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, particularly a turbomolecular pump, includes a housing having an inlet and an outlet. Within the housing, a rotor assembly is rotated by an electric motor and supported by a bearing or bearing system. The rotor assembly includes at least one rotor element that interacts with at least one stator element to transport the gas medium from the inlet to the outlet. In particular, in the case of a turbomolecular pump, the rotor assembly includes a plurality of vanes that interact with vanes of the stator. In this regard, the rotor assembly is typically supported by two bearings, which can be formed as roller bearings or magnetic bearings. In particular, the bearing on the inlet side, i.e., toward the end of the rotor assembly in the direction of the vacuum pump inlet, 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 disposed on a trunnion extending into a recess in the rotor assembly, and the rotating magnetic element surrounds 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, consequently, for the permanent magnet bearing itself.

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

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a magnetic bearing hub and a vacuum pump that reduce damage to a vacuum device coupled to the vacuum pump in the event of a crash of the vacuum pump. [Means for solving the problem]

[0005] This problem is solved by a magnetic bearing hub according to claim 1 and 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, particularly a turbomolecular vacuum pump. The magnetic bearing hub includes 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 includes a trunnion extending from the base element, the trunnion configured to receive a stationary magnetic element of the magnetic bearing. Specifically, the stationary magnetic element can include a plurality of permanent magnet rings. In an assembled state, the trunnion can extend into a recess in a rotor assembly of the vacuum pump, with 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. Therefore, if the vacuum pump crashes, the trunnion breaks at the predetermined breaking point and separates from the base element. This separation between the base element coupled to the web and the trunnion protects the web from being broken or damaged and helps the rotor assembly crash against the stator element. 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, by controlling the breakage of components, energy is released, thereby reducing the risk of further component breakage.

[0007] Preferably, the predetermined breaking point is formed by a thinned section, which is a section of reduced thickness such that the predetermined breaking point breaks at the location of the thinned section.

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

[0009] Preferably, the groove has a conical, wedge-shaped, or rectangular shape. The particular choice of shape allows for the stability of a given break point to be adjusted, 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 formed by an internal bore extending into the trunnion from one end opposite the base element to the axial end of the thinned section or beyond the thinned section, thereby reducing the material strength of the trunnion and enabling the trunnion to be separated from the base element.

[0011] Preferably, the wall thickness of the thinned section is less than 80% compared to the wall thickness of the rest of the trunnion. Thus, in a preferred embodiment, if the minimum wall thickness of the rest of the trunnion is 10 mm, the thinned section will have a wall thickness of less than 8 mm. Preferably, the thinned section has a thinned section of less than 60%, most preferably less than 50%. The thickness is selected so that on the one hand sufficient stability of the magnetic bearing hub is maintained and on the other hand fracture of the magnetic bearing hub in the area of ​​the thinned section is permitted.

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

[0013] Preferably, the predetermined breaking point is configured to break at 10% to 50% of the maximum torque of the rotor of the vacuum pump during the crash, i.e., within a time window of up to 20 ms, preferably up to 10 ms, after the crash. 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, 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 separates from the spider leg or web supporting the magnetic bearing hub, preferably ensuring that the break occurs without damaging the web or spider leg.

[0014] Preferably, the predetermined breaking point is located between the stationary magnetic element and the base element. This ensures that the stationary magnetic element, together with the trunnion, is separated from the base element. Specifically, in the event of a crash, the rotating magnetic element and the stationary magnetic element collapse and bond together. Additionally, by collapsing the magnetic elements together, the fragile magnetic material is trapped and cannot escape to other areas of the vacuum pump and / or vacuum system. At the same time, the trunnion split of the base element is also attached to the rotor assembly by magnetic force and cannot escape in an undesirable manner. However, additionally or alternatively, the web can also stop any parts being ejected toward 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 the 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 breaking 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 breaking of the magnetic bearing hub, the predetermined breaking point can be configured to result in 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 breaking 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 breaking point.

[0018] Preferably, the magnetic bearing hub has only one predetermined breaking point, or alternatively, the magnetic bearing hub has two or more predetermined breaking 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 entrance to the vacuum side, of the vacuum pump.

[0021] Preferably, the magnetic bearing hub is connected to the housing via webs, and these webs 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 improves 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 magnetic bearing hub are made of aluminum, stainless steel, or carbon fiber material. In particular, in this regard, the web and / or magnetic bearing hub are formed by an additive manufacturing process such as 3D printing. Alternatively, the web and / or magnetic bearing hub are formed by conventional machining methods.

