Magnetic bearing hub and vacuum pump

Abstract

A magnetic bearing hub (21) for a vacuum pump comprises a base element (24) to be connected to the housing (10) of the vacuum pump, and a trunnion (20) extending from the base element (24), where the trunnion (20) is configured to receive a static magnetic element of the magnetic bearing (18), where the trunnion (20) has a predetermined breaking point (28).

Description

Technical Field

[0001] The invention relates to a magnetic bearing hub for a vacuum pump and a vacuum pump having such a magnetic bearing hub. Background Art

[0002] Common vacuum pumps and in particular turbomolecular pumps include a housing with an inlet and an outlet. In the housing, a rotor assembly is rotated by an electric motor and supported by a bearing or a bearing system. The rotor assembly includes at least one rotor element, which interacts with at least one stator element to transport a gas medium from the inlet to the outlet. In particular, for a turbomolecular pump, the rotor assembly includes a plurality of blades that interact with the blades of the stator. Among them, the rotor assembly is supported by usually two bearings, wherein the bearings can be constructed as roller bearings or magnetic bearings. In particular, the bearings toward the inlet side (i.e., the end of the rotor assembly in the inlet direction of the vacuum pump) can be constructed as permanent magnetic bearings. Among them, a rotating magnetic element is connected to the rotor, wherein a static magnetic bearing is connected to the housing. The static magnetic bearing and the rotating magnetic bearing are close to each other and repel each other to support the rotor shaft. Among them, the static magnetic element of the permanent magnetic bearing can be arranged at the ear shaft extending into the recess of the rotor assembly so that the rotating magnetic element surrounds the static magnetic element. The trunnions are connected to the housing by webs or legs (which are sometimes also referred to as "spider frames" or "envelopes") to provide structural stability to the trunnions and thereby to the permanent magnet bearings themselves.

[0003] Due to the high rotational speeds, there are high rotational forces which must be released in the event of a crash of the vacuum pump. As a result, there is a risk that parts of the vacuum pump enter the connected vacuum equipment and cause damage. This is particularly the case when the web holding the trunnion breaks in an uncontrolled manner.

[0004] Therefore, an object of the present invention is to provide a magnetic bearing hub and a vacuum pump, wherein damage to vacuum equipment connected to the vacuum pump is reduced when the vacuum pump crashes. Summary of the invention

[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 invention relates to a magnetic bearing hub for a vacuum pump and in particular for a turbomolecular vacuum pump. The magnetic bearing hub comprises a base element, which is to be connected to the housing of the vacuum pump, for example via two or more webs or legs. In addition, the magnetic bearing hub comprises a trunnion extending from the base element, wherein the trunnion is configured to receive a static magnetic element of a magnetic bearing. In particular, the static magnetic element may comprise several permanent magnet rings. In an assembled state, the trunnion may extend into a recess of a rotor assembly of the vacuum pump, wherein the static magnetic element is surrounded by a rotating magnetic element, which is connected to the rotor assembly. Alternatively, the static magnetic element surrounds the rotating magnetic element. According to the invention, the trunnion has a predetermined breaking point. Thus, in the event of a crash of the vacuum pump, the trunnion breaks at the predetermined breaking point and separates from the base element. This split between the base element connected to the web and the trunnion will protect the web from breaking or damage, and will help the rotor assembly to crash into the stator element. Thereby, the rotation of the rotor assembly is braked by the friction between these components. Therefore, the web is protected from breaking and thereby avoids large pieces of the vacuum pump being ejected into the vacuum chamber of the vacuum device connected to the vacuum pump.In addition, by the controlled breaking of the component, energy can be released, thereby reducing the risk of breaking other components.

[0007] Preferably, the predetermined breaking point is constructed by a thinned wall section. Thus, the predetermined breaking point is provided by a thin-wall section, wherein a thinned wall section is a section with a reduced wall thickness so that a break can occur at the location of the thinned wall section.

[0008] Preferably, the thinned wall section is constructed as an annular groove. Wherein, the groove can be constructed at the inner surface of the trunnion. However, for ease of manufacturing, the groove can be provided at the outer surface of the trunnion, wherein the wall thickness of the trunnion is reduced by the groove.

