WO2023051861A1

WO2023051861A1 - Laminated electrical steel core for an electric machine and method for producing a laminated electrical steel core

Info

Publication number: WO2023051861A1
Application number: PCT/DE2022/100635
Authority: WO
Inventors: Wilfried Schwenk; Jürgen Seifermann; Tobias Doll; Martin Bühler; Volker Lang
Original assignee: Schaeffler Technologies AG & Co. KG
Priority date: 2021-09-29
Filing date: 2022-08-24
Publication date: 2023-04-06
Also published as: DE102021125212A1; DE102021125212B4

Abstract

The invention relates to a laminated electrical steel core (2) for an electric machine, comprising a number of individual sheets (3), which are stacked so as to be electrically insulated from one another and have through-holes (4, 8) that are aligned with one another, and a duroplastic potting element (5) which penetrates the through-holes (4, 8) and thus engages behind the individual sheets (3) with a form-fit.

Description

Electrical laminated core for an electrical machine and method for producing an electrical laminated core

The invention relates to an electrical laminated core for a stator or rotor of an electrical machine. Furthermore, the invention relates to a method for producing an electrical laminated core which is suitable for use in an electrical machine.

EP 0 729 665 B1 discloses a method for producing an armature for an electric motor. This method may include creating a plastic fill by injection molding, transfer molding, or compression molding. In the case of EP 0 729 665 B1, the plastic filling is attributable to a commutator which, like a laminated core, is arranged on a shaft.

In contrast to injection molding, in which thermoplastic material is processed, duroplastic material is processed in transfer molding. This can be done by using a piston to introduce molding compound from a heated antechamber into a cavity and hardens there. Also known in principle is the production of fiber-reinforced workpieces by transfer molding.

The encapsulation of a stator of an electrical machine with a duroplastic compound is described, for example, in DE 10 2013 227 054 A1. In this case, a floating bearing is molded into the overmolding. Instead of a duroplastic, a fiber matrix semi-finished product with a duroplastic matrix should also be usable. The stator can in particular be designed as a segmented stator.

DE 10 2015 212 007 A1 discloses a device for forming an overmolding at least in sections. In this case, a rotor shaft is overmoulded with a duroplastic or thermoplastic material. The device after

SUBSTITUTE SHEET (RULE 26) DE 10 2015 212 007 A1 includes a clamping element which is designed to fix an insert in an insertion recess.

DE 10 2017 220 123 A1 discloses slot wall insulation for a stator of an electric motor. The slot wall insulation should be able to be formed directly on a surface of a stator lamination in an injection molding process. Thus, the slot wall insulation is tooth-shaped. Due to the tooth-shaped design, a recess is formed which is suitable for receiving an electrical conductor.

DE 10 2008 032 214 B4 discloses a reluctance motor, the rotor of which has recess areas arranged regularly in the circumferential direction. The rotor is designed as a laminated core, with the recesses being punched out of the sheet metal parts. The individual sheet metal parts can be held together by punching. Optionally, the recesses are injected with plastic.

DE 10 2016 24 249 A1 describes a method for producing a rotor for a synchronous reluctance machine, which comprises the method steps of stacking a rotor stack and spraying flux barriers within the rotor stack with a plastic material containing magnetic particles. The magnetic particles are also aligned by applying an external magnetic field.

DE 25 36 390 B1 discloses a squirrel-cage rotor for an electrical machine with a squirrel cage injected into the laminated rotor core. The squirrel-cage cage keeps the laminated rotor core pressed together and comprises short-circuit rings on the face side, with at least one of the short-circuit rings being toothed with a rotor hub or rotor shaft in a way that prevents it from twisting and shifting.

The invention is based on the object of further developing components of electrical machines, ie electric motors, generators or transformers, in the manufacture of which transfer molding is used, compared to the prior art mentioned, in particular with regard to manufacturing aspects. This object is achieved according to the invention by an electrical laminated core having the features of claim 1 . The object is also achieved by a method for producing a stack of electrical laminations suitable for use in an electrical machine according to claim 9. In the following in connection with the production method, the configurations and advantages of the invention also apply analogously to the device, i.e. for use in an electrical machine provided lamination stack, and vice versa.

The stack of electrical laminations comprises a number of individual laminations which are stacked in an electrically isolated manner from one another and have openings which are aligned with one another. Furthermore, a duroplastic casting element produced by injection molding is provided, which penetrates the entirety of the openings and thereby engages behind the individual sheets in a form-fitting manner.

