Rotor lamination for an electric machine, electric machine, vehicle and method for manufacturing rotor laminations

Abstract

The present disclosure relates to rotor laminations (10) comprising a first region (11) and a second region (12), wherein the first region (11) is larger than the second region (12), and the first region (11) contains a first alloy and the second region (12) contains a second alloy. According to the disclosure, the second alloy is soft magnetic and exhibits a higher magnetic permeability than the first alloy. The present disclosure further relates to an electric machine (10) and an electrically powered vehicle. Furthermore, a method for manufacturing the aforementioned rotor laminations (10) is disclosed. For this purpose, a corresponding green body (50) is printed in a stencil printing process and subsequently sintered to form the rotor lamination.

Description

[0001] The present disclosure relates to a rotor for an electric machine, such an electric machine, and a method for producing electric machines. Furthermore, an electrically powered vehicle is disclosed.

[0002] The performance or power density of electric machines and their efficiency play a major role, especially—but not exclusively—in electromobility. Various approaches exist to optimize these parameters.

[0003] For example, the torque and efficiency of electrical machines can be increased by reducing sheet thickness or by selecting high-performance alloys. However, these soft magnetic high-performance alloys are often extremely difficult to machine. The resulting manufacturing costs are correspondingly high.

[0004] Various approaches to solving this problem can be found in the state of the art. The following examples are discussed below.

[0005] US 2021 / 0111613 A1 addresses the topic of modifying the insulation density of electrical steel sheets for electric motors. The main effect is to minimize eddy currents and thus increase efficiency.

[0006] US 2018 / 0233997 A1 relates to additively manufactured iron cores for electric motors with increased efficiency through the introduction of air gaps between and within the layers. The main purpose is to reduce iron losses.

[0007] US 11,362,552 B2 teaches the use of differently shaped sheets that are stamped and stacked. Some layers are manufactured in 3D form. Non-ferromagnetic material is used in certain areas to reduce stray flux.

[0008] US 11,025,142 B2 discloses a process in which stamped metal sheets are combined with additional reinforcements made of powder melted with a laser. The goal is to reduce flux leakage and increase the structural strength of the rotor. There is a need to eliminate or at least reduce the disadvantages of known systems without having to make the compromises that have been necessary to date. In particular, there continues to be a need to optimize electrical machines in terms of performance / power density and efficiency.

[0009] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are specified in the dependent patent claims and the following description, each of which, individually or in (sub)combination, may represent aspects of the disclosure. Individual aspects are explained with regard to devices, others with regard to a method. However, the aspects are to be transferred reciprocally accordingly.

[0010] According to one aspect, a rotor lamination is provided. The rotor lamination has a first region and a second region. The first region is larger than the second region. Furthermore, the rotor lamination has a first alloy in the first region and a second alloy in the second region. The second alloy is magnetically soft and has a higher magnetic permeability than the first alloy.

[0011] Soft magnetic materials are materials that can be easily demagnetized or remagnetized in a magnetic field. For the purposes of this disclosure, soft magnetic alloys are alloys with a coercive field strength of less than 1000 A / m.

[0012] Soft magnetic high-performance alloys are preferred, which have an even lower coercive field strength of less than 100 A / m. Examples include certain cobalt-iron alloys (FeCo) or silicon-iron alloys (FeSi) with a comparatively high silicon content of approximately 0.5 to 8 percent by weight.

[0013] The use of soft magnetic alloys with increased permeability enables higher magnetic flux and thus higher rotor torque. Furthermore, the magnetic flux is guided along deliberately designed flux paths by the high-performance soft magnetic material.

[0014] According to an advantageous aspect, the first alloy is also magnetically soft. Alternatively, it can also be a non-magnetic iron-based alloy. The choice of materials allows for the targeted conduction of the subsequent magnetic flux in the rotor. Areas with non-magnetic iron-based alloys can be used, in particular, for the mechanical strengthening of the rotor core.

[0015] This means that the combination of soft magnetic high-performance alloys with conventional soft magnetic or non-magnetic alloys utilizes the material properties specifically where they have a particularly positive impact on the efficiency and performance of the electrical machine. This can significantly reduce the use of resource-intensive alloys.

[0016] The rotor lamination can have a plurality of cutouts. At least some of these cutouts then form pockets in the subsequent rotor stack for accommodating permanent magnets. The use of these rotor laminations is particularly advantageous in reluctance-torque-assisted permanent magnet machines, where the permanent magnet component can be reduced.

[0017] At least parts of the area with the higher permeability can advantageously be located between the magnet pockets and an outer circumference of the rotor lamination.

