GB2518167A

GB2518167A - A getter

Info

Publication number: GB2518167A
Application number: GB1316200.3A
Authority: GB
Inventors: Andrew Farquhar Atkins
Original assignee: Ricardo UK Ltd
Current assignee: Ricardo UK Ltd
Priority date: 2013-09-11
Filing date: 2013-09-11
Publication date: 2015-03-18
Also published as: GB201316200D0; WO2015036752A3; WO2015036752A2

Abstract

A drive assembly comprising a wall 25 defining a chamber 40 containing a drive assembly component, a port 7 on the wall of the chamber to enable access to the chamber and a removable getter device 4, wherein the getter is exposed within the chamber when the port is closed. Preferably the getter is carried by a port closure element 8. The getter may be sealed within a breachable capsule 6 which is breached by a breaching mechanism when the port is closed, where the breaching mechanism may be a mechanical piercing element or a pressure difference. Preferably there may be a heater carried by the closure element or chamber that is used to activate the getter. A drive assembly with a magnetic field generating device, a method of maintaining an environment, a getter capsule and a chamber port closing element is also claimed.

Description

A getter This invention relates to a getter.

Placing a drive assembly within a low pressure chamber can lead to a significant reduction in the windage (aft resistance) during use and therefore reduce losses due to air friction. The advantages of placing the drive assembly within a chamber are dependent on the maintenance of the low pressure within the chamber, despite the effect of processes such as out-gassing and leaks at joints and seals in the chamber. To maintain the low pressure or vacuum, despite the effect of processes such as out-gassing and leaks at joints and seals in the chamber, the chamber can be pumped out continuously or at regular intervals using a mechanical pump. As anothcr possibility or additionally, a getter material may be provided inside the chamber to adsorb gaseous molecules and/or particulate matter.

Generally, a getter may need to be baked-out or treated to remove afready sorbed material or may need to be activated, for example by removing a passivation layer on the surface of the getter. Once the passivation layer has been removed, the getter can sorb gaseous molecules and/or particulate matter from the environment. A getter may be activated by heating the getter material above an activation temperature at which the passivation layer is removed.

Over time, the efficacy of a getter decreases as a consequence of the already-adsorbed material. A getter thus has a limited lifetime and will need to be replaced before its ability to adsorb material becomes so low that the required low pressure can no longer be maintained.

However controlling the activation of a getter and enabling replacement of the getter material in the low pressure chamber may prove difficult.

Statements of invention

An embodiment of the disclosure provides a drive assembly comprising: at least one wall defining a chamber to contain a drive assembly component; a port on the wall of the chamber to enable access to the chamber a removable getter device comprising a getter, wherein the getter is exposed within the chamber when the port is closed.

The removable getter device may comprise a port closure member to close the port, the getter being carried by the port closure member.

The removable getter device may be removably carried by a port closure member.

The getter device may comprise a barrier protecting the getter, and the barrier is breached when the port is closed.

The getter may be sealed within a breachable getter capsule.

The getter device may comprise a membrane defining with the closure member a space within which the getter is sealed and providing a bather which is breached when the port is closed. The space may comprise an inert gas.

The membrane may be frangible to expose the getter to the chamber A drive assembly may comprise a breaching member to breach the barrier.

The breaching member may be a mechanical device located on one of the chamber or closure member to breach the barrier when the port is closed. The breaching member may be a piercing member.

The getter device may be configured such that a pressure difference between the interior of the getter device and the chamber breaches the barrier.

The drivc assembly may further comprisc a heater to activatc the getter. The heater may be carried by the closure member or the chamber. The heater may be a resistance or inductive heater. The heater may be configured to heat the getter is to a temperature of at least 500°C.

The getter may be mechanically activatable. The drive assembly may comprise a mechanical activator to remove sorbed material and/or a passivation layer to activate the getter.

The getter may be a non-evaporablc getter.

In an embodiment a drive assembly comprises: at least one wall defining a chamber to contain a drive assembly component; a getter receiving member within the chamber; and a magnetic field generating device associated with the chamber, wherein the magnetic field generating device is arranged to induce a current to heat and activate a getter received by the getter receiving member.

