Method and apparatus for testing an SMC stator core

Abstract

An SMC stator core (2) for an electrical machine (10), more particularly an electric motor, is tested in the following steps: - providing a plurality of windings, which are in the form of printed circuits (5, 6) and which each have openings (7) matched to the shape and arrangement of teeth (3) of an SMC stator core (2) to be tested, - placing the printed circuits (5, 6), which are stacked one on the other, onto the teeth (3) of the SMC stator core (2), - covering the assembly of the SMC stator core (2) and the printed circuits (5, 6) with an iron return ring (8), which contacts the teeth (3), - operating the printed circuits (5, 6) as transformer windings while measuring properties of the SMC stator core (2), which acts as the transformer core.

Description

[0001] Method and apparatus for testing an SMC stator core

[0002] The invention relates to a method for testing a stator core for an electrical machine made of a soft magnetic composite material (SMC). Furthermore, the invention relates to a device for testing such a stator core of an electrical machine, in particular an electric motor.

[0003] An electric motor with a stator core made of SMC material is known, for example, from EP 2 901 541 B1. The stator core of the known electric motor is pot-shaped, with tooth-like projections arranged on the pot edge. The rotor of the electric motor according to EP 2 901 541 B1 has a multilayer printed circuit board.

[0004] Further design options for stators and rotors of electrical machines are described, for example, in documents EP 1 598 920 B1, DE 10 2012 207 414 A1, and WO 2018 / 027330 A1. In principle, teeth of stators or rotors can be aligned either in the radial direction or in the axial direction of the respective electrical machine, as is evident from these documents.

[0005] Powder-based materials are known to represent an alternative to stator or rotor lamination stacks for reducing eddy current losses compared to solid metallic, electrically conductive components, and are considered for a wide variety of geometric designs of electric motor components. Compared to standard electrical laminations, stator cores made of SMC materials typically exhibit hardly any eddy current losses due to their low electrical conductivity, but tend to exhibit higher core losses, i.e., core remagnetization losses. With regard to a ferromagnetic powder suitable for the production of components for electric motors or transformers, reference is made to document US Pat. No. 9,640,306 B2 as an example. In this case, soft magnetic particles are surrounded by various layers, including an inorganic insulating layer based on phosphorus.

[0006] As a rule, powder-based soft magnetic composite materials intended for use in electrical machines have largely isotropic magnetic properties. In contrast, a soft magnetic composite material described in WO 2016 / 020077 A1, for example, exhibits a high permeability anisotropy.

[0007] The toroidal core measurement method is particularly suitable for determining the material properties of soft magnetic materials. In this context, reference is made to the following dissertation:

[0008] Alexander Stadler: Metrological Determination and Simulation of Core Losses in Soft Magnetic Materials, Faculty of Engineering, University of Erlangen-Nuremberg, Erlangen 2009

[0009] This dissertation proposes a series connection of several identical toroidal cores. The resulting averaging effect is intended to reduce variation within a batch.

[0010] The invention is based on the object of achieving advances in the testing of SMC stator cores compared to the prior art, whereby efficient testing should also be possible in the context of series production of electric motors or generators. This object is achieved according to the invention by a method for testing a stator core according to claim 1. The method can be carried out using a device according to claim 5. The embodiments and advantages of the invention explained below in connection with the testing device also apply mutatis mutandis to the testing method, and vice versa.

[0011] The method by which a stator core made of a soft magnetic composite material can be tested comprises the following steps:

[0012] - Providing a plurality of windings in the form of printed circuits, each having recesses adapted to the shape and arrangement of teeth of an SMC stator core to be tested,

[0013] - Placing the stacked printed circuits onto the teeth of the SMC stator core,

[0014] - Covering the arrangement of SMC stator core and printed circuits by an iron return ring contacting the teeth,

[0015] - Operating the printed circuits as transformer windings while recording properties of the SMC stator core acting as the transformer core.

