Force-fitted binding band for a rotor of an axial-flux electric machine

Abstract

The invention relates to a force-fitted binding band (200) for a rotor of an axial-flux electric machine, comprising: - an inner ring (210) made of metal material intended to be in contact with magnets carried by the rotor; and - an outer ring (220) made of composite material.

Description

DESCRIPTION TITLE OF THE INVENTION: PRESS-FIT SHEAR FOR ROTOR OF AXIAL FLUX ELECTRIC MACHINE TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates generally to the field of electrical machines.

[0002] It relates more particularly to a press-fit ferrule for the rotor of an axial flux electric machine.

[0003] It also relates to a rotor comprising such a hoop and an axial flux electric machine comprising such a rotor.

[0004] The invention finds a particularly advantageous application in the production of electric or hybrid motor vehicles. STATE OF THE ART

[0005] An axial flux electric machine rotor generally includes a hub from which a plurality of legs extend and permanent magnets disposed between each pair of adjacent legs.

[0006] In order to resist centrifugal forces when the rotor is rotating, the latter classically includes a hoop, that is to say a peripheral retaining ring, surrounding the magnets.

[0007] The fret is made of composite material, which gives it strength and lightness.

[0008] To ensure that the magnets remain firmly attached to the hub, the hoop is force-fitted around the magnets so as to pre-stress them towards the centre of the hub. Before assembly, the internal diameter of the hoop is therefore very slightly smaller than the external diameter of the rotor body (which is formed by the hub, the branches and the magnets).

[0009] However, the composite material hoop can be damaged during its fitting. The adhesion of the resin matrix of the composite material to the rotor body (and in particular to the magnets) can generate defects in it, these defects then forming initiators for potential larger cracks which could propagate during operation of the electric machine.

[0010] In addition, it is sometimes necessary to rectify the internal diameter of the hoop by boring, which is not only complicated and expensive, but also risky to carry out on the composite material. PRESENTATION OF THE INVENTION

[0011] In this context, the present invention provides a press-fit ferrule for an axial flux electric machine rotor comprising: - an internal ring of metallic material intended to be in contact with magnets carried by the rotor; and - an external ring made of composite material.

[0012] Thus, thanks to the invention, the hoop has a metallic internal part particularly well suited to fitting around the rotor body. Indeed, the metallic material is less likely to deteriorate during fitting because it is slightly more deformable than the composite material. It also has a lower coefficient of friction on the magnets than that of the composite material.

[0013] Additionally, it is also much simpler to grind the inner diameter of the hoop by machining the metal material.

[0014] Finally, the metal ring allows the heat accumulated by the magnets to be efficiently dissipated when the electric machine is in operation.

[0015] The outer ring made of composite material makes the hoop lighter and stronger than its counterpart made entirely of metal material.

[0016] Other advantageous and non-limiting characteristics of the hoop according to the invention, taken individually or in all technically possible combinations, are the following: - the inner ring forms a circumferential groove into which the outer ring extends; - the groove opens radially outwards; - the surface of the inner ring which is intended to be in contact with the magnets has a beveled or curved edge; - the thickness, measured radially, of a base of the inner ring is less than the thickness of the outer ring; - the inner ring is open; - the opening of the internal ring delimits two ring edges facing each other at a distance less than 1 mm; - the composite material comprises, and preferably consists of, a resin matrix and fibers distributed in the resin matrix.

[0017] The invention also provides an axial flux electric machine rotor comprising: - a body provided with a hub from which a plurality of branches extend and a plurality of magnets arranged between the branches; - a fret as described above fitted around the body.

[0018] The invention also proposes an axial flux electrical machine comprising at least one stator and at least one rotor as described above, the rotor being arranged to be driven in rotation by the at least one stator.

[0019] The invention finally proposes a method of manufacturing a fret as described above comprising the following steps: - formation of the inner ring; - formation of the outer ring by winding fibers around the inner ring, the fibers being previously or subsequently impregnated with resin.

[0020] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. DETAILED DESCRIPTION OF THE INVENTION

[0021] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0022] On the attached drawings:

[0023] [Fig. 1] is a schematic perspective view of a rotor according to the invention.

[0024] [Fig. 2] is a schematic side sectional view of a hoop according to the invention which is adapted to the rotor of Figure 1.

