Electric machine rotor comprising at least one recess with a lug or a groove of rounded profile

Abstract

The invention relates to a rotor and an electric machine. The rotor comprises a rotor body and several pairs of magnetic poles. Each magnetic pole includes at least one flux barrier, and each flux barrier includes at least one recess (2a, 2b, 3, 4a, 4b, 11, 5). Each magnetic pole includes at least one permanent magnet in a recess (2a, 2b, 3, 4a, 4b). Each recess (2a, 2b, 3, 4a, 4b, 11, 5) is formed between two lines (17, 18). Each recess (2a, 2b, 3, 4a, 4b) into which a permanent magnet is inserted has a lug (12, 13, 14, 15, 16) or a groove, which is defined by a rounded profile with a predefined radius directly connected to one of the two lines (17, 18), the permanent magnet having a shape complementary to the lug (12, 13, 14, 15, 16) or the groove. Figure 2 to be published

Description

Title of the invention: Electric machine rotor comprising at least one recess with a lug or groove of rounded profile. Technical field

[0001] The present invention relates to a synchronous-reluctant rotating electric machine (assisted by permanent magnets) or with buried magnets and relates more particularly to the particular architecture of a rotor of such a machine.

[0002] Generally, such an electrical machine comprises a stator and a rotor arranged coaxially one inside the other.

[0003] The rotor is formed of a rotor body with a stack of laminations placed on a rotor shaft. These laminations include housings for permanent magnets and perforations to create flux barriers allowing the magnetic flux from the magnets to be directed radially towards the stator and to promote the creation of a reluctant torque, and to lighten this rotor to reduce the centrifugal forces that the stack of laminations must withstand.

[0004] This rotor is generally housed inside a stator which carries electrical windings to generate a magnetic field to drive the rotor in rotation. Previous technique

[0005] As is better described in particular in patent application WO2020 / 020580, the rotor of a synchronous reluctance machine comprises a plurality of axial recesses which pass through the laminations from one side to the other.

[0006] For the rotor design described in this patent application, a first series of axial recesses, arranged radially one above the other and at a distance from each other, form housings for magnetic flux generators, here permanent magnets in the form of a rectangular bar.

[0007] The other series of recesses consists of perforations in an inclined radial direction, which start from these housings to reach the vicinity of the edge of the sheets, in the vicinity of the air gap.

[0008] The inclined perforations are arranged symmetrically with respect to the magnet housings so as to form, in each case, a geometric figure substantially in the shape of a flattened V, with the flat base formed by the magnet housing and the inclined arms of this V formed by the perforations. This creates flux barriers formed by the perforations. The magnetic flux from the permanent magnets can then only pass through the solid sections between the perforations. These solid sections are made of a ferromagnetic material.

[0009] Patent application WO2022 / 128541 relates to an electric machine with a rotor comprising flux barriers adapted to rectangular-shaped permanent magnets.

[0010] Figure 1 illustrates the rotor of this prior art electrical machine. The rotor 1 consists of a plurality of rolled sheets. Fig. 1 is a partial view of a rotor in cross-section, representing a single pole of the electric machine rotor. The rotor 1 comprises several magnetic poles, and each magnetic pole here includes three flux barriers positioned radially one above the other.

[0011] The first flow barrier, the internal flow barrier (closest to the axis of the rotor 1) includes a central recess 3 and two lateral recesses 2a and 2b.

[0012] The second flow barrier comprises two lateral recesses 4a and 4b and the third flow barrier comprises a central recess 5.

[0013] Rectangular permanent magnets are placed in all the recesses 2a, 2b, 3, 4a, and 4b of the first and second flux barriers. The permanent magnets are guided, positioned, and held in that position in the recesses by means of stops 6a, 6b, 7a, 7b, 8a, and 8b. The stops 6a, 6b, 7a, 7b, 8a, and 8b center the magnet in the recess by bearing against the end faces of the magnets (on each end of the short sides of the rectangular magnet).

[0014] The stops 6a, 6b, 7a, 7b, 8a and 8b are formed by local reductions in the width of the recesses 2a, 2b, 3, 4a, 4b

[0015] Each stop 6a, 6b, 7a, 7b, 8a and 8b thus divides the space of the recesses 2a, 2b, 3, 4a and 4b into three volumes: a central volume located between the two stops of the recess in question, the central volume being occupied by a permanent magnet, and two peripheral volumes 9, 10, on each side of the central volume. The peripheral volumes 9, 10 allow airflow and therefore do not contain permanent magnets.

