Rotor for electric machine and axial flux rotating electric machine

Abstract

The invention relates to a rotor (3) for an axial flux electric machine (1), the rotor (3) comprising a disc (5) rotatably secured to an output shaft (4) and a plurality of permanent magnets (8) having the shape of a truncated disc sector; wherein at least one of said permanent magnets (8) is made in a single piece and comprises in a radial direction (R) from the X axis outwards a holding portion (14) and a grooved portion (15), said permanent magnet (8) comprising a plurality of grooves, the entire plurality of grooves being made on the grooved portion (15), wherein the holding portion (14) has a radial dimension comprised between 10 and 30% of a radial dimension of said permanent magnet (8), and wherein the plurality of grooves comprises at least one radial groove (16) extending in the radial direction (R), and at least one orthoradial groove extending in an orthoradial direction (O).Figure for abstract: 2.

Description

Title of the invention: Rotor for an electric machine and axial flux rotating electric machine Technical field

[0001] The invention relates to the field of axial flux rotating electrical machines, in particular for an electric or hybrid vehicle. The invention is more particularly concerned with the rotor of these axial flux rotating electrical machines. Technological background

[0002] Known axial flux rotating electrical machines comprise permanent magnets in the rotor(s) of the machine. These permanent magnets are subjected to the magnetic fields generated by the stator coils so as to drive the rotor in rotation.

[0003] The permanent magnets used in the automotive industry are of a particularly large size, which has the notable consequence of generating significant eddy currents when used. These eddy currents reduce the performance of the system by generating heat at the magnets, which can also damage the system.

[0004] In order to reduce eddy current losses, document WO2018172633 provides for the use of a large number of small magnets that are assembled together to form a permanent magnet. Assembling this type of magnet is difficult, time-consuming, and expensive. In addition, after assembly, it is difficult to ensure the shape and position tolerance of the magnets, and there is a risk that the magnet will disintegrate during positioning or use.

[0005] Document CN109921525A provides for the purpose of solving this problem of eddy current losses by producing orthoradial grooves in the permanent magnet over the entire surface of the magnet. These orthoradial grooves make it possible to reduce eddy current losses but weaken the mechanical strength of the permanent magnet, making it difficult to handle. Summary of the invention

[0006] An idea underlying the invention is to limit the eddy current losses of the permanent magnets of an axial flux rotating electrical machine.

[0007] Another idea underlying the invention is to facilitate the manufacture of permanent magnets for an axial flux rotating electrical machine.

[0008] Another idea underlying the invention is to facilitate the handling of the permanent magnets when positioning them on the rotor disc.

[0009] According to one embodiment, the invention provides a rotor for a machine axial flux electric rotor, intended to be mounted mobile in rotation around an axis X and positioned axially opposite a stator, the rotor comprising a disk integral in rotation with an output shaft and a plurality of permanent magnets distributed around the axis X, each permanent magnet having the shape of a truncated disk sector;wherein at least one of the permanent magnets of said plurality of permanent magnets is made in a single piece and is constituted by a holding portion and a grooved portion arranged in a radial direction of the X axis outside the holding portion, said permanent magnet comprising a plurality of grooves, the entire plurality of grooves being made on the grooved portion, wherein the holding portion has a radial dimension of between 10 and 50% of a radial dimension of said permanent magnet, said permanent magnet having a first surface located opposite the stator, and a second surface opposite the first surface, and wherein the plurality of grooves comprises at least one radial groove extending in the radial direction, and at least one orthoradial groove extending in an orthoradial direction. ;

[0010] Thanks to these characteristics, the grooves present on the permanent magnet make it possible to significantly limit eddy current losses and therefore to improve the efficiency of the rotating electrical machine. In addition, thanks to the holding portion which is therefore free of grooves likely to weaken it, the permanent magnet can be easily handled by this particularly robust holding portion. The holding portion being located closest to the X axis, the grooved portion is located in the radially outer zone where eddy current losses are the greatest. Thus, the position of the grooves is optimized to limit these losses. Finally, since the permanent magnet is a single piece, its manufacture is facilitated. Thus, all of these characteristics make it possible to obtain a good compromise between reducing eddy current losses and ease of manufacturing and handling of permanent magnets.

