GB2516644A

GB2516644A - A Magnetic Coupling

Info

Publication number: GB2516644A
Application number: GB1313425.9A
Authority: GB
Inventors: Richard Gordon; Andrew Farquhar Atkins; Hing W To
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2013-07-26
Filing date: 2013-07-26
Publication date: 2015-02-04
Also published as: GB201313425D0; WO2015011500A2; WO2015011500A3

Abstract

A magnetic coupling 300, comprising: a first member 10 having a first array of magnetic field generating elements 12; a second member 20 having a second array of magnetic field generating elements 22, the first and second members being arranged for relative movement; wherein a fluid path 100 extends at least partially through the first member 10 to enable cooling of at least one of the magnetic field generating elements 12 of the first array.

Description

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

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.

IS 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 amplify a high torque, low frequency input drive to produce a low torque, high frequency output. Housing the driven component of the 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 a first aspect, there is provided a magnetic coupling, comprising: a first member having a first array of magnetic field generating elements; a second member having a second array of magnetic field generating element, the first and second members being arranged for relative movement; wherein a 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.

In an embodiment, the fluid path is arranged to follow at least part of the surface of the at least one of the magnetic field generating elements of the first array.

In an embodiment, the fluid path extends at least partially through the first member in an axial direction.

In an embodiment, each of the first and second members has an outer cylindrical surface and is arranged for rotation about an axis.

In an embodiment, the fluid path extends in a circumferential direction to follow at least part of the circumferential surface of the first member.

In an embodiment, the fluid path is continuous in the circumferential direction.

In an embodiment, the fluid path comprises a plurality of fluid paths. The number of fluid paths may be equal to the number of magnetic field generating elements of the first array.

Each of the 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.

In an embodiment, 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. In an embodiment, the fluid path extends 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.

In an embodiment, the fluid path is sealed, such that the fluid path allows fluid flow in an outward direction and a return direction.

In an embodiment, the fluid path and reservoir provide a closed fluid system, wherein fluid flowing in the return direction is returned to the reservoir.

In an embodiment, there is provided a cooling system for cooling fluid flowing in the return direction.

In an embodiment, the cooling system is configured to cool the end wall.

In an embodiment, the cooling system is configured to cool fluid in a reservoir.

In an embodiment, the fluid path is open near a second end of a circumferential wall of the first member to allow used fluid to exit the first member.

In an embodiment, there is provided a casing arranged around the first member to collect the used fluid. A scavenger pump may be provided to remove the collected fluid from the casing.

In an embodiment, the fluid path has an opening through a second end of the circumferential wall to receive fluid.

In an embodiment, the fluid path has an opening through the end wall to allow used fluid to exit the first member.

In an embodiment, the first member is arranged to be mounted vertically to allow fluid to travel along the fluid path under the action of gravity.

In an embodiment, there is provided a pump configured to pump the fluid along the fluid path. The pump may comprise an electric pump and/or a mechanical pump and/or a hydraulically driven pump.

In an embodiment, there is provided a controller configured to control the flow of fluid along the fluid path.The controller may be 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 fluid path based on the measured temperature. The controller may be configured to store an indication of a reference temperature and to control the flow of fluid along the at least one fluid path based on a comparison between the measured temperature and the reference temperature. The controller may be configured to control the pump to control the flow of fluid along the fluid path.

In an embodiment, the first and second members are arranged concentrically such that magnetic flux couples between the first array of magnetic field generating elements and the second array of magnetic field generating elements in a radial direction.

In an embodiment, the first and second members are axially spaced apart such that magnetic flux couples between the first array of magnetic field generating elements and the second array of magnetic field generating elements in an axial direction.

In an embodiment, the first member, the second member and the coupling member are arranged coaxially.

In an embodiment, one of the first and second members is coupled to an input shaft and the other of the first and second members is coupled to an output shaft. The output shaft may be coupled to a flywheel. The output shaft is arranged in a vacuum chamber.

In an embodiment, the first and second arrays have a different number of magnetic field generating elements, further comprising a coupling member provided intermediate the first and second members for coupling magnetic flux between the first and second arrays to provide a magnetic gear.

