GB2519500A

GB2519500A - A magnetic gear

Info

Publication number: GB2519500A
Application number: GB1313428.3A
Authority: GB
Inventors: Andrew Farquhar Atkins; Joshua Dalby; Hing W To; Richard Gordon; Simon Shepherd
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2013-07-26
Filing date: 2013-07-26
Publication date: 2015-04-29
Also published as: WO2015011501A3; GB201313428D0; WO2015011501A2

Abstract

A magnetic gear 100 comprising: first 12 and second 8 members arranged for relative movement therebetween, the first member 12 having a first array of magnetic field generating elements 6 and the second member 8 having a second array of magnetic field generating elements 2; and a coupling member 10 having an array of coupling elements for coupling magnetic flux between the first and second arrays of magnetic field generating elements 6 & 2. wherein for at least one of the coupling elements, there is provided a cooling path (14, fig 2) in thermal communication with the at least one coupling element, wherein the cooling path is provided within at least one of the at least one coupling element and the coupling member, wherein a first member fluid path (16, fig 11a) extends at least partially through the first member to enable cooling of at least one of the magnetic field generating elements of the first array. A magnetic gear wherein at least one of the coupling elements (4, fig 4) has a substantially rectangular cross-section with at least one bevelled corner (16, fig 4), is also disclosed.

Description

A magnetic gear The present disclosure relates a magnetic coupling, for example a magnetic gear.

Magnetic gears allow contactless transmission of kinetic energy from a first member having a first array of magnetic field generating elements to a second member having a second array of magnetic field generating elements. This contactless transmission can reduce energy losses and also enables isolation of drive and driven components. This isolation allows the environment within which the driven component is placed to be sealed from the drive component, allowing, for example, the driven component to be placed within a chamber whose environment can be separately controlled, for example placed under vacuum or low pressure. Isolation of the driven member may also be advantageous in pumps because it can allow, for example, noxious or corrosive substances being pumped to be isolated from the drive component.

Magnetic gears may comprise a coupling member having an array of coupling elements for coupling magnetic flux between the first array of magnetic field generating elements and the second array of magnetic field generating elements.

In operation, magnetic flux will pass from the magnetic elements on the first and second member through coupling member. Relative movement, for example relative rotation, of the first and second members leads to a change in magnetic flux in the coupling member which, in turn, induces eddy currents in the coupling elements. The induced eddy currents will lead to inductive heating of the coupling elements and further heating will be created by the hysteresis affects due to the change in flux.

In an attempt to reduce heating and prevent overheating of the coupling elements the coupling elements can be designed to have a large surface area to volume ratio to enable heat flow from the coupling element to reduce heating of the coupling element during use.

However, increasing the surface area to volume ratio may not be sufficient to maintain the temperature of the coupling element within acceptable limits.

Magnetic couplings allow contactless transmission of kinetic energy from a first moving member to a second moving member. This can reduce energy losses across the coupling and also enables isolation of drive and driven components. This isolation allows the environment within which the driven member is placed to be sealed from the drive component, allowing, for example, the driven component to be placed within a chamber whose environment can be separately controlled, for example placed under vacuum or low pressure. Isolation of the driven member may also be advantageous in pumps because it can allow, for example, noxious or corrosive substances being pumped to be isolated from the drive component.

The inventors in the present case have appreciated that inefficiencies in transmitting energy across a magnetic coupling, for example due to energy losses from inductive heating, may lead to significant loss of performance, particularly in the case where the magnetic coupling is a geared magnetic coupling used to amplif' a high torque, low frequency input drive to produce a low torque, high frequency output. Housing thc driven component of thc magnetic coupling in a vacuum or low pressure chamber helps reduce such losses, but the heating effects caused by hysteresis and eddy currents may still impair efficiency. Additionally, improved control may be required for managing the magnetic coupling and in particular for extracting heat from the input (driving) side.

Aspects and examples of the invention are set out in the claims.

Embodiments of the present disclosure provide apparatus and methods which aim to facilitate increased efficiency and improved control of magnetic couplings, including magnetic gears, and in particular magnetic flywheels.

In an embodiment a magnetic gear comprises first and second members arranged for relative movement therebetween, the first member having a first array of magnetic field generating elements and the second member having a second array of magnetic field generating elements; and a coupling member having an array of coupling elements for coupling magnetic flux between the first array of magnetic field generating elements and the second array of magnetic field generating elements, wherein for at least one of the coupling elements! there is provided a cooling path in thermal communication with the at least one coupling element, wherein the cooling path is provided within at least one of the at least one coupling element and the coupling member, wherein a first member fluid path extends at least partially through the first member to enable cooling of at least one of the magnetic field generating elements of the first array.

The cooling path may be provided at least partially through the at least one coupling element.

The cooling path may comprise a channel extending at least partially through the at least one coupling element.

The cooling path may be provided adjacent to the coupling element.

The at least one cooling path may comprise a channel extending adjacent to a surface of the coupling element.

A cross section of the at least one coupling element may have at least one bevelled corner.

The at least one bevelled corner may provide at least part of the at least one fluid path between the at least one coupling element and surfaces of the coupling membei suppoiting the at least one coupling element.

The cooling path may extend only partially through the coupling element and/or the coupling member.

The magnetic gear may further comprise a heat exchanger at a closed end of the cooling path.

The at least one coupling element may have a single cooling path.

The at least one coupling element may have a single cooling path, wherein the single cooling path is provided within the coupling element.

The cooling path may be provided centrally within a cross section of the coupling element.

The at least one coupling element may be provided with two cooling paths.

The at least one coupling element may be provided with two cooling paths, wherein the two cooling paths are provided within the coupling element.

The two cooling paths may be airanged symmetiically about an axis of a cross section of the coupling element.

The two cooling paths may comprise fluid paths, wherein one of the two fluid paths is arranged to provide a fluid return path.

The at least one coupling element may be provided with a plurality of cooling paths.

The at least one coupling element may have a first cooling path and a plurality of further cooling paths arranged around the first cooling path.

The fiist cooling path may be airanged centrally within the at least one coupling element.

The further cooling paths may be arranged symmetrically about the central cooling path.

The further cooling paths may be provided by bevelled corners of the at least one coupling element.

At least two of the plurality of cooling paths may comprise providing forward and return fluid paths.

At least one cooling path may be provided for each of the coupling elements.

The or at least one cooling path may comprise a fluid path, comprising a flow control element configured to control the flow of a fluid therealong.

The flow control element may be configured to control the flow of fluid based on a temperature of the at least one coupling element.

The at least one cooling path may comprise a fluid path, and the gear further comprises a coupling member controller configured to control the flow of fluid along the fluid path.

The coupling member controller may be configuied to leceive an indication of a measuied temperature of the at least one coupling element and to control the flow of fluid based on the measured temperature.

The coupling member controller may be configured to store an indication of a reference temperature and to control the flow of fluid based on a comparison between the measured temperature and the reference temperature.

The coupling member controller may be configured to control a fluid pump to control the flow of fluid.

The fluid pump may comprise an electric pump, a mechanical pump and/or a hydraulically driven pump.

The coupling member controller may be configured to control the pressure of the fluid to control the flow of fluid.

The at least one fluid path may be coupled to a tap, wherein coupling member controller is configured to control the tap to control the pressure of the tluid.

The first and second members may be arranged concentrically for relative rotation therebeteen, wherein the coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second airays in a iadial direction.

The fiist and second membeis may be axially spaced apart, wherein the coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second arrays in an axial direction.

The fiist member, the second member and the coupling member may be arianged coaxially.

The one of the first and second members may be coupled to an input shaft of the magnetic gear and the other of the first and second members is coupled to an output shaft of the magnetic gear.

The output shaft may be coupled to a flywheel.

The output shaft may be arranged in a chamber, optionally the chamber is a low pressure or vacuum chamber.

The coupling member may form part of a barrier enclosing the chamber.

The at least one cooling path may comprise a fluid path and the magnetic gear comprises a mechanical gear mounted on the output shaft, wherein the mechanical gear is configured to cause a fluid to be pumped along the at least one fluid path in proportion to the rotational speed of the output shaft.

The at least one cooling path may comprise a fluid path, wherein the coupling member comprises a fluid supply path to supply fluid from a fluid reservoir to the at least one fluid path.

The coupling member may comprise a fluid return path to receive fluid which has passed along the at least one fluid path.

The fluid return path may be arranged to return fluid which has passed along the at least one fluid path to the reservoir.

The at least one cooling path may comprise a fluid path and the heat exchanger comprises a condensing plate.

The at least one cooling path may comprise a material of lower magnetic permeability in place of or in addition the at least one fluid path.

The material of lower magnetic permeability may comprise a solid, liquid or gas.

The material of lower magnetic permeability may comprise a material selected from the group consisting of a material comprising aluminium, a material comprising copper and a composite material.

In an embodiment a magnetic gear comprises: first and second members arranged for relative movement therebetween, the first member having a first array of magnetic field generating elements and the second member having a second array of magnetic field generating elements; and a coupling member having an array of coupling elements for coupling magnetic flux between the first array of magnetic field generating elements and the second array of magnetic field generating elements, wherein at least one of the coupling elements has a substantially rectangular cross section with at least one bevelled corner.

The bevelled corner may provide a cooling path between the at least one coupling element and surfaces of the coupling member supporting the coupling element.

Each of the corners of the at least one coupling element may be bevelled.

The first member fluid path may be arranged to follow at least part of the surface of the at least one of the magnetic field generating elements of the first array.

The first member fluid path may extend at least partially through the first member in an axial direction.

Each of the first and second members may have an outer cylindrical surface and is arranged for rotation about an axis.

The first member fluid path may extend in a circumferential direction to follow at least part of the circumferential surface of the first member.

The first memberfluid path may be continuous in the circumferential direction.

