GB2549449A

GB2549449A - A magnetically geared apparatus

Info

Publication number: GB2549449A
Application number: GB1600657.9A
Authority: GB
Inventors: James Powell David; Garcia Ferran; Wilson Gregg; Barrett Robert
Original assignee: Magnomatics Ltd
Current assignee: Magnomatics Ltd
Priority date: 2016-01-13
Filing date: 2016-01-13
Publication date: 2017-10-25
Also published as: GB201600657D0

Abstract

The rotor comprises an inner ring structure at least a portion thereof is formed from composite material comprising: a first plurality of fibers extending substantially in a first direction and a second plurality of fibers extending substantially in a second direction, the first direction and the second direction being non-parallel and the first direction and/or second direction being between a circumferential direction and an axial direction. An outer ring structure has a plurality of fibers arranged with a third and fourth plural extending in a third and fourth direction different to the first and second fibers, one of the third and fourth fiber sets extending axially of the rotor with the other extending circumferentially or at least partially radially. The walls of pole piece retaining portions extend radially through the radial width of the outer layer, the recess formed retaining a pole piece whose surface is flush with the surface of the outer ring. Various values are given for the orientation between first and second fiber sets, whose fibers may be of E-glass, S-glass, Kevlar, carbon fiber or natural fiber. The inner and outer rings may be bonded or mechanically fixed together.

Description

A MAGNETICALLY GEARED APPARATUS FIELD

The disclosure relates to a magnetically geared apparatus.

BACKGROUND

Existing magnetically geared devices utilise a modulating or pole-piece rotor to act both as a modulator for the electromagnetic field and to transfer torsional electromagnetic forces on the individual pole-pieces to motive power on an output shaft.

The pole-piece rotor of such a magnetically geared device may comprise a number of steel pole-pieces arranged in a radial array. Forces on the pole-pieces must be reacted in order to transfer torque from the pole-pieces to an output shaft or flange.

In some existing magnetically geared devices, a composite structure is used to react the forces generated on the pole-pieces. Figure 1 shows an existing rotor built up from multiple composite parts (pultruded unidirectional beams or multi-directional fibre beams) and laminated high permeability steel pole-pieces. The composite beams are bonded to the high permeability steel pole-pieces to form a cylinder which reacts the torsional output load of the motor. Hence, for the rotor to remain torsionally and radially stiff, the adhesive bonds between the composite beams and the laminated steel pole-pieces must also be relatively stiff. Although this provides a torsionally stiff rotor, it also provides very little damping, and hence, resonant modes of the cylinder are relatively undamped.

One solution to this problem is to increase the stiffness of the rotor such that the modes that have been identified to cause significant vibration in the rotor will occur outside the operating speed range of the motor. However, this is not always possible and, as many applications of magnetically geared devices require variable speed operation, it is possible that the rotor will be driven through or operate at a resonant modal frequency.

SUMMARY

In general, in at least certain examples, the present solution provides a pole piece rotor having a continuous radially inner portion formed from composite material. The material may comprise a plurality of fibres extending in different, non-parallel directions. One of these directions may be between a circumferential direction and an axial direction. The other of these directions may also be between a circumferential and an axial direction.

In an aspect, a magnetically geared apparatus comprises a rotor, the rotor comprising: a ring structure; wherein at least a portion of the ring structure is formed from composite material comprising: a first plurality of fibres extending substantially in a first direction and a second plurality of fibres extending substantially in a second direction, the first direction and the second direction being non-parallel and the first direction and/or second direction being between a circumferential direction and an axial direction.

Optionally, the ring structure is an inner ring structure, and wherein rotor further comprises an outer ring structure that is radially outer, the second ring structure having a pole piecereceiving portion therein.

Optionally, the inner and outer ring structures are concentric.

Optionally, the pole piece-receiving portion comprises walls extending radially through the outer ring structure. The walls may extend radially through the entirety of a radial width of the outer ring structure.

Optionally, the first and second crossed fibres form a layer in the inner ring structure.

Optionally, the outer ring structure is formed from composite material comprising a third plurality of fibres extending substantially in a third direction different from the first and/or second directions. The outer ring structure may further comprises a fourth plurality of fibres, the third and fourth plurality of fibres being aligned in respective third and fourth orientations, at least one of the third and fourth orientations being different to the first and second orientations. At least one of the third and fourth orientations may be aligned substantially along the axial direction, and the other of the third and fourth orientations may be aligned substantially along the circumferential direction.

Optionally, the third and fourth orientations are separated by an angle of substantially 90°.

Optionally, the third plurality of fibres comprise chopped strands of fibres.

Optionally, at least one of the third plurality of fibres extends at least partly, and optionally substantially, radially. The third plurality fibres may form a three-dimensional weave.

