Sheet metal for forming a laminated stack for a rotor of an electric machine and electric machine

Abstract

Sheet metal (100) for forming a laminated core (10) for a rotor (11) of an electric machine (200), wherein the sheet metal (100) is oriented with respect to a longitudinal axis (A L ) has a cylindrical lateral surface (12) and radially extending first cutouts (13) and radially extending second cutouts (14), each having closed lateral surfaces (151, 152), wherein each first cutout (13) and second cutout (14) are mirror-symmetric with respect to a radially extending common axis of symmetry (A S ) are formed, wherein the first cutouts (13) are designed to receive short-circuit bars (16), characterized in that the first cutouts (13) on the side facing the lateral surface (12) of the sheet (100) each have a bulge (17) with a convex surface section (18) and a first vertex (S1) which lies on the respective axis of symmetry (A S) is arranged, and the second cutouts (14) on the side facing away from the lateral surface (12) of the sheet (100) each have a recess (20) with a concave surface section (21) and a second vertex (S2) which lies on the respective axis of symmetry (A S ) is arranged.

Description

[0001] The invention relates to a sheet metal for forming a laminated core for a rotor of an electric machine according to the preamble of claim 1 and an electric machine with a stator and a rotor according to the preamble of claim 9.

[0002] The longitudinal axis of the sheet metal defines a cylindrical coordinate system. The directional specifications given here, in particular longitudinal, radial, and tangential, refer to this cylindrical coordinate system.

[0003] The generic patent CN 1 05 811 700 A shows a rotor groove of an asynchronous motor, comprising a rotor groove main body part and a rotor groove opening part, wherein the rotor groove main body part is used for casting a rotor conductor strip and an iron core bridge is formed between the rotor groove opening part and the rotor groove main body part. The main part of the rotor groove body and the opening part of the rotor groove are arranged on the rotor groove, and the iron core bridge is arranged between the opening part of the rotor groove and the main part of the rotor groove body.

[0004] It is known from the prior art that losses occur in the rotor of an electric machine, particularly an asynchronous machine, during operation, leading to heating of the machine. Dissipating this heat from the rotor is technologically challenging and, in the prior art, is typically achieved via the rotor shaft and thermally sensitive bearings. Alternative cooling concepts, such as internal cooling of the rotor shaft or forced cooling by impeller fans, are described in the prior art, but are always associated with high manufacturing costs or additional losses. Therefore, for the operation and economic efficiency of an electric machine, especially an asynchronous machine, it is crucial to minimize overall rotor losses.

[0005] One type of loss is electrical heat loss, which occurs particularly in the conductive areas of the rotor, such as the laminations of the core or the short-circuit discs. This electrical heat loss in the rotor results from the rotor currents flowing within individual short-circuit bars and the short-circuit discs. Various publications and measurements have shown that additional electrical heat losses occur in the rotor that cannot be explained solely by the current flowing in the rotor and the DC resistance of the rotor cage. According to current technology, these additional losses are accounted for by a general surcharge factor, which, by its very nature, provides no information about the actual distribution and impact of these losses within the rotor.These additional losses result from an increase in the effective resistance of the rotor due to current displacement effects and additional eddy currents caused by alternating magnetic fields entering the rotor.

[0006] According to DE 10 2016 124 830 A1, a sheet metal component of a laminated core of an electric machine is known, designed to reduce electrical heat losses. Specifically, a sheet metal component for forming a laminated core for a rotor of an electric machine, in particular an induction machine, is disclosed, wherein the sheet metal component has radially extending grooves for receiving short-circuit bars, with at least one groove having a first, radially inner end and a second, radially outer end. The sheet metal component has a recess in a region located radially further outward than the second end of the groove, wherein the recess is closed on at least one side in the radial direction. A completely closed configuration of the recess is also described.

[0007] Comparable sheets with completely closed recesses are described in EP 2 999 100 B1 and DE 692 02 702 T2.

[0008] Other prior art documents are known.

