Electric machine stator and method of manufacturing such a stator

Abstract

The invention relates to an electrical machine stator (3), comprising: - a body (10) which comprises a stack of layers of ferromagnetic sheet metal and which forms a base (11) and teeth (12), said teeth extending from said base to a free end and having lateral faces, - associated with each tooth, a winding support (30) made of non-magnetic and electrically insulating material, which extends against a part of the lateral face of the tooth, - around each winding support, a coil (20) of electrically conductive wire, and - at the free end of each tooth, two magnetically permeable edges (40) offering high electrical resistivity, which extend from two opposite sides of the lateral face of the tooth, against the winding support. Figure for abstract: Fig.4

Description

Title of the invention: Stator of an electric machine and method of manufacturing such a stator Technical field of the invention

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

[0002] It relates more particularly to an electrical machine stator and a method of manufacturing such a stator.

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

[0004] An electric machine is an electromechanical device allowing the conversion of electrical energy into mechanical energy and / or vice versa. Electric or hybrid cars are equipped with such electric machines (then commonly called "electric motors") which, when powered by a current source, allow the wheels of the vehicle to be driven.

[0005] An electrical machine comprises a part fixed relative to the vehicle chassis (the stator), and a moving part (the rotor). The movement of the rotor relative to the stator is due to an attraction and / or a repulsion between magnetic fields of the rotor and the stators.

[0006] In the case of an axial flux machine, the magnetic fields are mainly oriented parallel to an axis of rotation of the rotor, while in a radial flux machine, they are mainly oriented radially relative to this axis of rotation.

[0007] A conventional stator of an axial flux electrical machine comprises a generally disc-shaped base, which is centered on the axis of rotation of the rotor, and teeth which are distributed on the face of the base facing the rotor, all around the axis of rotation. These teeth are separated from each other by initially empty notches. Coils of electrically conductive wire are then placed around the teeth, through these notches, so that the circulation of electric currents within these coils generates the magnetic fields allowing the rotor to move.

[0008] Many types of stators are known.

[0009] Typically, it is known to use a stator whose teeth have a uniform section from the base to their free end. This type of stator has the advantage of facilitating the installation of the winding around each tooth. Unfortunately, it is noted that it suffers from defects such that its efficiency is not optimal. Indeed, it has eddy current losses and no-load losses ("iron losses"). "). It is also noted that the gaps between the teeth generate jumps in mechanical torque (i.e. jolts) when the machine is running at no load (without current in the coils).

[0010] For these various reasons, a stator is preferably used whose teeth are equipped, at their free ends, with edges projecting from their lateral faces (which therefore extend cantilevered relative to the teeth).

[0011] These edges, commonly called "isthmuses" or "notch beaks", then partially close the notches, between the free ends of the teeth. Thus they make it possible to overcome the aforementioned drawbacks of stators without such edges.

[0012] Their presence, however, has the disadvantage of complicating the automated winding process of the teeth. It is understood that they hinder the passage of any winding needle of the electric wire.

[0013] It is then known in the literature to start by manufacturing the body of the stator without the edges, to proceed with the winding of the electric wire, then to add to the top of each tooth a cap which overflows from the tooth to form the edges.

[0014] The disadvantage is that these thin caps are quite fragile. The solution currently used then consists of using a sintered material with high magnetic permeability which is compacted while hot and then bonded to the end face of each tooth. This solution remains difficult to implement, however, and is not optimal from a magnetic point of view, in particular because the contact between the cap and the tooth is never perfect. Presentation of the invention

[0015] In order to remedy the aforementioned drawbacks of the state of the art, the present invention proposes to attach the edges to the teeth in a different way.

[0016] More particularly, the invention proposes an electrical machine stator, comprising: - a body which comprises a stack of layers of ferromagnetic sheet metal and which forms a base and teeth, said teeth extending from said base to a free end and having lateral faces, - associated with each tooth, a winding support made of non-magnetic and electrically insulating material, which extends against a part of the lateral face of the tooth, - around each winding support, a coil of electrically conductive wire, and - at the free end of each tooth, two magnetically permeable edges offering high electrical resistivity, which extend from two opposite sides of the lateral face of the tooth, against the winding support.

[0017] The invention also proposes a method of manufacturing such a stator, comprising steps of: - stacking of layers of ferromagnetic sheet metal electrically insulated from each other to produce a body comprising a base and teeth, said teeth extending from said base to a free end and having lateral faces, - positioning of a winding support made of non-magnetic and electrically insulating material, against a part of the lateral face of each tooth, - placing a coil of electrically conductive wire around each winding support (said positioning and placing steps being carried out in any order), and - attachment to the free end of each tooth of two magnetically permeable and electrically insulating edges, so that they extend from two opposite sides of the lateral face of the tooth, against the winding support.

