Stator for axial flux electric machine

Abstract

The invention relates to a stator for an axial flux electric machine comprising: - a yoke (100) in the overall shape of a disc centered on a longitudinal axis (A1); - teeth (200) distributed on a principal face (101) of the yoke around the longitudinal axis, each tooth carrying a winding (300) of conducting wire. According to the invention, the yoke has, between at least one pair of adjacent teeth, a thickness (E1, E2), measured parallel to the longitudinal axis, which varies along a radial direction (A2) perpendicular to the longitudinal axis such that the thickness is greater in a region of the yoke away from the longitudinal axis than in a region of the yoke close to the longitudinal axis. Figure for the abstract: Fig. 2.

Description

Title of the invention: Stator for axial flux electric machine Technical field of the invention

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

[0002] It relates more particularly to a stator for an axial flux electric machine.

[0003] The invention finds a particularly advantageous application in electric motors for electric or hybrid motor vehicles. State of the art

[0004] A conventional axial flux electric machine stator comprises a yoke in the overall shape of a disc centered on a longitudinal axis and teeth distributed on a main face of the yoke around the longitudinal axis, each tooth carrying a winding of conductive wire. Under the effect of electric currents, the coils generate magnetic fields allowing the stator to set the rotor in motion.

[0005] The yoke conventionally forms a disc of radially constant thickness, that is to say of the same thickness from the center of the disc to its periphery, the thickness of the disc representing its dimension along the longitudinal axis. The teeth conventionally rise along the longitudinal axis from the yoke to a radially constant height.

[0006] The applicant has found that, when the stator is in operation, the density of the magnetic fluxes flowing through it is very inhomogeneous. Certain parts, such as the parts of the teeth close to the longitudinal axis and the peripheral part of the yoke, are traversed by high density fluxes, which generates significant iron losses (losses including eddy current and hysteresis losses). These significant iron losses limit the efficiency and power of an electrical machine comprising the stator. In addition, these high density fluxes also lead to an increase in the current injected into the coils and therefore to significant copper losses (Joule effect losses) in the latter. Conversely, other parts, such as the part of the yoke close to the longitudinal axis, are traversed by low density fluxes. Presentation of the invention

[0007] In order to overcome the aforementioned drawback of the state of the art, the present invention provides a stator as defined in the introduction, in which it is provided that the yoke has, between at least one pair of adjacent teeth (and preferably between at least two pairs of adjacent teeth), a thickness, measured parallel to the longitudinal axis, which varies along a radial direction perpendicular to the longitudinal axis such that the thickness is greater in an area of ​​the yoke spaced from the longitudinal axis than in an area of ​​the yoke close to the longitudinal axis. gitudinal.

[0008] Thus, thanks to the invention, the magnetic flux flowing through the peripheral portion of the yoke, which corresponds to the area spaced from the longitudinal axis, circulates in a large volume of material. The extra thickness of the yoke in its peripheral portion therefore makes it possible to reduce the density of the magnetic flux circulating there, and consequently to limit iron losses.

[0009] In a complementary manner, the stator according to the invention also makes it possible, compared to a conventional stator, to save material at the central portion, which corresponds to the area close to the longitudinal axis. Indeed, since the density of the magnetic flux circulating there is low, refining the yoke in its central portion does not increase, or only very little, the iron losses.

[0010] It therefore appears that, compared to a conventional stator of constant thickness, the stator according to the invention makes it possible to better distribute the magnetic material forming the yoke by providing more material in an area where the circulation of the magnetic flux is high and / or by saving material in an area where the circulation of the magnetic flux is low. Thus, the density of the magnetic flux passing through the yoke is much more homogeneous than in a conventional stator, which makes it possible to limit iron losses and to increase the efficiency or power of the stator.

