Stator teeth, associated yoke and stator for an electric machine

Abstract

The present invention relates to a stator tooth for an electric machine, the stator tooth comprising a sheath (12) extending between a first face (13) and an opposite second face (14), the first face having means for attachment to a stator yoke. The sheath accommodates one or more electrically conductive materials configured to direct the magnetic flux of the electric machine from one of said faces to the other face during operation.

Description

Technical Field

[0001] The present invention relates to a rotating electrical machine, and more particularly to a rotating electrical machine for an electric or hybrid motor vehicle.

[0002] More specifically, the present invention relates to a stator that includes teeth attached to a stator yoke. Background Art

[0003] Rotating electrical machines generate losses in the form of heat, particularly due to eddy currents. In the flux-conducting parts of such machines, the magnetic field causes heating because induced currents, known as eddy currents, flow there in short-circuit loops and because they exhibit resistance to the flow of the magnetic flux. To prevent this phenomenon, these flux-conducting parts of the stator and rotor are almost systematically made up of stacks of sheets that are electrically insulated from each other and oriented in the direction of the magnetic field.

[0004] In an electrical machine in which one or more rotors include permanent magnets, the magnetic properties of the permanent magnets depend on temperature, and the efficiency of the electrical machine depends in particular on the magnetization of the one or more rotors.

[0005] Specifically, if the temperature of the one or more rotors is higher than a critical temperature, the magnets irreversibly lose their magnetism. Additionally, eddy currents flow in the magnets, contributing to their heating.

[0006] Furthermore, the heat generated by the electrical machine reduces the overall efficiency of the electrical machine.

[0007] In a central-rotor axial-flux rotating electrical machine, the rotor is arranged between two stators, and the rotor and the stators dissipate heat.

[0008] Thus, the rotor is heated by the induced currents flowing through it and the heat radiated from the stators.

[0009] Document GB 2482928 discloses a central-stator axial-flux rotating electrical machine, that is, an electrical machine in which the stator is arranged between two rotors including magnets.

[0010] Since the rotors are arranged at the ends of the electrical machine, they are cooled by cold air.

[0011] This document also discloses that the central stator includes a disk made of a composite plastic material and a supporting stator pad made of compressed and sintered iron powder, the particles of the iron powder being coated with an electrical insulating material, which reduces the resistance of the supporting stator pad to the magnetic flux passing through them.

[0012] Thus, the induced currents that cause stator heating are reduced therein.

[0013] However, the magnetic losses of the rotors are increased by diverting the magnetic flux through the support plates for the magnets.

[0014] Reference FR 3 006 124 can also be cited, which discloses a central rotor axial flux rotating electrical machine.

[0015] The rotor includes a disk, which includes openings arranged circumferentially and accommodating magnets.

[0016] This configuration allows limiting the heating of the rotor.

[0017] However, the heat radiated from the stator heats the stator.

[0018] It is proposed to overcome the drawbacks associated with rotating electrical machines according to the prior art, in particular by limiting the heating of one or more stators surrounding the rotor. Summary of the Invention

[0019] In view of the above, a subject of the present invention is a stator tooth for an electrical machine, the stator tooth including an envelope extending between a first face and an opposite second face, the first face including means for attachment to a stator yoke.

[0020] The envelope houses one or more conductive materials configured to direct the magnetic flux of the electrical machine from one of the faces to the other during operation.

[0021] Preferably, the envelope is made of a stamped non-magnetic metal sheet.

[0022] Advantageously, the first face includes at least one tab intended for attachment to the yoke.

[0023] According to another feature, the second face includes at least one fin for fixing a pre-assembled winding inserted between the tab and the fin in the axial direction.

[0024] Preferably, the tooth further includes a pre-assembled winding inserted on the outer peripheral surface of the envelope.

[0025] Advantageously, the pre-assembled winding includes a support frame on which a wire is wound, the wire including a plurality of strands held in an insulating envelope to form turns.

[0026] According to a first embodiment, the conductive material includes needles extending from the first face to the second face.

[0027] Preferably, the needles are made of a material permeable to the magnetic field and having grains oriented along the length of these needles.

[0028] Advantageously, the peripheral surface of each needle not delimited by the first face and the second face is covered with an insulating material.

[0029] Preferably, the gap between the needles and the envelope is filled with an adhesive.

[0030] According to a second embodiment, the conductive material comprises laminae extending from a first face to a second face and stacked on top of one another.