[0018] The pockets can, for example, be arranged in pairs in a V-shape, defining a magnetic island between them. The region with the higher permeability (the second region) preferably comprises large portions of these magnetic islands.

[0019] The rotor laminations are preferably designed such that two pairs of pockets are arranged in a V-shape and superimposed radially in a double V shape. The second region with the more permeable alloy then comprises, in particular, a region between the superimposed pockets.

[0020] The magnetic pockets can also have lateral, free areas that serve as magnetic flux barriers. The first area, with the lower permeability, preferably also extends around these magnetic flux barriers.

[0021] The configurations described above have proven to be particularly suitable for the intended application.

[0022] Furthermore, an electrical machine with a rotor made of rotor laminations as previously described is provided.

[0023] These electrical machines are preferably reluctance torque-assisted permanent magnet machines. These electrical machines are particularly efficient while using reasonable materials and have a very good speed-torque ratio.

[0024] According to a further aspect, a vehicle with an electric machine as described above is also provided.

[0025] A vehicle, as used herein, is defined as a device configured to transport objects, cargo, or people between different destinations. Examples of vehicles include land-based vehicles such as motor vehicles, electric vehicles, hybrid vehicles, or similar, rail vehicles, aircraft, or watercraft. Preferably, vehicles in this context can be considered road-based vehicles, such as cars, trucks, buses, or the like.

[0026] In advantageous embodiments, the above-described electric machine can be arranged in the vehicle, for example, as a front-wheel drive, mid-wheel drive, underfloor drive or wheel hub drive.

[0027] A method for producing the rotor laminations described above is also disclosed. The method comprises the following process steps: S1: Creating a rotor sheet green body using a stencil printing process and S2: Sintering of the rotor sheet green body to a rotor sheet.

[0028] The production of the rotor sheet green body in turn includes the following sub-process steps: S1a: Applying a first suspension in a first area of ​​the rotor sheet green body defined by a first mask and S1b: Applying a second suspension in a second area of ​​the rotor sheet green body defined by a second mask.

[0029] Either the first suspension or the second suspension can be applied first.

[0030] A suspension is a heterogeneous mixture of a liquid and finely distributed solids (particles), in this case a metal powder.

[0031] The suspensions are preferably pastes. A paste is a suspension with a high solids content. Pastes are no longer flowable, but rather spreadable.

[0032] Pastes are particularly suitable for this manufacturing process, as otherwise the edges can flow after printing, resulting in a blurred component. Pastes with shear-thinning properties are particularly popular. These pastes decrease in viscosity at high shear rates (such as during contact with the squeegee). However, when there is no shear, such as after the printing process, the viscosity is very high.

[0033] When creating the rotor lamination green body, as already described, the first region is larger than the second region. The first suspension contains a powder of a first alloy, and the second suspension contains a powder of a second alloy. According to the disclosure, the second alloy is magnetically soft and also has a higher magnetic permeability than the first alloy.

[0034] The printing process allows the production of particularly thin electrical sheets with a thickness of less than 0.4 mm, in particular less than 0.3 mm, and preferably less than 0.25 mm. The thinner the electrical sheet, the lower the eddy current losses occurring at high frequencies and the higher the efficiency of the electrical machine. However, this does not apply indefinitely. Due to the proportionally thicker insulation layer between the electrical sheets, the stacking factor decreases with increasingly thin sheets. The electrical sheets should therefore have a minimum thickness of 0.05 mm, preferably at least 0.1 mm, and more preferably at least 0.15 mm.

[0035] Preferably, the first alloy and the second alloy may have thermal expansion coefficients that differ by no more than 20%. For example, the thermal expansion coefficients of both alloys are advantageously in the range of 8-14 ppm / K and preferably in the range of 10-12 ppm / K.

[0036] Additionally or alternatively, the first alloy and the second alloy may have elastic moduli that differ by no more than 20%. The elastic moduli of both alloys may, for example, be in the range of 160-200 GPa, preferably in the range of 170-190 GPa.

[0037] Preferably, the sintering shrinkage of the rotor sheet green body in the first area should not deviate by more than 20% from the sintering shrinkage in the second area.

[0038] Advantageously, the sintering temperatures of the first alloy and the second alloy differ by no more than 250 K. For example, the sintering temperatures can be in the range of 1200-1500°C, preferably in the range of 1300-1400°C.

[0039] The advantageous design variants of the process minimize the scrap rate and thus improve the efficient use of resources.

[0040] All features explained with regard to the various aspects can be combined individually or in (sub-)combination with other aspects.

