Rotor for an axial flux electric machine with a radial-arm portion of reduced cross section

Abstract

The present invention relates to a rotor (1) for an axial flux electric machine comprising a rotor disc (2) made of metallic material and permanent magnets (4), the rotor disc (2) comprising receptacles (5) in which the permanent magnets (4) are positioned. The rotor disc (2) comprises radial arms (17) separating said receptacles (5), and radial and circumferential blocking means for blocking the permanent magnets (4) radially and circumferentially in position in the rotor disc (2). Furthermore, each radial arm (17) comprises at least a first portion, the axial thickness of which is strictly less than the thickness of the rotor disc and / or the circumferential width of which is strictly less than the circumferential widths in second and third portions of the radial arm. The invention also relates to an electric machine with such a rotor.

Description

[0001] ROTOR FOR AXIAL FLUX ELECTRIC MACHINE WITH REDUCED SECTION RADIAL ARM PORTION

[0002] Technical field

[0003] The invention relates to the field of axial flux electrical machines and more particularly relates to a rotor for this type of electrical machine.

[0004] This type of axial flux electric machine can find applications in particular in electric or hybrid vehicles, such as cars, buses, trucks, construction machinery. This type of machine can also be used for stationary applications, such as industrial charging machines or electric generators.

[0005] Prior art

[0006] In recent decades, the development of electrical machines has focused mainly on radial flux electrical machines.

[0007] Radial flux electrical machines typically comprise a coaxial rotor and stator, one surrounding the other. Thus, the magnetic flux can pass radially from the rotor to the stator and vice versa, via a radial air gap which is defined as the radial clearance between the rotor and the stator.

[0008] In contrast, axial flux machines are characterized by at least one rotor and at least one stator that are arranged successively one behind the other in the axial direction (of the rotor's axis of rotation), so that the magnetic flux path between the rotor and the stator is axial. In other words, the rotor and the stator face each other and are separated by an axially thick air gap (or axial clearance between the rotor and the stator).

[0009] The rotor of permanent magnet axial flux electric machines generally comprises permanent magnets bonded to the rotor yoke or inserted into a rotor body and in this case, the permanent magnets are separated by radial arms from the rotor body. The stator generally comprises a ferromagnetic stator body with or without teeth. An electrical winding in the stator slots can be distributed or concentric, that is, each winding then surrounds a tooth.

[0010] In the context of the development of high power and torque density machines for electric or hybrid traction, particularly for electric or hybrid vehicle applications, the topology of axial flux machines is positioned among those with the highest potential, in particular due to the high axial size constraint. Axial flux electric machines are also of interest for stationary applications as well as for wind turbine applications.

[0011] Generally speaking, axial flux electric machines allow higher power and torque densities than radial flux electric machines. This gain is generally achievable by increasing the number of pole pairs in the rotor, which increases the rotation frequency as well as rotor losses (i.e. losses in the magnets). In addition, the use of a tooth winding allows for a reduction in the coil heads, but increases the harmonic content in the air gap, causing increased losses in the stator iron and in the magnets.

[0012] As a result, axial flux machines tend to heat up more and controlling heating and cooling is therefore an important issue for this type of machine.

[0013] Patent application WO22 / 128983 A1 relates to an axial flux electric machine rotor, with several unit magnets to form a group of magnets in each magnetic pole. Each group of magnets is placed in a housing in the rotor body and the housings are separated from each other by radial arms. The rotor body is non-magnetic. As a result, heating is limited. However, the production of this rotor body is expensive and complex to implement.

[0014] Patent application FR2 996377 A1 is also known, which also relates to an axial flux electrical machine rotor. To reduce the mass of the rotor body that holds the permanent magnets, the rotor body is made of two plates secured together. The axial thickness of the rotor body thus obtained is generally less than the axial thickness of the permanent magnets, which makes it possible to reduce the overall mass of the rotor body. However, the rotor body includes extensions to surround and hold the permanent magnets in position. The rotor body is made of a non-magnetic material. It therefore generates few losses and little heating, but it is expensive to manufacture. In addition, the manufacture of the rotor is more complex and compliance with the rotor dimensions is more difficult to achieve with such a manufacture.

[0015] Patent application WO22 / 223798 is also known, which relates to an axial flux electric machine in which the radial arms of the rotor body have a thickness that decreases from the inside to the outside so as to facilitate holding the permanent magnets in position.

[0016] Furthermore, in axial flux machines, it is necessary to ensure the magnets are held in the rotor during centrifugation and against axial forces due to magnetic interaction with the stators.

[0017] Thus, the technical problem that we propose to resolve consists of limiting heating of the rotor by limiting rotor losses, particularly those in its mechanical support, facilitating cooling of the rotor, ensuring that the magnets are kept in position, while maintaining a sufficient level of rigidity to limit the problems of vibration, noise and the phenomena of veiling of the rotor surface.

[0018] Summary of the invention

[0019] To meet these objectives, the invention relates to a rotor for an axial flux electrical machine comprising a rotor disc made of metallic material and permanent magnets, the rotor disc comprising an axial external thickness at its external cylindrical surface and housings distributed circumferentially within the rotor disc, the permanent magnets being positioned in said housings.

[0020] In addition, the rotor disc comprises radial arms separating said housings and radial and circumferential locking means for locking in position the permanent magnets radially and circumferentially in the rotor disc.

