Axial flux machine rotor assembly protected by a filament winding and method for manufacturing such an assembly

Abstract

The invention relates to a rotor assembly having a shaft along an axis of rotation, a base projecting radially from the shaft, and a ring projecting radially from the base and having two main faces, at least one of which comprises locations accommodating permanent magnets, the base projecting axially relative to the ring, characterised in that the ring is arranged inside a winding of at least one elongate and flexible reinforcing element in order to hold the permanent magnets in place in the locations; and in which method the reinforcing element comprises fibres and the fibres are wound around the rotor assembly with an orientation having an angle close to 0° with the first axis of rotation, thereby covering the two main faces and the outer periphery.

Description

[0001] Description

[0002] Title of the invention: Axial flux machine rotor assembly protected by a filament winding and method of manufacturing such an assembly.

[0003] The present invention relates to the manufacture of electrical machine components and more particularly to the fixing and / or protection of magnets in axial flux electrical machines.

[0004] BACKGROUND OF THE INVENTION

[0005] Radial flux electric machines are known, comprising a tubular stator in which a cylindrical rotor is mounted to rotate. The rotor's outer surface has recesses for permanent magnets. The magnetic attraction forces resulting from the radial magnetic flux produced by the permanent magnets, and the centrifugal force exerted on the permanent magnets due to the rotor's rotation, tend to pull the permanent magnets away and place significant stress on their attachment to the rotor. A permanent magnet, or a fragment of one, could become lodged in the air gap between the rotor and the stator, blocking the rotor's rotation. To reinforce the attachment of the permanent magnets to the rotor, a ring is known to be placed around the rotor to secure the permanent magnets and thus prevent them from being pulled away, either partially or completely.

[0006] There are also axial flux electric machines comprising a stator facing a discoidal rotor with a main face on which are slots for permanent magnets. The magnetic attraction forces resulting from the axial magnetic flux produced by the permanent magnets tend to pull them away and place significant stress on the permanent magnets' attachment to the rotor, with the same risks as for radial flux machines. To reinforce the attachment of the permanent magnets to the rotor, it has been considered to attach a thin plate covering the permanent magnets to the rotor. However, this results in constraints regarding the plate's attachment and its rigidity.

[0007] Furthermore, a filament winding manufacturing process is known and used, for example, for hollow parts, particularly large ones. These hollow parts are obtained by winding sheets of resin-impregnated composite fibers onto a support mold that acts as a mandrel. Positioning the fiber sheets in one direction or the other allows the resulting hollow part to have high mechanical strength in all directions, while maintaining a very thin wall thickness.

[0008] OBJECT OF THE INVENTION The invention aims in particular to improve the fixing and / or protection of permanent magnets to a rotor.

[0009] SUMMARY OF THE INVENTION

[0010] For this purpose, the invention provides a rotor assembly having:

[0011] - a tree along an axis of rotation;

[0012] - a base extending radially from the shaft;

[0013] - a ring extending radially from the base and having two main faces, at least one of which includes slots for permanent magnets, the base extending axially from the ring; the ring being arranged inside a winding of at least one elongated and flexible reinforcing element to hold said permanent magnets in the slots, the reinforcing element comprising at least one strip of composite fibers. Thus, the winding provides a strong hold for the permanent magnets without otherwise modifying the design of the rotor assembly. Depending on optional features, used individually or in whole or in combination:

[0014] - the reinforcing element extends tangentially to the base, on each of the main faces of the ring;

[0015] - the ring has a surface roughness arranged to oppose lateral sliding of the elongated element.

[0016] The invention further relates to an axial flux electric machine having such a rotor assembly.

[0017] The invention also provides a method for attaching permanent magnets to the ring of a rotor assembly by winding an elongated and flexible reinforcing element around the ring, comprising the steps of:

[0018] - place the permanent magnets in the slots provided on one of the main faces of the ring;

[0019] - rotate the rotor assembly around a first axis of rotation;

[0020] - unwind the reinforcing element from a mobile applicator making a revolution around the rotor assembly around a second axis of rotation, the second axis of rotation being coplanar and forming an angle with the first axis of rotation, said angle being chosen to form a predetermined winding pattern of the elongated element around the ring.

