METHOD FOR PRODUCING AN ELEMENT WITH MAGNETIC POLES

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of electrical machines.

[0002] It relates more particularly to a method of manufacturing an element with magnetic poles.

[0003] The invention finds a particularly advantageous application in the production of electric motors for electric or hybrid motor vehicles (cars, trucks, buses, etc.). It also applies more generally to other motorized devices, such as, for example, elevators, cranes, etc. STATE OF THE ART

[0004] An axial flux electric machine typically consists of at least a stator and a rotor, and an air gap separating the two elements through which the magnetic flux circulates. The rotor carries a series of large permanent magnets, while a series of coils are carried by the stator. When the coils are energized with an electric current, the rotor, which is secured to the motor's output shaft, is subjected to a torque resulting from the magnetic field (the magnetic flux created being an axial flux).

[0005] To reduce eddy current energy losses in the rotor, and thus increase the performance of the electric machine, large permanent magnets can be replaced by "magnetic pole elements" each comprising a plurality of small unit magnets. Indeed, a large permanent magnet is subject to greater eddy current losses than its equivalent in small unit magnets.

[0006] The unit magnets are arranged tightly to maximize the volume of magnetic material relative to the volume of the corresponding magnetic pole element and thus improve the performance of the electric machine.

[0007] For example, document FR3064422 discloses a structure comprising small unit magnets. These unit magnets have the advantage of being able to form a tight network while presenting a strong magnetic field. In this document, the unit magnets are held in relation to each other, for example by means of a holding mesh (typically in the form of a honeycomb when the unit magnets are hexagonal), then coated with a resin to form the element with magnetic poles.

[0008] Filling the volume of the magnetic pole element with the maximum number of individual magnets while limiting manufacturing costs is nevertheless complex. Indeed, each individual magnet must be handled individually. In addition, magnetic pole elements generally have two edges that are rectilinear but not parallel. Arranging identically shaped individual magnets necessarily creates empty spaces, filled by the resin, which reduces the magnetic efficiency of the magnetic pole element and therefore of the rotor. PRESENTATION OF THE INVENTION

[0009] In order to overcome the aforementioned drawbacks of the state of the art, the invention proposes a method for manufacturing a magnetic pole element for a rotor for an electrical machine, said magnetic pole element comprising a plurality of unit magnets, said method comprising the following steps: providing a magnetization block comprising a first main face and a second main face opposite the first main face, the first main face and the second main face delimiting between them a thickness of the magnetization block; machining, over only part of the thickness of the magnetization block, a first set of initial grooves from the first main face, such that the magnetization block remains in one piece; casting a first connecting material into the initial grooves; then machining a set of complementary grooves forming extensions of the initial grooves of the first set over the entire thickness of the magnetization block, so as to form the plurality of unit magnets separated from each other, the unit magnets being held together by the first connecting material.

[0010] Thus, thanks to the invention, the individual magnets are held together throughout the entire manufacturing process of the magnetic pole element. It is therefore not necessary to handle them individually to arrange them according to the shape of the magnetic pole element.

[0011] The first bonding material makes the intermediate structure (before the additional grooves are made) strong. This allows it to be handled, for example in a machining line, reducing the risk of breakage. With two separate bonding material casting steps, the likelihood of poor bonding material penetration at a given location is also reduced. The strength of the magnetic pole element is therefore increased.

[0012] In addition, the unit magnets are cut to best fill the volume of the magnetic pole element. The manufacturing process allows the production of unit magnets of different shapes so as to fill the volume of the magnetic pole element (which is then equal to the volume of the magnetization block minus the volume of the grooves) with the maximum number of unit magnets and therefore with the maximum amount of magnetic material.

