GB2590677A

GB2590677A - A motor core

Info

Publication number: GB2590677A
Application number: GB1919242.6A
Authority: GB
Inventors: James Bernard Smith Daniel
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2019-12-23
Filing date: 2019-12-23
Publication date: 2021-07-07
Anticipated expiration: 2039-12-23
Also published as: WO2021130470A1; GB2590677B; GB201919242D0; CN114902529A

Abstract

A motor core for an electric motor, the core comprising a stack of laminations 600, each lamination comprising a main body and cut-outs formed in the main body, where a sub-group of laminations of the stack comprise corresponding cut-outs having different geometries. The cut-outs may comprise air pockets (Fig 1, 111, 112, 1221, 122). The sub-group may comprise adjacent laminations, where the adjacent laminations may partially overlap to define a channel along the stack. The channel may include a flow guide 160 for generating and/or guiding a fluid flow along the motor core in use. The laminations of the subgroup may comprise a central opening 170 for receiving a motor shaft. The cut-outs may comprise a first portion for receiving a magnet 610, and a second portion extending from the first portion, the second portion comprising an air pocket, and the second portions of the sub-group may comprise different shapes and/or different orientations relative to the first portions. The laminations may comprise a yoke, stator teeth extending from the yoke, and a pole face located at the end of each tooth, and the cut-outs define the teeth and/or poles. The laminations may be formed by laser cutting an amorphous material comprising steel having a silicon content of greater than 3.5%. The core may form a stator or rotor core.

Description

A MOTOR CORE

TECHNICAL FIELD

The present invention relates to a motor core for an electric motor, a rotor core, a stator core and an electric motor.

BACKGROUND

Electric motors typically comprise stator and rotor cores which are constructed from stacked laminations, made of highly permeable material (typically steel), which are used for guiding magnetic flux around a set path.

A known problem with permanent magnet motors is torque ripple. Torque ripple is commonly mitigated by skewing the magnets used in the rotor. For at least interior permanent magnet motors, skewing the magnets requires skewing of the laminations too.

Skewed laminations are also known to provide other functionality, including to pump air or other fluids through the operating motor. It has previously been proposed to skew rotor core laminations in such a way that the poles of the full stack of laminations together spiral into a fan-like configuration. During rotation of the rotor, the skewed rotor generates a propulsive force that draws air through the motor. While this rotor design may work quite well for a reluctance motor that does not include permanent magnets in its rotor, applying it to an interior permanent magnet motor may lead to complex and costly magnet shapes.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a motor core for an electric motor, the motor core comprising a stack of laminations, each lamination comprising a main body and a plurality of cut-outs formed in the main body, wherein at least a sub-group of laminations of the stack comprise corresponding cut-outs having different geometries.

The motor core according to the first aspect of the present invention may be beneficial principally as at least a sub-group of laminations of the stack comprise corresponding cut-outs having different geometries. In particular, the use of laminations having corresponding cut-outs with different geometries, for example in a rotor core of an interior permanent magnet motor, may allow for an axial stack of laminations that can provide a reduction in torque ripple similar to that achieved by skewing packets of laminations relative to one another such that packets of magnets are skewed, but without physically having to skew the laminations within the sub-group, whilst also providing a net torque comparable to that of a skewed stack.

Use of such laminations in a rotor core of an interior permanent magnet motor may also enable the rotor core to be designed such that the cut-outs define a fan-like shape for guiding and or pumping air through the motor core in use, thereby providing enhanced cooling characteristics.

The use of laminations having corresponding cut-outs with different geometries may also be of benefit, for example in a stator core of an interior permanent magnet motor, where such cut-outs may be used to provide a variation in pole face and/or air gap and/or winding slot shape, along the axial length of the stack.

The cut-outs may either be fully enclosed within the lamination material of the main body, or recesses that are provided at the periphery of the main body. Such recesses are only partly enclosed by the lamination material and have an open boundary facing radially outward.

Corresponding' is herein to be understood as being present in all laminations of the sub-group of laminations and being, at least partly, in the same radial and circumferential position.

Corresponding cut-outs in different laminations of the sub-group will generally fulfil the same technical function and may be similar in shape and size. However, as claimed, at least one set of corresponding cut-outs of the sub-group of laminations have different geometries. Such differences in geometry may be in the shape or size of the cut-outs and or in their positions and/or orientation relative to other cut-outs formed in the main body.