[0009] CN 2 01 298 795 Y provides a squirrel-cage rotor for a variable-frequency induction motor, comprising a rotor iron core and a rotor guide bar, wherein the rotor iron core is manufactured from silicon steel sheets by overlapping pressing. The squirrel-cage rotor is characterized in that each rotor slot is formed from a main part of the rotor slot and an opening part of the rotor slot, wherein the rotor guide bar is formed within the main part of the rotor slot, the material filling the opening part of the rotor slot absorbs air, and the opening part of the rotor slot is positioned between a ferromagnetic bridge and the outer surface of the rotor iron core. The ferromagnetic bridge serves as part of the rotor iron core and forms a channel of the rotor slot through which the flux escapes by connecting both ends of the opening part of the rotor slot.

[0010] DE 689 11 929 T2 relates to a squirrel-cage induction motor for frequency converter operation with a rotor whose rotor core has a plurality of substantially axially extending rotor slots in which rotor conductors are arranged, wherein each rotor slot has a main part in which a rotor conductor is arranged, and a slot opening which lies between the main part and that surface of the rotor which delimits the air gap of the motor, wherein a magnetic bridge is provided for separating the slot opening from the main part of the slot, wherein the ends of the bridge adjoin the remainder of the rotor core on both sides of the slot opening, and wherein that surface of the bridge which faces the interior of the rotor conductor has a shape curved towards the interior of the rotor conductor.

[0011] The sheet metal components and / or electrical machines known according to the state of the art have proven to be improvable. In particular, known sheet metal components exhibit high electrical heat losses and are expensive to manufacture.

[0012] Starting from this premise, the object of the invention is to improve sheet metal and / or electrical machines known according to the prior art. In particular, a sheet metal and / or an electrical machine with low thermal losses is to be proposed, wherein the sheet metal should be inexpensive to manufacture. This object is achieved by the sheet metal according to claim 1 and by the electrical machine according to claim 9. According to the invention, the first cutouts on the side facing the outer surface of the sheet metal each have a bulge with a convex surface section and a first vertex located on the respective axis of symmetry. Furthermore, the second cutouts on the side facing away from the outer surface of the sheet metal each have a recess with a concave surface section and a second vertex located on the respective axis of symmetry.The unique geometry of the first and second punchings significantly reduces heat losses, leading to a substantial increase in efficiency. Furthermore, this special geometry results in a robust die contour, leading to exceptionally long tool life for the stamping presses used in sheet metal production. Finally, this unique geometry has proven advantageous in the casting of the short-circuit bars.

[0013] Regardless of this, the second set of cutouts allows for pressure equalization in the assembled state and during normal operation, so that pressure equalization does not occur via the air gap, thus reducing oil drag losses. If a pressure gradient occurs between the left and right sides of the motor housing, for example due to uneven fluid distribution, pressure equalization between the sides is necessary. Without air channels in the sheet metal stack, this occurs via the air gap. This creates the risk that oil will be drawn into the air gap by the airflow, resulting in the aforementioned drag losses.

[0014] Advantageous embodiments of the invention are specified below and in the dependent claims.

[0015] Preferably, the convex surface section of the bulge of the first cutout is bounded on both sides by inflection points and transitions there into surface sections with a concave curvature. The surface sections with concave curvatures preferably merge into a common convex surface section, thus providing a completely closed contour of the first cutout. Alternatively, further surface sections with different curvatures can be interposed.

[0016] The concave surface section of the indentation of the second cutout is preferably bounded on both sides by inflection points and transitions there into surface sections with a convex curvature. The surface sections with a convex curvature preferably have a third vertex and a fourth vertex in the radial direction. The third and fourth vertices are thus the points on the lateral surfaces of the second cutout, each at a minimal distance from the longitudinal axis. The convexly curved surface sections with the third and fourth vertices preferably transition into a common convex surface section, thus providing a completely closed contour of the second cutout. Alternatively, further surface sections with different curvatures can be interposed.