[0016] This technology is not optimal. Indeed, the presence of these stops in the form of "ears" is cumbersome, has complex shapes, increases the cost of the tool for shaping the rolled sheets, and can create concentrations of mechanical stress that limit the maximum permissible speed. The blocking shape, composed of the ears of the stops 6a, 6b, 7a, 7b, 8a, and 8b and the peripheral volumes 9 and 10, means that part of the flux barrier space is lost, whereas this space could be optimized for the magnetic circuit. Furthermore, this shape affects the geometry and positioning of the magnetic bridges that mechanically hold the sheet, and the magnetic bridges have a significant negative impact on rotor performance. Thus, these shapes limit the machine's performance.

[0017] Furthermore, installing the magnets in the recesses requires specific tooling. Therefore, the recesses are designed to allow the passage of this tooling (which is then removed once the magnets are positioned in the recesses). This tooling also requires precise design and manufacturing, implementation in an industrial environment, and regular verification.

[0018] US patent application 2015 / 137646, which relates to an electric machine rotor, is also known. In this patent application, the permanent magnets are positioned and centered by male studs formed by the rotor body, the permanent magnets having female orifices complementary to the male studs of the rotor body. However, the male studs include a straight portion before terminating in a rounded profile. This straight portion of the studs prevents any free rotational movement between the magnet and the rotor body. Positioning the permanent magnets in the rotor is therefore complicated and risks stressing the permanent magnet and / or the rotor body.

[0019] The technical problem that we propose to solve thus consists of designing a simple and easy-to-use solution for guiding and positioning magnets in the recesses of flux barriers, while increasing the electromagnetic and mechanical performance of the machine and reducing its cost. Summary of the invention

[0020] The invention relates to a rotor for an electric machine comprising: - a rotor body, formed by a stack of laminations, preferably configured to be positioned on a rotor shaft, and - a plurality of pairs of magnetic poles distributed circumferentially on the rotor body, each magnetic pole comprising at least one flux barrier, preferably at least two flux barriers located radially above each other, each flux barrier comprising at least one recess, each magnetic pole comprising at least one permanent magnet in a recess.

[0021] Furthermore, each recess is formed between two lines, each permanent magnet being adapted to be inserted into at least one recess, and each recess in which a permanent magnet is inserted has a lug or a groove, the lug or the groove being defined by a rounded profile with a predefined radius in direct connection with one of said two lines, the permanent magnet having a shape complementary to the lug or the groove.

[0022] Advantageously, each permanent magnet has a non-prismatic or prismatic shape to fit the shape of the recess in which it is inserted.

[0023] Preferably, the predefined radius is between 0.5 and 2 mm, preferably between 0.8 and 1.2 mm.

[0024] According to a variant of the invention, the lug or groove is positioned on the line of the recess closest to the axis of rotation of the rotor.

[0025] Advantageously, the ergot or the groove does not have any flat or straight part.

[0026] Preferably, the lug or the groove is open at an angle between 60° and 150°, preferably between 80° and 120° and even more preferably between 90° and 100°.

[0027] Advantageously, the rotor body includes three or four flow barriers.

[0028] Preferably the first and second flow barriers, from the center outwards, each have three recesses, one of said three recesses being a central recess and the other two being lateral recesses, the third flow barrier having two recesses and the possible fourth flow barrier having two recesses.

[0029] Advantageously, the first barrier comprises three permanent magnets, one in each recess, and the second flux barrier comprises two permanent magnets, one in each lateral recess, and the third and possible fourth flux barriers do not comprise permanent magnets.

[0030] According to one configuration of the invention, the width of the flow barriers can be constant or decreasing from the center to the radial ends.

[0031] The invention also relates to an electrical machine comprising a stator and a rotor as described above, said rotor being housed inside said stator.

