Rotor for an electric machine

Abstract

Rotor (1) for an electric machine, comprising a first permanent magnet (21) and a ferromagnetic structure (3) with a radially outer outer surface (4), wherein the ferromagnetic structure (3) is designed to enclose at least a part of the first permanent magnet (21), wherein a first intermediate region (81) of the ferromagnetic structure (3) is provided between a transverse side (6) of the first permanent magnet (21) facing away from the outer surface (4) and a cavity (42) of the ferromagnetic structure (3) located radially further inwards compared to the first permanent magnet (21), and wherein the cavity (42) comprises a material with a lower magnetic permeability than the ferromagnetic structure (3), and wherein the cavity (42) extends approximately along the entire transverse side (6) of the first permanent magnet (21).

Description

[0001] The invention relates to a rotor for an electric machine, in particular for an electric motor.

[0002] A variety of possible embodiments of a rotor of an electrical machine, in particular an electric motor, are known from the prior art. In particular, rotors with internal permanent magnets (i.e., internal permanent magnet motors, abbreviated to IPM) are known.

[0003] Electrical machines or rotors with internal permanent magnets (IPM) have both a reluctance torque and a torque which is formed from the magnetic interaction between the poles of a stator of the electrical machine and the internal permanent magnets.

[0004] A potential disadvantage of an electric machine with a rotor containing internal permanent magnets is that the magnetic field of the permanent magnets is present even when the electric machine is under no load (idling). The magnetic field of the permanent magnets, which varies over time relative to the stator, induces a countervoltage (counter-electromotive force; abbreviated to back EMF) in the stator windings, which counteracts the voltage applied to the stator windings. If the induced back EMF exceeds the applied voltage, a constant torque of the electric machine cannot be maintained as the rotor speed increases.

[0005] To reduce the magnetic field of the permanent magnets within the rotors themselves, air pockets can be provided within the rotor of the electric machine according to the prior art. Such air pockets are known, for example, from German patent applications DE 10 2008 059 347 A1 and DE 11 2010 005 756 T5.

[0006] Furthermore, DE 10 2013 223 671 A1 discloses an electric IPM lathe with a rotor in which several sets of permanent magnets are embedded and which has an outer circumference. The rotor is designed with a set of openings for the permanent magnets. The openings include magnet openings designed to receive and enclose the permanent magnets and radially inner flux barriers.

[0007] The present invention is based on the object of improving the rotor of an electrical machine.

[0008] The problem is solved by a rotor with the features of independent claim 1. Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0009] The rotor according to the invention for an electrical machine, in particular for an electric motor, comprises a first permanent magnet and a ferromagnetic structure with a radially outer side, wherein the ferromagnetic structure is designed to enclose at least a portion of the first permanent magnet. According to the invention, a first intermediate region of the ferromagnetic structure is provided between a transverse side of the first permanent magnet facing away from the outer side and a cavity of the ferromagnetic structure located radially further inward than the first permanent magnet, wherein the cavity comprises a material with a lower magnetic permeability than the ferromagnetic structure.

[0010] The axial, radial and azimuthal directions refer to a rotational axis of the rotor and together form a cylindrical coordinate system (rotor coordinate system).

[0011] The rotor according to the invention can generally be used in electrical machines, such as electric motors for electrically powered motor vehicles and / or generators. In the following, an electrical machine is defined as an electrical machine that includes the rotor according to the invention.

[0012] The rotor according to the invention generates a reluctance torque through interaction with a magnetic field of a stator of the electric machine via the ferromagnetic structure. In addition, the magnetic field of the permanent magnets makes a further contribution to the torque of the electric machine, which electric machine comprises the rotor according to the invention.

[0013] According to the invention, a first intermediate region of the ferromagnetic structure is provided radially between the cavity, which has a lower magnetic permeability than the ferromagnetic structure, and the transverse side of the first permanent magnet facing away from the outside of the rotor. In particular, the intermediate region is ferromagnetic.

[0014] If the electric machine, which comprises the rotor according to the invention, is operated at a constant torque (armature setting range) at an operating point of its power curve, the first intermediate region is magnetically saturated by the magnetic field of the stator. Due to the magnetic saturation of the first intermediate region, as well as the hollow with a low magnetic permeability, the inductance L d the d-axis (d-axis inductance) of the rotor. By reducing the inductance L dThe torque of the electric machine is advantageously increased along the d-axis. Generally, it is advantageous to have the smallest possible inductance L. d the d-axis and the largest possible inductance L q the q-axis (q-axis inductance). In other words, the torque of the electric machine is increased when the difference in magnitude between the inductances of the d- and q-axes is increased.