[0017] According to an advantageous embodiment, a web is arranged between each first and second cutout, which run along a common axis of symmetry. This web has a constant width in the area between the third and fourth vertices, particularly between the inflection points of the bulge or indentation. The width of the web is measured perpendicular to a center line that runs equidistantly between the bulge and the indentation. The constant width of the web has a beneficial effect on stability and acoustic properties. Furthermore, the geometry results in particularly high stability of the rotor lamination with respect to centrifugal force resistance under the influence of rotational speed, because the forces acting on the web are low due to the geometry.

[0018] The first and second cutouts, which run along a common axis of symmetry, are preferably arranged relative to each other such that the protrusions of the first cutouts are flanked, at least partially, in the tangential direction by the indentations of the second cutouts. In other words, it is preferably provided that the distance between the longitudinal axis of the sheet and the first vertex is greater than the distance between the longitudinal axis of the sheet and the third or fourth vertex.

[0019] The concave or convex curved surface sections of the first and second cutouts are preferably circularly curved, which has proven particularly advantageous for the tool life of the stamping presses during the production of the sheets. The sheets of the described type are preferably stamped from solid material using a stamping press. Alternatively, the sheets can be cast using a mold that has corresponding projections within the cavity, designed to receive the casting material, to form the cutouts. The geometries described have also proven advantageous in the casting process because they result in improved compression of the sheet metal stack within the casting tool. This provides advantages in terms of high manufacturing stability, regardless of the specific manufacturing method used for the sheets.Furthermore, the special geometry eliminates the need for cover lamellae during the casting process, which are designed as stamped rotor laminations without secondary cutouts and prevent the casting material from flowing into the air cavities during the casting process.

[0020] In a further advantageous development of the electric machine, the radius of the short-circuit discs is smaller than the distance between the longitudinal axis of the laminations and the third and fourth vertices. This allows the pressing tool to utilize the entire web as an interference fit, thus sealing the second punched holes against ingress of cast material. This also advantageously results in a reduction of the exposed end faces of the short-circuit bar.

[0021] Specific embodiments of the present invention are explained below with reference to the figures. These show: Fig. 1a a top view of a sheet of metal; Fig. 1b a first detailed view of a sheet of metal; Fig. 1c a second detailed view of a sheet metal part; Fig. 1d a third detailed view of a sheet metal part; Fig. 2 A cutaway side view of an electric machine.

[0022] Fig. Figure 1a shows a top view of a sheet of metal 100, and Fig. Figure 1b shows a first detailed view of the sheet 100. Several such sheets 100 are joined to form a laminated core 10 of a rotor 11, as used in an electric machine 200 according to Fig. 2 is typically installed.

[0023] The sheet metal 100 has, with respect to a longitudinal axis A, L a cylindrical and therefore depression-free outer surface 12. The sheet 100 has an annular arrangement of a plurality of first cutouts 13 and second cutouts 14, which are oriented with respect to the longitudinal axis A LThe first cutouts 13 and the second cutouts 14 are arranged coaxially and equiangularly to each other and extend radially. Both the first cutouts 13 and the second cutouts 14 each have a closed lateral surface 151, 152. Each first cutout 13 and each second cutout 14 are mirror-symmetrical with respect to a radially extending common axis of symmetry A. S The sheet metal 100 is designed such that it has an identical number of first cutouts 13 and second cutouts 14. Therefore, the sheet metal 100 is rotationally symmetric with respect to discrete rotation angles of 2π / N, where N is the number of first and second cutouts 13 and 14.

[0024] In the packaged state of the sheets 100, the first cutouts 13 are formed for receiving short-circuit bars 16 ( Fig. 2) In such lamination stacks 10, the short-circuit bars 16 are typically cast from a liquid material, such as copper, aluminum, or silver, into the first cutouts 13. The second cutouts 14 form air cavities in the assembled state of the lamination stack 10, thus reducing heat losses and providing indirect air cooling. The air cavities can also be filled with a casting-resistant material, such as gypsum, which has proven advantageous when casting the short-circuit bars 16 because the casting material of the short-circuit bars 16 cannot then penetrate the air cavities.