[0021] Further, each radial arm comprises at least a first portion, each first portion comprising:

[0022] - an axial thickness strictly less than the axial external thickness of the rotor disc and / or;

[0023] - a circumferential width strictly less than the circumferential widths in second and third portions of the radial arm positioned radially on either side of the first portion, the first portion being at a distance from the radial ends of the radial arm.

[0024] Advantageously, said housings are of substantially trapezoidal section, preferably the largest base of the trapezium is on the external side of the rotor.

[0025] Advantageously, said radial and circumferential locking means are formed by heels at the radial ends of the radial arms, at the junction between each radial arm and the housings on either side of said radial arm.

[0026] According to a configuration of the invention, said first portion is at a distance from the permanent magnets on either side of said radial arm.

[0027] Preferably, at least one radial arm, preferably each radial arm, comprises a radially extending cooling channel for circulating a cooling fluid.

[0028] According to a variant of the invention, each radial arm comprises a beam of I-shaped, H-shaped, L-shaped, T-shaped or cross-shaped section extending in the radial direction, preferably an I-shaped beam, the connecting bar of the I-shaped or H-shaped section extending in the circumferential direction or in the axial direction. According to a configuration of the invention, said radial arm comprises a radial bar and preferably ribs fixed to the radial bar and oriented towards the permanent magnets, on either side of the radial bar.

[0029] According to one embodiment of the invention, the rotor disk comprises a rotor support, the rotor support comprising the radial arms and a ring or annular hoop forming the radial locking means of the permanent magnets.

[0030] Advantageously, the rotor disc comprises an internal portion with at least one recess.

[0031] According to a variant of the invention, the rotor comprises an overmolding element, the overmolding element enveloping the rotor disc and the permanent magnets.

[0032] Preferably, the overmolding element is made of resin, preferably epoxy resin, or plastic, preferably PEEK.

[0033] Advantageously, the first portion and / or the second portion and / or the third portion of each radial arm has, in the radial direction, a constant or variable circumferential width, preferably when the circumferential width of the portion considered is variable, this circumferential width decreases from the internal radial end to the external radial end.

[0034] The invention also relates to an axial flux electric machine comprising at least one stator and at least one rotor as described according to one of the preceding variants or combinations of variants.

[0035] Preferably, the axial flux electric machine comprises two rotors and one stator, or two stators and one rotor, or two stators and two rotors.

[0036] List of figures

[0037] Other characteristics and advantages of the rotor and / or the electrical machine according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the figures appended and described below.

[0038] Figure 1 represents a first embodiment of an axial flux electric machine rotor according to the invention.

[0039] Figure 2 represents a second embodiment of an axial flux electric machine rotor according to the invention.

[0040] Figure 3 shows a sectional view of a radial arm at a rib according to the embodiment of Figure 2. Figure 4 shows a third embodiment of an axial flux electric machine rotor according to the invention.

[0041] Figure 5 represents an example of positioning of a first portion of a radial arm according to the invention.

[0042] Figure 6 represents a fourth embodiment of an axial flux electric machine rotor according to the invention.

[0043] Figure 7 represents a fifth embodiment of an axial flux electric machine rotor according to the invention.

[0044] Figure 8 shows an example of an axial flux electric machine with one rotor and two stators.

[0045] Figure 9 represents an example of an axial flux electric machine rotor according to the prior art.

[0046] Figure 10 represents an example of a radial arm of an axial flux electric machine rotor according to the invention.

[0047] Figure 11 shows another example of a radial arm of an axial flux electric machine rotor according to the invention.

[0048] Description of the embodiments

[0049] The terms “vertical”, “horizontal”, “upper”, “lower” are understood to mean the electrical machine of the invention in operating condition.

[0050] The "longitudinal" direction is the direction of the axis of the central shaft (or rotor shaft) and the electric machine.

[0051] The invention relates to a rotor for an axial flux electrical machine comprising a rotor disc made of metallic material and permanent magnets. Thus, when the coils of the stator of the electrical machine are crossed by an electric current, an electromagnetic torque is produced and drives the rotor of the machine in rotation, thanks to the interaction between the stator field produced by the winding and the rotor field produced by the permanent magnets. Conversely, when the rotor is driven in rotation by any rotation means (a rotation shaft for example), the permanent magnets induce a magnetomotive force in the stator coils. This makes it possible to transform the mechanical energy of the rotor into electrical energy in the stator. As a result, the electrical machine can be used as an electric motor that transforms electricity into mechanical energy, or as an electrical generator that transforms mechanical energy into electrical energy.

[0052] The rotor disc serves as a support for carrying the permanent magnets and to do this, it comprises housings distributed circumferentially within the rotor disc, the permanent magnets being positioned in said housings. The rotor disc comprises radial arms separating the housings.

[0053] Advantageously, the housings can axially pass through the rotor disc to open at both axial ends of the rotor disc. Thus, the permanent magnets can pass through the rotor disc axially on each side. This configuration is particularly advantageous when the electrical machine comprises a rotor and two stators, each stator being on either side of the rotor disc. This type of machine comprising a rotor and two stators, one stator on either side of the rotor with the permanent magnets passing completely through the rotor disc is called a "through-permanent magnet electrical machine".

[0054] The rotor disc has an annular shape between a cylindrical surface of inner diameter and a cylindrical surface of outer diameter. In addition, it has an axial external thickness (i.e. the axial length of the disc, taken at its outer surface) at its cylindrical outer surface.