Optionally, the axis of rotation of the rotor defines a Z axis, and wherein the first orientation is between 0° and 90° with respect to the XY plane, and the second orientation is between 0° and -90° with respect to the XY plane. The first orientation may be between 5° and 85°, and optionally the second orientation may be between -5° and -85°. The first orientation may be between 10° and 80°, and optionally the second orientation may be between -10° and -80°. The first orientation may be between 15° and 75°, and optionally the second orientation may be between -15° and -75°. The first orientation may be between 30° and 60°, and optionally the second orientation may be between -30° and -60°. The first orientation may be substantially 45°, and the second orientation may be substantially -45°.

Optionally, the first and second orientations are separated by an angle of substantially 90°.

Optionally, the walls of the pole piece-receiving portion do not extend into the inner ring structure. Alternatively, the walls may extend part of the way through a radial width of the inner ring structure.

Optionally, the pole piece-receiving portion has a length and a width, the length being greater than the width, and the length extending in the axial direction.

Optionally, the rotor is formed from a filament winding, a roll-wrap or a resin transfer mould technique.

Optionally, the fibres of the inner ring structure and the outer ring structure are different materials.

Optionally, the fibres of the inner ring structure are E-glass, S-glass, Kevlar, Carbon-fibre or natural fibres

Optionally, the inner ring structure is radially internal to the outer ring structure.

Optionally, the inner and outer ring structures are bonded or mechanically fixed together. The inner and outer ring structures may comprise a screw passing radially through the inner and outer ring structures, and a nut on one end of the screw to mechanically fix the inner and outer ring structures together. Additionally or alternatively, the inner and outer ring structures comprise a screw passing radially through the outer ring structure into a blind hole in the inner ring structure, thereby mechanically fixing the inner and outer ring structures together. The blind hole may have means for retaining the screw, for example a tapped hole or insert.

Optionally, the pole piece-receiving portion receives at least one pole piece therein. A surface of the at least one pole piece may form at least part of the radially outer surface of the rotor.

Optionally, the pole piece-receiving portion and the at least one pole piece are shaped to provide a mechanical keying of the at least one pole piece in the pole piece-receiving portion. The mechanical keying may be such that outward radial movement of the at least one pole piece is restricted.

Optionally, the walls of the pole piece-receiving portion comprise a circumferential spacing therebetween, the walls being inclined towards the radially inner surface.

Optionally, the pole piece-receiving portion has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially trapeziform, and the at least one pole piece has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially trapeziform. Alternatively, the pole piecereceiving portion has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially diamond-shaped, and the at least one pole piece has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially diamond-shaped. Other complementary shapes of pole pieces and pole piece-receiving portions are possible, as long as the result is mechanical keying.

Optionally, the walls of the pole piece-receiving portion comprise a circumferential spacing therebetween, the pole piece-receiving portion further comprising a wedge between one of the walls and the at least one pole piece. The wedge may have a radially extending wall inclined towards the radially inner surface.

Optionally, the rotor further comprises damping material and wherein, when the damping material is at a temperature within a range of 0°C to 150°, the damping material has a loss factor greater than 0.1. The loss factor may be greater than 1. Optionally, when the damping material is at a temperature within the range, the damping material has a

Young’s modulus between 1MPa and lOOMPa. The damping material may have a Young’s modulus between 1MPa and 30MPa.

Optionally, herein the damping material is provided between at least one pole piece received in the pole piece-receiving portion and the pole piece-receiving portion. The damping material may be provided between radially extending walls of the at least one pole piece and the walls of the pole piece-receiving portion. Additionally or alternatively, the damping material may be provided between a radially inner surface of the pole piece and the pole piece-receiving portion.

Optionally, the damping material comprises a tape, a post-cured pourable fluid, a mouldable putty, a loaded rubber, a visco-elastic or a visco-plastic.

Optionally, the damping material comprises a plurality of different materials having different values of the loss factor and/or the Young’s modulus. The different materials may be axially, circumferentially or radially layered.

Optionally, the damping material is provided in a cavity of at least one pole piece. The cavity may be completely enclosed by the pole piece. Alternatively, the cavity may be in communication with an exterior of the pole piece.

Optionally, the cavity comprises a slot extending towards a surface of the at least one pole piece. The slot may comprise a first slot extending radially, and a second slot extending circumferentially.

Optionally, the cavity comprises a diagonal slot oblique to the radial direction.

Optionally, cavity comprises one or more internal slots, each slot dividing the at least one pole piece into a plurality of pole pieces. The plurality of pole pieces may be enclosed by the damping material.

Optionally, the at least one pole piece comprises a laminated pole piece. The laminated pole piece may be formed of laminate sheets layered axially or radially. The pole piece may further comprise damping material between the laminate sheets.