The first member fluid path may comprise a plurality of first member fluid paths.

The magnetic coupling may comprise a number of first member fluid paths equal to the number of magnetic field generating elements of the first array.

Each of the first member fluid paths may be arranged to follow at least part of a surface of a respective one of the magnetic field generating elements of the first array.

The first member may comprise an end wall at a first end of a circumferential wall having the circumferential surface, wherein the end wall couples the first member to a rotor shaft.

The first member fluid path may extend through the end wall to couple to a reservoir external of the end wall.

The reservoir may be provided adjacent to the rotor shaft.

The reservoir may be provided between bearings which support the rotor shaft.

The bearings may provide seals for sealing the reservoir.

The first member fluid path may be sealed, such that the first member fluid path allows fluid flow in an outward direction and a return direction.

The first member fluid path and reservoir may provide a closed fluid system, wherein fluid flowing in the return direction is returned to the reservoir.

The magnetic coupling may comprise a cooling system for cooling fluid flowing in the return direction.

The cooling system may be configured to cool the end wall.

The cooling system may be configured to cool fluid in the reservoir.

The first member fluid path may be open near a second end of the circumferential wall to allow used fluid to exit the first member.

The magnetic coupling may comprise a casing arranged around the first member to collect the used fluid.

The magnetic coupling may comprise a scavenger pump to remove the collected fluid from the casing.

The first member fluid path may have an opening through a second end of the circumferential wall to receive fluid.

The first member fluid path may have an opening through the end wall to allow used fluid to exit the first member.

The first member may be arranged to be mounted vertically to allow fluid to travel along the first member fluid path under the action of gravity.

The magnetic coupling may comprise a pump configured to pump the fluid along the first member fluid path.

The magnetic coupling may comprise a first member controller configured to control the flow of fluid along the first member fluid path.

The magnetic coupling of claim 81, wherein the first member controller is configured to receive an indication of a measured temperature of the at least one magnetic field generating element and to control the flow of fluid along the first member fluid path based on the measured temperature.

The first member controller may be configured to store an indication of a reference temperature and to control the flow of fluid along the at least one first member fluid path based on a comparison between the measured temperature and the reference temperature.

The first member controller may be configured to control the pump to control the flow of fluid along the first member fluid path.

The coupling member may have an outer circumferential surface.

The outer circumferential surface may be configured to carry the coupling elements.

The outer circumferential may comprise a plurality of recesses for supporting the plurality of coupling elements therein.

The recesses may be configured such that outer surfaces of the respective coupling elements carried therein are flush with the outer circumferential surface.

The coupling elements may be provided beneath the outer circumferential surface.

The coupling member may have an inner circumferential surface.

Inner surfaces of the respective coupling elements may be flush with the inner circumferential surface.

The coupling elements may be provided beneath the inner circumferential surface.

A vehicle may comprise the magnetic gear.

A method of operating the magnetic gear may comprise effecting relative movement between the first and second members; and supplying fluid to the at least one first member fluid path to cool the at least one coupling element.

The method may comprise supplying water to the first member fluid path.

The method may comprise supplying glycol to the first member fluid path.

The method may comprise controlling the flow of fluid along the first member fluid path.

The method may comprise: effecting relative movement between the first and second members; and supplying fluid to the at least one cooling path to cool the at least one coupling element.

Aspects of the disclosure are also described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic cross sectional view of a flywheel assembly having a magnetic gear with a coupling member having a plurality of coupling elements and providing a barrier between the first and second array of magnetic field generating elements; Figure 2 shows a diagrammatic perspective view of an example of the barrier of Figure 1 illustrating the location of a coupling element; Figure 3 shows a diagrammatic cross-sectional view of an example of the magnetic gear; Figure 4 shows a diagrammatic cross sectional view of a coupling element with bevelled corners; Figure 5 shows a diagrammatic perspective view of the coupling element shown in Figure 4; Figure 6 shows a diagrammatic perspective view illustrating one example of a fluid flow associated with a coupling element; Figure 7 shows a diagrammatic perspective view illustrating another example of a fluid flow associated with a coupling element; and Figure 8 shows a diagrammatic perspective view illustrating another example of a magnetic gear.

Figure 9a shows a schematic cross-section of a magnetic gear in a plane normal to an axis of rotation of the magnetic gear; Figure 9b shows a schematic cross-section of part of a coupling member; Figure 10 shows a cross-section along an axis of rotation of a flywheel system comprising the a magnetic gear of Figure 9a; Figure 1 la shows a schematic cross-section along an axis of rotation of a first member having a closed fluid path; Figure llb shows a schematic cross-section of the magnetic coupling of Figure ha in a plane normal to the axis of rotation as indicated by the line A-A', and shows a first example of a closed fluid path; Figure 1 ic shows a schematic cross-section of the magnetic coupling of Figure 1 la in a plane normal to the axis of rotation as indicated by the line A-A', and shows a second example of a closed fluid path; Figure 12a shows a schematic cross-section along an axis of rotation of a first member having an open fluid path; Figure 12b shows a schematic cross-section of the magnetic coupling of Figure 12a in a plane normal to the axis of rotation as indicated by the line B-B, and shows a first example of an open fluid path; Figure 12c shows a schematic cross-section of the magnetic coupling of Figure 12a in a plane normal to the axis of rotation as indicated by the line B-B, and shows a second example of an open fluid path; and Figure 13 shows a partial cut-away view of a non-concentric magnetic gear.

The reference numerals used in Figures 1 to 8 correspond to the description of Figures 1 to 8. The reference numerals used in Figures 9 to 13 correspond to the description of Figures 9 to 13.

Referring now to the drawings in general, disclosed herein is a magnetic gear 1 having: first and second members 8 and 12 arranged for relative movement therebetween, the first member B having a first array of magnetic field generating elements 2 and the second member 12 having a second array of magnetic field generating elements 6; and a coupling member 10 having an array of coupling elements 4 for coupling magnetic flux between the first array of magnetic field genelating elements 2 and the second array of magnetic field generating elements 6, wherein for at least one of the coupling elements 4, there is provided a fluid path 16 in thermal communication with the at least one coupling element, wherein the fluid path 16 is provided within at least one of the at least one coupling element 4 and the coupling member 10.

Referring now specifically to Figure 1, there is shown a diagrammatic cross sectional view of a flywheel assembly 100 having such a magnetic gear 4. As shown in Figure 1, the flywheel assembly has a flywheel chambei 110 containing a flywheel 101 with a rim 102 (having the majority of the mass) coupled via a web 103 to an axially extending flywheel shaft 104. The web may be spoked or continuous. The flywheel shaft 104 may be integrally formed with the web or may be a separate component. In the example shown the rim is a composite rim.

The shaft 104 is supported for rotation about its axis relative to the flywheel chamber 110 by means of bearings, for example bearings 105 shown in Figure 1.

In the example shown in Figure 1, the first array of magnetic field generating elements 2 provides an annular body Ba of the first member which is coupled via a web 8b (which may be spoked or continuous) to an axle 8c through which an end portion of the flywheel shaft 104 is coupled so that the flywheel is coupled for rotation with the first member 8.

In the example shown in Figure 1, the coupling member 10 provides a barrier forming part of the flywheel chamber 110 which may in operation be under a low pressure or vacuum, that is may be a vacuum chamber, to reduce the windage (air resistance) on the flywheel.

Figure 2 shows a perspective view of an example of a barrier where the barrier has a top hat' form. In the interests of clarity in Figure 2 one elongate coupling element 4 is shown embedded within the barrier 10. It will be appreciated that in practice an array of elongate coupling elements will be positioned around the circumference of the barrier.

As shown in Figure 1, the second array of magnetic field generating elements 6 provides an annular body 12a of the second member 12. The annular body 12a is coupled (as shown integral with) a drive shaft 106 which in use of the flywheel assembly may be coupled to a drive motor, for example a drive motor (not shown) of a vehicle.

An example of a magnetic gear suitable for use in the flywheel assembly described above will now be described in more detail with reference to Figures 2 to 5.

In the embodiment shown in Figure 3 the first member 8, second member 12 and coupling member 10 are concentrically arranged annuli with the first member 8 providing an annular array of m magnetic field generating elements 2 and the second magnetic field generating elements 6 providing an annular array of n magnetic field generating elements 2, where the ratio mm represents the gear ratio so that the rotational speed of the first member 8 is n/m times the rotational speed of the second member 12. The member with the greater number of magnetic poles therefore rotates at a slower angular velocity than the member with fewer magnetic poles. In the case of the flywheel assembly discussed above the higher speed rotor will be the first member 8 located in the flywheel chamber.

The magnetic field generating elements 2 and 6 may be, for example, rare earth magnets, any other appropriate form of permanent magnets or electromagnets. It will be appreciated that Figure 3 is diagrammatic and that generally the coupling elements 4 will be equally sized and equally spaced around the circumference of the coupling member 10.

The coupling elements may be embedded within the coupling member or for example the coupling member may be keyed such that the coupling elements slot into the coupling member. Figures 6 and 7 show a coupling element 4 located within a coupling member 10 with a restraining band or bands 18 located on the coupling member to prevent movement of the coupling element during use. The restraining bands 18 may extend completely around the circumference of the coupling member. As another possibility, the restraining band or bands 18 may extend only partially around the circumference of the coupling member.

In this example, as shown in Figures 2 to 5, the fluid path is provided by an inner fluid channel 14 extending axially along the elongate coupling element. One end of the inner fluid channel 14 may be coupled to a fluid supply channel 20 provided in the brim' of the top hat' coupled via an annular manifold 21 to a fluid inlet 22 itself coupable to a fluid reservoir (not shown) provided outside of the barrier and in the example shown in Figure 1 outside of the flywheel assembly. The fluid reservoir may be a pump or gravity fed arrangement. The other end of the inner fluid channel 14 may be coupled to a void in the top hat' from which it can drain into a sump (not shown).