[0032] Preferably, said electrical machine is of the synchronous-reluctant electrical machine type. List of figures

[0033] Other features and advantages of the rotor and the electric machine according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. [Fig 1]

[0034] Fig. 1 represents an example of a rotor according to the prior art. [Fig 2]

[0035] Figure [Fig. 2] illustrates an electric machine rotor according to the invention. [Fig 3]

[0036] Fig. 3 illustrates an example of a lug or groove of a rotor recess of an electric machine according to the invention. Description of the implementation methods

[0037] The invention relates to a rotor for an electric machine, in particular an electric machine, for example, of the type with buried magnets and more particularly of the type synchronized-reluctant assisted by permanent magnets. Furthermore, the present invention relates to an electrical machine, preferably of the synchronized-reluctant type, comprising a rotor according to the invention and a stator, the rotor being arranged within the stator coaxially therewith.

[0038] Magnets that are inserted within the rotor itself are called "buried magnets", as opposed to surface magnets which are only arranged on the surface of the rotor and are only separated from the stator by an air gap corresponding to the functional clearance between the stator and the rotor (this clearance being generally called "air gap").

[0039] According to the invention, the rotor for an electric machine comprises: - a rotor body, formed by a stack of laminations, preferably configured to be positioned on a rotor shaft, and - a plurality of pairs of magnetic poles distributed circumferentially on the rotor body.

[0040] Each magnetic pole comprises at least one flux barrier, preferably at least two flux barriers located radially above each other, and each flux barrier comprises at least one recess. In addition, each magnetic pole comprises at least one permanent magnet in a recess.

[0041] The recesses in the flow barriers are axial. In other words, the recesses extend in the axial (longitudinal) direction, that is, along the axis of the rotor, crossing the rotor over its entire axial length.

[0042] Permanent magnets generate a magnetic flux, enabling the rotor to rotate by creating a rotating magnetic field that can also be generated by the stator. Flux barriers guide the magnetic field generated by the rotor and by at least one permanent magnet towards the air gap (the air gap being the space formed between the periphery of the rotor and the stator), so as to limit magnetic flux leakage and increase the performance (in particular torque and power) of the electric machine. A pair of magnetic poles comprises two magnetic poles of opposite polarity.

[0043] According to the invention, each recess is formed between two lines, for example, between an upper line and a lower line. The upper and lower lines define the upper and lower edges of the flow barriers. The terms "upper" and "lower" extend radially with respect to the rotor axis. In other words, the upper line (the upper edge) of a recess is farther from the rotor axis than the lower line (the lower edge) of the same recess.

[0044] The lines may be straight lines or include straight lines, for example for the placement of prismatic magnets.

[0045] Alternatively or additionally, the lines may be curved or comprise curved lines (associated or not with straight lines), by Example for the implementation of non-prismatic magnets. This shape of non-prismatic magnets allows for maximizing the electromagnetic performance of the electrical machine.

[0046] In addition, each permanent magnet is adapted to be inserted into at least one recess: the width of the permanent magnet is substantially equal to the width of the recess.

[0047] Preferably, at least one permanent magnet (preferably several of them) can be adapted to be inserted into several recesses of a magnetic pole of the electric machine, so as to limit the diversity of geometries and tooling. In other words, the rotor can comprise several identical permanent magnets (particularly in terms of shape and dimensions).

[0048] Furthermore, each recess into which a permanent magnet is inserted has a lug or a groove. A "lug" is understood to be a male portion of the rotor body facing the permanent magnet (protruding towards the permanent magnet). Conversely, a "groove" is understood to be a female portion of the rotor body facing away from the magnet. In other words, the lug forms a bump on the rotor body, while the groove forms a recess.

[0049] Advantageously, the lug or the groove can be arranged on the lower line or the upper line of the flow barrier recess.

[0050] According to one embodiment of the invention, each permanent magnet inserted into a recess that has a lug or a groove comprises a complementary shape. In other words, when the recess has a lug, the permanent magnet may include a groove with a shape similar to the lug, and conversely, when the recess has a groove, the permanent magnet may include a lug with a shape similar to the groove. Thus, the permanent magnet is adapted to the recess.

[0051] According to the invention, the lug or groove is defined by a rounded profile with a predefined radius directly connected to one of said two lines, and the permanent magnet has a shape complementary to the lug or groove. In other words, the lug or groove of the recess is formed by an arc of a circle of predefined radius, and the lug or groove has no straight portion. By straight portion, it is understood that the lug or groove has no part extending along a straight line. The lug forms a convex arc of a circle, and the groove forms a concave arc of a circle.

