DE-102024003722-A1 - Rotor for an axial flux machine

Abstract

The invention relates to a rotor (1) for an axial flux machine, wherein the rotor (1) has a magnetic cassette (2) in which a plurality of permanent magnets (3) are arranged, wherein a bandage (4) made of a fiber-reinforced plastic is arranged on an outer circumference of the rotor (1), wherein the bandage (4) is formed from at least one cord-like fiber assembly (5, 6), wherein the bandage (4) comprises fibers made of at least one electrically non-conductive material, in particular aramid, glass and/or ceramic fibers, and carbon fibers.

Inventors

• Cameron Sophie Kimmel
• Jonas Matt

Assignees

• Mercedes-Benz Group AG

Dates

Publication Date

20260513

Application Date

20241113

Claims (6)

1. Rotor (1) for an axial flux machine, wherein the rotor (1) has a magnet cassette (2) in which a plurality of permanent magnets (3) are arranged, wherein a bandage (4) made of a fiber-reinforced plastic is arranged on an outer circumference of the rotor (1), wherein the bandage (4) is formed from at least one cord-like fiber assembly (5, 6), characterized in that the bandage (4) comprises fibers made of at least one electrically non-conductive material, in particular aramid, glass and/or ceramic fibers, and carbon fibers.
2. Rotor (1) after Claim 1 , characterized in that the bandage (4) has at least two different cord-like fiber assemblies (5, 6), wherein a first cord-like fiber assembly (5) has at least substantially carbon fibers, wherein a second cord-like fiber assembly (6) has at least substantially fibers made of the at least one electrically non-conductive material, wherein the first fiber assembly (5) forms a first layer type and wherein the second fiber assembly (6) forms a second layer type, wherein the first and the second layer type are arranged alternately in the bandage (4) when viewed in the radial direction.
3. Rotor (1) after Claim 2 , characterized in that the radially innermost layer of the bandage (4) is of the second layer type.
4. Rotor (1) after Claim 1 , characterized in that the bandage (4) is formed from a cord-like hybrid fiber assembly which contains both carbon fibers and electrically non-conductive fibers.
5. Method for manufacturing a bandage (4) for a rotor (1) according to Claim 2 or 3 , characterized in that the first and the second cord-like fiber assembly (5, 6) are wound together in a double layer onto a cylindrical auxiliary body in a winding process, wherein - individual winding loops are wound axially side by side onto the cylindrical auxiliary body in a first axial winding direction until an axial end of the cylindrical auxiliary body is reached, - within a winding loop (360 degrees) and in the winding loops relative to each other, the radial position of the first and the second cord-like fiber assembly (5, 6) relative to each other is always the same, - at the end of the cylindrical auxiliary body, a second axial winding direction is changed in a direction opposite to the first axial winding direction.
6. Procedure according to Claim 5 characterized in that the fiber composites (5, 6) are impregnated with a liquid matrix material before wrapping or that pre-impregnated semi-finished products are used as fiber composites (5, 6).

Description

The invention relates to a rotor for an axial flux machine according to the preamble of claim 1 and a method for manufacturing a bandage for a rotor according to the preamble of claim 5. Axial flux machines have a disc-shaped design, conventionally employing either a double-rotor or a double-stator configuration. For traction machines with high torque and power density, double-rotor designs are predominantly used, incorporating rotor discs consisting of the main components: rotor carrier, electrical lamination stack, and magnet cassette. AFM magnet cassettes typically utilize passivated permanent magnets. To reduce eddy current losses within the magnet during operation, these magnets are segmented by an electrically non-conductive adhesive layer. To absorb the high rotational speeds and associated centrifugal forces on the magnets during operation, a pre-tensioned ring (e.g., made of carbon fiber reinforced plastic: CFRP ring) is mounted on the magnet cassette. This ring exerts compressive forces on the magnet cassette when the machine is stationary. The electrically conductive carbon component induces eddy currents within the CFRP ring due to the alternating magnetic field. Furthermore, individual magnetic segments can be short-circuited by the electrical connection across the carbon. This also results in eddy currents. These eddy currents generate higher rotor losses and consequently poorer AFM performance. The disc-shaped design of axial flux motors (AFMs) enables novel axle drive concepts for motor vehicles. These units are characterized by very high efficiency in a compact installation space. Manufacturing an AFM for series production is therefore complex and very demanding. Currently, laminated permanent magnets are pressed into a magnet cassette made of sheet molding compound (SMC), consisting of carbon fibers and a reactive resin. The magnets are held in the magnet cassette, both when the highly stressed AFM is stationary and during operation, by a pressed-on carbon fiber reinforced plastic (CFRP) ring. The carbon fibers in the ring are electrically conductive, which leads to eddy currents within the electric traction motor due to the alternating magnetic field. These eddy currents occur within the carbon. Furthermore, eddy current paths are also induced in the magnets (contact resistance). This is due to the electrical connection of the individual magnet segments via the carbon fibers. The eddy currents thus lead to a significant increase in rotor losses, which is detrimental both to efficiency and to magnetic performance (higher magnet temperature leads to derating due to lower remanence and opposing field stability). Through electrical contact between the CFRP ring (carbon fibers as the "noble" cathode) and the magnetic material (as the "less noble" anode), contact corrosion can occur with the aid of an electrolyte, causing the less noble material, i.e., the magnet, to corrode. Furthermore, the alternating electric field within the CFRP ring also induces eddy currents that form within the ring. DE 10 2020 105 588 A1 This document describes a rotor for a separately excited synchronous machine, comprising a rotor body, a rotor winding, and several permanent magnets. The rotor body has several longitudinal grooves extending radially to the outer circumferential surface, in which both the rotor winding and the permanent magnets are arranged. The permanent magnets form part of the outer circumferential surface, and a fiber-reinforced plastic bandage is applied to the outer circumferential surface to hold the permanent magnets in place. Furthermore, a method for manufacturing such a rotor and a separately excited synchronous machine with such a rotor are described. The invention is based on the objective of providing a novel rotor for an axial flux machine and a novel method for manufacturing a bandage for such a rotor. The problem is solved according to the invention by a rotor for an axial flux machine with the features of claim 1 and by a method for manufacturing a bandage for a rotor with the features of claim 5. Advantageous embodiments of the invention are the subject of the dependent claims. A rotor for an axial flux machine is proposed, wherein the rotor has a magnet cassette in which a plurality of permanent magnets are arranged, and wherein a bandage made of a fiber-reinforced plastic is arranged on an outer circumference of the rotor, the bandage being formed from at least one cord-like fiber structure. According to the invention, the bandage comprises fibers made of at least one electrically non-conductive material, in particular Aramid, glass and/or ceramic fibers, and carbon fibers. The problems described in the introduction are improved or minimized by the present invention. In particular, eddy current losses in the rotor resulting from the alternating magnetic field during operation of the electric traction machine can be reduced. Furthermore, costs can be reduced due to the lower propo