Method for fixing a permanent magnet in a rotor lamination stack for an electric machine

Abstract

Method for fixing a permanent magnet (2) in a rotor lamination stack (1) for an electric machine, wherein the rotor lamination stack (1) has several receptacles for permanent magnets distributed in the circumferential direction of the rotor lamination stack (1), and the receptacles have different transverse and / or radial dimensions in a stacking direction of the rotor lamination stack, wherein adjacent individual laminations of the rotor lamination stack (1) can be arranged rotated relative to each other such that different radial dimensions of the receptacles arise in the stacking direction of the rotor lamination stack (1), and undercuts, depressions or bulges result in the stacking direction due to the different dimensions, comprising the steps: - Providing at least one permanent magnet (2), - Providing a stacked rotor lamination stack (1) with at least one receptacle (3) for the permanent magnet (2), - Providing a bonding material that swells when heated (4), - Inserting the permanent magnet (2) into the receptacle (3) of the rotor lamination stack (1), - Inserting the connecting material (4) into the recess (3) of the rotor lamination stack (1) so that the recess (3) is not completely filled, and - Heating the bonding material (4) so ​​that - the connecting material (4) swells, - the recording (3) is completely filled and - the permanent magnet (2) is fixed to the rotor lamination stack (1), wherein the connecting material (4) which swells upon heating comprises a swelling mat (4), wherein the swelling mat (4), after its expansion and after its hardening, leads to a positive connection with the stacked individual sheets.

Description

[0001] The invention relates to technologies for fixing a permanent magnet or several permanent magnets within a rotor lamination stack for an electric machine. In particular, the invention relates to a method for fixing a permanent magnet in a rotor lamination stack and to an electric machine with a rotor lamination stack in which a permanent magnet is fixed according to the method.

[0002] An electric machine with internal permanent magnets generally contains a rotor, which has a multitude of permanent magnets of alternating polarity around the outer circumference of a rotor lamination stack. The rotor rotates within a stator, which generally contains a multitude of windings and magnetic poles of alternating polarity.

[0003] In the high-volume production of electric machines, particularly electric motors for hybrid vehicles, the assembly, especially the fixing of the permanent magnets in the rotor, is identified as having a comparatively large potential for cost savings. It is known to integrate permanent magnets into the rotor lamination stack of a permanent magnet electric machine rotor. The permanent magnets are inserted into designated slots and either clamped by additional elements or bonded in place within the slot openings. According to the current state of the art, bonding is the predominant technology; however, this method requires complex techniques for assembly and recycling, such as separating the permanent magnets from the motor components.Furthermore, the use of adhesives causes considerable effort because, depending on the adhesive used, corresponding safety regulations must be observed due to potentially evaporating solvents or the like.

[0004] Alternative methods have been developed, such as clamping and crimping the permanent magnets in the groove, as well as using clamping elements, e.g., made of plastic. While these methods simplify recycling, they are often difficult to implement in assembly due to a lack of flexibility, as relatively large tolerances must be bridged. Other known methods, particularly due to weak press fits, often do not offer sufficient reliability at high speeds and vibration loads, such as those required for belt-driven and crankshaft starter generators.

[0005] Due to the typically large tolerances of permanent magnets, achieving a permanent, force-fit coupling of the permanent magnets within the holding pockets of the laminated core is difficult. Therefore, there is a need to connect the permanent magnets to the rotor in the holding pockets in a force-fit and, above all, permanent manner, thus protecting the permanent magnets from vibration-induced fracture or destruction caused by vibrations and resonances.

[0006] DE 10 2011 088 540 A1 discloses an electrical machine, in particular an electric motor, a generator or a transverse flux machine, comprising at least a permanent magnet or magnetic field conductor, a rotor or a rotor component with at least one receiving space for the permanent magnet or magnetic field conductor, and an expanding structural material between a wall of the receiving space and the permanent magnet or magnetic field conductor.