[0011] Other advantageous and non-limiting characteristics of the stator according to the invention, taken individually or in all technically possible combinations, are the following: - the cylinder head comprises a flat secondary face opposite the main face and in which the distance between the main face and the secondary face increases as a function of the distance from the longitudinal axis; - the main face extends along a truncated cone-shaped surface; - at least one tooth has a height, measured parallel to the longitudinal axis, which varies along another radial direction perpendicular to the longitudinal axis such that the height is greater in an area of ​​said tooth close to the longitudinal axis than in an area of ​​said tooth away from the longitudinal axis; - the distance between the teeth of said pair, measured in an orthoradial direction orthogonal to the longitudinal axis, varies along said radial direction such that the distance is greater in an area away from the longitudinal axis than in an area close to the longitudinal axis; - the distance between the teeth of said pair increases as a function of the distance from the longitudinal axis; - the winding of at least one tooth extends over a greater height on a side close to said tooth located close to the longitudinal axis than on an opposite side and / or has a greater number of layers of wires on the opposite side than on the close side; - the conductive wire forming said winding comprises: an initial length wound so as to produce internal stacks, against said tooth, of triangular shapes and the bases of which extend opposite said tooth; and a terminal length, adjoining the initial length, wound so as to produce external stacks of triangular shapes, nesting in the internal stacks; - the stator further comprising a cooling duct between the teeth of said pair, the duct having a width, measured in another orthoradial direction orthogonal to the longitudinal axis, which varies along said radial direction such that said width is greater in an area of ​​the duct spaced from the longitudinal axis than in an area of ​​the duct close to the longitudinal axis; - said conduit is interposed between one of the teeth of said pair and the winding carried by said tooth or between the windings carried by the teeth of said pair; - said cooling channel has a base interposed between the winding of one of said teeth of said pair and the yoke, the base having a thickness, measured parallel to the longitudinal axis, decreasing as a function of the distance from the longitudinal axis.

[0012] 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

[0013] 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.

[0014] In the attached drawings:

[0015] [Fig-1] is a schematic view in perceptive of the cylinder head and the teeth forming a stator according to the invention;

[0016] [Fig.2] is a schematic exploded perspective view of an angular sector of a first embodiment of a stator according to the invention;

[0017] [Fig.3] is a schematic exploded perspective view of an angular sector of a second embodiment of a stator according to the invention;

[0018] [Fig.4] is a schematic sectional view of a winding of an alternative embodiment of the stator according to the second embodiment;

[0019] [Fig.5] is a schematic perspective view of cooling ducts of a another variant embodiment of the stator according to the second embodiment.

[0020] In [Fig.l], a stator according to the invention is shown comprising: - a 100 cylinder head; and - a plurality of teeth 200.

[0021] As illustrated in [Fig.2] or 3, each tooth 200 here carries a winding 300 of conductive wire.

[0022] This stator is intended to be assembled in an axial flux electric machine, in this case a motor for propelling an electric vehicle. Such an electric machine comprises at least one rotor and at least one stator. In practice, it comprises a rotor located between two stators.

[0023] The rotor generally comprises an annular-shaped body which houses a plurality of magnetic pole elements having the same function as permanent magnets. Magnetic pole elements consist of magnetic blocks arranged side by side so as to together form a sort of ring in the rotor. These magnetic pole elements are preferably made of small assembled permanent magnets.

[0024] When the windings 300 are supplied with electric current, they allow a magnetic field to be generated so as to rotate the rotor. The stators are generally identical.

[0025] In [Fig.2], for simplicity, only one angular sector 10 of the stator has been shown. Here, all the angular sectors 10 forming the stator 1 are identical and each angular sector comprises only one of the teeth 200.

[0026] As shown in [Fig.l], the yoke 100 essentially has the shape of a disc centered on a longitudinal axis AL. However, it has a circular central opening which is delimited by a central face 105 of the yoke 100. The yoke 100 also has a peripheral face 106 which here corresponds to its outer periphery, that is to say here its edge remote from the longitudinal axis AL. Thus, the yoke 100 here has the shape of a flattened ring whose thickness is less than the diameter.

[0027] The yoke 100 comprises a main face (facing the rotor), called the upper face 101, and a secondary face, called the lower face 102, opposite the upper face 101. Here, the lower face 102 is orthogonal to the longitudinal axis AL

[0028] The dimension of the yoke 100 parallel to the longitudinal axis A1 is called the thickness of the yoke 100. For any point on the upper face 101, the thickness of the yoke 100 is therefore here equal to the distance between the upper face 101 and the lower face 102 measured parallel to the longitudinal axis A1. The thickness of the yoke 100 is here measured between each pair of teeth 200.

