Method for manufacturing a magnetic cassette of a rotor for an axial flux machine

Abstract

The invention relates to a method for manufacturing a magnetic cassette (10) of a rotor for an axial flux machine, wherein the magnetic cassette (10) has an annular cross-section with radially extending webs (12) between which magnets (30), in particular individual magnetic elements, are arranged in the form of annular segments. The magnets (30) and the webs (12) are made of a hard magnetic material, wherein the magnets (30) are arranged with alternating polarity in an axial direction (22). The webs (12) are magnetically polarized in the circumferential direction (26). The method comprises at least: manufacturing the magnets (30) and the webs (12); finishing the side surfaces (42, 44) of the magnets (30) and the webs (12); arranging the magnets (30) and the webs (12) in the intended arrangement of the magnetic cassette (10) and bonding the side surfaces (42, 44). Finishing of an outer contour (40) of the magnetic cassette (10).

Description

[0001] The invention relates to a method for manufacturing a magnetic cassette of a rotor for an axial flux machine.

[0002] The disc-shaped design of axial flux machines (AFMs) enables novel axle drive concepts for motor vehicles. Due to space constraints, the AFM's outer diameter is relatively limited, especially for coaxial applications in passenger cars. Therefore, and for efficiency reasons, increasing its efficiency is a priority for future mass production applications.

[0003] In axial flux machines, laminated permanent magnets are typically pressed into a magnet cassette made of a fiber composite, a so-called sheet molding compound (SMC). Laminating the magnets reduces the eddy current losses occurring in the magnets.

[0004] Axial flux machines have a disc-shaped design, conventionally employing either a double-rotor or a double-stator arrangement. For traction machines with high torque and power density, double-rotor concepts are predominantly used, incorporating rotor discs consisting of the main components rotor carrier, electrical lamination stack, and magnet cassette.

[0005] The magnetic cassette consists of permanent magnets which are segmented by an electrically non-conductive adhesive layer to reduce eddy current losses within the magnet during operation of the electric machine.

[0006] To withstand the high rotational speeds during machine operation and the associated centrifugal forces of the magnets, an oversized or pre-tensioned ring made of carbon fiber reinforced plastic can be mounted on the magnet cassette. To absorb the compressive forces resulting from the ring, particularly when the machine is stationary, a magnet cassette consisting of magnets and carbon fiber reinforced SMC is typically used.

[0007] Furthermore, individual magnets are currently being joined together using the SMC pressing process. Due to the tolerance chain, consisting of magnet tolerances, batch and processing variations of the SMC material, and tool tolerances, this process necessitates a post-processing chain. Post-processing can include grinding, brushing, laser cleaning, and blasting. These post-processing procedures are, in some cases, very complex.

[0008] A disadvantage is the higher rotor losses due to the electrically conductive carbon content. This induces eddy currents within the SMC struts. Furthermore, the individual magnet segments are short-circuited, which also results in eddy currents.

[0009] Furthermore, due to its characteristic properties, SMC exhibits uneven electrical conductivity. This leads, on the one hand, to inhomogeneous contact resistances between the magnet and the SMC, and on the other hand, within the SMC itself. As a result, eddy current paths can increase significantly due to potential differences at the magnet cassette level. This also applies to any type of electrically conductive fiber composite material.

[0010] Furthermore, the SMC, consisting of short-fiber carbon and a resin matrix, is subjected to compressive stress. This is also unfavorable for short-fiber composite materials.

[0011] So-called Hallbach magnet arrangements are known to generate a higher magnetic flux density on the stator side or air gap side. This allows the torque and power of the axial flux machine to be increased.

[0012] DE 10 2022 004 611 A1 further discloses a method for manufacturing a rotor for an axial flux machine (AFM). In this method, at least one spring element, designed separately from the support unit, is attached to a support unit of the rotor comprising a laminated core. At least one permanent magnet is arranged in a corresponding pocket of the support unit and on the spring element such that the spring element is elastically deformed. This causes the spring element to provide a spring force acting radially to the rotor, by means of which the permanent magnet is clamped to the support unit and thereby fixed to the support unit.

