Bonded magnet pole for electrical machine, corresponding manufacturing process and device

Abstract

Bonded magnet pole for electric machine, corresponding manufacturing method and device. The present invention relates to a bonded magnet pole (20) for an electric machine, formed of magnetic powder consolidated in a resin, the bonded magnet pole (20) extending between two opposite edges (22, 24) and partially delimiting two surfaces (21, 23) intended to be positioned orthogonally to a direction parallel to a magnetic field generated by a stator of the electric machine. The bonded magnet pole (20) is characterized in that it has a higher density of magnetic powder in a central portion (25) of the bonded magnet pole (20) located between the two edges (22, 24) than in at least one lateral portion (27, 29) of the bonded magnet pole (20) located between one of the edges (22, 24) and the central portion (25). (Figure 2)

Description

Title of the invention: Bound magnet pole for electrical machine, corresponding manufacturing method and device

[0001] The present invention relates to the field of electrical engineering and more specifically concerns a bound magnet pole for an electric machine, an electric machine rotor comprising such a magnet pole, as well as a device and a method for manufacturing such a magnet pole.

[0002] Electrical machines comprise at least one rotor and one stator, the magnetic poles of one of these elements being based on permanent magnets. Particularly in permanent magnet synchronous machines, the use of magnets poses a number of problems for high-power applications, for example, for electric traction or propulsion machines in electric or hybrid vehicles. At high torque, the permanent magnets of such a machine increase in temperature due to eddy currents created by the magnetic field generated by the machine. These eddy currents produce electromagnetic losses and, through the temperature increase they induce, risk demagnetizing the magnets.

[0003] To limit these eddy currents, it is known to use segmented magnet poles, meaning that each magnetic pole using a magnetized material is made up of small magnets separated from each other by glue. These small magnets are formed by cutting large magnets. For manufacturing cost reasons, they are often identical in shape, for example, parallelepiped, which is not conducive to forming magnetic poles of arbitrary shape, particularly trapezoidal magnetic poles such as those found on the rotor of an axial flux machine. Consequently, the edges of the poles of such a machine do not contain magnetic material, but only a filler material, which reduces the machine's efficiency relative to the pole material used.

[0004] Another way to limit eddy currents is to use bonded magnets to form the magnet poles of an electric machine. These magnets are made from magnetic powder consolidated in resin. Magnet poles made with such bonded magnets exhibit virtually no eddy currents, but their magnetic field is weak and their homogeneity is not optimal for ensuring the best possible efficiency of the electric machine.

[0005] The present invention aims to remedy, at least in part, the drawbacks of the prior art, by providing a bound magnet pole exhibiting a field magnetic strong enough for applications such as electric traction or propulsion machines, an axial flux machine rotor comprising such a bound magnet pole and a method and device for manufacturing such a bound magnet pole.

[0006] To this end, the invention proposes a bonded magnet pole of an electrical machine, formed of magnetic powder consolidated in a resin, the bonded magnet pole extending between two angularly opposed edges and partially delimiting two surfaces intended to be positioned orthogonally to a direction parallel to a magnetic field generated by a stator of the electrical machine,

[0007] the bonded magnet pole being characterized in that it has a higher magnetic powder density in a median part of the bonded magnet pole located between the two edges than in at least one lateral part of the bonded magnet pole located between one of the edges and the median part.

[0008] The two opposite edges are angularly opposed with respect to a rotation angle of a rotor of the electric machine. The bonded magnet pole is preferably a single piece and is a magnet pole of the rotor of the electric machine, this machine being an axial flux or radial flux machine. The resin used is a binding agent, preferably polymer-based, capable of solidifying, for example, epoxy resin or polyethylene. This resin is, for example, thermosetting or thermoplastic, and is electrically insulating. It may also be formed from a mixture of such materials.

[0009] Preferably, the lateral portions of the bonded magnet pole all have a lower magnetic density than a central portion of the bonded magnet pole. In particular, according to an advantageous feature of the invention, the magnetic powder density is greater in the central portion than in a lateral portion of the bonded magnet pole located between the other edge and the central portion.

[0010] Thanks to the invention, the magnetic field created in the central part of the bound magnet pole is greater than in the lateral parts of the bound magnet pole that are angularly opposite to each other with respect to the central part. This makes it possible to reduce torque ripple compared to a prior art electrical machine, and therefore also to reduce noise, vibration, and electrical losses compared to a prior art machine.

