WO2024033321A1

WO2024033321A1 - Vacuum pump with improved balancing of the rotor

Info

Publication number: WO2024033321A1
Application number: PCT/EP2023/071849
Authority: WO
Inventors: Christian HOESGEN; Dirk Christian KALISCH; Alois Greven; Christian Berger; Heinz Englaender; Daniel Radermacher; Roman DEMBEK
Original assignee: Leybold Gmbh
Priority date: 2022-08-09
Filing date: 2023-08-07
Publication date: 2024-02-15
Also published as: GB2621345A; GB202211564D0; GB2621345B

Abstract

Vacuum pump, in particular turbomolecular pump, comprising: a housing having at least one housing element defining an internal volume; a rotor disposed at least partially in the internal volume of the housing element and rotatably supported by at least one bearing; wherein the minimum diameter of the internal volume is larger than the maximum diameter of the rotor.

Description

VACUUM PUMP WITH IMPROVED BALANCING OF THE ROTOR

The present invention relates to a vacuum pump and in particular to a turbo- molecular pump.

Common vacuum pumps comprise a housing having an inlet and an outlet. A rotor is disposed in the housing and rotatably supported by at least one bearing. The rotor comprises a rotor shaft and at least one pump element. In the case of a turbomolecular pump the rotor comprises a plurality of vanes as pump elements interacting with a plurality of vanes of a stator connected to the housing. Upon rotation of the rotor by an electromotor a gaseous medium is conveyed from the inlet of the vacuum pump to the outlet.

Due to the high rotational speed of a turbomolecular pump it is necessary to balance the rotor. Therein, any unbalancing of the rotor will cause vibrations and noise or even damage of the vacuum pump during operation. Thus, balancing is necessary which is performed outside the housing. Therein, several components are attached to the rotor interacting with corresponding elements in the housing, for instance as for the electromotor a stator is attached to the housing and a corresponding motor magent is attached to the rotor. Also, axial bearings or the like are arranged in an interlocking manner in the housing being nested with each other. Thus, these interlocking elements can not be preassembled and inserted into the housing together with the rotor, but instead are mated to the rotor after the rotor is inserted into the housing. Thus, as a consequence, these interlocking elements are also not assembled during the balancing process of the rotor which might result in unwanted unbalancing of the rotor by these interlocking elements.

Thus, it is an object of the present invention to provide vacuum pump with improved balancing of the rotor.

The problem is solved by a vacuum pump according to claim 1. In an aspect of the present invention a vacuum pump, in particular a turbomo- lecular pump, is provided. The vacuum pump comprises a housing having at least one housing element, wherein the at least one housing element defines an internal volume. Further, a rotor assembly comprises a rotor shaft and one or more pump elements which is disposed at least partially in the internal volume of the housing element and rotatably supported by at least one bearing. Therein, in accordance with the present invention the minimum inner diameter of the internal volume is larger than the maximum outer diameter of the rotor assembly preferably of the part of the rotor assembly that is within the housing or the respective housing element. Therein, the inner diameter of the internal volume might be defined at a radial inner surface of the housing element facing towards the centre, or centre axis, of the vacuum pump or of a component directly connected to the radial inner surface of the housing element extending in particular radially from the housing element into the internal volume. Consequently, the minimum inner diameter of the internal volume may be determined by the innermost radial surface of the housing element or a component directly connected to the housing element. The minimum inner diameter of the internal volume may be determined by the innermost radial surface of the part of the housing element, or component directly connected to the housing element, that defines the internal volume. Thus, the internal volume of the housing element surrounding the respective parts of the rotor assembly has a minimum inner diameter that is larger than the maximum outer diameter of these rotor parts such that the housing element can be interlock-free fitted around the rotor part or, the other way around, the rotor part can be interlock-free inserted into the internal volume of the housing element.

Preferably, the housing comprises only one housing element wherein by the single housing element the entire housing of the vacuum pump is provided. Alternatively, the housing comprises more than one housing elements built as separate housing parts that can be assembled in different steps of an assembly procedure to provide together the housing of the vacuum pump. Therein, at least one housing element is a cap element connected to another housing element in order to build the housing of the vacuum pump. Therein, in an assembly procedure a first housing element might be provided, the rotor is inserted into the first housing element and subsequently a second housing element for example built as cap element is inserted and connected to the first housing element in order to complete the housing of the vacuum pump.

Preferably, the at least one housing element is built as cap element including an interior wall wherein by the interior wall the internal volume is defined. In particular, consequently, the minimum inner diameter of the internal volume is then defined by interior wall and more specifically by an innermost radial surface of the interior wall.