[0009] Preferably, the recess has a conical or wedge-shaped or rectangular shape. By a specific choice of shape, the stability of the predetermined breaking point can be adjusted, wherein the trunnion is able to break at the location of the recess in the event of a crash of the vacuum pump.

[0010] Preferably, the thin-walled section is constructed by an internal bore extending from one end opposite to the base element into the trunnion as far as the axial end of the thinned-walled section or axially beyond the thinned-walled section. Thus, the material strength of the trunnion is reduced by the internal bore, thereby allowing the trunnion to be separated from the base element.

[0011] Preferably, the thinned wall section has a reduced wall thickness of less than 80% compared to the wall thickness of the remaining trunnion. Thus, if the minimum wall thickness of the remaining trunnion is 10 mm, a preferred embodiment is that the thinned wall section may have a wall thickness of less than 8 mm. Preferably, the thinned wall section has a reduced wall thickness of less than 60%, and most preferably less than 50%. By the choice of the wall thickness, on the one hand a sufficient stability of the magnetic bearing hub is maintained, while on the other hand a breakage of the magnetic bearing hub in the region of the thinned wall section is allowed.

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

[0013] Preferably, the predetermined breaking point is configured to break during a collision at 10% to 50% of the maximum torque of the rotor of the vacuum pump, i.e. within a time window of up to 20 ms and preferably up to 10 ms after the collision. Therein, during a collision, torque values ​​from 1 kN to 2.2 kN can be observed. 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% of the maximum torque of the rotor of the vacuum pump, and most preferably at 20% to 25% of the maximum torque. Thus, it is ensured that one of the parts that will break first is the trunnion, which will be separated from the spider leg or web carrying the magnetic bearing hub, and preferably breaks without damaging the web or spider leg.

[0014] Preferably, the predetermined breaking point is arranged between the static magnetic element and the base element. Thereby, it is ensured that the static magnetic element is separated from the base element together with the trunnion. In particular, during a collision, the rotating magnetic element and the static magnetic element collapse and contact each other. In addition, by collapsing the magnetic elements together, the brittle magnetic material is confined and cannot escape to other areas of the vacuum pump and / or the vacuum equipment. And at the same time, the trunnion fragment of the base element is attached to the rotor assembly by magnetic force and cannot escape in an undesirable manner. However, additionally or alternatively, the web may also block any parts that are directed toward the inlet of the vacuum pump.

[0015] Alternatively or additionally, the predetermined breaking point is arranged in close proximity to the base element.

[0016] Alternatively or additionally, the predetermined breaking point is arranged between an axial end of the rotor of the vacuum pump and the base element. Thus, the predetermined breaking point axially extends beyond the axial end of the rotor, or at least axially beyond the rotor extension extending into the trunnion, so that the trunnion surrounds the rotor extension / axial end of the rotor and enables the trunnion to be separated.

[0017] Preferably, the predetermined breaking point is configured so as not to excite the natural frequencies of the magnetic bearing hub and / or the packing plate / spider frame or any other components and sub-components 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 may also be configured to provide a reduced resonance in the frequency range of the vacuum pump during operation. Therein, the resonant frequency of the magnetic bearing hub may be adjusted by the shape of the predetermined breaking point, i.e. by changing the shape of the grooves, introducing more than one groove, etc., or by using a specific material in order to fill one or more of these grooves or to provide a weakened section as the predetermined breaking point.

[0018] Preferably, the magnetic bearing hub comprises only one predetermined breaking point. Alternatively, the magnetic bearing hub comprises more than one predetermined breaking point, wherein these more than one predetermined breaking points are configured to break under different torques / radial loads or the same torques / radial loads applied by the rotor upon collision.

[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, wherein the rotor assembly is 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 constructed at the suction side of the vacuum pump, ie at the end of the rotor assembly arranged towards the inlet of the vacuum side.

[0021] Preferably, the magnetic bearing hub is connected to the housing via webs, wherein these webs are preferably constructed integrally with the housing and / or the magnetic bearing hub. Thus, the webs can be constructed integrally with the housing (i.e. the flange of the vacuum pump) or the magnetic bearing hub. Alternatively, the webs are constructed integrally with the housing and the magnetic bearing hub. Thus, by constructing the webs and the magnetic bearing hub as a single piece, stability is increased.

