Rotor for an electric machine, in particular for a motor vehicle

Abstract

- Rotor for an electric machine, in particular for a motor vehicle. - The rotor (1) comprises at least one disc (2) comprising at least one star-shaped frame (4) having a hub (7) with an axis X and radial branches (8) extending from said hub (7), permanent magnets (5) received in housings (9) delimited between said radial branches (8), and an annular hoop (6) encircling the frame (4) and the permanent magnets (5), said disc (2) being configured such that a mechanical torque (C) is transmitted from the permanent magnets (5) to the frame (4) by means of the hoop (6).

Description

Rotor of an electric machine, particularly a motor vehicle. Technical field of the invention

[0001] The invention relates to the field of electrical machines. It relates in particular to an axial flux electric machine rotor, especially for motor vehicles. Technical background

[0002] An axial flux electric machine corresponds to an electric motor construction geometry where the air gap between the rotor and the stator, and therefore the direction of the magnetic flux between the rotor and the stator, is aligned parallel to the axis of rotation, rather than radially as with the concentric cylindrical geometry of the radial flux motor. An axial flux machine can generally comprise a rotor associated with two stators or two rotors associated with one stator. In the context of this invention, the rotor is that of a single-rotor axial flux machine.

[0003] Typically, the rotor is a disc containing a star-shaped element, magnets, and a retaining ring, also called a cage, to hold the magnets. This cage prevents the magnets from being ejected when the rotor spins at high speed. The star-shaped element can be made of a non-conductive composite material, usually fiberglass and resin. This star-shaped element may consist of a central disc to which arms are attached, between which the magnets are housed. The electromagnetic force applied to the magnet is transmitted to the star-shaped element through the arms against which the magnets bear.

[0004] Because it is not easy to precisely size the magnets so that they fit snugly into their housings between the arms, and because the magnets must be able to move radially due to the centrifugal forces acting on them, a polymer material is generally injected into the space between the magnets and the arms to ensure a flat and evenly distributed contact between the magnets and the arms. This polymer material also allows for the radial movement of the magnets.

[0005] This polymer material is in a fluid state to allow for injection, then it is polymerized and hardened. During operation, the magnet rests on this polymer and, consequently, on the arms. If the force exerted by the magnet is high and the temperature to which the polymer material is heated is high, then creep of this polymer material and, consequently, of the arms, can occur. Furthermore, polymer creep can lead to small, asymmetrical orthoradial displacements of the magnets and thus alter the position of the center of gravity, creating an imbalance in the disc.

[0006] Thus, existing solutions already known are not fully satisfactory to prevent creep of the arms of a rotor armature.

[0007] The invention satisfies this need by providing an electric machine rotor, particularly for motor vehicles.

[0008] According to the invention, the rotor comprises at least one disc, said disc comprising at least: - a star-shaped armature having a hub with axis X and radial arms extending from said hub, - permanent magnets received in delimited housings between said radial arms, and - an annular ring encircling said armature and said permanent magnets, in which said disc is configured so that a mechanical torque created by a magnetic field generated by at least one stator is transmitted from the permanent magnets to the armature via the ring.

[0009] Thus, the passage of the mechanical torque through a path passing through the periphery of the permanent magnets makes it possible to avoid the permanent magnets bearing on the radial branches and the bending or creep of the radial branches and / or the creep of the polymer serving as a joint between the branches and the magnets, which guarantees that the dimensions of the housings of the permanent magnets are maintained and that the permanent magnets are better held, so that it is no longer necessary to glue the magnets in the housings.

[0010] In addition, the mechanical torque is transmitted from the permanent magnets to the fret via first static friction forces between radial outer edges of the permanent magnets and an inner periphery of the fret, the mechanical torque being transmitted from the fret to the armature via second static friction forces between the inner periphery of the fret and radial ends of the radial arms of the armature.

[0011] In addition, the radial outer edges of the permanent magnets are configured to exert a first radial stress against the inner periphery of the fret, the radial ends of the radial branches being configured to exert a second radial stress against the inner periphery of the fret.

[0012] Furthermore, each of the permanent magnets is mounted radially to slide in its housing and is elastically pulled towards the inner periphery of the fret by a first elastic element interposed between the armature and said permanent magnet.

[0013] For example, the first elastic element is a compression spring interposed between the hub and a radial inner edge of said permanent magnet.

[0014] According to one embodiment, each of the radial branches is made of the same material as the hub.

[0015] According to another embodiment, each of the radial arms is mounted radially, at least in a sliding part, relative to the hub.

