Coated insulated electrical conductor for use in electric motor windings of electrical machines

Abstract

Coated insulated electrical conductor (10) for use in electric motor windings of electrical machines, comprising a metallic wire (12) and an insulating layer (14) made of polyetheretherketone surrounding the metallic wire (12), characterized in that the insulating layer (14) made of polyetheretherketone has a polyamide-imide coating (16) on its outer surface.

Description

The invention relates to a coated insulated electrical conductor for use in electric motor windings having the features of the preamble according to claim 1. In the manufacture of electric motors, particularly stator windings for vehicle propulsion systems, various materials are used for the electrical insulation of the winding conductors. Common examples include classic insulating varnishes such as polyamide-imide (PAI) or high-performance thermoplastic polymers such as polyetheretherketone (PEEK), which are applied as a coating or sheath around the conductor wire. Additionally, slot insulation paper is typically inserted into the stator slots to provide insulation from the metallic stator lamination stack, electrically insulating the conductor wires from the lamination. When the conductors are inserted into the paper-lined slots—for example, when inserting pre-fabricated rectangular hairpin conductors or when expanding a pre-wound wave winding—friction occurs between the conductor insulation and the slot insulation paper. In practice, certain insulation materials have proven to have disadvantages. In particular, PEEK-sheathed conductor wires generate comparatively high frictional forces at the contact surface with the slot insulation paper. This can lead to the slot insulation paper being displaced or damaged when the conductors are mounted in the stator slots. As a result, the affected components lose their function and must be discarded, leading to rejects and disruptions in the manufacturing process. A friction coefficient analysis of the material pairing confirms the significantly less favorable sliding behavior of PEEK-coated wires on insulation paper compared to wires with PAI lacquer insulation. Known solutions therefore often employ enamel-insulated conductor wires with lower surface friction. For example, switching from PEEK-sheathed conductor wires to PAI-coated conductors completely eliminated the problem of groove paper displacement in one specific application. However, PAI-coated wires do not always meet the necessary mechanical and thermal requirements that PEEK as an insulator fulfills. An example from the prior art is the German patent application DE 10 2010 002 721 A1, which describes an electrically insulated conductor for electric machines. However, this known solution does not disclose a combination of different insulation layers for reducing friction in the stator. Overall, the prior art lacks an approach that combines the excellent insulating properties of materials such as PEEK with low-friction behavior compared to slot insulation. It is therefore the object of the present invention to provide an insulated electrical conductor which, when installed in an electric motor stator, reliably prevents displacement or damage to the slot insulation without having to forgo the excellent dielectric, thermal and mechanical properties of known high-performance insulation materials. The problem is solved with a coated insulated electrical conductor for use in electric motor windings of electrical machines, comprising a metallic wire and an insulating layer of polyetheretherketone (PEEK) surrounding the metallic wire. The insulating layer of PEEK has a polyamide-imide coating on its outer surface. This material combination significantly reduces friction between the conductor and slot insulation paper. In this way, displacement or damage to the slot insulation during installation of the conductor wires in the stator slots can be prevented, while simultaneously maintaining the excellent dielectric, thermal, and mechanical properties of the PEEK insulating layer. It is particularly preferred that the metallic wire has a rectangular cross-section. This is especially advantageous for stator windings in hairpin configuration, since rectangular conductor wires with a large contact area to the slot insulation paper are used there. The PAI coating according to the invention allows such rectangular conductor wires to be inserted into the slots with low friction, without displacing or damaging the slot insulation paper. In a particularly advantageous embodiment, the polyamide-imide coating is designed as a lacquer layer. This allows the PAI coating to be easily applied to the PEEK insulating layer using conventional painting methods. The result is a uniform, thin layer with good adhesion, which specifically improves the surface properties of the conductor. It can also be advantageous for the insulating layer to be thicker than the coating. This allows the polyetheretherketone insulating layer to remain the primary insulator and continue to determine the mechanical robustness as well as the dielectric and thermal properties of the conductor. The thinner PAl coating, on the other hand, serves solely to reduce surface friction and has only a negligible effect on the overall dimensions of the conductor insulation. Furthermore, it is particularly advantageous that the coating has a thickness of 6 to 8 µm. A PAI layer in this thickness range has proven sufficient to significantly reduce friction in contact with slot insulation paper without substantially increasing the conductor dimensions. In particular, with a PAI coating approximately 6 to 8 µm thick, displacement of the slot insulation during stator slot assembly can be completely prevented, while keeping material costs and manufacturing effort low. The invention will now be explained in more detail by way of example with reference to a figure. This figure shows, schematically and not to scale, a cross-section through a coated insulated electrical conductor with a PEEK insulating layer and an outer PAI coating. The figure shows a cross-sectional view of a coated insulated electrical conductor 10. The conductor comprises a metallic wire 12 surrounded by an insulating layer 14 made of polyetheretherketone. An outer coating 16 made of polyamide-imide is applied to the outer surface of the insulating layer 14. In the illustrated embodiment, the metallic wire 12 has a rectangular cross-section. It is also clearly visible that the insulating layer 14 has a greater thickness than the outer coating 16. Reference symbol list 10 coated insulated electrical conductor 12 metallic wire 14 insulating layer made of PEEK 16 PAI coating QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature DE 10 2010 002 721 A1

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Claims

Coated insulated electrical conductor (10) for use in electric motor windings of electrical machines, comprising a metallic wire (12) and an insulating layer (14) of polyetheretherketone surrounding the metallic wire (12), characterized in that the insulating layer (14) of polyetheretherketone has a polyamide-imide coating (16) on its outer surface. Coated insulated electrical conductor (10) according to claim 1, characterized in that the metallic wire (12) has a rectangular cross-section. Coated insulated electrical conductor (10) according to claim 1 or 2, characterized in that the coating (16) is formed as a lacquer layer made of polyamide-imide. Coated insulated electrical conductor (10) according to one of the preceding claims, characterized in that the insulating layer (14) has a greater thickness than the coating (16). Coated insulated electrical conductor (10) according to one of the preceding claims, characterized in that the coating (16) has a thickness of 6 to 8 µm.

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