GB2592889A

GB2592889A - A rotor

Info

Publication number: GB2592889A
Application number: GB1918602.2A
Authority: GB
Inventors: K Molyneaux Alex; M Sharkh Suleiman; Szymko Shinri
Original assignee: Bowman Power Group Ltd
Current assignee: Bowman Power Group Ltd
Priority date: 2019-12-17
Filing date: 2019-12-17
Publication date: 2021-09-15
Also published as: GB201918602D0

Abstract

A rotor for a high-speed motor or generator has a core comprising laminations 10 that have a curved outer surface 50 and a central rotational axis. Within the core a pair of permanent magnets in apertures 30 are angled toward one another when viewed in a cross section. A void 100 located between the pair of permanent magnets reduces, during rotation of the rotor, the centrifugal load on the area 105 of the rotor core between the curved outer surface and the pole of the permanent magnet closest to the curved outer surface. Pairs of magnets (fig 2, 170) can be angled together in a V-shape, closer together at an apex proximate the axis and open-ended near the outer surface. The void 100 can: be in a valley of the V-shape; occupy at least 20 percent of the rotor core volume between the magnets; be circular in section; and extend the length of the core parallel to the axis. The rotor can comprise a bolt (fig 2, 150) extending through the void affixing end-caps (fig 2, 140) to the rotor. First and second air-channels (fig 3, 180,190) can extend adjacent respective poles of the magnets,

Description

A Rotor

Field of the Invention

A rotor for use in a high-speed motor or generator, and, in particular, to a rotor comprising a pair of permanent magnets within a laminated rotor core.

Background of the Invention

There are two main types of permanent magnet rotors used in of synchronous motors or generators: surface-mounted permanent magnet rotors and interior mounted permanent magnet rotors. However, for high-speed applications (over 10,000 rpm or a surface speed of greater than 60m/s) such as turbochargers and turbogenerators, surface-mounted permanent magnet rotors are high cost as they typically require a retaining sleeve to retain the magnets against the relatively large centrifugal forces. Including a retaining sleeve in the motor or generator is undesirable as it decreases efficiency of the system as it increases the electromagnetic air gap between the rotor and stator.

In some cases, interior permanent magnet rotors also use retaining sleeves to strengthen the rotor core. This is because the inclusion of permanent magnets inside the rotor core can weaken it. As such, the centrifugal forces encountered at high operational speeds can readily deform a typical rotor core with interior mounted permanent magnets. The inclusion of a retaining sleeve is, again, undesirable due to efficiency reduction and increased costs.

In addition, it can be beneficial to locate a pole of the permanent magnets embedded within the rotor core as close as possible to the curved outer surface of the rotor core to improve performance. However, the closer to the surface a magnet is positioned, the weaker the rotor core as the area of the laminations between the permanent magnet and the curved outer surface is reduced.

Objects and aspects of the present invention seek to alleviate at least the above problems with the prior art.

Summary of the Invention

According to the present invention there is provided a rotor for use in a high-speed motor or generator, the rotor comprising: a laminated rotor core comprising a curved outer surface and a central rotational axis; and at least one pair of permanent magnets within the rotor core, the pair of permanent magnets angled toward one another when viewed in a cross section substantially perpendicular with the central rotational axis; wherein the rotor core comprises a void located between the pair of permanent magnets which, during rotation of the rotor, reduces the centrifugal load on the area of the rotor core between the curved outer surface and the pole of the permanent magnet closest to the curved outer surface.

The presence of a void between the pair of permanent magnets reduces the weight and, therefore, the centrifugal force experienced by the portion of the rotor core located between the pair of permanent magnets. As such, the void reduces the centrifugal load and stress which is generated on the portion of the rotor core between the pole of the permanent magnets and the outer curved surface of the rotor core at a given rotational speed. This area is typically a weak spot in rotor cores comprising internal permanent magnetics as it represents, in a direction perpendicular to the rotational axis of the rotor, the thinnest or narrowest portion of the laminations. As such, including the void reduces the chance of failure and increases the maximum speed at which the rotor can operate compared to a rotor without the void. Further, the void increases the tolerances within which the rotor can be manufactured. In addition, the presence of the void can be used to guide the magnetic flux of the permanent magnets and thereby improve performance of the rotor.