[0011] According to another advantageous feature of the invention, the density of magnetic powder increases progressively from at least one of the edges towards the middle portion of the bonded magnet pole. This progressive increase is preferably continuous. This further reduces the torque ripples of the electrical machine comprising the magnet pole according to the invention.

[0012] According to yet another advantageous feature of the invention, the magnetic powder density is homogeneous in the direction parallel to the magnetic field generated by a stator of the electric machine. Thus, the magnetic distribution of the bound magnet pole is optimal. By homogeneous, we mean substantially homogeneous with a tolerance of, for example, ten percent relative to an average density value.

[0013] The invention also relates to an axial flux electric machine rotor comprising a hub, a non-magnetic armature around the hub and having housings, characterized in that at least one of the housings comprises a magnet pole bound according to the invention.

[0014] The invention also relates to an electrical machine comprising an axial flux machine rotor according to the invention.

[0015] The invention further relates to a method for manufacturing a bonded magnet pole of an electrical machine according to the invention, comprising the steps of:

[0016] - mixing of the magnetic powder in the liquid resin,

[0017] - insertion of the mixture into a mold whose useful part has a volume intended to form the bound magnet pole, the volume comprising a median section intended to form the median part of the bound magnet pole, and at least one lateral section intended to form at least one lateral part of the bound magnet pole,

[0018] - application of a magnetic field to the mold, the intensity of the magnetic field being more important in the median section of the volume than in the lateral section of the volume, and

[0019] - solidification of the volume.

[0020] In this manufacturing process, the usable volume of the mold can be used to form one or more bonded magnets or a portion of a bonded magnet, in particular half of a bonded magnet. The mold optionally includes the non-magnetic armature of the rotor according to the invention. In this case, the rotor magnet poles are molded directly into the armature recesses designed to receive these magnet poles. Furthermore, in this manufacturing process, the solidification step depends on the resin used; this step may require curing or cooling at room temperature, depending on the chemical reaction enabling this solidification. Preferably, in the step of applying the magnetic field to the mold, the magnetic field strength decreases from the midsection to the lateral section of the volume. This application of the magnetic field is carried out by permanent magnets or electromagnets.

[0021] The manufacturing process according to the invention makes it possible to concentrate the magnetic powder, during the manufacture of the bonded magnet pole, in the central part of this bonded magnet pole. Thus, the concentration of magnetic material at the center of the magnet pole is greater than in a prior art magnet pole. Consequently, the torque produced by the electrical machine incorporating the magnet pole according to the invention is greater than in a prior art machine using a magnet pole. related to the prior art. In general, this optimal distribution of magnetic material in the magnet pole improves the efficiency of the electrical machine compared to the prior art, particularly with regard to the mass of magnets used.

[0022] Advantageously, in the manufacturing process according to the invention, the solidification step is followed by a cutting step of an end section of the volume, the end section being adjacent to the lateral section of the volume, opposite the median section of the volume. This step makes it possible to increase the overall volume density of magnetic material in the magnet pole bound according to the invention, compared to the prior art.

[0023] According to an embodiment of the invention, in which the mold allows for the formation of one half of a bonded magnet pole, the manufacturing process for a bonded magnet pole of an electrical machine according to the invention comprises the following steps:

[0024] - mixing of the magnetic powder in the liquid resin,

[0025] - insertion of the mixture into a mold whose useful part has a volume intended to form half of a bound magnet pole, the volume comprising a portion intended to form half of the middle part of the bound magnet pole,

[0026] - positioning of the mold against a permanent magnet, the portion of the volume being positioned proximal to the permanent magnet,

[0027] - solidification of the volume,

[0028] - bonding of the volume to another solidified volume obtained by steps identical to the previous steps.

[0029] In this embodiment, the solidified volume has a surface intended to be positioned orthogonally to the direction parallel to the magnetic field generated by the stator of the electric machine. The magnetic field created by the permanent magnet between its north and south poles is, for example, parallel or orthogonal to this surface. Furthermore, in this embodiment, the solidification or bonding step is optionally followed by a cutting step of at least one end section of the solidified volume(s), this end section being distal to the portion of the volume having the highest magnetic density.

[0030] The invention also relates to a method for manufacturing an axial flux electric machine rotor according to the invention, wherein the bonded magnet pole is manufactured by the method for manufacturing a bonded magnet pole according to the invention, the method for manufacturing a rotor comprising the steps of:

[0031] - arrangement of the magnet pole bound in the housing of the magnetic armature, and

[0032] - magnetization of the bound magnet pole.