[0015] A further contribution to the torque of the electric machine is made by the magnetic field of the first permanent magnet, which is at least partially enclosed by the ferromagnetic structure. The first permanent magnet can be located, for example, on the outside of the rotor (surface-mounted permanent magnet machine; abbreviated SMPM) or inside the ferromagnetic structure (IPM).

[0016] Preferably, the electric machine comprises a plurality of permanent magnets. The ferromagnetic structure surrounding each permanent magnet is configured according to the first permanent magnet. In other words, the rotor has a plurality of first permanent magnets. The enclosing of the first permanent magnet or the plurality of permanent magnets by the ferromagnetic structure can be achieved through form-fit, material-fit, and / or force-fit.

[0017] The magnetic saturation of the first ferromagnetic intermediate section weakens the magnetic field of the permanent magnets, thus advantageously reducing the back EMF. A reduction in back EMF is particularly beneficial during no-load operation of the electric machine.

[0018] If the back EMF becomes too large, the electrical machine is operated at constant power (field control range). In the field control range, it is reduced by applying a negative d-current i d It is possible to magnetically desaturate the first ferromagnetic intermediate region on the stator windings. Magnetic desaturation of the first intermediate region advantageously increases the magnetic field of the first permanent magnet, allowing the torque of the electric machine to be increased in the field setting range.

[0019] Another advantage of the cavity is that it reduces losses in the ferromagnetic structure, since the cavity comprises a material with a lower magnetic permeability than the ferromagnetic structure and, in particular, is electrically non-conductive. Furthermore, the cavity allows for the guiding or adjustment of the magnetic fields or the overall magnetic field. In other words, the cavity can achieve a directed focusing of the magnetic field lines of the magnetic fields or the overall magnetic field, thus concentrating the magnetic field in an air gap between the rotor and the stator, which can further increase the torque of the electric machine. Additionally, the moment of inertia of the rotor can advantageously be reduced by the cavity, especially by multiple cavities.For this purpose, the cavity contains a material whose density is lower than the density of the ferromagnetic structure.

[0020] Preferably, the cavity comprises air as its substance. In other words, the cavity of the ferromagnetic structure is formed by an air-filled cavity, that is, by an air pocket of the ferromagnetic structure.

[0021] According to an advantageous embodiment of the invention, at least a part of the cavity is arranged on a first lateral side of the first permanent magnet.

[0022] This advantageously further reduces the inductance along the d-axis, thus further increasing the torque of the electric machine. Furthermore, the magnetic field of the first permanent magnet is directed and focused toward the air gap. Furthermore, stray magnetic fields, which can lead to losses and do not contribute to the torque of the electric machine, are advantageously reduced.

[0023] To further improve the rotor, a further cavity is preferably arranged on a second lateral side of the permanent magnet opposite the first lateral side.

[0024] This further improves the efficiency and torque of the electric machine.

[0025] Because the cavity extends, according to the invention, approximately along the entire transverse side of the first permanent magnet, advantageous guidance or conduction of the stator's magnetic field—which, according to the invention, generates the reluctance torque—through the rotor or through the rotor's ferromagnetic structure is enabled. The stator's magnetic field is guided into or out of the ferromagnetic structure essentially along the rotor's q-axis and, by means of the cavity extending approximately along the entire transverse side of the first permanent magnet, is guided around the first permanent magnet within the ferromagnetic structure. The inductance of the q-axis is consequently increased, thus further increasing the torque of the electric machine.

[0026] According to an advantageous embodiment, the rotor comprises a second permanent magnet which is at least partially enclosed by the ferromagnetic structure, wherein the first and second permanent magnets are arranged in a V-shape and a second intermediate area of ​​the ferromagnetic structure is provided azimuthally between the first and second permanent magnets.

[0027] In other words, a V-shaped magnetic pole of the rotor is formed by the V-shaped arrangement of permanent magnets. The magnetizations of the two permanent magnets are conically oriented towards each other, so that the V-shaped arrangement advantageously concentrates, or at least partially focuses, the magnetic field generated by the permanent magnets in the air gap of the electric machine. In other words, the field lines of the permanent magnets' magnetic field are concentrated in the air gap. Furthermore, the V-shaped arrangement advantageously results in a greater width of the magnetic pole, thus further strengthening the magnetic field in the air gap.