[0007] From DE 10 2011 119 512 A1, DE 10 2012 023 868 A1, DE 10 2015 211 410 A1, DE 10 2005 048 731 A1, and US 2011 / 0 057 529 A1, a method for manufacturing a rotor for a permanent magnet excited electric machine is known.

[0008] DE 10 2006 061 372 A1 discloses a PM rotor with radial cooling slots and a corresponding manufacturing process.

[0009] A rotor arrangement is shown in US 2008 / 0 284 267 A1.

[0010] DE 10 2014 211 113 A1 describes a rotor or a stator for an electric machine with improved flux guidance.

[0011] From DE 10 2012 202 529 A1, a permanent magnet fixation by means of a frame is known.

[0012] Starting from this, it is particularly an object of the invention to provide a method for fastening a permanent magnet or several permanent magnets within a rotor lamination stack of an electric machine, which overcomes the aforementioned disadvantages.

[0013] The problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims, the following description, and the figures.

[0014] The inventive method for fixing a permanent magnet in a rotor lamination stack for an electric machine comprises providing at least one permanent magnet and a stacked rotor lamination stack with at least one receptacle (“magnet pocket” or magnet receptacle) for the permanent magnet.

[0015] Furthermore, a heat-expanding bonding material is provided. The permanent magnet is inserted into the receptacle of the rotor lamination stack. The bonding material is also inserted into the receptacle of the rotor lamination stack, but not completely filled. This leaves a gap or space in the receptacle of the rotor lamination stack, which is not filled by the permanent magnet and / or the bonding material. The bonding material is then heated until it swells and completely fills the receptacle. The permanent magnet is also fixed to the rotor lamination stack by the heating of the bonding material. This is particularly effective after the bonding material has cured.

[0016] The invention is described below primarily with regard to fixing a permanent magnet in a receptacle. However, these descriptions also apply analogously to fixing further permanent magnets in further receptacles of the rotor lamination stack.

[0017] The permanent magnet can be connected to the rotor lamination stack, particularly by means of a force-fit and / or form-fit connection, using the swollen connecting material. Furthermore, the method is suitable for series production and allows for tolerance compensation of the permanent magnets, which are inserted into and fixed in the rotor lamination stack's receptacles, by means of the connecting material that swells upon heating (especially in the form of a swelling mat, see below).

[0018] The bonding material, in particular the expanding mat, is initially inserted into the rotor lamination stack with a relatively small dimension or height. This makes insertion particularly easy. Any remaining gap between the edge of the slot or magnet pocket and the permanent magnet after insertion of the permanent magnet and the bonding material is filled by the bonding material when it is heated to a sufficiently high temperature.

[0019] According to the invention, the connecting material, which swells upon heating, comprises a swelling mat. The swelling mat has proven to be particularly practical because it can provide a large surface area that can adapt to the geometry of the permanent magnet. When the swelling mat swells or increases in volume upon heating, it can very effectively compensate for tolerances of the permanent magnet and enable its fixation within the receptacle of the rotor lamination stack.

[0020] In addition to the frictional fixing of the permanent magnet to the rotor lamination stack described above, a resin can also be introduced into the bonding material so that, when the resin is heated to a sufficiently high temperature, the permanent magnet can also be bonded to the rotor lamination stack (material-bonded connection). In this sense, according to a further embodiment, a resin is introduced into the bonding material, whereby the resin begins to flow when heated.

[0021] The resin can flow both to the permanent magnet and to the rotor lamination stack, which defines the area where the permanent magnet is housed. At these points, the resin can wet the contact surfaces, so that upon subsequent curing, a metallurgical bond is formed between the rotor lamination stack and the permanent magnet. This metallurgical bond preferably exhibits the elastic and tough properties of the cured resin. This allows for particularly high tolerance compensation and, at the same time, a particularly strong connection between the rotor lamination stack and the permanent magnet. The resin can be, for example, an epoxy resin or a phenolic resin, especially in a modified form.