[0041] The disclosure as well as further advantageous embodiments and developments thereof are described and explained in more detail below with reference to the examples shown in the drawings. They show: - Fig. 1 a simplified schematic representation of a rotor lamination and a section thereof, - Fig. 2 a simplified schematic representation of a process for producing rotor laminations, - Fig. 3 a simplified schematic representation of an electrical machine, and - Fig. 4 a simplified schematic representation of a vehicle.

[0042] The following detailed description, taken in conjunction with the accompanying drawings, in which like numerals refer to like elements, is intended to describe various embodiments of the disclosed subject matter and is not intended to be the only embodiments. Each embodiment described in this disclosure is merely an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples contained herein are not exhaustive or limit the claimed subject matter to the precise forms disclosed. Various modifications of the described embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the described embodiments.Therefore, the described embodiments are not limited to the embodiments shown, but have the widest possible scope of application consistent with the principles and features disclosed herein.

[0043] All features disclosed below with respect to the embodiments and / or the accompanying figures may be combined alone or in any sub-combination with features of the aspects of the present disclosure, including features of preferred embodiments, provided that the resulting combination of features is meaningful to a person skilled in the art.

[0044] For the purposes of this disclosure, the phrase "at least one of A, B, and C" means, for example, (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all other possible combinations when more than three elements are listed. In other words, the phrase "at least one of A and B" generally means "A and / or B," namely "A" alone, "B" alone, or "A and B."

[0045] Fig. 1 shows a simplified plan view of a rotor lamination 10 and an enlarged section to the right of it.

[0046] The rotor lamination 10 is intended for an electrical machine that, through the arrangement of magnets within the rotor, combines the functionality of a permanent-magnet synchronous machine with an additional reluctance torque caused by the buried magnets. In principle, however, the technical teachings imparted can also be applied to pure reluctance synchronous machines or pure permanent-magnet synchronous machines.

[0047] The rotor lamination is essentially circular and flat and has a large number of cutouts 20. These have different functions depending on their position and orientation.

[0048] Some of the cutouts 20 are provided as pockets 21 for accommodating permanent magnets. They are generally elongated, but can also be shaped differently. Appropriate projections later hold the usually rectangular magnets in a defined position.

[0049] A magnetic force imposed by the stator's coil system is transferred to the rotor and generates the resulting torque.

[0050] Other cutouts 20 serve either to direct the magnetic flux along predetermined paths or to cool the rotor, for example, via formed coolant channels. Additional cutouts can be provided to reduce the rotor weight.

[0051] The cutouts 20, which form pockets 21 for receiving the magnets, additionally have lateral free areas as magnetic flux barriers 25.

[0052] The magnet pockets 21 are arranged in pairs in a V-shape and together form one pole of the synchronous machine. In the variant shown, two pairs of magnet pockets 21a, 21b are arranged radially one above the other. This arrangement is also known as a double-V configuration for electrical machines with buried permanent magnets.

[0053] Between the poles, further triangular or triangle-shaped free areas are formed, which also act as river barriers.

[0054] Other configurations to which the considerations made here can be easily transferred are arrangements with a single V-shaped arranged pair of magnetic pockets (“Single-V”) or the so-called “Delta” configuration, in which a third magnetic pocket is located (radially) above the V-shaped arranged pair of magnetic pockets.

[0055] In order to improve the efficiency and / or torque of an electric machine and in particular the range of such an electrically powered vehicle, a particularly advantageous hybrid electrical sheet layout for rotors is proposed.

[0056] The core idea is to combine high-performance soft magnetic alloys with conventional soft magnetic materials. The key is to avoid manufacturing the entire rotor core from such high-performance soft magnetic alloys, as this is very expensive, among other things.

[0057] Therefore, a layout is proposed that identifies specific areas that benefit most from the high-performance material and areas where the benefits are negligible.

[0058] In other words, the rotor lamination 10 comprises a first alloy in a first region 11 and a second alloy in a second region 12. At least the second alloy is soft magnetic and has a higher magnetic permeability than the first alloy. The first alloy can preferably also be soft magnetic or, alternatively, a non-magnetic iron-based alloy.

[0059] The first region 11 is larger than the second region 12. Particularly preferably, the second region 12 has only a small surface area relative to the first region 11. For example, the second region can account for a maximum of 25%, preferably a maximum of 20%, or even only 15% or less than 10% of the total surface area of ​​the rotor lamination 10 (without cutouts).

[0060] If necessary, it may be expedient to provide additional regions with different material properties in addition to the first and second regions 11, 12. For example, the first and second regions 11, 12 could be soft magnetic as described above, while the rotor lamination 10 additionally comprises a non-magnetic iron-based alloy in defined areas.