[0033] This last magnetization step makes it possible to form the north and south poles of the rotor according to the invention.

[0034] The invention also relates to a device for manufacturing a magnet pole bound to an electrical machine according to the invention, comprising:

[0035] - a mold,

[0036] - a first generator of a magnetic field in a direction of magnetization,

[0037] - a second generator of a magnetic field in the direction of magnetization,

[0038] - a support positioned between the two generators orthogonally to the direction of magnetization, the support being suitable for receiving the mold, and

[0039] - a magnetic flux guide capable of concentrating the field in the middle of the support magnetic field generated by at least one of the two generators.

[0040] The first and second generators are permanent magnets or electromagnets.

[0041] Advantageously, the magnetic flux guide comprises two ferromagnetic plates orthogonal to the direction of magnetization, each covering two ends of the generators. Each plate exhibits, on the support side from a first end of the plate, a change in thickness, the plate being thicker in its middle than at at least one of its ends. This embodiment has the advantage of simplicity.

[0042] The rotor according to the invention, the electric machine according to the invention and the manufacturing device according to the invention have advantages similar to those of the magnet pole according to the invention and the method for manufacturing a magnet pole according to the invention.

[0043] Other features and advantages of the invention will become apparent from the following description on the one hand, and from several illustrative and non-limiting examples of embodiments given with reference to the accompanying schematic drawings on the other hand, in which:

[0044] [Fig. 1] represents an electric machine rotor according to the invention, in one embodiment of the invention,

[0045] [Fig.2] represents a top view and a cross-sectional view of a magnet pole bound to the rotor of the [Fig.1],

[0046] [Fig.3] represents steps in a process for manufacturing a rotor according to the invention, and a bonded magnet pole according to the invention, in one embodiment of the invention,

[0047] [Fig.4] represents elements of a device for manufacturing a bound magnet pole according to the invention, forming an enclosure in which the elements generate a magnetic field, in one embodiment of the invention,

[0048] [Fig.5] represents a mold comprising a homogeneous mixture of magnetic powder and resin, inserted into the enclosure of the [Fig.4],

[0049] [Fig.6] represents the mold of [Fig.5] in the enclosure, after migration of the magnetic powder into a central part of the mold following the effect of the magnetic field,

[0050] [Fig.7] represents a microscopic view of magnetic powder grains in the homogeneous mixture of [Fig.5],

[0051] [Fig.8] represents a microscopic view of magnetic powder grains from an inhomogeneous mixture present in the mold of [Fig.6],

[0052] [Fig.9] represents a cutting step of end sections of a solidified volume resulting from demolding from the mold of [Fig.6],

[0053] [Fig. 10] represents in perspective the result of the step shown in [Fig. 9],

[0054] [Fig. 11] represents the rotor according to the invention at different stages of a process of manufacturing a rotor according to the invention, in an embodiment of the invention,

[0055] [Fig. 12] represents steps of a process for manufacturing a rotor according to the invention, and a bonded magnet pole according to the invention, in an embodiment of the invention,

[0056] [Fig. 13] represents a step of positioning a mold comprising a mixture of magnetic powder and resin against a permanent magnet, and a step of joining two solidified volumes from such a mold, in the embodiment of the invention, and

[0057] [Fig. 14] represents an alternative positioning step of a mold comprising a mixture of magnetic powder and resin against a permanent magnet, and a step of joining two solidified volumes from such a mold, in the embodiment variant of the invention.

[0058] According to an embodiment of the invention illustrated [Fig. 1], a rotor 30 of an axial flux electric machine according to the invention comprises a hub for receiving a shaft rotating about an axis of rotation X passing through the center O of the rotor 30. The rotor 30 comprises a non-magnetic armature 32, for example made of aluminum or a synthetic composite material. This non-magnetic armature 32 comprises an internal circular portion proximal to the hub and an external circular portion distal to the hub. The non-magnetic armature 32 comprises arms 34 joining these two circular portions, the arms 34 being regularly distributed angularly around the hub. By "angularly" is meant along an angular direction. An axial direction being defined by the axis of rotation X, the angular direction is defined as rotating about this axial direction, and a radial direction as orthogonal to the axial direction and passing through the center O of the rotor 30.