[0022] According to one embodiment, heating the bonding material creates gaps within it, and the resin is then introduced into these gaps. In this embodiment, the permanent magnet and the bonding material are first placed into the rotor lamination stack. Subsequently, the density of the bonding material is reduced by applying heat (causing it to swell). This creates gaps that can hold the resin, which begins to flow at higher temperatures. Thus, this process impregnates the bonding material already placed in the stack, particularly the swelling mat, with resin. The resin can then be deposited within the bonding material, gel, and harden.After curing, a strong bond with the properties of the cured impregnating resin is formed, particularly between a plastic ring and a winding head of an electric machine, which comprises a rotor lamination stack produced according to the inventive method. The preferably solvent-free resin system can be introduced into the spaces created by swelling within the bonding material and allowed to drip out. Furthermore, the resin can be gelled, cured, and cooled within the bonding material.

[0023] According to a further embodiment, the resin is introduced into the bonding material before the bonding material is heated. In particular, in a process step, the bonding material, especially the swelling mat, can be pre-impregnated with the resin, with the corresponding impregnation temperature being below the swelling temperature at which the bonding material begins to swell. Subsequently, in a further process step, the bonding material, especially the swelling mat, can swell so that—as described above—the permanent magnet is secured in the receptacle of the rotor lamination stack. The preferably solvent-free resin system can be heated, swelled, gelled, and cured in the spaces created by the swelling within the bonding material.

[0024] In particular, materials can be provided that are pre-impregnated or pre-soaked with resin in the form of sheets or mats, especially so-called prepregs (from the English: pre-impregnated). Prepregs are fiber-reinforced sheet materials impregnated with reactive resin compounds, which can be processed in a variety of ways and represent an ideal basis for construction materials. Prepreg systems are mostly based on reactive resins with a curing system that is latent at room temperature and highly reactive at elevated temperatures. Initially, the prepreg resins are in a reactive B state with medium to high viscosity. Further processing can be easily achieved by applying energy and simultaneously shaping the resin. This process converts low-molecular-weight, still meltable resins into the high-molecular-weight and meltable C state. Fabric prepregs are the most common, but tapes are also available.Modified epoxy resins or phenolic resins, which do not flow at room temperature, can be used as the resin matrix.

[0025] A prepreg described above can be inserted cold, along with the permanent magnet, into the rotor lamination stack. The prepreg resins may, for example, be in the reactive B state. Applying heat allows the prepreg to cure. Upon heating, the fabric swells, and the resin briefly liquefies, impregnating the fibers before the swollen fabric begins to disperse the impregnated fibers. Alternatively, the prepreg can transition to its final state through environmental conditions (such as humidity) or other phase-independent activators, for example, through chemical reaction, swelling, and / or embedding.

[0026] In a further embodiment, ceramic fibers are mixed with mica components within the bonding material. At sufficient temperature, these substances cause an increase in volume during the operation of an electric machine with a rotor lamination stack manufactured according to the inventive method. The bonding material, with its ceramic phases and mica components, can be heated and swell. The preferably solvent-free resin system can then be gelled and cured in the spaces created by the swelling within the bonding material.

[0027] The bonding material, which swells upon heating, can also comprise both swellable and non-swelling materials. The materials can be bound with a binder into a processable form, such as a mat. For example, a distribution of approximately 10% binder, 45% fibers, and 45% mica components might be used. The resin can then be introduced into the spaces created by the swelling within the bonding material and allowed to drip out. Furthermore, the resin can be gelled, cured, and cooled within the bonding material.

[0028] Furthermore, heating the bonding material can create a positive fit between the swollen bonding material and the rotor lamination stack. According to this embodiment, several receptacles for permanent magnets are provided, distributed circumferentially around the rotor lamination stack. These receptacles have different transverse and radial dimensions in the stacking direction of the rotor lamination stack. Specifically, in the individual laminations of the rotor lamination stack, a receptacle with a larger radial dimension can be followed by a receptacle with a smaller radial dimension in the circumferential direction. Adjacent individual laminations of the rotor lamination stack can be arranged rotated relative to each other such that the different radial dimensions of the receptacles arise in the stacking direction of the rotor lamination stack.