In an embodiment of the invention, the cut-outs may comprise air pockets. Air pockets are herein to be understood as the flux-blocking cavities provided in the rotors IPM (Interior Permanent Magnet) electric motors. Such air-pockets are generally used to direct the magnetic field of the embedded permanent magnets in such a way as to increase the torque produced by the electric motor, and to create a saliency in the rotor inductance that can be used to create torque. Whilst referred to herein as air-pockets, it will be appreciated that in practice the air pockets may have non-magnetic material, for example plastic, held therein in use.

The sub-group may comprise adjacent laminations of the stack. For example, the sub-group may comprise a plurality of adjacent laminations of the stack and the geometry of at least one of the corresponding cut-outs may be different for substantially all of those adjacent laminations. When the variation in geometry is provided gradually, i.e. in a step-wise manner, throughout multiple adjacent laminations, this allows for the layerwise construction of 3D structures and cavities of any desired shape. This may thereby provide more freedom compared to, for example, conventional stacks having skewed laminations of the same shape.

The cut-outs of adjacent laminations of the stack may at least partially overlap to define a channel along the stack. In a rotor core, such channels may be configured for receiving and retaining permanent magnets and/or may comprise channels that define an airflow guide through the rotor core. In a stator core, such channels may be configured for receiving and retaining stator windings, e.g. in the form of hairpins. When the cut-outs that together define the channel have different geometries, the channel gets a 3D shape that is more complex than a simple straight prism.

The geometry of cut-outs may vary symmetrically along the stack. For example, the stack may comprise a central lamination, and cut-outs of laminations either side of the central lamination may vary symmetrically.

The channel may comprise a flow guide for generating and/or guiding a fluid flow along the motor core in use. This may be beneficial as such a fluid flow may be used for pumping fluid and or for cooling the motor during use. When the cut-outs that together define the flow channel have different geometries, the flow channel may, e.g., be skewed or curved relative to the longitudinal axis of the motor core.

Each lamination of the sub-group may comprise a central opening for receiving a motor shaft, and an outer peripheral edge, and the cut-outs may comprise cut-outs formed in the main body between the central aperture and the outer peripheral edge. The thus obtained cut-outs will be fully enclosed by the lamination material. Cut-outs and added features may be provided at the boundary of the central aperture for engagement with corresponding features of the motor shaft.

The cut-outs may comprise a first portion for receiving a magnet, and a second portion extending from the first portion, the second portion comprising an air pocket, and the second portions of the sub-group may comprise different shapes and/or different orientations relative to the first portions. By varying the shapes and/or orientations of the air pockets, it is possible to vary the direction in which the flux of the magnetic field created by the magnet is directed and, thereby, to locally alter the periodicity of the armature flux ripples created by the saliency of the air pockets. As a result the torque peak and the average peak of the motor is reduced by aligning the ripples such that they cancel. As a result, the difference between the torque peak and the average peak of the motor may be reduced, which may lead to a reduction in torque ripple.

Furthermore, with a skewed stack that comprises packets of laminations skewed relative to one another, short-circuiting of magnetic flux may occur at the boundary between skew packets due to misalignment of magnets between the packets of laminations. The use of laminations having corresponding cut-outs with second portions of differing geometries, but first portions with the same geometry, may enable magnets to be aligned along the length of the stack, thereby preventing short circuiting of flux, whilst still providing reduction in torque ripple. Such prevention of short circuiting may result in a motor core which can deliver a higher net torque for the same mass of magnet.

The cut-outs may comprise cut-outs formed in an outer peripheral edge of the main body. Such cut-outs, also called recesses, are only partly enclosed by the lamination material and have an open boundary facing radially outward. Varying the shape of cut-outs formed in the outer peripheral edge of the main body may allow for a motor core, for example a stator core or a rotor core, that provides a varying air gap along the length of the stack.

Each lamination may comprise a yoke, a plurality of stator teeth extending from the yoke, and a pole face located at the end of each stator tooth, and the cut-outs may define the stator teeth and/or the pole faces. Winding slots between the stator teeth may be configured for receiving stator windings. Varying the geometry of the cut-outs, and therewith also of the stator teeth and the pole faces, may also help with reducing torque ripple.

The laminations may be formed by laser cutting. This may be beneficial as laser cutting may result in less damage to the lamination material than, for example, stamping, and so loss performance may be better in use. Laser cutting may also enable greater variation of the cut-outs at a lower cost than would be needed, for example, if similar variation in cut-outs were to be formed via stamping, due to the need for multiple stamping tools.