[0021] Furthermore, depending on optional features, used individually or in whole or in combination:

[0022] - the elongated element is positioned around the rotor assembly by making a number of turns allowing the pattern formed on the rotor assembly to have a regular and homogeneous structure;

[0023] - the number of patterns made during a winding is greater than one, and / or each of these patterns is positioned on the rotor assembly with an angular offset;

[0024] - the reinforcing element comprises fibers and the fibers are wound around the rotor assembly with an orientation having an angle close to 0° with the first axis of rotation, thus covering the two main faces and the outer perimeter of the ring.

[0025] Other features and advantages of the invention will become apparent from the following description of a particular and non-limiting embodiment of the invention.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Reference will be made to the attached drawings, including:

[0028] [Fig. 1] is an overall view of a rotor assembly;

[0029] [Fig. 2] is a schematic view of a polar winding around a discoidal rotor according to the method described in the invention;

[0030] [Fig. 3a] is an illustration showing the beginning of the filament winding operation, according to the process of the invention;

[0031] [Fig. 3b] is an illustration showing a first intermediate phase of the filament winding operation, according to the process of the invention;

[0032] [Fig. 3c] is an illustration showing a second intermediate phase of the filament winding operation, according to the method of the invention; [Fig. 3d] is an illustration showing the end of the filament winding operation, according to the method of the invention;

[0033] [Fig. 4] is an illustration of the angle a formed between the direction of the strip and the axis of rotation of the rotor, formed during winding on the outer circumference,

[0034] DETAILED DESCRIPTION OF THE INVENTION

[0035] Referring to Figure 1, a rotor assembly 1, which we will call rotor 1, is visible. It has a shaft 2 aligned with the axis of rotation of rotor 1. A circular base 3 extends radially from this shaft 2, and a ring or disk 4 also extends radially from this base 3. The base 3 and the disk 4 are centered on the axis of rotation of the rotor. The disk 4 has two main flat faces 4.1, and the base 3 extends axially from each of these two main faces 4.1. The disk 4 also has a peripheral surface connecting the two main faces 4.1 and forming an outer rim 4.2 of the disk 4. The main faces 4.1 of the disk 4 define locations, each receiving a permanent magnet 5, here in the form of an angular sector. Magnets have a magnetization vector (between south pole and north pole) extending parallel to the axis of rotation.Such a rotor is for example that of a permanent magnet synchronous electric machine in which said rotor is located between two stators coaxial to the rotor and the permanent magnets 5 generate an axial flux, between the rotor and the stators, which produces an axial attractive force.

[0036] The permanent magnets 5 are held in place on the disk 4 by at least one winding 6 of a flexible, elongated reinforcing element. This flexible, elongated reinforcing element is, in our case, a strip 7 of fibers. The winding 6 is arranged so as to at least partially cover both faces 4.1 and the outer edge 4.2 of the disk 4. The winding 6 serves to axially lock the permanent magnets 5, in order to prevent said permanent magnets 5, or any part thereof, from detaching during the operation of the rotor. This winding 6 is capable of holding the permanent magnets 5 subjected to axial forces due to magnetic attraction and radial forces generated by the rotation of the rotor, while significantly limiting the thickness of the disk 4 of the rotor 1.

[0037] The winding 6 is arranged around the rotor 1 in such a way that certain sections of the strip 7 wound around the rotor 1 can have an angle close to 0° with the axis of rotation of the rotor 1, thus allowing it to cover the two main faces 4.1 of the disk 4 in addition to the outer perimeter 4.2. The angle between the strip 7 and the axis of rotation of the rotor 1 is designated a in Figure 4. The strip 7 covers the entire disk 4 and is distributed evenly around the disk 4. The sections of the strip 7 extending over each main face 4.1 of the disk 4 are tangent to the base 3.

[0038] It should be noted that the band 7 is flexible enough to conform to the angles of the geometry of the disk 4, particularly at the edges between the main faces 4.1 and the outer perimeter 4.2.

