Permanent magnet rotor comprising asymmetrical magnetic poles and electric machine comprising such a rotor

Abstract

The invention relates to a permanent magnet rotor (4) for an electrical machine (1) intended to be driven in rotation about an axis X, the rotor (4) comprising a plurality of magnetic poles (22) having 2n magnetic poles with n: an integer greater than or equal to 1, said plurality of magnetic poles comprising n first magnetic pole(s) (22) and n second magnetic pole(s) having opposite polarity and arranged alternately about the axis X, the first n magnetic pole(s) (22) comprising a first magnetic assembly (23) having a concave shape which is directed radially outwards, said first magnetic assembly (23) comprising at least two housings (18, 19) and a permanent magnet (14, 15) positioned in each housing (18, 19) and in which said first magnetic assembly (23) is asymmetric with respect to a median radial axis (M) of the first magnetic pole (22). Figure for the abbreviation: 2

Description

Title of the invention: Permanent magnet rotor comprising asymmetric magnetic poles and electrical machine comprising such a rotor. Technical field

[0001] The invention relates to the field of rotating electrical machines and more particularly to synchronous machines equipped with a permanent magnet rotor. Technological background

[0002] Permanent magnet synchronous electric machines are known for their high efficiency. They have become popular because they eliminate the need for commutators and brushes. Permanent magnet synchronous electric machines comprise, on the one hand, a stator with a plurality of teeth carrying coils, supplied with three-phase current, and, on the other hand, a rotor equipped with permanent magnets. The rotor includes a metal body with housings in which the permanent magnets are inserted.

[0003] One of the well-known problems with this type of electrical machine is torque ripple, meaning that the instantaneous torque fluctuates depending on the rotor position. Such torque ripple is likely to generate unwanted noise and vibration.

[0004] In the prior art, to limit torque ripple, it is known to tilt the rotor's magnetic poles relative to the rotor's axis of rotation. The two ends of each magnetic pole, opposite along the rotor's axis, are circumferentially offset, creating a general spiral shape around the rotor's axis. This rotor design technique, which is generally referred to as "skew," has the disadvantage, however, of complicating the rotor manufacturing operations and consequently increasing its production cost. Summary of the invention

[0005] One idea at the heart of the invention is to propose a permanent magnet rotor that limits the amplitude of the torque undulations generated by the electrical machine incorporating it.

[0006] According to one embodiment, the invention provides a permanent magnet rotor for an electrical machine intended to be driven in rotation about an axis X, the rotor comprising a plurality of magnetic poles having 2n magnetic poles with n: an integer greater than or equal to 1, said plurality of magnetic poles comprising n first magnetic pole(s) and n second magnetic pole(s) having opposite polarity and arranged alternately around the axis X, the n first magnetic pole(s) comprising a first magnetic assembly having a concave shape which is directed radially outwards, said first magnetic assembly comprising at least two housings and a permanent magnet positioned in each housing and in which said first magnetic assembly is asymmetric with respect to a median radial axis of the first magnetic pole.

[0007] Thus, thanks to the asymmetry of the first magnetic assembly, the fluctuations of the instantaneous torque delivered by the electric machine are reduced.

[0008] By "concave shape which is directed radially outwards", it is meant that the opening of the concave shape is located radially outwards.

[0009] According to embodiments, such a rotor may include one or more of the following characteristics.

[0010] According to one embodiment, the concave shape can be in the form of a C, V or U.

[0011] According to one embodiment, the first magnetic assembly comprises exactly two housings and two permanent magnets respectively positioned in one and the other of the two housings, the two housings and / or the two permanent magnets being asymmetrical to each other with respect to the median radial axis of the first magnetic pole.

[0012] According to one embodiment, the two permanent magnets of the first magnetic assembly have a rectangular cross-section with a longitudinal axis, the longitudinal axes of each permanent magnet being inclined at angles

[31] and

[32] respectively with respect to the median radial axis M; the absolute difference between

[31] and

[32] being between 2 and 40°. The rectangular cross-section is obtained in a plane perpendicular to the X-axis. Such permanent magnets with a rectangular cross-section are simple to manufacture. Furthermore, such inclinations optimize the concentration of the magnetic flux while providing an asymmetry that yields excellent results in limiting torque fluctuations.

