Abstract:
The present invention provides a method for mounting at least one magnetic pole of a rotor of a motor of a synchronous electrical rotating machine from elementary elements, the rotor including a hub. The method includes the following successive steps: forming the set of elementary elements of rectangular parallelepipedal shape by fixing at least two elementary elements to each other with an electrical insulator being interposed therebetween; the set of elementary elements being magnetizable; machining a main face of the set of elementary elements in order to form a cylindrical face having a radius substantially equal to the predefined radius of the hub; magnetizing the set of elementary elements; and fixing the set of elementary elements to the hub, the set of elementary elements forming at least a portion of the magnetic pole.

Description:
Priority is claimed to French Patent Application No. 08 50804 filed on Feb. 8, 2008 which is hereby incorporated by reference herein. 
     The present invention relates to a method for mounting a magnetic pole of a rotor for a synchronous electrical rotating machine, for example, an electric motor or an alternator. 
     BACKGROUND OF THE INVENTION 
     The document EP 1 646 126 describes a rotor comprising magnetic poles which are constituted by a plurality of separate permanent magnets which are separated from each other by an electrically insulating sheet which is interposed therebetween. 
     It is known to form such magnetic poles in accordance with the following steps, arranged in the order described. 
     Firstly, elementary elements of rectangular parallelepipedal shape are magnetised in order to form permanent elementary magnets. Subsequently, the elementary magnets are adhesively bonded beside each other with the electrically insulating sheet being interposed in a recess formed over the periphery of the hub of the rotor. The recess has a convex bottom. The elementary magnets are adhesively bonded to each other and to the convex bottom of the recess with the magnetic poles (north/south) thereof directed in the same directions. 
     However, the step of adhesively bonding the elementary magnets is very long because the elementary magnets are fixed to each other and they repel each other. 
     Since the planar surface of the elementary magnets is further fixed to a surface having a convex bottom, there are gaps which form fissures or faults which are tapered at the surface of the magnetic pole formed in this manner. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method for mounting a magnetic pole which is simpler and more rapid. 
     The present invention provides a method for mounting a magnetic pole of a rotor for a synchronous electrical rotating machine, wherein the method includes the following successive steps: 
     a) forming a set of elementary elements by fixing at least two elementary elements to each other with an electrical insulator being interposed therebetween, said elementary elements being magnetizable; 
     b) magnetizing the set of elementary elements; 
     c) fixing the set of elementary elements to the hub, said set of elementary elements forming at least a portion of the magnetic pole. 
     According to specific embodiments, the method for mounting at least one magnetic pole may include one or more of the following features, taken in isolation or together:
         the set of elementary elements is of rectangular parallelepipedal shape and the method further includes a step of machining a main face of the set of elementary elements in order to form a cylindrical face which has a radius which is substantially equal to the radius (R) of the hub, said machining step being carried out before the magnetising step,   the cylindrical face has a cylinder axis (X-X), the axis (X-X) being perpendicular to the longitudinal faces of the set of elementary elements and parallel with the lateral faces of the set of elementary elements,   the elementary elements are fixed to each other by means of an adhesive and the electrical insulator is an electrically insulating sheet,   the elementary elements are fixed to each other by means of an adhesive which is charged with solid particles or an adhesive which is charged with non-conductive material fibres, said adhesive forming the electrical insulator,   the steps a) to c) are repeated in order to obtain a plurality of sets of elementary elements, said sets of elementary elements being fixed to the hub beside each other with an electrical insulator being interposed therebetween, a longitudinal face of a set of elementary elements forming a lateral face of the magnetic pole,   a step of fixing an electrical insulator to the hub, the electrical insulator being interposed between the hub and said sets of elementary elements,   a step of fixing an electrical insulator to the cylindrical face of the sets of elementary elements,   the set of elementary elements comprises from 2 to 20 elementary elements.       

     The invention further provides a rotor for a synchronous electrical rotating machine comprising a hub, characterized in that at least one magnetic pole is constructed on the hub by the mounting method described above. 
     By way of a variant, the rotor constructed on the hub may include recesses whose bottom surface is planar, the set of elementary elements being fixed against the bottom surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from a reading of the following description which is given purely by way of example and with reference to the drawings, in which: 
         FIG. 1  is an axial section of an electric motor having permanent magnets comprising a rotor in accordance with the invention; 
         FIG. 2  is a sectional view taken in a plane II-II of the rotor of  FIG. 1 ; 
         FIG. 3  is a flow chart illustrating the steps of the method for mounting a magnetic pole according to the invention; 
         FIG. 4  is a perspective view of an elementary element; 
         FIG. 5  is a perspective view of a set of elementary elements; 
         FIG. 6  is a perspective view of the set of  FIG. 5  after machining; 
         FIG. 7  is a side view of the set of  FIG. 6 ; and 
         FIG. 8  is a perspective view of four sets of elementary elements which are fixed in a recess of a rotor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a method for mounting magnetic poles on a rotor of a synchronous electrical rotating machine. This method is described by way of example by magnetic poles  2 ,  4  being mounted on the rotor  6  of an electric motor  8 . ( FIG. 1 ). 