The duroplastic material, which is processed by transfer molding, has electrically insulating properties. In this way, in particular, electrical flashovers between electrical lines and laminations of the electrical laminated core are ruled out. At the same time, the material composition can be selected in such a way that there is sufficiently high thermal conductivity for the application. In particular, epoxy resin can be used as the duroplastic material, which is available on the market, for example, under the name EPOXIDUR® EP 3161 E.

In order to produce the required form fit with the metallic components of the laminated core, the casting element, which is elongated overall, has a non-uniform width over its length. For example, the casting element has a maximum width between two individual sheets, which is at least 1.5 times the minimum width of the casting element to be measured in the openings. In this case, the maximum width is in particular no more than three times the minimum width of the casting element. According to various possible embodiments, the individual sheets are stacked one on top of the other without any positive locking formed directly between these individual sheets. This has the advantage that any process steps in which the individual sheets are formed, such as by clinching, can be omitted. Steps such as laser welding can also be omitted. The at least one casting element, which is produced by transfer molding, can represent the only means for holding the entire laminated core together.

As far as the shape of the openings in the sheet metal stack is concerned, a wide variety of variants are possible. If the openings have a closed border, they can in particular be circular, oval or polygonal holes. Likewise, the openings can have, for example, a cloverleaf, grandfather clock or dovetail shape. In all cases, as a result of the curing of the duroplastic material, tension can be generated within the laminated core stack of electrical conductors, with the casting element being particularly suitable for transmitting tensile forces and thus being able to represent a tie rod. The often given positive connection between the casting element and the individual laminations of the electrical laminated core can ensure that forces are not to be transmitted over the entire length of the casting element, but only over a fraction of its length. Overall, in relation to the dimensions of the casting element, high forces can therefore be transmitted within the laminated core stack.

In the case of openings without a closed border, these form in particular a groove, for example a U-shaped groove of a stator. Electrical conductors can be inserted into the stator slot. It is also possible to encapsulate conductors directly within the stator slot with duroplastic material. If copper windings are inserted using the hairpin method, a slot can be closed directly by transfer molding, so that there is no need to insert a sealing wedge.

In general, the stack of electrical laminations can be produced by using a stack of individual laminations that are electrically insulated from one another and have apertures that are aligned with one another. is provided by transfer molding with an overall bolt-shaped duroplastic casting element introduced into the openings, which is designed to absorb tensile forces between any of the individual sheets. In the case of transfer molding, that is to say injection molding, duroplastic material is introduced between the individual sheets in particular in such a way that a form fit is created between each of the individual sheets and the casting element.

If the laminated core is part of an electric motor rotor to be fitted with permanent magnets, the individual magnets can be fixed in a single operation together with the production of the connection between the individual laminations by transfer molding. Epoxy resin is particularly suitable as the material for this. Compared to conventional manufacturing methods, the number of work steps and the tuning effort are reduced, while at the same time a high geometric precision of the end product, ie the laminated core including the permanent magnets, can be achieved.

The process of transfer molding can be combined with a magnetic fixation of the laminated core. This applies in particular to process variants in which a stator slot is insulated by transfer molding. Regardless of the type of laminated core, the individual sheets can be centered using a mandrel, which also ensures the required squareness within the assembly to be assembled. At the same time, the laminated core can be adjusted in terms of its dimensions in the axial direction, ie the direction normal to the planes in which the individual sheets are arranged, by pressing together a tool provided for the transfer molding.

The particular advantage of the invention is that in the production of stators or rotors of electric motors or generators, complex production steps such as gluing or forming are completely eliminated or can at least be made much simpler compared to conventional solutions. Functional limitations of the manufactured component, i.e. stator or rotor, are not to be accepted here. Rather, the manufacturing process is characterized by an applicability for a large number of different electrotechnical products whose components are loaded by operational forces. A non-destructive dismantling of the laminated core stack, which is held together by the duroplastic casting element or a plurality of such casting elements, is generally not provided. The electrical sheet stack can be produced using standardized electrical sheets without a coating.