Preferably, the rotor core forms the outer surface of the rotor. In this way, the rotor core is not supported by a retaining sleeve. In this preferred embodiment, the void decreases the load sufficiently such that the rotor is suitable for operating at high-speeds without a retaining sleeve. This is advantageous as a retaining sleeve often increases the gap between the rotor and stator impacting efficiency. Exclusion of the retaining sleeve has the additional advantage of increasing the tolerances within which the rotor can be manufactured as it does not need to have a precise interference fit with the retaining sleeve.

Preferably, the void is located between the curved outer surface and the poles of the pair of permanent magnets proximate to the central rotational axis. Accordingly, the void, during rotation of the rotor, reduces the centrifugal load on the area of the rotor core between the poles of the pair of permanent magnets proximate to the central rotational axis. This location of the void is advantageous as the void reduces the stress or centrifugal load on the area of the rotor core between the poles of the pair of permanent magnets proximate to the central rotational axis. This area of the rotor core is typically another weak spot which is prone to failure at high operational speeds.

Preferably, the poles of the pair of permanent magnets proximate to the central rotational axis are closer together than the poles proximate the curved outer surface. This preferred configuration or arrangement of the permanent magnets has been found to be beneficial to the operation of the rotor core.

Preferably, the pair of permanent magnets are angled toward one another in a V-shaped configuration. In this V-shaped configuration, however, there is typically a gap between the arms of the V-shape. That is, each of the permanent magnets of the pair of permanent magnets is discrete and is housed or embedded within a discrete area of the rotor core. Together these two discrete areas provided a V-shaped configuration. This preferred configuration or arrangement of the permanent magnets has been found to be of particular benefit to the operation of the rotor core. Further preferably, the two arms of the V-shaped configuration are substantially straight. By keeping the arms of the V-shaped configuration straight, the cost of the permanent magnets within the arms is reduced substantially and the manufacturing tolerances are increased.

Preferably, the apex-end of the V-shaped configuration is proximate the central rotational axis and the open end of the V-shaped configuration is proximate the outer curved surface. This preferred configuration or arrangement of the permanent magnets has been found to be particular beneficial to the operation of the rotor core.

Preferably, the void is located in the valley of the V-shaped configuration. The weak spots of the rotor core are typically the areas adjacent and proximate the permanent magnets at the apex-end and open-end. Or, in other words, embedding or housing the permanent magnets within the rotor core causes areas of the rotor core surrounding the permanent magnets to be narrower and weakened. Locating the void within the valley of the V-shaped configuration reduces the stress and centrifugal load of the areas of the rotor core adjacent and proximate both the apex-end and the open-end. The valley of the V-shaped configuration is between the apex-end and open-end inside the V-shape.

Preferably, the void and the pair of permanent magnets are symmetrically arranged around a plane of reflection. More preferably, the plane of reflection extends in a radial direction from the central rotational axis.

Preferably, the void occupies between 10% and 50 % of the volume of the rotor core between the pair of permanent magnets. More preferably, the void occupies between 20 % and 40 % of the volume of the rotor core between the pair of permanent magnets. The volume between the rotor core and the permanent magnets extends the entire length of the rotor core in a direction parallel with the central rotational axis and in a circumferential direction around the rotor core between permanent magnets of the pair.

Preferably, the void occupies at least 20% of the volume rotor core between the pair of permanent magnets. More preferably, the void occupies at least 30% of the volume rotor core between the pair of permanent magnets.

In some embodiments of the invention, the void may be filled with a lightweight material. For example, the void may be filled with a foam.

Preferably, the void is substantially cylindrical with a circular cross-section. In this preferred embodiment, the cylinder extends in the same direction as the rotational axis of the rotor. It has been found that providing a circular void with is beneficial to guide the magnet flux of permanent magnets and avoid the creation of any weak spots in the rotor core in the area surrounding the void Alternatively, it may be preferable for the void to have a generally triangular cross section. More preferably, the generally triangular cross section comprises one or more curved sides. Most preferably, the void has a cross section which is a Reuleaux triangle.

Preferably, the void extends the entire length of rotor core. In this way, the entire length of the rotor core experiences the benefits of the void.

Preferably, the void extends in a direction substantially parallel to the central rotational axis.

Preferably, the rotor comprises an end-cap for reinforcing the rotor core. During use, the end-cap rotates with the rotor and can strengthen the rotor core.