[0029] In Figures 2 and 3, two embodiments of the stator are shown.

[0030] As clearly appears in Figures 2 and 3, in these two modes, the thickness of the yoke 100 varies along a first radial direction A2 such that the thickness is greater in an area of ​​the yoke 100 spaced from the longitudinal axis A1 than in an area of ​​the yoke 100 close to the longitudinal axis A2. A radial direction here means a direction perpendicular to the longitudinal axis A1

[0031] In other words, the cylinder head 100 is such that there is a first axis DI and a second axis D2 (see [Fig.2]): i) which are parallel to the longitudinal axis A1 and aligned radially, here along the first radial direction A2; ii) for which the distance between the longitudinal axis A1 and the first axis D1 is less than the distance between the longitudinal axis A1 and the second axis D2; and iii) for which the thickness E2 of the cylinder head 100 measured along the second axis D2 is greater than the thickness El of the cylinder head 100 measured along the first axis DE

[0032] The distance between the longitudinal axis Al and a parallel axis, here the first axis DI or the second axis D2, is the length of the shortest segment connecting them.

[0033] In the example illustrated in [Fig.l], the area of ​​the cylinder head 100 spaced from the longitudinal axis A1 corresponds to a peripheral portion of the cylinder head 100 adjoining the peripheral face 106 and the area of ​​the cylinder head 100 close to the longitudinal axis A1 corresponds to a central portion of the cylinder head adjoining the central face 105. Here, these peripheral and central portions of the cylinder head can be defined as parts that are separate and spaced radially from one another.

[0034] When the stator 1 is in operation, the magnetic flux is greater in the peripheral portion than in the central portion. The extra thickness of the peripheral portion makes it possible to reduce the density of the magnetic flux and therefore to limit iron losses and copper losses.

[0035] As shown in [Fig. 2], the thickness of the yoke 100 increases radially as a function of the distance from the longitudinal axis AL. Here, the thickness of the yoke 100 increases in any radial direction, in particular in the first radial direction A2. Thus, in general, the thickness of the yoke 100 increases from the central portion 105 to the peripheral portion 106.

[0036] In other words, the yoke 100 is such that for any third axis aligned with the first axis DI and the second axis D2 and located at a greater distance from the longitudinal axis A1 than the second axis D2, the thickness measured along the third axis is greater than the thickness E2 measured along the second axis D2.

[0037] The thickness of the cylinder head 100 preferably varies continuously with the distance from the longitudinal axis AL. This variation is more precisely strictly increasing.

[0038] As shown in [Fig.2], the thickness of the yoke 100 increases more specifically linearly as a function of the distance from the longitudinal axis AL. The upper face 101 thus extends along a truncated cone-shaped surface of revolution. This regular growth in the thickness of the yoke 100 facilitates the manufacture of the stator and gives it high mechanical strength.

[0039] Alternatively, the thickness of the cylinder head could increase in another way, for example in steps or according to a curve defined by the square root function.

[0040] As shown in [Fig.l], the teeth 200 are regularly distributed, that is to say with constant angular spacings, on the upper face 101 of the yoke 100 around the longitudinal axis A1.

[0041] Each tooth 200 extends in height parallel to the longitudinal axis A1 from the upper face 101 of the yoke 100. Each tooth 200 ends with a flat end face 201 opposite the lower face 102 of the yoke 100. Each tooth 200 generally has the shape of a right prism, with a trapezoidal section in a plane orthogonal to the longitudinal axis A1. Each tooth 200 here has a plane of radial symmetry.

[0042] The height of each tooth 200 is its dimension measured parallel to the longitudinal axis A1. The height of each tooth 200 corresponds here to the distance, measured parallel to the longitudinal axis A1, between the end face 201 of the tooth 200 and the upper face 101 of the yoke 100.