Preferably, the vacuum pump comprises a Holweck stage including a cylinder connected to the rotor rotor assembly wherein the interior wall is arranged within the cylinder.

Preferably, the vacuum pump comprises an electromotor wherein the minimum inner diameter of the internal volume is provided by the stator of the electromotor connected to the at least one housing element. Preferably, the stator of the electromotor is connected to the interior wall defining the minimum inner diameter of the internal volume defined by the interior wall. More specifically, the minimum inner diameter of the internal volume may then be defined by an innermost radial surface of the stator.

Preferably, the vacuum pump comprises an axial magnetic bearing including a radial protrusion connected to the rotor assembly wherein by a magnetic element an axial magnetic force is applied to the radial protrusion for axial support of the rotor shaft. Therein, the maximum outer diameter of the rotor assembly disposed in the internal volume is defined by the radial protrusion. Preferably, the axial magnetic bearing is arranged in the internal volume defined by the interior wall within the Holweck stage.

Preferably, the vacuum pump comprises an eddy current damper including a conductive disk arranged next to at least one and preferably arranged between two eddy current damper magnets being arranged axially next to the conductive disk. The connective disk is made from a conductive material such as copper or aluminium and the disk is connected to the at least one housing element and preferably to the interior wall. Thus, the disk is non-rotated or static while the eddy current damper magnets are rotated in connection with the rotor shaft. By movement of the eddy current damper magnets eddy currents are induced into the conductive disk creating a magnetic restoring force counteracting the movement of the vibration of the rotor shaft and thereby damping vibration of the rotor. In particular the eddy current damper is arranged in the internal volume defined by the interior wall within the Holweck stage. The maximum outer diameter of the rotor assembly disposed in the internal volume is defined by the outer diameter of the conductive disk. In order to insert the rotor assembly into the housing element in an interlock-free manner the minimum inner diameter, for exampled defined by the stator of the electromotor, of the respective housing element is to be larger than the maximum outer diameter defined by the outer diameter of the disk.

Preferably, the disk is separated into at least two parts along its circumferential direction. Thus, the one or two eddy current damper magnets can be assembled to the rotor assembly. Subsequently, balancing of the rotor assembly including the eddy current damper magnets can be performed. Subsequently, the disk being two-parted is assembled around the rotor shaft of the rotor assembly and the rotor assembly including the eddy current damper magnets and the disk are inserted into the housing element. In a last step the disk is connected to the at least one housing element and preferably to the interior wall of the housing element. Alternatively, the disk is assembled to the rotor shaft after inserting the rotor assembly into the housing.

Preferably, the difference between the minimum inner diameter of the internal volume and the maximum outer diameter of the rotor assembly disposed in the internal volume is between 0,1 mm and 10 mm, more preferably between 0,5 mm and 5 mm and most preferably between 1 mm and 2 mm. By these differences the rotor assembly can be assembled into the respective housing element in an interlock-free manner and balancing of the rotor assembly in a preassembled configuration can be performed.

The present invention is described in more detail with reference to the accompanied figures.

The figures show:

Figure 1 a first embodiment of the present invention and

Figure 2 another embodiment of the present invention.

Referring to Figure 1 showing a vacuum pump 10 comprising a first housing element 12 and a second housing element 14 together forming the housing of the vacuum pump. A rotor assembly 17 comprising a rotor shaft 16 is disposed in the housing and rotatable around the centre axis 11. The rotor assembly 17 is supported by a first bearing 20 exemplified as permanent magnetic bearing having a plurality of ring magnets 24 being in mutual repulsion to each other in order to provide radial support of the rotor assembly 17. Further, a second bearing 22 is provided also exemplified in Figure 1 as permanent ring magnet with a similar structure than the first bearing 20. Further, emergency running bearings 25, 27 are implemented built as roller bearings in order to avoid contact between the rotor assembly 17 and static parts of the vacuum pump 10 upon failure of the first and/or second bearing 20, 22.

A plurality of pump elements 26 are connected to the rotor shaft 16 built as vanes and arranged alternating with vanes 28 of the stator. Further, the rotor assembly 17 comprises a Holweck stage 29 comprising a rotating cylinder 34 connected to the rotor shaft 16, and a stator 31 comprising a threaded groove in order to convey a gaseous medium from an inlet 101 to an outlet (not shown).