[0055] Radial arms mean spokes located between the housings which extend radially from an inner end to an outer end.

[0056] The rotor disc also includes radial and circumferential locking means for locking the permanent magnets in position radially and circumferentially in the rotor disc. Thus, the permanent magnets are easily held in position both when mounting the permanent magnets in the rotor disc and when using the rotor, with the disc rotating.

[0057] Furthermore, in order to limit the currents induced in the radial arms, each radial arm comprises at least a first portion, each first portion comprising:

[0058] - an axial thickness (i.e. the length in the axial direction of the axis of rotation of the rotor) strictly less, for example by at least 30%, than the axial external thickness of the rotor disc and / or;

[0059] - a circumferential width (width in a direction substantially orthogonal to the radial direction) strictly less, for example by at least 30%, than the circumferential widths in a second and a third portion of the radial arm. In the case where the first portion comprises a circumferential width reduced compared to the circumferential widths of the second and third portions, the first portion is then located radially between these second and third portions and the first portion is then at a distance from the radial ends of the radial arm. In other words, the second and third portions are positioned radially on either side of the first portion. Thus, the first portion has a reduction in section (a reduced section) compared to the second and third portions of the radial arm and / or compared to the rotor disk.

[0060] A “reduced section” or “section reduction” means a section which has:

[0061] - An axial thickness strictly less than the axial external thickness of the rotor disc: the thickness of the first portion is then reduced compared to that of the disc;

[0062] - And / or a circumferential width strictly less than those of the second and third portions: the circumferential width of the first portion is then reduced compared to that of the second and third portions.

[0063] By "at a distance from the radial ends of the radial arms" is meant that the portion concerned may, for example, be located over a distance between 10% and 90% of the length of the radial arm, starting from the inner radial end of the radial arm. In other words, the portion concerned may, for example, be located at a distance starting at least 10% of the length of the radial arm, starting from the inner radial end and ending at most 90% of the length of the radial arm, starting from the outer radial end.

[0064] Thus, the first portion of limiting the volume of metallic material in the radial arms, in particular in areas conducive to the formation of induced currents, that is to say especially in the central part of the radial arms far from the radial ends of the radial arms to limit heating of the rotor disk and / or facilitate cooling.

[0065] For the purposes of the invention, the thicknesses are considered to be the dimensions in the axial direction and the circumferential widths are the lengths in the direction orthogonal to the radial direction and orthogonal to the axial direction, therefore substantially circumferential.

[0066] As the thickness of the first portion and / or its circumferential width are reduced relative to the external thickness of the disc or the circumferential width of the second and third portions, respectively, the mass of the metallic material of the radial arm is reduced and therefore, the induced currents and therefore heating of the rotor can be limited. Indeed, since the radial arms are close to the permanent magnets, these radial arms are conducive to the formation of induced currents and are therefore sources of rotor losses. Thus, it is easier to control the temperature of the rotor and avoid demagnetization of the magnets. In addition, by limiting the temperature of the rotor, the performance of the electrical machine can be improved because losses are reduced.

[0067] By limiting the metallic volume of the radial arm in the first portion, the radial ends can also be kept thicker, which allows these radial ends to be used to come into contact with the permanent magnets. Therefore, the radial ends can serve as a radial and / or circumferential locking means to lock the permanent magnets in position radially and / or circumferentially in the rotor disc.

[0068] For example, the section (orthogonal to the neutral line of the radial arm from the inner radial end to the outer radial end) of said first portion may be at least 30% smaller than the smallest of said sections (orthogonal to the neutral line of the radial arm from the inner radial end to the outer radial end) of the second and third portions. As a result, the section is significantly reduced to further limit heating of the rotor disk, while ensuring sufficient mechanical strength.

[0069] According to one configuration of the invention, said housings may be of substantially trapezoidal section or any similar shape. For example, the largest base of the trapezoidal shape may be on the side of the outer periphery of the rotor. Such a shape is advantageous for housing a large quantity of magnets in the rotor, while ensuring relatively simple machining for the housings in the rotor disc.

[0070] According to variants of the invention, the rotor disc may be a single solid part.

[0071] For example, the radial length of the first portion can be at least 10% of the radial length of the radial arm. Thus, the section is reduced significantly enough.

[0072] Advantageously, said radial and circumferential locking means may be formed by heels at the radial ends of the radial arms, at the junction between each radial arm and the housings on either side of said radial arm. The heels are then second and third portions, the circumferential width of which is strictly greater than that of the first portion and the circumferential widths of which are such that each heel comes into contact with the permanent magnets on either side of the radial arm. These heels therefore form solid parts between the permanent magnets. The heels thus come into circumferential contact, and preferably into radial contact, with the permanent magnets to allow the permanent magnet to be held in position in its housing, both during assembly and during rotation of the rotor during operation of the electrical machine.This solution allows for simple and effective holding of the magnets in position.

[0073] According to one embodiment of the invention, said first portion may be at a distance from the permanent magnets on either side of said radial arm. In other words, a gap separates the first portion from the permanent magnets on each side of the radial arm. This gap may be an air gap that improves the cooling of the rotor. Alternatively, this gap may be filled with an overmolding material.

[0074] According to an advantageous implementation of the invention, at least one radial arm, preferably each radial arm, may comprise a radially extending cooling channel for circulating a cooling fluid. Thus, it is possible to circulate a fluid in the cooling channel so as to further limit heating of the rotor. The fluid may be air or a liquid such as water or oil.

