Axial flux machines with reduced eddy current losses

Abstract

The present invention relates to an axial flux machine (1), having a stator (2) extending along a central axis (100), and at least one rotor (3) arranged next to the stator (2) in relation to the central axis (100), and comprises a return disc (4), on which magnets (5a), in particular permanent magnets, are arranged to form a plurality of rotor poles, wherein one of the two end faces (7a) of the return disc (4) faces the stator (2) and forms an air gap side, characterised in that the air gap side of the return disc (4) is grooved at least in sections or is designed with increased resistance on the surface in order to suppress eddy currents.

Description

[0001] Description

[0002] title

[0003] Axial flux machines with reduced eddy current losses

[0004] State of the art

[0005] The present invention relates to an axial flux machine. The axial flux machine exhibits reduced eddy currents and thus improved efficiency.

[0006] Axial flux machines are known from the prior art. Such machines can be designed with a centrally located stator and rotors arranged axially adjacent on either side. The stator is constructed, for example, with single-tooth windings. In these machines, the rotors consist of solid steel plates, which serve as a magnetic return path and also ensure the mechanical strength of the rotor. Magnets are attached to the surface, which create the field in the machine.

[0007] Disclosure of the invention

[0008] The axial flux machine according to the invention exhibits lower losses because eddy currents are reduced. This allows operation at higher speeds, while reliably cooling the machine is possible due to the minimized losses.

[0009] The axial flux machine has a stator and at least one rotor. The stator extends along a central axis, with the rotor arranged next to the stator with respect to the central axis. Thus, the rotor also extends along the central axis. The rotor also has a return plate. Magnets are arranged on the return plate to form several rotor poles. The magnets are, in particular, permanent magnets. The magnets can preferably be surface magnets or buried magnets. The magnets are particularly advantageously glued to the return plate and can additionally be supported by a bandage.

[0010] One of the two end faces of the return plate faces the stator and forms an air gap side. This air gap side of the return plate is grooved or has a surface with increased resistance, at least in sections, particularly at least in the pole sections of the rotor poles, to suppress eddy currents.

[0011] The grooving or increased electrical resistance impedes the formation of eddy currents. Such eddy currents originate from flux flux fluxes or air gap harmonics that do not rotate evenly with the rotor. This causes flux flux changes in the rotor, leading to eddy currents in the return flux discs. Without the suppression described above, these eddy currents would lead to significant losses in the rotor disc. This prevents excessive heat loss, which would otherwise insufficiently heat the rotor. This allows operation at high speeds, even over extended periods.

[0012] The subclaims show preferred developments of the invention

[0013] In the case of surface magnets, the rotor poles of the return plate are preferably grooved circumferentially over the entire rotor pole or the entire area facing the air gap. In the case of buried magnets, the return plates are preferably grooved in the pole gaps. Thus, the relevant areas for eddy current suppression are designed accordingly for the respective application. This enables reliable suppression of eddy currents.

[0014] Particularly advantageously, the grooving is formed by grooves that extend in the circumferential direction and are spaced radially from one another with respect to the central axis. Such grooves can be manufactured easily and inexpensively. Furthermore, optimal suppression of eddy currents is achieved by preventing the free propagation of eddy currents. In the case of surface magnets, the grooves of the grooving are particularly preferably annular.

[0015] In the case of surface magnets, the rotor poles of the magnetic return disc are preferably designed with increased resistance across their entire surface. In the case of buried magnets, the rotor poles of the magnetic return disc are designed with increased resistance in the pole gaps. Thus, the relevant areas for eddy current suppression are designed accordingly for the respective application. This enables reliable suppression of eddy currents.

[0016] The surface resistance increase of the rotor pole or pole section advantageously forms a resistance layer. This resistance layer has a higher specific electrical resistance than the rest of the return plate. This makes it difficult for eddy currents to form in the resistance layer.

[0017] The resistance layer particularly advantageously has an electrical conductivity of a maximum of 3.0 MS / m, preferably a maximum of 2.5 MS / m, particularly preferably 2.3 MS / m. This provides a low electrical conductivity, which prevents the formation of eddy currents.

