GB2621341A

GB2621341A - Vacuum pump

Info

Publication number: GB2621341A
Application number: GB2211560.4A
Authority: GB
Inventors: Hoesgen Christian; Christian Kalisch Dirk; Greven Alois; Erich Radermacher Daniel; Berger Christian; Dembek Roman; Jungmayr Gerald; Santner Robert
Original assignee: Leybold GmbH
Current assignee: Leybold GmbH
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2024-02-14
Also published as: WO2024033309A1; GB202211560D0

Abstract

A vacuum pump, in particular a turbomolecular pump, comprises a rotor shaft 16 rotatably supported in a housing 10 by at least one radial bearing 18, 20 and an axial / thrust bearing 44. The axial bearing comprises a yoke 106 connected to the rotor shaft and a first magnetic element 108 connected to the housing and arranged axially next to the yoke to generate a magnetic force to control the axial position of the rotor shaft. The first magnetic element is separated into at least two parts (108A, 108B, figure 3) along a circumferential direction. The first magnetic element may be connected to an electromagnet to create the magnetic force. A second magnetic element 109 may be magnetically connected to the first magnetic element and arranged on the opposite side of the yoke, and may be built as one piece. A method of assembling the vacuum pump comprises providing a rotor including the rotor shaft and at least one pump element, connecting the yoke to the rotor shaft, assembling the first magnetic element around the rotor shaft, inserting the rotor and the first magnetic element into the housing, and connecting the first magnetic element to the housing.

Description

VACUUM PUMP

The present invention relates to a vacuum pump and in particular to a turbo-molecular pump. Further, the present invention relates to a method for providing a vacuum pump.

Common vacuum pumps comprise a housing and a rotor shaft arranged in the housing and rotatably supported by at least one radial bearing. At least one pump element is connected to the rotor shaft. Upon rotation by an electrornotor a gaseous medium is conveyed from the inlet of the vacuum pump towards the outlet of the vacuum pump. For turbomolecular pumps a plurality of pump elements built as vanes are interacting with vanes of a stator connected to the housing to convey the gaseous medium.

In addition to the radial bearing the rotor shaft needs to be supported in the axial direction. Thus, it is known to implement an axial bearing comprising a magnetic element interacting with a yoke connected to the rotor shaft. Therein, the magnetic element and the yoke need to be arranged axially next to each other for most efficient operation of the axial bearing. However, this causes problems during the assembly process since usually the rotor including the rotor shaft and the pump elements is preassem bled and then inserted into the housing. However, this is not possible due to the interlocking configuration of the yoke and the magnetic element.

The solution is to rearrange the magnetic element and the yoke to increase the diameter of the magnetic element. Thus, it becomes possible to insert the rotor including the yoke in a preassembled configuration. However, thereby the efficiency of the axial bearing is reduced and the axial bearing needs to be built larger to provide the same axial support as for the interlock configuration increasing the space requirements or the overall size of the vacuum pump. -2 -

Thus, it is an object of the present invention to provide a vacuum pump which is easy to assemble with minimum space requirements.

A solution to the problem is provided by a vacuum pump according to claim 1 and a method for providing a vacuum pump according to claims 10 or 11.

In a first aspect of the present invention a vacuum pump, in particular built as a turbomolecular pump is provided. The vacuum pump comprises a housing having an inlet and an outlet. A rotor shaft is arranged in the housing and rotatably supported by at least one radial bearing. Usually two radial bearings are used in order to rotatably support the rotor shaft. Preferably, the rotor shaft comprises at least one pump element and, in the case of a turbomolecular pump, comprises a plurality of pump elements built as vanes interacting with pump elements of the stator which are connected to the housing of the vacuum pump. Preferably, the rotor including the rotor shaft and the pump elements are rotated by an electromotor. Furthermore, the vacuum pump comprises an axial bearing to support the rotor shaft in the axial direction. The axial bearing comprises a yoke connected to the rotor shaft and rotated together with the rotor shaft. Therein, the yoke is ring shaped or rotationally symmetrical. Further, the axial bearing comprises a first magnetic element connected to the housing and arranged in an axial direction next to the yoke to generate a magnetic force to the yoke to control the axial position of the rotor shaft. Therein, the first magentic element is ring shaped or rotationally symmetrical. Thus, by the first magnetic element a magnetic force is applied to the yoke for creating an axial force to the rotor shaft thereby adjusting the axial position of the rotor shaft in the housing.