The laminations may comprise an amorphous material. This may be beneficial as amorphous material may be a low loss material, which may provide performance gains in use. Laser cutting of amorphous material may be beneficial as amorphous material is typically hard and brittles, and hence traditional methods of forming laminations, such as stamping, may be unsuitable for use with amorphous material due to excessive wear and damage of tools.

The laminations may comprise steel having a silicon content of greater than 3.5%. This may be beneficial as it may provide enhanced efficiency in use.

According to a further aspect of the invention, an electric motor is provided comprising a motor core as described above. The invention may be used for a rotor core or for a stator core of such an electric motor. The invention may be implemented in both the rotor core and the stator core of the electric motor.

The electric motor may comprise a stator core and a rotor core mounted internally of the stator core to define an air gap between the stator core and the rotor core, the motor core may be one of the stator core and the rotor core, and the cut-outs may be formed in an edge of the motor core such that the air gap varies along the length of the stack.

According to a further aspect of the invention, a method is provided of manufacturing a motor core for an electric motor, the method comprising stacking a plurality of laminations, each lamination comprising a main body and a plurality of cut-outs formed in the main body, and at least a sub-group of laminations of the stack comprises corresponding cut-outs having different geometries.

The laminations may be stacked such that the sub-group comprises adjacent laminations of the stack.

The laminations may be stacked such that cut-outs of adjacent laminations of the stack at least partially overlap to define a channel along the stack.

According to a further aspect of the invention there is provided a method of manufacturing a motor core for an electric motor, the method comprising laser cutting a plurality of laminations such that at least a sub-group of the plurality laminations comprise corresponding cut-outs having different geometries, and stacking the plurality of laminations to define the motor core.

This may be beneficial as laser cutting may result in less damage to the lamination material than, for example, stamping, and so loss performance may be better in use. Laser cutting may also enable greater variation of the cut-outs at a lower cost than would be needed, for example, if similar variation in cut-outs were to be formed via stamping, due to the need for multiple stamping tools.

The laminations may comprise an amorphous material. This may be beneficial as amorphous material may be a low loss material, which may provide performance gains in use. Laser cutting of amorphous material may be beneficial as amorphous material is typically hard and brittle, and hence traditional methods of forming laminations, such as stamping, may be unsuitable for use with amorphous material due to excessive wear and damage of tools.

Optional features of aspects of the invention may be equally applied to other aspects of the invention, where appropriate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 schematically shows a front view of one pole region of a rotor lamination according to the invention.

Figure 2 schematically shows a perspective view of one pole region of a stack of rotor laminations according to the invention.

Figure 3 schematically shows a perspective view of one section of a stack of stator laminations according to the invention.

Figure 4 schematically shows a perspective view of part of a stack of stator laminations similar to the one shown in Figure 3, but with an added pole face cut-out.

Figure 5 schematically shows a perspective view of one way of configuring stator laminations in order to vary the air gap between the rotor and the stator.

Figure 6 schematically shows a perspective view of one pole region of a stack of rotor laminations according to the invention.

DETAILED DESCRIPTION

The motor core according to the invention may, for example, be a rotor core or a stator core.

An electric motor according to the invention may comprise such a rotor or stator core or a combination of both. In the following, with reference to Figure 1-6, some particularly useful examples of lamination variation in rotor cores and/or stator cores will be described. It is, however, to be noted that many other variations may be used without departing from scope of the invention as defined by the claims.

Figure 1 schematically shows a front view of one pole region of a rotor lamination 100 according to the invention. Each lamination 100 of a rotor core comprises a plurality of such pole regions which together form a full ring or circle. In the rotor of an electric motor, a plurality of such rotor laminations 100 is stacked together to form the rotor core. The rotor lamination has an outer radius 102 and an inner radius 101.

Preferably, the rotor laminations 100 are made of a single sheet of ferromagnetic material, such as iron, amorphous iron or special amorphous metal alloys (e.g. Metglas®). It is noted that when the rotor laminations 100 are made of a single sheet of material, the sides drawn in Figure 1 only indicate a side edge of the pole region, not of the rotor lamination 100 or part of the rotor lamination itself. Pole regions of laminations 100 may be generally the same around the circumference of the lamination, or may be varied depending on the desired characteristics. Rotor laminations 100 may be produced from larger sheets of rotor lamination material using, e.g., a stamping tool or laser-cutting. When many rotor laminations with different geometries are needed, a fully automated laser cutting process is preferred.

At the inner radius 101, the rotor laminations are typically mounted to a shaft. The shaft may have an outer radius that is substantially equal to the inner radius 101 of the rotor lamination 100 shown in Figure 1.