[0043] As illustrated in Figures 2 and 3, the top of each tooth 200 is bordered by a pair of lateral flanges extending radially from the central opening to the outside of the stator 1. The lateral flanges of each tooth 200 extend opposite the lateral flanges of the adjacent teeth 200 to improve the circulation of the magnetic flux. Two teeth 200 are here adjacent when they are located side by side along the circumference of the stator 1.

[0044] The winding 300 of each 200 is here carried by an envelope (not shown) made of non-magnetic material and the shape of which matches that of the tooth 200.

[0045] Here, as appears for example in Figures 2 and 3, the yoke 100 and the teeth 200 are produced by cutting, for example by punching, and stacking the metal sheets. Each angular section 10 can be manufactured individually. Each angular section 10 comprises a stack of metal sheets, for example made of grain-oriented or non-grain-oriented magnetic steel, in which each sheet forms both a part of the tooth 200 and the yoke 100. The yoke 100 and the teeth 200 can also be manufactured in one piece by winding a cut sheet around the longitudinal axis A1. Alternatively, the teeth could be manufactured independently of the yoke and then attached to it.

[0046] In the first embodiment shown in [Fig.2], the height of each tooth 200 is constant. This constant height of the teeth 200 makes it possible to use a conventional winding 300 which is simple to implement. In this conventional winding, the conductive wire is first wound so as to form an inner layer 301 (represented by solid horizontal grooves) then upper layers 302, 303 (represented by solid and dotted vertical grooves).

[0047] Here, since the thickness of the yoke 100 increases linearly, the distance between the end face 201 of each tooth 200 and the lower face 102 of the yoke 100 increases also linearly as a function of the distance from the longitudinal axis A1. All the end faces 201 of the teeth 202 therefore extend along a common frustoconical surface. Such a stator 1 is therefore used as a reference in conjunction with a rotor having an end face which is generally frustoconical.

[0048] In the second embodiment shown in Figures 3 and 5, not only does the yoke 100 have an optimized thickness compared to a conventional stator yoke, but each tooth 200 also has an optimized shape compared to a conventional stator tooth.

[0049] Indeed, the magnetic flux passing through a peripheral part of a tooth 200 is weak, it is therefore possible to reduce the volume of the tooth 200, in proportion to the volume of the stator 1, at this location without the increase in flux density causing significant iron losses.

[0050] Here, the peripheral portion of a tooth 200 corresponds to its portion rising from the peripheral portion of the yoke 100. Conversely, each tooth 200 has a central portion corresponding to its portion rising from the central portion of the yoke 100.

[0051] Advantageously, in the second embodiment, the material used to manufacture the stator can then be distributed between the teeth 200 and the yoke 100 so as to limit even more, compared to the first embodiment, the iron losses and thus to increase the efficiency or the power of the stator.

[0052] A first way of reducing the volume of the peripheral part of the tooth 200 is to vary its height, for example so that its height decreases radially with the distance from the longitudinal axis A1.

[0053] Thus in this second embodiment, each tooth 200 has a height which varies along a second radial direction A3 such that the height is greater in a zone of the tooth 200 close to the longitudinal axis A1 than in a zone of the tooth 200 spaced from the longitudinal axis A1.

[0054] In the example illustrated in [Fig.3], the area of ​​the tooth 200 close to the longitudinal axis A1 corresponds to the central part of the tooth 200 and the area of ​​the tooth 200 away from the longitudinal axis A1 corresponds to the peripheral part of the tooth 200.

[0055] In other words, each tooth 200 is such that there is a fourth axis D4 and a fifth axis D5 which are parallel to the longitudinal axis A1 and aligned radially, here along the second radial direction A3, the distance between the longitudinal axis A1 and the fourth axis D4 being less than the distance between the longitudinal axis A1 and the fifth axis D5, the height H5 measured along the fifth axis D5 being less than the height H4 measured along the fourth axis D4.

[0056] In the example illustrated in [Fig.3], the reduction in the height of the tooth 200 is accompanied by a significant increase in the thickness of the cylinder head 200, here more important than in the first embodiment. This makes it possible to better homogenize the density of the magnetic flux, which circulates more in the peripheral portion 106 of the yoke 100 than in the peripheral part of the tooth 200.