In this example at least one longitudinal edge of the coupling element is bevelled to provide a "bevelled corner" defining with the barrier an outer fluid channel providing part of the fluid path 16. In the example shown all four longitudinal edges are bevelled to provide four outer fluid channels which has the advantage of more even cooling throughout the coupling element and reduction of edge effects therefore reducing heating due to concentration of the magnetic flux at the corner of the coupling element. In this case the fluid flow can be enter in through the inner fluid channel pass the length of the coupling element and out through the outer channels via a void inside the top hat. The outer channels may drain into a sump (not shown) or may couple back to the manifold forming a closed system. As another possibility the flow can be reversed.

The fluid reservoir or sump may be positioned within the bearing arrangement of the drive shaft in the case of the flywheel shown in Figure 1, for example at 107 shown in Figure 1.

As another possibility, as shown in Figure 5, the inner fluid channel 14 may extend only partially through the coupling member 4 or may be sealed at one end and in either case the closed end of the inner fluid channel is coupled to a condensing plate so that the inner channel forms a heat pipe in which fluid is heated, evaporates and then re-condenses within the channel to effect cooling. In another embodiment the inner fluid channel contains a solid material that on heating evaporates of sublimes causing latent heat cooling upon change of state of the solid material. In either of these cases the channel may be completely sealed or open at the other end. Similarly or alternately the bevelled corner may be completely sealed or open at the other end providing a heat pipe as described above.

In the examples described above, a fluid path is provided in thermal communication with the at least one coupling element to provide a cooling path. As another possibility, a cooling path may be provided by a material of a lower magnetic permeability than the material of the coupling member extending at least partially through the at least one coupling element. In an example the lower magnetic permeability may have a relative permeability of 1, i.e. the same relative permeability as air.

In an example the material of lower magnetic permeability may be thermally conductive, to enable heat to conductive through the lower magnetic permeability forming a heat path.

Thus, in this example, the inner channel or inner channels 14 may comprise a material of a lower magnetic permeability than the material of the coupling member to provide a cooling path extending at least partially through the at least one coupling element. The magnetic flux in the coupling member will pass through the material of the coupling member, not through the material of lower magnetic permeability in the inner channel. The lower magnetic flux concentration in the material of the inner channel reduces the change of the flux in the material of the inner channel, therefore reducing the induced current and subsequent inductive heating. The material of lower permeability in the inner channel will be subjected to less inductive heating and therefore have a lower temperature relative to the material of the coupling member.

The material of lower magnetic permeability in the inner channel may be solid, liquid or gas.

When a solid is used in the inner channel the solid may be, for example aluminium, copper or a composite material wherein the composite material may be a carbon fibre composite. In this example, the coupling elements may be formed about the material of lower magnetic permeability or the material of lower magnetic permeability may be introduced into the channel in liquid form and then allowed to solidify, or may be provided as a separate rod or wire of solid material.

The solid material in the inner channel may provide an interference fit within the channel. In another example the solid material may have a smaller cross section than the inner channel.

The material of lower magnetic permeability in the inner channel may be coupled to a heat sink away from the coupling member, allowing heat to flow from the material of the inner channel away from the coupling member and to dissipate via the heat sink. The inner channel may be a coated with a material different to the coupling member and the material of the inner channel! for example a coating may be applied to the surface of the inner channel using a material with a low magnetic permeability prevent magnetic flux penetrating into the inner channel.

Although the Figures show one inner cooling channel, the inner cooling channel may be a number of cooling channels passing through the coupling member. The channels may be arranged with a first inner channel forming a first cooling path and plurality of further inner channels forming cooling paths arranged around the first cooling path. The first cooling path may be arranged centrally within the coupling element and for example the further channels may be arranged symmetrically around the first channel. The cooling paths can be used as either a fluid supply path or a return path as discussed above. As another possibility, at least one inner cooling channel may provide a fluid supply path and at least one inner cooling channel may provide a return path.

Where there is more than one inner cooling channel, then one or more inner cooling channels may provide a fluid path and one or more inner cooling channels may contain material of lower magnetic permeability.

Only one, or two or more or all of the coupling elements may be provided with inner and outer cooling channels, or with only an inner cooling channel or channels or only an outer cooling channel or channels. As another possibility, at least one coupling element may have only an inner cooling channel or channels and no outer cooling channel or channels and at least one coupling element may have no inner cooling channel or channels and only an outer cooling channel or channels. The inner and/or outer cooling channels may be a mix of sealed and open channels, or all sealed channels or all open channels.

In some embodiments the coupling elements will have a mixture of coupling elements with at least one cooling channel and coupling elements without cooling channels.

As described above the fluid may be pumped or gravity fed. Where a pump 109 is provided, the pump may be coupled to a controller 110 configured to control the flow of fluid from the reservoir the fluid path, as show diagrammatically in Figure 1. The controller may be configured to receive an indication of a measured temperature, for example from a temperature sensor thermally coupled to the coupling member, and to control the flow of fluid based on the comparison between the measured temperature and a reference temperature. The fluid pump may be, for example, an electric pump, a mechanical pump, or a hydraulically driven pump.

The fluid passes through a channel 14 and then passes back along a fluid path 16 adjacent to the coupling element. In the example shown in figure 5 a fluid is passed along a fluid supply path from a reservoir provided between the bearings on the input shaft to the fluid path 14, after passing through the coupling element the fluid is passes along cooling path 16 adjacent to the coupling element and is received by a return path returning the fluid to the reservoir.

The cooling path may be coupled to a tap and the controller configured to control the tap to control the pressure and/or mass flow of the fluid. Where the magnetic gear is associated with a hydraulic system, for example in the case of a vehicle, the hydraulic system may be used to provide the fluid, for example fluid may be bled under pressure from the hydraulic system.

Figures 6 and 7 show a perspective view of a coupling element 4 showing examples of fluid flow associated with a coupling element 4. The coupling elements in Figures 6 and 7 each comprise an inner cooling channel 14 and four cooling paths 16 adjacent to the coupling element. The arrows on Figures 6 and 7 provide a diagrammatic representation of the direction of flow of the fluid relative to the coupling element.

Figure 6 shows an example where fluid from the fluid supply channel (Figure 2) passes into a first end 17 of the inner cooling channel 14 of the elongate coupling element 4, along the length of the coupling element to a second end 19 of the inner cooling channel 14. At the second end 19 the fluid passes from the inner cooling channel 14, via a void (not shown) in the "top hat" coupling member, to one or more of the four cooling paths adjacent to the coupling element 4. The fluid then passes along the one or more of the four cooling paths back along the length of the coupling element 4 towards the first end 17 where the fluid may return to the reservoir or pass to a sump (neither shown in Figure 6).

Figure 7 shows an example where fluid passes along the length of the coupling element 4, from the first end 17 of the coupling element to a second end 19 of the coupling element, via the inner cooling channel 14 and the four cooling paths 16 adjacent to the coupling element 4. In this example fluid flows in the same direction in the inner cooling channel 14 and the four cooling paths 16.

In other examples than those shown in Figures 6 and 7, the fluid flow may not be in the same direction in each of the four cooling paths 16. For example, fluid may flow in one direction (for example in the direction from the end 17 to the end 19) in two of the cooling paths 16 and in the opposite direction in the other two of the cooling paths 16, or may flow in the same direction in three of the four cooling paths 16 and in the opposite direction in the other of the four cooling paths 16. In each case the fluid may flow in the inner cooling channel 14 from the first end 17 of the elongate coupling element 4 to the second end 19 of the elongate coupling element 4 or from the first end 17 of the elongate coupling element 4 to the second end 19 of the elongate coupling element 4.

As another possibility, a coupling element may have a porous or open cell structure with a plurality of channels each extending at least partially through the coupling element. The channels may be form capillary tubes in the coupling element. In this embodiment the capillary action of the channel may provide a force sufficient to move the fluid, in the liquid phase, relative to the coupling element. In an example the fluid may undergo a phase change, as described above, and the latent heat associated with that phase change may cool the coupling element.

As another possibility the material of lower magnetic permeability may have a cooling channels or a porous or open cell structure as described above.

Although as described above the reservoir, if present, is located between the bearings on the input shaft any such reservoir may be located at a different location on the flywheel assembly or elsewhere exterior to the flywheel assembly, for example another source within a structure, such as a vehicle, containing the flywheel assembly.

As another possibility, a local reservoir may not required, rather fluid may be supplied directly from an external fluid supply source.

After passing through and/or past the coupling element fluid may drain into a sump, pass into the flywheel assembly and evaporate or pass into the flywheel assembly and drain out of the flywheel assembly.

As another possibility, at least one cooling path may pass in a direction other than along the longitudinal axis of the elongate coupling member 4, for example in a direction transverse to the longitudinal axis. Also, one or more of the cooling paths need not necessarily be straight but could loop back upon itself to enter and exit the same end of the coupling element or may have a tortuous (non-linear) path between the ends 17 and 19. Any appropriate shape or configuration of cooling paths may be used to pass fluid within or along the coupling element.

As described above the magnetic gear has a concentric arrangement. As another possibility a linear arrangement may be used, with the relative movement between the first member 8 and second member 12 being linear ratherthan rotary.

As another possibility, as shown in Figure 8, the first member 8, coupling member 10' and second member 12' may be circular components stacked one on top of each other with a common axis A about which relative rotation is enabled. In this arrangement, the magnetic field generating elements 2' and 6' may be sectors of the respective circular components and the coupling elements 4' may extend radially from the common axis, or a plurality of coupling elements may be distributed about the circumferences at a various radial distances from the axis.