[0013] One object of the invention is to provide an improved method for manufacturing a magnetic cassette of a rotor for an axial flux machine.

[0014] The aforementioned problem is solved using the features of an independent claim.

[0015] Favorable embodiments and advantages of the invention will become apparent from the further claims, the description and the drawing.

[0016] According to one aspect of the invention, a method for manufacturing a magnetic cassette of a rotor for an axial flux machine is proposed, wherein the magnetic cassette has an annular cross-section with radially extending webs, between which magnets, in particular individual magnetic elements, are arranged in the form of annular segments. The magnets and the webs are made of a hard magnetic material, wherein the magnets are arranged with alternating polarity in an axial direction. The webs are magnetically polarized in the circumferential direction. The method comprises at least: manufacturing the magnets and the webs; finishing the side surfaces of the magnets and the webs; arranging the magnets and the webs in the intended arrangement of the magnetic cassette and bonding the side surfaces; finishing an outer contour of the magnetic cassette.

[0017] The proposed method can, in particular, increase the magnetic power in the form of the rotor's magnetic flux density, thus enabling the generation of improved torque and power densities during the operation of the axial flux machine while maintaining the same installation space requirement.

[0018] Furthermore, the process improves the tolerance chain of the magnet cassette and the rotor, thus enabling improved geometric and mechanical properties during motor operation.

[0019] The proposed method thus enables both product and process improvements. By strategically combining the process chain for manufacturing magnetic cartridges with the functional integration of a so-called Hallbach magnet arrangement, both product and manufacturing advantages are achieved. In a Hallbach arrangement, the magnetic flux on one end face of the component almost cancels out, while it is amplified on the other end face.

[0020] The magnetic cassette consists of individual magnetic segments, which are manufactured as sub-assemblies: a magnetic segment configured as a north pole, a magnetic segment configured as a south pole, and connecting elements. Each component is made of hard magnetic material. In particular, this can be NdFeB, SmCo, or polymer-bonded magnets. The individual sub-assemblies are then further processed.

[0021] Furthermore, the magnetic cassette is manufactured in such a way that the individual magnetic segments are finished and bonded to their side surfaces. The polarization of the magnets is arranged to create a Hallbach configuration.

[0022] After that, the outer contour of the magnetic cassette is finished. This includes, among other things, the outer and inner radii, as well as the two parallel end faces.

[0023] The manufacturing process results in a geometrically and mechanically high-performance magnetic cassette. In particular, the outer diameter can be precisely machined within the composite, for example, by circular grinding. Furthermore, the composite can be ground flat and parallel, thus ensuring optimal adhesion between the magnetic cassette and a subsequent electrical steel stack.

[0024] The Hallbach arrangement allows for the generation of a higher torque from the axial flux machine. At the same time, the installation space requirement of the axial flux machine remains the same.

[0025] The use of the bridges, and optionally an inner ring and / or outer ring, made of hard magnetic materials in combination with the manufacturing process of the magnetic cassette reduces the complexity of the rotor process chain as well as the costs and cycle time of the manufacturing process.

[0026] Advantageously, this results in improved tolerances regarding geometry, for example in parallelism, roundness, flatness, diameter, which are always uniform with respect to webs, joints, homogeneous surface for a subsequent coating process of the surface, for example as a corrosion protection layer.

[0027] Integrating magnetic cassette manufacturing into magnet production results in a reduction of complexity as well as economic advantages.

[0028] The magnetic cassette can be manufactured close to the component in the magnet manufacturing process.

[0029] This advantageously results in a streamlining of the entire production chain, including manufacturing, logistics, and handling.

[0030] The process chain can reduce logistics costs.

[0031] This process enables a uniform material pairing, resulting in uniform thermal expansion. This reduces or eliminates the induction of mechanical residual stresses within the magnetic cassette. Consequently, the functionality and lifespan of the magnetic cassette can be improved.