[0025] The first punched-out 13 has a bulge 17 on the side facing the lateral surface 12 of the sheet 100, with a convex surface section 18 and a first vertex S1, which lies on the axis of symmetry A Sis arranged. The convex surface section 18 of the bulge 17 is bordered on both sides by turning points W. 1,2 The area is bounded and transitions there into surface sections 191 and 192 with a concave curvature. Surface sections 191 and 192 transition into convex surface sections 281 and 282.

[0026] The second punched-out 14 has on the side facing away from the lateral surface 12 of the sheet 100 a recess 20 with a concave surface section 21 and a second vertex S2, which lies on the respective axis of symmetry A S is arranged. The concave surface section 21 of the indentation 20 is bordered on both sides by turning points W. 3,4 The area is bounded and transitions there into surface sections 221 and 222 with a convex curvature. These surface sections 221 and 222 with the convex curvature have a third vertex S3 and a fourth vertex S4 in the radial direction. The third and fourth vertices S 3,4This results in the points of the lateral surfaces 152 of the second cutouts 14 being at a minimum distance to the longitudinal axis A. L The surface sections 221, 222 transition at least indirectly into convex surface sections 291, 292.

[0027] A web 23 is arranged between the first cutout 13 and the second cutout 14, which is located in the area between the third vertex S3 and the fourth vertex S4, and thus also between the turning points W 3,4 The bulge 17 or the indentation 20 has a constant width. The width of the web 23 is measured perpendicular to a center line that runs equidistant between the bulge 13 and the indentation 14.

[0028] The first cutouts 13 and the second cutouts 14 are arranged relative to each other such that the protrusions 17 of the first cutouts 13 are flanked, at least partially, in a tangential direction by the indentations 20 of the second cutouts 14. Thus, the distance between the longitudinal axis A L of sheet 100 and the first vertex S1 greater than the distance between the longitudinal axis A L of sheet 100 and the third vertex S3 or the fourth vertex S4.

[0029] In one specific embodiment, the concave or convex curved surface sections of the lateral surfaces of the first cutouts 13 and second cutouts 14 are circularly curved. With reference to Fig. The following dimensions are observed in 1a, c, d: 0.15 mm≤dSheet≤0.35 mm 2 mm≤b1≤7 mm 0.35 b1≤b2≤0.65 b1 4.5 b1≤h1≤7 b1 0.3 b1≤r1≤0.7 b1 2 h1≤rRotor≤4 h1 0.5 dBlech≤dk1≤2.5 dBlech 0.5 dBlech≤dst1≤3 dBlech 0.5 dBlech≤dk2≤4 dBlech 0.5 dBlech≤dk3≤4 dBlech r2 <r1 rk1=r2+dst1 dst2=dst1 0.9 b1≤bk1≤1.1 b1 rksr≤rRotor−2 rk3−dst2

[0030] Fig. Figure 2 shows an electric machine 200, which in the illustrated embodiment is designed as an asynchronous machine. The electric machine 200 has a housing 26 that accommodates a stator 24 with winding heads 27. The rotor 11 is coaxially and rotatably mounted in the stator 24, the rotor 11 comprising the laminated core 10 consisting of a plurality of laminations 100. The laminated core 10 is penetrated by several short-circuit bars 16, which are connected at the end faces of the laminated core 10 to short-circuit discs 25. Reference symbol list 100 sheet metal 200 electric machine 10 sheet metal packages 11 Rotor 12 Surface area 13 first die-cut 14 second die-cut 151 Surface area of ​​the first punch-out 152 Surface area of ​​the second punch-out 16 Short-circuit rod 17 bulge 18 Area section 191 Area section 192 Area section 20 indentation 21 Area section 221 Area section 222 Area section 23 Bridge 24 Stator 25 Short-circuit washer 26 cases 27 winding heads 281 Area section 282 Area section 291 Area section 292 Area section A L Longitudinal axis A S axis of symmetry S N Vertex (N = 1,..., 4) W N Inflection point (N = 1,..., 4) d Blech Sheet thickness b1 maximum width of the first cutout b2 Width of the first cutout at the inner end h1 Length of the first cutout r1 Radius of surface sections 281, 282 r2 radius of the area section 18 r Rotor Rotor radius d k1 Distance between two cutouts d st1 Bridge width d st2 Bridge width dl distance between rotor and stator r k1 Radius of area section 21 r k2 Radius of area section 291, 292 r k3 Radius of area section 221, 222 b k1 Width of the second cutout r ksr Radius of the short-circuit ring

