FR3041183A1 - ROTATING ELECTRIC MACHINE STATOR WITH SHEETS FIXED BY BUTTONING - Google Patents

Abstract

The invention relates mainly to a rotating electric machine stator, in particular intended for an electric compressor for a motor vehicle, the stator comprising a body (16) comprising: - a cylinder head, - a plurality of teeth distributed angularly on an internal periphery of said cylinder head, each tooth coming from material with said cylinder head, - said stator body (16) being composed of a plurality of sheet sheets (37) superimposed axially on each other, - at least one sheet has on its surface a stud (45) intended to cooperate with a recess (46) of an adjacent sheet (37), characterized in that a ratio between a larger diameter (L7) of said pad and an outer diameter of said stator is between 5 % and 15%, especially between 2% and 10%.

Description

ROTATING ELECTRIC MACHINE STATOR WITH SHEETS

The invention relates to a stator of a rotating electrical machine provided with plates fixed by buttoning. The invention finds a particularly advantageous, but not exclusive, application with electric motor vehicle compressors.

In known manner, the rotating electrical machines comprise a stator and a rotor secured to a shaft. The rotor may be integral with a driving shaft and / or driven and may belong to a rotating electrical machine in the form of an alternator, an electric motor, or a reversible machine that can operate in both modes.

The rotor comprises a body formed by a stack of sheets of sheet metal held in pack form by means of a suitable fastening system. The rotor has poles formed by permanent magnets housed in cavities in the rotor body.

Furthermore, the stator is mounted in a housing configured to rotate the shaft for example by means of bearings. The stator comprises a body consisting of a stack of thin sheets forming a crown-shaped yoke whose inner face is provided with notches open towards the inside to receive phase windings.

In a distributed corrugated type winding, the windings are obtained for example from a continuous wire coated with enamel or from conductive elements in the form of pins connected together by welding. Alternatively, in a "concentric" type winding, also referred to as "concentrated" winding, the phase windings are constituted by closed coils on themselves which are wound around the stator teeth. These windings are polyphase windings connected in star or delta whose outputs are connected to a control electronics.

Rotating electrical machines are known that are coupled to a shaft of an electric compressor. This electric compressor makes it possible to compensate, at least in part, for the loss of power of the reduced-displacement heat engines used on many motor vehicles in order to reduce their consumption and the emissions of polluting particles (so-called "downsizing" principle in English). For this purpose, the electric compressor comprises a turbine disposed on the inlet duct upstream or downstream of the heat engine to allow compression of air to optimize the filling of the cylinders of the engine. The electric machine is activated to drive the turbine in order to minimize the torque response time, in particular during the transient phases during acceleration, or in the automatic restart phase of the engine after a standby ("stop and start" operation in English).

However, given the small dimensions of the electric machine and the high performance required, it is difficult to optimally size the various elements, in particular the sheet metal sheet fastening means of the stator body.

The present invention aims in particular to remedy this difficulty by proposing a rotating electric machine stator, in particular for an electric compressor for a motor vehicle, the stator comprising a body having: - a cylinder head, - a plurality of teeth angularly distributed on a periphery internal of said yoke, each tooth coming from material with said yoke, - said stator body being composed of a plurality of sheets of sheet metal superimposed axially on each other, - at least one sheet has on its surface a stud intended for cooperating with a hollow of an adjacent sheet, characterized in that a ratio between a larger diameter of said pad and an outer diameter of said stator is between 5% and 15%, especially between 2% and 10%.

Such a ratio defined by the invention makes it possible not to disturb the magnetic flux of the stator while guaranteeing good mechanical strength of the sheet package of a stator of reduced dimensions. In addition, such a ratio makes it easier to assemble the package by allowing precise positioning of one sheet relative to the other.

In one embodiment, each sheet metal sheet has at least one face directly in contact with a single face of another sheet.

According to one embodiment, the largest diameter of each pad is between 0.5 and 5mm.

According to one embodiment, a number of pads per sheet is between two and the number of teeth of said stator.