[0028] The V-shaped arrangement of the two permanent magnets results particularly from an axial cross-sectional view of the rotor. A V-shaped arrangement of the two permanent magnets is defined, for example, as an arrangement that essentially corresponds to the geometric shape of the letter V in an axial section of the rotor, with the two legs of the letter V being formed by the permanent magnets. In contrast to the geometric shape of the letter V, a direct connection between the legs (first and second permanent magnet) is not provided; instead, a second intermediate section of the ferromagnetic structure lies azimuthally between the first and second permanent magnets. This allows the second intermediate section to be magnetically saturated, thus further reducing the inductance of the d-axis. Advantageously, this further increases the torque of the electric machine.

[0029] Preferably, the second intermediate region is rectangular and has an aspect ratio greater than two.

[0030] As a result, the magnetic saturation of the second intermediate region is already achieved by a relatively weak magnetic field.

[0031] Furthermore, in an advantageous embodiment of the invention, the cavity is L-shaped.

[0032] In other words, the cavity in an axial section of the rotor has approximately the geometric shape of the letter L. Advantageously, the longer leg of the cavity extends along the first transverse side and the shorter leg along the first lateral side of the first permanent magnet.

[0033] According to an advantageous development of the invention, the first ferromagnetic intermediate region is wedge-shaped and / or triangular.

[0034] In an axial section of the rotor, the first ferromagnetic intermediate region has a triangular geometric shape. This advantageously improves the path of the field lines of the magnetic field of the first, second, or a plurality of permanent magnets, particularly adjacent ones. In particular, the radial penetration depth of the magnetic field of the permanent magnets into the ferromagnetic structure is reduced.

[0035] According to an advantageous embodiment of the invention, the first and / or second permanent magnet is designed as a Halbach array.

[0036] One advantage of a Halbach array is that the magnetic field is essentially located in the air gap, which lies radially between the stator and rotor. For example, the Halbach array can be formed using a plurality of individual permanent magnets, so that a special arrangement of the individual permanent magnets weakens the magnetic field in a radially inward direction (inside the rotor), while it is amplified and / or concentrated in the air gap (outside the rotor). By weakening the magnetic field within the rotor, losses that occur due to eddy currents in the rotor or within the ferromagnetic structure are reduced. In addition, the magnetic field amplified and / or concentrated in the air gap provides higher torque for the electric machine and increases the power density.In general, even a conventional iron return path can be dispensed with, which further reduces the moment of inertia of the rotor.

[0037] In state-of-the-art IPMs, the magnetic field pattern in the air gap can be approximately rectangular. The steep edges of the rectangular shape lead to the generation of higher harmonic components. The use of Halbach arrays smooths these steep edges, enabling an approximately sine- or cosine-shaped, and thus spatially harmonic, pattern of the magnetic field in the air gap.

[0038] According to a particularly advantageous embodiment of the invention, the rotor has a rosette-like ferromagnetic structure which is formed by means of a plurality of radially extending columnar ferromagnetic substructures, wherein the columnar substructures are arranged azimuthally evenly distributed around a rotational axis of the rotor, each have a cavity, and at least one further cavity is located between each two adjacent columnar substructures.

[0039] The aforementioned rosette-like design of the ferromagnetic structure is evident in an axial section of the ferromagnetic structure or rotor. The special rosette-like design of the ferromagnetic structure enables a plurality of cavities, thus reducing the rotor's mass moment of inertia. The rotor's permanent magnets are radially fixed by means of the column-like substructures. Furthermore, the rosette-like ferromagnetic structure is comparable in its geometric design to a rose window in a building. The column-like substructures extend from a radially inner region of the rotor to the radially outer side of the rotor. For example, they are arranged azimuthally evenly around a radially inner shaft of the rotor and are attached to the shaft or fixed in a torque-locking manner.

[0040] Furthermore, the numerous configurations of a rosette, which correspond to the configurations of the ferromagnetic structure, can optimize the guidance of the magnetic fields or the overall magnetic field. The rosette-like ferromagnetic structure thus synergistically combines mechanical advantages with electromagnetic ones.