     As illustrated in  FIG. 1 , the electric motor  8  includes a stator  10  which is fixedly joined to a casing  12 , and a rotor  6  which is fixedly joined to a shaft  16 . 
     The stator  10  surrounds the rotor  6  and includes windings  18  which are capable of generating a magnetic flux. 
     The rotor  6  includes a hub  20  which is fixed in terms of rotation to the shaft  16  by drive means, such as, for example, grooves. The hub  20  is of cylindrical outer shape having a predefined radius R. The hub  20  may be made exclusively from a metal or a metal alloy which conducts a magnetic field, in particular a ferromagnetic material. 
     As shown in  FIG. 2 , recesses  22 ,  24  are formed over the periphery of the hub  20 . The recesses  22 ,  24  are regularly spaced apart from each other. 
     The recesses  22 ,  24  are intended to receive permanent magnets in order to constitute the magnetic pole  2 . 
     The recesses  22 ,  24  have a flat bottom wall  34 . The recesses  22 ,  24  have a width and a length which are equal to the width l E  and the length L E  of the magnetic pole  2 . 
     The method for mounting a magnetic pole  2  according to the invention is illustrated in  FIG. 3 . It starts with a step  36  of forming a set  37  of elementary elements by adhesively bonding elementary elements  38 ,  40  to each other with an electrical insulator  32  in the form of a sheet being interposed, this being referred to below as an insulating sheet  32 . 
     Each elementary element  38 ,  40  is formed from a magnetizable material such as a magnetically hard material. 
     A plurality of elementary elements, for example, between 1 and 20, preferably between 6 and 10, are adhesively bonded to each other in order to form the set  37 . ( FIG. 5 ). 
     As is visible in  FIG. 4 , each elementary element  38  is of rectangular parallelepipedal shape having two main faces  42 ,  44 , two longitudinal faces  46 ,  48  and two lateral faces  50 ,  52 . 
     Elementary element  38  has, for example, a width of 6 mm, a length of from 30 to 60 mm and a thickness of approximately 15 mm. 
     The main face  42 ,  44  of an elementary element has a width which is, for example, from 0.05 to 1 times the width l E  of the magnetic pole  2 . 
     The main face  42 ,  44  of an elementary element has a length which is, for example, from 0.05 to 1 times the length l E  of a magnetic pole  2 . 
     All of the surface of the longitudinal faces  46 ,  48  of each elementary element  38 ,  40  is fixed to all of the surface of each insulating sheet  32  so that the set  37  forms a solid block which is in one piece. In this manner, the outer surface of the set  37  is continuous. The set  37  does not include any faults or fissures. 
     The insulating sheet  32  allows the magnets to be electrically insulated from each other in order to reduce the electrical losses arising from the passage of eddy currents which are induced by the magnetic fluxes which pass between the rotor and the stator. 
     The insulating sheet  32  does not prevent the passage of the magnetic fluxes. 
     The insulating sheet  32  is constructed, for example, from a paper which is composed of meta-aramide fibers known as “Nomex” (registered mark) or a polyimide film known as “Kapton” (registered mark), or any other electrically insulating material such as a pure or charged technical polymer. 
     The insulating sheet  32  is of small thickness (for example, 20 μm) relative to the thickness of the elementary elements  38 ,  40 . 
     As shown in  FIG. 5 , the set  37  is of rectangular parallelepipedal shape. It has two main faces  56 ,  58 , two longitudinal faces  60 ,  62  and two lateral faces  64 ,  66 . 
     The length L b  of a longitudinal face  60  of the set  37  is equal to the width l E  of the magnetic pole  2 . The length L l  of a lateral face  64 ,  66  of the set  37  is equal to 0.05 to 1 times the length L E  of the magnetic pole  2 . 
     Subsequently, during a machining step  68 , a main face  56  of the set is machined in such a manner that the face has a cylindrical shape having a radius R equal to the radius R of the hub  20  which is intended to receive the set  37 . ( FIGS. 2 and 3 ). 
     The cylindrical face  56  has a cylinder axis X-X which is perpendicular to the longitudinal faces  60 ,  62  of the set  37  of elementary elements and which is parallel with the lateral faces  64 ,  66  of the set  37  of elementary elements. 
     During a step  70 , the set  37  is magnetized by a device which is capable of applying to set  37  a large magnetic field. 
     The magnetization of a set is advantageously carried out at this stage, because it is not possible to do it when the poles are constituted on the rotor owing to the dimensions of the rotor and the poles, and the energy levels to be involved in the magnetization. 
     The set  37  is magnetized in such a manner that the magnetic axis generated by magnetization extends parallel with the longitudinal faces  46 ,  48  of the elementary elements  38 ,  40  which constitute it. 