According to one embodiment, on each sheet, pads on are positioned in the middle of each tooth and on the same diameter.

In one embodiment, on a sheet metal sheet, pads are arranged on a first face and recesses are arranged on a second face opposite the first face.

In one embodiment, each recess is axially aligned with a corresponding pad.

According to one embodiment, said stator comprises a coil comprising a plurality of coils, each coil being formed by a wire wound around a tooth.

According to one embodiment, a ratio between a diameter of a conductive portion of said wire and an internal diameter of said stator is between 5 and 10%, especially between 5 and 7%, for example between 5.2% and 6.3%. . This makes it possible to obtain an optimal compromise between the inertia of the electric machine and the filling rate of the notches of the stator.

According to one embodiment, said diameter of said conductive portion of said wire is between 1mm and 2mm.

According to one embodiment, a ratio between a diameter of a conductive portion of said unglazed wire, expressed in mm, and a number of turns of each coil is between 5% and 25%, especially between 10% and 20%. This optimizes the magnetic performance of the electric machine while facilitating the insertion of the winding needle inside the notches to make the coils around the teeth of the stator.

According to one embodiment, each coil is formed by a number of turns between 5 and 20.

In one embodiment, each coil is formed by nine turns.

According to one embodiment, said stator comprises six coils.

According to one embodiment, said winding is of the three-phase type, each phase being formed in particular by two diametrically opposed coils.

In one embodiment, said coils are electrically connected in pairs in parallel.

In one embodiment, said coils are coupled in a triangle. Such a coupling makes it possible to minimize the number of connections to be made.

According to one embodiment, around each tooth, a number of coil turns located on the side of said yoke is greater than a number of turns located on the axis side of said stator.

In one embodiment, a ratio between a smaller notch opening measured between two adjacent tooth legs, and an outer diameter of said stator is between 5% and 25%, especially between 5% and 15%. This optimizes the magnetic performance of the electric machine while facilitating the insertion of the winding needle inside the notches to make the coils around the teeth of the stator.

According to one embodiment, said machine comprises a rotor provided with buried permanent magnets for example four in number.

According to one embodiment, said rotor body has an outer periphery delimited by a cylindrical face of external diameter between 20 mm and 50 mm, in particular between 24 mm and 34 mm, and preferably of the order of 28 mm.

According to one embodiment, said machine has a response time of between 100 ms and 600 ms, in particular between 200 ms and 400 ms, for example being of the order of 250 ms to go from 0 or 5000 to 70,000 revolutions / min.

In one embodiment, plating elements are interposed between the rotor body and each permanent magnet. The invention will be better understood on reading the description which follows and the examination of the figures which accompany it. These figures are given for illustrative but not limiting of the invention.

Figure 1 is a sectional view of an electric compressor comprising a rotary electric machine according to the present invention;

Figure 2 shows a perspective view of the stator of the rotating electrical machine according to the present invention;

Figure 3 is a top view of the single stator of the rotating electrical machine according to the present invention;

Figure 4 is a top view of the stator according to the invention provided with turns for the formation of a coil portion occupying a half-notch;

Fig. 5 shows a partial sectional view illustrating the configuration of a stator tooth according to the present invention;

Figure 6 is a sectional view of a wire used for producing a coil belonging to the stator winding according to the present invention.

FIG. 7 shows an evolution of the filling ratio (01) in percentages as well as the inverse of the inertia of the machine (02) as a function of the ratio between the diameter of a conductive portion of the winding wire and the internal diameter stator;

Figure 8 is a sectional view illustrating an interlocking between the sheet metal sheets of the stator in the case of a button assembly;

Fig. 9 shows a perspective view of the rotor of the rotating electrical machine according to the present invention;

Fig. 10 is a cross-sectional view of the rotor of the rotating electrical machine according to the present invention. i

Identical, similar or similar elements retain the same reference from one figure to another.