In the examples described above the magnet gear has a gearing ratio where the number of magnetic field generating elements on the first member is not equal to the number of magnetic field generating elements on the second member. The magnetic gear ratio may, as another possibility, be 1:1 with the number of magnetic field generating elements on the first member being equal to the number of magnetic field generating elements on the second member.

Figure 9a shows a schematic cross-section of a magnetic gear 200 in a plane normal to the axis of rotation of the gear (the axis of rotation being normal to the plane of the page). The magnetic gear 200 comprises a first member 10, a second member 20 and a coupling member 30. The first member 10 has a first array of magnetic field generating elements 12.

The second member 20 has a second array of magnetic field generating elements 22. The coupling member 30 has an array of coupling elements 32. The first member 10, second member 20 and coupling member 30 all have an axial extent.

The first member 10, the coupling member 30 and the second member 20 are arranged concentrically. The first member 10 and the second member 20 are arranged for relative rotation about a common axis. The coupling member 30 is provided intermediate the first member 10 and the second member 20 to couple magnetic flux between the first and second arrays of magnetic field generating elements 12,22 in a radial direction.

The first member 10 is arranged for rotation with an input rotor 14 (shown in Figure 10).

The first array of magnetic field generating elements 14 comprises an array of m permanent magnetic poles, in which consecutive magnetic poles are of opposite polarity as represented by the arrows in Figure 1. The first member 10 comprises a circumferential wall 17 comprising a non-conductive material (not shown) having an inner circumferential surface 16 and an outer circumferential surface 18 (the outer circumferential surface 18 being radially outward of the inner circumferential surface 16). Respective magnetic field generating elements of the first array of magnetic field generating elements 12 are spaced apart on the inner circumferential surface 16. In another example, respective magnetic field generating elements of the first array of magnetic field generating elements 12 are provided in the non-conductive material such that consecutive magnetic field generating elements 12 are spaced apart by the non-conductive material, and the magnetic field generating elements 12 may be fully or partially embedded in the non-conductive material.

The second member 20 is coupled to a flywheel 90 (shown in Figure 10) for rotation with the flywheel. The second member 30 and the flywheel 90 are arranged in a chamber 40 which may be maintained under a vacuum or at low-pressure.

The second member 20 comprises a non-conductive material (not shown), and the second array of magnetic field generating elements 22 are provided in the non-conductive material such that consecutive magnetic field generating elements 22 are spaced apart by the non-conductive material, and the magnetic field generating elements 22 may be fully or partially embedded in the non-conductive material. In another example, the chamber 40 may contain a gas other than air, in particular a gas having a lower viscosity than air, such as Helium.

The second array of magnetic field generating elements 22 comprises an array of n permanent magnetic poles, in which consecutive magnetic poles are of opposite polarity as represented by the arrows in Figure 1. The second member 20 comprises a non-conductive material (not shown), and respective magnetic field generating elements of the second array of magnetic field generating elements 22 are spaced apart on an outer circumferential surface 28 of the non-conductive material. In another example, respective magnetic field generating elements of the second array of magnetic field generating elements 22 are provided in the non-conductive material such that consecutive magnetic field generating elements 22 are spaced apart by the non-conductive material. The magnetic field generating elements 22 may be fully or partially embedded in the non-conductive material.

The number of magnetic field generating elements, m, of the first member 10 is larger than the number of magnetic field generating elements, n, of the second member 20. The illustrated gear therefore provides a step-up gear from the first member 10 (and input rotor) to the second member 20 (and output rotor! flywheel), wherein when the first and second members 10, 20 are in synchronous relative rotation, the second member 20 rotates faster than the first member 10 by a factor of n/rn, where n/rn is the gear ratio of the magnetic gear 100.

The coupling member 30 forms pad of a barrier at least partially enclosing the chamber 40 containing the second member 20. The barrier forms part of a housing of the chamber 40.

As shown in Figure 10, the coupling member 30 has a "top hat" geometry, comprising a circumferential wall 36, a "top" 34 and a "rim" 38. The view shown in Figure 9a is a cross-section through the circumferential wall 36. By locating the second rnember 20 inner of the circumferential wall 36 and the top 34 and the first member 10 on the outside of the circumferential wall 36 and top 34, and by sealing the rim 38 of the top hat to a housing wall of the chamber 40, the coupling member 30 may provide a barrier which seals the second member 20 from the first member 10. This may reduce the transmission of perturbations across the magnetic coupling. When the barrier is a sealed barrier with a sealed coupling to the wall of the chamber 40, a sealed chamber 40 may be provided. The chamber may be at vacuum or low-pressure chamber or may contain a low viscosity gas such as Helium.

Housing the second member 20 in such a chamber may reduce "windage" and other frictional losses.

Figure 9b illustrates the structure of the circumferential wall 36 of the coupling member 30, showing in more detail a portion of the cross sectional view shown in Figure 9a. As illustrated in Figure 9b, the coupling member 30 comprises a non-conductive material 31 having an outer circumferential surface 31a with a plurality of recesses 31b for supporting coupling elements of the array of coupling elements 32. The recesses are 31 b spaced apart around the outer circumferential surface 31 a such that consecutive coupling elements 32 are spaced apart by the non-conductive material 31. The recesses 31b are such that outer surfaces 32a of the coupling elements 32 (surfaces that face away from the chamber 40) received in the recesses may be flush with the outer circumferential surface of the coupling member 30, or may be beneath the outer circumferential surface. Inner circumferential surfaces 32b of the coupling elements 32 (surfaces that face towards the chamber 40) are provided beneath an inner circumferential surface 31c of the coupling member 30. In this way the coupling elements 32 are sealed from the chamber 40 by a layer of the non-conductive material 31 of the coupling member 30.

The coupling elements (or pole pieces) 32 comprise a magnetically permeable material, for example a ferrous or ferrite material. The coupling elements 32 are in this example elongate in the axial direction and may have a rectangular cross-section. In use the coupling elements 32 couple magnetic flux from the first array of magnetic field generating elements 12 to the second array of magnetic field generating elements 22 to permit synchronous relative rotation of the first and second arrays. Synchronous relative rotation corresponds to the magnetic gear being in a coupled configuration in which the second member 20 rotates at n/m times the speed of the first member 10.

As used herein the phrase "non-conductive material" means a material which is electrically non-conductive or electrically semi-insulating and which has a relative permeability close to 1, such as a ceramic, plastic or composite material. The magnetic field generating elements may be any suitable form of permanent magnetic poles such as rare earth magnets. The magnetic field generating elements 12 will generally be equally sized. Similarly, the magnetic field generating elements 22 will generally be equally sized. Also, the coupling elements 32 will generally be equally sized and equally spaced.

Figure 10 shows a cross-section along the axis of rotation of a flywheel system 300 comprising the magnetic gear 200 of Figure 1, showing the first member 10 coupled to the input rotor 14 for rotation with the input rotor 14 and the second member 20 and the flywheel coupled to the output rotor 24 for rotation with the output rotor 24. The first member 10 and the input rotor 14 are at least partially enclosed within a first housing portion 60. The second member 20, flywheel 90 and output rotor 24 are provided within the chamber 40 which is at least partially enclosed by a second housing portion 70. The coupling member 30 is disposed between the first and second member 10, 20 and provides a barrier that forms part of a housing of the chamber 40, together with the second housing portion 70. Two elements of the first array of magnetic field generating elements 12 carried on the inner surface 16 of the first member 10, two elements of the second array of magnetic field generating elements 22 carried on the outer surface 28 of the second member 20, and one of the coupling elements 32 carried in the circumferential wall 36 of the coupling member 30 can be seen in cross-section.

Figure 10 shows a cross-section through the top 34, circumferential wall 36 and rim 38 of the "top hat" coupling element 30. The second member 20 is provided inside of the circumferential wall and the top and the first member 10 is provided outside of the circumferential wall and top. The circumferential wall is concentric and coaxial with the circumferential walls of the first and second members 10, 20. The rim 38 is coupled between the first housing portion 60 and the second housing portion 70. In an example, the coupling of the rim 38 to the first and second housing portions 60, 70 comprises a sealed coupling to seal the second member 20 from the first member 10 within the chamber 40. In another example, the coupling member 10 is continuous with at least one of the first and second housing portions 60, 70. In another example, the circumferential wall of the coupling member 30 is joined to at least one of the first and second housing portions 60, 70 by a further wall or sealing means extending therebetween.

The first member 10 comprises an axially extending circumferential wall 17, as in Figure 9a, and an end wall 11 coupled to the circumferential wall. The end wall 11 couples the first member 10 to the input rotor 14 for rotation with the input rotor 14. The end wall 11 may be continuous or spoked, and may have a central hub for coupling to the input rotor 14.

First bearings 70a,b space the input rotor 14 from the first housing portion 60 and support the input rotor 14 for rotation. The first bearings 70a, b may comprise cylindrical bearings, an array of ball bearings or any other suitable arrangement of bearings to permit rotation of a rotor.

The input rotor 14 may be coupled to a drive shaft (not shown) of a motor or a pump or another drive assembly, for example a drive assemble of a vehicle.

The second member 20 comprises an axially extending circumferential wall 17, and a web 21 coupled to the circumferential wall. The web 21 couples the second member to the output rotor 24. The web 21 may be spoked or continuous, and may have a hub for coupling the second member 20 to the output rotor 24. In the illustrated example, the web 21 is coupled to the circumferential wall 13 intermediate the first and second ends for effective balance. In another example, the web may be coupled at or near the first end or the second end.

Second bearings 70c,d space the output rotor 24 from the second housing portion 70 and support the second member 20 for rotation. The second bearings 70c,d may comprise cylindrical bearings, an array of ball bearings, passive and or active magnetic bearings or any other suitable arrangement of bearings to permit rotation of a rotor.