[0013] Finally, the invention makes it possible to reduce the waste of expensive magnetic material since the minimum amount of material is removed from the magnetization block, namely only a volume corresponding to the grooves. Other advantageous and non-limiting characteristics of the manufacturing method according to the invention, taken individually or in all technically possible combinations, are as follows: said method comprises, before casting the first bonding material, a step of machining, over only part of the thickness of the magnetization block, a second set of initial grooves from the second main face, and in which the set of complementary grooves also forms extensions of the initial grooves of the second set; the initial grooves of the first set extend in first substantially parallel directions and in which the initial grooves of the second set extend in second substantially parallel directions, the first directions preferably being substantially orthogonal to the second directions; the first set comprises initial grooves extending in one direction and initial grooves extending in another direction;the first set of initial grooves comprises a subset of initial grooves located opposite the initial grooves of the second set; the magnetization block has lateral faces, each lateral face being orthogonal to one of two lateral directions orthogonal to each other, and in which the initial grooves extend in directions substantially parallel to one or other of the two lateral directions; the complementary grooves have a width greater than that of the initial grooves; the complementary grooves are offset, in the thickness of the magnetization block, relative to the initial grooves;said method comprises a step of casting a second bonding material between the unit magnets, which is preferably carried out after a step of placing the magnetic pole element in a housing provided in the rotor, the second bonding material also being cast around the magnetic pole element to fix it in the housing; the first bonding material and / or the second bonding material is made of a material comprising a magnet powder mixed in a matrix.;

[0014] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION

[0015] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0016] On the attached drawings: there figure 1 is a block diagram of a sequence of steps allowing the manufacture of a magnetic pole element according to the invention; the figure 2 is a schematic perspective view of a magnetization block illustrating a second step of a first embodiment of the method of the figure 1 ; there figure 3 is a schematic perspective view of the magnetization block of the figure 2 illustrating a third step of the first embodiment of the method; figure 4 is a schematic perspective view of the magnetization block of the figure 2 illustrating a fourth step of the first embodiment of the method; the figure 5 is a schematic perspective view of the magnetization block of the figure 2 illustrating a fifth step of the first embodiment of the method; figure 6 is a schematic perspective view of a magnetization block illustrating a second embodiment of the method of the figure 1 ; there figure 7 is a schematic perspective view of a magnetization block illustrating a third embodiment of the method of the figure 1 ; there figure 8 is a schematic perspective view, from above, of a magnetization block illustrating a fourth embodiment of the method of the figure 1 ; there figure 9 is a schematic perspective view, from below, of the magnetization block of the figure 8 ; there figure 10 is a schematic perspective view of a magnetization block illustrating the positioning of grooves; the figure 11 is a schematic perspective view of the magnetization block of the figure 4 located in a housing provided in a rotor.

[0017] On the figure 5 , a magnetic pole element 1 is shown. The magnetic pole element 1 is designed to be installed within a rotor (not shown) for an electric machine, here an axial flux electric machine, in this case a motor for propelling an electric vehicle.

[0018] Such an electric machine comprises at least one rotor 100, only a part of which is shown in the figure 11 , and at least one stator (not shown). In an axial flux electric machine, the stators have the shape of flattened rings and are equipped, on their faces located on the side of the rotor 100, with teeth around which are wound windings of electrically conductive wires. When these windings are supplied with electric current, they allow a magnetic field to be generated. The magnetic field is axial for an axial flux electric machine.

[0019] The rotor 100 comprises for its part an annular-shaped body 110 which houses a plurality of magnetic pole elements 1. The magnetic field generated by the windings is then designed to act on the magnetic pole elements 1 so as to rotate the rotor 100. The body 110 has the overall shape of a disc, in that it is substantially circumscribed by a cylinder of revolution. The body 110 delimits a plurality of hollow housings 120 (only one of which is shown in figure 11 ), each housing 120 comprising a magnetic pole element 1. The housings 120 are distributed regularly around the axis of rotation A1 of the rotor 100.

[0020] As shown by the figures 4 et 5 , each magnetic pole element 1 comprises a plurality of unit magnets 2. These unit magnets 2 have a size much smaller than that of the magnetic pole element 1 (at least ten times smaller). Here, for example, the magnetic pole element 1 comprises approximately one hundred unit magnets 2. The unit magnets 2 here have a generally parallelepiped shape.

[0021] Within the magnetic pole element 1, the unit magnets 2 are separated from each other. Here, this means that each unit magnet 2 is physically disjointed from the other unit magnets 2 in the sense that it is not in direct contact with them. This separation of the unit magnets limits eddy current losses within the magnetic pole element 1 when the electrical machine is in operation. At the extreme limit, separated from each other means that the unit magnets can be in contact with each other by contact lines, typically by their edges. The eddy current losses are then slightly higher but still much lower than those of a large permanent magnet.