[0031] Preferably, the gap between these laminae and the envelope is filled with an adhesive.

[0032] According to a third embodiment, the tooth comprises a one-piece pad, the conductive material being made by compacting iron powder coated with an electrical insulator.

[0033] Preferably, the conductive material further comprises lateral extensions which extend outwards from the envelope and which comprise recesses for receiving clips attached to the yoke.

[0034] A further subject of the invention is a yoke comprising at least one stator tooth as defined above, a stator for a central rotor motor comprising such a yoke, and a central rotor axial flux motor comprising such a stator. Description of the Drawings

[0035] Other objects, features and advantages of the invention will become clear by reading the following description given by way of non-limiting example only and with reference to the drawings, in which:

[0036] - Figure 1 a cross-sectional view of a central rotor axial flux rotating motor according to the invention is shown;

[0037] - Figure 2 a view of the yoke and stator teeth according to the invention is shown;

[0038] - Figure 3 and Figure 4 a first embodiment of the stator teeth according to the invention is shown;

[0039] - Figure 5 a second embodiment of the stator teeth according to the invention is shown; and

[0040] - Figure 6 a third embodiment of the teeth formed by the stator pads according to the invention is shown. Detailed Description

[0041] Reference Figure 1 , which shows a cross-sectional view of a central rotor axial flux rotating motor 1 in the axial direction. In this exemplary embodiment of the invention, this machine is a traction motor for an electric vehicle or a hybrid vehicle.

[0042] The motor 1 comprises a housing 2 and an axis (A) which coincides with the axis of rotation of the rotor 4, the housing comprising two stators 3a and 3b of the same architecture, which surround the rotor 4.

[0043] Each stator 3a and 3b is separated from the rotor by an air gap ENT.

[0044] The rotor 4 is guided by ball bearings 5 and 6 supported by the housing 2 .

[0045] The rotor 4 comprises a hub 7 to which is attached a disk 8 comprising openings arranged circumferentially and housing magnets 9 which are preferably segmented and electrically insulated in order to limit the currents induced in the magnets.

[0046] The heating of the rotor 4 is thus reduced.

[0047] The disc is preferably made of a composite material, for example a fiber reinforced polymer, thus reducing eddy currents. The disc is preferably surrounded by a hoop to improve its mechanical strength.

[0048] The rotor 4 is positioned axially between the stators 3a and 3b to obtain an air gap of equal thickness. For this purpose, an adjustment piece is provided on one side (for example on the right side). Measurements are taken to determine the thickness of this piece. In order to keep the rotor in this position, a spring is placed opposite to this piece behind the bearing.

[0049] The stators are each centered in the two half-shells and are held axially compressed by means of pin connections welded to the yoke 10 and nuts regularly and circumferentially distributed around the yoke 10 .

[0050] For cooling the stators 3a and 3b, water chambers are arranged in each housing. The sealing of these chambers is provided by O-rings.

[0051] Since the stators 3 a and 3 b have the same architecture, only the stator 3 a will be described in detail hereinafter.

[0052] The stator 3 a comprises a yoke 10 around which stator teeth 11 are arranged, the stator teeth being all identical.

[0053] The yoke 10 has a constant thickness and comprises, for example, a thin sheet whose surface is electrically insulated and which is wound in a spiral and has steel grains oriented in the winding direction. As a variant, the yoke is made of non-oriented steel grains. Thus, in operation, the magnetic flux that must flow between two adjacent teeth will follow the orientation given by the winding of the sheet. As a variant, a magnetically conductive material other than steel is used.

[0054] Figure 2 , Figure 3 and Figure 4 A view of a yoke 10 of a first preferred embodiment including stator teeth 11 is shown, as well as a partial section through the yoke 10, and in Figure 2 The stator teeth 11 are shown in the direction III-III.

[0055] More specifically with reference to Figure 3 .

[0056] The stator tooth 11 includes a sheath 12 that extends between a first face 13 and a second face 14 attached to the yoke 10. These faces are orthogonal to the axial direction (the rotation axis (A) of the rotor).

[0057] The sheath 12 houses one or more conductive materials.

[0058] According to a first preferred embodiment, the conductive material includes pins 15. The sheath 12 is, for example, an isosceles triangle with rounded vertices and its equal-length sides oriented such that the tooth is symmetric with respect to the symmetry axis (B). The common vertex of the two equal-length sides is oriented towards the axis (A).