The flywheel 90 is axially spaced from the second member 20 on the output shaft 24. The flywheel 90 has a rim 92, which has the majority of the mass of the flywheel 90 and a web 91 which couples the rim 92 to the output shaft 24. The web 91 may be spoked or continuous and may be integrally formed with the web or may be a separate component. In the example the web 91 is a steel web but a composite solid alternative could be considered for example.

In the example shown the rim 92 is a composite rim.

The input and output rotors 14, 24 are axially spaced apart on a common axis of rotation.

The structure of the first member 10, with the end wall 11 at one end of the magnet-carrying circumferential wall 17, allows the magnet-carrying circumferential wall of the second member 20 to be nested within the first member to allow concentric and coaxial relative rotation of the magnetic arrays, which may provide efficient flux coupling between the arrays.

In operation, rotation of the input rotor 14 causes rotation of the first member 10 and hence first array of magnetic field generating elements 12 to provide the first moving magnetic field.

The coupling elements 32 of the coupling member 30 couple magnetic flux of the first moving magnetic field to the second array of magnetic field generating elements 22 on the second member 20, and the flux coupling causes the second member 20 to contra rotate relative to the first member 10 at a speed determined by the gear ratio mm. The output rotor 24 rotates with the second member 20. causing the flywheel 90 to rotate at the speed of the second member 20. Eddy currents and hysteresis losses may arise from the movement of the first and second moving magnetic fields, which may cause heating in the first and second arrays of magnetic field generating elements 12, 22.

Since the second array of magnetic field generating elements 22 is located within a chamber 40, which may be a vacuum or low pressure chamber or may contain a low viscosity gas such as Helium, it is preferable, to avoid interfering with the chamber and the pressure therein, to remove heat from the first array of magnetic field generating elements 12 rather than from the second array 22.

While the coupling elements 32 of the coupling member 30 are described as being provided in recesses of the outer surface of the coupling member 30 and beneath the inner surface of the coupling member 30, in other examples, the coupling elements could be provided on either or both of the outer and inner surfaces, could be partially embedded in one of the outer and inner surface, could be flush with one or both of the outer and inner surfaces of could be fully embedded within the coupling member 30.

While the above disclosure describes a step-up gear, it will be appreciated that may aspect of the disclosure could be applied to a step-down gear.

While a vacuum or low pressure chamber is described, it will be appreciated that in other examples the chamber may not be at vacuum or low pressure and may not be sealed. In the above description, the high speed (second) member 20 is described as being contained in a chamber, but in other examples the low speed (first) member 10 may be provided within a chamber. In other examples, no chamber is provided.

Figures ha to 12c show examples in which the first member 10 has a fluid path extending at least partially therethrough to allow cooling of the first array of magnetic field generating elements 12.

Figure 1 la shows an example of a flywheel system 300' which comprises a fluid cooling system. Figure 1 la shows a cross-section along the axis of rotation of the flywheel system 300', showing the input rotor 14', the first housing portion 60', the first bearings 70a,b' which space the input rotor 14' from the first housing portion 60', and an example of a first member 10' having a closed fluid path. For simplicity, other features of the flywheel system 300' are not shown. Unless otherwise indicated, the flywheel system 300' has all of the features of the flywheel system 300 shown in Figure 10.

The fluid cooling system comprises seals 382, a channel 106 in the input rotor 14', a fluid path 100 in the first member 10', a sensor 370, a controller 320 and a cooling apparatus 360.

The channel 106 of the input rotor 14' is closed ata first end and fluidly continuous with the fluid path 100 of the first member 10' at a second end where the input rotor 14' couples to the second member 10' at a midpoint of the end wall 11'. The seals 382 are arranged to seal the first end of the channel to prevent or reduce egress or ingress of fluid yet allows rotation of the input rotor 14'. In the illustrated example, the fluid path 100 of the first member 10' extends radially from the midpoint of the end wall 11', through the end wall 11' and axially therefrom through the circumferential wall 17'. In the circumferential wall 17', the fluid path is arranged to follow at least part of the inner surface 16 of the first member 10' and so may in this way follow at least part of the surface of one or more of the magnetic field generating elements 22'. The fluid path 100 is in thermally coupled to the one or more magnetic field generating elements but may not necessarily be physically touching. The fluid path 100 has a closed end near at its outer axial extent (away from the end wall 11').

The illustrated seal is provided by a lip seal, but any appropriate fluid seal could be used that allows rotation of the input rotor 14'.

The fluid path 100 and the channel 106 are configured to allow the flow of a fluid coolant, such as water or glycol, therethrough.

Two examples of a closed fluid path 100 are shown in Figures llb and llc. Both Figures show a cross-section through the first member 10' in a plane normal to the cross-section of Figure 1 la, along the line A-A'.

Figure llb shows an example in which the fluid path 100 comprises a plurality of fluid paths lOla-h, each provided by a channel or lumen through the circumferential wall 17' of the first member 10'. Preferably the number of channels is equal to the number of magnetic field generating elements 12 carried on the first member 10', and preferably each channel 101 is arranged to follow at least part of the surface of a respective magnetic field generating element so that each of the magnetic field generating elements 12 may be cooled by the passage of the fluid through a respective channel 101. Tracing the geometry of the channels back towards the input rotor 14, the channels 101 extend through the circumferential wall 17 to the end wall 11 in a circumferentially spaced-apart configuration as shown in cross-section in Figure 1 lb and through the end wall 11, iadially conveiging theiein on the channel 106 at the midpoint of the end wall 11. In other examples, a different number of channels is provided. The number of channels may be different than the number of magnetic field generating elements 12. Each channel may be arranged to follow at least part of the surface of one or more of the magnetic field generating elements 12.

When the first member 10 is at rest, fluid in the fluid path will sink the gravitationally lowest point to which the fluid can flow, and this may create imbalance in the first member 10 when the first member 10 is rotated from rest. Providing the fluid path as a channel which extends continuously in a circumferential direction, for example as shown in Figure 3c, helps to ensure that fluid which has sunk to the gravitationally lowest point of the channel may quickly spiead out aiound the full circumference of the channel when the first membei lOis iotated.

This may result in improved balance of the first member 10 compared to the case where the fluid path is not circumferentially continuous.

Figure llc shows a second example, in which a single fluid path 102 is provided through the ciicumfeiential wall 17. As well as extending axially through the ciicumferential wall as in Figure llb, the fluid path 102 also extends continuously in a circumferential direction, as shown, to follow a full circumference of the inner circumferential surface 16 of the circumferential wall 17. In this way, the fluid path 102 follows at least part of the surfaces of the all of the first array of magnetic field generating elements 12. In other examples, the fluid path 102 may extend in a circumferential diiection to follow only part of a ciicumterence of the inner circumferential surface 16 of the fiist member 10, so as to follow at least pad of the surfaces of at least some of the first array of magnetic field generating elements 12.

It will be appreciated that the system shown in Figure 1 la could comprise a fluid path like that shown in Figure 11 b oi like that shown in Figuie 11 c.

The sensor 370 is arranged to sense a temperature of at least one of the magnetic field generating elements 22. The sensor 370 is coupled to the controller 320 and the controller 320 is coupled to the cooling apparatus 360. The controller 320 is configured to control operation of the cooling apparatus 360 based on the tempelature sensed by the sensor 370.

The sensor 370 may comprise an infra-red sensor, bar or strip sensor, for example a bar strip colour sensor which displays a temperature-dependent colour, a thermocouple or any other suitable temperature sensor.

The controller 320 may comprise a processor and memory and may be embodied in hardware, software, firmware or any combination thereof. In the case where the flywheel system 300 is a flywheel system of a vehicle, the controller 320 may be provided by the vehicle management system.

The cooling apparatus 360 may comprise a splash cooling apparatus arranged to cool the end wall 11 or the input rotor 14 via the application of a fluid, in order to cool the fluid in the fluid path 100 or channel 106 respectively therein. The cooling apparatus 360 may additionally or alternatively comprises a heat exchanger and/or a fan or blower for blowing air over the end wall 11 or the input rotor 14 in order to cool the fluid in the fluid path 100 or channel 106 and/or any other suitable means for cooling the end wall 11 and/or input rotor to cool the fluid in the fluid path 100 or channel 106.

In operation, a liquid phase of the fluid is provided in the fluid path 100/channel 106.

Rotation of the input rotor 14 and the first member 10 creates a centrifugal force which causes the liquid to travel radially outward through the end wall 11 and to flow along the axially extending part of the fluid path 100 and past the magnetic field generating elements 12. The rotation also causes the first array of magnetic field generating elements 12 to provide a first moving magnetic field which causes heating in the magnetic field generating elements 12 also heating any liquid in thermal communication with the magnetic field generating element(s). Heat which is absorbed from the magnetic field generating element(s) into the liquid, which may cause the liquid to boil. Pressure created by the expansion of the liquid to the gas phase (via boiling) allows the gas to overcome the centrifugal force to move back towards the end wall 11 Upon reaching the closed axial end of the fluid path 100, the gas travels back along the fluid path towards the end wall 11 and back toward the channel 106.

Meanwhile, the heating of the magnetic field generating elements 12 is sensed by the sensor 370 and an indication of the temperature is passed to the controller 320. The controller 320 causes the cooling apparatus 360 to cool of the end wall 11 and/or input rotor 14. The cooling causes fluid to return to its liquid phase from the gas phase. The condensed fluid then travels back out towards the magnetic field generating elements under the centrifugal force. The fluid path 100/channel 106 therefore provides a heat pipe. The cooling apparatus 360 helps to ensure efficient circulation of the fluid within the heat pipe.