Optionally, the at least one pole piece comprises a plurality of axially adjacent pole pieces. The pole piece may further comprise damping material between the axially adjacent pole pieces.

Optionally, the at least one pole piece comprises a plurality of pole piece portions, the pole piece portions being radially layered on top of each other. The pole piece portions may comprise inner and outer pole piece portions, the outer pole piece portion forming a shell radially outer of the inner pole piece portion. The plurality of pole piece portions may comprise 2 or more pole piece portions, for example 3 pole piece portions.

Optionally, the rotor comprises first and second end plates at opposite axial ends of the rotor, the first and second end plates being fixed to the ring structure.

Optionally, the first ring structure is of one-piece construction. The first and second ring structures may be of one-piece construction.

The magnetically geared apparatus may be a motor/generator.

The magnetically geared apparatus may provide magnetic gearing between an input shaft and an output shaft, one of the input shaft and output shaft comprising the rotor.

The apparatus further may further comprise: another rotor comprising a first plurality of permanent magnets; a stator comprising a second plurality of permanent magnets and windings; wherein the rotor is arranged to interact with the another rotor in a magnetically geared manner; and wherein the windings are arranged to magnetically interact with the first or fundamental harmonic of the magnetic field of the first plurality of permanent magnets.

Optionally, first plurality of permanent magnets has a respective first number of pole-pairs, and the second plurality of permanent magnets has a respective second number of pole-pairs, wherein the at least one pole piece is arranged to modulate the magnetic fields of the first and second pluralities of permanent magnets to produce mutually matching pole-pairs, thereby enabling magnetic coupling and torque transmission between the first and second pluralities of permanent magnets, and wherein the windings are arranged to magnetically couple with the first or fundamental harmonic of the magnetic field of the first plurality of permanent magnets.

The rotor and the another rotor may be configured to transfer torque therebetween in a magnetically geared manner. Optionally, the rotor is mechanically coupled to one of an input or output shaft, and the another rotor is mechanically coupled to the other of an input or output shaft.

FIGURE LISTING

Specific embodiments in which the invention is embodied are described below by way of example only and with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a prior art rotor.

Figure 2 is an axial view of an embodiment of a rotor for a magnetically geared apparatus.

Figure 3 is two graphs showing how Young’s modulus and material loss factor vary with temperature for a variety of materials.

Figure 4 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 5 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 6 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 7 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 8 is a perspective view of the rotor of any of figures 2 and 4 to 7.

Figure 9 is as axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 10 is a perspective view of the rotor of figure 9.

Figure 11 is an axial view of the rotor of figures 9 and 10, with various elements absent.

Figure 12 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 13 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 14 is an axial view of another embodiment of a rotor for a magnetically geared apparatus.

Figure 15 is an axial view of an embodiment of a pole piece for the rotors of figures 2 and 4-14.

DETAILED DESCRIPTION

If we consider a pole-piece rotor built using the same structure as figure 1, but with a compliant adhesive, it is evident that both the torsional stiffness and the cylinder wall radial stiffness will be significantly lower and the rotor will have limited utility in terms of the load carrying capability due to the large displacements that would occur.

Figure 2 shows an embodiment of a pole-piece rotor. The rotor may be constructed from a single tube (ideally non-metallic) with machined slots. This could also be constructed from a number of parts to build up the geometry shown. Such a rotor may be used as part of a magnetically geared apparatus having a stator with relatively high number of magnetic poles, the pole piece rotor and an inner rotor having a relatively low number of magnetic poles. The inner rotor is a high-speed rotor. Alternatively, the high-speed rotor could be an outer rotor.

An important part of this type of construction is that a torque tube is retained on the inner surface of the rotor. The advantage of having the torque tube on the inner surface is that the system is less sensitive to the magnetic air gap between the pole-pieces and the highspeed low-pole inner rotor. Extending the outer gap between the pole-pieces and the high pole number outer stator or array would significantly reduce the air gap shear-stress and hence torque capability of the magnetic gear. This is predominantly due to the ratio of magnet pole width to the air gap length and results in higher levels of magnetic leakage i.e. flux which goes from magnet-to-magnet without crossing the air gap or perhaps more precisely isn’t in the correct orientation in the air gap to contribute to the production of a tangential force and hence torque.

This torque tube is torsionally stiff, and is capable of reacting the maximum torsional load without additional support from the laminated pole-pieces (as was the case with the rotor in figure 1). The high permeability pole-pieces are placed in the slots as shown in figure 2. The pole-piece slots provide a means of carrying the pole-pieces on the rotor which may also form a non-re-entrant shape for the pole-piece so it cannot exit the rotor under high loads (electromagnetic or centrifugal). The combination of a torque tube to react the torsional load and non-re-entrant slots to hold the pole-pieces allows the pole-pieces to be used to transfer loads without needing to contribute to the overall rotor structure torsional stiffness. In the known device of figure 1, the pole-pieces do need to contribute to the overall rotor structure torsional stiffness.