[0011] According to embodiments, such a rotor may comprise one or more of the following characteristics.

[0012] According to one embodiment, several permanent magnets of said plurality of permanent magnets are produced in a single piece and each consist of a holding portion and a grooved portion arranged radially outside the holding portion, said permanent magnets each comprising a plurality of grooves, the entire plurality of grooves being produced on the grooved portion.

[0013] According to one embodiment, each permanent magnet of said plurality of permanent magnets is produced in a single piece and consists of a holding portion and a grooved portion arranged radially outside the holding portion, each permanent magnet having a plurality of grooves, the entire plurality of grooves being provided on the grooved portion.

[0014] According to one embodiment, the disk comprises housings distributed all around the X axis, the permanent magnets each being arranged in one of the housings of the disk.

[0015] According to one embodiment, the radial groove is produced in a thickness direction parallel to the X axis from the first surface of said permanent magnet.

[0016] Thus, the radial groove is made as close as possible to the stator in the area where it is advantageous to limit eddy current losses.

[0017] According to one embodiment, the radial groove is made in a through manner from the first surface to the second surface of said permanent magnet.

[0018] Thus, it is possible to limit eddy current losses as much as possible using a through groove.

[0019] According to one embodiment, the plurality of grooves comprises a plurality of radial grooves spaced from each other.

[0020] According to one embodiment, the plurality of grooves comprises a plurality of orthoradial grooves spaced from each other.

[0021] Thus, by increasing the number of radial and / or orthoradial grooves, it is possible to further limit eddy current losses.

[0022] According to one embodiment, the orthoradial groove is made in a thickness direction parallel to the X axis from the first surface of the permanent magnet.

[0023] Thus, the orthoradial groove is made as close as possible to the stator in the area where it is advantageous to limit eddy current losses.

[0024] According to one embodiment, the orthoradial groove extends in a thickness direction parallel to the X axis over only a portion of one dimension of the permanent magnet in the thickness direction.

[0025] According to one embodiment, the orthoradial groove has a dimension in a thickness direction parallel to the X axis of between 10% and 90% of a dimension of the permanent magnet in the thickness direction.

[0026] Thus, thanks to the thickness of the orthoradial groove contained in said interval, it is possible to optimize the limitation of eddy current losses with the strength of the permanent magnet.

[0027] According to one embodiment, the orthoradial groove is a first orthoradial groove, and wherein the plurality of grooves comprises a second orthoradial groove having a dimension in the thickness direction of between 10% and 90% of a dimension of the permanent magnet in the thickness direction, the second orthoradial groove being formed in the thickness direction from the second surface of the permanent magnet, the first orthoradial groove and the second orthoradial groove being spaced from each other by a non-zero distance in the radial direction.

[0028] According to one embodiment, the plurality of grooves comprises a plurality of first orthoradial grooves and a plurality of second orthoradial grooves, the first orthoradial grooves being alternated with the second orthoradial grooves in the radial direction.

[0029] According to one embodiment, the permanent magnets and the rotor disc are held in position relative to each other using overmolding.

[0030] According to one embodiment, the invention also provides an axial flux electric machine comprising: - a casing defining an internal space; - at least one aforementioned rotor, the rotor being mounted to move in rotation in the internal space of the casing around the X axis; - at least one stator which is positioned in the internal space, axially opposite the rotor, and comprises a stator body equipped with teeth which project towards the rotor and which are distributed around the X axis and coils each comprising a winding which is mounted around one of the teeth.