[0059] The arms 34 define, between the circular portions of the frame 32, recesses in which magnetic poles 20 are fixed, each of which, in this embodiment of the invention, is a bonded magnet pole according to the invention. Each bonded magnet pole 20 emits a magnetic field M in the axial direction and is formed of magnetic powder consolidated in a resin, for example, an epoxy resin. Each bonded magnet pole 20 extends between two angularly opposed edges 22 and 24, and between two radially opposed edges 26, 28, edge 26 being proximal to the hub. Each bound magnet pole 20 takes the form of a right trapezoidal prism, the edges 22, 24, 26, 28 delimiting two trapezoidal surfaces 21, 23 of the same dimensions. These surfaces 21, 23 themselves define the thickness of the magnet pole 20 in the axial direction. The surfaces 21, 23 are designed to orthogonally receive a magnetic field generated by one or more stators of the operating electrical machine. The electrical machine may, for example, comprise two stators clamping the rotor 30 in the axial direction, or a single stator whose magnetic poles face, at least partially, the magnetic poles of the rotor 30 in the axial direction.

[0060] The magnetic powder density in each bound magnet pole 20 is not homogeneous, as can be more easily seen in [Fig. 2], which shows in detail one of the bound magnet poles 20 of the rotor 30. The magnetic powder density in a portion of the bound magnet pole 20 shown in this [Fig. 2] is greater the darker the color of that portion. A cross-section S of the bound magnet pole 20 in the angular direction shows that the magnetic powder density of the bound magnet pole 20 in the axial direction is homogeneous. Conversely, in the angular direction, the bonded magnet pole 20 has a central portion 25 occupying most of the center of this bonded magnet pole 20, in which the density of magnetic powder is greater than in lateral portions 27, 29 of the bonded magnet pole 20, angularly opposite to the central portion 25. Typically:

[0061] - the remanent magnetic field in the median part 25 is between 0.6 and 1T (Tesla), and

[0062] - the remanent magnetic field in the lateral parts 27, 29 is between 0 and 0.2T.

[0063] Similarly, the density of magnetic powder is greater in the middle part 25 than on the peripheral parts of the bonded magnet pole 20 adjoining the inner circular part or the outer circular part of the non-magnetic armature 32.

[0064] As can also be seen in [Fig.2], the magnetic powder density gradually decreases from the middle part 25 towards the angularly opposite edges 22, 24 of the bonded magnet pole 20.

[0065] It should be noted that in this application the angular, radial, or axial directions are sometimes used to describe the bonded magnet poles 20 or parts thereof before they are inserted into the rotor housings 30. The very geometry of the poles is indeed intimately linked to their position in the rotor housings 30. It is therefore understood that in this case, the axial direction is always orthogonal to the larger dimension surfaces 21, 23 of the bonded magnet pole 20 under consideration, and that the radial direction is always orthogonal to the axial direction. substantially parallel to one of the edges 22, 24 of the considered bound magnet pole, while the angular direction is always orthogonal to the axial direction and substantially parallel to one of the edges 26, 28 of the considered bound magnet pole 20.

[0066] Obtaining a bonded magnet pole 20 according to the invention requires a step of concentrating the magnetic powder in the resin at the center of the bonded magnet pole 20 before solidification of the resin.

[0067] Figure 3 describes an embodiment of a manufacturing process 1 for the rotor 30 according to the invention, including a manufacturing process 10 for a bonded magnet pole 20 according to the invention. However, other methods of obtaining such a rotor 30 according to the invention or a bonded magnet pole 20 according to the invention are conceivable. More specifically, the first steps 11 to 15 of the manufacturing process 1 for the rotor 30 according to the invention are steps of the manufacturing process 10 for a bonded magnet pole 20 according to the invention.

[0068] The first step 11 of the process 10 for manufacturing a bonded magnet pole 20 is the mixing of a magnetic powder, for example a Neodymium Iron Boron (NdFeB) or Samarium Cobalt (SmCo) powder, in a liquid resin such as an epoxy resin. Alternatively, another type of resin is used, for example a polyamide. The mixture produced in this first step 11 is a homogeneous mixture of the magnetic powder in the resin. A second step 12 of the process 10 of manufacturing a bonded magnet pole 20 is the insertion of the mixture made in the previous step into a mold 4 (referenced [Fig.5]) whose internal volume takes the form of a right prism with a trapezoidal base, of the same thickness as the bonded magnet pole 20 but more extended radially and angularly. This internal volume is intended to form the bonded magnet pole 20, and therefore comprises a median section intended to form the median part 25 of the bonded magnet pole 20, and lateral sections intended to form the lateral parts 27, 29 of the bonded magnet pole 20. Alternatively, the internal volume of the mold 4 is intended to form several bonded magnet poles 20 at once, for example by having a thickness that is a multiple of the thickness of the bonded magnet pole 20, or, in another variant, the internal volume of the mold 4 takes exactly the form of a bonded magnet pole 20 or of several bonded magnet poles 20 superimposed axially on each other.