[0022] Unit magnets 2 can be of any type. They can be sintered neodymium magnets, commonly known as NdFeB magnets. These magnets are composed of an alloy of neodymium, iron, and boron. Alternatively, they can be ferrite magnets, for example, SmCo magnets (made of Samarium-Cobalt) or AlNiCo magnets (composed mainly of aluminum, nickel, and cobalt).

[0023] As shown in the figure 5 , the unit magnets 2 are held together by a first bonding material 30 and by a second bonding material 50 possibly different from the bonding material 30. These bonding materials 30, 50 may be thermosetting polymers, such as epoxies, silicones, in any applicable form, for example in the form of glue, resin, single-component or two-component casting, or thermoplastic polymers such as Nylon or PPS (Polyphenylene sulfide). The bonding materials 30, 50 may be applied by any method known to those skilled in the art. These bonding materials 30, 50 make it possible, in addition to providing mechanical reinforcement for the magnetic pole element 1, to electrically insulate the unit magnets from each other (while securing them) and thus to reduce eddy current losses.

[0024] The method of manufacturing the magnetic pole element 1 (a method which is more particularly the subject of the present invention) illustrated in figure 1 and which includes the following four main stages

[0025] A first step e1 comprises the provision of a magnetization block 10. As illustrated for example in figure 2 , the magnetization block 10 has an upper face 11, here called upper face 11, and a lower face 12, here called lower face 11, which is opposite the upper face 11. The upper face 11 and the lower face delimit between them a thickness of the magnetization block 10. The magnetization block 10 is made of a magnetic material. The magnetic material is the same as that described previously for the unit magnets 2 since the latter are directly and integrally derived from the magnetization block 10.

[0026] The shape of the magnetization block 10 corresponds, in negative, to that of the housing 120 of the body 110 of the rotor 100 in which the element with magnetic poles is intended to be housed. The dimensions of the magnetization block 10 are nevertheless slightly smaller than those of the housing 120 in order to be able to place it there. As shown in figure 10 , the upper face 11 and the lower face 12 each have in particular a generally trapezoidal shape similar to that of the housing 120. The thickness of the magnetization block 10 is itself substantially equal to the thickness of the body of the rotor 100 (its dimension along its axis of rotation A1).

[0027] The magnetization block 10 obtained during this first step e1 is solid, in the sense that it is devoid of a groove.

[0028] As shown for example by the figure 2 , both the upper face 11 and the lower face 12 of the magnetization block 10 are parallel to each other. The thickness of the magnetization block 10 then corresponds to the distance between the upper face 11 and the lower face 12 and is therefore constant. The thickness here corresponds to the dimension of the magnetization block 10 extending along the axis of rotation A1 of the rotor 100.

[0029] In addition to the upper face 11 and the lower face 12, the magnetization block 10 has lateral faces 13 connecting the upper face 11 to the lower face 12. Here, these lateral faces 13 are orthogonal to the upper face 11 and to the lower face 12. Once the magnetic pole element has been manufactured and installed in the housing 120, the lateral faces 13 extend opposite the body 110 of the rotor 100. More specifically, the lateral faces 13 then extend opposite an internal surface 113 delimiting the housing 120.

[0030] A second step e2 comprises the machining of an upper assembly 21, here called upper assembly 21, of initial grooves 20 from the upper face 11, over only a portion of the thickness of the magnetization block 10. Here, this means that the depth of the initial grooves 20, that is to say their dimension in a direction substantially orthogonal to the upper face 11, is, at least in places, strictly less than the thickness of the magnetization block 10. “From” is understood to mean that the initial grooves 20 of the upper assembly 21 open onto the upper face 11.

[0031] The machining of the initial grooves 20 is carried out in such a way that the magnetization block 10 remains in one piece. In other words, none of the initial grooves 20 separates the magnetization block 10 into two distinct parts. After this machining step e2, the volume forming the magnetization block 10 is therefore continuous. For example, the figure 2 represents a magnetization block 10 after machining the initial grooves 20. Machining here means any process allowing material to be removed from the magnetization block 10, in particular sawing, milling, drilling, turning, etc.

[0032] A third step e3, illustrated in figure 3 , comprises casting the first bonding material 30 into the initial grooves 20. When cast, the first bonding material 30 is in a liquid or at least viscous state to fill all the machined grooves. The third step e3 here comprises a sub-step of hardening the first bonding material 30.