By virtue of the pole-pieces not needing to contribute to the overall rotor structure torsional stiffness, it is possible to introduce a layer of compliant (low modulus) damping material between the pole-piece and the composite structure, as shown in Figure 2.

Damping materials may be selected based on a multi-physical set of parameters: • Loss factor over application operating temperature range • Young’s modulus over application operating temperature range • Maximum and minimum operating temperatures • Bonding compatibility with other materials

Young’s modulus and loss factor parameters for a range of materials are shown in figure 3 over a large temperature range.

The working temperature range for the pole-piece rotor is between the minimum defined ambient temperature and the maximum operating temperature in service. This range is between 0 and 150°C, so it is immediately clear from figure 3 that the physical properties for both loss factor and Young’s modulus show significant variations over this range. By considering the practical operating temperature range for a magnetically geared system, for example a magnetically geared motor or generator used as an industrial drive, transportation (for example a rail traction motor or a marine propulsion motor) or renewable energy systems (for example wind or marine current turbine generators), after a few hours of operation, which will be between 50 and 150°C, it can be seen that some of the damping materials are more stable.

The loss factor (sometimes termed tan-delta) is a measure of the hysteretic damping under deformation in a given material. Elastomeric materials can have high loss factors (~1.0) and are useful as dampers and isolators.

Where η is the loss factor, C and Cq are the actual damping coefficient and critical damping coefficient, respectively, and z is the damping ratio.

From figure 3 it is clear that DYAD 609 and ISD 110 exhibit high loss factors in the 50 -100 °C temp range. DYAD 609 is a known constrained layer damping polymer manufactured by Soundcoat. ISD 110 is a known viscoelastic damping polymer.

It is important to consider how the vibration energy is dissipated within the damper. Firstly, to impart energy to a visco-elastic damper, there must be relative movement. The amount of movement is determined partly by the overall geometry and applied forces and partly by the Young’s modulus of the damping material. The amount of energy dissipated in the damping material due to this relative movement (for instance shear) is a function of the loss factor. Hence, the modulus and loss factor must be chosen for a specific application (and temperature range) with care. A useful loss factor could be 0.1 or above, where >0.9 is seen as high. A typical useful Young’s modulus for this application is between IMPa and lOOMPa, and preferably between IMPa and 30MPa. This is extremely low when compared to conventional structural adhesives, which are typically between 0.1 GPa and lOGPa.

The use of different damping materials for any one of the pole-pieces, or using multiple materials for each pole-piece (either layered in parallel or in series to produce a single layer) should be considered, as it will be an advantage to provide damping over a wide temperature range as typical applications will require the magnetically geared system (for example a magnetically geared motor/generator)to “start-up” from cold and operate without delay such as rail propulsion.

The damping layer of the embodiment of figure 2 is typically a material with a high loss factor (tan-delta) and is securely attached to both the pole-piece and the structure by an adhesive or other means. The resonant wall-bending modes that can be excited in a pole-piece rotor result in relative motion between the pole-piece and the composite structure during operation. The damping layer between the pole-piece and the structure is then subjected to a shearing force which may comprise a number of harmonics due to the electromagnetic excitation forces of the magnetic gear. This results in dynamic shearing in the damping layer. The loss factor of the material dictates the proportion of the energy that is dissipated in the layer during shearing (kinetic energy from the vibrations is reduced to heat energy in the damping layer). The amount of damping is a function of the material shear modulus, the loss factor and the thickness of the damper layer.

The rotor comprises a tube structure which may be manufactured from a single-piece composite tube or other non-metallic tube with machined slots. The tube structure may be constructed using a resin-transfer mould technique, where no, or minimal post-machining is required. The tube structure may be manufactured from multiple parts to provide a rotor with a torque tube feature and slots to hold the pole-pieces.

The slots in the tube may be trapezoidal or another shape (round, diamond, hexagon etc., etc.) which results in mechanical keying of the pole-piece shape (pole-pieces are unable to be removed from the structure in the radial direction).

In an embodiment shown in figure 11, the slots may be parallel sided to allow insertion of the pole-pieces from the top of the slot (inserted in a radial direction). The circumferential gap between the pole-piece and the parallel sided slot wall in the tube structure is then filled with a non-metallic wedge as shown in figures 9 and 10. The damper layer is fixed between the pole-piece and the wedge. The interface between the wedge and the tube structure is hard bonded or made secure (see figures 9 and 10).

In an embodiment, the pole-pieces may be trapezoidal in shape or another shape which results in mechanical keying of the pole-piece shape in the slot.

In the embodiment shown in figures 6 and 7, the pole-pieces may be provided with slots in that extend to the periphery of the pole-piece, but the pole-piece remains as a single part. Any number of slots may be provided in a pole-piece. The slots may be filled with damping material (high loss factor material with low modulus).