[0041] Further advantages, features, and details of the invention will become apparent from the exemplary embodiments described below and from the drawings. These show: Fig. 1 is a schematic axial sectional view of a rotor of an electrical machine having an annular ferromagnetic structure, wherein a plurality of adjacent permanent magnets are enclosed by means of the structure and the structure has a plurality of cavities; Fig. 2 a schematic axial sectional view of a rotor of an electric machine with a rosette-like ferromagnetic structure; and Fig. 3 A schematic axial sectional view of a rotor segment of a rotor of an electric machine.

[0042] Similar or equivalent elements in the figures may be provided with the same reference symbols.

[0043] The directions axial 100, radial 101 and azimuthal 106 always refer to a rotational axis 100 of a rotor 1 and, as a whole, form a cylindrical coordinate system (rotor coordinate system).

[0044] In Fig. 1 shows a schematic axial sectional view of a rotor 1 of an electrical machine (not shown) with an annular ferromagnetic structure 3. The ferromagnetic structure 3 can be designed as a sheet metal shape and comprises a plurality of azimuthally adjacent permanent magnets 21, 22, wherein a first permanent magnet 21 and a second permanent magnet 22 each form a magnetic pole 24 of the rotor 1. The permanent magnets 21, 22 are partially enclosed by the ferromagnetic structure 3 in a form-fitting, material-fitting, and / or force-fitting manner. Furthermore, the ferromagnetic structure 3 of the rotor 1 has a plurality of cavities 42, which cavities 42 are designed as air pockets 42. The corners and / or edges of the cavities 42 or the air pockets 42 can be rounded to improve mechanical stability. The rotor 1 can be made from a plurality of sheet metal shapes, according to the Fig. 1, can be constructed in axial layers. Furthermore, the rotor 1 can have non-magnetic intermediate layers to reduce eddy currents in the axial direction 100.

[0045] The Fig. The rotor 1 shown in Figure 1 has eight identical magnetic poles 24. The number of magnetic poles 24 can be adapted as required. The permanent magnets 21, 22 of a magnetic pole 24 are almost completely enclosed by the ferromagnetic structure 3 and are arranged in a V-shape in the axial section shown.

[0046] In the following, the first permanent magnet 21 of a magnetic pole 24 is considered as an example.

[0047] A first ferromagnetic intermediate region 81 of the ferromagnetic structure 3 is arranged between a transverse side 6 of the first permanent magnet 21 and the cavity 42. The first ferromagnetic intermediate region 81 is triangular in shape. Furthermore, the transverse side 6 of the first permanent magnet 21 faces away from an outer surface 4 of the rotor 1. In other words, the first ferromagnetic intermediate region 81 lies radially between the radially inner transverse side 6 of the first permanent magnet 21 and the cavity 42. The cavity 42 extends approximately along the entire transverse side 6 of the first permanent magnet 21.

[0048] At least a portion 421 of the cavity 42 is arranged on a first lateral side 5 of the first permanent magnet 21. In other words, the cavity 42 has an L-shape, with the short leg of the L-shape being arranged on the first lateral side 5 directly at the first permanent magnet 21, and the long leg of the L-shape extending approximately over the entire transverse side 6 of the first permanent magnet 21. The short leg of the L-shape extends approximately radially, while the long leg of the L-shape extends substantially azimuthally.

[0049] A further cavity 43 adjoins a second lateral side 7 of the first permanent magnet 21. The cavities 42, 43 are formed as a hollow space in the ferromagnetic structure 3, so that the cavity 42 and the further cavity 43 are filled with air. This improves the moment of inertia of the rotor 1.

[0050] The arrangement of the second permanent magnet 22, as well as the corresponding arrangement and design of the cavities 42, 43, results from that already mentioned for the first permanent magnet 21, if the aforementioned arrangements and designs are mirrored on a d-axis 103 of the rotor 1. For example, the two short legs of the respective L-shaped cavities 42 are azimuthally opposite each other. The d-axis 103 of the rotor 1 extends in the radial direction and runs approximately azimuthally centrally through the magnetic pole 24. It should be noted that the rotor 1 has a plurality of d-axes 103 and q-axes 102, which are assigned to the respective magnetic poles 24.

[0051] Through the cavities 42, 43, a magnetic field (magnetic flux density) with an exemplary field line 104, which is generated by the permanent magnets 21, 22, is guided within the ferromagnetic structure 3 of the rotor 1. In particular, the first ferromagnetic intermediate region 81 is magnetically saturated due to the magnetic field of the first and / or second permanent magnet 21. This magnetic saturation of the first ferromagnetic intermediate region 81 reduces the d-axis inductance of the rotor 1 and consequently increases the torque of the electric machine comprising the rotor 1.