[0069] A third step 13 of the process 10 for manufacturing a bonded magnet pole 20 is the application of a magnetic field to the mold 4. For this, a manufacturing device according to the invention of a bonded magnet pole 20 is used, shown in Figures 4 to 6. In these figures, two permanent magnets 6 and 8, spaced apart, generate magnetic fields ml and m2, respectively. The direction of the magnetic fields ml and m2 in each permanent magnet 6, 8 between the south and north poles of that permanent magnet 6, 8, is called the magnetization direction. This direction is the same for each of the magnets 6, 8 whose magnetic moments are parallel and of the same direction. A first ferromagnetic plate 7 joins the north poles of the permanent magnets 6 and 8, and a second ferromagnetic plate 9 joins the south poles of the permanent magnets 6 and 8. The permanent magnets 6, 8 and the plates 7, 9 together form an enclosure in which the magnetic fields created by the permanent magnets 6, 8 circulate.

[0070] The first ferromagnetic plate 7 guides the magnetic field lines from the north poles of the respective permanent magnets 6, 8 to its middle, these field lines looping back halfway between the permanent magnets 6, 8 towards the south poles of the respective permanent magnets 6, 8 by passing through the enclosure and then through the second ferromagnetic plate 9. The second ferromagnetic plate 9 guides the magnetic field lines coming out of the south poles of the respective permanent magnets 6, 8 in a manner symmetrical to the guidance provided by the first ferromagnetic plate 7.

[0071] To concentrate the magnetic field lines passing through the enclosure between the two ferromagnetic plates 7, 9 at mid-distance from the permanent magnets 6, 8, each ferromagnetic plate 7, 9 has, on the side of the enclosure, a thickness evolution so as to be thicker in its middle than at its ends, which reduces the distance to travel in the air for the magnetic field lines passing through the enclosure at mid-distance from the permanent magnets 6, 8, compared to the distance between the ferromagnetic plates near the permanent magnets 6, 8.

[0072] In particular, the first ferromagnetic plate 7 has, from a first plateau covering the north pole of the permanent magnet 6, increasing steps 70, 72 and 74, which progressively increase the thickness of the first ferromagnetic plate 7 up to its middle, consequently decreasing the distance between the first ferromagnetic plate 7 and the second ferromagnetic plate 9 at its middle compared to the distance between these plates near the permanent magnet 6. Then the first ferromagnetic plate 7 has, from the median step 74 to this plate, decreasing steps 76, 78 up to a second plateau of the first ferromagnetic plate 7 covering the north pole of the permanent magnet 8.

[0073] Symmetrically, the second ferromagnetic plate 9 has, from a first plateau covering the south pole of the permanent magnet 6, increasing steps 90, 92, and 94, which progressively increase the thickness of the second ferromagnetic plate 9 up to its midpoint. Then, from the median step 94 of the second ferromagnetic plate 9, the second ferromagnetic plate 9 has decreasing steps 96, 98 up to a second plateau of the second ferromagnetic plate 9 covering the south pole of the permanent magnet 8.

[0074] Alternatively, the thickness evolution of the ferromagnetic plates is more gradual; for example, each of these plates has a convex, rounded surface. or formed of two inclined planes, on the side of the enclosure traversed by the magnetic field resulting from the fields ml and m2 generated by the magnets. In the following, this resulting magnetic field is referred to, unless otherwise indicated, when discussing the magnetic field generated by magnets 6 and 8. This magnetic field is, for example, between 0.5 and 1 T.

