ROTOR FOR AN ELECTRIC MACHINE AND ELECTRIC LATHE WITH AXIAL FLOW

Description

technical field

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

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

[0003] The permanent magnets used in the automotive industry are particularly large, which results in significant eddy currents during operation. These eddy currents reduce system performance by generating heat at the magnets, which can also damage the system.

[0004] To reduce eddy current losses, document WO2018172633 proposes using a large number of small magnets assembled together to form a permanent magnet. Assembling this type of magnet is difficult, time-consuming, and expensive. Furthermore, after assembly, it is difficult to guarantee the shape and positional tolerances of the magnets, and there is a risk that the magnet may break during positioning or use.

[0005] Document CN109921525A proposes, to resolve the problem of eddy current losses, to create orthoradial grooves in the permanent magnet across its entire surface. These orthoradial grooves reduce eddy current losses but weaken the permanent magnet's mechanical strength, making it difficult to handle.

[0006] Documents FR3119703A1 and FR3127344A1 propose radial and orthoradial grooves distributed uniformly on the magnet but do not have a groove-free holding portion. Summary of the invention

[0007] One idea behind the invention is to limit eddy current losses in the permanent magnets of a rotating electrical machine with axial flux.

[0008] Another idea underlying the invention is to facilitate the manufacture of permanent magnets for a rotating electrical machine with axial flux.

[0009] Another idea behind the invention is to facilitate the handling of permanent magnets when positioning them on the rotor disc.

[0010] According to one embodiment, the invention provides a rotor for an axial flux electric machine, intended to be mounted to rotate freely around an X axis and positioned axially opposite a stator, the rotor comprising a disk fixed in rotation to an output shaft and a plurality of permanent magnets distributed around the X axis, each permanent magnet having the shape of a truncated disk sector;in which at least one of the permanent magnets of said plurality of permanent magnets is made in a single piece and consists of a retaining portion and a grooved portion disposed in a radial direction from the X-axis outside the retaining portion, said permanent magnet having a plurality of grooves, the entire plurality of grooves being made on the grooved portion, in which the retaining portion has a radial dimension 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 in which the plurality of grooves includes at least one radial groove extending in the radial direction, and at least one orthoradial groove extending in an orthoradial direction.;

[0011] Thanks to these characteristics, the grooves on the permanent magnet significantly reduce eddy current losses, thus improving the efficiency of the rotating electrical machine. Furthermore, because the retaining portion is free of grooves that could weaken it, the permanent magnet can be easily handled by this particularly robust retaining section. Since the retaining portion is located closest to the X-axis, the grooved portion is situated in the radially outer zone where eddy current losses are greatest. Therefore, the position of the grooves is optimized to minimize these losses. Finally, because the permanent magnet is a single piece, its manufacturing is simplified. Thus, all these characteristics result in a good compromise between reducing eddy current losses and facilitating the manufacturing and handling of permanent magnets.

[0012] According to embodiments, such a rotor may include one or more of the following characteristics.

[0013] According to one embodiment, several permanent magnets of said plurality of permanent magnets are made in a single piece and each consists of a retaining portion and a grooved portion arranged radially outside the retaining portion, said permanent magnets each having a plurality of grooves, the entire plurality of grooves being made on the grooved portion.

[0014] According to one embodiment, each permanent magnet of said plurality of permanent magnets is made in a single piece and consists of a retaining portion and a grooved portion arranged radially outside the retaining portion, each permanent magnet having a plurality of grooves, the entire plurality of grooves being made on the grooved portion.

[0015] According to one embodiment, the disk has housings distributed all around the X axis, the permanent magnets being arranged each in one of the housings of the disk.

[0016] According to one embodiment, the radial groove is made in a thickness direction parallel to the X axis from the first surface of said permanent magnet.

[0017] 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.

[0018] 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.

[0019] Thus, it is possible to minimize eddy current losses using through grooves.

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

[0021] According to one embodiment, the plurality of grooves comprises a plurality of orthoradial grooves spaced apart from each other.

[0022] Thus, by increasing the number of radial and / or orthoradial grooves, it is possible to further limit eddy current losses.

[0023] 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.

[0024] 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.

[0025] According to one embodiment, the orthoradial groove extends in a thickness direction parallel to the X axis over only a part of one dimension of the permanent magnet in the thickness direction.

[0026] According to one embodiment, the orthoradial groove has a dimension in a thickness direction parallel to the X axis between 10% and 90% of a dimension of the permanent magnet in the thickness direction.

[0027] 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 holding of the permanent magnet.

[0028] According to one embodiment, the orthoradial groove is a first orthoradial groove, and in which the plurality of grooves includes 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 made 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.

[0029] 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.