In accordance with the present invention, the first magnetic element is separated into at least two parts along a circumferential direction. Thus, the first magnetic element can be easily placed around the rotor shaft during assembly. By building the first magnetic elements into at least two parts, an interlocking -3 -configuration of the yoke and the first magnetic element is feasible while still the preassembled rotor including the rotor shaft can be inserted into the housing of the vacuum pump. It is not necessary to mate parts of the rotor to the rotor shaft within the housing of the vacuum pump. Thus, an efficient axial bearing is provided with minimum space requirements which can be easily assembled.

Preferably, the first magnetic element is intersected along the circumferential direction in axial direction. Thus, the connecting faces are aligned with the axial direction of the vacuum pump. Since in the axial bearing the magnetic field is also in the axial direction, the intersections do not have any or only little influences on the strength of the magnetic field of the first magnetic element. Thus, by building the first magnetic element by at least two parts the efficiency of the axial bearing is maintained.

Preferably, the first magnetic element is separated into more than two parts along a circumferential direction. Thereby, the number of parts can be adapted to the space available for assembly.

Preferably, the first magnetic element is connected to an electromagnet or coil in order to create the magnetic force. Thus, by the electromagnet an adjustable magnetic force can be applied to the yoke in order to adapt the axial position of the rotor shaft.

Preferably, the minimum inner diameter of the first magnetic element is smaller than the maximum outer diameter of the yoke. Thus, an interlocking configuration of the first magnetic element and the yoke is provided maintaining the efficiency of the axial bearing without the need to increase for example the size of the electromagnet of the axial bearing.

Preferably, the first magnetic element is on the inner side of the rotor shaft relative to the yoke away from the end of the rotor shaft. Usually, the axial -4 -bearing is arranged at one of the ends of the rotor shaft wherein the first magnetic element is opposite to the end of the rotor shaft relative to the yoke. Thereby, the first magnetic element can be placed within the vacuum pump reducing the overall space requirements and in particular the length of the vacuum pump.

Preferably, the first magnetic element is arranged along an insertion direction of the rotor into the housing before the yoke. Thus, the first magnetic element can be placed inside the housing reducing the space requirements and the overall length of the vacuum pump.

Preferably, the axial bearing comprises a second magnetic element magnetically connected to the first magnetic element and arranged on the opposite side of the yoke relative to the first magnetic element. Thus, by the first magnetic element and the second magnetic element a gap is formed between the first magnetic element and the second magnetic element wherein the yoke is arranged in the gap. Due to this configuration a sufficient magnetic force in the axial direction can be applied to the yoke by the magnetic field created by the first magnetic element and the second magnetic element.

Preferably, the second magnetic element can be built by at least two parts similar than the first magnetic element being separated along a circumferential direction. Alternatively, the second magnetic element is built as one piece for ease of assembly. If the first magnetic element is placed towards the inner side of the rotor shaft away from the end of the rotor shaft, the second magnetic element is arranged towards the end of the rotor shaft and can be assembled after complete insertion of the rotor into the housing.

Preferably, the at least one radial bearing is built as permanent magnetic bearing. In particular, the vacuum pump comprises two radial bearings that are built as permanent magnetic bearings. Thus, the rotor of the vacuum pump is -5 -completely magnetically supported by the two permanent magnetic radial bearings and the one axial bearing.

Preferably, the axial bearing is arranged at the exhaust side of the rotor shaft towards the outlet of the vacuum pump and away from the inlet of the vacuum pump or the low pressure/high vacuum side of the vacuum pump.