[0033] A fourth step e4 comprises the machining of a set of complementary grooves 40 forming extensions of the initial grooves 20, in particular those of the upper set 21, over the entire thickness of the magnetization block 10, so as to form the plurality of unit magnets 2. As shown in figure 4 , the fourth step e4 thus aims to extend, by means of the complementary grooves 40, the initial grooves 20 over the entire thickness of the magnetization block 10. This fourth step e4 is preferably carried out after the hardening of the first bonding material 30.

[0034] In practice, the machining of the complementary grooves 40 is done by the main face which is opposite to that from which the initial grooves 20 are made. For example, the upper set 21 of initial grooves 20 being machined from the upper face 11, the complementary grooves 40 extending the upper set 21 are made from the lower face 12.

[0035] After machining the complementary grooves 40, the unit magnets 2 are therefore separated from each other. This means that the unit magnets 2 are no longer connected to each other by magnetic material. They are, however, held together by the first connecting material 30.

[0036] Preferably, between the second step and the third step, the method comprises an additional step of cleaning the grooves which makes it possible to remove from the initial grooves residues of magnetic material resulting from the machining of the initial grooves.

[0037] This cleaning is carried out, for example, by injecting a pressurized jet of air or a cleaning solution, preferably non-corrosive (without or, preferably, with surfactant) into the initial grooves 20.

[0038] A second cleaning step is provided here after the machining of the complementary grooves 40. Remarkably, the machining of the complementary grooves 40 forms a plurality of recesses passing through the magnetization block 10, which facilitates its cleaning.

[0039] We will now describe in detail, with reference to the figures 2 à 5 , a first embodiment of the method for manufacturing the magnetic pole element 1.

[0040] In this first embodiment, the second step e2 comprises, in addition to the machining of the upper set 21 of initial grooves 20 from the upper face 11, the machining of a second set 22, here called the lower set 22, of initial grooves 20 from the lower face 12. In other words, at this step, grooves are machined from the upper face 11 and from the lower face 12. As shown in the figure 2 , the initial grooves 20 are here rectilinear, which facilitates their machining and cleaning. The initial grooves 20 of the upper assembly 21 extend more particularly in substantially parallel first directions. Similarly, the initial grooves 20 of the lower assembly 22 extend in substantially parallel second directions.

[0041] The initial grooves 20 are regularly distributed on the upper face 11 and the lower face 12. On each of these faces 11, 12, all the initial grooves 20 are located at the same distance from its adjacent initial groove(s) 20. Here, the distance between two adjacent initial grooves 20 is the same for those of the upper assembly 21 as for those of the lower assembly 22. The upper assembly 21 thus forms a network of rectilinear, parallel and regularly spaced initial grooves 20 on the upper face 11. The same is true for the lower assembly 22 on the lower face 12.

[0042] Alternatively, the initial grooves are not regularly distributed on the upper face. For example, the initial grooves could be spaced further apart in the center of the magnetization block than at the periphery. Thus, the unit magnets located at the periphery of the magnetic pole element would be smaller.

[0043] The first directions, along which the initial grooves of the first group are machined, are here preferably substantially orthogonal to the second directions. The unit magnets 2 formed are thus rectangular parallelepipeds. This orthogonal configuration facilitates the machining of the grooves, in particular because it reduces the stresses on the machining tool during the machining of the complementary grooves 40 and because it reduces the risk of cracking and breaking of the unit magnets 2 during formation. Alternatively, the second and first directions may not be orthogonal. Machining in non-orthogonal directions is slightly more complex but makes it possible to reduce eddy currents.

[0044] As represented on the figures 2 et 3 , the initial grooves 20 extend in depth over approximately 75% of the thickness of the magnetization block. Generally, the initial grooves 20 extend in depth from 60% to 90% of the thickness of the magnetization block 10. Preferably, the initial grooves 20 extend over at least 50% of the thickness of the magnetization block 10. In length, each initial groove 20 here extends from one side of the upper face 11 or the lower face 12 to another side of the perimeter of the same face 11, 12.

[0045] To obtain initial grooves 20 having a reduced width (dimension in a direction orthogonal to the rectilinear extension and to the depth), i.e. thin initial grooves 20, the initial grooves 20 are here produced by means of a wire saw. Thus, the width of the initial grooves 20 is less than 0.3 mm and preferably less than 0.2 mm. This makes it possible to maximize the volume of magnetic material in the magnetic pole element. Here, all the initial grooves 30 have the same width. Alternatively, the initial grooves may have different widths.

