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EP-3849063-B1 - ELECTRICAL MACHINE AND ROTOR FOR ELECTRICAL MACHINE

EP3849063B1EP 3849063 B1EP3849063 B1EP 3849063B1EP-3849063-B1

Inventors

  • LOOSER, Andreas
  • Blaser, Manuel
  • Hertig, Konrad

Dates

Publication Date
20260513
Application Date
20170524

Claims (16)

  1. A rotor (5) for a high-speed electrical machine comprising a rotor shaft (51), the shaft (51) comprising a rotor core (55) and a rotor sleeve (56), a compensation element (57; 58) being arranged between the rotor core (55) and the rotor sleeve (56) to absorb differences in thermal expansion of the rotor core (55) and the rotor sleeve (56), characterised in that between the compensation element (57) and the rotor core (55), and/or between the compensation element (57) and the rotor sleeve (56) hollow spaces (64) are formed.
  2. The rotor of claim 1, wherein the hollow spaces are ventilated by ventilation openings (60), the ventilation openings being, for example, holes in the compensation element (57).
  3. The rotor of claim 1 or 2, wherein the compensation element (57) is made of a metal material.
  4. The rotor of one of claims 1 to 3, wherein the compensation element (57) comprises first sections (61) in contact with only the rotor core (55) and not the rotor sleeve (56), and second sections (62) in contact with only the rotor sleeve (56) and not the rotor core (55), and compensating sections (63) linking the first and second sections.
  5. The rotor of claim 4, wherein the second sections comprise a plurality of separate support sections, and wherein the separate support sections are separated by hollow spaces that can comprise air, a gas or another substance that is more compressible than the support sections.
  6. The rotor of claim 4, wherein the second sections (62) comprise one or more support sections at one or more locations between second sections (62) that are located at ends of the compensation element (57).
  7. The rotor of one of claims 4 to 6, wherein the second sections (62) comprise a plurality of separate support sections.
  8. The rotor of claim 6 or 7, wherein for each point in a compensating section (63), a line in the radial direction passes through a hollow space (64) before reaching the rotor sleeve (56) and also passes through a hollow space (64) before reaching the rotor core (55).
  9. The rotor of claim 7 or claim 8, wherein the compensating sections (63) extend along at least one of the axial direction of the rotor (5) and the circumferential direction of the rotor (5).
  10. The rotor of one of claims 1 to 9, wherein at at least some of the second sections (62) the compensation element (57) is attached to the rotor sleeve (56), and at other second sections (62) the compensation element (57) and the rotor sleeve (56) are not attached to one another and are able to move relative to one another in the axial direction.
  11. The rotor of claim 10, wherein the compensation element (57) has the shape of a corrugated cylinder.
  12. The rotor of one of claims 1 to 2, wherein the compensation element comprises a synthetic elastic compensation material (58), wherein between the rotor core (55) and the rotor sleeve (56), and adjacent to or enclosed by the compensation material (58), pockets of gas are present, increasing the compressibility of the compensation material (58).
  13. The rotor of claim 12, wherein the compensation material (58) comprises a filler material for adjusting its Young's Modulus.
  14. The rotor of one of claims 12 to 13, wherein the pockets of gas are formed by gas bubbles (64a) within the compensation material (58).
  15. The rotor of claim 14, wherein the gas bubbles (64a) are formed by expandable hollow microspheres, in particular thermoplastic expandable hollow microspheres.
  16. The rotor of one of claims 12 to 13, wherein the compensation element (57) comprises a plurality of elastic elements (58b) attached to the rotor core (55) and deformable by sliding the rotor sleeve (56) over the rotor core (55) with the elastic elements (58b), thereby aligning and centering the rotor sleeve (56) with respect to the rotor core (55).