[0075] Circulation through the channel can be active, i.e. forced for example via a pump, or passive, i.e. natural circulation without equipment forcing the passage of the fluid in said cooling channel.

[0076] The fluid can advantageously be a liquid and more particularly cooling oil.

[0077] Preferably, each radial arm may comprise a beam of I, H, L, or T or cross section, the direction of the beam extending in the direction of the radially oriented neutral fiber, preferably an I beam, the central bar (or connecting bar) of the I or H extending in the circumferential direction or in the axial direction. When the central bar of the I or H extends in the circumferential direction, the thickness of this central bar is reduced compared to the parallel bars of the beam and compared to the axial external thickness of the rotor disk. When the central bar of the I or H extends in the axial direction, the axial thickness of the parallel bars is then less than the axial external thickness of the rotor disk.Thus, the contact surface between the permanent magnet and the radial arm is reduced, which further limits eddy current losses in the rotor disc and therefore limits rotor heating.

[0078] According to a variant of the invention, said radial arm may comprise a radial bar, of substantially rectangular, square, circular section, or of any similar shape and ribs fixed on the radial bar and oriented towards the permanent magnets, on either side of the radial bar. Thus, the area of ​​the radial arm between the ribs may form a first portion whose circumferential width is strictly less than the circumferential width of the arm at the ribs. The ribs make it possible to stiffen the arm, while limiting its mass and therefore to limit the inertial forces on the one hand and the induced currents on the other hand. In addition, the areas located between the ribs may be used for air circulation so as to improve the cooling of the rotor disk and the permanent magnets.Indeed, the addition of ribs makes it possible to increase the convective exchange surface and the natural air mixing of the assembly to limit the heating effect of the magnets, while increasing the rigidity of the structure.

[0079] Advantageously, the ends of the ribs in contact with the permanent magnets can be chamfered so as to limit the contact surface between the permanent magnets and the ribs.

[0080] Alternatively, the areas between the ribs can be used to fill this space with overmolding material, such as a resin (e.g. epoxy resin) or a plastic (e.g. PEEK), to reduce mass and limit induced currents.

[0081] Advantageously, the rotor disk may comprise a rotor support and an outer ring or an outer annular hoop forming the radial locking means for the permanent magnets, the rotor support comprising the radial arms. For example, the rotor support may comprise an inner ring and the radial arms are integral with the inner ring and extend from the inner ring. The outer ring or the outer annular hoop then serves to retain the permanent magnets, in particular when they are subjected to centrifugal forces in rotation. The outer ring or the annular hoop can be mounted on the rotor support after the permanent magnets are placed in the housings. As a result, the manufacture of the rotor is simple.

[0082] Advantageously, the rotor disc may comprise an internal portion (e.g. an internal ring) with at least one recess. The recess makes it possible to reduce the mass of the rotor disc and therefore to reduce the inertial forces.

[0083] According to one embodiment of the invention, the rotor may comprise an overmolding element, the overmolding element enveloping (or covering) the rotor disc and the permanent magnets, for example being able to form a solid annular disc. The overmolding element makes it possible to bond the rotor disc and the permanent magnets together and possibly to replace metallic areas of the rotor disc with a material of density inside the material of the rotor disc (to reduce the total mass and therefore the inertia) and with a material not allowing any induced current. The overmolding also makes it possible to stiffen the structure to improve resistance to the forces of the torque to be transmitted, while reducing the effect of the rotor disc running. The overmolding is also advantageous for reducing the friction of the rotor in the air and consequently reducing the level of noise from aerodynamic sources.

[0084] Preferably, the overmolding element may be made of resin, preferably epoxy resin, or plastic, preferably PEEK. These materials are both compatible with the operating temperatures of the rotor, of lower density than metallic materials (particularly those of the rotor disc) and of a material which does not generate induced current.

[0085] According to a variant of the invention, the first portion and / or the second portion and / or the third portion of each radial arm has, in the radial direction, a constant or variable circumferential width. The constant width is simpler to manufacture; the variable width makes it possible to adapt to more design constraints.

[0086] Preferably, when the circumferential width of the portion considered is variable, this circumferential width can decrease from the inner end to the outer end, so as to promote the maintenance of the magnets in position. This also makes it possible to reduce the masses, inertias and induced currents.

[0087] Figure 10 illustrates, in a schematic and non-limiting manner, an example of a radial arm with a portion which has a circumferential width decreasing from the inner end towards the outer end.

[0088] Diagram a) on the left represents the section of the radial arm in a longitudinal plane and perpendicular to the radial direction of the radial arm (a plane which includes the longitudinal axis Long), while diagram b) on the right represents the left view of the radial arm of diagram a).

[0089] The radial arm shown comprises a cross-section beam, the longitudinal bar 30 of the cross-section beam extending in the axial (or longitudinal) direction Long and the circumferential bar 31 of the cross-section beam extending in the circumferential direction Cire. The circumferential bar 31 has a circumferential width which decreases from the inner end to the outer end (see diagram b)): in other words, the circumferential bar 31 of the cross-section beam is of trapezoidal shape allowing the decreasing circumferential width. The circumferential bar 31 of the cross-section beam has a thickness (in the longitudinal direction Long) strictly less than the outer thickness of the disc and therefore forms a first portion of reduced section. In diagram a), the permanent magnets 4 are shown on either side in phantom, to facilitate the reader's understanding.