In the embodiment shown in figure 2, the pole-pieces may be provided with slots in that do not penetrate the periphery of the pole-piece. The pole-pieces still remain as a single part. The slot pattern may be a cruciform as shown or comprise a number of slots which are internal to the geometry (do not break through the outer edge of the pole-piece).

In an embodiment shown in figure 5, the pole-pieces may be split in to a number of individual parts. The parts may have damping material between them and also around the re-constructed form of the whole pole-piece. A damper layer may be provided between the pole piece and the slot wall as shown in figure 2. A damper layer may be provided in the slots of the pole-pieces as shown in figures 4, 5 and 6.

The damper layer may be in the form of a tape. The damper layer may be in the form of a pourable fluid that is post-cured. The damper layer may be in the form of a mouldable putty or equivalent. The damper layer may be a single part injection-mould material such as a loaded rubber, visco-elastic, visco-plastic etc.

More than one type of damping material may be utilised in each slot, either layered (in series) or adjacent to each other (in parallel).

In the embodiments of figures 4 to 7, different damper materials may be used for the slots within the extents of the pole-piece shape and the interface between the overall pole-piece form and the tube structure.

Each pole-piece may use a different damping material. Each pole-piece may use a number of different damping materials along the axial length, whether internal to the pole-piece (slots cut in the pole-pieces) or in the layer between the pole-piece and the tube structure. The pole-pieces may be a plurality of pole pieces segmented in the z-direction as shown in figure 8. A damper layer may be introduced between the segments.

If the pole-pieces are manufactured from thin laminations, a damper layer as previously described may be applied to the lamination before it is cut in the form of a thin coating. There will then be a damping layer between adjacent laminations.

The rotor may be formed as a composite tube structure. The composite tube structure may be formed from either a filament winding or roll-wrap or other technique available to produce a tube. The lay of the fibres is controlled such that predominantly 45/-45 degree fibres (angled with respect to the XY plane, where the Z-axis of the tube is taken to be the centre of the tube axis) are used to form a first proportion of the thickness and predominantly 0/90 degree fibres (angled with respect to the XY plane) are used to form the remaining thickness of the tube.

The machined slots are cut to a pre-determined depth to leave a thickness of “torque tube” section at the bore of the tube which is left un-machined. The 45/-45 fibres may be a different material to the remaining thickness of the tube to provide a stronger and stiffer rotor, such as S-glass, Kevlar or Carbon-fibre etc. or a combination of these fibres. A mandrel may be manufactured such that the cured diameter of the rotor bore is within the final tolerance required. This removes the need to machine the bore and risk cutting through some of the fibre layers in the torque tube (concentricity is maintained).

The machined slots may be trapezoidal or parallel or diamond-shaped, or any other shape that would provide mechanical keying. The pole pieces may be any corresponding shape in order to by keyed into the slots, such as trapezoidal, parallel or diamond-shaped, or any other shape.

The rotor may be a tube manufactured from two tubes with one nested coaxially and concentrically internal to the other.

In an embodiment, a first composite tube structure of the rotor (outer part of the tube shown in figure12) is manufactured from predominantly 0/90 fibres or a combination of fibres (including chopped strand) with a number of trapezoidal or diamond or parallel shaped slots that are cut all the way through the tube. Pole-pieces are mounted in the slot by inserting them from the inner bore of this first composite tube. A second composite tube structure of the rotor, manufactured from 45/-45 fibres, may be inserted at the bore of the first tube as shown in figure 12 (the tubes may be bonded or fixed together mechanically using screws or other means). The two tubes may be manufactured from different materials

The fibres of the first composite tube structure may instead be a 3D weave having fibres penetrating in the radial direction. Such a weave is less susceptible to delamination than an 0/90 degree fibre configuration, and less susceptible to delamination than a 45/-45 degree fibre layup. Indeed, the weave is less susceptible to delamination than any layup predominantly in the theta plane of a polar coordinate system (XY plane of a Cartesian coordinate system, the Z axis being the axis of rotation of the rotor). For example, such a 3D weave is less susceptible to delamination than a filament wind or roll-wrap, as these structures lack fibres penetrating the radial direction.

The second tube (the “torque tube”) is manufactured from predominantly 45/-45 fibres, however other fibre lays are also possible. Any fibre lay that provides a useful torsional load transmission may be used in the second tube, for example 30/-30 degree fibres or other angles.

In an embodiment, the second tube is produced to a thickness extending from the bore of the rotor to a proportion of the full rotor thickness that is greater than the torque tube (second tube) thickness (as shown in figure 13). This ensures that all fibres in the second tube are 45/-45 degrees. A number of slots may be machined in the predominantly 45/-45 tube to a depth which results in the formation of the “torque tube” at the inner bore. This is typically from 0.3 to 10mm depending on the size of the rotor. The slots may be parallel sided or trapezoidal. The pole-pieces are then placed/bonded in the slots.