The heating of the magnetic field generating elements 12 generally increases in proportion to the speed of rotation of the first member 10. In general, any rotation of the first member 10 relative to the second member 20 will produce heating in the first array of magnetic field generating elements 12, and the amount of heat produced increases with increasing rotational frequency. Therefore cooling is beneficial and/or necessary when the first member rotates (at any speed), and is increasingly beneficial and/or necessary when the first member 10 rotates at a higher frequency. Therefore additionally or alternatively the cooling apparatus 360 is controlled based on an indication of the rotation of the first member 10. The cooling apparatus could be controlled based on an indication of whether or not the first member 10 is rotating, and in this case the sensor 370 could comprise any appropriate sensor for sensing rotational movement of the first member 10. In order to provide a degree of cooling commensurate with the heat generated in the first array of magnetic field generating elements 12, the cooling apparatus could be controlled based on the rotational speed of the first member 10/input rotor 14. In this case, a speed or frequency sensor may be provided on the first member 10 or the input rotor 14. The speed or frequency sensor may comprise a tachometer or other instrument capable of measuring a rotational frequency.

The speed or frequency sensor may comprise a Hall Effect sensor or may otherwise be a contactless sensor, for example by using a magnetic coupling, to avoid mechanically interfering with the rotating members 10/rotor 14.

Figure 12a shows a flywheel system 300" having a second example of a fluid cooling system. Unless otherwise indicated, the flywheel system 300" has all of the features of the flywheel system 300 shown in Figure 10. Figure 12a shows a cross-section along the axis of rotation of the flywheel system 300", showing the input rotor 14", the first housing portion 60", the first bearings 70a,b" which space the input rotor 14' from the first housing portion 60", and an example of a first member 10" having an open fluid path. For simplicity, other features of the flywheel system 300" are not shown.

The fluid cooling system comprises a reservoir 380, seals 382a,b for sealing the reservoir, a channel 106' in the input rotor 14", a fluid path 100" in the first member 10", a sump 395 and a scavenger pump 390, a sensor 370", a controller 320" and a primer pump 340".

The seals 382a,b are spaced apart in the space between the first bearings 70a,b,and prevent ingress and egress of fluid to/from the reservoir 380 while allowing rotation of the input rotor 14". The reservoir 380 is provided around the input rotor 14". and the extent of the reservoir 380 is defined in a radial direction by the first housing portion 60" and in an axial direction by the seals 382a,b. the seals 382a,b and the reservoir 380 may be radially spaced form the input rotor 14" to allow rotation of the input rotor 14". The reservoir 380 is configured to house a fluid coolant, such as water or glycol.

The channel 106" of the input rotor 14" is fluidly coupled to the reservoir 380 at a first end and fluidly coupled to the fluid path 100" at the midpoint of the end wall 11 at a second end.

The channel 106" is configured to supply fluid from the reservoir 80 to the fluid path 100". In the illustrated example, the fluid path 100" extends radially from the midpoint of the end wall 11", through the end wall 11", axially therefrom through the circumferential wall 17" to an outer axial extent, and radially therefrom, via an outwardly extending portion bOa to the outer surface 18" of the circumferential wall 17". The fluid path 100" opens through the outer surface 18". In the circumferential wall 17", the fluid path 100" is arranged to follow at least part of the inner surface 16" of the first member 10" and may in this way follow at least part of the surface of one or more of the magnetic field generating elements 12". The fluid path 100" is in thermally coupled to the one or more magnetic field generating element(s) but may not necessarily be physically touching. The fluid path 100" has a closed end near at its outer axial extent (away from the end wall 11").

The illustrated seals 382a,b are provided by lip seals, but any appropriate fluid seals could be used, which allow rotation of the input rotor 14".

The fluid path 100" and the channel 106" are configured to allow the flow of a fluid coolant, such as water or glycol, therethrough.

Two examples of an open fluid path 100" are shown in Figures 12b and 12c. Both Figures show a cross-section through the first member 10" in a plane normal to the cross-section of Figure 12a, along the line B-B'.

Figure 12b shows an example in which the fluid path 100 comprises a plurality of fluid paths 104a-h, each provided by a channel or lumen through the first member 10". The outwardly extending portion bOa of each of the channels 104 is shown. Preferably the number of channels is equal to the number of magnetic field generating elements carried on the first member 10', and each is arranged to follow at least part of the surface of a respective magnetic field generating element so that each of the magnetic field generating elements may be cooled by the passage of the fluid through the respective channel 104. Tracing the geometry of the channels back towards the input rotor 14", the channels 104 extend through the circumferential wall 17" to the end wall 11" in a circumferentially spaced-apart configuration as shown in cross-section in Figure 12b and through the end wall 11", radially converging therein on the channel 106" at the midpoint of the end wall 11". In other examples, a different number of channels is provided. The number of channels may be different than the number of magnetic field generating elements 12. Each channel may be arranged to follow at least part of the surface of one or moie of the magnetic field generating elements 12.

Figure 12c shows a second example, in which a single fluid path 105 is piovided thiough the circumferential wall 17'. As well as extending axially through the circumferential wall 17" as in Figure 12b, the fluid path 105 also extends continuously in a circumferential direction through to follow a full circumference of the inner ciicumferential surface 16" of the ciicumferential wall 17". In this way, the fluid path 105 follows at least pail of the surfaces of the all of the first array of magnetic field generating elements 12. A plurality of outwardly extending portions lOOb extend radially form the fluid path 105 to the outer surface 18' of the circumferential wall 17". In other examples, the fluid path 105 may extend in a ciicumfeiential diiection to follow only pait of a circumfeience of the inner circumferential surface 16 of the first member 10', to follow at least part of the surfaces of at least some of the first array of magnetic field generating elements 12.

It will be appreciated that the system shown in Figure 12a could comprise a fluid path like that shown in Figure 12b or like that shown in Figure 12c.

The sensor 370" is arranged to provide a sensor signal to the controller 320. The controller 320' is coupled to the primer pump 340 to control operation of the primer pump 340 based on the sensor signal, and is coupled to the scavenger pump 390 control operation of the scavengei pump 390 based on the sensor signal. The primer pump 340 is arranged to pump fluid along the channel 106'. The sump 395 is provided within the fiist housing portion 60" to collect fluid which exits the fluid path 100 via the open ends of the fluid path 100'. The sump may be a pan or may be provided by an inner surface of the first housing portion 60".

The scavenger pump 390 is aiianged to collect fluid from the sump 395 and to return the collected fluid to the reseivoir 380.

The sensor 370" may compiise a temperature sensor to sense a temperatuie of ci moie of the magnetic field generating elements 12, and/or it may comprise a sensor configured to sense rotation of, or the rotational speed or frequency of, the first member 10 to obtain an indirect indication of the temperature of the magnetic field generating elements 12 as described above. The sensor 370" is coupled to provide the controller 320" with an (direct or indirect) indication of the temperatuie of the magnetic field geneiating elements 12, and the controller 320 is coupled to the primer pump 340 and to the scavenger pump 360. The controller 320 is configured to control operation of the primer pump 340 and the scavenger pump 360 based on the indication of the temperature.

The sensor 370" may comprise any suitable temperature and/or speed or frequency sensor as described above, and the controller 320" may comprise a processor and memory and may be embodied in hardware, software, firmware or any combination thereof. In the case where the flywheel system 300 is a flywheel system of a vehicle, the controller 320 may be provided by the vehicle management system as described above.

The primer pump 340 may comprise any suitable electrical or mechanical pump, as may the scavenger pump 390.

In operation, a fluid coolant, in either a liquid or a gas phase, is housed in the reservoir 380.

Rotation of the input rotor 14 causes the first array of magnetic field generating elements 12 to provide a first moving magnetic field which causes heating in the magnetic field generating elements 12. The heating and/or the rotation of the first member 10" is sensed by the sensor 370" and a sensor signal is passed to the controller 320". In response, the controller 320" causes the primer pump 340 to start pumping fluid along the channel 106 from the reservoir 308. Only a small amount of energy is required from the primer pump 340 to give the fluid an initial velocity, and the fluid is then accelerated and flung outwardly along the fluid path 100" by the centrifugal force of the rotating first member 10". The fluid travels past the magnetic field generating elements 12 on its outward path through the circumferential wall 17", removing heat from the magnetic field generating elements as it does so, and is then flung out through the openings of the outwardly extending portions bOa by the centrifugal force. The spent fluid hits the inner wall of the first housing portion 60" and drains to the sump 395. In response to a command from the controller 320", the scavenger pump 390 collects the tluid from the sump and returns it to the reservoir 380.

The fluid path in Figures 9a to 13 may also be referred to as a first member fluid path.

The mechanical gear referenced in relation to Figures 1 to 8 may be the same mechanical gear as that referenced in relation to Figures 9a to 13, or they may be different.

It will be appreciated that the cooling path and the first member fluid path may be thermally or fluidically coupled together. In the latter case, they may share a common fluid supply path and/or primer pump and/or reservoir and/or sump and scavenger pump. In any event, they may share a common controller and/or sensor and/or cooling system and any one or more of other features of the flow control systems described herein.

The controller described in relation to Figures 1 to 8 may also be referred to as a coupling member controller and the controller referred to in relation to Figures 9a to 13 may also be referred to as a first member controller. It will be appreciated that these controllers may be provided separately or in a single controller.

While in the above description the input and output rotors 14, 24 are spaced apart on a common axis, in other examples the input and output rotors 14, 24 may be axially offset from one another.

In some examples, the "top hat" coupling member 30 may be symmetrical about the axis of rotation of the magnetic gear 200. In other examples the top hat" coupling member 30 may be asymmetrical about the axis of rotation. The coupling member 30 may have a lug which is configured to engage with a corresponding recess in the housing of the magnetic gear (for example in the first housing portion 60 or second housing portion 70) for securing the coupling member 30 in place relative to the housing. When a passive pump is used, it may be the case that a controller and sensors are not required.

In some examples, the fluid path may have a curved, spiral or serpentine path through the first member and/or may comprise channels extending through the first member 10 in a direction which is not perpendicular to the rotational axis.