[0016] The invention is based on the idea that powder-based soft magnetic materials can generally be tested by forming a special test specimen from the soft magnetic material. The properties of the test specimen can then be determined, particularly using the toroidal core measurement method. The disadvantages of this approach are the high cost of sample preparation and the fact that the geometry of the test specimen does not correspond to the geometry of the component intended for use in an electrical machine. These disadvantages are inherently absent in the test method according to the application, which uses the SMC stator core in its final form, intended for installation in an electrical machine, during testing.Another advantage is the use of prefabricated printed circuits, which eliminate the need to wrap a sample and are available for testing virtually any number of stator cores one after the other, even in a semi-automated manner.

[0017] The stacked printed circuit boards, which are to be placed on the SMC stator core for testing, can be positioned either manually or robotically. The same applies to the iron return ring. In each case, a test setup is created that is designed for testing according to the transformer principle. In addition, it is possible to perform a temperature rise measurement.

[0018] According to one possible design of the test procedure, primary and secondary windings, each in the form of printed circuits, are alternately placed on the SMC stator core. A total of eight or more printed circuits, i.e., at least four primary windings and at least four secondary windings, are stacked on top of one another. Within the transformer thus manufactured, completed by the iron return ring, the magnetic circuit is closed, among other things, by the ring-shaped stator core to be tested. During the test, a time-varying current is impressed in the sense of current control, which creates a magnetic flux in the stator core. The magnetic flux, in turn, induces an electrical voltage in the secondary winding that can be easily and reliably measured.

[0019] In accordance with the basic shape of the SMC stator cores to be tested, the printed circuits are particularly ring-shaped with recesses evenly distributed around the circumference for each tooth of the stator core. It is assumed that the teeth extend in the axial direction of the electrical machine. The thickness of the printed circuits depends on the height of the teeth of the SMC stator core and the number of printed circuits to be stacked within a measuring arrangement. For various SMC stator cores to be tested with different dimensions, in particular with different diameters, differently dimensioned printed circuits can be provided. A uniform measuring and evaluation device can be used to carry out and evaluate the measurements used to determine the magnetic properties.

[0020] In contrast to the SMC stator core, which is later incorporated into the series production of electrical machines, the iron return ring represents a component of the test fixture. The iron return ring can, in principle, be a solid metallic component or a component constructed from electrical steel sheet. In the latter case, a structure of the iron return ring made of concentric rings is advantageous in terms of magnetic flux, but this is challenging in terms of manufacturing. A structure of the iron return ring made of stacked, disc-shaped sheets is simpler in terms of manufacturing, but less favorable in terms of magnetic flux and resulting eddy currents.

[0021] Particularly for frequencies in the kHz range, it is advantageous to manufacture the iron return ring from a soft magnetic powder-based composite material. In an advantageous embodiment, this is the same SMC material from which the stator cores to be tested are made.

[0022] Overall, the testing device is particularly suitable for incoming goods inspection of an industrial production line, where SMC stator cores are fully automatically inserted into the testing device and magnetically measured. Any rejects regarding stator cores are thus detected right at the beginning of production. The electric motors to be manufactured, whose stator cores are 100% inspected using the test method according to the application, are, in particular, permanent magnet motors. The motors are intended, for example, for use in cobots. Reference is made in this context to documents EP 3 643 455 A1 and US 2021 / 0114239 A1 as examples.

[0023] An exemplary embodiment of the invention is explained in more detail below with reference to a drawing. The drawings show, partially schematically:

[0024] Fig. 1 shows a device for testing an SMC stator core of an electrical machine,

[0025] Fig. 2 shows the stator core of the arrangement according to Fig. 1,

[0026] Fig. 3 shows an iron return ring placed on the stator core within the arrangement according to Fig. 1,

[0027] Fig. 4 shows one of several printed circuits used in the arrangement according to Fig. 1,

[0028] Fig. 5 shows an electric motor comprising two stator cores in an exploded view.

[0029] A testing device, designated overall by reference numeral 1, is used to test stator cores 2, which are installed in electric motors 10. Each stator core 2 has a crown shape with a ring section 4 and numerous teeth 3 adjoining the ring section 4 and aligned in the axial direction of the ring section 4. The stator cores 2 are made of a soft magnetic composite material, i.e., SMC material.