In the embodiment of figure 9, the wedge-shaped parts may be manufactured from composite material and then placed between the pole-pieces to provide mechanical keying. These parts may be manufactured from pressed composite plate with a predominantly 0/90 fibre direction layup. The wedge parts may be secured to the composite tube part using adhesive or mechanical fixings such as screws, rivets, etc. or a combination of these.

In an embodiment, mechanical fixings may be in the form of those shown in figure 14, where (on the left hand side) a hole is made all the way through the rotor structure and a screw/nut combination is used to hold the structure together. Alternatively or additionally, the mechanical fixings may be as on the right hand side in figure 14, where a blind hole is made in the top surface of the composite tube structure and a hole is made all the way through the wedge parts. A thread insert may be fitted in the blind hole in the top surface of the 45/-45 degree fibre tube structure, and a screw from the top of the wedge part used to fix the parts together. The screws may be composite or metallic. Any number of screws may be used along the length of the rotor.

An alternative method of fixing the composite wedges to the composite tube is to provide a number of trapezoidal features in the tube and slide a corresponding shaped wedge along the axis of the rotor (male/female dovetail joint). This may be a bonded joint or screwed together in a similar way to the options discussed for the embodiments of figure 14.

The pole-pieces may have a “Russian Doll” structure, as shown in figure 15. Such a pole-piece is formed from a series of individual pole-pieces layered radially and having complementary shapes. For example, a pole-piece may be formed of 3 pole-piece portions: inner, middle and outer pole piece portions. The middle and outer pole-piece portions form successive shells over the inner pole piece portion, as shown in figure 15. Although 3 pole-piece portions are shown in figure 15, 2 or more than 3 pole-piece portions could be used.

Claims

1. A magnetically geared apparatus comprising a rotor, the rotor comprising: a ring structure; wherein at least a portion of the ring structure is formed from composite material comprising: a first plurality of fibres extending substantially in a first direction and a second plurality of fibres extending substantially in a second direction, the first direction and the second direction being non-parallel and the first direction and/or second direction being between a circumferential direction and an axial direction.

2. The magnetically geared apparatus of claim 1, wherein the ring structure is an inner ring structure, and wherein rotor further comprises an outer ring structure that is radially outer, the second ring structure having a pole piece-receiving portion therein.

3. The magnetically geared apparatus of claim 2, wherein the inner and outer ring structures are concentric.

4. The magnetically geared apparatus of claim 2 or 3, wherein the pole piecereceiving portion comprises walls extending radially through the outer ring structure.

5. The magnetically geared apparatus of claim 4, wherein the walls extend radially through the entirety of a radial width of the outer ring structure.

6. The magnetically geared apparatus of any preceding claim, wherein the first and second crossed fibres form a layer in the inner ring structure.

7. The magnetically geared apparatus of any of claims 2 to 6, wherein the outer ring structure is formed from composite material comprising a third plurality of fibres extending substantially in a third direction different from the first and/or second directions.

8. The magnetically geared apparatus of claim 7, wherein the outer ring structure further comprises a fourth plurality of fibres, the third and fourth plurality of fibres being aligned in respective third and fourth orientations, at least one of the third and fourth orientations being different to the first and second orientations.

9. The magnetically geared apparatus of claim 8, wherein at least one of the third and fourth orientations is aligned substantially along the axial direction.

10. The magnetically geared apparatus of claim 9, wherein the other of the third and fourth orientations is aligned substantially along the circumferential direction.

11. The magnetically geared apparatus of any of claims 8 to 10, wherein the third and fourth orientations are separated by an angle of substantially 90°.

12. The magnetically geared apparatus of claim 7, wherein the third plurality of fibres comprise chopped strands of fibres.

13. The magnetically geared apparatus of claim 7, wherein at least one of the third plurality of fibres extends at least partly, and optionally substantially, radially.

14. The magnetically geared apparatus of claim 13, wherein the third plurality of fibres form a three-dimensional weave.

15. The magnetically geared apparatus of any preceding claim, wherein the axis of rotation of the rotor defines a Z axis, and wherein the first orientation is between 0° and 90° with respect to the XY plane, and the second orientation is between 0° and -90° with respect to the XY plane.

16. The magnetically geared apparatus of claim 15, wherein the first orientation is between 5° and 85°, and optionally the second orientation is between -5° and -85°.

17. The magnetically geared apparatus of claim 16, wherein the first orientation is between 10° and 80°, and optionally the second orientation is between -10° and -80°.

18. The magnetically geared apparatus of claim 17, wherein the first orientation is between 15° and 75°, and optionally the second orientation is between -15° and -75°.