[0046] There figure 3 illustrates the pouring of the first bonding material 30 into the initial grooves 20, that is to say here both in those of the upper assembly 21 and in those of the lower assembly 22. The viscosity of the first bonding material 30 is here low to be able to penetrate effectively into the initial grooves 20. As shown in figure 3 , the first bonding material 30 here completely fills the initial grooves 20.

[0047] Once the first bonding material 30 has hardened, the complementary grooves 40 are machined. The result of this fourth step e4 is shown in figure 4 .

[0048] As shown in the figure 4 , the complementary grooves 40 are located opposite the initial grooves 20, that is to say in the extension thereof. The complementary grooves 40 thus form a network of rectilinear, parallel and regularly spaced grooves both on the upper face 11 and on the lower face 12.

[0049] The complementary grooves 40 here correspond to an extension of the initial grooves 20 over the entire thickness of the magnetization block 10. Thus, each pair formed by an initial groove 20 and a complementary groove 40 located opposite the latter forms a recess passing through the magnetization block 10 over the entire thickness and from one lateral face 13 to another. The machining of the complementary grooves 40 therefore results in the formation of the plurality of unit magnets 2 separated from each other. The magnetic pole element 1 is then formed. It comprises the plurality of unit magnets 2 and the first connecting material 30 securing the unit magnets 2.

[0050] In this embodiment, each complementary groove 40 is centered relative to the initial groove 20 with which it is opposite. The network of complementary grooves 40 is thus aligned with the network of initial grooves 20.

[0051] We observe on the figure 4 that the complementary grooves 40 are distributed between a first group 41 of complementary grooves 40 and a second group 42 of complementary grooves 40. The complementary grooves 40 of the first group 41 extend the initial grooves 20 of the upper assembly 21. Conversely, the complementary grooves 40 of the second group 42 extend the initial grooves 20 of the lower assembly 22.

[0052] The complementary grooves 40 of the first group 41 are here machined from the lower face 12. Conversely, the complementary grooves 40 of the second group 42 are here machined from the upper face 11.

[0053] As it appears on the figure 4 , volumes filled with the first bonding material 30 are machined. To limit the clogging of the machining tool by the first bonding material 30, the machining of the complementary grooves 40 is here carried out by a blade saw.

[0054] The complementary grooves 40 can also be machined by laser cutting. Laser cutting is particularly advantageous when the remaining thickness to be cut is small (i.e. when the initial grooves 20 extend over a significant portion of the thickness of the magnetization block 10), for example when the complementary grooves 40 extend over a thickness of less than 0.5 mm. Laser cutting can also be used for the initial grooves 20.

[0055] The complementary grooves 40 preferably have a width greater than that of the initial grooves 20. Here, the complementary grooves 40 all have the same width which is for example less than 0.8 mm and preferably less than 0.5 mm. Alternatively, the complementary grooves could have a width less than that of the initial grooves, in particular in the case where the complementary grooves are produced by laser cutting. Generally speaking, it is indeed simpler to produce thin complementary grooves than thin initial grooves. In all embodiments (but illustrated only in this first embodiment), the method also comprises a step e5 of casting the second connecting material 50. As illustrated in figure 5 , the second bonding material 50 is cast into the complementary grooves 40. The second bonding material 50 makes it possible to solidify the magnetic pole element 1.

[0056] In practice, the casting of the second connecting material 50 is preferably carried out when the magnetic pole element 1 is positioned in the housing 120 of the body 110 of the rotor 100 provided for this purpose (as is the case on the figure 11 ). Thus, the second connecting material 50 can be cast both in the complementary grooves 40 and around the magnetic pole element 1 to fix the latter relative to the body. The second connecting material 50 is then more specifically cast on the periphery of the lateral faces 13, between the latter and the internal surface 113 of the housing 120. Alternatively, the second connecting material is cast only in the complementary grooves, for example by placing the magnetic pole element in a mold.

[0057] Here, the second bonding material 50 comprises a matrix into which a magnet powder is mixed. Thus, a large majority of the volume of the housing 120 is filled with a material having magnetic properties (the magnetic pole element 1 or the second bonding material 50), which makes it possible to improve the magnetic performance of the rotor. The use of a magnet powder makes it possible, in particular, to create an intermediate magnetism zone between a non-magnetic zone (the body) and a strongly magnetic zone (the magnetic pole element), which contributes to reducing losses. Finally, the magnetic pole element 1 itself comprises more material having magnetic properties.

