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

Abstract

A rotor assembly having a shaft about an axis of rotation, a base extending radially from the shaft, a ring extending radially from the base and having two principal faces, at least one of which includes locations for permanent magnets, the base extending axially from the ring, characterized in that the ring is arranged inside a winding of at least one elongated and flexible reinforcing element to hold said permanent magnets in the locations; and a method in which 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 principal faces and the outer circumference. Figure 3

Description

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

[0001] The present invention relates to the manufacture of electrical machine elements and more particularly to the fixing and / or protection of magnets in axial flux electrical machines.

[0002] BACKGROUND OF THE INVENTION

[0003] 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 piece of a permanent magnet that has been pulled away, could become lodged in the air gap between the rotor and the stator and block the rotor's rotation. To reinforce the attachment of the permanent magnets to the rotor, it is known to place a ring around the rotor to cover the permanent magnets and thus prevent them from being pulled away, either partially or completely.

[0004] There are also axial flux electric machines comprising a stator facing a discoidal rotor having a main face on which are located permanent magnets. The magnetic attraction forces resulting from the axial magnetic flux produced by the permanent magnets tend to pull the permanent magnets away and place significant stress on the attachment of the permanent magnets 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 attachment of the plate and its rigidity.

[0005] Furthermore, a filament winding manufacturing process is known, used for example for hollow parts, particularly large ones. These hollow parts are obtained by winding sheets of resin-prepreg composite fibers onto a support mold that constitutes 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, even with a very small wall thickness.

[0006] SUBJECT OF THE INVENTION

[0007] The invention is notably aimed at improving the attachment and / or protection of permanent magnets to a rotor. Summary of the invention

[0008] To this end, the invention provides a rotor assembly having: - a tree along an axis of rotation; - a base extending radially from the shaft; - a ring extending radially from the base and having two main faces, at least one of which includes locations for receiving permanent magnets, the base extending axially relative to the ring;

[0009] the ring being arranged inside a winding of at least one reinforcing element, elongated and flexible, to hold said permanent magnets in place in the locations.

[0010] Thus, the winding allows for a resistant holding of the permanent magnets in position without otherwise modifying the design of the rotor assembly.

[0011] According to optional features, used individually or in whole or in combination: - the reinforcing element extends tangentially to the base, on each of the main faces of the ring; - the ring has a surface roughness arranged to oppose lateral sliding of the elongated element; - the reinforcing element includes at least one strip of composite fibers;

[0012] The axial flux electric machine has such a rotor assembly. The invention also provides a method for attaching permanent magnets to the ring of a rotor assembly by winding an elongated, flexible reinforcing element around the ring, comprising the steps of:

[0013] - arrange the permanent magnets in the slots provided on one of the faces main parts of the ring;

[0014] - to rotate the rotor assembly around a first axis of rotation;

[0015] - unwind the reinforcement element of a mobile applicator performing 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.

[0016] Furthermore, according to optional features, used individually or in whole or in combination: - 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; - 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; - 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.

[0017] Other features and advantages of the invention will become apparent from the following description of a particular, non-limiting embodiment of the invention. Brief description of the drawings

[0018] Reference will be made to the attached drawings, among which:

[0019] [Fig.1] is an overall view of a rotor assembly;

[0020] [Fig.2] is a schematic view of a polar winding around a discoidal rotor according to the method described in the invention;

[0021] [Fig. 3a] is an illustration showing the beginning of the filament winding operation, according to the process of the invention;

[0022] [Fig. 3b] is an illustration showing a first intermediate phase of the filament winding operation, according to the process of the invention;

[0023] [Fig. 3c] is an illustration showing a second intermediate phase of the filament winding operation, according to the process of the invention;

[0024] [Fig. 3d] is an illustration showing the end of the filament winding operation, according to the process of the invention;

[0025] [Fig.4] is an illustration of the angle α formed between the direction of the band and the axis of rotor rotation, formed during winding on the outer circumference, DETAILED DESCRIPTION OF THE INVENTION

[0026] With reference to [Fig. 1], a rotor assembly 1, which we will call rotor 1, is visible. It has a shaft 2 along the axis of rotation of rotor 1. From this shaft 2 extends a circular base 3 in radial projection, and from this base 3 also extends a ring or disk 4 in radial projection. The base 3 and the disk 4 are centered on the axis of rotation of the rotor. The disk 4 has two main plane faces 4.1, and the base 3 extends axially from each of the two main faces 4.1. The disk 4 also has a peripheral surface connecting the two main faces 4.1 and forming an outer perimeter 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. The magnets have a magnetization vector (between the south and north poles) extending parallel to the axis of rotation. Such a rotor is, for example, that of a permanent magnet synchronous electric machine in which the rotor is located between two stators coaxial with the rotor, and the permanent magnets 5 generate an axial flux between the rotor and the stators, which produces an axial attractive force.

[0027] 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.

[0028] 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.

[0029] 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 α in [Fig. 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.

[0030] It should be noted that the band 7 is sufficiently flexible to conform to the angles of the geometry of the disk 4, in particular at the edges between the main faces 4.1 and the outer perimeter 4.2.