[0090] Figure 11 illustrates, in a schematic and non-limiting manner, another example of a radial arm with a portion which has a circumferential width decreasing from the inner end towards the outer end.

[0091] Diagram a) on the left represents the section of the radial arm in a longitudinal plane and perpendicular to the radial direction of the radial arm (a plane which includes the longitudinal axis Long), while diagram b) on the right represents the left view of the radial arm of diagram a).

[0092] The radial arm shown comprises a beam of I-shaped (or H-shaped) section, the central bar 32 of the I-shaped beam extending in the axial (or longitudinal) direction Long and the parallel bars 33 of the I-shaped beam extending in the circumferential direction Cire and have a circumferential width which decreases from the inner end to the outer end (see diagram b)): in other words, the parallel bars 33 of the I-shaped section beam are of trapezoidal shape allowing the decreasing circumferential width. The parallel bars 33 have a thickness (in the longitudinal direction Long) strictly less than the outer thickness of the disc and therefore form a first portion of reduced section.

[0093] In diagram a), the permanent magnets 4 are shown on either side in dot-and-dash lines, to facilitate the reader's understanding.

[0094] The invention also relates to an axial flux electrical machine comprising at least one stator and at least one rotor as described above. Indeed, with a rotor as described above, heating of the rotor is reduced and / or its cooling improved. Thus, the current density in the windings can be increased in continuous operation.

[0095] According to the invention, the axial flux machine can thus comprise at least one rotor and at least one stator which are arranged successively one behind the other in the axial direction (of the axis of rotation of the at least one rotor), so that the path of the magnetic flux between each successive rotor and each stator (i.e. which follow one another directly) is axial. In other words, each successive rotor and stator face each other and are separated by an air gap of axial thickness (or axial clearance between the rotor and the stator). Advantageously, the axial flux electrical machine can axially comprise a succession of rotors and stators. The multiplication of rotors and / or stators makes it possible to increase performance (torque and power in particular), and this in a restricted space requirement.Preferably, the axial flux electric machine may comprise two rotors and one stator, or two stators and one rotor (so-called "double stator and single rotor" machine) or an alternation of rotors and stators. The rotor of the invention is particularly advantageous when it is sandwiched between two stators since its thickness can then be reduced to a minimum.

[0096] A machine with two rotors and one stator can thus successively axially comprise a first rotor, a central stator (i.e. between the two rotors) and a second rotor. A machine with two stators and one rotor can thus successively axially comprise a first stator, a central rotor (i.e. between the two stators) and a second stator. A machine with two rotors and two stators can thus successively axially comprise a first rotor, a first stator, a second rotor and a second stator.

[0097] Figure 1 illustrates, in a schematic and non-limiting manner, a first embodiment of an axial flux electric machine rotor according to the invention.

[0098] The rotor 1 comprises a rotor disc 2 made of metallic material comprising housings 5 ​​distributed circumferentially in the rotor disc 2. The housings 5 ​​pass completely through the rotor disc axially. Inside these housings 5, permanent magnets 4 are placed. The permanent magnets 4 pass completely through the rotor disc 2 so as to create a rotor with permanent through magnets, making it possible to limit the axial size of an axial flux machine, in particular of the permanent through magnet type. Indeed, with this type of rotor, it is possible to use a machine with one rotor and two stators, one stator facing each face of the rotor disc.

[0099] The rotor disk 2 may comprise an external ring 3 for retaining the permanent magnets 4 radially, in particular when the rotor 1 is rotating.

[0100] The internal part of the rotor disc 2 may comprise recesses 6 so as to limit the mass of the rotor and therefore to limit the inertial forces.

[0101] The rotor disc 2 comprises radial arms 17 extending radially between the housings 5 ​​(and therefore between the permanent magnets 4) from an inner radial end

[0102] 13 to an outer radial end 12. At the inner 13 and outer 12 radial ends, the radial arms 17 have heels 11 and 16 which come into contact 7 and

[0103] 14 circumferentially and radially with the permanent magnets so as to maintain the permanent magnets 4 in position during assembly and in service. Between these heels 11 and 16, acting as second and third portions, there is a first portion 8 whose circumferential width is strictly less than the circumferential width of the heels 11 and 16. Thus, the permanent magnets 4 are not in contact with the first portion 8 and circumferential clearances 9, 10 separate the first portion 8 and the permanent magnets 4. These circumferential clearances 9 and 10 can be left empty to allow air to circulate or be filled with an overmolding (or coating) material, such as a resin or a plastic (epoxy resin or PEEK for example).

[0104] The rotor disc 2 also includes a central circular opening 15 for the installation of a rotor shaft (not visible).

[0105] The housings 5 ​​and the permanent magnets 4 have a shape which makes it possible to maximize the electromagnetic torque of the electric machine, a shape which is generally of the trapezoidal type with the largest base on the external side of the rotor, but other shapes can be considered.

[0106] To improve the mechanical connection, an overmolding material can optionally be put in place to form a solid disc around the rotor disc 2 and the permanent magnets 4. This coating material can in particular fill the empty spaces between the radial arms 17 and the permanent magnets 4 and fill the recesses 6 of the internal part of the rotor disc 2. This also makes it possible to lighten the rotor.

[0107] Figure 2 illustrates, in a schematic and non-limiting manner, a second embodiment of an axial flux electric machine rotor according to the invention.