[0025] [Fig. 3] is a schematic sectional view from above of a first embodiment of the hoop of Figure 2 along plane AA.

[0026] [Fig. 4] is a schematic sectional view from above of an inner ring of a hoop according to a second embodiment of the hoop of Figure 2.

[0027] [Fig. 5] is a schematic sectional view from above of part of a inner ring according to a variant of the second embodiment.

[0028] [Fig. 6] is a schematic sectional view from above of a portion of an inner ring according to another variant of the second embodiment.

[0029] [Fig. 7] is a schematic side sectional view of the rotor of Figure 1.

[0030] A rotor 1 according to the invention is shown in Figure 1.

[0031] This rotor 1 is intended to be assembled in an axial flux electric machine (not shown), in this case a motor for propelling an electric vehicle (car, truck, boat, airplane, etc.). Such an electric machine comprises at least one rotor and at least one stator. In practice, it comprises the rotor 1 located between two generally identical stators. These stators each comprise several windings of electric wires which, when supplied with electric current, make it possible to generate a magnetic field so as to rotate the rotor. Since these stators are not specifically the subject of the present invention, they will not be described in more detail here.

[0032] As shown in Figure 1, rotor 1 comprises: - a 110 hub; - a plurality of branches 120 extending from the hub 110; - a plurality of permanent magnets 130 arranged between the branches 120; - a hoop 200 arranged on the periphery of the rotor 1.

[0033] The hub 110, the branches 120 and the permanent magnets 130 (hereinafter called magnets 130) form a body 100 of the rotor 1. The body 100 of the rotor 1 has an annular shape around an axis of rotation A1 of the rotor 1. The hub 110 comprises means 111 for fixing an output shaft extending around the axis of rotation A1. In this case, as shown in FIG. 1, these fixing means 111 are threaded recesses (typically bores) provided to receive holding screws. Alternatively, these fixing means may comprise bolts consisting of screws and nuts. Here, the branches 120 extend in radial directions relative to the axis of rotation A1, that is to say directions perpendicular to the axis of rotation A1, while becoming thinner towards the periphery of the rotor 1. Here, the hub 110 and the branches 120 are preferably made of a single piece of composite material in order to limit eddy currents.

[0034] The branches 120 are all identical and regularly distributed around the hub 110 so as to be separated two by two by a space or a notch, here of trapezoidal shape, a magnet 130 of shape complementary to said space being arranged in each space. The magnets 130 are elements with magnetic poles. They are preferably made up of small unitary magnets assembled by gluing (as shown diagrammatically in FIG. 7). To ensure the maintenance of the magnets 130 along the axis of rotation A1, each magnet 130 is for example clamped between two adjacent branches 120 by means of sliding connections of the groove-rib type. In other words, the branches may comprise, on their faces facing the magnets, grooves which extend from the hub 110 to the periphery of the rotor 1. The magnets may then have ribs which fit into the grooves so that, when the magnet is well engaged at the bottom of the notch, these connections block the magnets along the axis of rotation A1.

[0035] The hoop 200 is a ring for holding the magnets at the bottom of the notch. It is arranged around the magnets 130 to oppose the centrifugal forces that the latter undergo during the rotation of the rotor 1 by constraining them against the hub 110. As shown in FIG. 1, the hoop 200 has a shape adapted to that of the body 100 of the rotor 1. The hoop 200 thus has here a circular ring shape (see FIGS. 3 and 4).

[0036] As Figure 2 clearly shows, the fret 200 includes: - an internal ring 210 made of metallic material; and - an external ring 220 made of composite material.

[0037] Preferably, such a composite material comprises fibers embedded in a binder, for example a resin.

[0038] Here, the hoop 200 comprises only the inner ring 210 and the outer ring 220; it is therefore made up of the latter.

[0039] The inner ring 210 and the outer ring 220 each have the shape of a circular ring centered on a central axis A2 of the hoop 200. The central axis A2 of the hoop 200 corresponds to the axis of rotation A1 of the rotor 1 once the hoop 200 is installed around the body 100 of the rotor 1, in the sense that these two axes are substantially coincident as shown in Figure 7.

[0040] The terms "internal" and "external" are used in relation to the central axis A2 of the hoop 200. The internal ring 210 therefore corresponds overall to a central part of the hoop 200 while the external ring 220 corresponds to a peripheral part of the hoop 200. Here, this means that the internal ring 210 comprises at least at least one part (here the base 211 described below) having a diameter less than that of the external ring 220.