[0013] According to one embodiment, the absolute difference between [31 and [32 is between 10 and 30°.

[0014] According to one embodiment, the angles [31 and [32 are each between 30 and 80° and advantageously between 45 and 70°.

[0015] According to one embodiment, the at least two permanent magnets of the first magnetic assembly have identical shapes. This simplifies the manufacture of the rotor.

[0016] Alternatively, the at least two permanent magnets of the first magnetic assembly have an arcuate section.

[0017] According to one embodiment, the first magnetic pole further comprises a second magnetic assembly which is arranged radially outside the first magnetic assembly. This means that the inner radial end of the second The magnetic assembly is located radially outside the inner radial end of the first magnetic assembly.

[0018] According to one embodiment, the second magnetic assembly has a concave shape which is directed radially outwards.

[0019] According to one embodiment, the first magnetic assembly comprises permanent magnets that are more powerful and larger than those of the second magnetic assembly.

[0020] According to one embodiment, the second magnetic assembly is symmetrical with respect to the median radial axis M.

[0021] According to one embodiment, the second magnetic assembly comprises a single permanent magnet positioned in a housing.

[0022] According to another embodiment, the second magnetic assembly comprises two permanent magnets which are each positioned in a respective housing.

[0023] According to one embodiment, the second magnetic assembly is asymmetric with respect to the median radial axis M.

[0024] According to one embodiment, the second magnetic assembly comprises two housings and two permanent magnets respectively positioned in one and the other of the two housings, the two housings and / or the two permanent magnets being asymmetrical to each other with respect to the median radial axis of the first magnetic pole.

[0025] According to one embodiment, the two permanent magnets of the second magnetic assembly have a rectangular section having a longitudinal axis, the longitudinal axes of each of said permanent magnets being respectively inclined at an angle [33 and an angle [34 with respect to the median radial axis M; an absolute difference between [33 and [34 being between 2 and 40°, preferably between 5 and 20°.

[0026] According to one embodiment, angles [33 and

[34] are each between 50 and 90°.

[0027] According to one embodiment, the median radial axis M passes through the axis of rotation X of the rotor and divides the angle a of the magnetic pole into two equal half-angles, the angle a of the magnetic pole being defined, in a radial plane orthogonal to the axis X, between two straight lines passing through the axis X and respectively through one and the other of the two most extreme parts, in the circumferential direction, of the permanent magnets of said magnetic pole.

[0028] According to one embodiment, each housing has free ends that are unoccupied by their respective permanent magnet. Such free ends form flux barriers that control the passage of magnetic flux into the iron core of the rotor.

[0029] According to one embodiment, the rotor comprises an iron core having a generally cylindrical shape which is connected, in a non-rotating manner, to a rotor shaft, the iron core comprising a plurality of discs, for example made of electrical steel, which are stacked axially against each other, the housings each being formed by cutouts which are made in the discs of the iron core and are arranged axially one after the other.

[0030] According to one embodiment, the n second magnetic pole(s) comprise a first magnetic assembly having a concave shape which is directed radially outwards, said first magnetic assembly comprising at least one housing and a permanent magnet positioned in said housing and in which said first magnetic assembly is asymmetric with respect to a median radial axis of said first magnetic pole.

[0031] According to one embodiment, the first magnetic assembly of the n second magnetic pole(s) comprises two housings and two permanent magnets respectively positioned in one and the other of the two housings, the two housings and / or the two permanent magnets being asymmetrical to each other with respect to the median radial axis of the second magnetic pole.

[0032] According to one embodiment, the permanent magnets are made of ferrite or rare earths chosen from samarium-cobalt and neodymium.

[0033] According to one embodiment, the first n magnetic pole(s) are South poles and the second n magnetic pole(s) are North poles. According to another alternative, the first n magnetic pole(s) are North poles and the second n magnetic pole(s) are South poles.

[0034] According to one embodiment, the invention also provides an electrical machine comprising a rotor with permanent magnets as mentioned above and a stator surrounding said rotor with permanent magnets. Brief description of the figures

[0035] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent from the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings.