In an embodiment, the coupling member forms part of a barrier enclosing a chamber. The chamber may be at vacuum or low pressure or may contain a low viscosity fluid such as Helium.

In an embodiment, the coupling member comprises a plurality of coupling elements for coupling the flux between the first and second arrays of magnetic field generating elements.

In an embodiment, the coupling member has an outer circumferential surface. The outer circumferential surface is configured to carry the coupling elements. The outer circumferential surface may comprises 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 has an inner circumferential surface. Inner surfaces of the respective coupling elements may be flush with the inner circumferential surface. The coupling elements are preferably provided beneath the inner circumferential surface.

In an embodiment, there is provided 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.

In an embodiment, there is provided a vehicle comprising a magnetic gear as described herein.

In a second aspect, there is provided a method comprising: effecting relative movement between the first and second members; and supplying fluid to the at least one fluid path to cool the at least one coupling element.

An embodiment comprises supplying water to the fluid path.

An embodiment comprises supplying glycol to the fluid path.

An embodiment comprises controlling the flow of fluid along the fluid path.

A method of operating a magnetic gear substantially as described herein with reterence to the accompanying drawings.

Embodiments of the invention will now be described! by way of example only, with reference to the accompanying drawings in which: Figure la shows a schematic cross-section of a magnetic gear in a plane normal to an axis of rotation of the magnetic gear; Figure lb shows a schematic cross-section of part of a coupling member; Figure 2 shows a cross-section along an axis of rotation of a flywheel system comprising the a magnetic gear of Figure la; Figure 3a shows a schematic cross-section along an axis of rotation of a first member having a closed fluid path; Figure 3b shows a schematic cross-section of the magnetic coupling of Figure 3a 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 3c shows a schematic cross-section of the magnetic coupling of Figure 3a 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 4a shows a schematic cross-section along an axis of rotation of a first member having an open fluid path; Figure 4b shows a schematic cross-section of the magnetic coupling of Figure 4a 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 4c shows a schematic cross-section of the magnetic coupling of Figure 4a 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 5 shows a partial cut-away view of a non-concentric magnetic gear.

Figure la 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 airays 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 2).

The first array of magnetic field generating elements 12 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 2) 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. 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 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.

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/m, where n/m is the gear ratio of the magnetic gear 100.

The coupling member 30 forms part 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 2, 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 la is a cross-section through the circumferential wall 36. By locating the second member 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 lb 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 la. As illustrated in Figure ib, 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 31b spaced apart around the outer circumferential surface 31a 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 2 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 torms 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 2 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 la, 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 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 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 IS 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 ot the coupling member 30 are described as being provided in recesses of the outer surface ot 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 tully 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 3a to 4c 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 3a shows an example of a flywheel system 300' which comprises a fluid cooling system. Figure 3a 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 2.

The fluid cooling system comprises a sea1382, 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 at a 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 seal 382 is 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 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 a closed fluid path 100 are shown in Figures 3b and 3c. Both Figures show a cross-section through the first member 10' in a plane normal to the cross-section of Figure 3a, along the line A-A'.

Figure 3b 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 3b 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 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 spread out around the full circumference of the channel when the first member 10 is rotated.

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

Figure 3c shows a second example, in which a single fluid path 102 is provided through the circumferential wall 17. As well as extending axially through the circumferential wall as in Figure 3b, 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 direction to follow only part of a circumterence of the inner circumferential surface 16 of the first member 10, so as 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 3a could comprise a fluid path like that shown in Figure 3b or like that shown in Figure 3c.

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 temperature 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/oi necessary when the fiist membei 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 appalatus 360 is controlled based on an indication of the lotation of the fiist 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 piovided on the first member 10 oi the input rotol 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 interfeiing with the rotating members 10/rotor 14.

Figure 4a 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 2. Figure 4a shows a cross-section along the axis of rotation of the flywheel system 300", showing the input rotor 14", the first housing poition 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 aiound 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 iotoi 14" to allow lotation of the input iotoi 14". The leservoir 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 1 06" is configured to supply fluid from the reservoir 80 to the fluid path 1 00'. 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 lOOa 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 4b and 4c. Both Figures show a cross-section through the first member 10" in a plane normal to the cross-section of Figure 4a, along the line B-B'.