[0058] The matrix is ​​for example made from one of the bonding materials presented previously. To improve the adhesion between the first and second bonding materials, the matrix is ​​made from the same material as the first bonding material 30.

[0059] The magnet powder is formed from crystals, for example spherical in shape. The magnetic powder content by volume in the polymer material is preferably between 50 and 85%. The grain diameter in the magnet powder is preferably between 2 and 100 micrometers (µm). In particular, it is between 80 and 100 µm in the case of injection molding.

[0060] The magnet powder makes the second bonding material 50 more viscous (than the matrix itself) when it is cast. However, the fact that the complementary grooves 40 are wider than the initial grooves 20 facilitates the penetration of the second bonding material 50 between the complementary grooves 40. As a variant of this first embodiment, the first bonding material may also comprise a magnet powder. As a further variant, the second bonding material may not comprise a magnet powder.

[0061] A second embodiment is illustrated in figure 6 . There figure 6 illustrates more particularly the second step e2 of the method. It differs from the first embodiment in that the upper assembly 21 comprises, in addition to the initial grooves 20 extending in one direction, initial grooves 20 extending in another direction (still from the upper face 11).

[0062] The idea here is to anticipate the fourth step e4 by machining more initial grooves 20 during the second step e2. This makes it possible, in particular, during the fourth step e4, to machine a more limited volume of first connecting material 30. This also makes it possible to make the magnetic pole element more resistant once the fourth step e4 is completed since the complementary grooves 40 occupy a smaller volume.

[0063] As shown in the figure 6 , the upper assembly 21 more specifically comprises initial grooves 20 extending in a reference direction D1 and initial grooves 20 extending in a direction D2 perpendicular to this reference direction D1. The initial grooves 20 extending in this perpendicular direction D2, consist of a sub-assembly 23, included in the upper assembly 21, of initial grooves 20.

[0064] The initial grooves 20 of the subassembly 23 are here located opposite the initial grooves 20 of the lower assembly 22. Preferably, the initial grooves 20 of the subassembly 23 are contiguous with the initial grooves 20 of the lower assembly 22. This means that the pair formed by an initial groove 20 of the subassembly 23 and an initial groove 20 of the lower assembly 22 constitutes a continuous opening over the entire thickness of the magnetization block 10, that is to say from the upper face 11 to the lower face 12 (but without separating the magnetization block in two).

[0065] The initial grooves 20 of the subassembly 23 extend in an area of ​​the upper face 11 circumscribed within the perimeter of the upper face 11. In other words, the initial grooves 20 of the subassembly 23 do not open onto the lateral faces 13.

[0066] In a third embodiment, illustrated in figure 7 , the side faces 13 are planar and arranged orthogonally to each other along the periphery of the upper face 11 and the lower face 12.

[0067] As shown in the figure 7 (which more particularly illustrates the second step e2 of the method) the initial grooves 20 extend either parallel or orthogonally to the lateral faces 13. This means that each initial groove 20 extends parallel to some of the lateral faces 13 and orthogonally to the other lateral faces 13.

[0068] Thus, in this third embodiment, all the unit magnets 2 are substantially identical and have the shape of a rectangular parallelepiped. This makes the magnetic pole element 1 stronger than that of the first and second embodiments shown in figures 2 à 6 . Indeed, compared to these two modes, the magnetic pole element 1 does not here comprise fine unitary magnets 2 of pyramidal shape at the level of the lateral faces 13. These unitary magnets 2 in question are more fragile and therefore more likely to detach from the magnetic pole element 1 during its manufacture or its transport.

[0069] In a fourth embodiment, illustrated in figures 8 et 9 (which represent the front and back of the same magnetic pole element), all the initial grooves 20 are machined from the upper face 11. Thus, in the second step e2, only the upper set 21 of initial grooves 20 is produced. In the example illustrated in figure 8 , the upper assembly 21 comprises initial grooves 20 extending in a reference direction and initial grooves 20 extending in a direction perpendicular to this reference direction.