In another aspect a method for providing a vacuum pump is provided in particular for a turbomolecular pump. The method comprises the steps of: providing a rotor including a rotor shaft and at least one pump element; connecting a yoke to the rotor shaft; assembling a first magnetic element around the rotor shaft wherein the first magnetic element is separated into at least two parts along a circumferential direction; inserting the rotor in the first magnetic element into a housing element wherein the housing element partially forming the housing of the vacuum pump; and connecting the first magnetic element to the housing element.

In another aspect a method for providing a vacuum pump is provided in particular for a turbomolecular pump. The method comprises the steps of: providing a rotor including a rotor shaft and at least one pump element; connecting a yoke to the rotor shaft; inserting the rotor into a housing element wherein the housing element partially forming the housing of the vacuum pump; assembling a first magnetic element around the rotor shaft inside the housing wherein the first magnetic element is separated into at least two parts along a circumferential direction; and connecting the first magnetic element to the housing element. -6 -

Thus, the rotor including rotor shaft, at least one pump element and the yoke can be preassembled outside the housing and mating elements of the rotor inside the housing is not necessary. Therein, interlocking configuration of the first magnetic element and the yoke can be maintained due to the two part or multi part design of the first magnetic element. Therein, the preassembled rotor can be inserted first into a first housing element, the first magnetic element can be assembled around the rotor shaft and then a second housing element can be put over the remaining part of the rotor. Alternatively, the housing comprises only a single housing element and the rotor can be directly inserted into this single housing element.

Preferably, before assembling the first magnetic element around the rotor shaft, balancing of the preassembled rotor is performed. Thus, the rotor including the yoke can be balanced improving the running conditions of the rotor of the vacuum pump.

Preferably, the method is further built along with the features described with respect to the vacuum pump above.

In the following the invention is described in more detail with reference to the accompanying drawings.

The figures show: Figure 1 a vacuum pump according to the present invention, Figure 2 a detailed view of an embodiment of the present invention, Figure 3 a top view of the first magnetic element according to the present invention and -7 -Figure 4 flow diagram of the method according to the present invention.

Referring to figure 1 showing a vacuum pump built as turbomolecular pump. The vacuum pump comprises a housing 10 including an inlet 12 and an outlet 14. A rotor 16 is disposed in the housing and supported by a first radial bearing 18 built as permanent magnetic bearing, and a second radial bearing 20 also built as permanent magnetic bearing. The first radial bearing 18 and the second radial bearing 20 comprise a plurality of magnet rings 22, 23. Therein the static magnet rings 23 of the first radial bearing 18 are attached to a trunnion 24 extending into a recess 26 of the rotor shaft 16. The rotated magnet rings 22 are arranged at the inner surface of the recess radially next to the static magnet rings 23. For the second radial bearing 20 the rotated magnet rings 22 are attached inside a bell-shaped element 28 radially next to the static magnet rings 23 connected to the housing. Therein, the static magnet rings 23 of the first radial bearing 18 and the second radial bearing 20 are in mutual repulsion to each of the rotated magnet rings 22 of the first radial bearing 18 and the second radial bearing 20, respectively, thereby providing a rotatably support of the rotor 16 within the housing 10 Further, the first radial bearing 18 and the second radial bearing 20 comprise emergency running bearings 30 built as ball bearings. The rotor shaft 16 is driven by electromotor 32. Attached to the rotor shaft 16 are a plurality of pump elements 34 built as vanes interacting with stator elements 36 connected to the housing 10 of the vacuum pump and arranged alternating with the pump elements 34. In addition, the vacuum pump of figure 1 comprises a Holweck stage 38 comprising a rotating cylinder 40 interacting with a threated stator 42 connected to the housing. By rotating of the rotor shaft 16 a gaseous medium is conveyed from the inlet 12 of the vacuum pump towards the outlet 14.