19. The magnetically geared apparatus of claim 18, wherein the first orientation is between 30° and 60°, and optionally the second orientation is between -30° and -60°.

20. The magnetically geared apparatus of any of claims 15 to 19, wherein the first orientation is substantially 45°, and the second orientation is substantially -45°.

21. The magnetically geared apparatus of any preceding claim, wherein the first and second orientations are separated by an angle of substantially 90°.

22. The magnetically geared apparatus of any of claims 4 to 21, wherein the walls do not extend into the inner ring structure.

23. The magnetically geared apparatus of any of claims 4 to 21, wherein the walls extend part of the way through a radial width of the inner ring structure.

24. The magnetically geared apparatus of any of claims 2 to 23, wherein the pole piece-receiving portion has a length and a width, the length being greater than the width, and the length extending in the axial direction.

25. The magnetically geared apparatus of any preceding claim, wherein the rotor is formed from a filament winding, a roll-wrap or a resin-transfer mould technique.

26. The magnetically geared apparatus of claims 7 to 25, wherein the fibres of the inner ring structure and the outer ring structure are different materials.

27. The magnetically geared apparatus of any preceding claim, wherein the fibres of the inner ring structure are E-glass, S-glass, Kevlar, Carbon-fibre or natural fibres.

28. The magnetically geared apparatus of any of claims 2 to 27, wherein the inner ring structure is radially internal to the outer ring structure.

29. The magnetically geared apparatus of any of claims 2 to 28, wherein the inner and outer ring structures are bonded or mechanically fixed together.

30. The magnetically geared apparatus of any of claims 2 to 29, wherein the inner and outer ring structures comprise a screw passing radially through the inner and outer ring structures, and a nut on one end of the screw to mechanically fix the inner and outer ring structures together.

31. The magnetically geared apparatus of any of claims 2 to 30, wherein the inner and outer ring structures comprise a screw passing radially through the outer ring structure into a blind hole in the inner ring structure, thereby mechanically fixing the inner and outer ring structures together.

32. The magnetically geared apparatus of any of claims 2 to 31, wherein the pole piece-receiving portion receives at least one pole piece therein.

33. The magnetically geared apparatus of claim 32, wherein a surface of the at least one pole piece forms at least part of the radially outer surface of the rotor.

34. The magnetically geared apparatus of claim 32 or 33, wherein the pole piecereceiving portion and the at least one pole piece are shaped to provide a mechanical keying of the at least one pole piece in the pole piece-receiving portion.

35. The magnetically geared apparatus of claim 34, wherein the mechanical keying is such that outward radial movement of the at least one pole piece is restricted.

36. The magnetically geared apparatus of any of claims 4 to 35, wherein the walls comprises a circumferential spacing therebetween, the walls being inclined towards the radially inner surface.

37. The magnetically geared apparatus of any of claims 30 to 36, wherein the pole piece-receiving portion has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially trapeziform, and the at least one pole piece has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially trapeziform.

38. The magnetically geared apparatus of any of claims 30 to 36, wherein the pole piece-receiving portion has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially diamond-shaped, and the at least one pole piece has a cross section in a plane substantially perpendicular to the axis of rotation of the rotor that is substantially diamond-shaped.

39. The magnetically geared apparatus of any of claims 4 to 35, wherein the walls comprise a circumferential spacing therebetween, the pole piece-receiving portion further comprising a wedge between one or both of the walls and the at least one pole piece.

40. The magnetically geared apparatus of claim 39, wherein the wedge has a radially extending wall inclined towards the radially inner surface.

41. The magnetically geared apparatus of any of claims 2 to 40, wherein the rotor further comprises damping material and wherein, when the damping material is at a temperature within a range of 0°C to 150°C, the damping material has a loss factor greater than 0.1.

42. The magnetically geared apparatus of claim 41, wherein the loss factor is greater than 1.

43. The magnetically geared apparatus of claim 41 or 42, wherein, when the damping material is at a temperature within the range, the damping material has a Young’s modulus between IMPa and lOOMPa, and optionally a Young’s modulus between IMPa and 30MPa.

44. The magnetically geared apparatus of any of claims 41 to 43, wherein the damping material is provided between at least one pole piece received in the pole piece-receiving portion and the pole piece-receiving portion.

45. The magnetically geared apparatus of claim 44, wherein the damping material is provided between radially extending walls of the at least one pole piece and the walls of the pole piece-receiving portion.

46. The magnetically geared apparatus of claim 44 or 45, wherein the damping material is provided between a radially inner surface of the pole piece and the pole piece-receiving portion.

47. The magnetically geared apparatus of any of claims 44 to 46, wherein the damping material comprises a tape, a post-cured pourable fluid, a mouldable putty, a loaded rubber, a visco-elastic or a visco-plastic.