[0018] The grooves preferably have a depth of less than 1 mm. The resistance layer preferably has a thickness of less than 1 mm. This is optimal for suppressing eddy currents. The penetration depth δ of the eddy currents can be calculated using the following equation:

[0019] Where p is the specific electrical resistance of the reflux disc, p r The specific permeability of the reflux disc, p0 the absolute permeability in vacuum, and f the frequency of the flux fluctuations in the reflux disc. The penetration depth into the rotor disc is preferably very small due to the very high specific permeability (>100) and the high frequencies at high speeds, and is usually well below 1 mm. The eddy currents are therefore only present on the surface of the reflux disc. Therefore, it is optimal to use a relatively thin layer with increased resistance or grooves with a relatively shallow depth to suppress eddy currents.

[0020] The surface resistance increase of the pole or pole section is preferably formed by a surface coating of the return plate or by alloying the surface of the return plate. In particular, the surface coating or alloying is based on or with carbon, silicon, aluminum or phosphorus. The return plate is thus processed accordingly in order to achieve the surface resistance increase. Alternatively, the surface resistance increase is formed by a separate cover layer or cover lamination. The cover layer is in particular a ferromagnetic cover layer. The cover lamination is in particular a cover lamination, which is particularly preferably formed from electrical steel sheet. By using a separate cover layer or cover lamination, advantageously no surface treatment is necessary.

[0021] In the case of surface magnets, the magnets are preferably arranged on the grooved or surface-resistance-enhanced air gap side of the return plate. Thus, the area below the surface magnets is machined accordingly to suppress eddy currents.

[0022] The return plate is preferably a solid steel plate. The solid steel of the rotor plate has a specific conductivity of 4.65 MS / m.

[0023] To increase stability, the rotor is advantageously enclosed in a bandage. The axial flux machine is designed specifically for higher speeds, which is why the strength-enhancing bandage is advantageous. This minimizes rotor heating at high speeds and maximizes the rotor's speed stability.

[0024] In the case of buried magnets, recesses are preferably formed on the air gap side of the return plate to accommodate the buried magnets and each pole segment covering the buried magnets. The buried magnets are preferably glued. The pole segments are preferably made of SMC (soft magnetic composite or pressed powder iron), or as a laminated core.

[0025] The stator preferably has a plurality of individual teeth. Each individual tooth is, in particular, enclosed by a coil winding. This allows for a simple and cost-effective design. Both the teeth in the stator and the individual-tooth winding, along with the associated concentrated winding, generate large harmonics in the machine. These harmonics also reach the rotor yoke and the return plates. These harmonics have a different rotational speed than the rotor. This causes induction fluctuations in the rotor, which lead to eddy currents in the return plates, but the propagation of these eddy currents is suppressed.

[0026] Short description of the drawings

[0027] Embodiments of the invention are described in detail below with reference to the accompanying drawings. In the drawing:

[0028] Figure 1 is a first schematic representation of an axial flow machine according to a first embodiment of the invention,

[0029] Figure 2 shows a second schematic representation of the axial flow machine according to the first embodiment of the invention,

[0030] Figure 3 is a schematic exploded view of the

[0031] Axial flux machine according to the first embodiment of the invention,

[0032] Figure 4 is a schematic representation of a part of a

[0033] Return disk of the axial flux machine according to the first embodiment of the invention,

[0034] Figure 5 is a schematic exploded view of a

[0035] Axial flux machine according to a second embodiment of the invention, Figure 6 is a schematic representation of a reflux disk of a

[0036] Axial flux machine according to a third embodiment of the invention,

[0037] Figure 7 is a schematic representation of a reflux disc of a

[0038] Axial flux machine according to a fourth embodiment of the invention, and

[0039] Figure 8 is a schematic representation of a reflux disc of a

[0040] Axial flux machine according to a fifth embodiment of the invention.

[0041] Embodiments of the invention

[0042] Preferably, all identical components, elements and / or units in all figures are provided with the same reference numerals.

