Magnetic bearing hub and vacuum pump

Abstract

A magnetic bearing hub (21) for a vacuum pump includes a base element (24) coupled to a housing (10) of the vacuum pump and a trunnion (20) extending from the base element (24), the trunnion (20) configured to receive a stationary magnetic element of a magnetic bearing (18), the trunnion (20) having a predetermined break point (28).

Description

[Technical field]

[0001] The present invention relates to a magnetic bearing hub for a vacuum pump and to a vacuum pump equipped with such a magnetic bearing hub. [Background technology]

[0002] A typical vacuum pump, and in particular a turbomolecular pump, comprises a housing having an inlet and an outlet. In the housing, a rotor assembly is rotated by an electric motor and supported by a bearing or bearing system. The rotor assembly comprises at least one rotor element interacting with at least one stator element to convey the gas medium from the inlet to the outlet. In particular, in the case of a turbomolecular pump, the rotor assembly comprises a number of vanes interacting with vanes of the stator. In this regard, the rotor assembly is usually supported by two bearings, which can be formed as roller bearings or magnetic bearings. In particular, the bearing on the inlet side, i.e. towards the end of the rotor assembly in the direction of the inlet of the vacuum pump, can be formed as a permanent magnetic bearing. In this regard, a rotating magnetic element is coupled to the rotor and a stationary magnetic bearing is coupled to the housing. The stationary magnetic bearing and the rotating magnetic bearing repel each other in close proximity to support the rotor shaft. In this regard, the stationary magnetic element of the permanent magnetic bearing can be arranged on a trunnion extending into a recess of the rotor assembly, the rotating magnetic element being adapted to surround the stationary element. The trunnion is connected to the housing by webs or legs, also called "spiders" or "envelopes," which provide structural stability for the trunnion, and thus for the permanent magnet bearing itself.

[0003] Due to the high rotational speeds, the rotational forces that need to be released in the event of a vacuum pump crash are large. There is therefore a risk that parts of the vacuum pump will enter the associated vacuum system and cause damage. This is especially true if the webs that hold the trunnions break in an uncontrolled manner. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE PRESENT EMBODIMENT It is therefore an object of the present invention to provide a magnetic bearing hub and a vacuum pump which reduces damage to a vacuum system coupled to the vacuum pump in the event of a vacuum pump crash. [Means for solving the problem]

[0005] This problem is solved by a magnetic bearing hub according to claim 1 and by a vacuum pump according to claim 11.

[0006] In a first aspect, the present invention relates to a magnetic bearing hub for a vacuum pump, in particular a turbomolecular vacuum pump. The magnetic bearing hub comprises a base element coupled to a housing of the vacuum pump, for example via two or more webs or legs. The magnetic bearing hub further comprises a trunnion extending from the base element, the trunnion being configured to receive a stationary magnetic element of the magnetic bearing. In particular, the stationary magnetic element may comprise a plurality of permanent magnet rings. In an assembled state, the trunnion may extend into a recess of a rotor assembly of the vacuum pump, the stationary magnetic element being surrounded by a rotating magnetic element coupled to the rotor assembly. Alternatively, the stationary magnetic element surrounds the rotating magnetic element. According to the present invention, the trunnion has a predetermined breaking point. Thus, when the vacuum pump crashes, the trunnion breaks at the predetermined breaking point and separates from the base element. This division between the base element coupled to the web and the trunnion protects the web from being broken or damaged and helps the rotor assembly to crash against the stator element. The rotation of the rotor assembly is thereby inhibited by friction between these components. Thus, the web is protected from breakage, thereby avoiding the release of large pieces of the vacuum pump into the vacuum chamber of a vacuum device coupled to the vacuum pump. Furthermore, the controlled breakage of the components releases energy, thereby reducing the risk of further component breakage.

[0007] Preferably, the predetermined breaking point is formed by a thinned section, thus providing the predetermined breaking point by a thinned section, the thinned section being a section of reduced thickness such that the breaking point occurs at the location of the thinned section.

[0008] Preferably, the thinned section is formed as a circumferential groove, in which case the groove may be provided on the inner surface of the trunnion, however, for ease of manufacture, the groove is provided on the outer surface of the trunnion, which reduces the wall thickness of the trunnion.

[0009] Preferably, the groove has a conical, wedge or rectangular shape. The particular choice of shape allows for tuning of the stability of a given break point, allowing for breakage of the trunnion at the location of the groove in the event of a vacuum pump crash.

