent magnets  30 , as explained hereinafter with reference to  FIG. 10 . 
     An excitation winding  34  is placed between the flanges  24  of the pole wheels  20  and  22 . 
     Each pole wheel  20 ;  22  includes a bore forming an interior passage  38  adapted to receive the shaft  14 . 
     The pole wheels  20  and  22  are produced in steel, for example. 
     When the shaft  14  is rotating and the excitation winding  34  is activated by an electrical power supply, the inductor rotor  12  generates an induced alternating current in the stator  16 . 
     The shaft  14  carries at its front end a pulley  40  belonging to a device for transmitting motion via at least one belt (not shown) between the alternator  1  and the internal combustion engine of the automobile vehicle and at its rear end  42  collector rings connected by wire connections (not shown) to the excitation winding  34  of the rotor  12 . 
     Brushes on a brush-holder  44  represented in a highly diagrammatic manner rub on the collector rings in order to supply the winding  34  with electric current. 
     In the embodiment considered here, the casing  10  comprises two parts, namely a front bearing  46  substantially adjacent the pulley  40  and a rear bearing  48  carrying the brush-holder  44 . 
     The bearings  46  and  48  each carry a respective ball bearing  50  and  52  for rotational mounting of the shaft  14 . 
     The alternator  1  also includes means for cooling it. 
     For example, as shown in  FIG. 1 , the bearings  46  and  48  include perforations to enable cooling of the alternator by circulation of air. 
     In the embodiment described, at least one of the axial ends of the rotor  12  carries a fan adapted to circulate air. A first fan element  54  is provided on the front transverse face of the rotor  12 , for example, and a second fan element  56  is provided on the rear face of the rotor  12 . Each fan element  54  and  56  is provided with a plurality of blades  58  and  60 . 
     In the embodiment described, each pole wheel  20 ;  22  includes six claws  26  so as to define a rotor with 12 interpole spaces  28 . 
     Alternatively, the rotor  12  can include 2, 4, 6, 8 or 10 interpole spaces  28 , according to the type of electrical machine required. 
     A detail of the rotor  12  is described next with reference to  FIGS. 5 and 10 . 
     Each claw  26  of a pole wheel  20 ;  22  has two lateral faces  70  defining with faces  70  of the other pole wheel  20 ;  22  the interpole spaces  28 . 
     Each lateral face  70  is provided with a groove  71  of substantially rectangular section, which is produced in the embodiment considered here by a machining process, as explained hereinafter. 
     The magnets  30  inserted in the interpole spaces  28  are permanent magnets, for example rare earth or ferrite magnets, in particular with a rectangular cross section. 
     If necessary, a plate or foil  72  can be disposed on the radially exterior face of each magnet  30  with an adhesive layer  73  between them. 
     Of course, inserting the magnets  30  in the interpole spaces  28  without using the plates  72  does not depart from the scope of the present invention. 
     Various steps in the manufacture and assembly of the pole wheels  20  and  22  are described hereinafter, in particular with reference to  FIG. 2 . 
     In a first step  80 , the pole wheels  20  and  22  are produced by moulding them in steel. 
     Each pole wheel  20 ;  22  produced by moulding includes the flange  24  and the claws  26 . 
     Then, in a step  81 , there is produced on each pole wheel  20 ;  22  at least one angular indexing mark  90 , visible in  FIG. 4 , for example, the function of which is explained hereinafter. 
     In the embodiment described, this indexing mark  90  is formed during calibration of the pole wheel  20 ;  22  by machining the pole wheel. 
     Alternatively, the indexing mark  90  can be formed beforehand when moulding the pole wheel  20 ;  22  and then made good by cold forging to eliminate any flash at the location of the indexing mark  90 . 
     In the embodiment shown in  FIGS. 4 to 6 , the indexing mark  90  includes a notch formed on a flank or lateral face  91  of the flange  24  of the pole wheel  20 ;  22  so as to extend substantially in the axial direction A. 
     This mark  90  lies in one of the recesses  27  between two consecutive claws  26  of the pole wheel  20 ;  22  at an equal angular distance from those two claws  26  as best shown in  FIGS. 4 and 5 . 
     The indexing mark  90  can have a circular arc shaped cross section, as shown in  FIG. 5 . 
