Vacuum pump

Abstract

Vacuum pump, in particular turbomolecular vacuum pump, comprising: a housing defining a pump chamber, a rotor assembly arranged in the pump chamber comprising a rotor shaft and at least one rotor element connected to the rotor shaft, an electromotor to rotate the rotor assembly comprising a motor stator and a motor magnet rotated with the rotor assembly and a first bearing to rotatably support the rotor shaft built as permanent magnetic bearing comprising one or more static ring magnets and one or more rotated ring magnets radially next to the static ring magnets. The rotor assembly comprises a carrier element built as separate element from the rotor shaft, the carrier element is connected to and rotated with the rotor shaft of the rotor assembly, wherein the motor magnet and the one or more rotated ring magnets are connected to the carrier element.

Description

[0001] VACUUM PUMP

[0002] The present invention relates to a vacuum pump and in particular a turbo-molecular pump. Further, the present invention relates to a method of assembly of a rotor assembly for a vacuum pump and method of assembly of such a vacuum pump.

[0003] Common vacuum pumps comprise a housing having an inlet and an outlet. In the housing a rotatably supported rotor assembly is disposed that is rotated by an electromotor. The rotor assembly is rotatably supported by bearings, wherein in common vacuum pumps these bearings can either be roller bearing or magnet bearings. Further, the rotor assembly comprises at least one rotor element. In the case of a turbo-molecular pump, the rotor assembly comprises a plurality of rotor elements built as vanes arranged in one or more stages interacting with respective stator elements connected to the housing. In the case of a turbo-molecular pump also the stator elements are built as vanes arranged in an alternating manner with the one or more stages of the rotor assembly. By the rotation of the rotor assembly, a gaseous medium is conveyed from the inlet of the vacuum pump to the outlet of the vacuum pump.

[0004] In particular, if the vacuum pump comprises two permanent magnetic bearings, the second permanent magnetic bearing needs to be arranged towards an end of the rotor shaft opposite to the inlet of the vacuum pump. While at the inlet of the vacuum pump the permanent magnetic bearing can be arranged inside the shaft at a location of maximum shaft diameter, this is not possible for the second permanent magnetic bearing since the shaft diameter continuously decreases. The decreasing shaft diameter does not allow a second permanent magnetic bearing to be placed along the rotor shaft in the same way as with the high vacuum bearing at the inlet.

[0005] In addition, for each element connected to the rotor shaft, the rotor shaft needs to provide a shaft shoulder or axial abutment face, which decreases further the diameter of the shaft, thereby deteriorating the rotordynamic behavior, which leads to higher vibrations and difficulties during the balancing process.Hence, it is an object of the present invention to provide a vacuum pump with an improved design of the rotor assembly.

[0006] The problem is solved by a vacuum pump according to claim 1 , a method of assembly of a rotor assembly according to claim 12 and a method off assembly of a vacuum pump according to claim 14.

[0007] According to the present invention a vacuum pump and in particular a turbo-molecular vacuum pump is provided. The vacuum pump comprises a housing defining a pump chamber. Further, the vacuum pump comprises a rotor assembly arranged in the pump chamber and comprising a rotor shaft and at least one rotor element connected to the rotor shaft. The rotor shaft may have a first end towards the inlet of the vacuum pump and an opposite second end. Therein, the first end may be located in an area of low pressure / high vacuum and the second end may be located in an area of high pressure / low vacuum. In the case of a turbo-molecular vacuum pump, the rotor assembly may comprise a plurality of vanes arranged in one or more rotor stages along the axial length of the rotor shaft. Further, the vacuum pump may comprise one or more stator elements connected to the housing and arranged to interact with the at least one rotor element in order to convey a gaseous medium upon rotation of the rotor assembly. In the case of a turbo-molecular vacuum pump, the vacuum pump comprises a plurality of vanes arranged in one or more stator stages in an alternating manner with the rotor stages.

[0008] For rotation of the rotor assembly, the vacuum pump comprises an electromotor comprising a motor stator connected to the housing of the vacuum pump and a motor magnet rotated with the rotor assembly.

[0009] Further, the vacuum pump comprises a first bearing to rotatably support the rotor shaft or the rotor assembly, wherein according to the present invention the first bearing is built as permanent magnetic bearing comprising one or more static ring magnets and a preferably corresponding number of one or more rotated ring magnets arranged radially next to the static ring magnets. Due to the repulsive magnetic force between the static ring magnets and the rotated ring magnets, the rotor shaft is levitated.According to the present invention, the rotor assembly comprises a carrier element built as separate element from the rotor shaft. The carrier element is connected to and rotated with the rotor shaft of the rotor assembly. Therein, the motor magnet and the one or more rotated ring magnets of the first bearing are connected to the carrier element. Hence, the carrier element provides an intermediate part or subassembly in order to connect both the motor magnet and the one or more rotated ring magnets of the first bearing together to the rotor shaft. If the motor magnet is integrated into the same subassembly as the rotated ring magnets of the first permanent magnetic bearing, there is no need for an extra shaft shoulder or axial abutment surface for the individual elements. This enables a thicker shaft on the fore-vacuum side / low pressure side opposite to the inlet and thus improved rotodynamic behavior, which leads to lower vibrations and simplify balancing. Another advantage of combining the rotated ring magnets and the motor magnet in one subassembly is that the first bearing can be placed in the middle of the rotor shaft and not necessarily at the end of the rotor shaft opposite to the inlet of the vacuum pump. Consequently, other elements such as eddy current dampers and / or active axial bearings can be placed at the second end of the rotor shaft.