While in the above examples the flywheel system 300, 300', 300" is illustrated with the axis in a horizontal plane (for example parallel with the plane of a vehicle axle or where the vehicle is a car, the road), which may require a primer pump 340 to be used to provide the fluid with an initial velocity, the flywheel system 300, 300', 300" may be mounted vertically (for example in a plane perpendicular to the plane of a vehicle axle or where the vehicle is a car, the road) such gravity may provide the momentum needed to initiate circulation of the fluid. It will be appreciated that illustrated examples having a primer pump 340 could instead be mounted vertically to use gravity in place of the primer pump 340, and examples not having a primer pump 340 could instead have a primer pump to assist the initial circulation of fluid.

While embodiments described above describe controlling the supply of fluid to the fluid path using a pump 340 controlled by a controller, additionally or alternatively a "passive" pump may be provided on the input shaft for pumping fluid to the fluid path in proportion to the rotational frequency of the input shaft. For example such a pump may be mounted on the input shaft, and may be arranged to be driven by the rotational energy of the input shaft to pump fluid from a reservoir or other fluid source to the fluid path in proportion to the rotational frequency of the input shaft. When a passive pump is used, it may be the case that a controller and sensors are not required.

Referring to the description of Figure 12a, it will be appreciated that rather than returning the fluid to the reservoir 380, the fluid could be allowed to leave the flywheel system 300" and the reservoir could be replenished with a supply of new fluid. In an example where the fluid is not collected after leaving the open ends of the fluid path 100", a reservoir may not be required and new fluid may be channelled directly into the channel 106/fluid path 100". In such examples, it will be appreciated that a sump 395 and a scavenger pump 390 may not be provided.

While embodiments describe the fluid being supplied from a reservoir, when the magnetic gear is provided in a vehicle, the fluid could be supplied by bleeding fluid from a hydraulic system of the vehicle. In embodiments where pumping or the controlled supply of fluid to the fluid path is described, the pressure required to pump the fluid along the fluid path additionally or alternatively by provided by the pressure inherent in the hydraulic system.

While the above disclosure is couched in terms of a concentric magnetic gear, those skilled in the art will appreciated that a magnetic gear could be provided in which the first and second members are axially spaced apart, and in which the coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second arrays in an axial direction. The first and second members of such a magnetic gear would preferably be arranged coaxially, although non-coaxial arrangements are possible. An example of such an arrangement is shown in Figures 13, which shows a cut-away view of a non-concentric magnetic gear 400 having a first member 10", coupling elements 32" and second member 20". The first and second member 10", 20" are provided by disk-like bodies, each having an array of elongate magnetic field generating elements provided on an inwardly facing surface of the respective body and extending radially outward from a midpoint of the body in a "spoked" arrangement (magnetic field generating elements not shown). Although a coupling member 30" is not shown, in practice the coupling elements 32" may be embedded in or on a disk-like coupling member. It will be appreciated that a fluid path may be provided through the first member 10" and that the fluid path could have one of several geometries, for example a linear channel, a spiral channel or an arrangement of radially extending channels.

As set out above, a linear gear may be provided, in which the first array of magnetic field generating elements 12 is provided in a first linear array, the second array of magnetic field generating elements 22 is provided in a second linear array, and the coupling elements are provided in a third array intermediate the first and second arrays. First and second moving magnetic fields may be provided by providing the first and second arrays of magnetic field generating elements by way of first and second arrays of permanent magnetic poles on first and second moveable members respectively, or one or both of the moving magnetic fields may be provided by an array of sequentially activated electromagnets. In a case where the first member is arranged to move, the first (linear) member may be coupled to the input rotor 14 via a rotational to linear converter or actuator, or the first member 10 may be driven by linear motion. The second (linear) member may be coupled to a flywheel or other rotational output via a linear to rotational converter or actuator or may be arranged to drive linear motion. It will be appreciated that a fluid path may be provided through the first (linear) member and that the fluid path could have one of several geometries, and could comprise for example one or more linear channels, curved channels, spiral channels or serpentine channels. The one or more channels may extend at least partially through the first (linear) member. The channels may be open at at least one end, or may be closed-ended. Closed-ended channels may form part of a sealed fluid system, and the closed channels may function like heat pipes in a manner similar to that described in relation to Figures 1 la to 11 c.

The fluid paths described herein may comprise channels provided at least partially through the first member 10, and they may be provided by lengths of tubing provided within the first member. The tubing would preferably comprise thin-walled tubing to reduce or avoid needing to increase the proportion of the first member 10 to accommodate the tubing, and to reduce adding extra weight and/or bulk to the first member 10.

It will be appreciated that while the above disclosure is couched in terms of a magnetic gear, aspects of the disclosure are also applicable to a magnetic coupling having a 1:1 torque transmission ratio. Such a magnetic coupling may have first and second members having geometries as described in relation to any of the drawings above, excepting that first and second arrays of magnetic field generating elements carried thereon would have an equal number of magnetic field generating elements. A coupling member 30 and/or coupling elements 32 may not be required in such a magnetic coupling.

While in the above disclosure the arrays of magnetic field generating elements are provided by permanent magnetic poles, in applications of a magnetic gear or coupling which do not require rotation of both of the first and second members 10, 20, the array of magnetic field generating elements of a non-rotating one of the first and second members could instead be provided by an array of electromagnets. For example, the array of electromagnets could be configured to provide a moving magnetic field by the application of a multiphase current to the array of electromagnets.

It will be appreciated that elements described herein in relation to a given embodiment herein could be used in another embodiment, and that modifications and variations within the contemplation of that skilled in the art may be made to any of the disclosed embodiments without departing from the scope of the invention as set out in the claims.

Embodiments shown in figures 1 to 8 may comprise any of the features of the embodiments shown in figures 9a to 13 and vice versa.

Embodiments of the invention may include any of the described features, described above in any combination.