FIG. 1 shows an electric compressor 1, comprising a turbine 2 equipped with fins 3 able to suck, via an inlet 4, uncompressed air coming from an air source (not represented) and to repress the compressed air via the outlet 5 after passing through a volute referenced 6. The output 5 may be connected to an intake manifold (not shown) located upstream of the engine to optimize the filling of the cylinders of the engine. In this case, the suction of the air is performed in an axial direction, that is to say along the axis X1 of the turbine 2, and the discharge is carried out in a radial direction perpendicular to the axis X1 of the turbine 2. Alternatively, the suction is radial while the discharge is axial. Alternatively, the suction and the discharge are made in the same direction relative to the axis of the turbine (axial or radial). For this purpose, the turbine 2 is driven by an electric machine 7 mounted inside the housing 8. This electric machine 7 comprises a stator 9, which may be polyphase, surrounding a rotor 10 with the presence of an air gap 11. This stator 9 is mounted in the housing 8 configured to rotate a shaft 12 through bearings 13. The shaft 12 is rotatably connected to the turbine 2 and the rotor 10. The stator 9 is preferably mounted in the housing 8 by hooping.

In order to minimize the inertia of the turbine 2 during an acceleration request from the driver, the electric machine 7 has a short response time of between 100 ms and 600 ms, in particular between 200 ms and 400 ms. , for example being of the order of 250ms to go from 0 or 5000 to 70000 revolutions / min. Preferably, the operating voltage is 12V. Preferably, the electric machine 7 is able to provide a current peak, that is to say a current delivered over a continuous period of less than 3 seconds, between 150 A and 300 A, in particular between 180 A and 250 A .

Alternatively, the electric machine 7 is able to operate in alternator mode, or is a reversible type electric machine.

As can be seen in Figure 2, the stator 9 comprises a body 16 and a coil 17. The stator body 16 has an annular cylindrical shape of axis X and consists of an axial stack of flat sheets. More precisely, the stator body 16 is delimited radially by an inner cylindrical face 21 and by an outer cylindrical face 22. The body 16 is moreover defined axially by end faces 23 and 24.

The body 16 has teeth 27 distributed angularly in a regular manner on an inner circumference of a yoke 28. These teeth 27 delimit notches 29, so that each notch 29 is delimited by two successive teeth 27. The yoke 28 thus corresponds to the solid outer annular portion of the body 16 which extends between the bottom of the notches 29 and the outer periphery of the stator 9.

The notches 29 open axially into the axial end faces 23, 24 of the body 16. The notches 29 are also radially open in the internal cylindrical face of the body 16.

As can be seen in FIGS. 3 and 4, the teeth 27 of the stator 9 are preferably with parallel edges, so that the internal faces facing each other of the notches 29 are inclined. one with respect to the other. The notches 29 are angularly distributed regularly around the X axis.

Preferably, the stator 9 is provided with tooth roots 34 on the free end side of the teeth 27 (see FIG. Each tooth root 34 extends circumferentially on either side of a corresponding tooth 27.

The stator 9 is an unsegmented piece made of laminated sheets of magnetic material. In addition, the teeth 27 are made of material with the yoke 28. Alternatively, the stator 9 may however be segmented, that is to say that it is made from several angular segments assembled together. In this case, the cylinder head 28 radially has a continuity of material along its circumference and radially throughout its thickness. Alternatively, the teeth 27 may be reported relative to the yoke 28 and fixed to the inner periphery of the yoke by a tenon-mortise type system.

Advantageously, a ratio between a radial thickness L1 of the gap 11 and an external diameter L2 of the stator 9 is between 0.1% and 2%, especially between 0.2% and 1%. This ratio makes it possible to maximize the torque developed by this type of machine provided with a stator 9 of small dimensions. The gap 11 is chosen as a function of a thickness L13 of permanent magnets 62 of the rotor 10 (see FIG. Thus, a second ratio between a thickness of the gap 11 and a thickness of magnets L13 is between 0.9 and 0.15.

In addition, in order to optimize the passage of the magnetic flux in the stator 9 while having an effective mechanical strength, a ratio between a thickness L3 of the yoke 28 measured radially and an internal diameter L4 of the stator 9 measured between two teeth 27 diametrically opposed is between 10% and 20%, especially between 12% and 15%, and is preferably about 13%.