Figure 4b 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 4b 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 more of the magnetic field generating elements 12.

Figure 4c shows a second example, in which a single fluid path 105 is provided through the circumferential wall 17". As well as extending axially through the circumferential wall 17" as in Figure 4b. the fluid path 105 also extends continuously in a circumferential direction through to follow a full circumference of the inner circumferential surface 16" of the circumferential wall 17". In this way, the fluid path 105 follows at least part 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 circumferential direction to follow only part of a circumference 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 4a could comprise a fluid path like that shown in Figure 4b or like that shown in Figure 4c.

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 scavenger 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 first 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 arranged to collect fluid from the sump 395 and to return the collected fluid to the reservoir 380.

The sensor 370" may comprise a temperature sensor to sense a temperature of or more 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 temperature of the magnetic field generating 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 fluid from the sump and returns it to the reservoir 380.

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 its axis of rotation. In other examples the "top hat" coupling member 30 may be asymmetrical about its axis of rotation. For example, 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 may be mounted on the input shaft, and 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.

Referring to the description of Figure 4a, 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 5, 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.

In another possibility, 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 re 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 3a to 3c 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.

Claims

CLAIMS1. A magnetic coupling, comprising: a first member having a first array of magnetic field generating elements; a second member having a second array of magnetic field generating element, the first and second members being arranged for relative movement; wherein a 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 coupling of claim 1, wherein the fluid path is arranged to follow at least part of the surface of the at least one of the magnetic field generating elements of the first array.
3. The magnetic coupling of claim 1 or 2, wherein the fluid path extends at least partially through the first member in an axial direction.
4. The magnetic coupling of any of claims 1 to 3, wherein each of the first and second members has an outer cylindrical surface and is arranged for rotation about an axis.
5. The magnetic coupling of claim 4, wherein the fluid path extends in a circumferential direction to follow at least part of the circumferential surface of the first member.
6. The magnetic coupling of claim 5, wherein the fluid path is continuous in the circumferential direction.
7. The magnetic coupling of any of claims 1 to 5, wherein the fluid path comprises a plurality of fluid paths.
8. The magnetic coupling of claim 7, wherein the number of fluid paths is equal to the number of magnetic field generating elements of the first array.
9. The magnetic coupling of claim 8, wherein each of the 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.
10. The magnetic coupling of any of claims 4 to 9, 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.
11. The magnetic coupling of claim 10, wherein the fluid path extends through the end wall to couple to a reservoir external of the end wall.
12. The magnetic coupling of claim 11, wherein the reservoir is provided adjacent to the rotor shaft.
13. The magnetic coupling of claim 12, wherein the reservoir is provided between bearings which support the rotor shaft.
14. The magnetic coupling of claim 13, wherein a seal is provided between the bearings for sealing the reservoir.
15. The magnetic coupling of any preceding claim, wherein the fluid path is sealed, such that the fluid path allows fluid flow in an outward direction and a return direction.
16. The magnetic coupling of claim 15, wherein the fluid path and reservoir provide a closed fluid system, wherein fluid flowing in the return direction is returned to the reservoir.
17. The magnetic coupling of claim 15 or 16, comprising a cooling system for cooling fluid flowing in the return direction.
18. The magnetic coupling of claims 17, wherein the cooling system is configured to cool the end wall.
19. The magnetic coupling of claim 17 or 18, wherein the cooling system is configured to cool fluid in the reservoir.
20. The magnetic coupling of any of claims 4 to 14, wherein the fluid path is open near a second end of the circumferential wall to allow used fluid to exit the first member.
21. The magnetic coupling of claim 20, comprising a casing arranged around the first member to collect the used fluid.
22. The magnetic coupling of claim 21, comprising a scavenger pump to remove the collected fluid from the casing.
23. The magnetic coupling of claim 10, wherein the fluid path has an opening through a second end of the circumferential wall to receive fluid.