Preferably, the end-cap comprises a bolt which extends into the void in the rotor core. The bolt acts to reinforce, strengthen and rigidify the rotor core. The bolt is typically fabricated from stronger materials than the laminations used to form the rotor core. Providing a bolt which extends into the void in the rotor core may be advantageous as it assists in creating a rigid rotor so that the first bending resonance frequency of the shaft is increased above the operating range. Preferably, the bolt extends the whole length of the void. Preferably, the bolt extends between two end-caps located on either side of the rotor. Preferably, the bolt affixes the end-cap to the rotor core.

Preferably, the rotor core comprises a first air channel adjacent to one of the poles of the permanent magnets. Preferably, the rotor core comprises a second air-channel located adjacent to the other pole of the permanent magnet. The first and second air-channels are located directly adjacent to the poles or ends of the permanent magnets and aim to provide cooling air channels to the magnets and to guide magnetic flux.

Preferably, the rotor comprises two or more pairs of permanent magnets and each pair of permanent magnets is associated with a separate void. Each of the pairs of permanent magnets can comprise any of the preferred or optional features described above. Further, each of associated voids can comprises any of the preferred or optional features described above. Preferably, each of the pairs of permanent magnets in the two or more pairs of permanent magnets is substantially identical and, preferably, each of the associated separate voids is substantially identical Preferably, the two or more pairs of permanent magnets and the associated separate voids are evenly spaced around the rotor core.

Detailed Description of the Invention

Specific embodiments will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 depicts a side-on view of a lamination for use in a rotor in accordance with the present intention Figure 2 depicts a perspective view of a rotor in accordance with the present invention comprising a rotor core formed from the laminations of Figure 1; and Figure 3 depicts a cross-section of the rotor and rotor core of Figure 2.

Figure 1 of the drawings depicts a lamination 10 from which a rotor 110 and rotor core 120 (see Figure 2) in accordance with the present invention are formed.

Each lamination 10 is substantially disk-like and comprises two substantially planar circular faces. The lamination 10 comprises an array of apertures which extend completely through the lamination 10.

Firstly, the lamination 10 comprises a central aperture 20 where the central aperture 20 is substantially circular and centrally aligned with the planar circular face of the lamination 10.

Secondly, the lamination 10 comprises eight magnet apertures 30. The magnet apertures 30 are substantially rectangular with additional stepped portions 35 to give the apertures 30 larger profiles in the plane of the lamination 10. The magnet apertures 30 are arranged in four pairs 40 which are evenly spaced around and proximate to the curved outer surface 50 of the lamination 10, such that the lamination 10 has four-fold rotational symmetry. Each pair of magnet apertures 40 is formed from two discrete magnet apertures 30 that are orientated towards one another at one end, the apex-end 60, and orientated away from each other at the opposing end, the open-end 70. In this embodiment, the magnets substantially have a V-shaped configuration. The open-ends 70 are proximate the curved outer surface 50 of the lamination 10 whereas the apex-ends 60 are proximate the central aperture 20. The magnet apertures 30 in the pairs 40 are discrete and comprise a central bridge 80 which is the area of the lamination 10 between their apex-ends 70. Further, the area of lamination 10 between the terminus of the magnet apertures 30 at the open ends 70 and curved outer surface 50 are known as the outer bridges 90.

Thirdly, the lamination 10 comprises four void apertures 100 which are substantially circular. The four void apertures 100 are each associated with one of the pairs 40 of magnet apertures 30. The void apertures 100 are located in the valley of the V-shaped configuration of the pairs 40. That is, the void apertures 100 are located at an intermediate position to the open-ends 70 and the apex-end 60. The distance between the edge of the void apertures 100 and the curved outer surface 50, which is known as the void bridge 105, is greater than the distance between the curved outer surface 50 and the closest edge of the magnet apertures 30. Or, in other words, the void bridge 105 is larger than the outer bridges 90. The four void apertures 100 are evenly spaced around the lamination 10. Each void aperture 100 is centrally aligned with its associated pair 40 and central bridge 80. Accordingly, the lamination 10 has a fourfold axis of rotational symmetry.

Figure 2 of the drawings depicts a perspective view of a rotor 110 in accordance with the present invention. The rotor 110 comprises a rotor core 120 with a substantially cylindrical with a circular cross-section which is formed from a stack of laminations 10 attached together.

The rotor core 120 is formed from a stack of identical laminations 10 which are all centrally and rotationally aligned. The individual laminations 10 are omitted for Figure 2 for clarity.