[0029] These differing expansion rates result in undercuts, depressions, or bulges in the stacking direction. When the bonding material, particularly the expanding mat, expands after curing, these features create a positive fit with the stacked individual laminations. In other words, the individual laminations of the rotor lamination stack are joined by a positive fit. This is achieved by varying the transverse expansion of the magnet pockets in the transverse or radial direction along the stacking direction, and by filling the magnet pockets with the expanding mat as it heats up to the magnet cross-section. The positive fit described above creates an additional clamping structure within the lamination stack, thereby increasing the dynamic rotor strength. Creating such a positive fit is suitable for mass production and can be easily integrated into the manufacturing process.

[0030] Furthermore, the source mat can have an I-shaped, L-shaped, U-shaped, or O-shaped cross-section. The permanent magnet can be covered or encased in the source mat in various ways, depending on the cross-sectional shape.

[0031] According to a further embodiment, it is provided that several receptacles for permanent magnets are distributed in the circumferential direction along the rotor lamination stack, with two adjacent receptacles arranged in a V-shape relative to each other.

[0032] An electric machine according to the invention comprises a rotor lamination stack in which at least one permanent magnet is fixed according to the method described above according to the invention.

[0033] Exemplary embodiments of the invention are explained in more detail below with reference to the schematic drawing. This shows Fig. 1 A cross-sectional view of part of a rotor lamination stack with a permanent magnet and source material included therein before heating, Fig. 2 the rotor lamination stack after Fig. 1 after heating the source material, Fig. 3 A top view of a single lamination of a rotor lamination stack with alternating smaller and larger retaining pockets, Fig. 4 a longitudinal section view through a part of a rotor lamination stack with several individual laminations arranged twisted relative to each other according to Fig. 3, wherein the individual sheets are positively connected to each other by a swelling mat, Fig. 5 a cross-sectional view of a part of a rotor lamination stack with a permanent magnet included therein, which is fixed within the rotor lamination stack by means of a source mat with an I-shaped cross-section, Fig. 6 a cross-sectional view of a part of a rotor lamination stack with a permanent magnet included therein, which is fixed within the rotor lamination stack by means of a source mat with an L-shaped cross-section, Fig. 7 a cross-sectional view of a part of a rotor lamination stack with a permanent magnet included therein, which is fixed within the rotor lamination stack by means of a source mat with a U-shaped cross-section, Fig. 8 a cross-sectional view of a part of a rotor lamination stack with a permanent magnet included therein, which is fixed within the rotor lamination stack by means of a source mat with an O-shaped cross-section, and Fig. 9 a cross-sectional view of a part of a rotor lamination stack with permanent magnets included therein, which are fixed by means of a source mat with an L-shaped cross-section within V-shaped receptacles of the rotor lamination stack.

[0034] Fig. 1 and Fig. Figure 2 illustrates an embodiment of a method for fixing a permanent magnet 2 in a rotor lamination stack 1 for an electric machine (not shown in detail). The rotor lamination stack 1 accommodates several permanent magnets 2 in receptacles 3, which are preferably equidistantly distributed around the rotor lamination stack 1 in its circumferential direction. The following descriptions focus primarily on fixing one permanent magnet 2 in a receptacle 3. However, these descriptions also apply analogously to fixing the remaining permanent magnets 2 in the remaining receptacles 3 of the rotor lamination stack 1.

[0035] First, the permanent magnet 2 and the stacked rotor lamination stack 1 are provided with a receptacle 3 (“magnetic pocket” or magnet receptacle) for the permanent magnet 2. Furthermore, a connecting material that swells upon heating, in the illustrated embodiment in the form of a swelling mat 4, is provided. The permanent magnet 2 is inserted into the receptacle 3 of the rotor lamination stack 1. The connecting material 4 is also inserted into the receptacle 3 of the rotor lamination stack 1, such that the receptacle 3 is not completely filled ( Fig. 1).