[0031] According to one embodiment, the invention also provides a motor vehicle comprising a aforementioned electric machine. Brief description of the figures

[0032] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely for illustrative and non-limiting purposes, with reference to the appended drawings.

[0033] [Fig.l] represents a schematic sectional view of an axial flux rotating electrical machine comprising a rotor and two stators.

[0034] [Fig.2] represents a schematic sectional view of an axial flux rotating electrical machine comprising two rotors and a stator.

[0035] [Fig.3] represents a perspective view of a disc and permanent magnets of the rotor of the axial flux rotating electric machine of [Fig.l].

[0036] [Fig.4] represents a perspective view of a permanent magnet taken in isolation from the rotor of the axial flux rotating electrical machine.

[0037] [Fig.5] represents a perspective view of a rotor of the axial flux rotating electrical machine after overmolding. Description of the embodiments

[0038] [Fig.l] represents an axial flux rotating electrical machine 1, of the permanent magnet type comprising a casing 10 defining an internal space 11, two stators 2 and a rotor 3 positioned in the internal space 11, the stators 2 being placed on either side of the rotor 3 and axially opposite the rotor 3. The rotor 3 is axially spaced from the two stators so as to form two air gaps.

[0039] In the example described, the axial flux electric machine 1 is configured to operate in motor mode and in generator mode. This is a permanent magnet synchronous motor, for the propulsion of an electric vehicle.

[0040] By vehicle is meant any vehicle capable of transporting goods or people, such as a car, truck, bicycle or drone.

[0041] The power of the electric machine may be between 4 kW and 850 kW. In the example considered, the electric machine advantageously has an operating voltage of less than 60 Volts, and preferably 48 Volts. Typically, the torque provided by the electric machine is between 30 Nm and 2000 Nm. Alternatively, the electric machine may have an operating voltage of more than 60 V, or even more than 80 V or more than 100 V, in particular 300 V or more. In this case, the power of the machine may be between 60 kW and 300 kW.

[0042] The axial flux electric machine 1 comprises an output shaft 4 extending along an axis X, integral with the rotor 3 and passing through the rotor 3 and the stators 2. The output shaft 4 comprises an output pinion which meshes with a reduction gear (not shown).

[0043] The rotor 3 comprises a disc 5 integral in rotation with the output shaft 4 and comprising an orifice 6 crossed by the output shaft 4. The disc 5 also comprises housings 7 distributed regularly around the axis X in which permanent magnets 8 are arranged which have, for example, a disc sector shape. The rotor 3 will be more particularly described in relation to FIGS. 2 to 4.

[0044] The stators 2 each comprise a stator body provided with a plurality of electrical windings and a plurality of teeth carrying the electrical windings. A housing is configured to carry the plurality of teeth.

[0045] The windings on the teeth together form a general winding of the stator, for example of the three-phase type. These windings are made by turns of electric wires around each tooth.

[0046] The windings are configured to be electrically powered so as to generate a magnetic field capable of producing, with the rotor 3 of the axial flux electric machine 1, an output torque.

[0047] [Fig.2] illustrates another embodiment of the axial flux rotating electrical machine 1. Indeed, and unlike the embodiment of [Fig.1], the axial flux rotating electrical machine 1 of [Fig.2] comprises a stator 2 and two rotors 3 placed on either side of the stator 2, axially facing each other with the stator 2.

[0048] [Fig. 3] more particularly represents the disc 5 of the rotor 3 and the associated permanent magnets 8.

[0049] As visible in [Fig.3], the permanent magnets 8 each have the shape of a truncated disk sector and are distributed regularly around the X axis. Each of the permanent magnets 8 is placed in one of the housings 7 of the disk 5. The housings 7 thus have shapes complementary to the permanent magnets 8.

[0050] The permanent magnets 8 are arranged in the housings 7 so that a first surface 12 of the permanent magnets 8 projects from one side of the disc 5 which is intended to be opposite one of the stators 2 and that a second surface 13 opposite the first surface 12 projects from another side of the disc 5 which is intended to be opposite the other of the stators 2 in the case of the electrical machine 1 with two stators of [Fig. 1].