[0108] The rotor comprises a rotor disc 2 made of metallic material comprising housings distributed circumferentially in the rotor disc 2. The housings pass completely through the rotor disc axially. Inside these housings, permanent magnets 4 are placed. The permanent magnets 4 pass completely through the rotor disc 2 so as to create a rotor with permanent through magnets, making it possible to limit the axial size of an axial flux machine, in particular of the permanent through magnet type. Indeed, with this type of rotor, it is possible to use a machine with one rotor and two stators, one stator facing each face of the rotor disc.

[0109] The rotor disk 2 may comprise an external ring 3 for retaining the permanent magnets 4 radially, in particular when the rotor is rotating.

[0110] The internal part of the rotor disc 2 may comprise recesses 6 so as to limit the mass of the rotor and therefore to limit the inertial forces.

[0111] The rotor disc 2 comprises radial arms 17 extending radially between the housings (and therefore between the permanent magnets 4) from an inner radial end 13 to an outer radial end 12.

[0112] The radial arms 17 comprise, in this embodiment, a central bar 18 which extends radially between the inner 13 and outer 12 radial ends. These radial arms 17 also comprise ribs 19 starting from the central bar 18 and extending towards the permanent magnets 4, on either side of the central bar 18. The ends of these ribs 19 serve as a circumferential locking means for the magnets. Thus, the ends of the ribs 19 are in contact 20 with the permanent magnets 4. Optionally and as shown, the ribs 19 are chamfered (they have a chamfer 21) so as to limit the contact surface between the permanent magnets 4 and the ribs 19, which makes it possible to limit heating of the rotor. Of course, the ribs 19 may not be chamfered.

[0113] Thus, at least a portion of the central bar 18 forms a first portion 22 whose circumferential width may be at least 30% less than the circumferential width of the second and third portions, the second portion comprising the central bar 18 and the ribs 19 just before (radially from the inside to the outside) the first portion 22, and the third portion comprising the central bar 18 and the ribs 19 just after (radially from the inside to the outside) the first portion 22.

[0114] Thus, the permanent magnets 4 are not in contact with the first portion 22 and circumferential clearances 20 and 21 separate the first portion 22 and the permanent magnets 4. These circumferential clearances 20 and 21 can be left empty to allow air to circulate or be filled with an overmolding (or coating) material, such as a resin or a plastic (epoxy resin or PEEK for example).

[0115] Rotor disc 2 also includes a central circular opening for the installation of a rotor shaft (not visible).

[0116] The housings and permanent magnets 4 are substantially trapezoidal in shape with the largest base on the external side of the rotor to optimize the volume of permanent magnets in the rotor and therefore the performance of the electric machine.

[0117] To improve the mechanical connection, an overmolding material can optionally be put in place to form a solid disc around the rotor disc 2 and the permanent magnets 4. This coating material can in particular fill the empty spaces between the radial arms 17 and the permanent magnets 4 and fill the recesses 6 of the internal part of the rotor disc 2. This also makes it possible to lighten the rotor.

[0118] Figure 3 illustrates, in a schematic and non-limiting manner, a sectional view, in a plane orthogonal to the radial axis, of a radial arm according to Figure 2, at the level of the ribs.

[0119] The arm comprises a central bar 18, here of rectangular section (but it could have another type of section) and two ribs 19, on either side of the central bar 18. The ribs 19 comprise chamfers 21 so as to limit the contact surface of the ribs 19 with the permanent magnets (not shown). Figure 4 illustrates, in a schematic and non-limiting manner, a third embodiment of a rotor according to the invention.

[0120] The figure illustrates only a portion of rotor 1 with a permanent magnet and half of the radial arms on either side of the permanent magnet.

[0121] As for the embodiments of Figures 1 and 2, the rotor comprises a magnetic metal rotor disc. The rotor disc comprises an outer ring (not shown) and radial arms between the permanent magnets 4 of section here substantially trapezoidal whose largest base is on the outer side of the rotor (but other shapes could be used).

[0122] The rotor disc also includes an internal part 27 with recesses 6.

[0123] Here, the radial arms of the rotor are formed from an I- or H-shaped beam 23.

[0124] The connecting bar (also called central bar) 25 of the beam 23 extends in the axial direction and the side bars (also called parallel bars) 24 of the beam extend substantially in the circumferential direction (orthogonal to the radial direction). As a result, the surface area of ​​the radial arms in contact with the permanent magnets 4 is minimized.

[0125] To improve the mechanical connection, an overmolding material 26 (or coating) is placed to form a solid disc around the rotor disc and the magnets. This coating material can in particular fill the empty spaces between the radial arms and the permanent magnets and fill the recesses 6 of the internal part 27. This also makes it possible to lighten the rotor.

[0126] The potting material (as in Figures 1 and 2) can be a resin, such as epoxy resin, or a plastic, such as PEEK.

[0127] Of course, the potting material is optional here. When not in use, the spaces are left empty, allowing air to circulate for rotor cooling.

[0128] Figure 5 illustrates, in a schematic and non-limiting manner, a radial arm according to an embodiment of the invention illustrated in Figure 1.