The getter receiving member may be electrically conductive.

The getter receiving member may be mounted to the wall of the chamber.

The drive assembly may comprise a magnetic drive arrangement comprising a first member having a first array of magnetic field generating clement and a second member having a sccond array of magnetic field generating elements, the first member may be providcd within the chamber and being coupled to the drive assembly component and the second member provided outside the chamber and arranged to be coupled to a drive.

The drive assembly may comprise a magnetic field generating device comprising a magnetic drive arrangement comprising a first member having a first array of magnetic field generating element and a second member having a second array of magnetic field generating elements, the first member may be provided within the chamber and be coupled to the drive assembly component and the second member may be provided outside the chamber and arranged to be coupled to a drive.

The drive assembly may comprise a coupling member, wherein the coupling member may be provided between the first and second members for coupling magnetic flux between the first and second arrays.

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

The first and second members 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 first member, the second member and the coupling member may be arranged coaxially.

The coupling member may form part of the at least one wall of the chamber.

Thc chamber may be a vacuum chamber.

The drive assembly may be a flywheel assembly and the drive assembly component comprises a flywheel.

The drive assembly may be a pump assembly and the drive assembly component comprises a pump impeller.

An embodiment may provide a method of a maintaining an environment within a chamber of a drive assembly, the method comprising heating a getter device to activate the getter and then introducing the heated getter into the chamber via a port of the chamber.

The method may comprise the getter device being carried by or comprises a port closure member and the getter device is heated prior to or during closure of the chamber. The getter may be heated to a temperature of at least 500°C. Heating the getter device may activate the getter by removing sorbed material and!or a passivation layer.

The method may comprise removing the getter device after use and replacing the getter device with a new getter device.

The method may comprise removing the getter device after use and replenishing the getter device with getter.

The method may comprise the getter being a non-evaporable getter.

In an embodiment a getter capsule comprises a substrate carrying a getter and a breachable barrier protecting the getter. The barrier device may comprise a membrane defining with the substrate a space within which the getter is scaled. The space may comprise an inert gas. The membrane may be frangible to expose the getter.

The vacuum chamber port closure member may comprise a getter capsule.

Detailed description

Embodiments will now be described, by way of example, with reference to the accompanying drawings in which: Figure Ia shows a diagrammatic cross-sectional view of a port closure member of a low pressure chamber with a getter device carried by the port closure member and sealed within a barrier; Figure lb shows a diagrammatic cross-sectional view of a getter capsule with a getter device sealed within a barrier; Figure 2 shows a diagrammatic cross-sectional view of a chamber wall, a port and an example of the port closure member of Figure Ia; Figure 3a shows a schematic cross-section of a magnetic gear in a plane normal to an axis of rotation of the magnetic gear; Figure 3b shows a schematic cross-section of part of a coupling member; Figure 4 shows a diagrammatic cross-sectional view of a drive assembly similar to that shown in Figure 4 but with a gefter provide by a port closure member; Figure 5 shows a diagrammatic cross-sectional view of a drive assembly having a magnetic gear with a flywheel located within a low pressure chamber containing a getter capsule; and Figure 6 shows a diagrammatic cross-sectional view of drive assembly similar to that shown in Figure 4 but with a getter received by a wall of the low pressure chamber.

Referring now to Figures 1 to 4, particularly Figure 4, disclosed herein is a drive assembly 300 having at least one wall defining a chamber 40 to contain a drive assembly component 90; a port 7 on the wall of the chamber 25 to enable access to the chamber; a removable getter device 4 comprising a getter, wherein the getter is exposed within the chamber when the port 7 is closed.

Referring now specifically to Figures Ia and 2, there is shown a diagrammatic cross-sectional view of such a port closure member 8.

Figure 2 shows the port closure member 8 located within the port 7 of the chamber 40 defined by the wall of the chamber 25. In the example shown in Figure 2 the port closure member 8 is fixable to the port of the chamber 40 with thc port closure member 8 comprising a fixing member 26 and a fixing receiving member 19 located on an interface between the port 7 and the chamber wall 15. In this example the fixing mechanism is a screw and thread mechanism where the port closure member 8 is fixed to the chamber 40 by rotating the port

S

closure member 8 relative to the chamber 40. The port closure member 8 also comprises a seal 9 that can be coupled to the chamber wall 15 to form a seal between the port closure member 8 and the port 7.