[0051] In the case of an electric machine 1 with two rotors of [Fig.2], the permanent magnets 8 are fixed to a flange and have a single surface projecting from the disc 5 and intended to be opposite the stator 2.

[0052] The permanent magnets 8 are more particularly illustrated in [Fig.4]. As can be seen in this figure, each permanent magnet 8 is made in a single piece and is made up of two portions: a holding portion 14 and a grooved portion 15 which is arranged radially outside the holding portion 14.

[0053] Each permanent magnet 8 also comprises a plurality of grooves and all of these grooves are made on the grooved portion 15 so that the holding portion 14 is free of grooves.

[0054] The holding portion 14 advantageously has a radial dimension, measured in the radial direction R, of between 10 and 30% of a radial dimension of the permanent magnet 8. In the example illustrated in FIGS. 3 and 4, the radial dimension of the holding portion 14 is approximately 26% of the radial dimension of the permanent magnet 8.

[0055] The grooved portion 15 has a radial dimension complementary to the radial dimension of the holding portion 14, i.e. in the example approximately 74% of the total radial dimension of the permanent magnet 8.

[0056] In order to limit the eddy current loss, the permanent magnet 8 comprises, among the plurality of grooves, radial grooves 16 which extend in the radial direction R and spaced apart from each other. In the example illustrated in [Fig.4], the radial grooves 16 are three in number and thus cut the grooved portion 15 of the permanent magnet 8 in an orthoradial direction O into four parts. In other embodiments, this number could be more or less important depending on the dimension of the permanent magnet 8.

[0057] Each radial groove 16 is made in a through manner in one direction of thickness E parallel to the X axis from the first surface 12 to the second surface 13.

[0058] Still in order to limit eddy current losses, the permanent magnet 8 comprises, among the plurality of grooves, orthoradial grooves extending in the orthoradial direction O, parallel to each other and spaced apart from each other.

[0059] Among the orthoradial grooves, the permanent magnet 8 comprises first orthoradial grooves 17 made in the thickness direction E from the first surface 12, and second orthoradial grooves 18 made in the thickness direction E from the second surface 13. In addition, as visible in [Fig.4], the first orthoradial grooves 17 are alternated with the second orthoradial grooves 18 in the radial direction R.

[0060] The first orthoradial grooves 17 and the second orthoradial grooves 18 each advantageously have a dimension in the thickness direction E of between 10 and 90% of a dimension in the thickness direction E of the permanent magnet 8. In the example illustrated in [Fig.4], the dimension in the thickness direction of the orthoradial grooves 17, 18 is approximately 60% of the dimension in the thickness direction E of the permanent magnet 8.

[0061] In the example illustrated in [Fig.4], the first orthoradial grooves 17 are six in number and the second orthoradial grooves 18 are also six in number. In other embodiments, this number could be more or less important depending on the dimension of the permanent magnet 8. In addition, the number of first orthoradial grooves 17 could be different from the number of second orthoradial grooves 18, with for example five first orthoradial grooves 17 and four second orthoradial grooves 18.

[0062] In another embodiment not illustrated, the grooved portion 15 may comprise only first orthoradial grooves 17 or second orthoradial grooves 18, for example in the case where the electrical machine 1 comprises a single stator 2 and two rotors 3.

[0063] The grooves 16, 17, 18 are for example produced by wire cutting or laser cutting operations.

[0064] [Fig. 5] represents the rotor 3 after an overmolding step aimed at holding the permanent magnets 8 in position in the housings 7 of the disc 5. Indeed, the disc 5 makes it possible to position the magnets circumferentially and radially before overmolding, and as visible in this [Fig. 5], the assembly of the disc 5 and the permanent magnets 8 of the rotor 3 are enveloped by a layer of resin 19, preferably made of plastic material, during an overmolding step which precisely locks the positions of the different permanent magnets 8. The holes 20 visible on the [Fig.5] represent the location of pins which are positioned in the mold in order to guarantee a precise position of the permanent magnets 8 during overmolding.