[0129] The radial arm has a length L between the inner radial end 13 and the outer radial end 12. The first portion, located between the heels located at the radial ends (according to FIG. 1) is located over the distance L1, from point P1 to point P2. Point P1 is at least 10% of the length L starting from the inner radial end 13 and point P2 is at most 90% of the length L starting from the inner radial end 13. As a result, heels can be used to block the magnets at the radial ends 12 and 13 and the quantity of metallic material in the radial arms can be reduced, particularly in the areas conducive to the formation of induced currents, i.e. the areas furthest from the ends. Figure 6 illustrates, in a schematic and non-limiting manner, a fourth embodiment of an axial flux electric machine rotor according to the invention.

[0130] The rotor 1 comprises a rotor disc 2 made of magnetic metallic material comprising housings distributed circumferentially in the rotor disc 2. The housings pass completely through the rotor disc axially. Inside these housings, permanent magnets 4 are placed. The permanent magnets 4 pass completely through the rotor disc 2 so as to create a rotor with permanent through magnets, making it possible to limit the axial size of an axial flux machine, in particular of the permanent through magnet type. Indeed, with this type of rotor, it is possible to use a machine with one rotor and two stators, one stator facing each face of the rotor disc.

[0131] The rotor disk 2 may comprise an external ring 3 for retaining the permanent magnets 4 radially, in particular when the rotor is rotating.

[0132] The internal part of the rotor disc 2 may include recesses so as to limit the mass of the rotor and therefore to limit the inertial forces.

[0133] The rotor disc 2 comprises radial arms 17 extending radially between the housings (and therefore between the permanent magnets 4) from an inner radial end 13 to an outer radial end 12.

[0134] The radial arms 17 comprise in this embodiment a beam 23 of I- or H-shaped section with the connecting bar 28 of this beam (or central bar connecting the two parallel bars) which extends in the circumferential direction and the two parallel (or lateral) bars 29 extend in the axial direction. Thus, the parallel bars 29 are in contact with the permanent magnets 4 over the entire axial length of the permanent magnets 4 and at the connecting bar 28, the thickness in the axial direction is reduced compared to the thickness in the axial direction at the parallel bars 29. The axial thickness at the parallel bars 29 may be less than or equal to the thickness of the rotor disk and the axial thickness at the connecting bar 28 is strictly less than the axial external thickness of the rotor disk. Thus, the connecting bar 28 forms a first portion.

[0135] The rotor disc 2 also includes a central circular opening 15 for the installation of a rotor shaft (not visible).

[0136] The housings and permanent magnets 4 are substantially trapezoidal in shape to optimize the volume of permanent magnets in the rotor and therefore the performance of the electric machine.

[0137] To improve the mechanical connection, an overmolding material can optionally be put in place to form a solid disc around the rotor disc 2 and the permanent magnets 4. This coating material can in particular fill the empty spaces between the radial arms 17 and the permanent magnets 4 and fill the recesses in the internal part of the rotor disc 2. This also makes it possible to lighten the rotor.

[0138] Figure 7 illustrates, in a schematic and non-limiting manner, a portion of a rotor according to a fifth embodiment of the invention.

[0139] This embodiment is a variation of Figure 2.

[0140] The portion shown illustrates a sector with a permanent magnet 4 and two halves of the radial arms 17 located on either side of the permanent magnet.

[0141] The rotor comprises a rotor disc 2 made of magnetic metallic material comprising housings (a single housing shown in the figure) distributed circumferentially in the rotor disc. The housings pass completely through the rotor disc axially. Inside these housings, permanent magnets 4 are placed. The permanent magnets 4 pass completely through the rotor disc so as to create a rotor with through permanent magnets, making it possible to limit the axial size of an axial flux machine, in particular of the through permanent magnet type. Indeed, with this type of rotor, it is possible to use a machine with one rotor and two stators, one stator facing each face of the rotor disc.

[0142] The rotor disk may comprise an outer ring 3 for retaining the permanent magnets 4 radially, in particular when the rotor is rotating.

[0143] The internal part of the rotor disc may include recesses 6 so as to limit the mass of the rotor and therefore to limit the inertial forces.

[0144] The rotor disc comprises radial arms 17 extending radially between the housings (and therefore between the permanent magnets 4) from an inner radial end to an outer radial end.

[0145] The radial arms 17 comprise in this embodiment a central bar 18 which extends radially between the inner and outer radial ends. These radial arms 17 also comprise ribs 19 starting from the central bar 18 and extending towards the permanent magnets 4, on either side of the central bar 18. The ends of these ribs 19 serve as a circumferential locking means for the magnets. Thus, the ends of the ribs 19 are in contact with the permanent magnets 4. Optionally and not shown, the ribs 19 could be chamfered so as to limit the contact surface between the permanent magnets 4 and the ribs 19, which makes it possible to limit heating of the rotor.

[0146] Thus, at least a part of the central bar 18 forms a first portion whose circumferential width may be strictly less, for example by at least 30%, than the circumferential width of the second and third portions, the second portion comprising the central bar 18 and the ribs 19 just before (radially from the inside to the outside) the first portion and the third portion comprising the central bar 18 and the ribs 19 just after (radially from the inside to the outside) the first portion.

[0147] Thus, the permanent magnets 4 are not in contact with the first portion and circumferential clearances separate the first portion 22 and the permanent magnets 4. These circumferential clearances can be left empty to allow air to circulate or be filled with an overmolding (or coating) material, such as a resin or a plastic (epoxy resin or PEEK for example).

[0148] Rotor disc 2 also includes a central circular opening for the installation of a rotor shaft (not visible).