[0075] Returning to step 13 of applying a magnetic field to the mold 4, the mold is placed in this step within the enclosure formed by the permanent magnets 6, 8 and the ferromagnetic plates 7, 9, as shown in [Fig. 5]. A support (not shown) positioned between the two permanent magnets 6, 8 holds the mold 4 orthogonally to the direction of magnetization. The mold 4 is positioned on the support so that the median section of the internal volume of the mold is centered opposite the median steps 74 and 94 of the two ferromagnetic plates 7, 9, that is, at the point where the magnetic flux generated by the permanent magnets 6, 8 in the enclosure has a maximum intensity. The lateral sections of the internal volume are traversed by a magnetic flux of lower intensity.

[0076] On [Fig.5], the color of the mixture contained in the mold 4 is homogeneous because the magnetic field generated by the permanent magnets 6, 8 has not yet altered the homogeneity of the mixture.

[0077] Figure 6 shows the result of step 13, which involves applying the magnetic field generated by the permanent magnets 6 and 8 to the mold 4 after a few minutes. The magnetic powder has concentrated under the effect of this magnetic field in the median section of the mold's internal volume. Consequently, the median section will form the central part 25 of the bonded magnet pole 20, and the lateral sections will form the lateral parts 27 and 29 of the bonded magnet pole 20.

[0078] Figure 7 shows the magnetic powder grains in the mixture before insertion of mold 4 in the chamber. Figure 8 shows the magnetic powder grains in the mixture after step 13, which involves applying the magnetic field to the mixture within the chamber. After step 13, the magnetic powder grains concentrated in the middle section of the mold and preferentially aligned themselves in the direction of magnetization, resulting in a greater magnetic flux generated by the powder grains in this direction. It should be noted that the arrows on the magnetic powder grains indicate a more favorable direction of magnetization than other directions, but do not indicate a final direction. The final magnetization of the bonded magnet pole 20 occurs after the mixture has solidified.

[0079] The next step 14 of the process 10 for manufacturing a bonded magnet pole 20 is the solidification of the mixture in the mold, achieved by drying the epoxy resin within the enclosure of the device shown in Figures 4 to 6. For this purpose, the resin is heated to a temperature between 120° and 140°. Alternatively, depending on the type of resin used, the mixture is cooled, with the mold 4 remaining in the enclosure traversed by the magnetic field generated by the permanent magnets 6, 8.

[0080] The next step 15 of the process 10 for manufacturing a bonded magnet pole 20 is, as shown in [Fig. 9], a cutting of end sections 44 from the solidified volume 40 demolded from the mold 4 after step 14 of solidifying the mixture, these end sections being adjacent to the lateral sections of the volume 40, opposite the median section of the volume 40. In this step, the bonded magnet pole 20 is obtained more generally by cutting out excess peripheral parts from the volume 40. These peripheral parts are much less dense in magnetic powder than the rest of the volume 40. The resulting bonded magnet pole 20, trapezoidal in shape, is illustrated in perspective in [Fig. 10].

[0081] The next step 16 is a step in the process 1 for manufacturing the rotor 30, in which the bonded magnet poles 20 obtained by repeating steps 11 to 15 for each bonded magnet pole of the rotor 30 are inserted into the non-magnetic armature 32. This insertion is done, for example, using a two-part non-magnetic armature, the outer circular part being, for example, a ring closing the housings for the magnetic poles of the rotor 30, once these housings have been filled with the bonded magnet poles 20. These are, for example, slid between the arms 34 of the non-magnetic armature 32 by means of ribs on the edges of the poles, complementary to grooves on the arms 34 of the non-magnetic armature 32.

[0082] Finally, a last step 17 of the process 1 of manufacturing the rotor 30 is the magnetization of the poles of the bonded magnet 20, to form the north and south poles of the rotor 30. Each magnet pole is subjected for this purpose to a magnetic field of, for example, between 4 and 5T, the adjacent magnetic poles being subjected to a magnetic field of opposite direction.

[0083] Of course the order of steps 16 and 17 can be reversed.

[0084] In an embodiment of the invention, illustrated [Fig. 11], the method for manufacturing a rotor according to the invention comprises a mixing step similar to step 11 described above, followed by a step of inserting the resulting liquid mixture into a mold delimited at least in part by the non-magnetic armature 32. In this embodiment, the non-magnetic armature 32 is placed flat on a support, which serves, for example, to hold the liquid mixture in the housings of the magnetic poles of the rotor 30. Each housing thus forms itself a mold for a bonded magnet pole 20. In addition, a permanent magnet is arranged on each arm 34 of the non-magnetic armature 32 so as to create lines of magnetic fields concentrated along a radial axis of symmetry of each housing.