[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, the web and / or the magnetic bearing hub are constructed by an additive manufacturing process such as 3D printing. Alternatively, the web and / or the magnetic bearing hub are constructed by conventional machining methods.

[0024] Preferably, the web has a predetermined breaking point, which is preferably arranged at the connection between the web and the housing. Wherein the predetermined breaking point of the web is configured to break when the rotational force and / or radial force is greater than the force required to break the predetermined breaking point of the magnetic bearing hub. Thus, it is ensured that the trunnion is separated from the base element first. In any case, if separation does not occur, the web can be broken at the predetermined breaking point in a next step so as to avoid damage caused by the components of the vacuum pump breaking in an uncontrolled manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described in more detail below with reference to the accompanying drawings.

[0026] The accompanying drawings show:

[0027] Figure 1 is a schematic diagram of a turbomolecular pump according to the present invention,

[0028] Figure 2 A detailed view of the magnetic bearing hub, and

[0029] Figure 3 for Figure 1 Top view of a vacuum pump. DETAILED DESCRIPTION

[0030] Figure 1 The vacuum pump comprises a housing 10 with an inlet 12 and an outlet 14. A flange 13 is connected at the inlet side of the vacuum pump. The vacuum pump can be connected to a vacuum device via the flange 13. The vacuum pump comprises a rotor assembly 16, wherein a plurality of rotor elements 34 are connected to the rotor assembly. The rotor elements 34 are constructed as blades, which interact with blades of a stator element 36, which is connected to the housing 10. In addition, Figure 1 The vacuum pump comprises a Hollweck stage 18, which comprises a rotating cylinder 40 and a threaded stator 42, wherein the Hollweck stage 38 is arranged downstream of the turbomolecular pump stage. Other molecular drag stages such as the Siegbahn stage may be used instead of the Hollweck stage 28.

[0031] The rotor assembly 16 is rotated by an electric motor 32 and is rotatably supported by a roller bearing 33 at the outlet side of the rotor assembly (i.e., at the end of the rotor assembly 16 toward the outlet 14 and opposite to the axial end of the rotor assembly 16 toward the inlet 12 of the vacuum pump). In addition, the rotor assembly is rotatably supported by a magnetic bearing 18 arranged in the inlet side of the rotor assembly 12. The magnetic bearing 18 includes a magnetic bearing hub 21. The magnetic bearing hub 21 is connected to the housing 10 of the vacuum pump and in particular to the flange 13 via a web 25 or a leg. The magnetic bearing hub 21 includes a base element 24 connected to the web 25. In addition, the magnetic bearing hub 21 includes a trunnion 20, which extends from the base element 24 into a recess of the rotor assembly 16. The static magnetic element of the magnetic bearing 18 is connected to the trunnion 20, which is surrounded by a rotating magnetic element, which is connected to the rotor assembly 16. Therein, the static magnetic element and the rotating magnetic element may include a plurality of magnetic rings that repel each other to support the rotor assembly. The trunnion 20 of the magnetic bearing hub 21 may include a hole 26 extending into the trunnion from the end opposite to the base element 24. An axial extension 29 of the rotor assembly 16 extends into the hole 26. In addition, an emergency bearing 30 may be arranged in the hole 26, surrounding the axial extension 29 of the rotor assembly 16.

[0032] According to the present invention, Figure 1 In the example of , the magnetic bearing hub 21 includes a predetermined breaking point, which is constructed as a groove 28. The groove 28 may be a recessed portion so as to provide a thinned wall section in the region of the groove 28. Alternatively, the groove 28 may be filled with a weaker material, such as plastic, a softer metal, to allow the trunnion 20 to separate from the base element 24 when the rotor assembly 16 of the vacuum pump collides into the stator element 36. In addition, the hole 26 extends axially until the end of the predetermined breaking point (i.e., the groove 28) to further reduce the material thickness at the predetermined breaking point and allow the trunnion to break and the trunnion 20 to separate from the base element 24.