[0043] Figures 1 and 2 each show schematic views of an axial flux machine 1 according to a first exemplary embodiment of the invention. Figure 3 shows an exploded view of the axial flux machine 1 according to the first exemplary embodiment. The axial flux machine 1 has a stator 2 and two rotors 3. The stator 2 extends along a central axis 100. The stator 2 has a plurality of individual teeth 10, each enclosed by a coil winding. The rotors 3 are arranged next to the stator 2 with respect to the central axis 100. Each rotor 3 has a return disk 4, to which surface magnets 5a are attached to form several rotor poles. The surface magnets 5a are, in particular, permanent magnets. The return disk 4 is a solid steel disk. To increase strength, the rotor 3 is enclosed, for example, by a bandage.

[0044] Each of the return plates 4 has an end face 7a facing the stator 2, which forms an air gap side. This air gap side of the return plates 4 serves to accommodate the surface magnets 5a. Furthermore, it is provided that the return plates 4 are grooved on the air gap side, i.e. on the end face 7a facing the stator 2, to suppress eddy currents. In the exemplary embodiment, the return plate 4 is grooved on the entire end face 7a in the circumferential direction 300; however, it would also be possible for the return plate 4 to be grooved only in pole sections of the rotor poles. It is thus provided that at least the area of ​​the return plate 4 below the surface magnets 5a is grooved.

[0045] Figure 4 shows a section of the return plate 4 of the axial flux machine 1 according to the first exemplary embodiment. The grooving is formed by grooves 8 that extend in the circumferential direction 300 and are spaced apart from one another in the radial direction 200 with respect to the central axis 100. In the exemplary embodiment shown, the grooves 8 are annular. A depth d of the grooves 8 is less than 1 mm. It is to be expected that eddy currents will not penetrate into the return plate 4 more than said depth d. Thus, the formation of eddy currents can be reliably suppressed by the grooves 8. The current paths of the current eddies are interrupted by the grooves, and the eddy current losses can be effectively reduced without significantly weakening the mechanical strength of the return plate 4. This allows higher speeds of the axial flux machine 1 to be achieved.

[0046] Figure 5 shows an exploded view of an axial flux machine 1 according to a second embodiment. The basic structure is identical to the first embodiment; the only difference is that there is no grooving on the return plate 4. Instead, the air gap side of the return plate 4 is designed with increased resistance to suppress eddy currents. This is achieved by applying a separate cover layer 9 or cover lamination to the return plate 4. The cover layer is a ferromagnetic cover layer. A ferromagnetic cover lamination, for example, made of electrical steel, can also be used.

[0047] A thickness d of the cover layer 9 is less than 1 mm. As previously explained, the formation of eddy currents can be reliably suppressed in this way. The increased electrical resistance suppresses the formation of eddy currents. This allows higher speeds of the axial flux machine 1 to be achieved. Figure 6 schematically shows a return plate 4 of an axial flux machine 1 according to a third exemplary embodiment. The third exemplary embodiment is almost identical to the second exemplary embodiment, although no separate cover layer 9 is provided. Instead, a resistance layer 6 is formed in the surface of the return plate 4. The resistance layer 6 locally increases the electrical resistance of the return plate 4.

[0048] In particular, the end face 7a of the return plate 4 facing the stator 2 is designed with increased resistance over its entire surface. Alternatively, the return plate 4 can be designed with increased resistance only in pole sections of the rotor poles.

[0049] The resistance layer 6 is formed, for example, by a surface coating or by alloying the surface of the return plate 4, in particular with carbon, silicon, aluminum, or phosphorus. The resistance layer 6 has a higher specific electrical resistance than the rest of the return plate 4. The electrical conductivity of the resistance layer 6 is a maximum of 3.0 MS / m, preferably a maximum of 2.5 MS / m, particularly preferably 2.3 MS / m. In this exemplary embodiment, the thickness d of the resistance layer 6 is also less than 1 mm. As previously described, eddy currents can thus be effectively suppressed, which allows operation of the axial flux machine 1 at higher speeds.

[0050] Figure 7 is a schematic representation of a return plate 4 of an axial flux machine 1 according to a fourth embodiment of the invention. The axial flux machine 1 according to the fourth embodiment of the invention is almost identical to the first embodiment, except that buried magnets 5b are used instead of surface magnets 5a.