[0030] According to one embodiment, the permanent magnets and the rotor disc are held in position relative to each other by means of an overmolding.

[0031] According to one embodiment, the invention also provides an axial flux electrical machine comprising: a housing defining an internal space; at least one of the aforementioned rotors, the rotor being mounted to rotate freely in the internal space of the housing 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 protrude towards the rotor and are distributed around the X axis and coils each comprising a winding which is mounted around one of the teeth.

[0032] According to one embodiment, the invention also provides a motor vehicle comprising the aforementioned electric machine. Brief description of the figures

[0033] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings. There figure 1 This represents a schematic cross-sectional view of a rotating axial flux electrical machine comprising a rotor and two stators. figure 2 This represents a schematic cross-sectional view of a rotating axial flux electrical machine comprising two rotors and a stator. figure 3 represents a perspective view of a disk and the permanent magnets of the rotor of the axial flux rotating electric machine of the figure 1 . There figure 4 This represents a perspective view of a permanent magnet isolated from the rotor of a rotating electrical machine with axial flux. figure 5represents a perspective view of a rotor of the axial flux rotating electrical machine after overmolding. Description of the implementation methods

[0034] There figure 1 represents a rotating electrical machine with axial flux 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.

[0035] In the example described, the axial flux electric machine 1 is configured to operate in both motor and generator modes. This is a permanent magnet synchronous motor for propelling an electric vehicle.

[0036] The term "vehicle" refers to any vehicle capable of transporting goods or people, such as a car, truck, bicycle, or drone.

[0037] The power of the electric machine can range from 4 kW to 850 kW. In the example considered, the electric machine advantageously has an operating voltage below 60 volts, preferably 48 volts. Typically, the torque supplied by the electric machine is between 30 Nm and 2000 Nm. Alternatively, the electric machine can have an operating voltage above 60 V, or even above 80 V or 100 V, particularly 300 V or more. In this case, the machine's power can range from 60 kW to 300 kW.

[0038] The axial flux electric machine 1 includes an output shaft 4 extending along an axis X, fixed to the rotor 3 and passing through the rotor 3 and the stators 2. The output shaft 4 has an output pinion which meshes with a reducer (not shown).

[0039] The rotor 3 comprises a disk 5 fixed for rotation to the output shaft 4 and having an orifice 6 through which the output shaft 4 passes. The disk 5 also has recesses 7 regularly distributed around the X-axis in which permanent magnets 8 are arranged, which have, for example, a sector-like shape. The rotor 3 will be described in more detail in relation to the figures 2 to 4 .

[0040] The stators 2 each comprise a stator body equipped 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.

[0041] The windings on the teeth together form a general stator winding, for example, of the three-phase type. These windings are made by turns of electrical wire around each tooth.

[0042] 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.

[0043] There figure 2 illustrates another embodiment of the axial flux rotating electrical machine 1. Indeed, and unlike the embodiment of the figure 1 , the axial flux rotating electric machine 1 of the figure 2 comprises a stator 2 and two rotors 3 placed on either side of the stator 2, facing each other axially with the stator 2.

[0044] There figure 3 represents more specifically the disc 5 of the rotor 3 and the associated permanent magnets 8.

[0045] As seen in figure 3The 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.

[0046] The permanent magnets 8 are arranged in the housings 7 such that a first surface 12 of the permanent magnets 8 protrudes from one side of the disk 5 which is intended to be opposite one of the stators 2, and a second surface 13 opposite the first surface 12 protrudes from the other side of the disk 5 which is intended to be opposite the other of the stators 2 in the case of the two-stator electric machine 1. figure 1 .

[0047] In the case of a two-rotor electric machine 1 of the figure 2, the permanent magnets 8 are fixed to a flange and have a single surface protruding from the disk 5 and intended to be opposite the stator 2.

[0048] Permanent magnets 8 are illustrated in particular in figure 4 As can be seen in this figure, each permanent magnet 8 is made in one piece and consists of two portions: a retaining portion 14 and a grooved portion 15 which is arranged radially outside the retaining portion 14.

[0049] Each permanent magnet 8 also has a plurality of grooves and all of these grooves are made on the grooved portion 15 so that the retaining portion 14 is without grooves.

[0050] The retaining 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 figures 3 and 4, the radial dimension of the retaining portion 14 is approximately 26% of the radial dimension of the permanent magnet 8.

[0051] The grooved portion 15 has a radial dimension complementary to the radial dimension of the retaining portion 14, i.e. in the example about 74% of the total radial dimension of the permanent magnet 8.

[0052] To limit eddy current losses, the permanent magnet 8 has, among its plurality of grooves, radial grooves 16 extending in the radial direction R and spaced apart from each other. In the example illustrated in figure 4 The radial grooves 16, of which there are three, divide the grooved portion 15 of the permanent magnet 8 in an orthoradial direction O into four parts. In other embodiments, this number could be greater or lesser depending on the size of the permanent magnet 8.