[0052] Thanks to this rounded lug or groove directly connected to the line on which it is mounted, the magnet can be guided into the recess and benefits from a degree of rotational freedom to facilitate its placement: thus, the magnet can be mounted without stressing it. Furthermore, this lug or groove ensures that the magnet remains in position over time.

[0053] This particular shape also allows the entire cross-section of the recess to be used for inserting a permanent magnet: it is no longer necessary to provide air spaces on either side of the permanent magnet. Thus, the electromagnetic performance of the electric machine can be increased, and this configuration allows for easier mechanical optimization. This also makes it possible to reduce the cost of tooling for manufacturing the lamination on an industrial scale.

[0054] According to one configuration of the invention, the grooves or lugs of different recesses or of the same recess can be defined by rounded arc profiles with different predefined center radii. For example, one of the grooves or lugs may have a first predefined radius that is different from a second predefined radius of another groove or lug.

[0055] Advantageously, each permanent magnet has a non-prismatic or prismatic shape to adapt to the shape of the recess in which it is inserted. The non-prismatic shape is particularly suitable when the recess extends between two curved lines. These shapes increase the performance of the electrical machine. The prismatic shape of the magnets allows for a more conventional design and is suitable for recesses extending, in particular, between two straight lines.

[0056] Prismatic or non-prismatic permanent magnets can be produced by machining, for example, or by powder sintering techniques or by injection.

[0057] Advantageously, the predefined radius can be between 0.5 and 2 mm, preferably between 0.8 and 1.2 mm. Such a radius allows both the guiding and the holding of the magnet in position while ensuring easy placement of the permanent magnet in the recess. It therefore offers an excellent compromise.

[0058] According to one configuration of the invention, the lug or groove can be positioned on the line of the recess closest to the axis of rotation of the rotor (on the lower line of the recess).

[0059] Alternatively, the lug or groove can be positioned on the line of the recess furthest from the axis of rotation of the rotor (on the upper line of the recess).

[0060] Preferably, each recess into which a permanent magnet is inserted has a single lug or a single groove. The single lug or groove may be on the upper or lower line, but if one line includes a lug or a groove, the other line of the recess has neither. This is because positioning the magnet is facilitated by maintaining a degree of rotational freedom, which would not be the case if the recess included at least two lugs, at least two grooves, or at least one lug and one groove.

[0061] Advantageously, the lug or groove may not have any flat or straight parts. Indeed, by not having any flat or straight parts, the magnet retains a degree of rotational freedom around the lug or groove to facilitate its insertion into the recess.

[0062] According to one configuration of the invention, the lug or groove can be opened at an angle between 60° and 150°, preferably between 80° and 120°, and even more preferably between 90° and 100°. This opening maintains the degree of rotational freedom to facilitate the placement of the magnet, while ensuring its guidance within the recess and its retention in position. The opening is defined by the opening of the arc of a circle formed by the radius of curvature of the lug or groove.

[0063] According to one embodiment of the invention, the rotor body may include three or four flux barriers. Indeed, the more flux barriers the rotor body includes, the better the magnetic field is guided. The number of three or four barriers offers an excellent compromise between the expected performance and manufacturing complexity.

[0064] Preferably, the first and second flow barriers, from the center outwards, each have three recesses. One of the three recesses in these first and second flow barriers is a central recess: it is positioned on a radial axis of symmetry of the flow barriers, and the central recess is symmetrical on both sides of this radial axis of symmetry. The other two recesses in the first and second flow barriers are lateral (peripheral) recesses, one lateral recess on each side of the central recess. The lateral recesses are symmetrical to each other with respect to the radial axis of symmetry.

[0065] The two lateral recesses are thus positioned and spaced on either side of a central recess.

[0066] For this configuration, the recesses of each internal flow barrier substantially form a U (according to a cross-section to the axis of the rotor, which corresponds to the plane of a sheet constituting the rotor body), the bottom of the U being formed by the central recess, and the opposite segments of the U being formed by the lateral recesses.

[0067] The rotor body laminations can be made of ferromagnetic material so as to guide the magnetic flux created by permanent magnets and optionally the stator winding. The flux barrier recesses can be obtained by perforations in the stacked laminations forming the rotor body, and the magnetic bridges are formed by the lamination itself.

[0068] For this configuration, preferably, the third flow barrier may comprise (or consist of) two recesses (which are two lateral recesses symmetrical to each other with respect to the radial axis of symmetry) and the optional fourth flow barrier may also comprise (or consist of) two recesses (which are two lateral recesses symmetrical to each other with respect to the radial axis of symmetry).