[0039] Rotor 1 incorporates an imbalance correction element, meaning a component attached to the rotor that improves its balance during rotation. For example, if the distribution of the strip 7 is not perfectly homogeneous, it is necessary to rebalance the rotor 1 by correcting the imbalance. This can be achieved by attaching balancing weights to the base 3, either by screwing or welding, or by locally removing material, for instance. Furthermore, it is important that the strip 7 wound around the disk 4 does not disrupt the operation of the electrical machine, and more specifically, the flow of magnetic flux emitted by the permanent magnets: the strip 7 must not act as a magnetic shield, blocking or altering the magnetic flux. Therefore, for example, the use of magnetic flux-conducting fibers in the strip 7, which could divert the magnetic flux, should be avoided.The thickness of the strip 7, or the cumulative thickness at the points where sections of strip 7 overlap, must be less than the maximum air gap between the rotor and stators in the electric machine. The mass of strip 7 wound around the disk 4 must also be compatible with the intended rotational speed of the rotor 1 and the maximum forces that can be withstood by the bearings in which the shaft 2 is mounted.

[0040] The manufacturing process of the rotor assembly will now be described.

[0041] We begin by manufacturing the shaft 2, the base 3, and the rotor disc 4 of the rotor 1 using a known method, for example, by forging, casting, machining, and / or assembly. Locations are defined on the disc 4 to accommodate the permanent magnets 5, which are attached to them, for example, by gluing. The complete and permanent attachment of the permanent magnets is achieved by a winding operation, which will be described with reference to Figures 2, 3a to 3d, and 4. The winding operation is carried out here according to a polar winding method on a winding machine comprising a frame 10, a support 11 mounted on the frame 10 to support and drive in rotation the rotor 1 around an axis of revolution XI coinciding with the axis of rotation of the rotor 1 and a tape applicator 12 mounted on the frame 10 to pivot around the support 11 along an axis of revolution X2 located in the same plane as the axis of revolution XI.Thus, by rotating the rotor 1 around the axis of revolution XI and the tape applicator 12 around the axis of revolution X2 simultaneously and regularly, the tape 7 is wound onto the disk 4, forming circuits (the straight sections extending over the main face 2.1 cross around the base 2, forming approximately a capital letter A - see figure 3a, which shows the first circuit) until a homogeneous pattern is formed on the disk 4 (in figure 3b, we see that the straight sections extending over the main face 2.1 cross around the base 2, forming approximately six capital letters A intertwined with each other and regularly offset angularly from each other). The pattern is said to be homogeneous in the sense that it is balanced around the axis of rotation of disk 4 and therefore does not generate imbalance in theory.By repeating this homogeneous pattern while offsetting it angularly from the previous one (see figure 3c representing three homogeneous patterns side by side), we can cover the entire disk 4 (see figure 3d representing six homogeneous patterns side by side).

[0042] It is noted that the realization of a polar winding requires two different degrees of rotation between the axis of rotation of the part on which the strip 7 is wound and the axis of revolution of the applicator 8. Thus, during the polar winding of the strip 7 around the disc 4 of the rotor 1, said rotor 1 is in rotation around the axis of revolution XI, the strip applicator 12 is in revolution around the axis of revolution X2. These two axes of revolution XI and X2 are coplanar and intersect at the center of the rotor 1. The angle formed by the axes of revolution XI and X2 is constant during winding and its value influences the winding pattern 6 formed by the band 7 around the disk 4 of the rotor 1. It is noted that the arrangement of the pattern is influenced by several factors such as the diameter of the disk 4, the diameter of the base 3, the thickness of the disk 4, or the thickness of the band 7.The thickness of the strip 7, the angle a and the diameter of the disc 4 are chosen so as to avoid slippage of the strip 7 on the disc 4 during the winding operation, particularly at the outer edge 4.2.

[0043] It is understood that, since each straight section of strip 7 extending over the main faces 4.1 of the disk 4 is tangent to the base 3, there is an overlap of strip 7 sections in the vicinity of said base 3, and therefore an excess thickness which must be ensured does not exceed the air gap provided between the rotor and the stator. Alternatively, a base with a smaller diameter can be provided so that this excess thickness is located opposite a clearance provided in a non-active part of the stator.

[0044] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0045] In particular, although here the base 3 is circular in shape, it is possible that it could be of a different shape, such as a regular polygon for example, the straight sections of strip 7 could be parallel to the faces of this polygon.

