RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 national stage application of PCT Application No. PCT/EP2017/080039, filed on Nov. 22, 2017, which claims priority from Great Britain Patent Application No. 1619856.6, filed on Nov. 24, 2016, the contents of which are incorporated herein by reference in their entireties. The above-referenced PCT International Application was published in the English language as International Publication No. WO 2018/095969 A1 on May 31, 2018.

TECHNICAL FIELD

The present disclosure relates to an electric machine apparatus. Particularly, but not exclusively, the present disclosure relates to a rotor for an electric machine; to an electric machine comprising a rotor; and to a vehicle comprising an electric machine.

BACKGROUND

A particular design challenge for electric machines is the design of the rotor to reduce magnetic flux leakage between magnet poles. The positioning and arrangement of the permanent magnets affects the magnetic flux path within the rotor. The rotor may comprise flux barriers in the form of internal apertures for controlling the magnetic flux generated by the permanent magnets. At least in certain embodiments, the present invention seeks to reduce magnetic flux leakage within the rotor of an electric machine.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a rotor for an electric machine; to an electric machine comprising a rotor; and to a vehicle as claimed in the appended claims.

According to an aspect of the present invention there is provided a rotor for an electric machine, the rotor comprising:

a plurality of magnet poles each comprising a plurality of permanent magnets, the magnet poles being angularly separated from each other and an inter-pole region being formed between adjacent magnet poles;

the permanent magnets being arranged in at least first and second layers in each magnet pole, the first and second layers being radially offset from each other and the first layer being disposed in a radially outer position;

wherein first and second external flux barriers are disposed in each said inter-pole region, the first and second external flux barriers each comprising an external aperture, the first and second external flux barriers being associated with the permanent magnets in the second layer. Each external aperture is open to an exterior of the rotor. For example, each external aperture may form an open channel in an outer surface of the rotor. The open channel may extend substantially parallel to a longitudinal axis of the rotor. The at least one external flux barrier is adapted to reduce flux leakage from the magnet pole. At least in certain embodiments, the magnetic flux at the outer surface of the rotor may be reduced proximal to the external flux barrier.

The rotor may comprise first and second external flux barriers in each said inter-pole region. The first and second external flux barriers may be symmetrical about a central inter-pole axis of each said inter-pole region. The first and second external flux barriers may be angularly separated from each other. The first and second external flux barriers may form an inter-pole tooth. The inter-pole tooth may be formed between said first and second external flux barriers. The rotor may comprise more than two external flux barriers. For example, the rotor may comprise a third external flux barrier; and optionally a fourth external flux barrier.

The rotor may comprise a third external flux barrier in each said inter-pole region. The rotor may comprise a fourth external flux barrier in each said inter-pole region. The third and fourth external flux barriers may be disposed between said first and second external flux barriers in each said inter-pole region. The third and fourth external flux barriers may be symmetrical about a central inter-pole axis of each inter-pole region.

Each magnet pole has a first radius may comprise a part-cylindrical outer surface. Each inter-pole tooth may comprise a part-cylindrical outer surface.

The magnet poles may each have a first outer surface having a first radius. The inter-pole teeth may each have a second outer surface having a second radius. The first and second radii may be the same as each other. Alternatively, the first and second radii may be different from each other. The first radius may be less than said second radius. Alternatively, the first radius may be greater than said second radius.

The first outer surface may form part of a first circular cylinder. The first outer surface may comprise a first circular arc in transverse section. Alternatively, the first outer surface may form part of a first non-circular cylinder. The first outer surface may comprise a non-circular arc in transverse section.

The second outer surface may form part of a second circular cylinder. The second outer surface may comprise a second circular arc in transverse section. Alternatively, the second outer surface may form part of a second non-circular cylinder. The second outer surface may comprise a non-circular arc in transverse section.

At least one internal flux barrier may be provided in each said inter-pole region. The at least one internal flux barrier may comprise an internal aperture. The term internal aperture is used herein to refer to an aperture which is inset from the outer surface of the rotor. Thus, the internal aperture does not interrupt the outer surface of the inter-pole region. First and second internal flux barriers may be provided in each said inter-pole region.

The at least one external flux barrier may be disposed between said first and second internal flux barriers within each said inter-pole region.

In embodiments in which first and second external flux barriers are provided in each said inter-pole region, the at least one internal flux barrier may be disposed between said first and second external flux barriers within each said inter-pole region.

The rotor may comprise a first inter-pole region having a first central inter-pole axis. Within the first inter-pole region, each internal flux barrier may be disposed in an inner position proximal to the first central inter-pole axis and each external flux barrier may be disposed in an outer position distal from the first central inter-pole axis.

The rotor may comprise a second inter-pole region having a second central inter-pole axis. Within the second inter-pole region, each internal flux barrier may be disposed in an outer position distal from the second central inter-pole axis and each external flux barrier may be disposed in an inner position proximal to the second central inter-pole axis.

The first and second inter-pole regions may be arranged consecutively within the rotor. The consecutive arrangement of said first and second inter-pole regions may be repeated around the rotor.

The one or more permanent magnet may be arranged in one or more layer in each magnet pole. Each magnet pole may comprise one or more layer of said permanent magnet. For example, each magnet pole may comprise first, second and third layers each comprising one or more permanent magnet. The at least one internal flux barrier may be associated with respective layer(s) in the magnet pole.

According to a further aspect of the present invention there is provided an electric machine comprising a rotor as described herein. The electric machine may be a permanent magnet synchronous machine.

According to a still further aspect of the present invention there is provided a vehicle comprising an electric machine as described herein. The electric machine may be configured to generate a traction force for propelling the vehicle. The electric machine may be used as the sole means of propelling the vehicle or may be used in conjunction with another torque generating machine, such as an internal combustion engine.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