Several exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Show in it:

1 shows the structure of an electrical laminated core for an electrical machine in a schematic sectional view,

2 shows an electrical laminated core of a stator of an electric motor in a perspective view,

3 shows an arrangement for connecting the individual laminations of the electrical laminated core according to FIG. 2 by means of transfer molding,

4 shows the arrangement according to FIG. 3 without the laminated core,

5 shows a detail of an electrical laminated core of a rotor of an electric motor,

6 shows the cross section of a casting element of the arrangement according to FIG. 1,

7 shows a further casting element for an electrical laminated core in a view analogous to FIG. 6, 8 a detail of a rotor of an electric motor comprising an electrical laminated core in a plan view,

FIG. 9 shows the arrangement according to FIG. 8 in a perspective view.

Unless otherwise stated, the following explanations relate to all exemplary embodiments. Parts that correspond to one another or have the same effect in principle are identified by the same reference symbols in all figures.

A functional part of an electric motor, identified overall by the reference number 1 , that is to say a stator or a rotor, comprises an electrical laminated core 2 which is made up of a large number of individual laminations 3 . Electrically insulating layers are located between the individual sheets 3 and can be provided either by separate components or by coatings of the individual sheets 3 . It is also possible to produce the electrical insulation within the electrical laminated core 2 exclusively by the transfer molding method, which will be discussed in detail below.

In all cases, the stacked individual laminations 3, ie the individual electrical laminations, have a plurality of openings 4 with a closed border, in particular circular holes, and/or grooves 8, which are generally referred to as openings without a closed border. The openings 4, 8 can be produced, for example, by punching. At least individual openings 4, 8 are completely or partially filled with a casting element 5 made of duroplastic material. The casting elements 5 are electrically insulating and produce positive-locking, mechanically resilient connections between the individual sheets 3 .

Each casting element 5 extends parallel to the central axis of the functional part 1 and comprises so-called constricted sections 6 and form-fitting terminations 7 arranged alternately. The width of the constricted sections 6 is indicated by Bmin, the width of the form-fitting sections 7 by Bmax. In the axial direction of Each constricted section 6 of the functional part 1 and thus also of the casting element 5 has a thickness DE which corresponds to the thickness of an individual sheet 3 . The given between the individual sheets 3 thickness of the form-fitting section 7 is D? specified.

In the exemplary embodiment according to FIG. 1, the casting element 5 is in the form of a bolt, the constricted sections 6 of which are designed as annular circumferential grooves. The diameter of a cylinder circumscribing the bolt has a diameter which corresponds to the maximum width Bmax. The form-fitting sections 7 and the constricted sections 6 arranged between them have the shape of circular discs or bar sections. Forces acting on the individual sheets 3 , including axial forces, in relation to the central axis of the functional part 1 , are absorbed by the casting elements 5 with the aid of the form-fitting sections 7 . This also applies in cases in which - in contrast to what is shown in Fig. 1 - the form-fitting sections 7 are significantly less extended in the axial direction than the constricted sections 6.

Steps in the production of the electrical laminated core 2 according to FIG. 2 are explained in more detail below with reference to FIGS. 3 and 4. To introduce the mechanically resilient casting elements 5, a tool designated 11 overall is used, which includes a sprue plate 12, a ventilation plate 13 and a support plate 14 and is designed as a transfer molding tool, ie a tool for injection molding. In the state visible in FIG. 3 , duroplastic, preheated material is pressed from the sprue plate 12 through the openings 4 , the openings 4 being present in the present case in the form of nine through-holes distributed uniformly around the circumference of the stator 1 .

During the injection molding, that is to say transfer molding, the form-fitting sections 7 of the casting element 6 are also automatically produced, it being possible for the actual shape of the form-fitting elements 7 to deviate from the idealized shape illustrated in FIGS. After the casting elements 5 have hardened, the functional part 1 can be removed from the tool 11 . As can be seen from Fig. 4, the tool 11 has in its middle section, the height of which corresponds to the axial extension of the stator 1, several, in the present case three, strip-shaped centering swords 15, with which the correct positioning of the laminated core 2 relative to the tool 11 is ensured during transfer molding.

5 shows a detail of a rotor 1 as a functional part of an electric motor, namely an internal rotor. The rotor 1 can also be produced with the aid of a tool 11, the basic structure of which corresponds to the design according to FIGS. In the case of FIG. 5, the opening 8 is in the form of a groove, the flanks of which are denoted by 9 and the base of which is denoted by 10. In adaptation to the shape of the groove 8, the casting element 5 also has a U-shaped cross section. The open area of the slot 8 can be filled with windings or magnets. The windings or magnets can be embedded directly in the casting element 5 in a manner that is not shown.