The port closure member 8 comprises a getter device 4, in this example a non-evaporable getter, coupled to the port closure member 8 such that the getter device is exposed within the chamber when the port is closed by the port closure member.

The getter may be a non-evaporable getter, for example a mixture of Aluminium, Zirconium, Titanium, Vanadium andior Iron.

Figures Ia and 2 show an example of a port closure member 8 where a barrier 6 is arranged to protect the getter device 4. In the example shown in Figures Ia and 2, the barrier 6 is frangible or may be breached by a breaching member 5 as the port closure member 8 closes the port 7. The breaching member 5 may be a piercing member, as shown in Figure 2, which breaches the barrier 6 as soon as the port closure member is in place. In this example the breaching member 5 is coupled to the chamber wall 25 and is positioned such that when the port closure closes the port, the barrier 6 is moved towards the breaching member 5 and as the port closes tines 5a of the breaching member pierce the barrier. In other examples the breaching member may breach the barrier by cutting or tearing the barrier. In other examples, the breaching member may be coupled to the port closure member and movable into a breaching position as thc port is closed, the fixing member 26 or fixing receiving member 19.

The space within the barrier may comprise an inert gas, in this example Helium gas. In other examples, the space defined by the barrier and the port closure member may comprise a vacuum or any other gas that is unreactive with the surface of the getter and suitable for use within the low pressure chamber, for example Argon, Nitrogen, or any suitable noble gas.

In the example described above, the barrier is breached by a breaching member, in other examples the barrier 6 may be configured such that a pressure difference between the interior of the getter device and the chamber causes rupture or breaching of the barrier. In another example the barrier may be breached by applying heat to the barrier, for example by deforming the barrier on the application of heat or by melting the barrier.

In another example, the space defined by the barrier and the port closure member may comprise a solid or a liquid that when heated sublimes or evaporates so to increase the pressure difference between the interior of the getter device and the chamber and cause rupture or breaching of the barrier.

In another example, there may not be a space defined by the barrier and the port closure member, for example the barrier may be provide by a material coating that may be breached by, for example, heating to remove (e.g. by sublimation) or melt at least part of the coating.

In another example, as shown in Figure ib, the getter device 4 of Figure la may not be coupled to a port closure member S. In this example the getter device is sealed within the barrier 6 (as described in Figure Ia) to form a capsule 3. The barrier 6 may be breached by a breaching member inside the chamber using any of the various mechanisms described above.

In another example the capsule may comprise a getter device 4 coupled to a substrate with the getter device sealed with a barrier 6. The capsule may be removably carried by a port closure member or be placed into the chamber before closing the port.

The getter material may comprise sorbed material and/or a passivation layer on the surface that inhibits the rate of adsorption of material onto the surface of the getter. Such a getter is activated to increase the rate of adsorption by an activation process that removes the sorbed material and/or the passivation layer, at least partially, from the surface of the getter. The getter may be activated by heating the getter to above an activation temperature at which the sorbed material on the getter is at least partially removed and/or passivation layer is at least partially removed or by a process of mechanical activation.

The getter may be activated before being introduced into the chamber, for example by heating the getter above the activation temperature. In an example where the getter is activated before being introduced into the chamber it may be activated a shortly before entering chamber, or activated and then sealed using the barrier 6 to inhibit the active getter reacting with the atmosphere. In another example the getter may be activated whilst in the chamber, for example by heating the getter when the getter is within the chamber. When the getter is mechanically activated, this may be either whist the getter is in the chamber or before the getter enters the chamber, a process using, for example, a percussive, cutting or abasing device is used to mechanically activate the getter. The process of mechanical activation may shatter the getter device or abrade/scrape to expose the getter material covered by the sorbed material and!or the passivation layer.