[0061] At least parts of the second region 12 lie between the magnetic pockets 21 and an outer circumference Ra of the rotor lamination 10. Preferably, the entire second region 12 can be arranged in a circular ring which is determined radially outwardly by the outer circumference Ra and inwardly essentially by the position of the pockets 21.

[0062] The V-shaped pockets 21 define a so-called magnetic island between them. The second region 12 comprises at least large portions of the magnetic islands 23. A web between the magnetic pockets 22 can comprise the first alloy.

[0063] In particular, the second region 12 comprises a region 24 between the superimposed pairs of pockets 21a, 21b.

[0064] The first region 11 or a third region, which specifically comprises a non-magnetic iron-based alloy, extends around the magnetic flux barriers 25 of the pockets 21.

[0065] Since the described rotor laminations 10 cannot be produced using conventional rolling and punching processes, a novel manufacturing process is proposed.

[0066] As an alternative to obvious manufacturing processes such as joining (e.g. laser welding) separately manufactured sheet metal parts, which would, however, cause a high expenditure in material handling, or generative layer construction processes such as selective laser sintering, which would generally be uneconomical in large-scale production, a production process is proposed in which a corresponding green body is first printed from suitable pastes using stencil printing and then sintered to form the rotor sheet.

[0067] Such a procedure is simplified and shown in a sketch in Fig. 2. It includes the following steps: First, in a first process step S1, a rotor sheet green body 50 is produced using a stencil printing process, for example screen printing.

[0068] In the production of sintered workpieces, a green compact or green body is an unsintered blank that is still easy to process. For example, it is powder bonded with a binder. A green body is dimensioned so that the final product achieves the desired size through shrinkage during sintering.

[0069] The production of the green compact comprises (in a suitable order) the application S1a of a first suspension 61 in a first region 51 of the rotor sheet green compact 50 defined by a first mask 71 and the application of a second suspension 62 in a second region 52 of the rotor sheet green compact 50 defined by a second mask 72. The suspensions 61, 62 can preferably be pastes.

[0070] The applied suspensions should be allowed to dry before the next processing step. Drying can be assisted, for example, with infrared radiators and takes approximately 1-25 seconds, depending on the layer thickness.

[0071] The first suspension 61 contains a powder of a first alloy and the second suspension 62 contains a powder of a second alloy.

[0072] The second alloy is soft magnetic and has a higher magnetic permeability than the first alloy.

[0073] Although the green compact 50 already corresponds in shape to the future rotor lamination 10, the metal powder is merely bound by a suitable binder as a matrix. The dimensions also differ from the final product. Nevertheless, the first area 51 of the green compact 50 is already larger than the second area 52.

[0074] In a second process step S2, the rotor sheet green body 50 is then sintered into a rotor sheet 30.

[0075] Preferably, the first alloy and the second alloy have thermal expansion coefficients that differ by no more than 20%, so that the rotor lamination 30 does not develop cracks or ripples during sintering. In particular, the thermal expansion coefficients are in the range of 8-14 ppm / K, preferably in the range of 10-12 ppm / K.

[0076] The elastic moduli of the first alloy and the second alloy should also not differ by more than 20%. Particularly suitable materials have elastic moduli in the range of 160-200 GPa, preferably in the range of 170-190 GPa.

[0077] To minimize unevenness, the sintering shrinkage of the rotor sheet green body 50 in the first area should not deviate by more than 20% from the sintering shrinkage in the second area. The printing pastes containing the alloys should be selected accordingly.

[0078] The sintering temperatures of the first alloy and the second alloy should also not differ by more than 250 K. In particular, the sintering temperatures can be in the range of 1200-1500°C, preferably in the range of 1300-1400°C.

[0079] In Fig. 3 shows an electrical machine 30 in a simplified perspective view. The electrical machine 30 comprises a rotor 31 having a plurality of rotor laminations 10, as previously shown and described. The electrical machine is a reluctance synchronous machine with buried magnets. These types of electrical machines are also known by the abbreviations IPM / IPSM ("Interior Permanent Magnet" or "Interior Permanent Magnet Synchronous Machine", i.e. permanent magnet machines with integrated magnets), PMa-SynRM ("Permanent Magnet Assisted Synchronous Reluctance Motor"), or IPM-SynRM ("Internal Permanent Magnet Synchronous Reluctance Motor", i.e. synchronous reluctance motor with buried permanent magnets).

[0080] This combination is particularly suitable for electric vehicles because it combines desirable properties, namely high efficiency at both low and high speeds. It also allows for a significant reduction in the proportion of permanent magnets.