[0036] Fig. 1 is a schematic view of a rotating electrical machine.

[0037] Fig. 2 is a partial cross-sectional view along a radial plane of the electric machine of Fig. 1 and illustrating a magnetic pole of the rotor according to one embodiment as well as the corresponding angular sector of the stator.

[0038] Fig. 3 is a partial cross-sectional view along a radial plane of a rotor according to a second embodiment and illustrating a magnetic pole of the rotor.

[0039] Fig. 4 is a partial cross-sectional view along a radial plane of a rotor according to a third embodiment and illustrating a magnetic pole of the rotor.

[0040] Fig. 5 is a partial cross-sectional view along a radial plane of a rotor according to a fourth embodiment and illustrating a magnetic pole of the rotor.

[0041] Fig. 6 is a partial cross-sectional view along a radial plane of a rotor according to a fifth embodiment and illustrating a magnetic pole of the rotor.

[0042] Fig. 7 is a schematic illustration showing the alternation of the magnetic poles of a rotor. Description of the implementation methods

[0043] In the description and claims, the terms "external" and "internal," as well as the orientations "axial" and "radial," will be used to designate, according to the definitions given in the description, elements of the electric machine 1. By convention, the X-axis of rotation of the rotor 4 defines the "axial" orientation. The terms "external" and "internal" are used to define the relative position of one element with respect to another, with reference to the X-axis; an element close to the X-axis is thus described as internal, as opposed to an external element located radially further from the X-axis.

[0044] In relation to figures 1 and 2, an electrical machine 1 is described according to a first embodiment.

[0045] The electric machine 1 is a permanent magnet synchronous machine. It can in particular be used as a motor to provide propulsion for an electric or hybrid vehicle and / or as a generator for such a vehicle.

[0046] As shown in [Fig.1], the electric machine 1 comprises a housing 2 and a stator 3 and a rotor 4 which are housed in the housing 2. The stator 3 is fixed inside the housing 2 and radially surrounds the rotor 4.

[0047] The stator 3 comprises an iron core 5 which carries coils 6, visible in [Fig. 2]. The iron core 5 comprises, for example, several plates, for example of electrical steel, which are axially superimposed to form a laminate. As illustrated in [Fig. 2], the iron core 5 has an external cylindrical portion 7 and a plurality of teeth 8 which project radially inward from the external portion 7. The teeth 8 are spaced from each other by a predetermined interval in the circumferential direction so as to provide slots 9 between the teeth 8. The coils 6 are thus housed in the slots 9 and wound around the teeth 8.

[0048] The electric machine 1 also includes an interconnector, not shown, which allows, on the one hand, the coils 6 to be connected to each other and, on the other hand, to be connected to a control module of the electric machine, not shown, such that an inverter configured to convert direct current (DC) into alternating current (AC) to power the electrical machine 1.

[0049] Returning to [Fig. 1], it can be seen that the rotor 4 is mounted to rotate about an axis of rotation X. More specifically, the rotor 4 comprises an iron core 10 having a generally cylindrical shape which is connected, in a non-rotating manner, to a rotor shaft 11. The iron core 10 of the rotor 4 consists of a plurality of discs, for example of electrical steel, which are stacked axially against each other to form a laminate. The rotor shaft 11 is mounted to rotate about the axis X. To this end, in the embodiment shown, the rotor shaft 11 is guided in rotation on the housing 2 by means of a pair of roller bearings 12, 13, each of which is housed in a recess in the housing 2.

[0050] The rotor 4 is equipped with permanent magnets 14, 15, 16, 17, some of which are illustrated in [Fig. 2]. The permanent magnets 14, 15, 16, 17 are, for example, made of ferrite or rare earth elements, i.e., based on samarium-cobalt or neodymium, for example. The permanent magnets 14, 15, 16, 17 are inserted into recesses 18, 19, 20, 21 of the rotor 4.