48. The magnetically geared apparatus of any of claims 44 to 46, wherein the damping material comprises a plurality of different materials having different values of the loss factor and/or the Young’s modulus.

49. The magnetically geared apparatus of claim 48, wherein the different materials are axially or circumferentially or radially layered.

50. The magnetically geared apparatus of any of claims 41 to 49, wherein the damping material is provided in a cavity of at least one pole piece.

51. The magnetically geared apparatus of claim 50, wherein the cavity is completely enclosed by the pole piece.

52. The magnetically geared apparatus of claim 50, wherein the cavity is in communication with an exterior of the pole piece.

53. The magnetically geared apparatus of any of claims 50 to 52, wherein the cavity comprises a slot extending towards a surface of the at least one pole piece.

54. The magnetically geared apparatus of claim 53, wherein the slot comprises a first slot extending radially, and a second slot extending circumferentially.

55. The magnetically geared apparatus of any of claims 50 to 54, wherein the cavity comprises a diagonal slot oblique to the radial direction.

56. The magnetically geared apparatus of claim 50, wherein the cavity comprises one or more internal slots, each slot dividing the at least one pole piece into a plurality of pole pieces.

57. The magnetically geared apparatus of claim 56, wherein the plurality of pole pieces are enclosed by the damping material.

58. The magnetically geared apparatus of any of claims 32 to 57, wherein the at least one pole piece comprises a laminated pole piece.

59. The magnetically geared apparatus of claim 58, wherein the laminated pole piece is formed of laminate sheets layered axially or radially.

60. The magnetically geared apparatus of any of claims 41 to 57, wherein rotor comprises at least one pole piece received in the pole piece-receiving portion, the at least one pole piece comprising a laminated pole piece formed of laminate sheets layered axially or radially, the pole piece further comprising the damping material between the laminate sheets.

61. The magnetically geared apparatus of any of claims 32 to 57, wherein the at least one pole piece is a soft magnetic composite.

62. The magnetically geared apparatus of any of claims 32 to 61, wherein the at least one pole piece comprises a plurality of axially adjacent pole pieces.

63. The magnetically geared apparatus of any of claims 32 to 62, wherein the rotor comprises at least one pole piece received in the pole piece-receiving portion, the at least one pole piece comprising a plurality of axially adjacent pole pieces, the pole piece further comprising the damping material between the axially adjacent pole pieces.

64. The magnetically geared apparatus of any of claims 32 to 63, wherein the at least one pole piece comprises a plurality of pole piece portions, the pole piece portions being radially layered on top of each other.

65. The magnetically geared apparatus of claim 64, wherein the pole piece portions comprise inner and outer pole piece portions, the outer pole piece portion forming a shell radially outer of the inner pole piece portion.

66. The magnetically geared apparatus of claim 64 or 65, wherein the plurality of pole piece portions comprises 2 or more pole piece portions.

67. The magnetically geared apparatus of claim 66, wherein the plurality of pole piece portions comprises 3 pole piece portions.

68. The magnetically geared apparatus of any preceding claim, wherein the rotor comprises first and second end plates at opposite axial ends of the rotor, the first and second end plates being fixed to the ring structure.

69. The magnetically geared apparatus of any preceding claim, wherein the first ring structure is of one-piece construction.

70. The magnetically geared apparatus of any of claims 2 to 69, wherein the first and second ring structures are of one-piece construction.

71. The magnetically geared apparatus of any preceding claim, wherein the apparatus further comprises: another rotor comprising a first plurality of permanent magnets; a stator comprising a second plurality of permanent magnets and windings; wherein the rotor is arranged to interact with the another rotor in a magnetically geared manner; and wherein the windings are arranged to magnetically interact with the first or fundamental harmonic of the magnetic field of the first plurality of permanent magnets.

72. The magnetically geared apparatus of claim 71, wherein the rotor has at least one pole piece, the first plurality of permanent magnets has a respective first number of pole-pairs, and the second plurality of permanent magnets has a respective second number of pole-pairs, wherein the at least one pole piece is arranged to modulate the magnetic fields of the first and second pluralities of permanent magnets to produce mutually matching pole-pairs, thereby enabling magnetic coupling and torque transmission between the first and second pluralities of permanent magnets, and wherein the windings are arranged to magnetically couple with the first or fundamental harmonic of the magnetic field of the first plurality of permanent magnets.

73. The magnetically geared apparatus of any preceding claim, wherein the rotor and another rotor are configured to transfer torque therebetween in a magnetically geared manner.

74. The magnetically geared apparatus of claim 73, wherein first rotor is mechanically coupled to one of an input or output shaft, and the another rotor is mechanically coupled to the other of an input or output shaft.

75. A rotor having according to any preceding ciaim.