The rotor further comprises an axle 130, where the axle 130 extends along the centre point of rotor core 120 for its entire length of cylindrical body. The rotor 110 additionally comprises an end-cap 140 which is attached to the end of the rotor 110 to reinforce and strengthen the rotor core 120. The end-cap 140 comprises four bolts 150.

Figure 3 of the drawings depicts a cross-section of the rotor of Figure 2. From Figure 3, it can be seen that the four bolts 150 extend into the four voids 160 formed from the alignment of the four void apertures 100. Thus, the voids 160 are substantially cylindrical and complementary to the bolts 150. The end-cap 140 and bolts stiffen and strengthen the rotor core 120. The axle 130 is centrally aligned with the central aperture 20.

Cuboid permanent magnets 170 are housed or embedded within the rotor core 120. Specifically, one cuboid permanent magnets 170 is located within each of cavities in the rotor core 120 formed by the alignment of the magnet apertures 30. Since the permanent magnets 170 are located within the apertures they adopt the same orientation as the apertures 30. As such, the permanent magnets 170 as arranged in pairs which adopt a substantially V-shaped configuration. The shape of the magnet apertures 30 are mismatched from the cuboid permanent magnets 170 by the stepped portions 35 at either end. Accordingly, adjacent to both poles of the permanent magnets 170 extends a secondary void 180 and a tertiary void 190 along the length of the rotor core. The first air-channel 180 and second air-channel 190 provide channels for air-cooling.

The presence of the void 160 in the rotor core 120 significantly increase the yield strength of the central bridge 80 and outer bridges 90 compared to rotor cores not comprising a void.

Claims

Claims 1 A rotor for use in a high-speed motor or generator, said rotor comprising: a laminated rotor core comprising a curved outer surface and a central rotational axis; and at least one pair of permanent magnets within said rotor core, said pair of permanent magnets angled toward one another when viewed in a cross section substantially perpendicular with said central rotational axis; wherein said rotor core comprises a void located between said pair of permanent magnets which, during rotation of the rotor, reduces the centrifugal load on the area of said rotor core between said curved outer surface and the pole of said permanent magnet closest to said curved outer surface.
2. The rotor of claim 1, wherein the rotor core forms the outer surface of said rotor.
3 The rotor of claim 1 or claim 2, wherein said void, during rotation of the rotor, reduces the centrifugal load on the area of said rotor core between the poles of said pair of permanent magnets proximate to said central rotational axis.
4 The rotor of any one preceding claim, wherein the poles of said pair of permanent magnets proximate to said central rotational axis are closer together than the poles proximate said curved outer surface.
5. The rotor of any one preceding claim, wherein said pair of permanent magnets are angled toward one another in a V-shaped configuration.
6 The rotor of claim 5, wherein the apex-end of said V-shaped configuration is proximate said central rotational axis and the open end of said V-shaped configuration is proximate said outer curved surface.
7. The rotor of claim 5 or claim 6, wherein said void is located in the valley of said V-shaped configuration.
8. The rotor of any one preceding claim, wherein said void occupies at least 20% of the volume rotor core between said pair of permanent magnets.
9. The rotor of any one preceding, wherein said void is substantially cylindrical with a circular cross-section.
10. The rotor of any one preceding claim, wherein said void extends the entire length of rotor core.
11. The rotor of any one preceding claim, wherein said void extends in a direction substantially parallel to said central rotational axis.
12. The rotor of any one preceding claim, wherein said rotor comprises an end-cap for reinforcing said rotor core.
13. The rotor of claim 12, wherein said end-cap comprises a bolt which extends into the void in the rotor core.
14. The rotor of claim 13, wherein said bolt extends the whole length of said void.
15. The rotor of claim 13 or claim 14, wherein said bolt affixes said end-cap to said rotor core
16. The rotor of any one preceding claim, wherein said rotor core comprises a first air channel adjacent to one of the poles of said permanent magnets.
17. The rotor of claim 16, where said rotor core comprises a second air channel located adjacent to the other pole of said permanent magnet.
18. The rotor of any one preceding claim, wherein said rotor comprises two or more pairs of permanent magnets and each pair of permanent magnets is associated with a separate void.
19. The rotor of claim 18, wherein said two or more pairs of permanent magnets and said associated separate voids are evenly spaced around said rotor core.