In the example shown in Figures la and 2 the getter may be activated by heating the getter when the getter is in the chamber. For example, when the port closure member 8 is located in the port 7, as shown in Figure 2, to close the chamber heat may be applied to the port closure member 8 using a resistive heater (not shown) carried by the port closure member 8. The temperature to which the getter needs to be heated to remove the sorbed material and/or the passivation layer may depend upon the getter and could be, for example, at least 500°C.

In other examples the port closure member 8 may be heated by, for example an inductive heater as well as or instead of the resistive heater described above.

The heater described above is carried by the port closure member 8, in another example the heater may be carried by the chamber or any other appropriate part of the drive assembly.

In other examples, a remote heater may be used to heat up a surface of the port closure member, for example a laser or microwave remote heater may be used.

The drive assembly may comprise a driving and driven member, as shown in Figures 3 to 6.

The driving and driven member may be coupled using a magnetic gear, as shown in Figures 3a and 3b. The drive assembly and magnetic gear shown in Figures 3 to 6 comprises a first member 10 provided within a chamber coupled to a drive assembly component of the drive assembly, and a second member 20 provided outside the chamber 40 and arranged to be coupled to the drive member. As described above, the driven member is provided within a low pressure chamber 40 to reduce windage. In the examples described in Figures 4 to 6 a getter device is located within the low pressure chamber to reduce the pressure in the chamber.

Figure 3a shows a schematic cross-section of an example of a maguetic 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 of the drive assembly comprises the first member 10, the 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 mcmbcr 10, the coupling member 30 and the second mcmbcr 20 are arranged concentrically. The first member 10 and the sccond 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 Figures 4 to 6) providing the drive member.

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 3. 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 Figures 4 to 6) of the driven member 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 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 3. 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 arc spaced apart by the non-conductive material. The magnetic field generating elements 22 may be frilly or partially embedded in the non-conductive material.

Thc number of magnctic field generating clcmcnts, m, of the fir st mcmbcr 20 is largcr than the number of magnetic field generating elements, n, of the second member 20. The illustrated gear therefore provides a step-up gear, 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/m is the gear ratio of the magnetic gear 100.

Thc coupling mcmbcr 30 forms part of a barrier at least partially cnclosing thc chamber 40 containing the second member 20. The bather forms part of a housing of the chamber 40. 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 3a 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 bather is a sealed barrier with a sealed coupling to the wall of the chamber 40, a scaled chamber 40 may be provided, such as a vacuum or low-pressure chamber. I-lousing the second member 20 in such a chamber may reduce "windage" and other frictional losses.

Figure 3b 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 3a. As illustrated in Figure 3b, the coupling member 30 comprises a non-conductive material 31 having an outer circumferential surface 3 Ia with a plurality of recesses 3 lb for supporting coupling elements of the array of coupling elements 32. The recesses 31 b are spaced apart around the outer circumferential surface 31a such that consecutive coupling elements 32 arc spaced apart by the non-conductive material 31. The recesses 3 lb are such that outer surfaces 32a of the coupling elements 32 (surfaces that face away from the chamber 40) received in the recesses are flush with the outer circumferential surface of the coupling member 30. Inner circumferential surfaces 32b of the coupling elements 32 (surfaces that face towards the chamber 40) may be provided beneath an inner circumferential surface 31 c 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 cxamplc 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 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.

Each of Figures 4 to 6 shows cross-sections along the axis of rotation of a flywheel system 300 comprising the magnetic gear 200 of Figure 3, 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 which is at least partially enclosed by a second housing portion 70. The coupling member is disposed between the first and second member 10, 20 and provides a bather that forms part of a housing of the chamber 40, together with the second housing portion 70. Two elements of the fir st array of magnetic field generating elements 12 carried on the inner surface 16 of the 1ff st 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.

Figures 4 to 6 show 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 3a, 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 aweb 21 coupled to the circumfercntial 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 fbr 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 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 shown the rim 92 is a composite rim.

The output rotor 24 may be arranged to couple the flywheel 90 to a drive system, for example a drive system of in a vehicle, or to another rotationally driven system such as an impeller pump.

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 rotate relative to the first member 10 at a speed determined by the gear ratio m'n. 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, 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.