[0070] The particularity of this fourth embodiment is that some of the initial grooves 20 extend, over only part of their length, over the entire thickness of the magnetization block 10. This is particularly visible on the figure 9 which represents the magnetization block 10 seen from the lower face 12 (at the end of the third step e3). Here, in a central zone of the magnetization block 10, all the initial grooves 20 extending in a lateral direction D3 extending in depth over the entire thickness of the magnetization block 10. In a central zone here means that this extension over the entire thickness is not carried out from one lateral face 13 to another so as to preserve the unity of the magnetization block 10.

[0071] In this fourth embodiment, the complementary grooves 40 are then all machined from the lower face 12. This embodiment simplifies the manufacturing process of the magnetic pole element 1 since it is not necessary to turn the magnetization block 10 over, either in the second step e2 or in the fourth step e4.

[0072] There figure 10 illustrates a part of a magnetization block 10 comprising initial grooves 20 and on which is indicated the position of the complementary grooves 40 which will be machined in the fourth step e4. Here, the complementary grooves 40 are offset, in the thickness of the magnetization block 10, relative to the initial grooves 20. By “offset” is meant that each complementary groove 40 is off-center relative to its associated initial groove 20. Thus, for example, on the figure 10 , each complementary groove 40 is in contact with the initial groove 20 opposite at a rectilinear edge.

[0073] The present invention is in no way limited to the embodiments described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention. In particular, the invention is applicable to elements with parallelepiped magnetic poles, for example in the shape of a rectangular parallelepiped as in figure 10 The invention is also applicable to radial flux machines comprising a permanent magnet rotor. In this case, the lower and upper faces are preferably curved around the axis of rotation of the rotor.

Claims

1. Method for manufacturing an element having magnetic poles (1) for a rotor for an electric machine, said element having magnetic poles (1) comprising a plurality of unit magnets (2), said method comprising the steps of: - providing (e1) a magnetisation block (10) comprising a first main face (11) and a second main face (12) opposite to the first main face (11), the first main face (11) and the second main face (12) delimiting a thickness of the magnetisation block (10) therebetween; - machining (e2), over only part of the thickness of the magnetisation block (10), a first set (21) of initial slots (20) starting from the first main face (11), such that the magnetisation block (10) remains integral; - pouring (e3) a first connecting material (30) into the initial slots (20); characterized in that it further comprises machining (e4) a set of complementary slots (40) forming extensions of the initial slots (20) of the first set (21) across the entire thickness of the magnetisation block (10), so as to form the plurality of unit magnets (2) separated from each other, the unit magnets (2) being held secured together by the first connecting material (30).

2. Method according to claim 1, said method comprising, before pouring the first connecting material (30), a step of machining, over only part of the thickness of the magnetisation block (10), a second set (22) of initial slots (20) starting from the second main face (12), and wherein the set of complementary slots (40) also forms extensions of the initial slots (20) of the second set (22).

3. Method according to claim 2, wherein the initial slots (20) of the first set (21) extend according to substantially parallel first directions and wherein the initial slots (20) of the second set (22) extend according to substantially parallel second directions, the first directions preferably being substantially orthogonal to the second directions.

4. Method according to one of claims 1 to 3, wherein the first set (21) comprises initial slots (20) extending according to one direction (D1) and initial slots (20) extending according to another direction (D2).

5. Method according to one of claims 2 to 4, wherein the first set (21) of initial slots (20) comprises a subset (23) of initial slots (20) located opposite the initial slots (20) of the second set (22).

6. Method according to one of claims 1 to 5, wherein the magnetisation block (10) has lateral faces (13), each lateral face (13) being orthogonal to one amongst two lateral directions orthogonal to each other, and wherein the initial slots (20) extend in directions substantially parallel to either one of the two lateral directions.

7. Method according to one of claims 1 to 6, wherein the complementary slots (40) have a width larger than that of the initial slots (20).

8. Method according to one of claims 1 to 7, wherein the complementary slots (40) are offset, across the thickness of the magnetisation block (10), with respect to the initial slots (30).

9. Method according to one of claims 1 to 8, said method comprising a step of pouring (e5) a second connecting material (50) between the unit magnets (2), which is preferably carried out after a step of placing the element having magnetic poles (1) in a compartment (120) provided for in the rotor (100), the second connecting material (50) being also poured around the element having magnetic poles (1) to fasten it in the compartment (120).

10. Method according to claim 9, wherein the first connecting material (30) and / or the second connecting material (50) is made of a material including a magnet powder mixed in a matrix.