[0032] Eddy current losses in the rotor resulting from the alternating magnetic field during operation of the electric traction machine can be advantageously reduced. No or reduced eddy current paths occur within the magnet cassette assembly because, unlike carbon fibers, the material is non-conductive. No additional eddy currents are induced in the magnets through electrical connections between the carbon fibers and the individual magnet segments. Inhomogeneous electrical conductivity is thus prevented. This also leads to reduced losses in the rotor.

[0033] The magnetic performance data is improved due to reduced heat generation resulting from lower eddy current losses in the rotor. This allows for an increase in the efficiency of the axial flux machine by reducing rotor losses.

[0034] Due to the reduced proportion of rare earth elements in the permanent magnets, achieved by reducing the coercive field strength as a result of the lower operating temperatures of the machine, costs can be reduced.

[0035] According to an advantageous embodiment of the method, an inner ring and / or an outer ring can be arranged on an inner circumference.

[0036] In the first process step, the inner ring, which consists of a hard magnetic material, is inserted. Then the individual magnets (north and south poles) and the bridges are inserted, and finally the outer ring is put in place.

[0037] The outer ring, for example made of carbon fiber reinforced plastic, can then be attached to the magnet cartridge. The ribs serve both as a magnetic reinforcement of the magnetic flux density on the air gap / stator side and as a mechanical stiffener of the magnet cartridge with respect to the high forces that act radially inwards on the magnets of the magnet cartridge as a result of the pressed-on ring.

[0038] The functional integration of the inner ring and outer ring in the form of improved mechanical stability can be used to obtain a more speed-resistant and more robust magnetic cassette, and thus an axial flux machine.

[0039] According to an advantageous embodiment of the method, the inner ring and / or the outer ring can be made of a hard magnetic material.

[0040] In this invention, the webs, inner rings, and outer rings serve both as a magnetic enhancement of the magnetic flux density on the air gap / stator side and as a mechanical stiffener of the magnet cassette with respect to high forces. Thus, in addition to their mechanical function, the webs, inner rings, and outer rings implement a further function in the form of magnetic properties.

[0041] According to an advantageous embodiment of the method, areas of the inner ring and / or areas of the outer ring adjacent to the magnets can be magnetically polarized in the radial direction, with the magnetic field lines oriented such that they reinforce the magnetic field lines of the adjacent magnet. Thus, areas of the inner ring and / or areas of the outer ring can be magnetized alternately according to the number of pole pairs, and the magnetic field lines of the adjacent magnet can be reinforced in the direction of the air gap or the stator of the axial flux machine. This increases the magnetic power of the axial flux machine. The magnetization of the inner ring and / or outer ring does not have to be carried out before assembly, but can also be performed in a single process step after completion of the magnet cassette or the entire rotor.

[0042] According to an advantageous embodiment of the method, the manufacture of the magnetic cassette can further comprise: arranging the inner ring; arranging the magnets and the bridges. In this way, the magnetic cassette can be manufactured cost-effectively.

[0043] According to an advantageous embodiment of the method, the manufacture of the magnetic cassette can further comprise: arranging the magnets and the bridges; arranging the outer ring. In this way, the magnetic cassette can be manufactured cost-effectively.

[0044] According to an advantageous embodiment of the method, the manufacture of the magnetic cassette can further comprise: arranging the inner ring; arranging the magnets and the bridges; arranging the outer ring. In this way, the magnetic cassette can be manufactured cost-effectively.

[0045] According to an advantageous embodiment of the method, the fully assembled magnetic cassette can be ground flat and parallel on its end faces. This allows for easy final machining of the magnetic cassette.

[0046] According to an advantageous embodiment of the method, the adhesive used to bond the side surfaces of the magnets and the webs can be electrically non-conductive and contain a filler to ensure a minimum electrically non-conductive distance between the side surfaces. The adhesive used between the individual magnet segments and subassemblies can also contain a filler that ensures a distance between the individual hard magnetic elements, thus maintaining electrical non-conductive properties.