[0051] Buried magnets 5b are arranged in recesses 7 of the return plate 4 and covered by pole segments 4a, for example made of Soft Magnetic Composite (SMC) or designed as a laminated core. Pole gaps 11 are located between the recesses 7, wherein the pole gaps 11 are designed to increase resistance. In the fourth exemplary embodiment, grooving is carried out with grooves 8 extending in the circumferential direction 300, analogous to the first exemplary embodiment. Thus, the same advantages as previously described for surface magnets 5a can also be achieved for buried magnets 5b. Figure 8 is a schematic representation of a return plate 4 of an axial flux machine 1 according to a fifth exemplary embodiment of the invention. The axial flux machine 1 according to the fifth exemplary embodiment of the invention is almost identical to the fourth exemplary embodiment, wherein instead of grooves 8 for

[0052] To increase the resistance, a resistance layer 6 is provided as described in the third embodiment. The resistance layer 6 is thus formed in the pole gaps 11, which also enables reliable suppression of eddy currents in this embodiment and therefore operation of the axial flux machine 1 at higher speeds.

Claims

Claims 1. Axial flux machine (1) comprising a stator (2) extending along a central axis (100), and at least one rotor (3) arranged next to the stator (2) with respect to the central axis (100), and comprising a return plate (4) on which magnets (5a, 5b), in particular permanent magnets, are arranged to form a plurality of rotor poles, wherein one of the two end faces (7a) of the return plate (4) faces the stator (2) and forms an air gap side, characterized in that the air gap side of the return plate (4) is grooved at least in sections or has an increased surface resistance to suppress eddy currents.

2. Axial flux machine (1) according to claim 1, characterized in that the rotor poles of the return disc (4) are grooved in the circumferential direction (300) over the entire rotor pole in the case of surface magnets (5a) or are grooved in the pole gaps in the case of buried magnets (5b).

3. Axial flux machine (1) according to one of the preceding claims, characterized in that the grooving is formed by grooves (8) which extend in the circumferential direction (300) and are spaced apart from one another in the radial direction (200) with respect to the central axis (100), wherein the grooves (8) of the grooving are annular in the case of surface magnets (5a).

4. Axial flux machine (1) according to claim 1, characterized in that the rotor poles of the return disc (4) are designed with increased resistance over their entire surface in the case of surface magnets (5a) or are designed with increased resistance in the pole gaps (11) in the case of buried magnets (5b).

5. Axial flux machine (1) according to one of the preceding claims, characterized in that the surface resistance increase of the rotor pole or pole section forms a resistance layer (6) which has a higher specific electrical resistance than the remaining return plate (4).

6. Axial flux machine (1) according to claim 5, characterized in that the resistance layer (6) has an electrical conductivity of at most 3.0 MS / m, preferably at most 2.5 MS / m, particularly preferably 2.3 MS / m.

7. Axial flow machine (1) according to claim 3, 5 or 6, characterized in that the grooves (8) or the resistance layer (6) has a depth or layer thickness of less than 1 mm.

8. Axial flux machine (1) according to one of the preceding claims, characterized in that the superficial resistance increase of the pole or pole section is formed by a surface coating, by alloying the surface of the return plate (4), in particular with carbon, silicon, aluminum or phosphorus, or by a separate cover layer (9) or cover lamination, in particular a ferromagnetic cover layer or cover lamination, especially in particular made of electrical sheet.

9. Axial flux machine (1) according to one of the preceding claims, characterized in that the magnets (5a, 5b) in the case of surface magnets (5a) are arranged on the grooved or surface-resistance-increased air gap side of the return plate (4).

10. Axial flux machine (1) according to one of the preceding claims, characterized in that the return disc (4) is a solid steel disc. 11 . Axial flow machine (1) according to one of the preceding claims, characterized in that the rotor (3) is enclosed by a bandage.

12. Axial flux machine (1) according to one of the preceding claims, characterized in that on the air gap side of the return plate (4), in the case of buried magnets (5b), recesses (7) are formed for receiving the buried magnets (5b) and for receiving a pole segment (4a) covering the buried magnets (5b).

13. Axial flux machine (1) according to one of the preceding claims, characterized in that the stator (2) has a plurality of individual teeth (10), each of which is enclosed by a coil winding.

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