[0051] The permanent magnets 14, 15, 16, 17 create 2n magnetic poles 22, 40, distributed around the X-axis, where n is an integer greater than or equal to 1, and preferably between 2 and 5. As illustrated in [Fig. 7], the magnetic poles 22, 40 are arranged alternately around the X-axis, which means that the polarities of adjacent magnetic poles 22, 40 are opposite. This arrangement thus creates an alternating magnetic field around the rotor 4.

[0052] To obtain this alternation of polarity, according to one embodiment, the permanent magnet(s) 14, 15, 16, 17 of the first magnetic poles 22 have a North pole oriented radially outwards while the one or those of the second magnetic poles 40 have a South pole oriented radially outwards.

[0053] According to an alternative embodiment, all the permanent magnets 14, 15, 16, 17 of the rotor 4 have the same outward radial polarity, North or South, so that the areas of the iron core of the rotor 4 that are positioned circumferentially between the permanent magnets 14, 15, 16, 17 are magnetized with opposite polarities. In other words, in such an embodiment, the angular sectors of the rotor 4 that lack permanent magnets form magnetic poles with polarities opposite to those of the permanent magnets 14, 15, 16, 17.

[0054] Figure 2 illustrates one of these magnetic poles 22. The angle α of the magnetic pole 22 is shown in this figure. By convention, the angle α of the magnetic pole 22 is defined, in a radial plane orthogonal to the X-axis, between two straight lines d1 and d2 passing through the X-axis and respectively through one of the two most extreme parts, in the circumferential direction, of the permanent magnets 14, 15, 16, 17 of the pole magnetic 22. We also observe the median radial axis M which passes through the axis of rotation X of the rotor 4 and which divides the angle a of the magnetic pole 22 into two equal half-angles.

[0055] In the illustrated embodiment, the magnetic pole 22 comprises two magnetic assemblies 23, 24 having a concave, V-shaped form, the concavity of which is directed radially outwards. This arrangement allows the magnetic flux to be concentrated radially outwards. The first magnetic assembly 23 comprises the two permanent magnets 14, 15 and their respective housings 18, 19, while the second magnetic assembly 24 comprises the two permanent magnets 16, 17 and their respective housings 20, 21. The housings 18, 19, 20, 21 are not entirely occupied by the permanent magnets 14, 15, 16, 17 and thus have free ends 25, that is to say ends which are unoccupied by the permanent magnets 14, 15, 16, 17. These free ends 25 fulfill reluctance and magnetic barrier functions to control the passage of the magnetic flux in the iron core 10 of the rotor 4.The housings 18, 19, 20, 21 are each formed by cutouts which are made in the discs of the iron core 10 of the rotor 4 and are arranged axially one after the other.

[0056] At least one of the magnetic assemblies 23, 24 is asymmetric with respect to the median radial axis M of the magnetic pole 22. It has been observed that such an asymmetry makes it possible to reduce the fluctuations of the instantaneous torque delivered by the electric machine 1. This asymmetry of the magnetic assembly 23, 24 may be due to an asymmetry of its permanent magnets 14, 15, 16, 17 - for example due to a difference in their intrinsic shape and / or in their inclination with respect to the median radial axis M - and / or to an asymmetry of the housings 18, 19, 20, 21 - for example due to a difference in their shape, for example of their free ends, or in their inclination with respect to the median radial axis M.

[0057] The first magnetic assembly 23 is arranged radially inside the second magnetic assembly 24 and consequently comprises the most powerful and largest permanent magnets 14, 15 of the magnetic pole 22.

[0058] In the embodiment of [Fig. 2], the two permanent magnets 14, 15 of the first magnetic assembly 23 have identical shapes, which limits the variety of permanent magnets used. The two permanent magnets 14, 15 and their respective housings 18, 19 are not arranged symmetrically with respect to the median radial axis M. Each of the permanent magnets 14, 15 has a rectangular cross-section whose longitudinal axis is inclined with respect to the median radial axis M at an angle [31,

[32] which is preferably between 30 and 80° and advantageously between 45 and 70°. Furthermore, the absolute difference between the value The angles [31, [32 of inclination mentioned above are preferably between 2 and 40° and advantageously between 10 and 30°.