[0010] Preferably, the thinned section is defined by an internal bore extending into the trunnion from an end opposite the base element to an axial end of the thinned section or beyond the thinned section, thereby reducing the material strength of the trunnion and enabling it to be separated from the base element.

[0011] Preferably, the wall thickness of the thin-walled section is less than 80% compared to the wall thickness of the remainder of the trunnion. Thus, in a preferred embodiment, if the minimum wall thickness of the remainder of the trunnion is 10 mm, the thin-walled section will have a wall thickness of less than 8 mm. Preferably, the thin-walled section has a thin section of less than 60%, most preferably less than 50%. The wall thickness is selected such that on the one hand a sufficient stability of the magnetic bearing hub is maintained and on the other hand a breakage of the magnetic bearing hub in the region of the thin-walled section is permitted.

[0012] Preferably, the cross-sectional area of ​​the thinned section is smaller than the cross-sectional area of ​​one of the legs or webs, in particular, the cross-sectional area of ​​the thinned section is between 4% and 20%, preferably between 4% and 10%, more preferably between 5% and 8% of the cross-sectional area of ​​one of the legs or webs.

[0013] Preferably, the predetermined breaking point is configured to break during the crash, i.e. in a time window up to 20 ms, preferably up to 10 ms, after the crash, at 10% to 50% of the maximum torque of the rotor of the vacuum pump. In this regard, torque values ​​of 1 kN to 2.2 kN can be observed during the crash. However, these values ​​depend on the rotor speed, the pump type and other parameters. More preferably, the predetermined breaking point is configured to break at 15% to 40%, most preferably 20% to 25% of the maximum torque of the rotor of the vacuum pump. Thus, one of the first parts to break is the trunnion, which is separated from the spider legs or webs supporting the magnetic bearing hub, preferably ensuring that it breaks without damaging the webs or spider legs.

[0014] Preferably, the predetermined breaking point is located between the stationary magnetic element and the base element. This ensures that the stationary magnetic element is separated from the base element together with the trunnion. In particular, in the event of a crash, the rotating magnetic element and the stationary magnetic element collapse and join together. In addition, by collapsing the magnetic elements together, the fragile magnetic material is trapped and cannot exit to other areas of the vacuum pump and / or vacuum device. At the same time, the trunnion split of the base element is also attached to the rotor assembly by magnetic forces and cannot exit in an undesirable way. However, additionally or alternatively, the web can also stop any parts that are ejected towards the inlet of the vacuum pump.

[0015] Alternatively or additionally, the predetermined break point is located directly adjacent the base element.

[0016] Alternatively or additionally, the predetermined break point is located between an axial end of the rotor of the vacuum pump and the base element, such that the predetermined break point is axially beyond the axial end of the rotor or at least beyond the rotor extension that extends into the trunnion, the trunnion surrounding the axial end of the rotor / rotor extension and allowing separation of the trunnion.

[0017] Preferably, the predetermined break point is configured so as not to cause natural frequencies of the magnetic bearing and / or the envelope / spider or other assemblies and subassemblies of the pump in the operating frequency range of the vacuum pump. Thus, in addition to determining the break of the magnetic bearing hub, the predetermined break point can be configured to provide reduced resonance in the frequency range of the vacuum pump during operation. In this regard, the resonant frequency of the magnetic bearing hub can be adjusted by adapting the shape of the predetermined break point, i.e. the shape of the groove, introducing two or more grooves, etc., or using a specific material to fill one or more of these grooves, or by providing a weakened section as the predetermined break point.

[0018] Preferably, the magnetic bearing hub has only one predetermined break point, or alternatively, the magnetic bearing hub has two or more predetermined break points configured to break under different or the same torque / radial loads applied by the rotor during a crash.

[0019] In another aspect, the present invention relates to a vacuum pump comprising a housing having an inlet and an outlet, and a rotor assembly supported by at least one permanent magnetic bearing, wherein the magnetic bearing comprises a magnetic bearing hub as described above.

[0020] Preferably, the magnetic bearing is formed at the end of the rotor assembly located towards the suction side, i.e. the inlet to the vacuum side, of the vacuum pump.

[0021] Preferably, the magnetic bearing hub is connected to the housing via webs, which are preferably formed integrally with the housing and / or the magnetic bearing hub. Thus, the webs can be formed integrally with the housing, i.e. the flange of the vacuum pump, or with the magnetic bearing hub. Alternatively, the webs are formed integrally with the housing and the magnetic bearing hub. Thus, forming the webs and the magnetic bearing hub integrally increases stability.