Further, at least the first bearing 20 might comprise an adjustment element 114 to adjust the axial position of the ring magnets 24 of the static part. Thereby, by the adjustment element 114 the axial position of the ring magnets 24 of the static element is adjusted against the restoring force of the spring element 116. Therein, the static ring magnets 24 of the respective bearing might be connected to a trunnion 30 extending into a respective recesses of the rotor assembly 17. Other configurations of the bearings 20, 22 are also possible.

Further, the vacuum pump might comprise one or more of an eddy current damper 100 for damping of rotational vibrations of the rotor 16, an electromotor 18 for rotation of the rotor assembly 17, and an axial bearing 50 for axial support of the rotor assembly 17.

The eddy current damper 100 comprises in the example of Figure 1 two eddy current damper magnets 120A, 120B connect to the rotor assembly 17. Further, the eddy current damper 100 comprises a disk 118 made of a conductive material and arranged between the two eddy current damper magnets 120A, 120B. In the embodiment of Fig. 1, the disk 118 is connected to the second housing element 14.

The electromotor 18 comprises an electromotor stator 110 and a motor magnet

112 connected to the rotor assembly 17 interacting with the electromotor stator 110 connected to the second housing element 14 to rotate the rotor assembly 17.

The axial bearing 50 comprises a radial protrusion 104 which is arranged axially between two yoke elements 103A, 103B of an electromagnet 102 and connected to the rotor assembly 17 in order to apply an adjustable axial magnetic force onto the protrusion 104 and thereby also to the rotor assembly 17.

The second housing element 14 comprises an interior wall 32 extending into the internal volume defined by the first housing element 12. In particular, the interior wall 14 is arranged inside the cylinder 34 of the Holweck stage 29. By the interior wall 32 of the second housing element 14 an internal volume 36 is defined. In the embodiment of Figure 1, the disk 118 of the eddy current damper 100 is connected to the interior wall 32 and arranged in the internal volume 36 defined by the interior wall 32. Further, the stator of the electromotor 110 is connected to the interior wall 32 and arranged in the internal volume 36 defined by the interior wall 32. Further, the electromagnet 102 of the axial bearing 50 is attached to the second housing element 14 and arranged in the internal volume 36 defined by the interior wall 32.

For assembly of the vacuum pump of Figure 1, first the first housing element 12 is provided and the rotor assembly 17 is inserted into the first housing element 12. Subsequently, the second housing element 14 is inserted in an insertion direction indicated by the arrow 38 and assembled to the first housing element 12. Thereby, the second housing element 14 might be built as cap element closing the housing of the vacuum pump. Before inserting the rotor assembly 17, the rotor assembly 17 is balanced in order to avoid unbalancing which might cause noise and vibrations or might even damage the rotor. However, insertion of the second housing element 14 is only possible if no interlocking elements are present. Otherwise, these interlocking elements need be joined to the rotor assembly 17 after insertion of the second housing element 14. Thus, it is an object of the present invention to set the minimum inner diameter of the internal volume 36 larger than the maximum outer diameter of the rotor assembly 17 and in particular that part of the rotor assembly 17 which is disposed in the internal volume 36, i.e. in the example to Figure 1 surrounded by the interior wall 32 that defines the interior volume 36, including the elements of the eddy current damper 100, electromotor 18 and the axial bearing 50. For example, in Figure 1 the minimum inner diameter of the internal volume 36 is defined by the inner diameter of the stator 110 of the electromotor 18. At the same time the maximum outer diameter of the part of the rotor assembly disposed in the internal volume 36 is defined by the maximum diameter of the radial protrusion 104 of the axial bearing 50. In order to preassemble the radial protrusion 104 before balancing and being able to include the radial protrusion 104 into the process of balancing, the inner diameter of the stator 110 of the electromotor 18 is set to be larger than the outer diameter of the radial protrusion 104 of the axial bearing 50 to be able to move the stator 110 of the electromotor 18 past the radial protrusion 104 of the axial bearing 50. Thus, the distance Di between the outer diameter of the radial protrusion 104 of the axial bearing 50 and the inner diameter of the stator 110 of the electromotor 18 is set to be between 0.1mm to 10mm and preferably between 0.5mm and 5mm and more preferably between 1mm and 2mm. Thus, by increasing the inner diameter of the stator 110 of the electromotor 18 accordingly, an interlock-free assembly can be achieved such that all elements of the rotor assembly 17 arranged in the internal volume 36 defined by the interior wall 32 of the second housing element 14 can be preassembled to the rotor shaft 16 and thus properly balanced in a balance process.