[0149] The housings and permanent magnets 4 are substantially trapezoidal in shape with the largest base on the external side of the rotor to optimize the volume of permanent magnets in the rotor and therefore the performance of the electric machine.

[0150] To improve the mechanical connection, an overmolding material can optionally be used to form a solid disc around the rotor disc 2 and the permanent magnets 4. This coating material can in particular fill the empty spaces between the radial arms 17 and the permanent magnets 4 and fill the recesses 6 in the internal part of the rotor disc. This also makes it possible to lighten the rotor.

[0151] This variant is distinguished from figure 2 by the addition of a cooling channel 30 in the central bar 18. This cooling channel 30 extends radially, over at least the entire radial length of the permanent magnets 4 so as to allow the circulation of a cooling fluid in the central bar 18, between the permanent magnets 4.

[0152] Figure 8 illustrates, in a schematic and non-limiting manner, an example of an axial flux electric machine according to the invention.

[0153] The electric machine comprises a rotor 1 and two stators 100, one on each side of the rotor 1.

[0154] Rotor 1 rotates around an axis of rotation A shown by the dot-dash line.

[0155] The rotor comprises permanent magnets 4 passing completely through the rotor 1 to be opposite a stator 100 on each side. Thus, the axial size of the electrical machine is reduced.

[0156] The rotor of the electric machine is compatible with other designs of electric machines (number of rotors and stators).

[0157] Examples

[0158] The various embodiments of the invention have been compared to an example of an axial flux electric machine of the prior art. Figure 9 illustrates the rotor of the axial flux electric machine of the prior art. This rotor comprises axial arms 17 of constant section between the permanent magnets 4 and filling all the empty space between the permanent magnets 4 and on the external thickness of the rotor disk.

[0159] The energy losses of the different rotors of the invention were compared with the rotor of Figure 9. The embodiment of Figure 1 makes it possible, for example, to reduce this temperature by 13°C compared to the rotor of Figure 9 of the prior art, all other things being equal.

Claims

Claims 1. Rotor (1) for an axial flux electrical machine comprising a rotor disc (2) made of metallic material and permanent magnets (4), the rotor disc (2) comprising an axial external thickness at its external cylindrical surface and housings (5) distributed circumferentially within the rotor disc (2), the permanent magnets (4) being positioned in said housings (5), the rotor disc (2) comprising radial arms (17) separating said housings (5), the rotor disc (2) comprising radial and circumferential locking means for locking in position the permanent magnets (4) radially and circumferentially in the rotor disc (2), characterized in that each radial arm (17) comprises at least a first portion (8, 22), each first portion (8,22) comprising an axial thickness strictly less than the axial external thickness of the rotor disc (2) and / or a circumferential width strictly less than the circumferential widths in a second and a third portion of the radial arm (17) positioned radially on either side of the first portion (8, 22), the first portion (8, 22) being at a distance from the radial ends (12, 13) of the radial arm (17)., 2. Rotor (1) according to claim 1, in which said housings (5) are of substantially trapezoidal section, preferably the largest base of the trapezium is on the external side of the rotor.

3. Rotor (1) according to one of the preceding claims, in which said radial and circumferential locking means are formed by heels (11, 16) at the radial ends (12, 13) of the radial arms (17), at the junction between each radial arm (17) and the housings (5) on either side of said radial arm (17).

4. Rotor (1) according to one of the preceding claims, in which said first portion is at a distance from the permanent magnets (4) on either side of said radial arm (17).

5. Rotor (1) according to one of the preceding claims, wherein at least one radial arm (17), preferably each radial arm (17), comprises a radially extending cooling channel, for circulating a cooling fluid.

6. Rotor (1) according to one of the preceding claims, in which each radial arm (17) comprises a beam (23) of I-, H-, L-, T-, or cross-section extending in the radial direction, preferably an I-beam, the connecting bar (25) of the I- or H-section extending in the circumferential direction or in the axial direction.

7. Rotor (1) according to one of the preceding claims, wherein said radial arm (17) comprises a radial bar (18) and preferably ribs (19) fixed on the radial bar (18) and oriented towards the permanent magnets (4), on either side of the radial bar (18).

8. Rotor (1) according to one of the preceding claims, wherein the rotor disc (2) comprises a rotor support, the rotor support comprising the radial arms (17) and a ring (3) or an annular hoop forming the radial locking means of the permanent magnets.

9. Rotor (1) according to one of the preceding claims, wherein the rotor disc (2) comprises an internal part (27) with at least one recess (6).

10. Rotor (1) according to one of the preceding claims, wherein the rotor (1) comprises an overmolding element (26), the overmolding element (26) enveloping the rotor disc (2) and the permanent magnets (4).

11. Rotor (1) according to claim 10, wherein the overmolding element (26) is made of resin, preferably epoxy resin, or plastic, preferably PEEK.

12. Rotor (1) according to one of the preceding claims, in which the first portion (8, 22) and / or the second portion and / or the third portion of each radial arm (17) has, in the radial direction, a constant or variable circumferential width, preferably when the circumferential width of the portion in question is variable, this circumferential width decreases from the inner radial end (13) to the outer radial end (12).

13. Axial flux electric machine comprising at least one stator (100) and at least one rotor (1) according to one of the preceding claims.

14. Axial flux electric machine according to the preceding claim, comprising two rotors (1) and one stator (100), or two stators (100) and one rotor (1) or two stators (100) and two rotors (1).

Images