[0046] Although here the ring forming the disk 4 of the rotor 1 is circular in shape, we consider the case where this annular part is of another shape such as a regular polygon for example, the winding of the band 7 around this rotor would then possibly be less subject to the slippage of the band 7 on the outer perimeter 4.2.

[0047] Although here the edges formed by the meeting of the outer perimeter with the faces of the disk are salient, it is possible that these edges are replaced by fillets, or chamfers, or even that the outer perimeter is only an edge.

[0048] Although here the elongated element chosen to form winding 6 includes a strip, it is possible that winding 6 is made from yarn(s), fiber(s), or even a flexible film of varying thickness or width.

[0049] Although here the band 7 wound around the rotor 1 is a composite material comprising continuous fibers and a resin acting as a matrix, it can be composed of any other flexible material, composite or not.

[0050] Although here an angular offset is provided between the application of each winding circuit, it is possible that a constant angular offset is applied to the winding so as to form a single, denser 7-band winding circuit, possibly better balanced.

[0051] The fibers included in band 7 can be aligned, braided, wound, or woven together and bonded by a resin, matrix, or any other manufacturing process.

[0052] The outer perimeter 4.2 and / or the main faces 4.1 of the disk 4 may have a surface roughness arranged to oppose lateral sliding of the elongated element 7 relative to the disk 4.

[0053] Winding 6 can comprise a single homogeneous pattern. Even if this does not completely cover the permanent magnets, it still ensures that the permanent magnets are held in place.

[0054] The invention is applicable to any type of electrical machine having a rotating rotor carrying magnets that generate a magnetic flux parallel to the axis of rotation of the rotor.

[0055] The angle a may not be close to zero degrees.

[0056] An annular insert can be positioned around the outer perimeter to hold the magnets during rotor manufacturing, or, by adapting the manufacturing process, the positioning of the strip 7 may suffice to radially hold the magnets in place. Although the invention has been described as an application to a permanent magnet synchronous electric machine comprising a rotor between two stators coaxial to the rotor, the invention is applicable to any type of machine comprising at least one rotor equipped with magnets and at least one stator.

Claims

DEMANDS 1. Rotor assembly (1) having: - a tree (2) along an axis of rotation (XI); - a base (3) extending radially from the shaft; - a ring (4) extending radially from the base (3) and having two main faces (4.1) at least one of which includes locations receiving permanent magnets (5), the base extending axially relative to the ring (4); characterized in that the ring (4) is arranged inside a winding (6) of at least one reinforcing element (7), elongated and flexible, to hold said permanent magnets in place in the locations, the reinforcing element (7) comprising at least one strip of composite fibers.

2. Rotor assembly (1) according to claim 1, in which the reinforcing element (7) extends tangentially to the base (3) , on each of the main faces (4.1) of the ring (4) .

3. Rotor assembly according to claim 1 or 2, wherein the ring (4) has a surface roughness arranged to oppose lateral slippage of the elongated element (7).

4. Axial flux electric machine having a rotor assembly (1) according to any one of the preceding claims.

5. A method for attaching permanent magnets (5) to the ring (4) of a rotor assembly (1) according to any one of claims 1 to 3, by winding an elongated and flexible reinforcing element (7) around the ring, comprising the steps of: arranging the permanent magnets (5) in the housing units provided on one of the main faces (4.1) of the ring (4); - rotate the rotor assembly around a first axis of rotation (XI); unwind the reinforcing element (7) from a mobile applicator (8) making a revolution around the rotor assembly (1) around a second axis of rotation (X2), the second axis of rotation (X2) being coplanar and forming an angle with the first axis of rotation (XI), said angle being chosen to form a predetermined winding pattern of the elongated element (7) around the ring (4).

6. Method according to claim 5, wherein the elongated element (7) is positioned around the rotor assembly (1) by making a number of turns enabling the pattern formed on the rotor assembly (1) to have a regular and homogeneous structure.

7. Method according to claim 6, wherein the number of patterns made during a winding is greater than one, and where each of these patterns is positioned on the rotor assembly (1) with an angular offset.

8. A method according to any one of claims 5 to 7, wherein the reinforcing element (7) comprises fibers and the fibers are wound around the rotor assembly (1) with an orientation having an angle close to 0° with the first axis of rotation (XI), thus covering the two main faces (4.1) and the outer perimeter (4.2) of the ring (4).

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