The rotor lamination 100 in this example is part of an IPM (interior permanent magnet) motor. Each pole region comprises one or more magnet pockets 110, 120 for receiving a permanent magnet. Each magnet pocket 110, 120 is accompanied by two air pockets 111, 112, 121, 122 that serve to conduct the magnetic flux and increase the torque produced by the motor. In the prior art, such air pockets 111, 112, 121, 122 are generally provided symmetrically at both sides of the magnet pockets 110, 120. In the exemplary embodiment shown here, the air pockets 111, 112, 121, 122 and their corresponding magnet pockets 110, 120 are different parts of the same cut-outs in the main body of the rotor lamination 100. One larger inner cutout is configured for receiving a first magnet. One smaller, outer cut-out is configured for receiving a smaller magnet. In other embodiments, the magnet pockets 110, 120 and the air pockets 111, 112, 121, 122 may be formed as separate cut-outs. Also the number of magnet pockets and air pockets may vary between different rotors.

A common problem in IPM motors of such design is torque ripple. Torque ripple is caused by a periodic increase or decrease in output torque as the motor shaft rotates. It is measured as the difference in maximum and minimum torque over one complete revolution and generally expressed as a percentage of the maximum or average torque. Torque ripple leads to excess noise and vibration from the system, as well as ultimately affecting wear and reliability over the life of the motor.

According to the invention, the problem of torque ripple is mitigated by varying the design of the pole regions along the rotational axis of the rotor. This is achieved by varying the geometry and configuration of the air pockets 111, 112, 121, 122 relative to the magnet pockets 110, 120 per rotor lamination 100. As can be seen in Figure 1, the air pockets 111, 121 to the left of the magnet pockets 110, 120 in this rotor lamination 110 extend away from their respective magnetic pockets 110, 120 further than the air pockets 112, 122 to the right. In other rotor laminations 100 of the same rotor core, the air pockets 111, 112, 121, 122 are provided more symmetrically or extend further to the right side of the magnet pockets 110, 120 than to the left. Because of the difference in geometry of the air pockets 111, 112, 121, 122 of different rotor laminations 100, the magnetic flux is conducted in slightly different direction in different rotor laminations 100. As a result torque ripple is reduced or even completely avoided. In addition to, or as an alternative of varying the relative orientation of the air pockets 111, 112, 121, 122, similar advantages can be obtained by varying their size or shape.

Figure 2 schematically shows a perspective view of one pole region of a stack of rotor laminations 100 according to the invention. For clarity only, this drawing does not show the individual rotor laminations. In the drawing, dotted lines indicate how the boundaries of the magnet pockets 110, 120 and the air pockets 111, 112, 121, 122 run through the stack of rotor laminations 100. Preferably, the magnet pockets 110, 120 have the same position and geometry all through the stack. This makes it possible to use simple magnet shapes, such as right prisms or even rectangular boxes. Alternative magnet shapes, such as an oblique prism can be used if the collection of magnet pockets 110, 120 in a stack of laminations is shaped to receive and retain such magnet shapes.

When following the rotor laminations in the stack along the rotational axis of the rotor from the first lamination On the front) to the last one On the back), the air pockets 111, 121, 112, 122 have a gradually changing geometry. As a result, the magnetic flux is conducted in a different direction at the front face of the stack than at the rear face. In addition to the air pockets 111, 112, 121,122, also described with reference to Figure 1, the rotor laminations in this drawing comprise a further recess or cut-out 130 at the outer radius 102 that may further assist in varying the direction of the magnetic flux, but also introduces a variation of the air gap width between the rotor and the stator.

Other pole regions of the rotor lamination 100 may exhibit the same or a different geometrical variation. Similarly, a full rotor core may consist of a plurality of the same, similar or different lamination stacks as shown in this drawing. For example, an adjacent stack of rotor laminations 100 may be a mirrored version of the one shown in this drawing. Additional toque ripple mitigation may be achieved, by skewing adjacent stacks of rotor laminations 100 over an angle that is different from the opening angle of a magnetic pole (360° divided by the number of pole regions in each rotor lamination 100).

Usually, the stator of an electric motor is also made of a plurality of stacked laminations. Variations in stator lamination geometry can be used for mitigating torque ripple and/or varying the air gap width in ways similar to those described above for the rotor laminations 100. Such stator lamination variation can be used either as an alternative, or in addition to the rotor lamination variations.