[0069] Such a rotor thus makes it possible to better guide the magnetic field towards the stator and to increase the reluctance torque.

[0070] Advantageously, the first flux barrier may comprise three (and preferably only three) permanent magnets, one in each recess, and the second flux barrier may comprise two (and preferably only two) permanent magnets, one in each lateral recess. Furthermore, the third and optional fourth flux barriers do not comprise permanent magnets. This configuration maximizes the torque and power density of the machine by limiting the number of permanent magnets required. Limiting the number of permanent magnets also reduces industrial constraints on the dimensions of the permanent magnets and lowers manufacturing costs.

[0071] Advantageously, the width of the flux barriers (particularly the recesses in the flux barriers) can decrease from the center to the radial ends. In other words, the width of the various recesses in the different flux barriers decreases from the center to the radial ends of the flux barriers. This configuration maximizes the torque and power density of the electric machine.

[0072] Preferably, the magnets can then have a suitable shape with a decreasing thickness, corresponding to the width of the recesses in which they are inserted, from the center to the outside of the rotor body.

[0073] Alternatively, the width of the flux barriers can be constant from the center to the radial ends, so as to simplify the manufacture of the sheets and permanent magnets for example.

[0074] Preferably, the magnets can then have a suitable shape with a constant thickness, corresponding to the width of the recesses in which they are inserted, from the center to the outside of the rotor body.

[0075] Figure 2 illustrates, schematically and without limitation, a rotor for an electric machine according to the invention. Figure 2 is a partial view of a rotor along a cross-section, which represents a single pole of the electric machine's rotor.

[0076] The rotor has several magnetic poles and each magnetic pole includes at least one flux barrier. Here, the magnetic pole shown includes three flux barriers.

[0077] The first flow barrier, proceeding from the center outwards, comprises a central recess 3 and two lateral recesses 2a and 2b; the second flow barrier, proceeding from the center outwards, comprises two lateral recesses 4a and 4b. and a central recess 11 and the third flow barrier includes two lateral recesses 5.

[0078] The lateral recesses 5 of the third flux barrier do not contain any permanent magnets. The lateral recesses 2a, 2b, 4a, 4b of the first and second flux barriers and the central recess 3 of the first flux barrier contain permanent magnets whose shape is substantially identical to the shape of the recesses in which they are inserted. Thus, there is no loss of volume in the recesses where part of the volume would consist solely of air, thereby generating an electromagnetic loss.

[0079] The recesses shown are formed between lines, an upper line and a lower line. For example, the lateral recess 4a is formed between the lower line 17 and the upper line 18. As shown, the lower line 17 and the upper line 18 are curved lines, but they could be or include straight lines.

[0080] Each recess 2a, 2b, 3, 4a, and 4b in which a permanent magnet is inserted comprises herein one (and only one) lug 12, 13, 14, 15, 16 (alternatively, it could comprise a groove) forming a male portion oriented towards the permanent magnet inside the recess. The lug 12, 13, 14, 15, 16 forms a rounded, arc-shaped portion extending directly from the bottom line and joining directly to the bottom line. The lug 12, 13, 14, 15, 16 therefore has no straight (or planar) portion and consists solely of the rounded, arc-shaped profile of a predetermined radius.

[0081] The lugs 12, 13, 14, 15, 16 are represented on the lower lines of the different recesses 2a, 2b, 3, 4a and 4b but they could just as well be represented on the upper lines of these different recesses.

[0082] When the lugs are replaced by grooves, these form female parts in the opposite direction to the permanent magnet. The groove forms a rounded, arc-shaped part extending directly from the lower line and joining directly to the lower line.

[0083] The throat therefore does not include any straight (or planar) part and consists only of the rounded profile in the form of a circular arc of predefined radius.

[0084] Each permanent magnet has a shape adapted to the shape of the recess in which it is inserted. In particular, each permanent magnet has a shape complementary to the lug 12, 13, 14, 15, 16 or to the groove of the recess. When the recess includes a lug, the permanent magnet then includes a complementary shape in the form of a circular arc groove (or a groove) whose radius is substantially equal to the predefined radius of the lug. When the recess includes a groove, the permanent magnet then includes a complementary shape in the form of arc-shaped protrusion (or lug) whose radius is approximately equal to the predefined radius of the groove.