[0018] Thus, thanks to the invention, the edges extend exclusively on the sides of the tooth. The latter, which is made of the most magnetically optimal material (in layers of sheets), can thus extend as close as possible to the rotor.

[0019] On the contrary, the edges are made of a material offering high electrical resistivity, which makes it possible to avoid any electrical interaction between the free ends of the different teeth. On the other hand, they are magnetically permeable, which allows them to reduce as much as possible the aforementioned phenomenon of jolts when the stator is rotating at no load.

[0020] The manufacture of these edges also remains simple and does not disrupt the stator manufacturing process.

[0021] Preferably, each winding support delimits with the tooth with which it is associated, two hollow cavities relative to the free end of the tooth, in which the two edges extend.

[0022] Thus, the flanges are manufactured simply, using the winding support as a mold so as to ensure that once polymerized, the flanges have exactly the desired shape. This aspect makes it possible to ensure that not only is the geometry of the flanges exactly that sought, but also that their positions relative to the teeth are very precise.

[0023] Other advantageous and non-limiting characteristics of the stator according to the invention, taken individually or in all technically possible combinations, are the following: - each rim has a face which extends in line with the free end of the tooth from which this rim extends; - each rim comprises a thermosetting or thermoplastic material loaded with a powder of ferromagnetic material; - each rim comprises a thermosetting or thermoplastic material loaded with a powder consisting of fine grains of ferromagnetic material covered with a thin layer of electrical insulation; - said base has an annular shape around a main axis, said teeth rising from a face of said base, parallel to said main axis.

[0024] The invention also proposes an electrical machine comprising at least one rotor and at least one stator as mentioned above.

[0025] Other advantageous and non-limiting characteristics of the manufacturing method according to the invention, taken individually or in all technically possible combinations, are the following: - each edge is molded or cast in a cavity delimited at least in part by the winding support and then is polymerized; - each flange is molded or cast onto the winding support when the winding support is already positioned against the tooth; - each coil is wound around each winding support at a distance from the body, and each winding support equipped with a coil is then positioned and fixed around each tooth, preferably by gluing.

[0026] 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

[0027] 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.

[0028] In the attached drawings:

[0029] [Fig-1] is a schematic perspective view of part of an electrical machine in accordance with the invention, comprising two stators;

[0030] [Fig.2] is a schematic perspective view of the body of one of the stators of the [Fig.l];

[0031] [Fig.3] is a schematic perspective view of a winding support adapted to be assembled to the stator body of [Fig.2];

[0032] [Fig.4] is a schematic sectional view of one of the stators of [Fig.l], in which a single tooth of the stator body of [Fig.2] is illustrated;

[0033] [Fig.5] is a schematic sectional view of an alternative embodiment of the stator according to the invention;

[0034] [Fig.6] is a schematic perspective view of a tool for manufacturing of the stators of [Fig.l], in which one end of a tooth of the stator body of [Fig.2] is illustrated.

[0035] In [Fig.l], a part of an electric machine 1 is partially represented. This is an axial flux electric machine, in this case a motor for propelling an electric vehicle (car, truck, bus, boat, plane, etc.).

[0036] Such an electrical machine 1 comprises a casing (not shown) which houses at least one rotor 2 and at least one stator 3. In practice, it comprises here a single rotor 2 located between two identical stators 3, only one of which will be described below.

[0037] The rotor 2 comprises for example an annular-shaped yoke which is fixed to a rotating shaft (not shown) and which houses a plurality of magnetic pole elements such as permanent magnets. These magnetic pole elements are arranged side by side in order to form together a sort of ring. They are preferably made up of small assembled permanent magnets. This rotor 2 not being the subject of the present invention itself, it will not be described here in more detail.

[0038] The stator 3 firstly comprises an annular body 10 centered on a main axis A1, which is in practice the axis of rotation of the rotor 2.

[0039] This annular body 10 has a magnetic circuit function. It is preferably made in one piece.

[0040] As shown in [Fig.2], it comprises a base 11 and teeth 12.

[0041] The base 11 essentially has the shape of a thick disc centered on the main axis AL. It delimits a circular central opening allowing in particular the passage of the rotor shaft. It thus has, in the example shown, the shape of a flattened ring, with an internal face and an external face which are cylindrical in revolution around the main axis Al, and two main faces which are flat and orthogonal to this axis.

[0042] Alternatively, the base could have a different shape. Typically, it could have a polygonal shape, for example with as many sides as it has teeth.