Description

The invention relates to the field of electrical machines, in particular to high-speed electrical machines with gas bearings. An electric motor generally comprises a rotor and a stator, the stator comprising a stator body supporting and housing an electrical stator and bearings. The position of the bearings relative to the stator body can be defined by bearing flanges of the stator body. Often, two journal bearings are present, typically located at opposite sides of the stator, as shown in the arrangement of Figure 1a (wherein the stator body is not shown). The precision of the alignment of the bearings in this case is mainly defined by the precision with which the bearing flange and stator body are machined. With fluid film and in particular for gas bearings, precise alignment is crucial and this arrangement in general requires special measures such as self-aligning or compliant bushing mountings, or machining, e.g. reaming, of the pair of bearings after assembly. Alternatively, the journal bearings can be arranged on the same side of the stator. This arrangement is often called overhanging motor design (Figure 1b). With the overhanging design, the two journal bearings can be integrated into a single part, thus precise bearing alignment is easier to achieve. However, this approach generally results in longer rotors and therefore more critical dynamic behaviour of the rotor. Furthermore, windage losses, caused by air resistance, are increased, with a negative impact on the overall motor efficiency. US 3'502'920 discloses a slotted electrical machine with air gap bearings, in which a bushing is located in the magnetic gap between the stator and the rotor. The bushing can be elastically suspended relative to the stator. It defines on the one hand a radial bearing and can comprise a centrally located thrust bearing or thrust block as an axial bearing. In order to assemble the machine, the rotor needs to be separated in the axial direction. This design is unfit for high-speed motors. WO 03/019753 A2 shows a spindle motor in which the rotor rotates in the stator within a thin layer of epoxy forming a cylindrical through bore in the stator and serving to define both a radial bearing surface and an axial bearing surface. The thin layer of epoxy is directly coupled to the stator housing, and any thermally induced deformations of the housing will immediately affect the geometry of the bearing. US 2006/0061222 A1 and US 2006/0186750 A1 show conventional air bearings. US 2010/0019589 A1 discloses a slot configuration of an electrical machine, and, inter alia, a rotor having a multi-layer fiber-reinforced composite sleeve wrapping. Layers can be cosmetic or have functional characteristics, e.g. for achieving strength and rigidity and controlling thermal expansion in one or multiple directions. This can be done by having fibres in a particular layer oriented axially, thereby providing axial strength and limiting axial thermal expansion. In another layer, fibers can be oriented circumferentially, thereby providing circumferential strength and limiting radial thermal expansion. Thus, these layers are configured to stiffen the rotor. They would not be suited to carry an outer sleeve of a relatively stiff material required by a gas bearing, since their purpose is to control, i.e. limit, thermal expansion of the rotor, rather than absorbing differences in thermal expansion between a hard rotor core and a hard rotor sleeve. KR 101 187 919 B1 shows a rotor with an inner magnet, an outer sleeve and an elastomer cylinder in between, compensating for differences in thermal expansion. EP 3301316 A1, with its filing date 29.09.2016 being in the priority year of the parent application of the present divisional application, discloses a connection between two rotating parts by means of an adapter sleeve establishing, preferably in each plane normal to the axis of rotation, a radial gap between the two rotating parts. Mainly with gas bearings, the bearing member's materials are chosen to have high rigidity and a low coefficient of thermal expansion, in order to ensure well-defined bearing clearances under the various operating and environmental conditions of the motor. The high rigidity of the materials however also causes the disadvantage of high stresses in the material at already low strain, e.g when combining these materials with other materials having a higher coefficient of thermal expansion. There is a need for a rotor that is suited for high-speed electrical machines that overcomes the abovementioned disadvantages at least in part. It is therefore an object of the invention to create a rotor for a high-speed electrical machine of the type mentioned initially, which overcomes the disadvantages mentioned above. These objects are achieved by a rotor according to claim 1. Accordingly, a rotor for a high-speed electrical machine is provided. The rotor comprises a rotor shaft, the shaft comprising a rotor core and a rotor sleeve, an