In addition, a ratio between the internal diameter L4 and an external diameter L2 of the stator 9 is between 40% and 60%, and is preferably of the order of 51.5%. This optimizes the coil space of the notches 29 and the inertia of the rotor 10.

As can be seen in FIG. 2, the stator body 16 is preferably formed by an axial stack of sheet metal sheets 37 each extending in a radial plane perpendicular to the axis X. This stator body 16 is formed in ferromagnetic material. The sheets 37 are held by fixing means 41 for forming a manipulable and transportable assembly. For this purpose, a plurality of fixing holes 40 are made in the stator body 16 to allow each passage of a fastening means 41 of the sheets of the stator body 16. In this case, the fixing holes 40 are preferably through, that is to say that they open axially on each of the axial ends 23, 24 of the stator body 16, so that it is possible to pass inside each fixing hole 40 a rod 41 provided chine head or not 42 at one of its ends and whose other end or both will be (have) deformed (s) for example by a bouterollage process to ensure the axial retention of the sheet package.

Advantageously, a ratio between a distance L5 between the axis X of the stator 9 and a Z axis of an attachment hole 40 (see FIG. 3) and half of the external diameter L2 of the stator 9 is between 80% and 97%. %, especially between 85% and 95%. This makes it possible to obtain an optimum between a good mechanical strength and the magnetic performance of the electrical machine 7 in which the stator 9 is mounted. The Z axis of each fixing hole 40 is included in a plane of symmetry P d. a corresponding tooth 27. The Z axes of the fixing holes 40 are also preferably positioned on the same circle C (see FIG.

The stator 9 has a number of fixing holes 40 between three and the number of teeth 27, here equal to six. In addition, the fixing holes 40 pass through the yoke 28, in particular by passing only the yoke 28, that is to say without encroaching on the corresponding tooth 27. A ratio between the maximum diameter L6 of each fixing hole 40 and the external diameter L2 of the stator 9 is between 2% and 10%.

Alternatively, the rod 41 has no head 42 and the two ends are then deformed by a method of pegging. As a variant, the fixing holes 40 may have a section of square, rectangular shape, or any other shape adapted to the passage of the fixing means 41.

Alternatively, the sheets may be held together by buttoning, or bonding, or laser welding.

In the embodiment of Figure 8, each sheet 37 has on its surface a stud 45 intended to cooperate with a recess 46 of an adjacent sheet. The last leaf is pierced. A ratio between the largest diameter L7 of the stud 45 and an external diameter L2 of the stator 9 is between 5% and 15%, especially between 2% and 10%. Such a ratio allows a good mechanical strength of the sheet package of such a stator type 9 of reduced dimensions, while limiting the magnetic disturbances related to the presence of the pads 45. In addition, such a ratio makes it easier to manufacture the sheets 37 while ensuring a precise positioning of a sheet 37 relative to the other.

Each sheet of sheet 37 has at least one face directly in contact with a single face of another sheet 37. Preferably, the largest diameter of each pad 45 and included 0.5mm and 5mm and is preferably 3mm. The number of pads 45 per sheet 37 is between 2 and the number of teeth of the stator 9. On a metal sheet 37, the pads 45 are arranged on a first face and the recesses 46 are arranged on a second face opposite to the first face. In addition, each recess 46 is axially aligned with a stud 45 corresponding to an axis referenced A1 in Figure 8. In one embodiment, the pads 45 on the sheet are positioned in the middle of each tooth 27, and on the same diameter for example of the order of 47mm. In a variant, the yoke 28 is solid and radially has a continuity of material along its circumference and radially throughout its thickness.

As can be seen in Figures 2 and 4, to form the winding 17 of the stator 9, a plurality of phase windings are formed by coils 50 wound around the teeth 27 of the stator 9, here six in number. Each coil 50 is formed from a wire 51. This wire 51 shown in section in Figure 6 is provided with a conductive portion 52, made for example of copper or aluminum, covered with an insulating layer 53 , such as enamel.

