VACUUM PUMP COMPRISING AN AXIAL MAGNETIC BEARING AND A RADIAL GAS FOIL BEARING

Abstract

A vacuum pump and method of mounting a shaft within a vacuum pump is disclosed. The vacuum pump comprises a rotor and a stator. The rotor comprises a shaft comprising pumping elements extending therefrom. The shaft is mounted to rotate and is supported by a plurality of bearings, the plurality of bearings comprising: an axial magnetic bearing and two radial bearings, at least one of the two radial bearings comprising a gas foil bearing.

Claims

1. A vacuum pump comprising a rotor and a stator, said rotor comprising a shaft comprising pumping elements extending therefrom; said shaft being mounted to rotate and being supported by a plurality of bearings, said plurality of bearings comprising: two radial bearings, at least one of said two radial bearings comprising a radial gas foil bearing; and an axial bearing, said axial bearing consisting of an axial active magnetic bearing.

2-4. (canceled)

5. The vacuum pump according to claim 1, wherein said two radial bearings comprise said gas foil bearing and a radial magnetic bearing said radial magnetic bearing being located close to a portion of said shaft supporting said pumping elements and said radial gas foil bearing being located remotely from said portion of said shaft supporting said pumping elements.

6. The vacuum pump according to claim 5, wherein said radial magnetic bearing comprises a radial passive magnetic bearing.

7. (canceled)

8. The vacuum pump according to claim 1, said vacuum pump further comprising a seal to seal a portion of said vacuum pump comprising said pumping elements from a portion of said vacuum pump comprising said at least one radial gas foil bearing.

9. The vacuum pump according to claim 8, said vacuum pump comprising a sealing element to seal a portion of said vacuum pump comprising said pumping elements and said magnetic bearing from a portion of said vacuum pump comprising said radial gas-foil bearing.

10. The vacuum pump according to claim 1, said vacuum pump, further comprising a motor for rotating said shaft, said motor being mounted between said two radial bearings.

11. The vacuum pump according to claim 1, said vacuum pump being configured to operate in an orientation where said shaft extends vertically and said axial magnetic bearing is configured to support and levitate said shaft.

12. The vacuum pump according to claim 1, wherein said vacuum pump comprises a turbomolecular pump.

13. A method of mounting a shaft of a rotor of a vacuum pump, said method comprising: supporting said shaft with an axial active magnetic bearing and with two radial bearings, at least one of said two bearings comprising a radial gas foil bearing.

14. The method according to claim 13, wherein said two radial bearings comprise said gas foil bearing and a radial magnetic bearing, said radial magnetic bearing being located close to a portion of said shaft supporting said pumping elements and said radial gas foil bearing being located remotely from said portion of said shaft supporting said pumping elements.

15. The vacuum pump according to claim 1, wherein said two radial bearings comprise radial gas foil bearings.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0034] FIG. 1 shows a rotor of a vacuum pump according to an embodiment; and

[0035] FIG. 2 shows a vacuum pump according to a further embodiment.

DETAILED DESCRIPTION

[0036] Before discussing the embodiments in any more detail, first an overview will be provided.

[0037] Vacuum pumps that have shafts supported by five axis active magnetic bearings provide an effective, oil free bearing system that is however, expensive. As an alternative to a 5 axis active magnetic bearing oil free system some vacuum pump use a 1 axis active system, that is a system with an active axial magnetic bearing and with 2 passive radial magnetic bearings. Such a system takes advantage of the relatively low cost of a simpler 1 axis system. However the cost of the permanent magnets for the radial bearings is still significant and these bearings also inherently provide low damping. Such a system therefore requires additional dampers and/or may have limited operating conditions.

[0038] An alternative is the use of gas bearings, in particular gas foil bearings for the 2 radial and the 1 axial, double acting active bearing. However, the power losses and the starting torque of such an arrangement is high and this may be an issue for certain vacuum pumps.