[0033] Therefore, when the vacuum pump sends a collision, due to the predetermined breaking point of the magnetic bearing hub 21, the trunnion 20 is broken and separated from the base member 24 without damaging or destroying the web 25. At the same time, due to the magnetic force between the rotating magnetic element and the static magnetic element of the magnetic bearing, the loosened trunnion 20 collapses together with the rotor assembly 16 due to the magnetic force, and thus does not generate parts that can be injected into an undesirable area (i.e., a vacuum device connected to the vacuum pump).

[0034] In the example of the figures, the predetermined break constructed as a groove 28 is arranged adjacent to the base element 24 and above the static magnetic element of the magnetic bearing 18. In addition, the predetermined break point is arranged axially beyond the axial extension 29 of the rotor assembly 16 to allow complete separation, and to enable contact between the rotor element 34 and the stator element 36 and between the rotating cylinder 40 and the threaded stator 42 to terminate the rotation of the rotor assembly 16 as quickly as possible.

[0035] In addition, the web 25 may have a predetermined breaking point at a connection point 44 between the web 25 and the flange 13 or between the web 25 and the base element 24 of the magnetic bearing hub 21, so that in any case, if the trunnion cannot be separated from the base element 24 in a controlled manner, then the web 25 breaks in a controlled manner.

[0036] Reference numerals

[0037] 10 Shell

[0038] 12Entrance

[0039] 13 Flange

[0040] 14Exit

[0041] 16 rotor assembly

[0042] 18 Magnetic bearings

[0043] 20 trunnion

[0044] 21 Magnetic bearing hub

[0045] 24 base elements

[0046] 25 webs or legs

[0047] 26 holes

[0048] 28 grooves

[0049] 29 axial extension

[0050] 30 Emergency bearing

[0051] 32 Electric Motor

[0052] 33 Roller bearings

[0053] 34 rotor elements

[0054] 36 stator elements

[0055] 38 Holweg class

[0056] 40 cylinder block

[0057] 42 thread stator

[0058] 44 connection points

Claims

1. A magnetic bearing hub for a vacuum pump, comprising: a base element to be connected to the housing of the vacuum pump, and a trunnion extending from the base element, wherein the trunnion is configured to receive a static magnetic element of the magnetic bearing, Wherein, the trunnion has a predetermined breaking point.

2. The magnetic bearing hub according to claim 1, wherein: The predetermined breaking point is formed by thinning the wall section.

3. The magnetic bearing hub according to claim 2, wherein: The thinned wall section is designed as an annular groove.

4. The magnetic bearing hub according to claim 3, wherein: The groove has a wedge shape or a rectangular shape.

5. The magnetic bearing hub according to any one of claims 2 to 4, wherein: The thinned wall section is constructed by an internal bore extending from an end opposite the base element into the trunnion to the end of the thinned wall section or beyond the thinned wall section.

6. The magnetic bearing hub according to any one of claims 2 to 5, wherein: The thinned wall 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 remaining trunnion.

7. The magnetic bearing hub according to 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 at 15% to 40% of the maximum torque, and most preferably at 20% to 25% of the maximum torque.

8. The magnetic bearing hub according to any one of claims 1 to 7, wherein: The predetermined breaking point is arranged between the static magnetic element and the base element; and / or wherein the predetermined breaking point is arranged in close proximity to the base element; and / or Therein, the predetermined breaking point is arranged between the end of the rotor of the vacuum pump and the base element.

9. The magnetic bearing hub according to any one of claims 1 to 8, wherein: The predetermined breaking point is designed to suppress a natural frequency of the magnetic bearing hub and / or a web of the vacuum pump in the operating frequency range of the vacuum pump.

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

11. The vacuum pump according to claim 10, wherein: The magnetic bearing hub is connected to the housing via a web, and wherein the web is preferably constructed integrally with the housing and / or the magnetic bearing hub.

12. The vacuum pump according to claim 11, wherein The predetermined breaking point is configured to break before the connection between the web and the outer shell breaks.

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

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

15. The vacuum pump according to any one of claims 11 to 14, wherein: The web has a predetermined breaking point, which is preferably arranged at the connection between the web and the outer shell.

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