[0041] The inner ring 210 is designed to be in contact with the magnets 130. As explained in the introduction, the fact that the inner ring 210 is made of metal makes the hoop 200 particularly well suited to being fitted around the magnets 130. The inner ring 210 is for example made of steel or stainless steel.

[0042] It is here provided that the internal ring 210 is only in contact with the magnets 130. This means that the internal ring 210 extends away from the branches 120. For this, the magnets 130 protrude slightly from the branches 120 at the periphery of the rotor 1. All the stress exerted by the hoop 200 is thus applied to the magnets 130, which improves their retention.

[0043] The inner ring 210 thus has a diameter, referenced D in FIGS. 3 and 4, substantially equal to the diameter of the cylindrical surface along which the peripheral edges 131 of the magnets 130 extend. This diameter D corresponds here to the distance between two radially opposite points of the inner ring 210. The terms radial or radially refer in particular to directions perpendicular to the central axis A2, such radial directions are referenced A3 in FIGS. 2 and 3. By "substantially equal" is meant the fact that the diameter of the inner ring 210 is very slightly smaller, for example 0.03% to 0.3% smaller, than that of said cylindrical surface of the peripheral edges 131 of the magnets 130 in order to forcefully fit the hoop 200 around the magnets 130. The diameter D of the inner ring 210 is for example between 20 cm and 25 cm. cm.

[0044] Alternatively, the inner ring could come into contact with the magnets and the branches which would then be flush with the peripheral edges of the magnets.

[0045] As clearly shown in Figure 2, the inner ring 210 more specifically comprises a base 211 and two side walls 212 projecting from the base 211. It therefore has a U-shaped section. The base 211 extends here along a cylindrical surface of revolution centered on the central axis A2. As illustrated in Figure 7, the base 211 here constitutes the part of the inner ring 210 arranged to be in contact with the magnets 130. As shown in Figure 7, the base 211 has a height substantially equal to, here very slightly greater than, the height of the body 100 of the rotor 1 (dimensions along the axis of rotation A1 and / or the central axis A2).

[0046] As can be seen in Figure 2, the side walls 212 are located at the two ends of the base 211. In the examples shown in Figures 2 and 7, the side walls 212 rise perpendicular to the base 211, that is to say radially relative to the central axis A2 (they are therefore parallel to each other).

[0047] The inner ring 210 thus defines a circumferential groove 213, in the sense that the groove 213 extends around the circular periphery of the hoop 200, here around this entire periphery. As clearly shown in Figures 2 and 7, the groove 213 extends in a plane comprising the central axis A2. The groove 213 opens radially outwards, which means that the depth of the groove is oriented radially. In other words, the groove 213 opens opposite the central axis A2.

[0048] The outer ring 220 extends into contact with the inner ring 210. Here, the outer ring 220 is more particularly in direct contact with the inner ring 210, and in particular with the base 211 of the inner ring 210. The outer ring 220 extends more particularly in the groove 213 formed by the inner ring 210. Thus, as clearly shown in FIG. 3, the outer ring 220 encases the base 211 of the inner ring 210.

[0049] The composite material of the outer ring 220 here comprises fibers embedded, that is to say dispersed, in a resin matrix. The fibers are for example glass fibers, polymer fibers or mineral fibers. Preferably, these fibers are carbon fibers, which are at the same time strong, rigid, and light. As shown schematically in Figure 3, the fibers (referenced F in this figure) extend in a substantially orthoradial direction, i.e. orthogonally both to the central axis A2 and to a radial direction A3. The fibers thus surround the inner ring 210. Here, the resin is a thermosetting resin, for example an epoxy-based resin.

[0050] Alternatively, the resin is a thermoplastic resin. The outer ring can then be formed by winding strips of carbon fibers pre-coated with said thermoplastic resin. The resin is then melted by a local heating process, such as by laser or hot air.

[0051] The groove 213 makes it possible to confine the outer ring 220, which makes the outer ring 220 particularly strong. Indeed, the side walls 212 of the inner ring 210 provide lateral support preventing the fibers from shifting laterally (along the central axis A2) in reaction to the stress of the magnets 130. pressing on the hoop 200 during rotation of the rotor 1 . This thus prevents the collapse of the resin matrix. The stiffness of the hoop 200, which comes mainly from the outer ring 220, is thus maintained during the life of the rotor 1 . Remarkably, it is also possible to use cheap and less efficient fibers and / or resin since the strength of the outer ring 220 is improved by the groove 213.