[0031] A counterweight correction element is provided in the rotor 1; that is, an element attached to the rotor that improves the balance of the rotor 1 during rotation. For example, if the distribution of the band 7 is not perfectly homogeneous, it is necessary to rebalance the rotor 1 by correcting the counterweight. This can be done by attaching balancing weights to the base 3, either by screwing or welding, or by locally removing material, for example.

[0032] It is also important that the strip 7 wound around the disk 4 does not disrupt the operation of the electric machine, and more specifically the path of the magnetic flux emitted by the permanent magnets: the strip 7 must not constitute 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 the strip 7 overlap, must be less than the maximum air gap between the rotor and stators in the electric machine. The mass of the strip 7 wound around the disk 4 must also be compatible with the intended rotational speed of the rotor 1 and the maximum stresses that the bearings in which the shaft 2 is mounted can withstand.

[0033] The manufacturing process of the rotor assembly will now be described.

[0034] We begin by manufacturing, in a manner known in itself, the shaft 2, the base 3 and The rotor 1 disc 4 is shaped, 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.

[0035] The winding operation is carried out here according to a so-called polar winding method on a winding machine comprising a frame 10, a support 11 mounted on the frame 10 to support and drive the rotor 1 in rotation about 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 about the support 11 about an axis of revolution X2 located in the same plane as the axis of revolution XL

[0036] Thus, by rotating the rotor 1 around the axis of revolution XI and the band applicator 12 around the axis of revolution X2 simultaneously and regularly, the band 7 is wound on the disk 4 forming circuits (the straight sections extending over the main face 2.1 cross around the base 2 forming substantially a capital letter A - see [Fig. 3a] on which the first circuit is shown) until a homogeneous pattern is formed on the disk 4 (in [Fig. 3b], it can be seen that the straight sections extending over the main face 2.1 cross around the base 2 forming substantially 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 [Fig. 3c] representing three adjoining homogeneous patterns), it is possible to cover the entire disk 4 (see [Fig. 3d] representing six adjoining homogeneous patterns).

[0037] It is noted that achieving a polar winding requires two different degrees of rotation between the axis of rotation of the workpiece around 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 disk 4 of the rotor 1, said rotor 1 rotates about the axis of revolution XI, and the strip applicator 12 rotates about 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 the winding, and its value influences the winding pattern 6 formed by the strip 7 around the disk 4 of the rotor 1.

[0038] It is noted that the arrangement of the pattern is influenced by several factors such as, for example, the diameter of the disc 4, the diameter of the base 3, the thickness of the disc 4, or the thickness of the band 7. The thickness of the band 7, the angle a and the diameter of the disc 4 are chosen so as to avoid slippage of the band 7 on the disc 4 during the winding operation, particularly at the outer edge 4.2.

[0039] 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. Optionally, a base of smaller diameter can be provided such that said excess thickness is located opposite a clearance provided in a non-active part of the stator.

[0040] 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.

[0041] In particular, although here the base 3 is circular in shape, it is possible that it may be of a different shape, such as a regular polygon for example, the straight sections of strip 7 may be parallel to the faces of this polygon.

[0042] 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 external circumference 4.2.

[0043] 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 may be replaced by fillets, or chamfers, or even that the outer perimeter may be only an edge.

[0044] Although here the elongated element chosen to form the winding 6 comprises a strip, it is possible that the winding 6 is made from yarn(s), fiber(s), or even a flexible film, of variable thickness or width.

[0045] 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 composite or non-composite materials.

[0046] Although here an angular offset is provided between the application of each winding circuit, it is possible that a constant angular offset may be applied to the winding so as to form a single denser winding circuit of band 7, possibly better balanced.

[0047] The fibers included by band 7 can be aligned, braided, wound, or woven together and bonded by a resin, a matrix or any other manufacturing process.

[0048] 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.

[0049] The winding 6 may 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.

[0050] The invention is applicable to any type of electrical machine having a rotating rotor carrying magnets generating a magnetic flux parallel to the axis of rotation of the rotor.

[0051] The angle a may not be close to zero degrees.

[0052] An annular insert can be positioned around the outer perimeter to hold the magnets during the manufacture of the rotor, or, by adapting the manufacturing process, the positioning of the band 7 may be sufficient to radially hold the magnets in place.

[0053] Although the invention has been described in 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 provided with magnets and at least one stator.

Claims

Demands

1. Rotor assembly (1) having: - a shaft (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 elongated and flexible reinforcing element (7) to hold said permanent magnets in place in the locations.

2. Rotor assembly (1) according to claim 1, wherein the reinforcing element (7) extends tangentially to the base (3), on each of the principal 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. Rotor assembly (1) according to any one of the preceding claims, wherein the reinforcing element (7) comprises at least one composite fiber strip.

5. An axial flux electric machine having a rotor assembly (1) according to any one of the preceding claims.

6. A method for attaching permanent magnets (5) to the ring (4) of a rotor assembly (1) according to any one of claims 1 to 4, by winding an elongated, flexible reinforcing element (7) around the ring, comprising the steps of: - arranging the permanent magnets (5) in the recesses provided on one of the principal faces (4.1) of the ring (4); - rotating the rotor assembly about a first axis of rotation (X1); - unwinding the reinforcing element (7) from a movable applicator (8) that rotates around the rotor assembly (1) about 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).

7. A method according to claim 6, 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.

8. A method according to claim 7, 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.

9. A method according to any one of claims 6 to 8, 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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