Figures 4, 5 and 6 show examples of the getter device within a vacuum or low pressure chamber. Figure 4 shows an example where the port closure member of Figures la and 2 is fixed in the port of the vacuum or low pressure chamber. The port 7 is located on the chamber wall 15 with the port closure member 8 of Figures 1 and 2 fixed to the port 7 and the getter device 4 is within a space defined by the port closure member 8 and the barrier 6.The barrier may be breached to expose the getter to the atmosphere of the chamber 40 in any of the ways described above.

Figure 5 shows an example of the capsule of Figure lb positioned in the low pressure chamber. In this example, the capsule comprises a getter device 4 and barrier 6 and is placed in the chamber via the port 7. In this example the barrier may be breached in any of the ways described above, for example from the pressure differential between the gas within the barrier to the pressure of the chamber.

Figures 4 and 5 show the port in close proximity to the flywheel, in other examples the port may be located in any location on the wall of chamber, therefore providing access for the getter 4 on the port closure member 8 to the atmosphere of the chamber.

Figure 6 shows an embodiment in which a getter receiving member 4a is provided within the chamber; and a magnetic field generating device associated with the chamber 40, wherein the magnetic field generating device in the drive assembly is located so that it provides a changing magnetic field that passes through the getter receiving member 4a will induce an eddy current and thus lead to inductive heating of the getter receiving member 4a. The increased temperature of the getter receiving member 4a will activate the getter material and lead to gaseous molecules being adsorbed by the getter.

The getter receiving member described with reference to Figure 6 may be mounted to any of the walls of the chamber that is exposed to a change in magnetic field. In another example the getter receiving member may be the wall of the chamber and the getter received by the wall of the chamber with the eddy current induced in the chamber wall 15 heating the getter.

In the example described in Figure 6 the getter is exposed to the atmosphere of the chamber, in another example the getter may be enclosed by a barrier as described above.

It will be appreciated that while the above disclosure is couched in terms of a magnetic gear, aspects of the disclosure arc also applicable to a magnctic 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 req uire 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 fir st 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.

The above disclosure describes material being adsorbed onto the surface of the getter, it will be appreciated that material may also be absorbed in to the getter.