[0043] As [Fig. 2] also shows, the teeth 12 all rise from one of the two main faces of the base 11, along an axis parallel to the main axis AL. Each tooth 12 thus has an end by which it is attached to the base 11 and an opposite free end. As a result, each tooth 12 has, at its free end, a distal face 13, and, all around this distal face, a lateral face.

[0044] Preferably, the distal faces 13 of the teeth extend orthogonally to the main axis A1, at the same height along this axis, so as to be able to be placed as close as possible to the rotor 2 and thus optimize the efficiency of the electrical machine 1.

[0045] Here, each tooth 12 has a plane of radial symmetry, that is to say a plane of symmetry containing the main axis A1.

[0046] More precisely, each tooth 12 has in the illustrated example a shape of a right prism, of trapezoidal section (here isosceles trapezoidal) in a plane orthogonal to the main axis A1.

[0047] The lateral face of each tooth thus has four sides, namely: - an inner side (facing the main axis Al) which can be flat or curved around this axis, - an outer side which can also be flat or curved around this axis, and - two flanks which are flat, except possibly at their junctions with the base 11.

[0048] As a variant, the teeth could have other shapes. However, very preferably, whatever this shape, each tooth 12 will be profiled along the main axis Al (the shape of its section in a plane orthogonal to the main axis Al not varying over the entire height of the tooth, except possibly at its junction with the base 11).

[0049] The teeth are separated two by two by a space hereinafter called “notch 14”.

[0050] In the context of the invention, the base 11 and the teeth 12 are formed from a stack of layers of sheet metal made of ferromagnetic material.

[0051] Preferably, the layers of sheets are stacked radially on top of each other. Here they have a thickness of the order of 0.2 mm to 0.3 mm.

[0052] Different methods could be envisaged in this regard.

[0053] For example, a plurality of sheet metal sections could be cut, for example by punching, then stacked, rolled, and securely assembled.

[0054] But preferably, the base 11 and the teeth 12 are manufactured in one piece by winding around the main axis A1 a single metal sheet cut into notches. The sheet is thus wound in a spiral and the cut notches have widths which vary so that, once the sheet is wound, the annular body 10 has the shape described above and shown in [Fig.2].

[0055] The ferromagnetic sheet used in this regard may, for example, be made of non-grain-oriented magnetic steel. Alternatively, it may also be made of grain-oriented magnetic steel.

[0056] The stator 3 further comprises coils 20 of conductive electrical wires ([Fig.4]) placed around the teeth 12 and allowing, when an electric current flows through this wire, to form a magnetic field capable of forcing the rotor 2 to turn.

[0057] The electrically conductive wire could be wound around these teeth in situ. In this event, a polymeric winding support will be placed or overmolded on each tooth before the electrical wire is wound, to form an electrical insulator between the coil and the tooth.

[0058] But preferably, the coils 20 will be produced ex situ, that is to say at a distance from the annular body 10.

[0059] The winding support 30 therefore has an architecture enabling it to support the coil on its own, and then to be threaded with the coil that it carries onto the tooth 12 by a sliding movement parallel to the main axis A1.

[0060] In [Fig. 3], such a winding support 30 is shown.

[0061] This winding support 30 forms an envelope made of non-magnetic and electrically insulating material, for example made of polymer material (here made of plastic material). It is shaped to match the shape of the tooth over part of its height from the base 11.

[0062] In this case, it comprises a frame 31 formed of four sides adapted to be applied against the four sides of the lateral face of the corresponding tooth 12. The external faces of these four sides are here grooved so as to facilitate the regular winding of the conductive electric wire.

[0063] This frame 31 is bordered, projecting from the external faces of its four sides, by two peripheral sidewalks which are here respectively located at its two ends. Thus, on the side of its proximal end, the frame 31 is bordered by a proximal sidewalk 34 adapted to be placed at the bottom of the two notches 14 located on either side of the tooth 12. On the side of its distal end, it is bordered by a distal sidewalk 32 adapted to be placed in the mouths of these two notches 14.

[0064] In the following, the term “proximal” will be used to designate the side of any element facing the bottom of the notches 14, while the term “distal” will designate the opposite side.

[0065] As shown in [Fig.3], the winding support 30 therefore has a contour closed, allowing it to extend all the way around tooth 12.

[0066] Alternatively, it could have a different shape. Typically, it could be split along its entire height. In another example, the winding supports could all be connected to each other so as to form a single, single-piece part.

[0067] However, to the extent that the coils 20 are produced ex situ, the shape described above remains preferred since it will facilitate the winding of the electric wire and it will allow the winding supports 30 to resist the compressive stresses exerted by the electric wire when it is wound around these supports.