Claims

Sheet metal (100) for forming a laminated core (10) for a rotor (11) of an electric machine (200), wherein the sheet metal (100) has a cylindrical outer surface (12) and radially extending first cutouts (13) and radially extending second cutouts (14) with respect to a longitudinal axis (AL), each having closed outer surfaces (151, 152), wherein each first cutout (13) and each second cutout (14) are mirror-symmetrical with respect to a radially extending common axis of symmetry (AS), wherein the first cutouts (13) are designed to receive short-circuit bars (16), characterized in that the first cutouts (13) each have a bulge (17) on the side facing the outer surface (12) of the sheet metal (100) with a convex surface section (18) and a first vertex (S1) which lies on the respective axis of symmetry (AS) is arrangedand the second cutouts (14) on the side facing away from the lateral surface (12) of the sheet (100) each have a recess (20) with a concave surface section (21) and a second vertex (S2) which is arranged on the respective axis of symmetry (AS). Sheet (100) according to claim 1 , characterized in that the convex surface section (18) of the bulge (17) is bounded on both sides by turning points (W1,2) and transitions there into surface sections (191, 192) with a concave curvature. Sheet (100) according to one of claims 1 or 2, characterized in that the concave surface section (21) of the indentation (20) is bounded on both sides by turning points (W3,4) and transitions there into surface sections (221, 222) with a convex curvature. Sheet (100) according to claim 3, characterized in that the surface sections (221, 222) with a convex curvature in the radial direction have a third vertex (S3) and a fourth vertex (S4). Sheet (100) according to claim 4, characterized in that a web (23) is arranged between each of a first punching (13) and a second punching (14) which run along a common axis of symmetry (AS), the web having a constant width in the area between the third vertex (S3) and the fourth vertex (S4), in particular between the turning points (W1,2,3,4) of the bulge (17) or the indentation (20), wherein the width of the web (23) is preferably measured perpendicular to a center line which runs equidistantly between the bulge (17) and the indentation (20). Sheet metal (100) according to one of claims 1 to 5, characterized in that first cutouts (13) and second cutouts (14), which run along a common axis of symmetry (AS), are arranged to each other such that the protrusions (17) of the first cutout (13) are flanked in a tangential direction at least partially by the indentations (20) of the second cutouts (14). Sheet (100) according to one of claims 1 to 6, characterized in that the distance between the longitudinal axis (AL) of the sheet (100) and the first vertex (S1) is greater than the distance between the longitudinal axis (AL) of the sheet (100) and the third vertex (S3) or the fourth vertex (S4). Sheet (100) according to one of claims 1 to 7, characterized in that the concave or convex curved surface sections (18, 191, 192, 21, 211, 222) of the lateral surfaces (151, 152) of the first cutouts (13) and second cutouts (14) are circularly curved. Electric machine (200) with a stator (24) and a rotor (11), wherein the rotor (11) has a laminated core (10) with a plurality of stacked laminations (100) which are penetrated by short-circuit bars (16), wherein the laminated core (10) has short-circuit discs (25) on opposite end faces, characterized in that the laminations (100) of the electric machine (200) are designed according to one of claims 1 to 8. Electric machine (200) according to claim 9, characterized in that the radius of the short-circuit disks (25) is smaller than the distance between the longitudinal axis (AL) of the laminations (100) and the third and fourth vertices (S3,4).

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