[0085] Fig. 3 illustrates, schematically and not in a limiting manner, an example of a groove or lug of a rotor recess according to the invention.

[0086] The rotor includes at least one recess in which a permanent magnet is placed. The recess includes a lug (facing the permanent magnet, forming a male part) or a groove (facing away from the permanent magnet, forming a female part) 21. The permanent magnet has a shape complementary to this lug or groove 21.

[0087] The lug or groove 21 is a rounded profile in the shape of a circular arc of predefined radius R, preferably between 0.5 mm and 2 mm, preferably close to 1 mm.

[0088] The rounded arc profile starts from line 20 forming one end of the recess and joins line 20. Line 20 can be an upper or lower line of the recess, it can be straight or curved or include straight and / or curved parts.

[0089] The lug or groove 21 forms a rounded profile in the form of a circular arc of predefined radius R and whose center of this arc corresponds to the point C. The lug or groove 21 is open at an angle 0 between 60° and 150°, preferably between 80° and 120° and even more preferably between 90° and 100°.

Claims

Demands

1. Rotor for an electric machine comprising: - a rotor body, formed by a stack of laminations, preferably configured to be positioned on a rotor shaft, and - a plurality of pairs of magnetic poles distributed circumferentially on the rotor body, each magnetic pole comprising at least one flux barrier, preferably at least two flux barriers located radially above each other, each flux barrier comprising at least one recess (2a, 2b, 3, 4a, 4b, 11, 5), each magnetic pole comprising at least one permanent magnet in a recess (2a, 2b, 3, 4a, 4b), each recess (2a, 2b, 3, 4a, 4b, 11, 5) being formed between two lines (17, 18), each permanent magnet being adapted to be inserted into at least one recess (2a, 2b, 3, 4a, 4b, 11, 5). 4b), characterized in that each recess (2a, 2b, 3, 4a, 4b) in which a permanent magnet is inserted has a single lug (12, 13, 14, 15,16) or a single groove (21), the lug (12, 13, 14, 15, 16) or the groove (21) being defined by a rounded profile with a predefined radius (R) in direct connection with one of said two lines (17, 18, 20), the permanent magnet having a shape complementary to the lug (12, 13, 14, 15, 16) or the groove (21), the lug (12, 13, 14, 15, 16) or the groove (21) being open at an angle between 60° and 150°, the predefined radius (R) being between 0.5 and 2 mm.

2. Rotor according to claim 1, wherein each permanent magnet has a non-prismatic or prismatic shape to fit the shape of the recess (2a, 2b, 3, 4a, 4b) into which it is inserted.

3. Rotor according to any one of the preceding claims, wherein the predefined radius (R) is between 0.8 and 1.2 mm.

4. Rotor according to any one of the preceding claims, wherein the lug (12, 13, 14, 15, 16) or the groove (21) is positioned on the line (17) of the recess closest to the axis of rotation of the rotor.

5. Rotor according to any one of the preceding claims, wherein the lug (12, 13, 14, 15, 16) or the groove (21) does not have any flat or straight part.

6. Rotor according to any one of the preceding claims, wherein the lug (12, 13, 14, 15, 16) or the groove (21) is open at an angle between 80° and 120° and more preferably between 90° and 100°.

7. Rotor according to any one of the preceding claims, wherein the rotor body comprises three or four flow barriers.

8. Rotor according to claim 7, wherein the first and second flow barriers, from the center outwards, each have three recesses, one of said three recesses being a central recess (3, 11) and the other two being lateral recesses (2a, 2b, 4a, 4b), the third flow barrier having two recesses (5) and the optional fourth flow barrier having two recesses.

9. Rotor according to claim 8, wherein the first barrier comprises three permanent magnets, one in each recess (2a, 2b, 3), wherein the second flux barrier comprises two permanent magnets, one in each lateral recess (4a, 4b) and wherein the third and optional fourth flux barriers do not comprise permanent magnets.

10. Rotor according to any one of the preceding claims, wherein the width of the flow barriers is constant or decreasing from the center to the radial ends.

11. An electrical machine comprising a stator and a rotor according to any one of the preceding claims, said rotor being housed inside said stator.

12. Electric machine according to claim 11, wherein said electric machine is of the synchronous-reluctant electric machine type.

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