[0052] As clearly shown in Figure 2, the thickness E1, measured radially, of the base 211 of the inner ring 210 is smaller than the thickness E2 of the outer ring 220. This makes it possible to limit the stresses linked to thermal expansions that the inner ring 210 can undergo while conferring, via the thicker outer ring 220, a high stiffness to the hoop 200. The outer ring 220 here has a diameter equal to the diameter D of the inner ring 210 plus twice the thickness E1 of the base 211.

[0053] As shown in Figure 2, the thickness E2 of the outer ring 220 is equal to the radial extension of the side walls 212 of the inner ring 210. Thus, here, the outer ring 220 exactly fills the groove 213. Alternatively, the outer ring could protrude from the groove.

[0054] In a first embodiment, shown more specifically in Figure 3, the internal ring 210 is a closed ring. The hoop 200 is thus particularly simple to produce.

[0055] Thus, in this first embodiment, the hoop 200 has a cross-section of invariable shape along its entire circumference. In other words, the hoop 200 has invariance by rotation around the central axis A2.

[0056] The base 211 of the inner ring 210 then has the shape of a flattened tube whose height is much less than the diameter. The side walls 212 have the shape of flattened rings.

[0057] In a second embodiment, shown in Figures 4 to 6, the inner ring 210 is open. This second embodiment differs from the first embodiment only in that the inner ring 210 comprises an opening 214. The outer ring 220 remains closed to ensure that the magnets 130 are held in place.

[0058] As shown in Figures 4 to 6, the opening 214 of the inner ring 210 defines two ring edges 215 facing each other. Here, the two ring edges 215 face each other at a distance of less than 1 mm, preferably less than 0.1 mm. The opening 214 of the inner ring 210 is thus a slot 214. Thus, remarkably, the portion of the resin matrix which is not supported laterally by the side walls 212 remains very small.

[0059] The idea of ​​this second embodiment is to allow the inner ring 210, via the opening 214, to expand thermally without applying stresses to the outer ring 220. Indeed, the expansion of the inner ring 210 brings the two ring edges 215 closer together, which dissipates the stresses. The stiffness of the outer ring 220 is thus preserved for holding the magnets 130.

[0060] The slot 214 here extends over the entire height of the inner ring 210 (along the central axis A2). The slot 214 can for example extend radially, as in Figure 4, which makes it possible to start from a regular metal profile for the manufacture of the inner ring 210.

[0061] However, the slot 214 can also extend obliquely relative to a radial direction, as in Figure 5. The slot 214 can also take a shape which corresponds, seen from above as in Figure 6, to a broken line. Advantageously, in these configurations, the outer ring 220 is never directly opposite the magnets 130, the inner ring 210 always being interposed between the latter.

[0062] Whatever the method of production of the 200 fret, its manufacture successively comprises the following two main stages: - formation of the internal ring 210; - formation of the outer ring 220.

[0063] Here, the internal ring 210 is formed by bending a metal profile, that is to say by rolling this profile. This metal profile is here a rectilinear rod whose section is U-shaped.

[0064] In the first embodiment, the profile is bent on a circular mandrel whose diameter corresponds to the target diameter of the internal ring 210, i.e. its intended design diameter D before positioning the hoop 200 around the body 100 of the rotor 1. During this bending, the base 211 is pressed against the mandrel. After bending, the length of the profile is adjusted by cutting and the two ends of the profile are welded to each other.

[0065] The outer ring 220 is then formed by winding a strip of composite material. This strip comprises the fibers dispersed in the unpolymerized resin matrix, that is to say in the uncured state before its curing.

[0066] In the second embodiment, the profile is first bent on a first circular mandrel whose diameter is greater than the target diameter of the inner ring 210. The profile is then sectioned so as to have an opening larger than the target opening. The cutting of the profile to form the opening is for example carried out by sawing or by wire EDM.

[0067] The inner ring 210 is then positioned on a second mandrel whose diameter corresponds to the target diameter of the inner ring 210.