[0057] As shown in [Fig.3], the height of each tooth 200 decreases linearly as a function of the distance from the longitudinal axis A1. The height of each tooth 200 decreases more specifically such that the end face 201 of each tooth 200 is parallel to the lower face 102 of the stator.

[0058] Thus, the stator generally has two faces parallel and orthogonal to the longitudinal axis Al: the lower face 102 and a face defined by all of the end faces 201 of the teeth 200. This configuration of the stator makes it easy to integrate it into an electrical machine, in particular without having to adapt the rotor, which generally also has a flat end face orthogonal to the longitudinal axis Al.

[0059] A second way of reducing the volume of the peripheral part of the tooth 200 is to make the latter thinner than a conventional stator tooth.

[0060] Here, the two ways of reducing the volume of the peripheral portion of the tooth 200 are presented in combination within the framework of the second embodiment. It is however possible to implement them independently of each other.

[0061] Remarkably, making each tooth 200 more refined generates additional space available between each pair of adjacent teeth 200, which in practice makes it possible to wind a greater length of conductive wire (as shown in [Fig.3]) to increase the efficiency of the stator or to provide larger cooling ducts 400 (as shown in [Fig.5]) to increase the power of the stator 1.

[0062] Remarkably, the additional space is also used here to wind a thicker conductive wire, i.e. with a larger cross-section, than a wire used in a conventional stator. Advantageously, this makes it possible to reduce copper losses (which are inversely proportional to the square of the diameter of the conductive wire) and therefore to further increase the efficiency of the stator.

[0063] Thus, in this second embodiment, the distance between the two teeth 200 of each pair of adjacent teeth 200, measured along a first orthoradial direction A4, varies along a radial direction, for example along the first radial direction A2, such that said distance is greater in an area spaced from the longitudinal axis A1 than in an area close to the longitudinal axis A1. An orthoradial direction, for example the first orthoradial direction A4 shown in [Fig.5], is here a direction perpendicular to a radial direction (the second radial direction A3 in [Fig.5]) and orthogonal to the longitudinal axis A1.

[0064] Here, this means that two adjacent teeth 200 are further apart at the level of the peripheral portion than the central portion.

[0065] In other words, two adjacent teeth 200 move apart with the distance from the longitudinal axis A1.

[0066] More specifically, the distance between the teeth 200 of each pair of adjacent teeth 200 increases linearly as a function of the distance from the longitudinal axis A1.

[0067] In a first variant of this second embodiment, illustrated in [Fig.3], the additional space between two adjacent teeth 200 is advantageously used to wind more conductive wire.

[0068] The distance between two adjacent teeth 200 being smaller at the level of the central portion than of the peripheral portion, it is provided that the winding 300 has a smaller number of layers of wires on a side close 205 to said tooth located close to the longitudinal axis A1 than on an opposite side 206. Here, the side close 205 is the side of the tooth 200 extending opposite the longitudinal axis A1 and the opposite side 206 is the side forming the external periphery of the stator 1.

[0069] Furthermore, since each tooth 200 is higher on the near side 205 than on the opposite side 206, it is intended that the winding 300 extends over a greater height on the near side 205 than on the opposite side 206. The height of the winding 300 is measured parallel to the longitudinal axis AL

[0070] As shown in [Fig. 3], the winding 300 of each tooth 200 here comprises one layer less on the near side 205 than on the opposite side 206. The number of turns surrounding the teeth 200 being the same on the near side 205 and on the opposite side 206, the winding 300 is distributed over a greater height on the near side 205. To facilitate understanding, the turns are not shown when they pass in front of the near side 205 and behind the opposite side 206.