     The invention is not limited to this notch shape, and the notch can have a part-polygonal section, for example. 
     Of course, in a variant that is not shown, the indexing mark  90  can be at a different location on the pole wheel  20 ;  22 , for example closer to one of the claws  26  than the other. 
     As represented in  FIGS. 5 and 6  in particular, each pole wheel  20 ;  22  includes two diametrally opposed angular indexing marks  90 . 
     Alternatively, each pole wheel  20 ;  22  can have a different number of the indexing marks  90 , for example only one indexing mark  90 . In any case, the number of the indexing marks  90  on each pole wheel  20 ,  22  is less than a number of claws  26  of each pole wheel  20 ,  22 , as shown, for example, in  FIG. 5 . 
     After the formation of the angular indexing marks  90 , in a step  82  represented in  FIG. 2 , the pole wheel  20 ;  22  is placed on a machine tool, not shown, with an angular orientation determined depending on the indexing marks  90 , which serve as angular references. 
     To this end, the machine is equipped with locating rods that can cooperate with the indexing marks  90  to locate the pole wheel  20 ;  22  in a predetermined angular position. 
     Once that angular position has been achieved, in a step  83 , a milling tool of the machine tool machines a circumferential face  94  of the claws  26  of the pole wheel  20 ;  22  (see  FIG. 4 ) to finish the outside diameter of the wheel. 
     The machine tool also produces a bore in the pole wheel  20 ;  22  to form the interior passage  38 . 
     Then, in a step  84 , the pole piece  20 ;  22  is transported to another machine tool on which the pole wheel is placed in a required angular position, in particular by causing a locating rod of the machine to cooperate with only one of the indexing marks, in conjunction with the introduction of an expandable chuck into the interior passage  38  of the pole wheel. 
     Thus only one of the two indexing marks  90  is used to locate the pole wheel during the step  84 . Alternatively, it is possible to use the two marks to locate the pole wheel. 
     Once the pole wheel  20 ;  22  has been located in this way, the grooves  71  are machined using a milling tool (not shown) of the machine. 
     Thus, machining being carried out before assembling the pole wheels, the type of milling tool used to machine the grooves  71  can be chosen so as to be able to form a groove  71 , and thus an interpole space  28 , of small size, thus enabling small magnets  30  to be inserted into the interpole spaces. 
     Then, in steps  86  and  87 , the two pole wheels  20  and  22  are placed on a base  103  of an assembly machine  100  represented in  FIGS. 7 to 9 . 
     Precise angular location of the pole wheels  20  and  22  is achieved by the cooperation of the locating rods  101  (see  FIG. 7 ) and  102  (see  FIG. 8 ) of the machine  100  with the angular indexing marks  90  of the wheels  20 ;  22 . 
     In the step illustrated in  FIG. 7 , the pole wheel  20  is introduced onto the shaft  14  via the interior passage  38 , whereas the pole wheel is located angularly by cooperation of the rod  90  with the indexing mark  90 . 
     In the  FIG. 8  step, the rod  101  is retracted and the other, shorter rod  102  engages with the indexing mark  90  so as to release the space necessary for mounting the other pole wheel  22  after fitting the coil  34 . 
     The pole wheel  22  is located in a predetermined angular position by one or more locating rods (not shown) of the machine  100 . 
     Once the wheels  20  and  22  have been pressed together, a tool  105  with a blade  106  is applied to the wheel  22  to crimp the wheel  22  onto the shaft  14 . 
     Steps in the manufacture of the rotor  12  from the pole wheels  20  and  22  are described next with reference to  FIG. 3 :
         pre-assembling (step  110 ) the pole wheels  20  and  22 , the shaft  14 , the coil  34 , the magnets  30  and the foils  72 , as described above,   crimping the pre-assembly to lock the various elements (step  111 ), compressing the material of the pole wheels onto a predetermined area of the shaft,   attaching and soldering the wires of the coil (step  112 ),   welding the fan elements  54  and  56  (step  113 ),   impregnating the coil  34 , fan elements and magnets  30  with varnish (step  114 ),   balancing the resulting rotor  12  (step  115 ), for example by forming one or more holes in the pole wheel,   finishing (step  116 ), for example machining conductive tracks of the collector.       

     Of course, the invention is not limited to the embodiment that has just been described.