[0016] In addition, each of the radial arms is elastically pulled towards the inner periphery of the fret by a second elastic element interposed between the hub and each of the radial arms.

[0017] Furthermore, the radial arms are overmolded with layers of prepreg.

[0018] The invention also relates to an electrical machine comprising at least one rotor as specified above and at least one stator configured to generate an electromagnetic field creating mechanical torque.

[0019] The invention also relates to a motor vehicle, comprising an electrical machine as specified above. Brief description of the figures

[0020] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent in the course of the detailed explanatory description which follows, of at least one embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the accompanying schematic drawings, among which:

[0021] Lare represents a perspective view of the rotor.

[0022] Lare represents a cross-section of an electrical machine including the rotor.

[0023] Lare represents a detail of the rotor seen from the front according to one embodiment.

[0024] Lare represents a detail of the rotor armature seen from the front according to a first variant of an embodiment.

[0025] Lare represents a detail of the rotor armature seen from the front according to another variant of the embodiment of the.

[0026] Lare represents a detail of the rotor seen from the front according to one embodiment.

[0027] Lare represents a detail of the rotor seen from the front according to another embodiment.

[0028] Lare represents a perspective view of a permanent magnet according to one embodiment.

[0029] Lare represents a perspective view of a detail of a radial branch according to an embodiment.

[0030] Lare represents a perspective view of a detail of a radial branch according to the embodiment of the.

[0031] Lare represents a front view of the central part according to one embodiment.

[0032] Lare represents a perspective view of a bar according to the second embodiment of the reinforcement.

[0033] The diagram schematically represents a manufacturing process for the frame.

[0034] The diagram schematically represents a motor vehicle equipped with an electric machine including the rotor. Detailed description of the invention

[0035] The rotor 1 of an electric machine 3, in particular of a motor vehicle V (), comprises at least one disk 2, as shown in the.

[0036] As shown in the figure, the electric machine 3 can comprise at least one rotor 1 and at least one stator S.

[0037] Disc 2 includes at least one armature 4, permanent magnets 5 and an annular fret 6.

[0038] The armature 4 is star-shaped, comprising a hub 7 with axis X intended to be mounted on a rotating shaft A of the electrical machine 3 () and radial arms 8 extending from said hub 7.

[0039] From there to there, only two or three radial branches 8 are represented so as not to clutter the figures.

[0040] The permanent magnets 5 are received in housings 9 delimited between the said radial branches 8.

[0041] The annular fret 6 circles said armature and said permanent magnets 5.

[0042] Preferably, fret 6 is substantially incompressible and undeformable.

[0043] The disc 2 is configured so that a mechanical torque C created by a magnetic field generated by at least one stator S is transmitted from the permanent magnets 5 to the armature 4 via the fret 6. In particular, the disc 2 is configured so that a mechanical torque C created by a magnetic field generated by at least one stator S is entirely transmitted from the permanent magnets 5 to the armature 4 via the fret 6.

[0044] The mechanical torque C can be transmitted from the permanent magnets 5 to the fret 6 by means of first static friction forces between radial outer edges 51 of the permanent magnets 5 and an inner periphery 61 of the fret 6. The mechanical torque C (transmitted from the permanent magnets 5 to the fret 6) can be transmitted from the fret 6 to the armature 4 by means of second static friction forces between the inner periphery 61 of the fret 6 and radial ends 81 of the radial branches 8 of the armature 4.

[0045] For this, said mechanical torque C is less than or equal to a first maximum torque transmissible between the fret 6 and the radial outer edges 51 of the permanent magnets 5 and to a second torque transmissible between the fret 6 and said radial ends 81 of said radial branches 8.

[0046] The first maximum transmissible torque is determined by a first coefficient of friction and a first radial stress of minimum intensity determined between the fret 6 and the radial outer edges 51 of the permanent magnets 5. The second maximum transmissible torque is determined by a second coefficient of friction and a second radial stress of minimum intensity determined between the fret 6 and the said radial ends 81 of the said radial branches 8.

[0047] In one embodiment, the radial outer edges 51 of the permanent magnets 5 are configured to exert a first radial stress S1 against the inner periphery 61 of the fret 6. The radial ends 81 of the radial arms 8 are configured to exert a second radial stress S2 against the inner periphery 61 of the fret 6.