The form-fitting sections 7 of the U-shaped casting element 5 according to FIG. 5 protrude beyond the groove flanks 9 and the groove base 10 into the areas between the individual sheets 3, so that in this case, as well as in the exemplary embodiment according to FIGS. 1 and 6, the desired form fit between the individual sheets 3 is given.

7 shows a dovetail-shaped cross-sectional design of the duroplastic casting element 5, which can be considered for both stators and rotors as functional parts 1 of electric motors or generators. In a way that is not shown, the casting element 5 could also have a cross section in the manner of an hourglass or a cloverleaf. In all cases, the form-fitting sections 7 protrude beyond the constricted sections 6 in the transverse direction of the casting element 5, which is elongated overall, so that the desired form-fitting function is provided. Connections between the individual sheets 3 that go beyond this, for example by means of stamped stacking, gluing or welding, are not required to produce the required mechanical stability of the functional part 1 . A rotor 1 of an electric motor is shown in detail in FIGS. 8 and 9, magnets 17, namely permanent magnets, being located in numerous recesses 16 provided by the laminated core 2 of the rotor 1. Furthermore, an opening 4 with a closed border can be seen in FIGS. 8 and 9, which is provided for receiving a casting element 5 (not shown in this case) made of a duroplastic material, namely epoxy resin.

In the present case, the opening 4 is designed in the manner of a four-leaf clover and is therefore particularly suitable for absorbing forces in a wide variety of directions. When the material from which the casting element 5 is formed hardens, mechanical stresses arise which hold the laminated core together particularly effectively. Several cloverleaf-shaped openings 4 of the type shown are distributed over the cross section of the electrical laminated core 2 and in particular replace separate metallic connecting elements and connections of conventional electric motors formed by deformation of the individual laminations 3 .

Reference character list

1 functional part, stator, rotor

2 sheet metal package

3 single sheet

4 breakthrough with closed border

5 potting element

6 constricted section of the casting element

7 form-fitting section of the casting element

8 slots

9 groove side

10 groove bottom

11 tool

12 sprue plate

13 vent panel

14 carrier plate

15 hundredweight sword

16 recess

17 magnets

Bmax maximum width

Bmin minimum width

D ₇ Thickness of the interlocking section

EN Thickness of the single sheet

Claims

patent claims

1 . Electrical laminated core (2) for an electrical machine, with a number of individual laminations (3) which are stacked and electrically insulated from one another and have apertures (4, 8) aligned with one another, and with one of the apertures

(4, 8) penetrating duroplastic casting element (5) which engages behind the individual sheets (3) in a form-fitting manner.

2. Electrical laminated core (2) according to claim 1, characterized in that the casting element (5) has a maximum width (Bmax), which is given between two individual sheets (3) and is at least 1.5 times the minimum width given in the openings (Bmin) of the casting element (5).

3. Electrical laminated core (2) according to claim 2, characterized in that the maximum width (Bmax) is no more than three times the minimum width (Bmin) of the casting element (5).

4. Electrical laminated core (2) according to any one of claims 1 to 3, characterized in that the individual sheets (3) are stacked on top of one another without any positive locking formed between these individual sheets (3).

5. Electrical laminated core (2) according to any one of claims 1 to 4, characterized in that the openings (4) each have a closed border.

6. Electrical laminated core (2) according to any one of claims 1 to 4, characterized in that the openings (8) are designed as a groove, in particular a stator groove.

7. Electrical laminated core (2) according to any one of claims 1 to 6, characterized in that this is attributable to a rotor of an electrical machine.

8. Electrical laminated core (2) according to any one of claims 1 to 6, characterized in that this is attributable to a stator of an electrical machine. Method for producing an electrical laminated core (2), wherein a stack of individual sheets (3) electrically insulated from one another and having openings (4, 8) aligned with one another, by transfer molding with at least one generally bolt-shaped duroplastic material introduced into the openings (4, 8). Casting element (5), which is designed to absorb tensile forces between any of the individual sheets (3), is provided. Method according to Claim 9, characterized in that duroplastic material is introduced between the individual sheets (3) during transfer molding in such a way that a form fit is produced between each of the individual sheets (3) and the casting element (5).