[0068] Since the method of winding this electric wire does not form the heart of the invention, it will not be described here. It can only be specified that the electric wire used will be varnished so that the different strands of electric wire in contact are electrically insulated from each other. Furthermore, as shown in [Fig. 4], the winding will preferably be carried out layer after layer and in a staggered manner, so as to maximize the density of electric wire in the notches 14 of the annular body 10.

[0069] The assembly formed by the winding support 30 and its coil 20 can then be engaged on the tooth 12, which will not pose any difficulty since the tooth 12 is profiled over its entire height (its section has a constant shape over its entire height). The different coils can then be electrically connected to each other.

[0070] It is then planned to attach two lateral edges 40 to the free end of each tooth 12.

[0071] Thus, as shown in [Fig.4], once the stator is assembled, each tooth 12 is equipped with a pair of lateral flanges 40 bordering its free end.

[0072] According to the invention, each of the two lateral edges 40 extends from one of the flanks of the tooth 12, towards the neighboring tooth, entirely in the notch 14.

[0073] Each lateral edge 40 extends over the entire length of the tooth (radially relative to the main axis A1).

[0074] It has a distal face 41 which extends in the same plane as the distal face 13 of the tooth 12, so as not to project beyond this face, so that it does not form an obstacle to the positioning of the free ends of the teeth 12 as close as possible to the rotor 2.

[0075] As shown in Figures 4 and 5, these edges can have various shapes.

[0076] In the embodiment illustrated in [Fig. 4], each lateral edge 40 tapers from the flank of the tooth 12 towards the neighboring tooth. Thus, each lateral edge 40 has in section (in an orthoradial plane parallel to the main axis A1) a triangular section, with a proximal face 42 inclined relative to the distal face 4L

[0077] In the embodiment illustrated in [Fig. 5], each lateral rim 40 has a parallelepiped shape, with a constant thickness. Thus, each rim has a rectangular cross-section in cross-section, with a proximal face parallel to the distal face.

[0078] Other forms would of course be possible.

[0079] As shown in these figures 4 and 5, the two lateral edges 40 fill cavities 33 provided in hollows in the distal sidewall 32 of the winding support 30 which, as will be explained below, facilitates their manufacture.

[0080] In practice, each winding support 30 has an end which extends in the plane of the distal face 13 of the tooth 12. The cavity 33 then extends in a hollow relative to this end. It preferably opens towards the inside (tooth side) and opposite the base 11.

[0081] Thus, the lateral edges 40 cast or injected into the cavities 33 are in contact with the tooth 12. The manufacturing method used also ensures perfect physical contact, and therefore high magnetic permeability.

[0082] These lateral edges 40 are here made of a material different from that of the tooth 12, and more precisely of a magnetically permeable material (in order to improve the coupling between the rotor and the stator while reducing the fluctuations of the magnetic field in the air gap and therefore, reducing the torque oscillations) and electrically insulating (in order to reduce the losses by eddy current).

[0083] “Magnetically permeable” means that the relative value qr of its magnetic permeability is greater than 50 and typically greater than 100 depending on the iron powder concentration.

[0084] On the contrary, a “non-magnetic” material such as that used to manufacture the winding support 30 has a relative magnetic permeability value qr of order 1.

[0085] “Electrically insulating” or “high electrical resistivity” means that the resistivity of the material used is greater than at least 10,000 times that of copper and typically greater than 50,000 times that of copper at 25°C.

[0086] By way of example, the lateral edges 40 may comprise a matrix made of polymer material (here plastic) and ferromagnetic metal particles, for example made of iron, electrically insulated from each other and embedded in the matrix. Insulated from each other by an insulating layer, the metal particles thus conduct the magnetic flux but do not conduct the electric currents that can circulate in the teeth.

[0087] Here, the material preferably used is called SMC (from the English "Soft Magnetic Composite"). It is a powder consisting of fine iron grains covered with a thin layer of electrical insulation, agglomerated in a binder made of polymer material.

[0088] This polymer material will preferably be of the thermosetting type. However, as a variant, a thermoplastic material could be used. However, in this eventuality, the material will be chosen to retain its hardness regardless of the normal operating temperature of the electrical machine.

[0089] Alternatively, another material, for example of the ferrite type, could be used to manufacture the edges.

[0090] The manufacture of the stator will therefore be carried out in several successive stages which can now be described.

[0091] The first step consists of manufacturing the annular body 10 by rolling up the ferromagnetic sheet and then welding it judiciously, so that it forms a single non-unrollable block.