[0071] Here, the winding 300 begins by being wound against the tooth 200 and therefore first forms an internal layer 301 (represented by solid horizontal grooves). The inner layer 301 is solid on the opposite side 206 but leaves gaps on the near side 205. The winding 300 then forms a first upper layer 302 (represented by dotted horizontal grooves) which is solid on the opposite side 206 and which occupies the gaps of the inner layer 301 while leaving new gaps, still on the near side 205. A third upper layer 303 (represented by solid vertical grooves) and a fourth upper layer 304 (represented by dotted vertical grooves) are then wound in the same way except that, on the near side 205, the fourth and last upper layer 304 only occupies the gaps of the third upper layer 303 without creating new gaps.On the near side 205, the winding 300 thus forms only three solid layers.

[0072] Alternatively, the winding of each tooth could comprise at least two more layers on the opposite side 206 than on the near side 205.

[0073] [Fig.4] illustrates one way of making the winding 300 to go from five layers of wire on the opposite side 206 (to the left of [Fig.4]) to four layers of wire on the near side 205 (to the right of [Fig.4]).

[0074] As shown in [Fig.4], the conductive wire forming the winding 300 of one of the teeth 200 comprises: - an initial length 310 (represented by solid vertical grooves) wound so as to produce internal stacks 311, 312, against the tooth 200, of triangular shape and the bases of which extend opposite the tooth 200; and - a terminal length 320 (represented by dotted vertical grooves), adjoining the initial length 310, wound so as to produce external stacks 321, 322 of triangular shape, fitting into the internal stacks 311, 312.

[0075] To reduce the number of layers on the near side 205, the internal stacks 311, 312 leave between them, on the near side 205, interstices in which the apexes of the triangular external stacks 321, 322 are housed. Thus, in a radial plane passing through the tooth 200, the winding 300 has a generally rectangular section on the near side 205 and on the opposite side 206. The two stacks seen in section in [Fig.4] illustrate said sections.

[0076] This way of winding the conductive wire makes it possible to obtain a regular winding 300 in which the free space, that is to say which is located between the wires, is limited.

[0077] In a second variant of this second embodiment, illustrated in [Fig. 5], the additional space between two adjacent teeth 200 is advantageously used to place a cooling duct 400 there. In general, a conventional stator already comprises cooling ducts. However, in this second variant of this second embodiment, the additional space between two adjacent teeth 200 makes it possible to place larger cooling ducts 400.

[0078] Consequently, the cooling ducts 400 of the stator 1 according to the invention make it possible to circulate more cooling liquid, the flow of which is represented by arrows in [Fig.5], and thus to improve the performance of the stator.

[0079] Thus, as shown in [Fig. 5], it is provided that the cooling duct 400 interposed between each pair of adjacent teeth 200 has a width, measured in an orthoradial direction, for example in the first orthoradial direction A4, which varies, along a radial direction, for example the first radial direction A2, such that said width is greater in a peripheral zone 406 of the cooling duct 400 which is spaced from the longitudinal axis A1 than in a central zone 405 of the cooling duct 400 which is close to the longitudinal axis Al.

[0080] Here, the cooling duct 400 is more particularly flared towards the peripheral zone 406. Conversely, the cooling ducts of a conventional stator have a constant width and more generally a radially constant orthoradial section.

[0081] The cooling ducts 400 are, for example, hollow parts made of plastic materials whose external structure is shown diagrammatically in [Fig. 5]. Advantageously, in a variant not shown, the cooling ducts envelop, at least in part, the windings so that the cooling liquid flows in contact with the conductive wire, which makes it possible to improve its cooling.

[0082] Alternatively, the stator can be cooled by an air flow. In this case, it is not necessary to have cooling ducts between the teeth. The additional space between the teeth again allows more air to circulate and therefore better cool the windings.

[0083] Here, as illustrated in [Fig.5], the cooling duct 400 also has a base 410 interposed between the windings 300 carried by two adjacent teeth 200 and the yoke 100. The base 410 has a thickness, measured parallel to the longitudinal axis A1, which decreases from the central zone 405 to the peripheral zone 406.

[0084] Indeed, in the example illustrated in [Fig.5], the windings 300 occupy a constant height around the entire circumference of the teeth 200. Each tooth 200 being higher on the near side 205, the base 410 of the cooling duct 400 makes it possible to take advantage of the space left free by the winding 300 on the near side 205 to improve the cooling of the stator 1.