     During the step  70 , only the set  37  is magnetized, that is to say that the set is not magnetized with the hub  20  or with a support for receiving the set  37 . 
     The set  37  constituted in this manner forms a continuous assembly (without faults) of permanent magnets which are secured to each other with an insulating sheet being interposed. 
     Since the set  37  constitutes only a portion of the pole  2  which extends in accordance with the width of the pole, the size of the set  37  is sufficiently small for a commercially available magnetization device to be able to magnetize it. 
     During a step  71 , an insulating sheet  32  is adhesively bonded to the bottom wall  34  of the recess  22 . At the step  72 , the planar main face  58  of the magnetized set  37  is adhesively bonded to the insulating sheet  32 . The set  37  is positioned in such a manner that its longitudinal face  60  forms the lateral face of the magnetic pole  2 . 
     The height of the set  37  corresponds to the depth of the recesses  22 ,  24  so that the cylindrical shape of the machined face  56  corresponds to the cylindrical shape of the hub  20 . 
     Subsequently, the steps  36  to  72  are repeated in order to construct and fix three other magnetized sets  74 ,  76 ,  78  in the recess  22  with an insulating sheet  32  being interposed. The magnetized sets  37 ,  74 ,  76 ,  78  from the whole of the magnetic pole  2 . 
     The magnetized sets  37 ,  74 ,  76  and  78  which are fixed in the same recess  22  all have the same polarities. 
     Subsequently, four magnetized sets having opposite polarities are constructed and adhesively bonded in the recess  24  with an insulating sheet  32  being interposed adjacent to the recess  22  in order to construct a new magnetic pole  4 . 
     When the assembly of the magnetic poles is constructed on the hub  20 , during a step  75 , an insulating sheet  32  is adhesively bonded to the assembly of the rotor  6  which is provided with the magnetic poles formed in this manner. That insulating sheet prevents short-circuits between the poles. 
     Finally, a retaining ring  79  for maintaining the magnetic poles  2 ,  4  is mounted around it during a step  80 . 
     The retaining ring is constructed from a composite material, such as, for example, glass, carbon and aramide fibers which are known under the name Kevlar (registered mark). 
     The insulating sheet  32  is adhesively bonded to the assembly of the magnetic poles during the step  75  only when the retaining ring is constructed from a non-insulating material, typically carbon fibers. 
     In a variant, the recesses  22  and  24  have a small depth of, for example, from 1 to 2 mm and interpolar blocks are interposed between each magnetic pole. 
     In a variant, the insulating sheet  32  may be replaced with an adhesive which is charged with solid particles which are electrically non-conductive or an adhesive which is charged with material fibers which are electrically non-conductive. 
     The insulating sheet  32  which is interposed between the magnetized sets  74 ,  76 ,  78  may be constructed from a material different from that of the insulating sheet  32  which is fixed between the elementary elements  38 ,  40 . 
     In a variant, the insulating sheet  32  may not be adhesively bonded to the assembly of the rotor  6 , but instead may be adhesively bonded only to each magnetic pole  2 ,  4 . 
     In a variant, the elementary elements  38 ,  40  may have a different height in order to minimize the quantity of material to be removed during the machining step  68 . 
     In another variant, the elementary elements may have different heights and each may have a main face  42  which forms a portion of the cylindrical surface so that it is not necessary to machine the main face  56  of the set  37  of elementary elements. 
     In another variant, the elementary elements may be of a parallelepipedal shape having a main face having a width and length which are equal to those of the magnetic pole, but having a height which is less than it. In this embodiment, the magnetic pole is formed by stacking in accordance with the axis of the rotor of elementary elements. 
     Advantageously, the surrounding insulating sheet  32  may facilitate the mounting of the retaining ring  79 . 
     Advantageously, the method may be applied in order to construct any rotor of a synchronous electrical rotating machine in which it is necessary to reduce the electrical losses which arise from the eddy current which is induced by the magnetic fluxes which pass between the stator and the rotor. 
     In particular, the method according to the invention may be applied in order to construct the rotor of motors of which the diameter of the rotor is greater than 100 mm, or high-power motors (power greater than 50 KW). 
     Advantageously, it may be simple to adhesively bond the elementary elements  38 ,  40  to each other before they are magnetized. In this manner, the mounting of a magnetic pole is simpler and more rapid. 
     Advantageously, the elementary elements are fixed to each other over the entire surface thereof so that the elementary elements form a monobloc assembly which does not include any gaps or fissures between the elementary elements. Thus, the magnetic pole constituted in this manner better withstands the mechanical pressures which are generated by the motor torque when the rotor is rotated. 
     Advantageously, the outer face of the magnetic pole  2  formed in this manner may be completely cylindrical. 
     Advantageously, this mounting method may allow rotors to be constructed more cheaply. 
     More generally, the invention provides an electric motor which includes a rotor as illustrated in  FIGS. 1 and 2 , having a hub  20  on which magnetic poles are constructed in accordance with the method described above.