[0059] The pins 15 extend from the first face 13 towards the second face 14. More precisely, the pins 15 extend in the axial direction. The length of the pins is preferably substantially equal to the axial dimension of the sheath 12, which is itself greater than the thickness of the yoke 10. The diameter of the pins (or the dimension of the cross-section in the case where the pins are not cylindrical) is preferably on the order of 0.5 mm and preferably less than 1 mm. It can be less than 0.5 mm and depends on the operating frequency of the rotating electrical machine 1. For example, at 1000 Hz, a diameter less than 0.3 mm is preferred.

[0060] A set of pins of the stator tooth 11 is substantially trapezoidal or triangular in axial cross-section with rounded corners. The perimeter of the sheath 12 forms a strip, the width of which extends in the axial direction between the faces 13 and 14 and the length of which extends angularly all around the shape outlined by the pins of the stator tooth 11. However, the sheath 12 does include tabs 16 that are positioned perpendicular to the strip formed by this perimeter of the sheath 12 on the surface of the yoke 10 that is orthogonal to the axis (A). Similarly, fins 22 positioned perpendicular to the strip formed by this perimeter hold the winding 17 assembled around the strip.

[0061] The sheath 12 is made, for example, by stamping a non-magnetic metal sheet.

[0062] The pins 15 are, for example, cylindrical and are preferably made of a material that is permeable to the magnetic field and has grains oriented in the direction of its length, for example made of magnetic steel. Of course, the shape of the cross-section of the pins can be different, for example polygonal.

[0063] The peripheral surface of each pin 15 that is not bounded by the first face 13 and the second face 14 is coated with an insulating material (not shown), such as varnish, so that the pins 15 are in magnetic contact with the yoke 10 and so that the magnetic field can be transferred from the yoke 10 to the rotor 4 via the pins 15 and the air gap ENT. In other words, the pins preferably make direct contact with the yoke 10 without an insulating material separating them.

[0064] The gap between the needles 15 and the envelope 12 is filled with an adhesive, such as a resin (not shown). In addition to having an adhesive function, this adhesive also has electrical insulation and heat conduction properties.

[0065] The insulation between the needles 15 from each other and from the envelope 12 allows the induction current responsible for heating the stator 3a to be reduced.

[0066] The first face 13 includes tabs 16 attached to the yoke 10 to fix the teeth 11 to the yoke 10.

[0067] Each tab 16 is attached to the yoke 10, for example, by a laser weld passing through the tab. Preferably, three tabs 16 attach the envelope containing the needles to the yoke 10, one tab 16 being located at the radially outer periphery of the tooth 11, and two side tabs 16 being located on both sides of the tooth 11 in the angular direction.

[0068] The stator tooth 11 further includes a pre-assembled winding 17 inserted on the outer peripheral surface of the envelope 12.

[0069] The pre-assembled winding 17 includes a support frame 18 around which the wire 19 is wound to form turns.

[0070] The wire 19 preferably includes a plurality of strands 20 held in an insulating envelope 21. For a given conductive cross-section of the wire, the use of a plurality of strands improves the current flow as compared to a one-piece wire.

[0071] The second face 14 of the envelope 12 includes deformable flaps 22 which are pressed back when the pre-assembled winding 17 is assembled onto the tooth 11 to axially fix the pre-assembled winding 17.

[0072] As Figure 2 can be seen, the teeth 11 are arranged uniformly around the yoke 10.

[0073] The yoke 10 is circular and includes a void at its center, the size of which is determined to accommodate the rotor 4.

[0074] In operation, the magnetic field generated by the turns of the teeth 11 of the stator 3a passes through the air gap ENT and the disc-shaped portion of the rotor 4, and penetrates into the stator teeth arranged facing the stator 3b.

[0075] The magnetic field is guided by the yoke of the stator 3b to the adjacent teeth, then again passes through the air gap ENT and the disc-shaped portion of the rotor 4, and penetrates into the stator teeth arranged facing the stator 3a, thus reaching the adjacent stator teeth via the yoke of the stator 3a.

[0076] The needles 15 of the stator teeth 11 are oriented in the direction of travel of the magnetic field, and the laminations of the yoke 10 are wound in the direction of travel of the magnetic field.

[0077] The circulation of the magnetic flux is optimized, thereby reducing the magnetic losses of the machine 1 and improving the efficiency of the machine 1.

[0078] Figure 4 A partial view of the tooth 11 is shown, which includes a needle 15 and a tab 16 received in a sheath 12.