[0085] Here, the reduction in thickness of the base 410 is complementary to the increase in thickness of the cylinder head 100.

[0086] Here, the cooling ducts 400 are interposed between the windings 300.

[0087] However, it is also possible to arrange the cooling ducts 400 between the teeth 200 and their windings 300. In this case, the cooling duct 400 can be included in the non-magnetic envelope carrying the winding 300. For this, each cooling duct 400 shown in [Fig. 5] can be separated into two cooling ducts, each arranged between a tooth 200 and its winding 300. It is also possible to alternate these arrangements of cooling circuits on either side of the same tooth 200.

[0088] Although they are not shown, cooling ducts, although less voluminous, are also provided in the first variant of this second embodiment and in the first embodiment.

[0089] When the additional space available between the teeth is sufficient, the stator can include both the windings 300 of the first variant of the second embodiment and the cooling ducts 400 of the second variant of the second embodiment.

Claims

Claims

1. Stator for an axial flux electrical machine comprising: - a yoke (100) in the overall shape of a disc centered on a longitudinal axis (Al); - teeth (200) distributed on a main face (101) of the yoke (100) around the longitudinal axis (Al), each tooth (200) carrying a winding (300) of conductive wire, characterized in that the yoke (100) has, between at least one pair of adjacent teeth (200), a thickness (El, E2), measured parallel to the longitudinal axis (Al), which varies along a radial direction (A2) perpendicular to the longitudinal axis (Al) such that the thickness (El, E2) is greater in an area of the yoke (100) spaced from the longitudinal axis (Al) than in an area of the yoke (100) close to the longitudinal axis (Al).

2. Stator according to claim 1, in which the yoke (100) comprises a planar secondary face (102) opposite the main face (101) and in which the distance between the main face (101) and the secondary face (102) increases as a function of the distance from the longitudinal axis (Al).

3. Stator according to claim 1 or 2, in which the main face (101) extends along a frustoconical surface.

4. Stator according to one of claims 1 to 3, wherein at least one tooth (200) has a height (H4, H5), measured parallel to the longitudinal axis (Al), which varies along another radial direction (A3) perpendicular to the longitudinal axis (Al) such that the height (H4, H5) is greater in an area of said tooth (200) close to the longitudinal axis (Al) than in an area of said tooth (200) spaced from the longitudinal axis (Al).

5. Stator according to one of claims 1 to 4, wherein the distance between the teeth (200) of said pair, measured in an orthoradial direction (A4) orthogonal to the longitudinal axis (Al), varies along said radial direction (A2) such that the distance is greater in an area away from the longitudinal axis (Al) than in an area close to the longitudinal axis (Al).

6. Stator according to claim 5, wherein the distance between the teeth (200) of said pair increases as a function of the distance from the longitudinal axis (Al).

7. Stator according to one of claims 1 to 6, wherein the winding (300) of at least one tooth (200) extends over a greater height on a near side (205) of said tooth (200) located near the longitudinal axis (Al) than on an opposite side (206) and / or has a greater number of layers (301, 302, 303, 304) of wires on the opposite side (206) than on the near side (205).

8. Stator according to claim 7, in which the conductive wire forming said winding (300) comprises: - an initial length (310) wound so as to produce internal stacks (311, 312), against said tooth (200), of triangular shapes and whose bases extend opposite said tooth (200); and - a terminal length (320), adjoining the initial length (310), wound so as to produce external stacks (321, 322) of triangular shapes, nesting in the internal stacks (311, 312).

9. Stator according to one of claims 1 to 8, further comprising a cooling duct (400) between the teeth (200) of said pair, the duct (400) having a width, measured in another orthoradial direction orthogonal to the longitudinal axis (Al), which varies along said radial direction (A2) such that said width is greater in an area of the duct (400) spaced from the longitudinal axis (Al) than in an area of the duct (400) close to the longitudinal axis (Al).

10. Stator according to claim 9, wherein said conduit (400) is interposed between one of the teeth (200) of said pair and the winding (300) carried by said tooth (200) or between the windings (300) carried by the teeth (200) of said pair.

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