[0039] The inventor of the present invention recognised that a high proportion of the losses and high starting torque of a system supported by gas foil bearings comes from the axial foil bearing, which has a higher load and a relatively large radius when compared to the radial bearings. Thus, these competing problems have been addressed by providing a system that uses a 1 axis axial magnetic bearing for the axial bearing, with radial bearings at least one of which is a gas foil bearing. Such a system combines the benefits of both technologies to provide an effective and lower cost solution for high speed vacuum pumps.

[0040] If a seal is required to separate the bearings from the vacuum (i.e. if the pump is not exhausting to atmosphere but to vacuum pressure, such as is the case for a turbomolecular pump) a shaft rotary seal can be used. In some embodiments the rotary seal may be a foil seal.

[0041] A vacuum pump is disclosed whose shaft is supported by a combination of different bearing technologies which include: [0042] an axial magnetic bearing, preferably an active magnetic bearing to support the shaft axially [0043] 2 radial bearings to support the shaft radially, at least one of which is a gas foil bearing.

[0044] In some embodiments, the pump is provided with a shaft rotary seal to separate the gas bearings from the vacuum and provide the necessary conditions for gas bearings to work; this may be a foil seal using the same principles as the gas foil bearing.

[0045] FIG. 1 schematically shows a vacuum pump 5 according to an embodiment. In this embodiment the vacuum pump is a turbomolecular pump. Turbomolecular pump 5 comprises a shaft 10 supporting a rotor 12 with pumping elements 14 extending therefrom within a stator (not shown). The shaft 10 is driven by motor 30 and is rotatably mounted within a pump housing by magnetic axial bearing 40 and two radial bearings 42 and 44. In this embodiment the lower bearing 42 comprises a gas foil bearing as does the upper bearing 44. In other embodiments one of the two bearings may be a different type of bearing such as a roller bearing or a different type of gas bearing.

[0046] The motor 30 and bearings 40, 42 and 44 are separated from the vacuum enclosure of the vacuum pump by a vacuum seal 50.

[0047] Gas foil bearings provide low friction operation when rotating at speeds sufficient for aerodynamic operation, however, at lower speeds such as at startup they require considerable torque for rotation. The use of a magnetic axial bearing 40, which as can be seen has a relatively large radius, significantly reduces the torque required to initiate rotation of the rotor when compared to one mounted exclusively on gas foil bearings and results in a system that can operate with a motor 30 that is of a similar size to a conventional motor for such a vacuum pump. The use of the gas foil bearings provides non-contacting bearings with good damping and vibration resistance. Their operation at high speed is particularly effective and allows the vacuum pump to operate effectively and power efficiently. Gas foil bearings operate at atmospheric pressure, and thus, a vacuum seal 50 is used to isolate the vacuum enclosure and the bearings. Mounting the motor between the bearings provides axial displacement of the two radial bearings allowing for more stable support of the shaft. Furthermore, the motor 30 is isolated from the vacuum enclosure by the same vacuum seal 50 that isolates the gas foil bearings.

[0048] FIG. 2 shows an alternative embodiment where there is a magnetic axial bearing 40 supporting the shaft and two radial bearings. One of the radial bearings 42 is a gas foil bearing. In this case, the upper radial bearing 46 is a magnetic bearing and is within the vacuum enclosure. Seal 50 is located between the two radial bearings 42, 46. In this embodiment, the upper radial magnetic bearing 46 is a passive magnetic bearing while the lower axial magnetic bearing 40 is an active magnetic bearing.

[0049] An advantage of having the upper bearing 46 as a magnetic bearing is that it can be within the vacuum enclosure and allows the two radial bearings to be spaced apart and the seal 50 to be located between the two bearings. Although magnetic bearings can be more expensive than gas foil bearings they do provide different properties and the gas foil bearing will provide resistance to vibrations and effective damping while the magnetic bearing will provide a lower starting torque and it is possible to place it within the vacuum environment.

[0050] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0051] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0052] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.