[0022] Preferably, the predetermined breaking point is configured to break before the connection between the web and the housing and / or the connection between the web and the magnetic bearing hub breaks.

[0023] Preferably, the web and / or the magnetic bearing hub are made of aluminum, stainless steel or carbon fiber material. In particular in this regard, the web and / or the magnetic bearing hub are formed by an additive manufacturing process such as 3D printing. Alternatively, the web and / or the magnetic bearing hub are formed by conventional machining methods.

[0024] Preferably, the web has a predetermined breaking point, preferably located at the connection of the web with the housing. In this regard, the predetermined breaking point of the web is configured to break at a rotational and / or radial force greater than the force required to break the predetermined breaking point of the magnetic bearing hub. Thus, it is ensured that the trunnion separates from the base element first. If for some reason separation does not occur in the next step, the web can break at the predetermined breaking point in order to avoid damage to the vacuum pump components due to breakage in an uncontrolled manner.

[0025] The invention will now be described in more detail with reference to the accompanying drawings, in which: FIG. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic diagram of a turbomolecular pump according to the present invention; [Diagram 2] FIG. 4 is a detailed view of the magnetic bearing hub. [Diagram 3] FIG. 2 is a top view of the vacuum pump of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The vacuum pump of FIG. 1 comprises a housing 10 having an inlet 12 and an outlet 14. In this regard, a flange 13 is coupled to the inlet side of the vacuum pump, by means of which the vacuum pump can be coupled to a vacuum device. The vacuum pump comprises a rotor assembly 16, to which a number of rotor elements 34 are coupled. The rotor elements 34 are formed as vanes that interact with vanes of a stator element 36 coupled to the housing 10. Furthermore, the vacuum pump of FIG. 1 comprises a Holweck stage 18 consisting of a rotating cylinder 40 and a threaded stator 42, the Holweck stage 38 being arranged downstream of the turbomolecular pump stage. Instead of the Holweck stage 28, other molecular drag stages, such as a Siegbahn stage, may be present.

[0028] The rotor assembly 16 is rotated by an electric motor 32 and rotatably supported by roller bearings 33 at the end of the rotor assembly 16 facing the outlet side, i.e. the outlet 14, and at the end opposite the axial end of the rotor assembly 16 facing the inlet 12 of the vacuum pump. In addition, the rotor assembly is rotatably supported by a magnetic bearing 18 arranged at the inlet side of the rotor assembly 12. The magnetic bearing 18 comprises a magnetic bearing hub 21. The magnetic bearing hub 21 is connected to the housing 10, in particular to the flange 13 of the vacuum pump, via a web 25 or foot. The magnetic bearing hub 21 comprises a base element 24 connected to the web 25. The magnetic bearing hub 21 further comprises a trunnion 20 extending from the base element 24 into a recess of the rotor assembly 16. The trunnion 20 is connected to a stationary magnetic element of the magnetic bearing 18 and is surrounded by a rotating magnetic element connected to the rotor assembly 16. In this regard, the stationary magnetic element and the rotating magnetic element may comprise a plurality of mutually repelling magnetic rings to support the rotor assembly. The trunnion 20 of the magnetic bearing hub 21 may comprise a bore 26 extending into the trunnion from an end opposite the base element 24. An axial extension 29 of the rotor assembly 16 extends into the bore 26. Further, an emergency bearing 30 may be disposed within the bore 26 surrounding the axial extension 29 of the rotor assembly 16.

[0029] In the present invention, the magnetic bearing hub 21 is provided with a predetermined break point, formed in the example of FIG. 1 as a groove 28. In this regard, the groove 28 may be a recess in order to provide a thin section in the region of the groove 28. Alternatively, the groove 28 may be filled with a weaker material, such as plastic, soft metal, etc., to allow the trunnion 20 to separate from the base element 24 upon crash of the rotor assembly 16 into the stator element 36 of the vacuum pump. In addition, the bore 26 extends axially to the end of the predetermined break point, i.e., the groove 28, to further reduce the thickness of the material at the predetermined break point and allow the trunnion to break and separate from the base element 24.

[0030] Thus, in the event of a crash of the vacuum pump, due to a predetermined breaking point of the magnetic bearing hub 21, the trunnion 20 will tear away and separate from the base element 24 without damaging or destroying the web 25. At the same time, due to the magnetic forces between the stationary and rotating magnetic elements of the magnetic bearing, the detached trunnion 20 will collapse together with the rotor assembly 16 due to the magnetic forces, resulting in no parts being released into undesired areas, i.e. into the vacuum equipment coupled to the vacuum pump.