In accordance with the present invention, the vacuum pump comprises an axial bearing 44 wherein the axial bearing comprises a yoke 106 attached to the rotor -8 -shaft 16 and rotated together with the rotor shaft 16. Furthermore, the axial bearing 44 comprise a first magnetic element 108 being ring-shaped and surrounding the rotor shaft 16. In the embodiment shown in the figures the axial bearing 44 further comprises a second magnetic element 109. By the first magnetic element 108 and the second magnetic element 109 a gap 111 (see Fig. 2) is created wherein the gap 111 is extending in a radial direction to enclose the radial extending part of the yoke 106. Thus, the yoke 106 extends into the gap 111. Thus, the first magnetic element 108 and the second magnetic element 109 are arranged axially to the yoke 106. The first magnetic element 108 and the second magnetic element 109 are both connected to an electromagnet 110 or coil in order to create a magnetic field applying a magnetic force onto the yoke 106 in order to adjust the axial position and provide axial support of the rotor shaft 16. Therein, the first magnetic element 108 and the yoke 106 are arranged in an interlocking manner. Thus, the minimum inner diameter of the first magnetic element 108 is smaller than the maximum outer diameter of the yoke 106.

In accordance with the invention, the first magnetic element is built by two parts, i.e. separated along its circumferential direction. Thus, the first magnetic element 108 can be easily assembled around the rotor shaft 16 before inserting the rotor shaft into the housing or inserting the cap element 116 in the already assembled housing. Alternatively, the first magnetic element can be assembled around the rotor shaft even if the rotor shaft is already inserted into the housing.

Referring to figure 2 showing a similar configuration. Same or similar elements are indicated by the same reference signs.

As shown in figure 2, the second magnetic element 109 is built by a cap element 116 of the housing 10. Further, the first magnetic element 108 is fixed to the cap element 116 by bolts 114 inserted into threated holes 118. -9 -

In addition, a bias magnet 112, built as permanent magnet, is arranged next to the yoke 106 opposite to the first magnetic element 108. Therein, the bias magnet 112 is magnetically connected to the second magnetic element 109 in order to create a magnetic circuit. As indicated in Fig. 2, a magnetic flux 113 is provided by the bias magnet 112. In dependence of the magnetic orientation of the bias magnet 112, the flux of the electromagnet 110 or coil weakens the magnetic flux in one airgap 111a between the first magnetic element 108 and the yoke 106 (or the flux in the airgap 111b between the second magnetic element 109 and the yoke) and strengthens the magnetic flux in the respective other airgap 111b (or 111a). Thus, the force applied to the yoke 106 can be provided in both axial directions depending on the current direction in the electromagnet or coil.

Referring to figure 3 showing a plane view of the first magnetic element 108 being separated into two parts 108A and 108B along a circumferential direction of the first magnetic element 108. Thus, the first magnetic element 108 can be assembled around the rotor shaft 116 before inserting the rotor shaft into the housing or even if the rotor shaft has been already inserted into the housing, if the yoke 106 is already attached to the rotor shaft 16. Thus, joining the yoke 106 to the rotor shaft need not to be performed within the housing during assembly but can be preassembled and also included in the balancing process of the rotor shaft 16. Thereby, the interlocking configuration of the axial bearing can be maintained providing an efficient axial bearing with minimum space requirements. Although figure 3 shows the first magnetic element 108 with two parts 108A, 108B, more parts are also possible to meet the space requirements during assembly of the first magnetic element 108 around the rotor shaft 16. Therein, the intersection 109 of the two parts 108A, 1086 is in the axial direction. Thus, the intersection has no or only a little impact on the magnetic field lines running also in the axial direction. Thus, the magnetic force applied to the yoke is not or only a little influenced by building the first magnetic element in the two-part design.

-10 -Referring to figure 4 showing a flow diagram for the method of assembly. In step 501 a rotor is provided including a rotor shaft and at least one pump element for example built by the cylinder 40 of the Holweck pump stage 38. In step SO2 a yoke is connected to the rotor shaft preferably at the end of the rotor shaft 16.