[0048] As shown in the figure, the rotor 1 may further include at least one first elastic element 10. Each of the permanent magnets 5 may be mounted radially sliding in its housing 9 and may be elastically returned towards the inner periphery 61 of the fret 6 by a first elastic element 10 interposed between the armature 4 and said permanent magnet 5.

[0049] The first elastic element 10 exhibits an initial stiffness that contributes to an elastic component of the first radial stress. Each of the permanent magnets 5 has a mass that determines an inertial component of the first radial stress.

[0050] Furthermore, when the rotor rotates around the X axis thanks to the mechanical torque C, the inertial force of the permanent magnets 5 can also contribute to an inertial part of the first radial stress.

[0051] By way of non-limiting example, the first elastic element 10 is a compression spring interposed between the hub 7 and a radial inner edge 52 of said permanent magnet 5.

[0052] In order for the permanent magnets 5 to remain in their respective housings 9 while being slidably mounted within their respective housings 9, each of the radial arms may include lateral grooves 82 (see below). Each of the radial arms 8 may include two lateral grooves 82a, 82b. One of the two lateral grooves 82a faces a first housing 9a. The other of the two lateral grooves 82b faces a second housing 9b. The first housing 9a and the second housing 9b are located on either side of said radial arm 8. Each of the permanent magnets 5 may have ribs 53 along its lateral edges. The lateral grooves 82a, 82b of two adjacent radial arms 8 facing the same housing 9a, 9b are intended to accommodate the ribs 53 of a permanent magnet 5 received in said housing 9a, 9b.

[0053] According to a first embodiment, each of the radial branches 8 of the frame 4 is made of the same material as the hub 7 ().

[0054] According to a second embodiment, each of the radial arms 8 is mounted radially with respect to the hub 7. As shown from 1 to 1 and 1 illustrating the second embodiment, the armature 4 may comprise at least a plurality of bars 13 and a central part 14 forming a hub 7 for a rotating shaft A of the electric machine 3. The central part 14 may comprise a plurality of blind holes 15 distributed regularly around an outer periphery 16 of the central part 14. Each bar 13 of the plurality of bars 13 may be mounted in a blind hole 15 of the plurality of blind holes 15 ( , , ). The plurality of bars 13 define, between two adjacent bars 13, housings 9 intended to receive each of a permanent magnet 5 of the rotor 1.

[0055] Each bar 13 may have a fully cylindrical portion as shown in the figure. As shown in the figure, each bar 13 may also have a first rectangular parallelepiped-shaped portion 13a extended by a second cylindrical portion 13b. The second portion 13b is intended to be inserted into a blind hole 15 in the central portion 14 when said bar 13 is mounted in the central portion 14.

[0056] By way of non-limiting example, each bar 13 of the plurality of bars 13 is made of a substantially incompressible material. Each bar 13 of the plurality of bars 13 may be made of a unidirectional composite material having fibers substantially parallel to the same direction. The direction of the fibers of a bar 13 is substantially parallel to the longitudinal axis of said bar 13. The fibers may be carbon fibers coated with an epoxy resin. Each bar 13 may also be made of glass-epoxy having unidirectional glass fibers in an epoxy resin.

[0057] The carbon fibers contained in the bars 13 are electrically conductive. Since the bars 13 are solid, eddy currents could appear within them. However, the numerous straight carbon fibers within the bars 13 are insulated from each other by the resin. This structure therefore significantly reduces the occurrence of eddy currents and the resulting heating of the bars 13.

[0058] Furthermore, the radial branches 8 are preferably made of electrically insulating materials because they constantly pass through areas of high induction which varies over time, during the rotation of the rotor 1. If the materials were conductive, strong eddy currents would develop in them and would cause heating of the radial branches 8 and a degradation of the efficiency of the electric machine 3.

[0059] As an example, the central part 14 is made of composite material or non-magnetic metal, such as copper, aluminum, titanium or certain stainless steels.

[0060] Metallic materials have at least the following advantages: - Homogeneity and isotropy of the material, - Good thermal conductivity (it can be used to attenuate the temperature of permanent magnets 5), - Good mechanical strength for the operating temperatures of the rotor 1 when hot, - No risk of creep of the central part 14 for the stress values ​​applied to the central part 14 in its assembly to the rotating shaft A screwed onto the central part 14.

[0061] Composite materials based on resins (epoxy, polyester, etc.) and glass or aramid fibers, or other non-conductive fibers, are completely insulating. Even when immersed in an area of ​​high and variable magnetic induction, no eddy currents develop in these materials, and therefore no heating of the central part 14 is to be feared, and it will not cause any degradation in the efficiency of the electrical machine 3.