FIG. 7 shows a change in the filling ratio (curve C1) as well as the inverse of the inertia of the machine (curve C2) as a function of the ratio between the diameter L8 of a conductive portion of said wire 51 and the internal diameter L4 of the stator 9. The ratio is between 5 and 10%, especially between 5 and 7%, for example between 5.2% and 6.3%. Preferably, the ratio is substantially equal to 5.4%, which corresponds to the intersection between the two curves C1 and C2.

The diameter L8 of the conductive portion of the wire 51 is of the order of 1.5 mm. With the enamel layer, the diameter of the wire is 1.602mm. The choice of the diameter of the wire 51 is an important choice to ensure the feasibility of a concentric winding type. Furthermore, the choice of the stator inner diameter L4 is guided by the minimization of the inertia (or the maximization of 1 / inertia which is optimal when this ratio is close to 1), as well as by the feasibility of the winding. Indeed, the greater the inner diameter of the stator 9 increases, the greater the outer rotor diameter increases, the more the inertia increases.

According to the calculation method, the stator can thus have a slot filling rate of the order of: - 50% when calculated according to a first calculation method in which a ratio between the total cumulated area ( in section) copper in the notch with assimilation of the enamel as copper and the total surface of the notch (with deduction of the space occupied by the insulator and assuming that the wire is of section square), or - 73% when calculated using a second method of calculation corresponding to the first method except that the area of the section for the passage of the needle is deducted from the notch section area. winding. The result provided by this second method is a so-called "useful" filling rate.

The table below details the calculation of the filling ratio with the two methods mentioned above: - First method:

- Second method: ____

In addition, preferably, a ratio between a smaller slot opening L9 measured between two adjacent tooth legs 34 (see FIG. 4), and the external diameter L 2 of the stator 9 is between 5% and 25%, in particular between 5% and 15%. This facilitates insertion of the winding needle into the notch 29.

Around each tooth 27, the number of turns 54 located on the side of the yoke 28 is greater than or equal to the number of turns 54 located on the X axis side of the stator 9. It is recalled here that a turn 54 corresponds to a turn of the wire around the tooth 27. In a given notch 29, the portion of the coil 50 filling the notch 29 is formed for example of three layers of turns 54. In each layer, the turns 54 are positioned side by side . Each coil 50 is preferably formed by nine turns 54.

In this case, the winding 17 is of the three-phase type, each phase being in particular made by two diametrically opposed coils 50. The diametrically opposed coils 50 are electrically connected in pairs in parallel. The phases each formed by two coils 50 in parallel are preferably connected in a triangle. This type of winding makes it possible to minimize the number of connections to be made. In addition, it should be noted that at low voltage, the choice of the number of wire and the coupling of the coils 50 is very restrictive, since at a turn 54 it can become impossible to achieve the required performance especially in terms of acceleration of the machine.

In the invention, the configuration with nine turns 54 in triangle makes it possible to fulfill the technical requirements of the compressor whereas a corresponding star coupling would not work since it would be necessary to realize 9 / root (3) = 5.2 turns 54 with a wire diameter equal to 1.5 * root (root (3)) = 1.97mm, which corresponds to a wire too difficult to wind with an infeasible filling rate. On the other hand, if more turns 54 were made, the filling rate would increase, but the winding lane would be lost in such a way that it would no longer be possible to use an unsegmented stator 9.

Alternatively, the coupling could be made in a triangle, coils in series, or star with coils either in series or in parallel.

In order to optimize the magnetic performance of such a winding 17 produced in situ on the stator 9, a ratio between the diameter L8 of the conductive portion 52 of the wire 51, expressed in mm, and a number of turns 54 of each coil 50 between 5% and 25%, especially between 10% and 20%. Thus, for a diameter L8 of the order of 1.5 mm and for 9 turns per coil, the ratio is of the order of 16.7%.