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 drive assembly comprising: at least one wall defining a chamber to contain a drive assembly component; a port on the wall of the chamber to enable access to the chamber; a removable getter device comprising a getter, wherein the getter is exposed within the chamber when the port is closed.
2. A drive assembly according to claim 1, wherein the removable getter device comprises a port closure member to close the port, the getter being carried by the port closure member.
3. A drive assembly according to claim 1, wherein the removable getter device is removably carried by a port closure member.
4. A drive assembly according to claim 1, 2 or 3, wherein the getter device comprises a barrier protecting the getter, and the barrier is breached when the port is closed.
5. A drive assembly according to claim 1, 2 or 3, wherein the getter is sealed within a breachable getter capsule.
6. A drive assembly according to claim 2 or 3, wherein the getter device comprises a membrane defining with the closure member a space within which the getter is sealed and providing a barrier which is breached when the port is closed.
7. A drive assembly according to claim 6, wherein the space comprises an inert gas.
8. A drive assembly according to claim 6 or 7, wherein the membrane is frangible to expose the getter to the chamber
9. A drive assembly according to any of claims 4 to 8, further comprising a breaching member to breach the bather.
10. A drive assembly according to claim 9, wherein the breaching member is a mechanical device located on one of the chambcr or closure member to breach the barrier when the port is closed.
11. A drive assembly according to claim 9 or 10, wherein the breaching member is a piercing member.
12. A drive assembly according to any of claims 4 to 8, wherein the getter device is configured such that a pressure difference between the interior of the getter device and the chamber breaches the barrier.
13. A drive assembly according to any preceding claim, further comprising a heater to activate the getter.
14. A drive assembly according to claim 13, wherein the heater is carried by the closnre member.
15. A drive assembly according to claim 13, wherein the heater is carried by the chamber.
16. A drive assembly according to claim 13, 14 or 15, wherein the heater is a resistance or inductive heater.
17. A drive assembly according to any of claims 13 to 16, wherein the heater is configured to heat the getter is to a temperature of at least 500°C.
18. A drive assembly according to any preceding claim, wherein the getter is mechanically aetivatable.
19. A drive assembly according to claim 18, comprising a mechanical activator to remove sorbed material and!or a passivation layer to activate the getter.
20. A drive assembly according to any preceding claim, wherein the getter is a non-evaporable getter.
21. A drive assembly comprising: at least one wall defining a chamber to contain a drive assembly component; a getter receiving member within the chamber; and a magnetic field generating device associated with the chamber, wherein the magnetic field generating device is arranged to induce a current to heat and activate a getter received by the getter receiving member.
22. A drive assembly according to claim 21, wherein the getter receiving member is electrically conductive.
23. A drive assembly according to claim 21 or 22, wherein the getter receiving member is mounted to the wall of the chamber.
24. A drive assembly according to any preceding claim, comprising a magnetic drive arrangement comprising a first member having a first array of magnetic field generating element and a second member having a second array of magnetic field generating elements, the first member being provided within the chamber and being coupled to the drive assembly component and the second member provided outside the chamber and arranged to be coupled to a drive.
25. A drive assembly according to claim 21, 22 or 23, wherein the magnetic field generating dcvicc comprises a magnctic drivc arrangcmcnt comprising a first mcmbcr having a first array of magnetic field generating element and a second member having a second array of magnetic field generating elements, the first member being provided within the chamber and being coupled to the drive assembly component and the second member provided outside the chamber and arranged to be coupled to a drive.
26. A drive assembly according to claim 24 or 25, wherein a coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and sccond arrays.
27. A drive assembly according to claim 24 or 25, wherein the first and second members arc arrangcd concentrically for relative rotation thcrcbctwccn, wherein a coupling member is provided intermediate the first and second members for coupling magnetic flux between the first and second arrays in a radial direction.
28. A drive assembly according to claim 24 or 25, wherein the first and second members are axially spaced apart, wherein the coupling member is provided intermediate the first and second members for coupling maetic flux between the first and second arrays in an axial direction.
29. A drive assembly according to claim 28, wherein the first member, the second member and the coupling member are arranged coaxially.
30. A drive assembly according to any of claims 26 to 29, wherein the coupling member forms part of the at least one wall of the chamber.
31. A drive assembly according to any preceding claim, wherein the chamber is a vacuum chamber.
32. A drive assembly according to any of claims 21 to 31, wherein the getter is a non-evaporable getter.
33. A drive assembly according to any preceding claim, wherein the drive assembly is a flywheel assembly and the drive assembly component comprises a flywheel.
34. A drive assembly according to any ofclaims I to 32, wherein the drive assembly is a pump assembly and the drive assembly component comprises a pump impeller.
35. A method of a maintaining an environment within a chamber of a drive assembly, the method comprising heating a getter device to activate the getter and then introducing the heated getter into the chamber via a port of the chamber.
36. A method according to claim 35, wherein the getter device is carried by or comprises a port closure member and the getter device is heated prior to or during closure of the chamber.
37. A method according to claim 35 or 36, wherein the getter is heated to a temperature of at least 500°C.
38. A method according to claim 35,36 or 37, wherein heating the getter device activates the getter by removing sorbed material and/or a passivation layer.
39. A method according to claim 35, 36, 37 or 38, further comprising removing the getter device after use and replacing the getter device with a new getter device.
40. A method according to claim 35, 36, 37 or 38, further comprising removing the getter device after use and replenishing the getter device with getter.
41. A method according to any of claims 35 to 40, whcrcin the getter is a non-cvaporable getter.
42. A getter capsule comprising a substrate carrying a getter and a breachable barrier protecting the getter.
43. A getter capsule according to claim 42, wherein the barrier device comprises a membrane defining with the substrate a space within which the getter is sealed.
44. A getter capsule according to claim 43, wherein the space comprises an inert gas.
45. A getter capsule according to claim 43 or 44, wherein the membrane is frangible to expose the getter.
46. A vacuum chamber port closure member comprising a getter capsule according to any of claims 42 or 45.