[0052] Due to the ferromagnetic structure 3, the rotor 1, through magnetic or electromagnetic interaction with the magnetic field of a stator (not shown), generates a reluctance torque. The magnetic field associated with the reluctance torque is represented by an exemplary spatial course of a field line 105. The magnetic field of the stator enters and / or exits the ferromagnetic structure 3 essentially along the q-axes 102 of the rotor 1.

[0053] An elongated, rectangular second ferromagnetic intermediate region 82 of the ferromagnetic structure 3 is arranged azimuthally between two adjacent cavities 42. Due to the relatively thin azimuthal configuration of the second intermediate region 82, the inductance of the d-axis 103 of the rotor 1 is further reduced, so that the torque of the electric machine can be further increased in accordance with this reduction.

[0054] If the electrical machine comprising the rotor 1 is operated with constant torque, i.e. within the armature setting range, the first and second ferromagnetic intermediate regions 81, 82 of the ferromagnetic structure 3 are magnetically saturated, so that overall the inductance of the d-axis 103 is reduced compared to the inductance of the q-axis 102. In other words, the Fig. 1, the rotor 1 shown in FIG. 1 increases the difference in magnitude between the inductance of the d-axis 103 and the q-axis 102, so that the torque of the electric machine in the armature setting range is increased.

[0055] If the voltage induced by the magnetic field of the permanent magnets 21, 22 within the stator windings (back EMF) becomes too high, especially during no-load operation, the electric machine will no longer operate with constant torque but with constant power (field control range). Within the field control range, it is advantageous to induce a negative d-current in the stator windings. This weakens the magnetic field of the permanent magnets 21, 22 of the rotor 1. This weakening of the magnetic field of the permanent magnets 21, 22 reduces the back EMF, which is particularly advantageous during no-load operation of the electric machine.

[0056] In operation of the electric machine under load, a further advantage of the illustrated rotor 1 is that, by means of the negative d-current and the resulting reduction or weakening of the magnetic field of the permanent magnets 21, 22, at least the first ferromagnetic intermediate region 81 of the rotor 1 is magnetically desaturated. This makes it possible to increase the torque of the electric machine in the field-setting range, since the contribution of the magnetic field of the permanent magnets 21, 22 to the torque is increased.

[0057] Fig. Figure 2 shows a schematic axial sectional view of a rotor 1 of an electric machine with a rosette-like ferromagnetic structure 3. The rotor 1 has a plurality of permanent magnets 21, 22, with one magnetic pole 24 of the rotor 1 being formed by the first and second permanent magnets 21, 22. Overall, the rotor 1 has Fig. 2 has twelve identical magnetic poles 24. The number of magnetic poles 24 can vary depending on the application.

[0058] The rosette-like ferromagnetic structure 3 of the rotor 1 is formed by a plurality of radially extending column-like ferromagnetic substructures 30. Each of these substructures 30 has a cavity 42.

[0059] Within a magnetic pole 24, the cavity 42 in the illustrated embodiment is triangular in shape, with the radially outer longitudinal side of the triangular cavity 42 lying radially below the permanent magnets 21, 22 and extending azimuthally along the transverse sides 6 of the permanent magnets 21, 22. Furthermore, a first ferromagnetic intermediate region 81 of the ferromagnetic structure 3 lies radially between the cavity 42 and the first and second permanent magnets 21, 22. A second ferromagnetic intermediate region 82 is arranged azimuthally between the first and second permanent magnets 21, 22.

[0060] By means of the uniform azimuthal arrangement of the columnar substructures 30, additional cavities 43 are formed, enabling a rosette-like configuration of the rotor 1. The columnar substructures 30 are designed and arranged in such a way that, in axial section, a pattern resembling a rose window is created. This has a plurality of arches, wherein the arches are arranged azimuthally around a rotational axis 100 of the rotor 1 or the electric machine. In general, a variety of rosette-like configurations of the ferromagnetic structure 3 are conceivable for optimizing the rotor 1, which are adapted to the mechanical loads and electromagnetic requirements.