Claims

CLAIMS1. A magnetic gear comprising: first and second members arranged for relative movement therebetween, the first member having a first array of magnetic field generating elements and the second member having a second array of magnetic field generating elements; and a coupling member having an array of coupling elements for coupling magnetic flux between the first array of magnetic field generating elements and the second array ofmagnetic field generating elements,wherein for at least one of the coupling elements, there is provided a cooling path in thermal communication with the at least one coupling element, wherein the cooling path is provided within at least one of the at least one coupling element and the coupling member, wherein a first member fluid path extends at least partially through the first member to enable cooling of at least one of the magnetic field generating elements of the first array.
2. The magnetic gear of claim 1, wherein the cooling path is provided at least partially through the at least one coupling element.
3. The magnetic gear of claim 1 or 2, wherein the cooling path comprises a channel extending at least partially through the at least one coupling element.
4. The magnetic gear of claim 1, wherein the cooling path is provided adjacent to the coupling element.
5. The magnetic gear of claim 4, wherein the at least one cooling path comprises a channel extending adjacent to a surface of the coupling element.
6. The magnetic gear of claim 4 or 5, wherein a cross section of the at least one coupling element has at least one bevelled corner.
7. The magnetic gear of claim 6, wherein the at least one bevelled corner provides at least part of the at least one fluid path between the at least one coupling element and surfaces of the coupling member supporting the at least one coupling element.
8. The magnetic gear of any of claims 2 to 7, wherein the cooling path extends only partially through the coupling element and/or the coupling member.
9. The magnetic gear of claim 8, further comprising a heat exchanger at a closed end of the cooling path.
10. The magnetic gear of any preceding claim, wherein the at least one coupling element has a single cooling path.
11. The magnetic gear of any of claims 1 to 3, 8 or 9, wherein the at least one coupling element has a single cooling path, wherein the single cooling path is provided within the coupling element.
12. The magnetic gear of claim 11, wherein the cooling path is provided centrally within a cross section of the coupling element.
13. The magnetic gear of any of claims 1 to 10, wherein the at least one coupling element is provided with two cooling paths.
14. The magnetic gear of any of claim 1 to 3, 8 or 9, wherein the at least one coupling element is provided with two cooling paths, wherein the two cooling paths are provided within the coupling element.
15. The magnetic gear of any of claim 14 or 15, wherein the two cooling paths are arranged symmetrically about an axis of a cross section of the coupling element.
16. The magnetic gear of claim 14, wherein the two cooling paths comprise fluid paths, wherein one of the two fluid paths is arranged to provide a fluid return path.
17. The magnetic gear of any of claims 1 to 3, 8 or 9, wherein the at least one coupling element is provided with a plurality of cooling paths.
1K The magnetic gear of claim 17, wherein the at least one coupling element has a first cooling path and a plurality of further cooling paths arranged around the first cooling path.
19. The magnetic gear of any of claims 18, wherein the first cooling path is arranged centrally within the at least one coupling element.
20. The magnetic gear of claim 18 or 19, wherein the further cooling paths are arranged symmetrically about the central cooling path.
21. The magnetic gear of claim 19, wherein the further cooling paths are provided by bevelled corners of the at least one coupling element.
22. The magnetic gear of any of claims 17 to 20, wherein at least two of the plurality of cooling paths comprise providing forward and return fluid paths.
23. The magnetic gear of any preceding claim, wherein at least one cooling path is provided for each of the coupling elements.
24. The magnetic gear of any preceding claim, wherein the or at least one cooling path comprises a fluid path, comprising a flow control element configured to control the flow of a fluid therealong.
25. The magnetic gear of claim 24, wherein the flow control element is configured to control the flow of fluid based on a temperature of the at least one coupling element.
26. The magnetic gear of any preceding claim, wherein the at least one cooling path comprises a fluid path, and the gear further comprises a coupling member controller configured to control the flow of fluid along the fluid path.
27. The magnetic gear of claim 26, wherein the coupling member controller is configured to receive an indication of a measured temperature of the at least one coupling element and to control the flow of fluid based on the measured temperature.
28. The magnetic gear of claim 27, wherein the coupling member controller is configured to store an indication of a reference temperature and to control the flow of fluid based on a comparison between the measured temperature and the reference temperature.
29. The magnetic gear of any of claims 26 to 28, wherein the coupling member controller is configured to control a fluid pump to control the flow of fluid.
30. The magnetic gear of claim 29, wherein the fluid pump comprises an electric pump.
31. The magnetic gear of claim 29 or 30, wherein the fluid pump comprises a mechanical pump.
32. The magnetic gear of any of claims 29 to 31, wherein the fluid pump comprises a hydraulically driven pump
33. The magnetic gear of any of claims 26 to 32, wherein the coupling member controller is configured to control the pressure of the fluid to control the flow of fluid.
34. The magnetic gear of claim 33, wherein the at least one fluid path is coupled to a tap, wherein coupling member controller is configured to control the tap to control the pressure of the fluid.
35. The magnetic gear of any preceding claim, wherein the first and second members are arranged concentrically for relative rotation therebetween, wherein the coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second arrays in a radial direction.
36. The magnetic gear of any of claims 1 to 34, wherein the first and second members are axially spaced apart, wherein the coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second arrays in an axial direction.
37. The magnetic gear of claim 36, wherein the first member, the second member and the coupling member are arranged coaxially.
38. The magnetic gear of any preceding claim, wherein the one of the first and second members is coupled to an input shaft of the magnetic gear and the other of the first and second members is coupled to an output shaft of the magnetic gear.
39. The magnetic gear of claim 38, wherein the output shaft is coupled to a flywheel.
40. The magnetic gear of claim 37 or 38, wherein the output shaft is arranged in a chamber, wherein the chamber may be at vacuum or low pressure or contain a low viscosity gas such as Helium.
41. The magnetic gear of claim 40, wherein the coupling member forms part of a barrier enclosing the chamber.
42. The magnetic gear of any of claims 38 to 41, wherein the at least one cooling path comprises a fluid path and the magnetic gear comprises a mechanical gear mounted on the input shaft, wherein the mechanical gear is configured to cause a fluid to be pumped along the at least one fluid path in proportion to the rotational speed of the input shaft.
43. The magnetic gear of any preceding claim! wherein the at least one cooling path comprises a fluid path, wherein the coupling member comprises a fluid supply path to supply fluid from a fluid reservoir to the at least one fluid path.
44. The magnetic gear of claim 43, wherein the coupling member comprises a fluid return path to receive fluid which has passed along the at least one fluid path.
45. The magnetic gear of claim 44, wherein the fluid return path is arranged to return fluid which has passed along the at least one fluid path to the reservoir.
46. The magnetic gear of claim 9, wherein the at least one cooling path comprises a fluid path and the heat exchanger comprises a condensing plate.
47. The magnetic gear of any preceding claim, wherein the at least one cooling path comprises a material of lower magnetic permeability in place of or in addition the at least one fluid path.
48. The magnetic gear of claim 47, wherein the material of lower magnetic permeability comprises a solid, liquid or gas.
49. The magnetic gear of claim 47, wherein the material of lower magnetic permeability comprises a material selected from the group consisting of a material comprising aluminium, a material comprising copper and a composite material.
50. A magnetic gear comprising: first and second members arranged for relative movement therebetween, the first member having a first array of magnetic field generating elements and the second member having a second array of magnetic field generating elements; and a coupling member having an array of coupling elements for coupling magnetic flux between the first array of magnetic field generating elements and the second array ofmagnetic field generating elements,wherein at least one of the coupling elements has a substantially rectangular cross section with at least one bevelled corner.
51. The magnetic gear of claim 50, wherein the bevelled corner provides a cooling path between the at least one coupling element and surfaces of the coupling member supporting the coupling element.
52. The magnetic gear of claim 50 or 51, wherein each of the corners of the at least one coupling element is bevelled.
53. The magnetic coupling of any preceding claim, wherein the first member fluid path is arranged to follow at least pad of the surface of the at least one of the magnetic field generating elements of the first array.
54. The magnetic coupling of any preceding claim, wherein the first member fluid path extends at least partially through the first member in an axial direction.
55. The magnetic coupling of any preceding claim, wherein each of the first and second members has an outer cylindrical surface and is arranged for rotation about an axis.
56. The magnetic coupling of claim 55, wherein the first member fluid path extends in a circumferential direction to follow at least part of the circumferential surface of the first member.
57. The magnetic coupling of claim 56. wherein the first member fluid path is continuous in the circumferential direction.
58. The magnetic coupling of any preceding claim, wherein the first member fluid path comprises a plurality of first member fluid paths.
59. The magnetic coupling of claim 58, wherein the number of first member fluid paths is equal to the number of magnetic field generating elements of the first array.
60. The magnetic coupling of claim 59, wherein each of the first member fluid paths is arranged to follow at least part of a surface of a respective one of the magnetic field generating elements of the first array.
61. The magnetic coupling of any of claims 55 to 60, wherein the first member comprises an end wall at a first end of a circumferential wall having the circumferential surface, wherein the end wall couples the first member to a rotor shaft.
62. The magnetic coupling of claim 61, wherein the first member fluid path extends through the end wall to couple to a reservoir external of the end wall.
63. The magnetic coupling of claim 62, wherein the reservoir is provided adjacent to the rotor shaft.
64. The magnetic coupling of claim 63, wherein the reservoir is provided between bearings which support the rotor shaft.
65. The magnetic coupling of claim 64, wherein a seal is provided between the bearings for sealing the reservoir.
66. The magnetic coupling of any preceding claim, wherein the first member fluid path is sealed, such that the first member fluid path allows fluid flow in an outward direction and a return direction.
67. The magnetic coupling of claim 66, wherein the first member fluid path and reservoir provide a closed fluid system, wherein fluid flowing in the return direction is returned to the reservoir.
68. The magnetic coupling of claim 66 or 67, comprising a cooling system for cooling fluid flowing in the return direction.
69. The magnetic coupling of claims 68, wherein the cooling system is configured to cool the end wall.
70. The magnetic coupling of claim 68 or 69, wherein the cooling system is configured to cool fluid in the reservoir.
71. The magnetic coupling of any of claims 55 to 65, wherein the first memberfluid path is open near a second end of the circumferential wall to allow used fluid to exit the first member.
72. The magnetic coupling of claim 71. comprising a casing arranged around the first member to collect the used fluid.
73. The magnetic coupling of claim 72, comprising a scavenger pump to remove the collected fluid from the casing.
74. The magnetic coupling of claim 61, wherein the first member fluid path has an opening through a second end of the circumferential wall to receive fluid.
75. The magnetic coupling of claim 74, wherein the first member fluid path has an opening through the end wall to allow used fluid to exit the first member.
76. The magnetic coupling of any preceding claim, wherein the first member is arranged to be mounted vertically to allow fluid to travel along the first member fluid path under the action of gravity.
77. The magnetic coupling of any preceding claim, comprising a pump configured to pump the fluid along the first member fluid path.
78. The magnetic coupling of claim 77, wherein the pump comprises an electric pump.
79. The magnetic coupling of claim 77 or 78, wherein the pump comprises a mechanical pump.
80. The magnetic coupling of any of claims 77 to 79, wherein the fluid pump comprises a hydraulically driven pump.
81. The magnetic coupling of any preceding claim, comprising a first member controller configured to control the flow of fluid along the first member fluid path.
82. The magnetic coupling of claim 81, wherein the first member controller is configured to receive an indication of a measured temperature of the at least one magnetic field generating element and to control the flow of fluid along the first member fluid path based on the measured temperature.
83. The magnetic coupling of claim 82, wherein the first member controller is configured to store an indication of a reference temperature and to control the flow of fluid along the at least one first member fluid path based on a comparison between the measured temperature and the reference temperature.
84. The magnetic coupling of any of claims 81 to 83 when dependent upon any of claims 26 to 29, wherein the first member controller is configured to control the pump to control the flow of fluid along the first member fluid path.
85. The magnetic gear of any of preceding claim, wherein the coupling member has an outer circumferential surface.
86. The magnetic gear of claim 85, wherein the outer circumferential surface is configured to carry the coupling elements.
87. The magnetic gear of claims 85 or 86, wherein the outer circumferential comprises a plurality of recesses for supporting the plurality of coupling elements therein.
88. The magnetic gear of claim 87, wherein the recesses are configured such that outer surfaces of the respective coupling elements carried therein are flush with the outer circumferential surface.
89. The magnetic gear of claim 87, wherein the coupling elements are provided beneath the outer circumferential surface.
90. The magnetic gear of any of claims 85 to 89, wherein the coupling member has an inner circumferential surface.
91. The magnetic gear of claim 90, wherein inner surfaces of the respective coupling elements are flush with the inner circumferential surface.
92. The magnetic gear of claim 90, wherein the coupling elements are provided beneath the inner circumferential surface.
93. A vehicle comprising the magnetic gear of any preceding claim.
94. A method of operating the magnetic gear of any of claims 1 to 92, the method comprising: effecting relative movement between the first and second members; and supplying fluid to the at least one first member fluid path to cool the at least one coupling element.
95. The method of claim 94, comprising supplying water to the first member fluid path.
96. The method of claim 94, comprising supplying glycol to the first member fluid path.
97. The method of any of claims 94 to 96, comprising controlling the flow of fluid along the first member fluid path.
98. A method of operating the magnetic gear of any of claims 1 to 59, the method comprising: effecting relative movement between the first and second members; and supplying fluid to the at least one cooling path to cool the at least one coupling element.
99. A magnetic gear substantially as described herein with reference to the accompanying drawings.
100. A method of operating a magnetic gear substantially as described herein with reference to the accompanying drawings.