[0065] Although the invention has been described in connection with several particular embodiments, it is quite obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0066] The use of the verb “comprise”, “comprise” or “include” and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0067] In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims

Claims

1. Rotor (3) for an axial flux electric machine (1), intended to be mounted mobile in rotation around an axis X and positioned axially opposite a stator (2), the rotor (3) comprising a disk (5) integral in rotation with an output shaft (4) and a plurality of permanent magnets (8) distributed around the axis X, each permanent magnet (8) having the shape of a truncated disk sector;wherein at least one of the permanent magnets (8) of said plurality of permanent magnets (8) is made in a single piece and is constituted by a holding portion (14) and a grooved portion (15) arranged in a radial direction (R) of the X axis outside the holding portion (14), said permanent magnet (8) comprising a plurality of grooves, the entire plurality of grooves being made on the grooved portion (15), wherein the holding portion (14) has a radial dimension comprised between 10 and 50% of a radial dimension of said permanent magnet (8), said permanent magnet (8) having a first surface (12) situated opposite the stator (2), and a second surface (13) opposite the first surface (12), and wherein the plurality of grooves comprises at least one radial groove (16) extending in the radial direction (R), and at least one orthoradial groove extending in a radial direction (R), orthoradial (0).;

2. Rotor (3) according to claim 1, wherein the radial groove (16) is formed in a thickness direction parallel to the X axis from the first surface (12) of said permanent magnet (8).

3. Rotor (3) according to claim 2, wherein the radial groove (16) is made in a through manner from the first surface (12) to the second surface (13) of said permanent magnet (8).

4. Rotor (3) according to one of claims 1 to 3, in which the plurality of grooves comprises a plurality of radial grooves spaced from each other.

5. Rotor (3) according to one of claims 1 to 4, wherein the plurality of grooves comprises a plurality of orthoradial grooves spaced from each other.

6. Rotor (3) one of claims 1 to 5, wherein the orthoradial groove is formed in a thickness direction parallel to the X axis from the first surface (12) of the permanent magnet (8).

7. A rotor (3) according to claim 6, wherein the orthoradial groove extends in a thickness direction parallel to the X axis over only a portion of one dimension of the permanent magnet (8) in the thickness direction.

8. The rotor (3) of claim 7, wherein the orthoradial groove is a first orthoradial groove (17), and wherein the plurality of grooves includes a second orthoradial groove (18) having a dimension in the thickness direction of between 10% and 90% of a dimension of the permanent magnet (8) in the thickness direction, the second orthoradial groove (18) being formed in the thickness direction from the second surface (13) of the permanent magnet (8), the first orthoradial groove (17) and the second orthoradial groove (18) being spaced apart from each other by a non-zero distance in the radial direction (R).

9. The rotor (3) of claim 8, wherein the plurality of grooves comprises a plurality of first orthoradial grooves and a plurality of second orthoradial grooves, the first orthoradial grooves alternating with the second orthoradial grooves in the radial direction (R).

10. Rotor (3) according to one of claims 1 to 9, in which the permanent magnets (8) and the disc (5) of the rotor (3) are held in position relative to each other using an overmolding.

11. An axial flux electrical machine (1) comprising: - a casing defining an internal space; - at least one rotor (3) according to one of claims 1 to 10, the rotor (3) being mounted to rotate in the internal space of the casing around the axis X; - at least one stator (2) which is positioned in the internal space, axially opposite the rotor (3), and comprises a stator body (2) equipped with teeth which project towards the rotor (3) and which are distributed around the axis X and coils each comprising a winding which is mounted around one of the teeth.

12. Motor vehicle comprising an electric machine according to claim 11.

Images