[0061] The rotor 1 has a circular opening arranged concentrically with the rotational axis 100, which allows the columnar substructures 30 and consequently the rotor 1 as a whole to be attached to a shaft of the electric machine. In this case, a torque-locking attachment or fixation of the rotor 1 to the shaft (not shown) is particularly advantageous.

[0062] In Fig. Figure 3 shows a schematic axial sectional view of a rotor segment 25 of another rotor 1 of an electric machine. The illustrated rotor segment 25 has at least a first permanent magnet 21 and a cavity 42. A second permanent magnet 22, as already illustrated in the previous figures, can be provided. The cavity 42 of the ferromagnetic structure 3 of the rotor segment 25 is designed as an air pocket 42. A first ferromagnetic intermediate region 81 of the ferromagnetic structure 3 is arranged radially between the cavity 42 and a radially inner transverse side 6 of the permanent magnet 21.

[0063] In addition to Fig. 1 and / or Fig. 2 indicates the rotor segment 25 in Fig. 3 has a web 50, which is formed as part of the ferromagnetic structure 3 and divides the cavity 42 azimuthally into two partial areas. The web 50 extends essentially along the radial direction 101. The web 50 can be provided for the mechanical stabilization of the illustrated rotor segment 25. A corresponding web 50 can also be used for the Fig. 1 and / or Fig. 2 rotors 1 shown are provided.

[0064] The rotor 1 shown in the figures enables magnetic flux paths (exemplified by field lines 104, 105) with different magnetic permeabilities, so that the reluctance torque is increased and the inductance of the d-axis 103 is reduced. Furthermore, the magnetic field of the permanent magnets 21, 22 is adapted, controlled, and / or regulated by means of the first intermediate region 81 and by controlling the d- and / or q-current within the stator windings. The d- and / or q-current can be adapted to the required torque, speed, and voltage level of the electrical machine. Furthermore, the mass moment of inertia of the rotor 1 can be reduced, for example, by the rosette-like design of the rotor 1 or the ferromagnetic structure 3, thereby increasing the performance of the electrical machine.Furthermore, the rotor 1 can be manufactured using a variety of known manufacturing processes.

Claims

[1] Rotor (1) for an electrical machine, comprising a first permanent magnet (21) and a ferromagnetic structure (3) with a radially outer side (4), wherein the ferromagnetic structure (3) is designed to enclose at least part of the first permanent magnet (21), wherein a first intermediate region (81) of the ferromagnetic structure (3) is provided between a transverse side (6) of the first permanent magnet (21) facing away from the outer side (4) and a cavity (42) of the ferromagnetic structure (3) that is radially further inward than the first permanent magnet (21), and the cavity (42) comprises a material with a lower magnetic permeability than the ferromagnetic structure (3), wherein the cavity (42) extends approximately along the entire transverse side (6) of the first permanent magnet (21). [2] Rotor (1) according to claim 1, characterized bythat the cavity (42) contains air as a substance. [3] Rotor (1) according to claim 1 or 2, characterized by that at least a part (421) of the cavity (42) is arranged on a first lateral side (5) of the first permanent magnet (21). [4] Rotor (1) according to one of the preceding claims, characterized by that a further cavity (43) is arranged on a second lateral side (7) of the permanent magnet (21) opposite the first lateral side (5). [5] Rotor (1) according to one of the preceding claims, with a second permanent magnet (22) at least partially enclosed by the ferromagnetic structure (3), wherein the first and second permanent magnets (21, 22) are arranged in a V-shape and a second intermediate region (82) of the ferromagnetic structure (3) is provided azimuthally between the first and second permanent magnets (21, 22). [6] Rotor (1) according to claim 5, characterized bythat the second intermediate region (82) is rectangular and has an aspect ratio greater than two. [7] Rotor (1) according to one of the preceding claims, characterized by that the cavity (42) is L-shaped. [8] Rotor (1) according to one of the preceding claims, characterized by that the first ferromagnetic intermediate region (81) is wedge-shaped and / or triangular. [9] Rotor (1) according to one of the preceding claims, characterized by that the first and / or second permanent magnet (21, 22) are designed as a Halbach array. [10] Rotor (1) according to one of the preceding claims, with a rosette-like ferromagnetic structure (3) which is formed by means of a plurality of radially extending columnar ferromagnetic substructures (30), wherein the columnar substructures (30) are arranged azimuthally evenly distributed around an axis of rotation (100) of the rotor (1), each having a cavity (42) and at least one further cavity (43) being located between each two adjacent columnar substructures (30).

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