In the particular embodiment of FIG. 3, the protection between the sheet package 16 and the winding wire 51 is provided by an overmoulded insulator 57 on the inner faces of the notches 29. To facilitate the readability of the figure, the overmoulded insulator 57 has been shown only on a portion of the stator body 13. The face of the tooth root 34 turned towards the X axis of the stator 9, that is to say the face of the tooth root 34 in contact with the gap 11 extending along a portion of the cylinder, is devoid of insulation 57. This avoids disturbing the passage of the flow in the gap 11.

Preferably, the overmolded insulation 57 covers the axial end faces of the teeth 27, and / or the axial end faces of the yoke 28. In other words, the overmolded insulation 57 may also cover the axial end faces. 23, 24 of the stator body 16.

Compared with the use of insulating paper as is the case in FIG. 2, such a configuration makes it easier to place the notch insulation, particularly for stators 9 of small diameter.

In an exemplary embodiment, the gap L1 is of the order of 0.3mm. The external diameter L2 of the stator 9 is between 40 mm and 60 mm, and is preferably 52 mm. The internal diameter L4 of the stator 9 is between 15mm and 35mm, in particular between 20mm and 30mm, for example of the order of 26.8mm. Advantageously, the wire 51 comprises a conductive portion 52 of diameter L8 between 1mm and 2mm and is preferably 1.5mm as indicated above; while each coil 50 has a number of turns 54 between 5 and 20, in particular equal to 9. The thickness L3 of the yoke 28 may advantageously be between 2mm and 5mm, and is preferably 3.5mm. In addition, a radial length L10 of each tooth 27 (see Figure 5) is between 5mm and 15mm. The smallest notch opening L9 measured between two adjacent tooth roots 34 is of the order of 4 mm. The fixing holes 40 may have a diameter L6 between 0.6m "tet 3mm, and worth for example 3mm; while the distance L5 between the axis X of the stator 9 and a center of a fixing hole 40 is of the order of 47mm.

On the other hand, the rotational axis rotor Y shown in detail in FIGS. 9 and 10 is permanent magnets. The rotor body 60 comprises a sheet package consisting of an axial stack of sheets. The rotor body 60 can be rotatably connected to the shaft 12 in various ways, for example by force-fitting the splined shaft 12 into the central opening 65 of the rotor 10, or by means of a keyed device.

Preferably, the ratio between the external diameter L2 of the stator 9 and an axial length L11 of the rotor 10 is between 3 and 4, and is preferably 3.25. This ratio makes it possible to reduce the inertia of the rotor 10 and therefore to reduce the time required to reach a high rotational speed corresponding, for example, to an operating speed of an electric compressor. Advantageously, the ratio between the external diameter L12 of the rotor 10 and the length L11 of the rotor 10 is between 1.1 and 1.8, and is for example about 1.6.

In an exemplary embodiment, the rotor 10 has for example an axial length L11 of between 10 mm and 20 mm and is preferably 16 mm, an external diameter L 12 of between 20 mm and 50 mm, especially between 24 mm and 34 mm, and preferably of the order of 26mm, and an internal diameter L13 of the order of 10mm.

The rotor 10 of the buried magnet type 62 comprises a plurality of cavities 61 in each of which is housed at least one permanent magnet 62. The magnets 62 are radially magnetized, that is to say that the two parallel faces 63, 64 each other having an orthoradial orientation are magnetized so as to be able to generate a magnetic flux in a radial orientation with respect to the Y axis.

As is clearly visible in FIG. 10, where the letters N and S respectively correspond to the North and South poles, the magnets 62 located in two consecutive cavities 61 are of alternating polarity.

In this case, the permanent magnets 62 have a rectangular parallelepiped shape whose angles are slightly beveled. The inner and outer faces 63, 64 of each magnet 62 are in this case planar. Alternatively, the outer face 64 of each magnet 62 is curved, while the inner face 63 of the magnet 62 is flat, or vice versa. Alternatively, the two faces 63, 64 are bent in the same direction, so that each magnet 62 generally has a tile shape.