24. The magnetic coupling of claim 23, wherein the fluid path has an opening through the end wall to allow used fluid to exit the first member.
25. The magnetic coupling of any preceding claim, wherein the first member is arranged to be mounted vertically to allow fluid to travel along the fluid path under the action of gravity.
26. The magnetic coupling of any preceding claim, comprising a pump configured to pump the fluid along the fluid path.
27. The magnetic coupling of claim 26, wherein the pump comprises an electric pump.
28. The magnetic coupling of claim 26 or 27, wherein the pump comprises a mechanical pump.
29. The magnetic coupling of any of claims 26 to 28, wherein the fluid pump comprises a hydraulically driven pump.
30. The magnetic coupling of any preceding claim, comprising a controller configured to control the flow of fluid along the fluid path.
31. The magnetic coupling of claim 30, wherein the 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 fluid path based on the measured temperature.
32. The magnetic coupling of claim 31, wherein the controller is configured to store an indication of a reference temperature and to control the flow of fluid along the at least one fluid path based on a comparison between the measured temperature and the reference temperature.
33. The magnetic coupling of any of claims 30 to 32 when dependent upon any of claims 26 to 29, wherein the controller is configured to control the pump to control the flow of fluid along the fluid path.
34. The magnetic coupling of any of claims 4 to 33, wherein the first and second members are arranged concentrically such that magnetic flux couples between the first array of magnetic field generating elements and the second array of magnetic field generating elements in a radial direction.
35. The magnetic coupling of any of claims 4 to 33, wherein the first and second members are axially spaced apart such that magnetic flux couples between the first array of magnetic field generating elements and the second array of magnetic field generating elements in an axial direction.
36. The magnetic coupling of claim 35, wherein the first member, the second member and the coupling member are arranged coaxially.
37. The magnetic coupling of any preceding claim, wherein one of the first and second members is coupled to an input shaft and the other of the first and second members is coupled to an output shaft.
38. The magnetic coupling of claim 37, wherein the output shaft is coupled to a flywheel.
39. The magnetic coupling 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.
40. The magnetic coupling of any preceding claim, wherein the first and second arrays have a different number of magnetic field generating elements, further comprising a coupling member provided intermediate the first and second members for coupling magnetic flux between the first and second arrays to provide a magnetic gear.
41. The magnetic coupling of claim 40 when dependent upon claim 39, wherein the coupling member forms part of a barrier enclosing the chamber.
42. The magnetic coupling of claim 40 or 41, wherein the coupling member comprises a plurality of coupling elements for coupling the flux between the first and second arrays ofmagnetic field generating elements.
43. The magnetic coupling of any of claims 40 to 42, wherein the coupling member has an outer circumferential surface.
44. The magnetic coupling of claim 43, wherein the outer circumferential surface is configured to carry the coupling elements.
45. The magnetic coupling of any of claims 43, wherein the outer circumferential comprises a plurality of recesses for supporting the plurality of coupling elements therein.
46. The magnetic coupling of claim 45, wherein the recesses are configured such that outer surfaces of the respective coupling elements carried therein are flush with the outer circumferential surface.
47. The magnetic coupling of claim 45, wherein the coupling elements are provided beneath the outer circumferential surface.
48. The magnetic coupling of any of claims 40 to 47, wherein the coupling member has an inner circumferential surface.
49. The magnetic coupling of claim 48, wherein inner surfaces of the respective coupling elements are flush with the inner circumferential surface.
50. The magnetic coupling of claim 48, wherein the coupling elements are provided beneath the inner circumferential surface.
51. The magnetic coupling of any of claims 37 to 50, comprising 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.
52. A vehicle comprising the magnetic gear of any preceding claim.
53. A method of operating the magnetic gear of any of claims 1 to 51, the method comprising: effecting relative movement between the first and second members; and supplying fluid to the at least one fluid path to cool the at least one coupling element.
54. The method of claim 53, comprising supplying water to the fluid path.
55. The method of claim 53, comprising supplying glycol to the fluid path.
56. The method of any of claims 53 to 55, comprising controlling the flow of fluid along the fluid path.
57. A magnetic gear substantially as described herein with reference to the accompanying drawings.
58. A method of operating a magnetic gear substantially as described herein with reference to the accompanying drawings.