In step 503 the first magnetic element 108 is assembled around the rotor shaft 16 by bringing together the two parts 108A, 108B of the first magnetic element 108.

In step SO4 the rotor shaft 16 together with the first magnetic element 108 is inserted into the housing along an insertion direction 113 indicated in figure 1. In step 505 the first magnetic element 108 is connected to the housing 10 or, in the example of the figures 1 and 2, to the cap element of 116 of the housing 10 via bolts 114 or in any other way.

Therein, in step 504, the rotor can be placed in a first housing element and a second housing element for example built by the cap element 116 is inserted into the rotor and connected to the first housing element.

Alternatively to what is described above, first the preassembled rotor is inserted into the housing and then, within the housing, the first magnetic element 108 is assembled around the rotor shaft 16, thereby changing the order of steps 503 and SO4 described above.

Before assembling the rotor and the housing, the rotor, including the rotor shaft 16, the yoke and at least one pump element can be balanced. Thus, the yoke is also included into the process of balancing. Any unbalance induced by the yoke can be minimized reducing running noise, vibration or even damage of the vacuum pump.

Thus, a compact axial bearing is provided that can be assembled in an interlocking manner providing an efficient spatial configuration of the electromagnet and the yoke.

Claims

-12 -CLAIMS1. Vacuum pump, in particular a turbomolecular pump, comprising a housing; a rotor shaft arranged in the housing and rotatably supported by at least one radial bearing; an axial bearing to support the rotor shaft in the axial direction, wherein the axial bearing comprises: a yoke connected to the rotor shaft, a first magnetic element connected to the housing and arranged in an axial direction next to the yoke to generate a magnetic force to the yoke to control the axial position of the rotor shaft, wherein the first magnetic element is separated into at least two parts along a circumferential direction.
2. Vacuum pump according to claim 1, wherein the first magnetic element is connected to an electromagnet to create the magnetic force.
3. Vacuum pump according to claim 1 or 2, wherein the minimum inner diameter of the first magnetic element is smaller than the maximum outer diameter of yoke.
4. Vacuum pump according to any of claims 1 to 3, wherein the first magnetic element is on the inner side of the rotor shaft.
-13 - 5. Vacuum pump according to any of claims 1 to 4, wherein the first magnetic element is arranged along an insertion direction of the rotor into the housing before the yoke.
6. Vacuum pump according to any of claims 1 to 5, comprising a second magnetic element magnetically connected to the first magnetic element and arranged on the opposite side of the yoke relative to the first magnetic element.
7. Vacuum pump according to claim 6, wherein the second magnetic element is built as one piece.
8. Vacuum pump according to any of claims 1 to 7, wherein the at least one radial bearing is built as permanent magnetic bearing and preferably two radial bearings are built as permanent magnetic bearing.
9. Vacuum pump according to any of claims 1 to 8, wherein the axial bearing is arranged at the exhaust side of the rotor shaft.
10. Method for providing a vacuum pump, in particular a turbomolecular pump, comprising: Providing a rotor including a rotor shaft and at least one pump element; Connecting a yoke to the rotor shaft; Assembling a first magnetic element around the rotor shaft, wherein the first magnetic element is separated into at least two parts along a circumferential direction; Inserting the rotor and the first magnetic element into a housing element; and Connecting the first magnetic element to the housing element.
-14 - 11. Method for providing a vacuum pump, in particular a turbomolecular pump, comprising: Providing a rotor including a rotor shaft and at least one pump element; Connecting a yoke to the rotor shaft; Inserting the rotor into a housing element; Assembling a first magnetic element around the rotor shaft, wherein the first magnetic element is separated into at least two parts along a circumferential direction; and Connecting the first magnetic element to the housing element.
12. Method according to claim 10 or 11, wherein before assembling a first magnetic element around the rotor shaft balancing of the rotor is performed.