Figure 3 schematically shows a perspective view of one section of a stack of stator laminations 200 according to the invention. Again, the section drawn does not show the full stator lamination 200, but only part thereof. The stator laminations 200 may be made from the same or similar materials as the rotor laminations 100 and can be produced in similar ways. To avoid wasting too much material, rotor laminations 100 and stator laminations 200 may be made from the same sheet of lamination material. This is, of course, only possible if the rotor and the stator core are made of the same material.

Each stator lamination 200 comprises a yoke 203 and a plurality of stator teeth 211 extending from the yoke 203. A plurality of cut-outs in the main body of the stator lamination 200 defines the stator teeth. The cut-outs form winding slots 210 that are shaped to receive the hairpins or stator windings. Adjacent winding slots 210 are separated from each other by the stator teeth 211. At the radially inner end of each stator tooth 211, a pole face 212 is provided. The pole face 212 will usually be wider than the stator tooth 211, in order to at least partly close off the winding slot 210. Stator openings 213 between adjacent pole faces 212 serve to direct the magnetic field created by the stator. To provide the stator openings 213, the cut-outs are provided in the form of recesses having an open boundary at the inner radius of the stator lamination 200.

When all winding slots 210, stator teeth 211 and pole faces are identical, periodic torque variations may result in torque ripple. According to the invention and as shown in Figure 3, this effect can be mitigated or avoided by introducing asymmetries into the stator design. For example, by varying the width and/or the position of the slot openings 213 relative to the corresponding winding slots 210, the orientation of the slot openings 213 relative to the rotational axis of the motor, the width of the slot openings 213 and the distance between adjacent slot openings 213 can be varied along the central axis of the motor and/or around the circumference of the stator. As for the rotor, these variations in stator features are obtained by providing and properly arranging a plurality of laminations with differently designed cutouts. Gradual design variations through the stack of stator laminations 200 can provide the skewed and tapered slot openings shown in Figure 3.

The stator lamination variations are preferably such that corresponding winding slots 210 of adjacent stator laminations 200 have the same geometry and are in the same position. As a result, the winding slots 210 of the stator core will be shaped as right prisms and the variation in stator lamination geometry does not influence the placement and installation of the stator wiring. Also within each stator lamination 200, it is preferred that all winding slots have the same shape and size and are provided at regular distances from their neighbouring winding slots 210. In most modern electric motors used for electric vehicles, hairpins are used for the stator windings. Especially when using hairpins, it is useful to have a stator core with a symmetric arrangement of geometrically identical and straight winding slots 210.

Figure 4 schematically shows a perspective view of part of a stack of stator laminations 200 similar to the one shown in Figure 3, but with an added pole face cut-out 214 or recess in the pole face 212. The pole face cut-out 214 results in a variation of the air gap width in a way similar to the rotor lamination cut-out 130 shown in Figure 2. Also in the stator, alternative ways of varying the air gap width can be used. For example, the length of the stator teeth 211 (including the pole faces 212) may be varied between stator teeth 211 of the same stator lamination 200 and/or between corresponding stator teeth 211 of adjacent stator laminations 200.

Figure 5 schematically shows a perspective view of part of a stator wherein different stator laminations 200 have stator teeth 211 of different lengths. As a result, the pole faces 212a of some stator laminations 200 will be closer to the outer radius 102 of the rotor than the pole faces 212b of other stator laminations 200 and the width of the air gap between the rotor and the stator varies along the rotational axis of the rotor. Instead of such a stepwise transition, the transition may be smoother, with the pole face 212 gradually tapering towards or away from the opposing outer surface of the rotor.

Figure 6 schematically shows a perspective view of one pole region of a stack of rotor laminations 600 according to the invention. In Figure 6, the pole region is shown with two permanent magnets 610, 620 inserted into their magnet pockets. A more significant difference with the rotor laminations 100 shown in Figures 1 and 2 is that a guide vane 160 extends from the inner radius 601 of the pole region section of the rotor lamination 600. At the radially inward end of the guide vane 160, a support hub 170 is provided. The inner surface of the support hub 170 is configured for being mounted to a central rotational shaft of the electric motor.