[0047] According to an advantageous embodiment of the method, the magnetic cassette can have a magnetic Hallbach arrangement. Such an arrangement can advantageously contribute to increased magnetic performance.

[0048] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. A person skilled in the art will expediently consider the features individually and combine them into meaningful further combinations.

[0049] This shows: Fig. 1 a top view of a part of a magnetic cassette of a rotor for an axial flux machine, manufactured by a method according to an embodiment of the invention; Fig. 2 a side view of the magnetic cassette Fig. 1; Fig. 3 a top view of a part of a magnetic cassette according to a further embodiment of the invention; Fig. 4 a top view of a part of a magnetic cassette according to a further embodiment of the invention; and Fig. 5 a top view of a part of a magnetic cassette according to a further embodiment of the invention.

[0050] In the figures, identical or similar components are numbered with the same reference symbols. The figures merely show examples and are not to be understood as limiting.

[0051] Fig. Figure 1 shows a top view of a part of a magnetic cassette 10 of a rotor for an axial flux machine, manufactured using a method according to an embodiment of the invention.

[0052] The magnetic cassette 10 has an annular cross-section with radially extending webs 12, between which magnets 30, in particular individual magnetic elements, are arranged in the form of annular segments. The webs 12 are shown in black.

[0053] The magnets 30 and the bridges 12 are made of a hard magnetic material, for example NdFeB, SmCo, or are polymer-bonded magnets. The magnets 30 are arranged with alternating polarities in an axial direction 22, so that each magnet 30 protrudes from the plane of the drawing as either a north pole 32 or a south pole 34. The bridges 12 are magnetically polarized in the circumferential direction 26. Magnetic field lines 36 in the bridges 12 are shown as white arrows on the black background of the bridges 12. The magnetic field lines 36 run from one magnet 30 to the next. The bridges 12 are therefore also designed as magnets.

[0054] The magnetic field pattern is in Fig. Figure 2 shows a side view of the magnetic cassette 10. The magnetic field lines 36 between adjacent magnets 30 are closed, but are influenced by the magnetic field lines 36 running in the webs 12 such that the magnetic flux on one end face 46 of the magnetic cassette 10 almost cancels out, while it is increased on another end face 48. Thus, the magnetic cassette 10 exhibits a magnetic Hallbach arrangement.

[0055] The bridges 12 thus provide a mechanical support structure for the magnets 30 and also serve to introduce magnetic properties in a targeted manner to exploit the Hallbach effect.

[0056] The magnetic cassette 10 is manufactured according to the proposed method by first producing the magnets 30 and the bridges 12. Then, the side surfaces 42, 44 of the magnets 30 and the bridges 12 are finished, and the magnets 30 and bridges 12 are arranged in the intended configuration of the magnetic cassette 10. The side surfaces 42, 44 are then bonded together.

[0057] The adhesive used to bond the side surfaces 42, 44 of the magnets 30 and the webs 12 is electrically non-conductive and contains a filler, ensuring a minimum electrically non-conductive distance between the side surfaces 42, 44. This minimizes eddy current losses in the rotor of the axial flux machine.

[0058] Next, the outer contour 40 of the magnetic cassette 10 is finished. Finally, the end faces 46, 48 of the fully assembled magnetic cassette 10 are ground flat and parallel.

[0059] Fig. Figure 3 shows a top view of a part of a magnetic cassette 10 according to a further embodiment of the invention.

[0060] In this embodiment, an inner ring 16 is arranged on an inner circumference 14 and an outer ring 20 on an outer circumference 18. The inner ring 16 and the outer ring 20 are made of a hard magnetic material. The inner ring 16 and the outer ring can be made of the same material as the webs 12. Therefore, the inner ring 16 and the outer ring 20 are shown in black in the figure.

[0061] Areas 28 of the inner ring 16 and areas 38 of the outer ring 20 adjacent to the magnets 30 are magnetically polarized in the radial direction 24. The magnetic field lines 36 are oriented such that they reinforce the magnetic field lines 36 of the adjacent magnet 30. Consequently, the areas 38 are polarized alternately in the circumferential direction 26 according to the magnetic field of the adjacent magnets 30 along the inner circumference 14 and the outer circumference 18, with the magnetic field lines 36 oriented radially outwards or inwards in the radial direction 24.