[0030] The testing of the stator cores 2 is carried out using printed, ring-disk-shaped circuits 5, 6. Each printed circuit 5, 6 has recesses 7 whose shape and arrangement corresponds to the cross-sectional shape of the teeth 3. Within the testing device 1, the printed circuits 5, 6 are stacked and placed on the teeth 3 of the stator core 2. An iron return ring 8 is then placed on the end faces of the teeth 3, resulting in the arrangement sketched in Figure 1. The printed circuits 5, 6 are connected to an evaluation unit 9, as indicated in Figure 1, in such a way that a printed circuit 5 as the primary winding and a printed circuit 6 as the secondary winding alternately form the stack of printed circuits 5, 6.

[0031] During the test, primary windings 5 ​​are energized. The electrical voltage induced in the secondary windings 6 is measured by the evaluation unit 9. After the tests have been completed, the stator core 2 is removed from the test fixture 1. The stator core 2, i.e., the SMC stator core, can then be installed as a component of an electric motor 10, provided the test of its magnetic properties is positive.

[0032] The electric motor 10, whose structure is illustrated in Figure 5, is a brushless permanent magnet motor. As an electrical machine, the electric motor 10 has stator cores 2 arranged on both its end faces in a mirror image of one another, the teeth 3 of which face toward one another. The teeth 3 of each stator core 2 engage with a printed circuit board arrangement 11, the basic shape of which corresponds to the shape of the printed circuits 5, 6 used for testing purposes. The rotor of the electric motor 10, designated overall by 16, comprises a rotor core 12 made of SMC material, into which cuboid-shaped permanent magnets 13 are inserted. The rotor 16 is fixedly connected to a shaft 14 of the electric motor 10. The housing of the electric motor 10 is designated by 15. Known means for supporting the shaft 14 are not shown in Figure 5.

[0033] List of reference symbols

[0034] 1 test device

[0035] 2 Stator core 3 Tooth

[0036] 4 ring section

[0037] 5 Primary winding, printed circuit

[0038] 6 Secondary winding, printed circuit

[0039] 7 Recess 8 Iron return ring

[0040] 9 Evaluation unit

[0041] 10 Electric motor, electric machine

[0042] 11 Circuit board arrangement

[0043] 12 Rotor core 13 Permanent magnet

[0044] 14 Wave

[0045] 15 housings

[0046] 16 Rotor

Claims

Patent claims Method for testing an SMC stator core (2) for an electrical machine (10), comprising the following steps: - Provision of a plurality of windings available as printed circuits (5, 6), each having recesses (7) adapted to the shape and arrangement of teeth (3) of an SMC stator core (2) to be tested, - Mounting the stacked printed circuits (5, 6) onto the teeth (3) of the SMC stator core (2), - Covering the arrangement of SMC stator core (2) and printed circuits (5, 6) by an iron back-end ring (8) contacting the teeth (3), - Operating the printed circuits (5, 6) as transformer windings while recording the properties of the SMC stator core (2), which here functions as the transformer core. A method according to claim 1, characterized in that primary and secondary windings (5, 6) are alternately plugged onto the SMC stator core (2). A method according to claim 2, characterized in that a total of at least eight printed circuits (5, 6) are stacked on top of each other. A method according to any one of claims 1 to 3, characterized in that the SMC stator core (2), the printed circuits (5, 6), and the iron return ring (8) are robotically assembled.Device for testing an SMC stator core (2) for an electric machine (10), comprising a plurality of windings provided as printed circuits (5, 6), each of which has recesses (7) adapted to the shape and arrangement of teeth (3) of an SMC stator core (2) to be tested, as well as an iron back-circuit ring (8) and a for carrying out. Evaluation unit (9) designed for electrical connection to the windings (5, 6) of the method according to one of claims 1 to 4.

6. Device according to claim 5, characterized in that the printed circuits (5, 6) each have a ring shape with uniformly distributed circuits around the circumference. have exceptions (7).

7. Device according to claim 5 or 6, characterized in that the printed circuits (5, 6) each have a thickness that is no more than one-eighth the height of the teeth of the SMC stator core (2).

8. Device according to any one of claims 5 to 7, characterized in that the iron return ring (8) is made of an SMC (soft magnetic composite) material.