[0024] Preferably, the web has a predetermined breaking point, preferably located at the connection between the web and 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 to avoid damage to the vacuum pump components due to uncontrolled breaking.

[0025] The invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

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

[0027] The vacuum pump of FIG. 1 includes a housing 10 having an inlet 12 and an outlet 14. A flange 13 is coupled to the inlet side of the vacuum pump, allowing the vacuum pump to be coupled to a vacuum system. The vacuum pump includes a rotor assembly 16 having a plurality of rotor elements 34 coupled to the rotor assembly. The rotor elements 34 are formed as vanes that interact with vanes of a stator element 36 coupled to the housing 10. The vacuum pump of FIG. 1 also includes a Holweck stage 18, consisting of a rotating cylinder 40 and a threaded stator 42, which is positioned 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 outlet end of the rotor assembly, i.e., the end of the rotor assembly 16 toward the outlet 14, and at the end opposite the axial end of the rotor assembly 16 toward the inlet 12 of the vacuum pump. Additionally, the rotor assembly is rotatably supported by a magnetic bearing 18 disposed on the inlet side of the rotor assembly 12. The magnetic bearing 18 includes a magnetic bearing hub 21. The magnetic bearing hub 21 is coupled to the housing 10, specifically the flange 13 of the vacuum pump, via webs 25 or legs. The magnetic bearing hub 21 includes a base element 24 coupled to the web 25. The magnetic bearing hub 21 further includes a trunnion 20 extending from the base element 24 into a recess in the rotor assembly 16. The trunnion 20 is coupled to a stationary magnetic element of the magnetic bearing 18 and is surrounded by a rotating magnetic element coupled to the rotor assembly 16. In this regard, the stationary and rotating magnetic elements may comprise a plurality of mutually repelling magnetic rings to support the rotor assembly. The trunnion 20 of the magnetic bearing hub 21 may include 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 as a groove 28 in the example of FIG. 1. In this regard, the groove 28 may be recessed to provide a thinned section in the region of the groove 28. Alternatively, the groove 28 may be filled with a weaker material, such as plastic, soft metal, or the like, to allow the trunnion 20 to separate from the base element 24 upon crashing of the rotor assembly 16 into the stator element 36 of the vacuum pump. Additionally, the bore 26 extends axially to the end of the predetermined break point, i.e., the groove 28, further reducing the thickness of the material at the predetermined break point and enabling trunnion fracture and separation of the trunnion 20 from the base element 24.

[0030] Thus, in the event of a crash of the vacuum pump, due to the 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 an undesired area, i.e., into a vacuum system 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 may have a predetermined breaking 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 bearing 34 rotor elements 36 stator elements 38 Holbeck Stage 40 cylinders 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; the predetermined breaking 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 breaking point is located between an end of the rotor of the vacuum pump and the base element; Magnetic bearing hub.

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 the 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.

5. 3. The magnetic bearing hub of claim 2, wherein the thinned section is defined by an internal bore that extends into the trunnion from an end opposite the base element to an end of the thinned section or beyond the thinned section.

6. The magnetic bearing hub of claim 2 , wherein the thinned section has a reduced wall thickness of less than 80% compared to the wall thickness of the remainder of the trunnion.

7. 2. The magnetic bearing hub of claim 1, wherein the predetermined break point is configured to break at 10% to 50% of the maximum torque of the rotor of the vacuum pump.

8. The magnetic bearing hub of claim 1 , wherein the predetermined break point is configured to suppress natural frequencies of the magnetic bearing hub and / or web of the vacuum pump in an operating frequency range of the vacuum pump.

9. 9. 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 8.

10. 10. A vacuum pump according to claim 9, wherein the magnetic bearing hub is coupled to the housing via a web, the web being integrally formed with the housing and / or the magnetic bearing hub.

11. 11. The vacuum pump of claim 10, wherein the predetermined break point is configured to break before the connection between the web and the housing breaks.

12. A vacuum pump as described in claim 10, wherein the predetermined breaking point is formed by a thin-walled section, the cross-sectional area of ​​the thin-walled section being smaller than the cross-sectional area of ​​one web.

13. 11. A vacuum pump according to claim 10, wherein the web and / or the magnetic bearing hub are made of aluminium, stainless steel or carbon fibre material.

14. 11. The vacuum pump of claim 10, wherein the web has a predetermined break point, the predetermined break point being located at the juncture of the web and the housing.

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