Preferably, the yoke elements 103A, 103B of an electromagnet 102 might be separated into two or more parts in order to be assembled around the rotor assembly 17 after inserting the rotor assembly into the housing. In this way the radial protrusion 104 of the axial bearing 50 can be preassembled to the rotor shaft 16 and included into the balancing process. In the embodiment shown in Figure 1 the eddy current damper 100 is arranged behind the electromotor 18 along the insertion direction 38.

Referring now to Figure 2 wherein same or similar elements are indicated with the same reference signs. Only the difference between the embodiment of figure 1 and figure 2 are described.

In the embodiment of Figure 2 the electromotor 18 is arranged after the eddy current damper 100 and the axial bearing 50 along the insertion direction 38 of the second housing element 14. Wherein the electromotor 18 in figure 2 is exemplified including a motor slug magnet 112.

In accordance to Figure 2 the minimum inner diameter of the internal volume 36 defined by the interior wall 32 of the second housing element 14 is defined by the inner diameter of the stator 110 of the electromotor 18. This diameter is set to be larger than the outer diameter of the disk 118 of the eddy current damper 100 and also the outer diameter of the radial protrusion 100 of the axial bearing 50 similar to the embodiment of Figure 1. Due to the difference D2 between the inner diameter of the stator 110 of the electromotor 18 and the outer diameter of the disk 118 of the eddy current damper 100, the stator 110 of the electromotor 18 can pass by the disk 118 of the eddy current damper. Therein, the distance D2 is set to be between 0.1mm to 10mm and preferably between 0.5mm and 5mm and more preferably between 1mm and 2mm. Therein, upon assembly of the vacuum pump the disk 118 is assembled around the rotor 16. Subsequently, the second housing element 14 is inserted and the disk 118 is connected to the interior wall 32 of the second housing element 14. Thus, the disk 118 might be separated into two or more parts in order to assemble the disk 118 around the rotor 16. In this way the two eddy current damper magnets 120A, 120B can be preassembled to the rotor shaftl6 and included into the balancing process. Preferably, also yoke elements 103A, 103B of an electromagnet 102 might be separated into two or more parts in order to be assembled around the rotor assembly 17 after inserting the rotor assembly 17 into the housing. In this way the radial protrusion 104 of the axial bearing 50 can be preassembled to the rotor shaft 16 and included into the balancing process.

Thus, by setting the minimum inner diameter of the internal volume defined by the respective housing element and the maximum outer diameter of the respective rotor elements, an interlock-free assembly of the vacuum pump is enabled providing the possibility to include all necessary elements of the rotor assembly into the balancing process of the rotor assembly.

Claims

CLAIMS Vacuum pump, in particular turbomolecular pump, comprising: a housing having at least one housing element, wherein by the at least one housing element an internal volume is defined; a rotor assembly comprising a rotor shaft and one or more pump elements and disposed at least partially in the internal volume of the housing element and rotatably supported by at least one bearing; wherein the minimum inner diameter of the internal volume is larger than the maximum outer diameter of the rotor assembly disposed in the internal volume. Vacuum pump according claim 1, wherein the at least one housing element is a cap element including an interior wall defining the internal volume. Vacuum pump according to claim 2, comprising a Holweck stage including a cylinder connected to the rotor assembly, wherein the interior wall is arranged within the cylinder. Vacuum pump according to any of claims 1 to 3, comprising an electromotor, wherein the minimum diameter of the internal volume is provided by the stator of the electromotor which is preferably connected to the interior wall. Vacuum pump according to any of claims 1 to 4, comprising an axial magnetic bearing including a radial protrusion connected to the rotor assembly, wherein the maximum diameter of the rotor assembly disposed within the internal volume of the housing element is defined by the radial protrusion. Vacuum pump according to any of claims 1 to 5, comprising an eddy current damper including a conductive disk arranged next to at least one, and preferably between two eddy current damper magnets connected to the rotor assembly, wherein the disk is connectable to the at least one housing element and preferably to the interior wall, wherein the maximum diameter of the rotor assembly disposed in the internal volume is defined by the outer diameter of the disk. Vacuum pump according to claim 6, wherein the disk is separated into at least two parts along its circumferential direction. Vacuum pump according to any of claims 1 to 7, wherein the difference between the minimum diameter of the internal volume and the maximum diameter of the rotor assembly dispose in the internal volume is between 0.1mm and 10mm, preferably between 0.5mm and 5mm and more preferably between 1mm and 2mm.