[0068] The outer ring 220 is then also formed by winding a strip of composite material. However, this winding also makes it possible to bring the two ring edges 215 together so as to press the base 211 against the second mandrel, which gives its target diameter to the inner ring 210, and which forms the slot 214 to the intended size.

[0069] Whatever the embodiment, once the outer ring 220 has been formed, the hoop 200 is baked, i.e. brought to a high temperature, to harden (i.e. polymerize) the resin of the outer ring 220. The baking time and temperature are adapted to the resin of the outer ring 220. The hoop 200 is for example brought to a temperature of 130°C for 60 minutes followed by maintenance at a temperature of 180°C for 120 minutes with heating and cooling ramps of approximately 10°C / minute.

[0070] The rotor 1 is then formed by assembling the hoop 200 around the body 100. The magnets 130 are for this purpose previously inserted between the branches 120 up to the hub 110.

[0071] Before being assembled, the hoop 200 can undergo an optional step of adjusting its diameter D by boring.

[0072] The hoop 200 is more specifically assembled around the body 100 by fitting, that is to say by force insertion. This step is sometimes called hooping. During this step, the hoop 200 is translated along the axis of rotation A1. The base 211 of the inner ring 210 then slides against the peripheral edges 131 of the magnets 130. The friction generated by this sliding is low since the inner ring 210 is metallic.

[0073] Advantageously, whatever the embodiment of the hoop 200, the surface of the internal ring 210 which is intended to be in contact with the magnets may have a beveled edge, i.e. a chamfer, or a curved edge, for example rounded, as shown in Figure 7. This shape makes it possible to reduce the risks for attaching the internal ring 210 to the magnets 130 and thus facilitates fitting.

[0074] In the example shown in Figure 7, each end edge 211A of the base 211 is curved. The base 211 here curves progressively up to the side walls 212.

[0075] The present invention is in no way limited to the embodiments described and shown, but those skilled in the art will be able to provide any variation in accordance with the invention.

[0076] For example, an intermediate layer, such as an adhesive layer, may be positioned between the inner ring and the outer ring.

[0077] The formation of the outer ring can be achieved not by winding fibers pre-impregnated with resin but by first winding only the fibers and then impregnating them with resin in a fluid state.

[0078] The side walls could also not be parallel but flared outwards so that the outer ring is wider at the periphery, and therefore stronger.

[0079] The inner ring could of course be devoid of side walls. It could then simply consist of the base and thus have a cylindrical tubular shape of revolution.

Claims

CLAIMS

1. Sleeve (200) for rotor (1) of axial flux electric machine comprising: - an internal ring (210) made of metallic material intended to be in contact with magnets (130) carried by the rotor (1); and - an external ring (220) made of composite material.

2. A hoop (200) according to claim 1, wherein the inner ring (210) forms a circumferential groove (213) into which the outer ring (220) extends.

3. A hoop (200) according to claim 2, wherein the groove (213) opens radially outward.

4. A hoop (200) according to one of claims 1 to 3, wherein the surface of the inner ring (210) which is intended to be in contact with the magnets (130) has a beveled or curved edge (211 A).

5. Hoop (200) according to one of claims 1 to 4, in which the thickness, measured radially, of a base of the inner ring (210) is less than the thickness of the outer ring (220).

6. A hoop (200) according to one of claims 1 to 5, wherein the inner ring (210) is open.

7. A hoop (200) according to claim 6, wherein the opening (214) of the inner ring (210) delimits two ring edges (215) facing each other at a distance of less than 1 mm.

8. A hoop (200) according to one of claims 1 to 7, wherein the composite material comprises a resin matrix and fibers (F) distributed in the resin matrix.

9. Rotor (1) of an axial flux electric machine comprising: - a body (100) provided with a hub (110) from which a plurality of branches (120) extend and a plurality of magnets (130) arranged between the branches (120); - a fret (200) according to one of claims 1 to 8 fitted around the body (100).

10. Axial flux electric machine comprising at least one stator and at least one rotor (1) according to claim 9, the rotor (1) being arranged to be driven in rotation by the at least one stator.

11. Method of manufacturing a hoop (200) according to one of claims 1 to 8 comprising the following steps: - formation of the internal ring (210); - forming the outer ring (220) by winding fibers (F) around the inner ring (210), the fibers (F) being previously or subsequently impregnated with resin.

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