[0010] Preferably, the motor magnet and / or the one or more rotated ring magnets are connected to the carrier element by an interference fit. Due to use of an additional carrier element, the motor magnets and the one or more rotated ring magnets can be assembled to the carrier in a separate assembly step independent from assembly of the rotor assembly.

[0011] Preferably, the carrier is a single piece. Thus, the number of parts can be maintained to be small simplifying the assembly procedure of the rotor assembly.

[0012] Preferably, the carrier element and the rotor shaft are in contact with each other at one axial abutment surface. Thus, there is no need for individual axial abutment surfaces or shoulders at the rotor shaft for each of the motor magnet and the one or more rotated ring magnets. Consequently, one step of a reduction of the rotor shaft diameter can be omitted. Of course, the carrier and the rotor shaft may be in contact at one or more than one radial surfaces.

[0013] Preferably, the carrier element comprises a recessed portion or a bell shaped portion. Therein, the rotated ring magnets are arranged at an inner surface of the recessed portion.Hence, the rotated ring magnets can be mounted at a position of maximal diameter of the carrier element allowing that the static ring magnets of the first bearing extend into the recess surrounded by the rotated ring magnets. Consequently, the rotated ring magnets are arranged at a larger diameter than the static ring magnets of the first bearing, i.e. the rotated ring magnets radially surround the one or more static ring magnets.

[0014] Preferably, the motor magnet is arranged at an outer surface of the carrier element. Hence, the motor magnet can be placed in direct radial vicinity to the motor stator in order to provide efficient operation of the electromotor.

[0015] Preferably, the motor magnet and the recessed portion flash at their radially outer surface. Thus, the carrier element together with the motor magnet comprise a substantially cylindrical outer surface.

[0016] Preferably, the motor magnet comprises a sleeve as reinforcement for the motor magnet. Preferably, the sleeve is made from a fiber reinforced material. In particular, the motor magnet is connected to the carrier element via the sleeve. In this case, the motor magnet may be connected to the sleeve via an interference fit for transfer of momentum during operation. Thus, the sleeve has an axial extension larger than the motor magnet. In particular, the sleeve may be connected to the carrier by an interference fit as well. In addition, a radial gap may be present between the carrier element and the motor magnet to prevent radial forces to be imposed onto the motor magnet.

[0017] Preferably, the sleeve extends over the recess position of the carrier element. Consequently, the sleeve may extend over the full axial length of the carrier element and provides a reinforcement to the motoric magnet and at the same time to the recess portion including the rotated ring magnets of the first bearing.

[0018] Preferably, the carrier element is made from a material different than the rotor shaft. For example, the material of the carrier element may include a Mu-metal or a steel which is able to shield magnetic stray fields of the motor magnet and / or the one or more rotated ring magnets. Alternatively or additionally, the material of the carrier element may have a lowthermal expansion for aid of positioning or with a thermal expansion substantially equal to the thermal expansion of the motor magnets and / or the one or more rotated ring magnets.

[0019] Preferably, the vacuum pump comprises a second bearing which may be built as roller bearing or permanent magnetic bearing and arrange at the inlet end of the rotor shaft, i.e. a first end of the rotor shaft. Consequently, all radial bearings of the vacuum pump may be provided by permanent magnetic bearings and the rotor shaft is fully magnetically levitated.

[0020] Preferably, the vacuum pump comprises an active axial bearing preferably arranged at an end of the rotor shaft opposite to the inlet i.e. the second end of the rotor shaft. By the arrangement of the first bearing in the middle of the rotor shaft in combination with the motor magnet via the carrier element, the active axial bearing can be arranged at the second end of the motor shaft.

[0021] Preferably, the vacuum pump comprises an damper in order to damp or reduce vibrations of the rotor assembly. Therein, in particular, the damper may be arranged between the carrier element and the active axial bearing or may be integrated in the active axial bearing at the second end of the roto shaft.

[0022] Preferably, the carrier element is arranged inside a Holweck rotor element. The Holweck rotor element is usually built as rotating cylinder, wherein the carrier element with the motor magnet and the one or more rotated magnets of the first bearing are at least partially arranged inside this cylinder of the Holweck rotor element.

[0023] Preferably, the carrier element is arranged in between the rotor elements and one or more of the active axial bearing, the second end of the rotor shaft and the damper.

[0024] Preferably, more than one motor magnet is connected to the carrier element.