[0036] Thus, a gap 5 remains in the receptacle 3 of the rotor lamination stack 1, whereby this gap 5 is not filled by the permanent magnet 2 and / or the bonding material 4. The bonding material 4 is then heated so that it swells and completely fills the receptacle 3. Furthermore, heating the bonding material 4 enables the permanent magnet 2 to be fixed to the rotor lamination stack 1, particularly by friction once the bonding material 4 has hardened.

[0037] By heating to a sufficiently high temperature, the swelling mat 4 expands and closes the gap 5 between the geometry of the receptacle 3 (retaining pocket geometry) and the permanent magnet 2. The density of the swelling mat 4 also decreases, creating or increasing the size of gaps 6. These gaps 6 can be impregnated or filled with a resin that begins to flow at higher temperatures. This resin can be, for example, an epoxy resin or a phenolic resin, particularly in a modified form.

[0038] The resin can be introduced into the resulting spaces 6 after the swelling mat 4 has been heated. Alternatively, a pre-impregnated swelling mat (PREPREG) can be used, into which no further resin needs to be introduced after the swelling mat 4 has been heated. After the resin has cured, a firm bond forms between the retaining pocket geometry 3 and the permanent magnet 2, preferably exhibiting the elastic-tough properties of the cured impregnating resin. This enables tolerance compensation and simultaneously creates a firm bond between the retaining pocket geometry 3 and the permanent magnet 2.

[0039] Fig. 3 and Fig. Figure 4 illustrates how stacked individual sheets 7 of a rotor lamination stack 1 can be connected to each other by means of a swelling mat 4 through a positive locking mechanism. This is achieved by Fig. The rotor lamination package 1 shown in section 4 comprises a plurality of individual laminations 7 according to Fig. 3, wherein the individual sheets 7 are stacked on top of each other in a stacking direction L. In the by Fig. In the embodiment shown in Figure 3, the single sheet 7 comprises a total of 8 receptacles 9 and 10 distributed equidistantly in the circumferential direction U. Immediately adjacent receptacles 9 and 10 are each arranged offset from each other by a division angle of 45°.

[0040] As from Fig. As can be seen in Figure 3, a larger recess 9 alternates with a smaller recess 10 in the circumferential direction U. The larger recess 9 has a greater extent than the smaller recess 10, particularly in a transverse direction or in a radial direction r of the sheet 7. The individual sheets 7 are stacked congruently on top of each other, with each sheet 7 being rotated or twisted by 45° in the circumferential direction U from one sheet 7 to the sheet 7 above it. This creates the Fig. Figure 4 shows the structure of undercuts 8 in the stacking direction L of the rotor lamination stack 1. The swelling mat 4 can fill these undercuts 8 and after the swelling mat 4 has hardened, the Fig. The positive locking mechanism shown in section 4 between the swelling mat 4 and the rotor lamination stack 1 with its undercuts 8 is created. This positive locking mechanism generates an additional clamping structure in the rotor lamination stack 1 and increases its dynamic strength.

[0041] Fig. Figure 5 shows another permanent magnet 2, which is mounted in a receptacle 3 of a rotor lamination stack 1. A swelling mat 4 was also arranged within the receptacle 3, the swelling mat 4 having already been heated so that it expanded and the receptacle 3 in the area by Fig. The state shown in Figure 5 is already completely filled without any remaining gap. After the swelling mat 4 has hardened, the permanent magnet 2 is fixed within the receptacle 3, whereby – as described above – resin can additionally be introduced into the swelling mat 4 to bond the permanent magnet within the receptacle 3 as well. Fig. 5 the source mat 4 has an I-shaped cross-section, so that the source mat 4 can completely cover one side surface of the permanent magnet 2.

[0042] The through Fig. The embodiment shown in section 6 differs from the embodiment shown in section 6. Fig. 5 by the shape of the source mat 4, which according to Fig. 6 has an L-shaped cross-section. Thus, the source mat 4 can, in particular, completely cover two adjacent, perpendicular side surfaces of the permanent magnet 2.