[0059] The two permanent magnets 16, 17 of the second magnetic assembly 24 have identical shapes. These two permanent magnets 16, 17, as well as their respective housings 20, 21, are also not arranged symmetrically with respect to the median radial axis M. Each of the permanent magnets 16, 17 has a rectangular cross-section whose longitudinal axis is inclined with respect to the median radial axis M at an angle [33,

[34] , which is preferably between 50 and 90°. Furthermore, the absolute difference between the aforementioned angles [33,

[34] of inclination is preferably between 2 and 40°.

[0060] Figure 3 illustrates a magnetic pole 22 of a stator 3 according to a second embodiment. This embodiment differs in particular from that described above in relation to Figure 2, by the structure of the second magnetic assembly 24. Indeed, in this embodiment, the second magnetic assembly 24 comprises only a single permanent magnet 26 inserted in a housing 27. Furthermore, the permanent magnet 26 of the second magnetic assembly 24 is symmetrical with respect to the radial median axis M.

[0061] Figure 4 illustrates a magnetic pole 22 of a stator 3 according to a third embodiment. This third embodiment differs from that described in relation to Figure 2 by the structure of the first magnetic assembly 23 and the second magnetic assembly 24. In this embodiment, in addition to having different inclinations with respect to the median radial axis M, the two permanent magnets 14, 15 of the first magnetic assembly 23 also do not have an identical shape.

[0062] Furthermore, the second magnetic assembly 24 comprises two permanent magnets 28, 29 which are inserted into respective housings 30, 31 of the rotor 4. The second magnetic assembly 24 is here symmetrical with respect to the median radial axis M, which means that the two permanent magnets 28, 29 as well as their respective housings 30, 31 are symmetrical to each other with respect to the median radial axis M.

[0063] Figure 5 illustrates a magnetic pole 22 of a stator 3 according to a fourth embodiment. In this embodiment, the first magnetic assembly 23 has a structure similar to the first magnetic assemblies 23 shown in Figures 2 and 3. Thus, the two permanent magnets 14, 15 of the first magnetic assembly 23 have identical shapes. Furthermore, the two permanent magnets 14, 15 and their respective housings 18, 19 are arranged asymmetrically with respect to the radial median axis M.

[0064] The second magnetic assembly 24 has a structure similar to that of [Fig. 4]. Thus, the second magnetic assembly 24 is symmetrical by relative to the median radial axis M and includes two permanent magnets 28, 29 which are inserted into respective housings 30, 31 of the rotor 4.

[0065] Figure 6 illustrates a magnetic pole 22 of a stator 3 according to a fifth embodiment. This embodiment differs in particular from those described previously in that the permanent magnets 32, 33, 34, 35 do not have a rectangular cross-section but an arcuate C-shaped cross-section with its concavity directed radially outwards. Consequently, their housings 36, 37, 38, 39 also have an arcuate shape. Furthermore, the two magnetic assemblies 23, 24 are asymmetrical with respect to the median radial axis M of the magnetic pole 22. Thus, the two permanent magnets 32, 33 and their respective housings 36, 37 of the first magnetic assembly 23 are arranged asymmetrically with respect to the median radial axis M. Similarly, the two permanent magnets 34, 35 and their respective housings 38, 39 of the second magnetic assembly 24 are arranged asymmetrically with respect to the median radial axis M.

[0066] If only one magnetic pole 22 of the rotor 4 is described above in relation to Figures 2 to 6, it is advantageous for all magnetic poles of the same polarity to have a similar structure. Furthermore, the asymmetrical nature of the magnetic poles can be applied to all the North magnetic poles, to all the South magnetic poles, or even to both the North and South magnetic poles of the rotor 4.

[0067] Furthermore, Figures 1 to 7 below represent only exemplary embodiments. Many other embodiments not shown are also conceivable. Thus, according to alternative embodiments not shown, each magnetic pole 22 comprises a number of magnetic assemblies 23, 24 other than two, for example, a single magnetic assembly or more than two. In addition, the magnetic assembly or each magnetic assembly 23, 24 may also comprise a number of permanent magnets other than two.

