Electric machine with magnetic wedges

Abstract

An electromagnetic machine comprising an armature, coils (7) received in slots (5) of the armature, and wedges (1) engaged in the slots (5) to at least partially close the slots (5), each of the wedges (1) being composed of at least one material permanently magnetized along one direction of polarization. An aircraft wheel (103) comprising a magnetic brake defined as such an electric machine. FIGURE IN ABRIDGED GRAPH: Fig. 1

Description

Title of the invention: Electric machine with magnetic wedges

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

[0002] BACKGROUND OF THE INVENTION

[0003] Rotating electrical machines comprising at least one stator assembly and one rotor assembly are known. At least one of these assemblies includes an armature carrying copper coils (also called windings or coils) intended to generate a magnetic field from a current flowing through them or to allow the circulation of a current induced by a magnetic field to which the coils are subjected. Each coil is generally made by winding an electrical conductor around a pole of the armature, each pole being laterally delimited by two adjacent slots formed in the armature parallel to the axis of rotation of the machine and receiving the turns of the electrical conductor forming the winding.After the electrical conductor is inserted, the slots are closed with wedges positioned at their openings to protect the coils, prevent the intrusion of external elements into the slots, and possibly hold the coils in place. These wedges are generally made of plastic or synthetic resin, materials that do not affect the magnetic fields induced or received by the coils. It is also known to use wedges made of non-magnetic materials to avoid interfering with the magnetic fields.

[0004] SUBJECT OF THE INVENTION

[0005] The invention is notably aimed at improving the performance of an electrical machine. Summary of the invention

[0006] For this purpose, according to the invention, an electromagnetic machine is provided comprising an armature, coils received in slots of the armature, and wedges engaged in the slots to at least partially close the slots, each of the wedges being composed of at least one material with permanent magnetization along a polarization direction.

[0007] Thus, the shims made of magnetized material are arranged to enhance the magnetic flux produced by the coils, for example by concentrating it, and to optimize the distribution of magnetic fields acting within the machine during operation. The magnetized shims can replace the existing shims of an electrical machine, improving its performance without modifying the machine's structure.

[0008] According to optional features, used individually or in whole or in combination: - the wedges and the powered coils are arranged with magnetization directions oriented to form a Halbach lattice; - the material of the shims has resistance to temperatures at least equal to a maximum operating temperature of the coils; - the wedges have hardness characteristics that facilitate their placement and retention in the slots; - the wedges include an outer coating having a hardness greater than that of the permanently magnetized material; - the wedges are formed by assembling sections; - the frame forms a rotor of the machine; - the frame forms a stator of the machine; - the electromagnetic machine is arranged to form an aircraft wheel brake.

[0009] The invention also relates to a wheel equipped with an electric machine according to the invention.

[0010] 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

[0011] Reference will be made to the attached drawings, among which:

[0012] [Fig-1] is a general view of an aircraft having braked wheels according to the invention;

[0013] [Fig.2] is a schematic cross-sectional view of an aircraft wheel equipped with an electromagnetic braking device according to the invention;

[0014] [Fig.3] is a cross-sectional view of a rotor armature of an electrical machine according to a first embodiment of the invention;

[0015] [Fig.4] is a schematic perspective view of one of the magnetized magnetic wedges that equip this rotor armature;

[0016] [Fig.5] is a diagram showing the orientation of the magnetization vectors of a series of magnetized wedges and adjacent alternating coils;

[0017] [Fig.6] is a schematic representation of the magnetic field lines in this rotor armature;

[0018] [Fig.7] is a schematic perspective view of the magnetic wedges according to one embodiment variant;

[0019] [Fig.8] is a partial schematic, perspective view of a stator armature of an electric machine according to a second embodiment;

[0020] [Fig.9] is a partial schematic view of the electrical machine according to the second method of implementation. DETAILED DESCRIPTION OF THE INVENTION

[0021] With reference to Figures 1 and 2, the invention is described herein in application to an aircraft 100 comprising landing gear 101, each having a leg with an end provided with at least one axle 102 on which is mounted, pivoting about an axis X of rotation, at least one braked wheel 103. Each wheel 103 comprises a rim 103.1 carrying a tire 103.2, a hub 103.3 extending coaxially with the rim 103.1, defining with it an annular space 103.5, and a disc 103.4 connecting the hub 103.3 to the rim 103.1.

[0022] Each wheel 103 is equipped with an electromagnetic braking device 2, here housed in the annular space 103.5.

[0023] The braking device 2 comprises a stator armature 3 and a rotor armature 4. The stator armature 3 is rotationally connected to the axle 102, while the rotor armature 4 is rotationally connected to at least one element of the wheel 103, here the hub 103.3. The stator armature 3 and the rotor armature 4 have annular shapes and the rotor armature 4 is housed in the stator armature 3 so as to have an external, cylindrical surface facing an internal, cylindrical surface of the stator armature 3.