[0081] Fig. Figure 4 shows a simplified, schematic representation of a vehicle 32 in a side view. The vehicle 32 has at least one electric machine as described above. The electric machine can be arranged in the vehicle 32, for example, as a front-wheel drive 41, a mid-wheel drive 42, an underfloor drive 43, or a wheel hub drive 44.

[0082] In this application, reference may be made to quantities and numbers. Unless expressly stated, such quantities and numbers are not to be considered limiting, but rather as examples of the possible quantities or numbers in connection with this application. In this context, the term "plurality" may also be used in this application to refer to a quantity or number. In this context, the term "plurality" means any number greater than one, e.g., two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus 5% of the stated value.

[0083] Although the disclosure has been shown and described with respect to one or more embodiments, those skilled in the art will be able to make equivalent changes and modifications after reading and understanding this description and the accompanying drawings. QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] US 2021 / 0111613 A1

[0005] US 2018 / 0233997 A1

[0006] US 11,362,552 B2

[0007] US 11,025,142 B2

[0008]

Claims

[1] Rotor lamination (10) comprising a first region (11) and a second region (12), wherein the first region (11) is larger than the second region (12), wherein the rotor lamination (10) has a first alloy in the first region (11) and a second alloy in the second region (12), wherein at least the second alloy is soft magnetic, and wherein the second alloy has a higher magnetic permeability than the first alloy. [2] Rotor lamination (10) according to claim 1, wherein the rotor lamination (10) has a plurality of cutouts (20), wherein at least some of the cutouts (20) form pockets (21) for receiving permanent magnets, and wherein at least parts of the second region (12) lie between the pockets (21) and an outer circumference (Ra) of the rotor lamination (10). [3] Rotor lamination (10) according to claim 2, wherein the pockets (21) are each arranged in pairs in a V-shape so that they define a magnetic island (23) between them, and wherein the second region (12) comprises major parts of the magnetic islands (23). [4] Rotor lamination (10) according to one of claims 2 or 3, wherein the pockets (21) are arranged such that two pairs of pockets (21a, 21b) are arranged in a V-shape and superimposed in the radial direction as a double V-shape, further wherein the second region (12) comprises a region (24) between the superimposed pockets (21a, 21b). [5] Rotor lamination (10) according to one of claims 3 or 4, wherein the pockets (21) have lateral, free regions as magnetic flux barriers (25), and wherein the first region (11) extends around the magnetic flux barriers (25). [6] Electrical machine (30) comprising a rotor (31) with rotor laminations (10) according to one of claims 1 to 5, in particular wherein the electrical machine (30) is a reluctance torque assisted permanent magnet machine. [7] Vehicle (32) with at least one electric machine (30) according to claim 6, in particular wherein the electric machine (30) is arranged as a front-wheel drive (41), mid-wheel drive (42), underfloor drive (43) and / or wheel hub drive (44) in the vehicle (32). [8] A method for producing rotor laminations (10) according to any one of claims 1 to 5, comprising the following steps: - S1: Creating a rotor sheet green body (50) in a stencil printing process, comprising • S1a: Applying a first suspension (61) in a first area (51) of the rotor sheet green body (50) defined by a first mask (71) and • S1b: Applying a second suspension (62) in a second area (52) of the rotor sheet green body (50) defined by a second mask (72), wherein the first area (51) is larger than the second area (52), wherein the first suspension (61) contains a powder of a first alloy and the second suspension (62) contains a powder of a second alloy, and wherein at least the second alloy is soft magnetic and has a higher magnetic permeability than the first alloy, - S2: Sintering the rotor sheet green body (50) to form a rotor sheet (30). [9] Method according to claim 8, wherein the first alloy and the second alloy have thermal expansion coefficients that differ by no more than 20%, in particular wherein the thermal expansion coefficients are in the range of 8-14 ppm / K, preferably in the range of 10-12 ppm / K, and / or wherein the first alloy and the second alloy have elastic moduli that differ by no more than 20%, in particular wherein the elastic moduli are in the range of 160-200 GPa, preferably in the range of 170-190 GPa. [10] Method according to one of claims 8 or 9, wherein the sintering shrinkage of the rotor sheet green body (50) in the first region does not deviate by more than 20% from the sintering shrinkage in the second region. [11] Method according to one of claims 8 to 10, wherein the sintering temperatures of the first alloy and the second alloy differ by no more than 250K, in particular wherein the sintering temperatures are in the range of 1200-1500°C, preferably in the range of 1300-1400°C.

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