[0062] The central part 14 can take different shapes. For example, the central part 14 can take a circular shape or a polygonal shape.

[0063] Advantageously, when the central part 14 is made of metallic material, its diameter is smaller than the minimum diameter of the magnetic circuit and preferably smaller than the minimum diameter of the stator windings S. The diameter of the central part 14 is preferably close to the diameter of the hub 7 to prevent significant magnetic fluxes from passing through it. The non-magnetic metallic material chosen for the central part 14 reduces the magnetic fluxes from the stator S passing through it. Thus, eddy currents are low, and the resulting heat losses in the central part 14 remain small and have no noticeable effect.

[0064] According to a first variant of the second embodiment, each of the bars 13 may include the first lateral groove 82a and the second lateral groove 82b. The first lateral groove 82a faces the first housing 9a adjacent to said bar 13, and the second lateral groove 82b faces the second housing 9b adjacent to said bar 13. The first lateral groove 82a is configured to accommodate a rib 53 of a first permanent magnet 5 intended to be received in the first housing 9a. The second lateral groove 82b is configured to accommodate a rib 53 of a second permanent magnet 5 intended to be received in the second housing 9b. In this first variant, each of the bars 13 preferably has a first rectangular parallelepiped-shaped portion 13a extended by a second cylindrical portion 13b, as described above.

[0065] Furthermore, in this first variant, the permanent magnets 5 are in direct contact with the bars 13. In the case where the bars 13 are made of resin and carbon fiber composite, carbon having a high thermal conductivity compared to that of glass, we can expect better heat dissipation from the permanent magnets 5 to the radial branches 8. The radial branches 8 being housed in a central part 14 made of material which may be metallic, the dissipation of heat from the permanent magnets 5 to the central part 14 will be much more efficient.

[0066] During operation, with increasing rotational speed, the ring 6 expands, the permanent magnets 5 move radially further apart, as do the radial arms 8. The space between the radial arms 8 and the permanent magnets 5 increases. The contact surface used for heat transfer from the permanent magnets 5 to the radial arms 8 and finally to the central part 14 decreases significantly, or even disappears. To maintain this efficient thermal path for heat transfer, thermal pads (not shown) can be inserted between the permanent magnets 5 and the radial arms 8. The thermal pads accommodate these expansions and displacements and provide a thermal bridge from the permanent magnets 5 to the radial arms 8, thus conducting heat to the central part 14.In this case, better conduction is possible if the central part 14 is made of aluminium, copper, titanium or certain stainless steels.

[0067] Furthermore, we can expect that the thermal cushions will provide a mechanical damping effect on the micro-vibrations that could appear between the permanent magnets 5 and the radial branches 8 in the absence of the thermal cushions.

[0068] According to a second variant of the second embodiment, the central part 14 and the bars 13 are overmolded with prepreg 12 (SMC or "sheet moulding compound"). The prepreg 12 forms at least one sleeve 17 around each of the bars 13.

[0069] A prepreg corresponds, for example, to a semi-finished composite product comprising a thermosetting resin or a thermoplastic polymer impregnating a reinforcement, such as a fabric.

[0070] In this second variant, the sleeve 17 of each of the bars 13 may include the first lateral groove 82a and the second lateral groove 82b. The first lateral groove 82a faces the first housing 9a adjacent to said sleeve 17, and the second lateral groove 82b faces the second housing 9b adjacent to said sleeve 17. The first lateral groove 82a is configured to accommodate the rib 53 of a first permanent magnet 5 intended to be received in the first housing 9a. The second lateral groove 82b is configured to accommodate the rib 53 of a second permanent magnet 5 intended to be received in the second housing 9b. In this second variant, each of the bars 13 preferably has a completely cylindrical shape, as described above.

[0071] According to an advantageous configuration, each of the radial branches 8 is mounted radially, at least in a sliding part, relative to the hub 7. The sleeve around each of the bars 13 forms part of a radial branch 8 fixed (non-sliding) to the central part 14.

[0072] In this advantageous embodiment, each of the radial branches 8 can be elastically recalled towards the inner periphery 61 of the fret 6 by a second elastic element 11 interposed between the central part 14 and each of the radial branches 8.

[0073] The second elastic element 11 exhibits a second stiffness which contributes to an elastic component of the second radial stress. Each of the radial branches 8 has a mass which determines an inertial component of the second radial stress.