[0068] Furthermore, according to one embodiment, the asymmetrical nature of the magnetic pole(s) 22 of the rotor 4 can be combined with an inclination of the magnetic pole(s) 22 of the rotor 4 with respect to the X axis so that the two ends, opposite along the X axis, of each magnetic pole 22 are circumferentially offset, creating a general spiral shape around the X axis (design technique referred to as "skew").

[0069] Although the invention has been described in connection with several particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

[0070] The use of the verb "comprise", "comprendre" or "include" and its conjugated forms does not exclude the presence of other elements or other steps than those stated in a claim.

[0071] In the claims, any reference sign in parentheses shall not be interpreted as a limitation of the claim.

Claims

Demands

1. A permanent magnet rotor (4) for an electrical machine (1) intended to be driven in rotation about an axis X, the rotor (4) comprising a plurality of magnetic poles (22, 40) having 2n magnetic poles with n: an integer greater than or equal to 1, said plurality of magnetic poles comprising n first magnetic pole(s) (22) and n second magnetic pole(s) (40) having opposite polarities and arranged alternately about the axis X, the first n magnetic pole(s) (22) comprising a first magnetic assembly (23) having a concave shape which is directed radially outwards, said first magnetic assembly (23) comprising at least two housings (18, 19, 36, 37) and a permanent magnet (14, 15, 32, 33) positioned in each housing (18, 19, 36, 37) and in which said first magnetic assembly (23) is asymmetric with respect to a median radial axis (M) of the first magnetic pole (22).

2. Permanent magnet rotor (4) according to claim 1, wherein the first magnetic assembly (23) comprises exactly two housings (18, 19, 36, 37) and two permanent magnets (14, 15, 32, 33) respectively positioned in one or the other of the two housings (18, 19, 36, 37), the two housings (18, 19, 36, 37) and / or the two permanent magnets (14, 15, 32, 33) being asymmetrical to each other with respect to the median radial axis (M) of the first magnetic pole (22).

3. Permanent magnet rotor (4) according to claim 1 or 2, wherein the two permanent magnets (14, 15) of the first magnetic assembly (23) have a rectangular section having a longitudinal axis, the longitudinal axes of each of the two permanent magnets (14, 15) being respectively inclined at an angle [31 and an angle [32] with respect to the median radial axis (M); an absolute difference between [31 and [32] being between 2 and 40°.

4. Permanent magnet rotor (4) according to any one of claims 1 to 3, wherein the at least two permanent magnets (14, 15) of the first magnetic assembly (23) have identical shapes.

5. Permanent magnet rotor (4) according to claim 1 or 2, wherein the two permanent magnets (32, 33) of the first magnetic assembly (23) have an arcuate section.

6. Permanent magnet rotor (4) according to any one of claims 1 to 5, wherein the first magnetic pole (22) further comprises a second magnetic assembly (24) which is arranged radially outside the first magnetic assembly (23).

7. Permanent magnet rotor (4) according to claim 6, wherein the second magnetic assembly (24) is symmetrical with respect to the median radial axis (M).

8. Permanent magnet rotor (4) according to claim 6, wherein the second magnetic assembly (24) is asymmetric with respect to the median radial axis (M).

9. Permanent magnet rotor (4) according to claim 8, wherein the second magnetic assembly (24) comprises two housings (20, 21, 38, 39) and two permanent magnets (16, 17, 34, 35) respectively positioned in one or the other of the two housings (20, 21, 38, 39), the two housings (20, 21, 38, 39) and / or the two permanent magnets (16, 17, 34, 35) being asymmetrical to each other with respect to the median radial axis (M) of the first magnetic pole (22).

10. Permanent magnet rotor (4) according to claim 8 or 9, wherein the two permanent magnets (16, 17) of the second magnetic assembly (24) have a rectangular cross-section having a longitudinal axis, the longitudinal axes of each of said permanent magnets (16, 17) being inclined at an angle [33° and an angle [34° respectively with respect to the median radial axis (M); an absolute difference between [33° and [34° being between 2° and 40°, preferably between 5° and 20°

11. Electric machine (1) comprising a permanent magnet rotor (4) according to any one of claims 1 to 10 and a stator (3) surrounding said permanent magnet rotor (4).

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