[0085] Figure 11 shows on the left the homogeneous mixture of magnetic powder and resin inserted into the cavities before the action of the magnetic field generated by the permanent magnets positioned on the arms 34 of the rotor 30. In the middle, the rotor 30 is shown with the inhomogeneous mixture obtained following the action of this magnetic field, the magnet poles having also been solidified. On the left, the rotor 30 is shown after a final magnetization step. In this embodiment, the edges of the solidified volume from the mold are not cut since the mold takes the exact shape of the bonded magnet poles.

[0086] In another embodiment of the invention shown [Fig. 12], a manufacturing process 100 for the rotor 30 according to the invention comprises steps 110 to 180, including steps of a manufacturing process 111 for a bonded magnet pole 20 according to the invention. More specifically, the first steps 110 to 160 of the manufacturing process 100 for the rotor 30 according to the invention are steps of the manufacturing process 111 for a bonded magnet pole 20 according to the invention.

[0087] The first step 110 of the process 111 for manufacturing a magnet pole 20 is the mixing of a magnetic powder and a liquid resin, in a manner similar to step 11 of the embodiment described above.

[0088] A second step 120 of the process 111 for manufacturing a bonded magnet pole 20 is the insertion of the liquid mixture obtained in the preceding step 110 into a mold 2 (referenced [Fig. 13]) whose useful volume allows the formation of one half of the bonded magnet pole 20 to be manufactured, this half being intended to form, together with another half of the bonded magnet pole manufactured in parallel with these steps 110, 120, the bonded magnet pole 20. The two halves are radially symmetrical to each other once inserted into one of the housings of the rotor 30. A portion 252 of the useful volume (referenced [Fig. 13]) is intended to form one half of the middle part 25 of the bonded magnet pole 20.

[0089] A third step 130 of the process 111 for manufacturing the bonded magnet pole 20, shown in [Fig. 13], is the positioning of the mold 2 against a permanent magnet 3, so that the portion 252 of the useful volume mentioned above is proximal to the permanent magnet 3. A support 5 holds the mold 2 in this position, the permanent magnet 3 generating between its north and south poles a magnetic field m3, directed axially with respect to the half of the bonded magnet pole being formed in the mold. In other words, the magnetic field m3 passes through the useful volume of the mold 2 in its thickness, the useful volume having approximately the thickness of the bonded magnet pole 20 to be manufactured. The [Fig.13] shows on the left the support 5 and the permanent magnet m3 without the mold 2, in the middle the mold 2 positioned in the support 5 against the permanent magnet m3, the liquid mixture still being homogeneous, and further to the right the mold 2 positioned in the support 5 against the permanent magnet m3, the magnetic powder in. mold 2 having concentrated in the portion 252 of the useful volume proximal to the permanent magnet 3.

[0090] A fourth step 140 of the process 111 of manufacturing the bonded magnet pole 20 is the solidification of the liquid mixture in the mold 2 always positioned against the permanent magnet 3, by increasing the temperature of the mixture to a temperature for example between 120° and 140°. A fifth step 150 of the process 111 for manufacturing the bonded magnet pole 20 is the joining, for example by gluing, of a solidified volume 41 from the previous step, to a solidified volume 42 from parallel steps 110 to 150 which formed the second half of the bonded magnet pole 20 to be manufactured. At the end of this joining step 150, the block shown completely to the right of [Fig. 13] is obtained.

[0091] A sixth step 160 of the process 111 of manufacturing the bonded magnet pole 20 is the cutting of peripheral end parts of this block, this cutting being identical to step 15 of the embodiment described above and allowing to obtain the bonded magnet pole 20.

[0092] In the same way as steps 16 to 17 of the embodiment described above, the following steps 170 and 180 of the manufacturing process 100 of the rotor 30 according to the invention are the insertion 170 of the previously obtained bonded magnet poles 20 into the non-magnetic armature 32 and the magnetization of these bonded magnet poles 20.

[0093] Figure 14 illustrates an alternative embodiment, which differs from this variant only in step 130, the positioning of the mold 2 against the permanent magnet 3. In this alternative, the portion 252 of the mold 2's usable volume is still positioned proximally to the permanent magnet 3, thanks to the support 5. However, the permanent magnet 3 is positioned so that the magnetic field m3 generated between the south and north poles of the permanent magnet 3 is directed parallel to the larger surfaces of the mold. This implies that the magnetic powder grains in the liquid mixture become magnetically oriented in this step 130, parallel to the larger surfaces of the bonded magnet pole 20 being manufactured. Of course, the magnetization step 180 then corrects this incorrect magnetic orientation of the magnetic powder grains in the solidified bonded magnet pole 20.However, this step 130 allows, as in the main embodiment of the invention, the magnetic powder to be concentrated in the portion 252 of the useful volume of the mold intended to form half of the middle part 25 of the bonded magnet pole 20.