[0031] In this regard, the predetermined breaking point, formed in the example shown as a groove 28, is located directly adjacent to the base element 24 and above the stationary magnetic element of the magnetic bearing 18. In addition, the predetermined breaking point is located axially beyond the axial extension 29 of the rotor assembly 16, allowing complete separation and contact between the rotor element 34 and the stator element 36, as well as between the rotating cylinder 40 and the threaded stator 42, to stop the rotation of the rotor assembly 16 as quickly as possible.

[0032] Additionally, the web 25 can have a predetermined break point at the connection point 44 between the web 25 and the flange 13 or at the connection point 44 between the web 25 and the base element 24 of the magnetic bearing hub 21, so that the web 25 breaks in a controlled manner even if controlled separation of the trunnion from the base element 24 is not possible. [Explanation of symbols]

[0033] 10. Housing 12 Entrance 13 Flange 14 Exit 16 Rotor assembly 18 Magnetic bearings 20 Trunnion 21 Magnetic bearing hub 24 Base Elements 25 Web or leg 26 Bore 28 Groove 29 Axial extension 30 Emergency bearing 32 Electric motor 33 Roller bearings 34 Rotor elements 36 Stator elements 38 Holbeck Stage 40 Cylinder 42 Stator 44 Connection points

Claims

1. 1. A magnetic bearing hub for a vacuum pump, comprising: a base element coupled to a housing of the vacuum pump; a trunnion extending from the base element and configured to receive a stationary magnetic element of a magnetic bearing; Equipped with The trunnion has a predetermined break point.

2. The magnetic bearing hub of claim 1 , wherein the predetermined break point is defined by a thinned section.

3. The magnetic bearing hub of claim 2 , wherein said thinned section is formed as a circumferential groove.

4. 4. The magnetic bearing hub of claim 3, wherein the groove is wedge-shaped or rectangular-shaped.

5. 5. A magnetic bearing hub as claimed in claim 2, wherein the thinned section is defined by an internal bore extending into the trunnion from an end opposite the base element to an end of the thinned section or beyond the thinned section.

6. 6. A magnetic bearing hub according to claim 2, wherein the thinned section has a reduced wall thickness of less than 80%, preferably less than 60%, and most preferably less than 50% compared to the wall thickness of the remainder of the trunnion.

7. 7. A magnetic bearing hub as claimed in any one of claims 1 to 6, wherein the predetermined breaking point is configured to break at 10% to 50% of the maximum torque of the rotor of the vacuum pump, preferably 15% to 40% of the maximum torque, and most preferably 20% to 25% of the maximum torque.

8. the predetermined break point is located between the stationary magnetic element and the base element; and / or the predetermined breaking point is located directly adjacent to the base element; and / or the predetermined break point is located between an end of the rotor and the base element of the vacuum pump; A magnetic bearing hub according to any one of claims 1 to 7.

9. 9. A magnetic bearing hub according to claim 1, wherein the predetermined breaking point is configured to suppress a natural frequency of the magnetic bearing hub and / or web of the vacuum pump in an operating frequency range of the vacuum pump.

10. 10. A vacuum pump comprising a housing having an inlet and an outlet, and a rotor assembly, the rotor assembly being supported by at least one magnetic bearing, the magnetic bearing comprising a magnetic bearing hub according to any one of claims 1 to 9.

11. 11. A vacuum pump according to claim 10, wherein the magnetic bearing hub is coupled to the housing via a web, the web being preferably integrally formed with the housing and / or the magnetic bearing hub.

12. The vacuum pump of claim 11 , wherein the predetermined break point is configured to break before a connection between the web and the housing breaks.

13. 13. A vacuum pump according to claim 11 or 12, wherein the cross-sectional area of ​​the thinned section is smaller than the cross-sectional area of ​​one web, preferably the cross-sectional area of ​​the thinned section is between 4% and 20%, more preferably between 4% and 10%, most preferably between 5% and 8% of the cross-sectional area of ​​one web.

14. 14. A vacuum pump according to any one of claims 11 to 13, wherein the web and / or the magnetic bearing hub are made of aluminium, stainless steel or carbon fibre material, preferably by additive manufacturing.

15. 15. A vacuum pump according to any one of claims 11 to 14, wherein the web has a predetermined breaking point, preferably located at the connection between the web and the housing.

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