[0043] The through Fig. The embodiment shown in section 7 differs from the embodiment shown in section 7. Fig. 5 by the shape of the source mat 4, which according to Fig. 7 has a U-shaped cross-section. Thus, the source mat 4 can, in particular, completely cover three adjacent, perpendicular side surfaces of the permanent magnet 2.

[0044] The through Fig. The embodiment shown in section 8 differs from the embodiment shown in section 8. Fig. 5 by the shape of the source mat 4, which according to Fig. 8 has an O-shaped cross-section. Thus, the source mat 4 can have a closed cross-section and, in particular, completely cover four adjacent, perpendicular side surfaces of the permanent magnet 2.

[0045] Fig.Figure 9 shows a rotor lamination stack 1, which comprises a total of eight receptacles 3 arranged equidistantly around the circumference of the rotor lamination stack 1 and arranged in pairs in a V-shape relative to each other. Two receptacles 3 arranged in pairs converge towards the radial interior of the rotor lamination stack 1. As described above, a permanent magnet 2 is fixed in one of the receptacles 3 by means of a source mat 4. In the illustrated embodiment, the source mats 4 each have an L-shaped cross-section.

Claims

[1] Method for fixing a permanent magnet (2) in a rotor lamination stack (1) for an electric machine, wherein the rotor lamination stack (1) has several receptacles for permanent magnets distributed in the circumferential direction of the rotor lamination stack (1), and the receptacles have different transverse and / or radial dimensions in a stacking direction of the rotor lamination stack, wherein adjacent individual laminations of the rotor lamination stack (1) can be arranged rotated relative to each other such that different radial dimensions of the receptacles are created in the stacking direction of the rotor lamination stack (1), and undercuts, depressions or bulges result in the stacking direction due to the different dimensions, comprising the steps: - Providing at least one permanent magnet (2), - Providing a stacked rotor lamination stack (1) with at least one receptacle (3) for the permanent magnet (2), - Providing a bonding material that swells when heated (4), - Inserting the permanent magnet (2) into the receptacle (3) of the rotor lamination stack (1), - Inserting the connecting material (4) into the recess (3) of the rotor lamination stack (1) so that the recess (3) is not completely filled, and - Heating the bonding material (4) so ​​that - the connecting material (4) swells, - the recording (3) is completely filled and - the permanent magnet (2) is fixed to the rotor lamination stack (1), wherein the connecting material (4) which swells upon heating comprises a swelling mat (4), wherein the swelling mat (4), after its expansion and after its hardening, leads to a positive connection with the stacked individual sheets. [2] Method according to one of the preceding claims, wherein a resin is introduced into the bonding material (4), wherein the resin begins to flow upon heating. [3] Method according to claim 2, wherein by heating the bonding material (4) gaps (6) are created within the bonding material (4), and wherein the resin is subsequently introduced into the gaps (6) created. [4] Method according to claim 2, wherein the resin is introduced into the bonding material (4) before the bonding material (4) is heated. [5] Method according to one of the preceding claims, wherein ceramic fibers are mixed with mica components within the connecting material (4). [6] Method according to any of the preceding claims, wherein the connecting material (4) which swells upon heating comprises swellable and non-swellable materials. [7] Method according to one of the preceding claims, wherein a positive connection is created between the swollen connecting material (4) and the rotor lamination stack (1) by heating the connecting material (4). [8] Method according to any of the preceding claims, wherein the swelling mat (4) has an I-shaped, an L-shaped, a U-shaped or an O-shaped cross-section. [9] Method according to one of the preceding claims, wherein several receptacles (3) for permanent magnets (2) are distributed in the circumferential direction along the rotor lamination stack (1), and wherein two adjacent receptacles (3) are arranged in a V-shape relative to each other. [10] Electric machine comprising a rotor lamination stack (1) in which at least one permanent magnet (2) according to one of the preceding claims is fixed.

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