[0094] Of course, the invention is not limited to the examples just described, and many modifications can be made to these examples without departing from the scope of the invention. In particular, the characteristics of the different modes or variants of implementation methods can be combined to implement the invention, provided that these methods or variants are not incompatible with each other.

Claims

Demands

1. A bonded magnet pole (20) of an electric machine, formed of magnetic powder consolidated in a resin, the bonded magnet pole (20) extending between two angularly opposed edges (22, 24) and partially delimiting two surfaces (21, 23) intended to be positioned orthogonally to a direction parallel to a magnetic field (M) generated by a stator of the electric machine, the bonded magnet pole (20) being characterized in that it has a higher density of magnetic powder in a median portion (25) of the bonded magnet pole (20) located between the two edges (22, 24) than in at least one lateral portion (27, 29) of the bonded magnet pole (20) located between one of the edges (22, 24) and the median portion (25), the density of magnetic powder increasing progressively from at least one of the edges (22, 24) towards the median portion (25) of the bound magnet pole (20).

2. Bound magnet pole (20) according to claim 1, wherein the magnetic powder density is greater in the middle part (25) than in a lateral part (27, 29) of the bound magnet pole (20) located between the other edge (22, 24) and the middle part (25).

3. Bonded magnet pole (20) according to claim 1 or 2, wherein the magnetic powder density is homogeneous in the direction parallel to the magnetic field (M) generated by a stator of the electric machine.

4. Axial flux electric machine rotor (30) comprising a hub, a non-magnetic armature (32) around the hub and having housings, characterized in that at least one of the housings comprises a magnet pole attached (20) according to any one of claims 1 to

5. d 3. A method for manufacturing (10) a bonded magnet pole (20) of an electrical machine according to any one of claims 1 to 3, comprising the steps of: - Mixing (11) the magnetic powder in the liquid resin, - Inserting (12) the mixture into a mold (4) the useful part of which comprises a volume (40) for forming the bonded magnet pole (20), the volume (40) having a median section for forming the median part (25) of the bonded magnet pole (20), and at least one lateral section intended to form at least one lateral part (27, 29) of the bound magnet pole (20), - Application (13) of a magnetic field (ml, m2) to the mold (4), the intensity of the magnetic field (ml, m2) being greater in the median section of the volume (40) than in the lateral section of the volume (40), and - solidification (14) of the volume (40).

6. Method of manufacturing (10) a bonded magnet pole (20) according to claim 5, wherein the solidification step (14) is followed by a cutting step (15) of an end section (44) of the volume, the end section adjoining the lateral section of the volume (40), opposite the median section of the volume (40).

7. A method of manufacturing (1) an axial flux electric machine rotor (30) according to claim 4, wherein the bonded magnet pole (20) is manufactured by the manufacturing method (10) according to claim 5 or 6, the manufacturing method (1) of a rotor (30) comprising steps of: - Disposing (16) of the bonded magnet pole (20) in the housing of the magnetic armature (32), and - Magnetizing (17) the bonded magnet pole (20).

8. Device for manufacturing a bonded magnet pole (20) of an electric machine according to any one of claims 1 to 3, comprising: - a mold (4), - a first generator (6) of a magnetic field (m2) in a direction of magnetization, - a second generator (8) of a magnetic field (ml) in the direction of magnetization, - a support positioned between the two generators orthogonally to the direction of magnetization, the support being suitable for receiving the mold (4), and - a magnetic flux guide (7, 9) suitable for concentrating in the middle of the support the magnetic field (ml, m2) generated by at least one of the two generators (6, 8).

9. Device for manufacturing a bonded magnet pole (20) for a rotor (30) of an electric machine according to claim 8, wherein the magnetic flux guide (7, 9) comprises two ferromagnetic plates orthogonal to the direction of magnetization and each covering two ends of the generators (6, 8), each plate showing on the side of the support from a first end of the plate, an evolution of plate thickness, the plate thickness being greater in its middle than at least one of its ends.

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