Furthermore, the magnets 62 do not completely fill the cavities 61, so that there are two voids 67 on either side of a given magnet 62 in a orthoradial direction. The volume of air delimited by all the spaces 67 of the rotor makes it possible to reduce the inertia of the rotor 10 and to optimize the magnetic flux.

The magnets 62 are preferably made of rare earth in order to maximize the magnetic power of the machine 7. Alternatively, however, they can be made of ferrite according to the applications and the desired power of the electric machine 7. Alternatively, the magnets 62 can be of different shades to reduce costs.

In addition, plating elements 70 are interposed between the rotor body 60 and each magnet 62, to ensure the maintenance of each permanent magnet 62 inside the corresponding cavity 61. The plating elements 70 are positioned on the Y-axis side of the rotor 10. Alternatively, the plating elements 70 could be positioned on the side of the gap 11 of the electric machine.

Each plating element 70 is constituted by an elastically deformable curved spring blade. In a variant, the plating element 70 consists of a pin, a spiral spring, or a spring mounted compressed by crushing along its height between the rotor body 60 and the permanent magnets 62.

Of course, the foregoing description has been given by way of example only and does not limit the scope of the invention which would not be overcome by replacing the different elements by any other equivalent.

Claims (15)

1. Stator (9) for a rotary electric machine, in particular for an electric compressor (1) for a motor vehicle, the stator (9) comprising a body (16) having: - a cylinder head (28), - a plurality of teeth ( 27) angularly distributed on an inner periphery of said yoke (28), each tooth being integral with said yoke (28), said stator body (16) being composed of a plurality of axially superimposed sheet sheets (37) on one another, - at least one sheet (37) has on its surface a stud (45) intended to cooperate with a recess (46) of an adjacent sheet (37), characterized in that a ratio between a larger diameter (L7) of said pad (45) and an outer diameter (L2) of said stator (9) is between 5% and 15%, especially between 2% and 10%. 2. Stator according to claim 1, characterized in that each sheet metal sheet (37) has at least one face directly in contact with a single face of another sheet. 3. Stator according to claim 1 or 2, characterized in that the largest diameter of each pad (45) is between 0.5 and 5mm. 4. Stator according to any one of claims 1 to 3, characterized in that a number of pads (45) per sheet (37) is between two and the number of teeth of said stator (9). 5. Stator according to any one of claims 1 to 4, characterized in that, on each sheet, pads (45) on are positioned in the middle of each tooth (27) and on the same diameter. 6. Stator according to any one of claims 1 to 5, characterized in that on a sheet metal sheet (37), pads (45) are arranged on a first face and recesses (46) are arranged on a second face. opposite to the first side. 7. Stator according to claim 6, characterized in that each recess is axially aligned with a stud (45) corresponding. 8. Stator according to any one of claims 1 to 7, characterized in that it comprises a coil (17) having a plurality of coils (50), each coil (50) being formed by a wire (51) wound around of a tooth (27). 9. Stator according to claim 8, characterized in that a ratio between a diameter (L8) of a conductive portion of said wire (51) and an inner diameter (L4) of said stator (9) is between 5 and 10 %, especially between 5 and 7%, for example between 5.2% and 6.3%. 10. Stator according to claim 9, characterized in that said diameter (L8) of said conductive portion of said wire (51) is between 1mm and 2mm. 11. Stator according to any one of claims 8 to 10, characterized in that a ratio between a diameter (L8) of a conductive portion of said unglazed wire (51), expressed in mm, and a number of turns ( 54) of each coil (50) is between 5% and 25%, especially between 10% and 20%. 12. Stator according to any one of claims 8 to 11, characterized in that each coil (50) is formed by a number of turns (54) between 5 and 20, for example equal to 9. 13. Stator according to any one of claims 8 to 12, characterized in that it comprises six coils (50). 14. Stator according to any one of claims 8 to 13, characterized in that said coil (17) is of the three-phase type, each phase being formed in particular by two coils (50) diametrically opposed. 15. Stator according to any one of claims 8 to 14, characterized in that said coils (50) are connected electrically in pairs in parallel.