[0024] In the first embodiment, and with reference to figures 3 to 6, the rotor armature 4 comprises a central annular body 4.1, centered on the X axis, and teeth 6 which extend radially outwards from the central annular body 4.1 and which are separated from each other by slots 5 opening onto the external surface 4.2 of the rotor armature 4. The slots 5 extend parallel to the X axis and are regularly distributed angularly around the X axis.

[0025] All the slots 5 are identical and have an opening 5.1 opposite the internal surface of the stator armature 3. Each slot 5 has, in the vicinity of the central annular body 4.1, a bottom 5.2 of a width greater than a width of the opening 5.1. This is due to the fact that the teeth 6 have substantially a T-shape, with each having a relatively narrow base 6.1 in the vicinity of the central annular body 4.1 and a relatively wide head 6.2 forming the external surface 4.2 of the rotor armature 4.

[0026] The rotor armature 4.1 is provided with coils 7 wound around the teeth 6 under the heads 6.2. The head 6.2 of the teeth 6 allows the coils 7 to be held in position by preventing them from sliding along the teeth 6 and separating from the rotor armature 4.

[0027] Each tooth 6 is thus surrounded by a coil 7, and when a current is sent through the coil, a magnetic field is induced. This induced magnetic field has a sense and a direction. The windings of the coils 7 are positioned around With six teeth extending radially around the rotor armature, the direction of the induced field is thus radial to the rotor armature. The direction of the field, however, is determined by the direction of the current flowing in the coil. The direction of the induced magnetic field is therefore determined during the winding and connection stages.

[0028] Between each of the heads 6.2 of the teeth 6 is placed a wedge 1 allowing to hold and protect the coils 7 extending in the slots 5. Each wedge 1 therefore closes the mouth of one of the slots 5.

[0029] The wedges 1 are bar-shaped and have two main faces: a first main face 1.1 facing outwards from the slot and a second main bottom face 1.2 facing inwards from the bottom of the slot 5, as well as a first secondary lateral face 1.3 and a second secondary lateral face 1.4 connecting the main faces 1.1 and 1.2 to each other. The two secondary lateral faces 1.3 and 1.4 bear against the teeth 6 of the rotor body 4.1 and have a profile that fits the heads 6.2 of said teeth 6. A chamfer 1.5 is present on these secondary lateral faces 1.3 and 1.4 to coincide with a chamfer shape present at the heads 6.2 of the teeth 6.

[0030] Each of these wedges 1 is composed of a permanently magnetized material inducing a magnetic field around it. Thus, each wedge 1 is a permanent magnet with two poles inducing a magnetic field around it from one pole to the other.

[0031] Each of the wedges is arranged in one of the slots 5 of the rotor armature 4 according to a particular magnetization vector orientation, such that the set of wedges 1 and the set of energized coils 7 form a Halbach pattern. For this purpose, with reference to [Fig.8], the wedges 1 and the teeth 6 equipped with coils 7 are arranged in successive series of wedges 1 and coils 7 such that the first lateral surface 1.3 and the second lateral surface 1.4 of each wedge 1 are adjacent to a tooth 6 equipped with a coil 7. The wedges 1 and the coils 7 are arranged in each series such that each series includes a first coil 7A generating a magnetic field going from the inside of the rotor armature to the outside, a first wedge IB, adjacent to this first coil 7A, having a magnetic field going from the first secondary lateral face 1.3 to the second secondary lateral face 1.4, a second coil 7C adjacent to the first wedge IB generating a magnetic field going from the outside of the rotor armature towards the inside, and a second wedge 1D, adjacent to the second coil 7C, generating a field going from the second lateral secondary face 1.4 towards the first lateral secondary face 1.3. It is understood that: . - the 7A coils, when energized, therefore have a magnetization vector extending radially along the X axis from the inside of the rotor armature outwards; - the IB wedges have a magnetization vector extending from the first secondary lateral face 1.3 to the second secondary lateral face 1.4; - the 7C coils, when energized, have a magnetization vector extending radially to the X axis from the outside of the rotor armature outwards; - the 1D wedges have a magnetization vector extending from the second lateral secondary face 1.4 to the first lateral secondary face 1.3.

[0032] In this configuration, the Halbach pattern amplifies the magnetic field intensity on the side of the first principal faces 1.1 and reduces the magnetic field intensity on the side of the second principal faces 1.2 (see the field lines symbolized in [Fig. 6]). The concentration of the magnetic flux outwards from the rotor assembly 4, and therefore towards the stator armature 3, is responsible for optimizing the performance of the magnetic braking device 2, particularly its torque characteristic.