[0092] The second step consists of manufacturing the winding supports 30, then winding the electric wire around these supports before attaching the assembly to the teeth 12 of the annular body 10. The supports are preferably, at this step, glued to the teeth. The different coils of electric wire can be electrically connected to each other.

[0093] The third step consists of bringing the lateral edges 40 to the ends of the teeth 12.

[0094] For this, various technical solutions are possible.

[0095] Typically, the annular body 10 - winding supports 30 - coils 20 assembly could be placed in a molding apparatus, in order to inject the SMC material into the cavities 33 of the winding supports 30, under pressure.

[0096] However, here, an apparatus 90 will be used as shown in [Fig.5], comprising a reservoir of SMC in the liquid state, a nozzle 91 for injecting SMC, and means for controlling the flow rate of SMC leaving the nozzle.

[0097] The SMC is then poured into the cavities 33 formed by the winding supports 30, so that it fills these cavities 33 but does not protrude (a scraper may possibly be used for this purpose).

[0098] The SMC is then polymerized, here by baking, so as to harden and rigidly attach to the side wall of the teeth 12 and to the winding supports 30.

[0099] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

[0100] Typically, it will be applicable to the stator of a radial flux machine.

[0101] According to a (non-preferred) variant of the invention, the edges may extend slightly outward (or inward) relative to the free ends of the teeth. In this eventuality, the SMC may cover the distal faces of the teeth.

[0102] According to another (non-preferred) variant of the invention, the edges may extend over the distal sidewalks of the winding supports if the latter do not delimit cavities to accommodate them.

[0103] As a further alternative, the flanges could be molded or cast onto the winding supports before the latter are attached to the teeth. Then, when they are placed on the teeth, they will be glued to them. According to this alternative, the flanges could even form an upper part of the winding supports shown in the figures (in other words, the polymer winding supports could be devoid of a distal sidewalk, the latter being formed by the flanges).

Claims

Claims

1. Stator (3) of an electrical machine (1), comprising: - a body (10) which comprises a stack of layers of ferromagnetic sheet metal and which forms a base (11) and teeth (12), said teeth (12) extending from said base (11) to a free end and having lateral faces, - associated with each tooth (12), a winding support (30) made of non-magnetic and electrically insulating material, which extends against a portion of the lateral face of the tooth (12), - around each winding support (30), a coil (20) of electrically conductive wire, and - at the free end of each tooth (12), two magnetically permeable rims (40) offering an electrical resistivity greater than at least 10,000 times that of copper, which extend from two opposite sides of the lateral face of the tooth (12), against the winding support (30).

2. Stator (3) according to claim 1, in which each winding support (30) delimits with the tooth (12) with which it is associated, two cavities (33) hollow relative to the free end of the tooth (12), in which the two rims (40) extend.

3. Stator (3) according to claim 2, in which each rim (40) has a face (41) which extends in the extension of the free end of the tooth (12) from which this rim (40) extends.

4. Stator (3) according to claim 2 or 3, in which each flange (40) comprises a thermosetting or thermoplastic material filled with a powder consisting of fine grains of ferromagnetic material covered with a thin layer of electrical insulation.

5. Stator (3) according to one of claims 1 to 4, in which said base (11) has an annular shape around a main axis (Al), said teeth (12) rising from a face of said base (11), parallel to said main axis (Al).

6. Electrical machine (1) comprising at least one rotor (2) and at least one stator (3) according to one of claims 1 to 5.

7. Method of manufacturing a stator (3) of an electrical machine (1), comprising steps of: - stacking of layers of ferromagnetic sheet electrically insulated from each other to produce a body (10) comprising a base (11) and teeth (12), said teeth (12) extending from said base (11) to a free end and having lateral faces, - positioning of a winding support (30) made of non-magnetic and electrically insulating material, against a part of the lateral face of each tooth (12), - placing of a coil (20) of electrically conductive wire around each winding support (30), said positioning and placing steps being implemented in any order, and - adding to the free end of each tooth (12) two magnetically permeable rims (40) offering an electrical resistivity greater than at least 10,000 times that of copper, so that they extend from two opposite sides of the lateral face of the tooth (12), against the winding support (30).

8. Manufacturing method according to claim 7, in which each rim (40) is molded or cast in a cavity (33) delimited at least in part by the winding support (30) and then is polymerized.

9. A manufacturing method according to claim 7 or 8, wherein each flange (40) is molded or cast onto the winding support (30) when the winding support (30) is already positioned against the tooth (12).

10. Manufacturing method according to one of claims 7 to 9, in which each coil (20) is wound around each winding support (30) at a distance from the body (10), and each winding support (30) equipped with a coil (20) is then positioned and fixed around each tooth (12), preferably by gluing.

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