[0062] The magnetic field lines 36 of rings 16, 20 are shown as white arrows on the black background of rings 16, 20.

[0063] In this embodiment, the magnetic cassette 10 has a mechanical banding provided by the outer ring 20 and the inner ring 16, for example against centrifugal forces during rotor operation and for pressure stabilization. Furthermore, specific magnetic properties are introduced into the magnetic cassette 10 to generate or enhance a three-dimensional Hallbach effect.

[0064] According to the proposed method, the magnetic cassette 10 is manufactured by first arranging the inner ring 16, then arranging the magnets 30 and the bridges 12, and finally arranging the outer ring 20.

[0065] Alternatively, only the outer ring can have 20 areas 38 that are magnetically polarized, as in Fig. 4 shown or only the inner ring 16, as in Fig. 5 shown. Reference symbol list 10 magnetic cassettes 12 Bridge 14 inner circumference 16 inner ring 18 outer circumference 20 outer ring 22 axial direction 24 radial direction 26 Circumferential direction 28 area 30 Magnet 32 North Pole 34 South Pole 36 magnetic field lines 38 area 40 Outer contour 42 side surface 44 side surface 46 Front surface 48 Front surface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 004 611 A1

[0012]

Claims

[1] Method for manufacturing a magnetic cassette (10) of a rotor for an axial flux machine, wherein the magnetic cassette (10) has an annular cross-section with radially extending webs (12) between which magnets (30), in particular individual magnetic elements, are arranged in the form of annular segments, wherein the magnets (30) and the webs (12) are made of a hard magnetic material, wherein the magnets (30) are arranged with alternating polarity in an axial direction (22), wherein the webs (12) are magnetically polarized in the circumferential direction (26), the method comprising at least: Manufacturing the magnets (30) and the bridges (12); Finishing of side surfaces (42, 44) of the magnets (30) and the bridges (12); Arranging the magnets (30) and the bridges (12) in the intended arrangement of the magnetic cassette (10) and gluing the side surfaces (42, 44); Finishing of an outer contour (40) of the magnetic cassette (10). [2] Method according to claim 1, wherein an inner ring (16) is arranged on an inner circumference (14) and / or an outer ring (20) is arranged on an outer circumference (18). [3] Method according to claim 2, wherein the inner ring (16) and / or the outer ring (20) are formed from a hard magnetic material. [4] Method according to one of claims 2 to 3, wherein areas (28) of the inner ring (16) and / or areas (38) of the outer ring (20) adjacent to the magnets (30) are magnetically polarized in a radial direction (24), wherein the magnetic field lines (36) are each such that the magnetic field lines (36) of the adjacent magnet (30) are reinforced. [5] Method according to any one of claims 2 to 4, wherein the manufacture of the magnetic cassette (10) further comprises: Arranging the inner ring (16); Arranging the magnets (30) and the bridges (12). [6] Method according to any one of claims 2 to 4, wherein the manufacture of the magnetic cassette (10) further comprises: Arranging the magnets (30) and the bridges (12); Arranging the outer ring (20). [7] Method according to any one of claims 2 to 4, wherein the manufacture of the magnetic cassette (10) further comprises: Arranging the inner ring (16); Arranging the magnets (30) and the bridges (12); Arranging the outer ring (20). [8] Method according to one of the preceding claims, wherein the fully assembled magnetic cassette (10) is ground parallel to the end faces (46, 48). [9] Method according to one of the preceding claims, wherein the adhesive for bonding the side surfaces (42, 44) of the magnets (30) and the webs (12) is electrically non-conductive and is provided with a filler so that an electrically non-conductive minimum distance between the side surfaces (42, 44) is maintained. [10] Method according to any of the preceding claims, wherein the magnetic cassette (10) has a magnetic Hallbach arrangement.

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