[0033] The shims 1 are monolithic and machined from a bar of a ferromagnetic or permanently magnetized ferrimagnetic material, possessing temperature resistance characteristics sufficient to withstand the maximum operating temperatures of the electromagnetic braking device 2, and more particularly the maximum temperature reached by the coils in operation. In particular, the material in question has a Curie temperature higher than the maximum operating temperature encountered in the machine.

[0034] The material that makes up the wedges 1 also has mechanical resistance characteristics enabling the wedges 1 to withstand the maximum forces attainable during the operation of the electromagnetic braking device 2. In addition, the material has a hardness that makes it easier to place the wedges 1 and to retain them in the slots 5 during the operation of the brake.

[0035] According to a first variant, the wedges 1 comprise an outer coating having advantageous characteristics to reinforce and protect said wedges 1. This coating has, for example, a hardness greater than that of the magnetic material which makes up the wedges 1.

[0036] According to a second variant, shown in [Fig. 7], each of the wedges 1 is an assembly of several sections joined lengthwise along the wedge 1. The sections here have a very small thickness. More precisely, the wedge 1 is laminated, That is to say, it is formed by assembling sheets. This assembled structure notably helps to reduce hysteresis losses.

[0037] According to a second embodiment shown in figures 8 and 9, it is the stator armature 3 which includes teeth delimited laterally by slots which receive coils and are closed by wedges 1 of magnetized material.

[0038] Just like the rotor assembly 4 of the first embodiment, the teeth 6 have a general T-shape and each tooth is surrounded by a coil 7.

[0039] The slots 5 are also closed and protected by the positioning of the same wedges 1 made of magnetized magnetic material. In this second embodiment, the openings of the slots 5 lead to the interior of the stator assembly 3, i.e. in the direction of the rotor assembly 4.

[0040] The wedges 1 and the current-supplied coils 7 also form, by their magnetization vector orientation, a Halbach lattice so as to increase the intensity of the magnetic field in the direction of the interior of the stator armature 3, i.e. in the direction of the rotor armature 4 which includes magnets 8.

[0041] In this second embodiment, the invention does not relate to a braking device for an aircraft wheel but to a rotating electrical machine 9'. In this embodiment, the coils 7 can be traversed by a direct current, the induced magnetic field then allowing the rotation of the rotor armature 4. The electrical machine can also be used as a generator. By applying a rotation to the rotor armature 4, the magnetic fields of the magnets of the stator assembly induce an electric current in the coils 7 of the rotor armature 4, thus generating a voltage at the output of the machine. In both cases, the arrangement of the magnetized wedges 1 and the coils 7 in a Halbach array serves to amplify the magnetic fields induced or received by the coils 7, thereby increasing the performance of the electrical machine 9'.

[0042] 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.

[0043] In particular, the shape of the wedge 1 is described as having a chamfer. However, the geometry of the wedge depends on the geometry of the space intended to receive the wedges, so the presence of a chamfer is not mandatory.

[0044] The permanent magnets 8 can be replaced by other sources of magnetic field such as coils to form electromagnets for example.

[0045] Although the sections that have been illustrated in [Fig.7] are represented in a direction perpendicular to the length of the wedge, it is possible that the cutting of the sections is carried out in another direction, such as parallel to the length of the wedge for example.

[0046] Although here, in each of the embodiments, the rotor armature is central and surrounded by a stator armature, it is possible that the stator armature is central and that it is surrounded by the rotor armature.

[0047] The invention is applicable to any type of electrical machine, synchronous machine, variable reluctance motor, shunt motor, series-wound motor, generator, magnetic brake, axial or radial flux machine...

Claims

Demands

1. Electromagnetic machine comprising an armature, coils (7) received in slots (5) of the armature, and wedges (1) engaged in the slots (5) to at least partially close the slots (5); characterized in that each of the wedges (1) is composed of at least one material with permanent magnetization along a polarization direction.

2. Machine according to claim 1, wherein the wedges (1) and the coils (7) fed are arranged with magnetization directions oriented to form a Halbach grating.

3. Machine according to any one of the preceding claims, wherein the material of the wedges (1) exhibits resistance to temperatures at least equal to a maximum operating temperature of the coils (7).

4. Machine according to any one of the preceding claims, wherein the wedges (1) have hardness characteristics facilitating their placement and retention in the slots (5).

5. Machine according to claim 4, wherein the wedges (1) comprise an outer coating having a hardness greater than that of the permanently magnetized material.

6. Machine according to any one of the preceding claims, wherein the wedges (1) are formed by assembling sections.

7. Machine according to any one of the preceding claims, wherein the armature (3) forms a rotor of the machine.

8. Machine according to any one of claims 1 to 6, wherein the armature (4) forms a stator of the machine.

9. Machine according to any one of the preceding claims, arranged to form an aircraft wheel brake (103).

10. Aircraft wheel (103) comprising a machine according to claim 9.

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