[0079] According to Figure 5 In the second embodiment of the tooth 11 shown, the conductive material includes thin sheets 23 stacked radially inside the sheath 12.

[0080] The thickness of the thin sheet 23 extends in the radial direction, the width of the sheet extends between the first face 13 and the second face 14, and the length of the sheet extends in a direction orthogonal to the radial direction.

[0081] The cross-section of the thin sheet 23 is, for example, rectangular.

[0082] The thin sheets 23 are stacked, for example, in a direction parallel to the side having a different length with respect to the lengths of the other two sides of an isosceles triangle.

[0083] The thin sheets 23 are fixed to each other, for example, by surface welding before being inserted into the sheath 12. After the thin sheets 23 have been inserted into the sheath 12, the gap between the sheets and the sheath is filled with an adhesive, such as resin.

[0084] The thickness of the thin sheet is preferably less than 0.35 mm, for example, equal to 0.2 mm. The choice of this thickness depends on the usage frequency of the rotating electric machine 1.

[0085] Figure 6 A third embodiment of the tooth 11 attached to the yoke 10 is shown.

[0086] This tooth 11 includes a pad and a tab 16.

[0087] In this embodiment, the pad is a one-piece pad and the conductive material is made by compacting iron powder coated with an electrical insulator.

[0088] The pad further includes lateral extensions 24 that extend towards the outside of the pad on both sides of the symmetry axis (B) and include recesses 25 at each end of the extensions. The lateral extensions 24 form constrictions, thereby increasing the torque generated by the rotating electric machine 1.

[0089] Clips 26 and 27 made of elastic steel and attached to the yoke 10 are received in the recesses 25 to hold the pad against the yoke 10.

[0090] The fins 22 clamp the clips 26 and 27 and hold a pre-assembled winding 17 (not shown) on the peripheral surface of the envelope 12 by welding its ends to the yoke. More specifically, the fins 22 ensure that the pads are pressed against the yoke 10 with a certain pressure via the clips in the recesses 25 supported on the pads. In this third embodiment, the fins hold the pads and the coils.

[0091] The steel grains of the iron powder are magnetically oriented in the axial direction.

[0092] The fine segmentation of the stator teeth 11 mounted on the yoke 10 makes it possible to prevent losses caused by eddy currents.

[0093] The present invention is not limited to the embodiments regarding the central rotor axial flux machine, and the described features can be easily converted to a radial flux machine. In this case, the stator yoke can be segmented to facilitate the assembly of the stator teeth and windings.

Claims

1. A stator yoke for an electric machine, the stator yoke comprising at least one stator tooth, the stator tooth comprising a sheath (12) extending between a first face (13) and an opposite second face (14), the first face being provided with means for attachment to said stator yoke (10), characterized in that, The envelope accommodates one or more conductive materials that are permeable to a magnetic field and are configured to direct the magnetic flux of the electric machine from one of the first and second faces to the other face during operation. The stator teeth further include a pre-assembled winding inserted on the outer peripheral surface of the envelope (12), the envelope being different from the support frame for the pre-assembled winding. The conductive material includes pins (15) extending from the first face to the second face.

2. The stator yoke according to claim 1, wherein, The envelope (12) is made of a stamped non-magnetic metal sheet.

3. The stator yoke according to any one of claims 1 and 2, wherein, The first face (13) is provided with at least one tab (16) intended to be attached to the stator yoke (10).

4. The stator yoke according to claim 3, wherein, The second face (14) is provided with at least one fin (22) for fixing the pre-assembled winding (17) inserted between the tab (16) and the fin in the axial direction.

5. The stator yoke according to claim 4, wherein, The pre-assembled winding (17) includes the support frame (18) on which a wire (19) is wound, the wire including a stranded wire held in an insulating envelope to form turns.

6. The stator yoke according to claim 1, wherein, The pins (15) are made of a material that is permeable to a magnetic field and has grains oriented along the length of the pins (15).

7. The stator yoke according to claim 1, wherein, The peripheral surface of each pin (15) not bounded by the first and second faces is covered with an insulating material.

8. The stator yoke according to claim 1, wherein, The gap between the pins (15) and the envelope (12) is filled with an adhesive.

9. A stator for a central rotor axial flux electric machine, the stator comprising a stator yoke (10) according to any one of claims 1 to 8.

10. A central rotor axial flux electric machine, comprising a stator according to claim 9.

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