The guide vane portion 160 extending from the pole region is positioned differently in different rotor laminations 600. In the rotor lamination 600 on the top of the stack, the guide vane portion 160 is situated close to the right edge of the pole region. In the rotor lamination 600 at the bottom of the stack shown in this drawing, the guide vane portion 160 is situated close to the left edge of the pole region. By stacking the rotor laminations 600 this way, a curved guide vane 160 is obtained, which can propel and guide air or other fluids when the rotor rotates. By varying the rotor lamination geometry of the rotor laminations 600 making up the rotor core, guide vanes 160 of any suitable design can be obtained. As an alternative to curved guide vanes 160, straight vanes that are skewed relative to the rotational axis of the rotor can be used. Also, the guide vane surface may not be flat like shown in Figure 6, but may comprise additional features (cut-outs or add-ons) to optimise the air flow created, and/or the noise emitted, by the rotating rotor.

Avoiding or mitigating torque ripple, varying the air gap between the rotor and the stator and providing air guides are just a few exemplary applications of the idea behind the invention, i.e. the variation of lamination geometry to allow arbitrarily shaped 3D features to be provided in the rotor and/or stator of the electric motor. Other useful 3D features that may be provided in this way are, e.g., mechanical retention features for easily connecting magnets, electrical wiring, sensors, electronics, rotor shafts or motor housings to the motor cores.

Although the invention as illustrated in Figures 1-6 has mainly been described with reference to an IPM electric motor, similar variations in lamination geometry can be equally useful in other types of electric motors, such as reluctance motors or surface permanent magnet motors (SPM), for providing location and retention features, improved airflow (drag) acoustic (tonal noise) behaviour when airflow is present though the motor. As well as mass reduction by removing underutilised lamination material as different axial locations. As in the examples described above, the geometrical variations in the laminations of the rotors and/or the stators of such motors may be variations in the shape and outline of the laminations, variations in the position, orientation and geometry of cut-outs in the laminations or a combination of both.

Claims

CLAIMS1. A motor core for an electric motor, the motor core comprising a stack of laminations, each lamination comprising a main body and a plurality of cut-outs formed in the main body, wherein at least a sub-group of laminations of the stack comprise corresponding cut-outs having different geometries.
A motor core as claimed in Claim 1, wherein the cut-outs comprise air pockets.
3. A motor core as claimed in Claim 1 or Claim 2, wherein the sub-group comprises adjacent laminations of the stack.
4. A motor core as claimed in any preceding claim, wherein cut-outs of adjacent laminations of the stack at least partially overlap to define a channel along the stack.
5. A motor core as claimed in Claim 4, wherein the channel comprises a flow guide for generating and/or guiding a fluid flow along the motor core in use.
6. A motor core as claimed in any preceding claim, wherein each lamination of the sub-group comprises a central opening for receiving a motor shaft, and an outer peripheral edge, and the cut-outs comprise cut-outs formed in the main body between the central aperture and the outer peripheral edge.
7. A motor core as claimed in any preceding claim, wherein the cut-outs comprise a first portion for receiving a magnet, and a second portion extending from the first portion, the second portion comprising an air pocket, and the second portions of the sub-group comprise different shapes and/or different orientations relative to the first portions.
8. A motor core as claimed in any preceding claim, wherein the cut-outs comprise cut-outs formed in an outer peripheral edge of the main body.
9. A motor core as claimed in Claim 8, wherein each lamination comprises a yoke, a plurality of stator teeth extending from the yoke, and a pole face located at the end of each stator tooth, and the cut-outs define the stator teeth and/or the pole faces
10. A motor core as claimed in any preceding claim, wherein the laminations are formed by laser cutting.
11. A motor core as claimed in any preceding claim, wherein the laminations comprise an amorphous material.
12. A motor core as claimed in any preceding claim, wherein the laminations comprise steel having a silicon content of greater than 3.5%.
13. An electric motor comprising a motor core as claimed in any preceding claim.
14. An electric motor as claimed in Claim 13, wherein the electric motor comprises a stator core and a rotor core mounted internally of the stator core to define an air gap between the stator core and the rotor core, the motor core is one of the stator core and the rotor core, and the cut-outs are formed in an edge of the motor core such that the air gap varies along the length of the stack.
15. A method of manufacturing a motor core for an electric motor, the method comprising laser cutting a plurality of laminations such that at least a sub-group of the plurality laminations comprise corresponding cut-outs having different geometries, and stacking the plurality of laminations to define the motor core.
16. A method as claimed in Claim 15, wherein the laminations comprise an amorphous material.
17. A method as claimed in Claim 15 or Claim 16, wherein the laminations are stacked such that the sub-group comprises adjacent laminations of the stack.
18. A method as claimed in any of Claims 15 to 18, wherein the laminations are stacked such that cut-outs of adjacent laminations of the stack at least partially overlap to define a channel along the stack.