[0074] Furthermore, when the rotor rotates around the X axis thanks to the mechanical torque C, the inertial force of the branches 8 can also contribute to an inertial part of the second radial stress S2.

[0075] By way of non-limiting example, the second elastic element 11 is a compression spring interposed between the hub 7 and each of the inner edges of the radial arms 8.

[0076] The frame 4 according to the second embodiment can be manufactured according to the following manufacturing process ().

[0077] The manufacturing process of a reinforcement 4 can include: a step E1 of manufacturing the central part 14, a step E2 of manufacturing the plurality of bars 13, a step E3 of mounting the plurality of bars 13 in the plurality of blind holes 15.

[0078] According to the second variant of the second embodiment, the process can also include an overmolding step E4 of the central part 14 and the bars 13 with prepreg 12. The prepreg 12 forms at least one sleeve 17 around each of the bars 13. Preferably, the overmolding step E4 follows the assembly step E3.

[0079] The manufacturing step E1 of the central part 14 may include at least: a substep E11 of cutting the central part (14) from a plate of material, a substep E12 of drilling the plurality of blind holes 15 regularly distributed on an external periphery 16 of the central part 14.

[0080] The manufacturing step E1 may also include a substep E13 of drilling an axial hole 18 for mounting the rotor 1 onto the rotating shaft A of the electric machine and fixing holes 19 for fixing the rotor 1 to the rotating shaft A ().

[0081] The manufacturing step E2 of the plurality of bars may include a substep E21 of grooving to produce for each bar 13 of the plurality of bars 13 the first lateral groove 82a and the second lateral groove 82b.

[0082] The manufacturing step E2 of the plurality of bars may include a substep E22 of machining the plurality of bars 13. This machining step E22 may include cutting bars into a plurality of bars 13. This machining step E22 may also include machining each bar 13 so that it has a first part in the shape of a rectangular parallelepiped 13a extended by a second part in the shape of a cylindrical 13b.

Claims

Rotor (1) of an electric machine (3), in particular of a motor vehicle (V), characterized in that it comprises at least one disk (2), said disk (2) comprising at least: - a star-shaped armature (4) having a hub (7) with axis X and radial arms (8) extending from said hub (7), - permanent magnets (5) received in housings (9) delimited between said radial arms (8), and - an annular ring (6) encircling said armature (4) and said permanent magnets (5), in which said disk (2) is configured so that a mechanical torque (C) created by a magnetic field generated by at least one stator (S) is transmitted from the permanent magnets (5) to the armature (4) via the ring (6). Rotor according to claim 1, characterized in that the mechanical torque (C) is transmitted from the permanent magnets (5) to the fret (6) by means of first static friction forces between radial outer edges (51) of the permanent magnets (5) and an inner periphery (61) of the fret (6), the mechanical torque (C) being transmitted from the fret (6) to the armature (4) by means of second static friction forces between the inner periphery (61) of the fret (6) and radial ends (81) of the radial branches (8) of the armature (4). Rotor according to claim 2, characterized in that the radial outer edges (51) of the permanent magnets (5) are configured to exert a first radial stress (S1) against the inner periphery (61) of the fret (6), the radial ends (81) of the radial arms (8) being configured to exert a second radial stress (S2) against the inner periphery (61) of the fret (6). Rotor according to any one of claims 1 to 3, characterized in that each of the permanent magnets (5) is mounted radially sliding in its housing (9) and is elastically returned towards the inner periphery (61) of the fret (6) by a first elastic element (10) interposed between the armature (4) and said permanent magnet (5). Rotor according to claim 4, characterized in that the first elastic element (10) is a compression spring interposed between the hub (7) and a radial inner edge (52) of said permanent magnet (5). Rotor according to any one of claims 1 to 5, characterized in that each of the radial arms (8) is made of the same material as the hub (7). Rotor according to any one of claims 1 to 5, characterized in that each of the radial arms (8) is mounted radially, at least in sliding part, relative to the hub (7). Rotor according to any one of claims 1 to 7, characterized in that each of the radial arms (8) is elastically pulled back towards the inner periphery (61) of the fret (6) by a second elastic element (11) interposed between the hub (7) and each of the radial arms (8). Rotor according to any one of claims 7 and 8, characterized in that the radial arms (8) are overmolded by layers of prepreg (12). electric machine, characterized in that it comprises at least one rotor (1) according to any one of claims 1 to 9 and at least one stator (S) configured to generate an electromagnetic field creating the mechanical torque (C). Motor vehicle (V), characterized in that it comprises an electrical machine according to claim 10.

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