[0053] Each radial groove 16 is made in a through-direction of thickness E parallel to the X axis from the first surface 12 to the second surface 13.

[0054] In order to limit eddy current losses, the permanent magnet 8 includes, among the plurality of grooves, orthoradial grooves extending in the orthoradial direction O, parallel to each other and spaced apart from each other.

[0055] Among the orthoradial grooves, the permanent magnet 8 has first orthoradial grooves 17 formed in the thickness direction E from the first surface 12, and second orthoradial grooves 18 formed in the thickness direction E from the second surface 13. Furthermore, as can be seen in figure 4 , the first orthoradial grooves 17 are alternated with the second orthoradial grooves 18 in the radial direction R.

[0056] The first orthoradial grooves 17 and the second orthoradial grooves 18 each advantageously present a dimension in the thickness direction E between 10 and 90% of a dimension in the thickness direction E of the permanent magnet 8. In the example illustrated in figure 4 , the dimension in the thickness direction of the orthoradial grooves 17, 18 is about 60% of the dimension in the thickness direction E of the permanent magnet 8.

[0057] In the example illustrated in figure 4The first six orthoradial grooves 17 and the second six orthoradial grooves 18. In other embodiments, this number could be greater or lesser depending on the size of the permanent magnet 8. Furthermore, the number of first orthoradial grooves 17 could be different from the number of second orthoradial grooves 18, for example, five first orthoradial grooves 17 and four second orthoradial grooves 18.

[0058] In another embodiment not shown, the grooved portion 15 may only have first orthoradial grooves 17 or second orthoradial grooves 18 for example in the case where the electrical machine 1 has a single stator 2 and two rotors 3.

[0059] Grooves 16, 17, 18 are for example made by wire cutting or laser cutting operations.

[0060] There figure 5Figure 3 represents the rotor after an overmolding step designed to hold the permanent magnets 8 in position within the housings 7 of the disc 5. Indeed, the disc 5 allows the magnets to be positioned circumferentially and radially before overmolding, as can be seen in this figure 5 The entire disc 5 and the permanent magnets 8 of the rotor 3 are encased in a layer of resin 19, preferably plastic, during an overmolding step which precisely locks the positions of the various permanent magnets 8. The holes 20 visible on the figure 5 represent the location of pins which are positioned in the mold to ensure precise positioning of the permanent magnets 8 during overmolding.

[0061] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention as defined by the claims.

[0062] The use of the verb "comporter", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or steps than those stated in a claim.

[0063] In claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

1. A rotor (3) for an axial-flux electric machine (1), designed to be mounted so as to rotate about an X-axis and positioned axially opposite a stator (2), the rotor (3) comprising a disc (5) rotatably secured to an output shaft (4) and a plurality of permanent magnets (8) distributed around the X-axis, each permanent magnet (8) having the shape of a truncated disc sector; in which at least one of the permanent magnets (8) of said plurality of permanent magnets (8) is formed as a single piece and comprises a retaining portion (14) and a grooved portion (15) arranged in a radial direction (R) relative to the X-axis radially outside of the retaining portion (14), said permanent magnet (8) comprising a plurality of grooves, the entirety of the plurality of grooves being formed on the grooved portion (15), wherein the retaining portion (14) has a radial dimension of between 10 and 50% of a radial dimension of said permanent magnet (8), said permanent magnet (8) having a first surface (12) facing 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 an orthoradial direction (O).

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 formed so as to pass through from the first surface (12) to the second surface (13) of said permanent magnet (8).

4. Rotor (3) according to any one of claims 1 to 3, wherein the plurality of grooves comprises a plurality of radial grooves spaced apart from one another.

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

6. Rotor (3) according to any 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. 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 a dimension of the permanent magnet (8) in the thickness direction.

8. Rotor (3) according to claim 7, wherein the orthoradial groove is a first orthoradial groove (17), and wherein the plurality of grooves comprises 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 one another by a non-zero distance in the radial direction (R).

9. Rotor (3) according to 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 being alternated with the second orthoradial grooves in the radial direction (R).

10. Rotor (3) according to any one of claims 1 to 9, wherein the permanent magnets (8) and the disc (5) of the rotor (3) are held in position relative to one another by means of an overmolding.

11. Axial-flux electric machine (1) comprising: - a housing defining an internal space; - at least one rotor (3) according to any one of claims 1 to 10, the rotor (3) being mounted so as to be rotatable within the internal space of the housing about the X-axis; - 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 X-axis, and coils each comprising a winding which is mounted around one of the teeth.

12. A motor vehicle comprising an electric machine according to claim 11.