[0025] Hence, by the carrier element according to the present invention a compact vacuum pump can be provided having improved rotor dynamic behavior and is simplified to manufacture.In another aspect of the present invention a method of assembly of a rotor assembly for a vacuum pump is provided. The method included the steps:

[0026] providing a rotor shaft;

[0027] connecting one or more rotor elements to the rotor shaft; and

[0028] providing a carrier element subassembly independent from the rotor shaft and the one or more rotor elements, wherein providing the carrier element subassembly includes:

[0029] providing a carrier element;

[0030] connecting a motor magnet to the carrier element;

[0031] connecting one or more ring magnets to the carrier element; and

[0032] connecting the carrier element subassembly to the rotor shaft.

[0033] Thus, the carrier element subassembly can be assembled independent of the rotor assembly and can be provided during the steps of the assembly of the rotor assembly. Therein, of course, the present invention is not limited to the timely order according to the order of steps indicated before. Consequently, the assembly of the carrier element subassembly can be performed prior to providing a rotor shaft or after providing a rotor shaft as well as prior to connecting one or more rotor elements to the rotor shaft or after connecting one or more rotor elements to the rotor shaft. However, usually the carrier element subassembly is connected to the rotor shaft after the one or more rotor elements are connected to the rotor shaft.

[0034] Preferably, at least one rotor element is a Holweck cylinder of a Holweck stage.

[0035] Preferably, the carrier element subassembly is built according to the features of the carrier element described before.

[0036] Preferably, the method of assembly of the rotor assembly further includes mounting the rotated ring magnets of the second permanent magnet bearing. In particular, the rotated ring magnets of the second permanent magnet bearing are mounted at a position opposite of the one or more rotor elements at the rotor shaft relative to the carrier element subassembly. Thus, the one or more rotor elements are in between the second permanent magnetic bearing and the carrier.In another aspect of the present invention the method of assembly of the vacuum pump and in particular turbo-molecular pump is provided. The method includes:

[0037] providing a rotor assembly according to the method described before; providing a housing of the vacuum pump and inserting the rotor assembly, and providing one or more stator elements and mounting the stator elements to the housing of the vacuum pump.

[0038] Preferably, the method further includes providing one or more stator elements and mounting stator elements to the housing of the vacuum pump.

[0039] In the following the present invention is described by way of example only with reference to the accompanying figures.

[0040] The figures show:

[0041] Figure 1 a vacuum pump according to the present invention,

[0042] Figure 2 a detailed view of the rotor assembly according to the present invention,

[0043] Figures 3A, 3B a detailed cross-sectional view of the carrier element according to the present invention.

[0044] Figure 1 shows a vacuum pump 10 according to the present invention. The vacuum pump 10 comprises a housing 12 having an inlet 14 and an outlet 16. By the housing 12 a vacuum chamber is defined. Therein, a rotor assembly is arranged in the pump chamber of the housing 12. The rotor assembly comprises a rotor shaft 13 having a first end 17 towards the inlet 14 of the vacuum pump 10 and an opposite second end 19. Further, the rotor assembly comprises a plurality of vanes 26 connected to the rotor shaft 13 in a turbo-molecular pumping stage 20. The vanes 26 are thereby arranged in rotor stages alternating with stator stages of a stator, wherein each stator stage comprises a plurality of stator vanes 24 connected to the housing 12. Downstream to the turbo-molecular pumping stage 20 a molecular drag stage 22 is arranged, wherein in the example of Figure 1 the molecular dragstage 22 is built as Holweck stage comprising a plurality of cylinders 30 which are connected to the rotor shaft 13 and are rotated therewith. These cylinders 30 are interacting with threaded stators 28 of the molecular drag stage 22 in the example of the Holweck stage. Therein, according to Figure 1, the rotor assembly is rotatably supported by a first permanent magnetic bearing 42 which is arranged in the middle of the rotor shaft 13 and in particular within the cylinders 30 of the molecular drag stage 22.

[0045] Further, the vacuum pump 10 comprises a second permanent magnetic bearing 18 arranged at the first end 17 of the rotor shaft 13, i.e. in the high vacuum / low pressure area of the vacuum pump 10. Each permanent magnetic bearing 18, 42 comprises a plurality of rotated ring magnets connected to the rotor assembly and a corresponding number of static ring magnets arranged in close proximity, i.e. radially next to the rotated ring magnets. Thereby, by their mutual repulsion, the rotor assembly is levitated by the magnetic force. Thus, by the first permanent magnetic bearing 42 and the second permanent magnetic bearing 18 radial support of the rotor assembly is provided.

[0046] In addition, the vacuum pump in the example of Figure 1 shows an active axial bearing assembly 44 which is arranged at the second end 19 of the rotor shaft 13. Further, the first permanent magnetic bearing 42 as well as the second permanent magnetic bearing 18 comprise emergency roller bearings 48 which are under normal operation not in contact with the rotor shaft and only come into contact with the rotor shaft upon failure of one or more of the permanent magnetic bearings.

[0047] Therein, the rotor assembly is rotated by an electromotor 40 which may also be arranged within the cylinders 30 of the molecular drag stage 22. Therein, the electromotor 40 comprises a motor stator 218 (see Figures 3A and 3B) and a rotated motor magnet 202 (see Figures 3A and 3B). Therein, the motor stator may be provided by one or more electromagnetic coils.

[0048] Figure 2 shows a detailed view of the rotor assembly. A carrier element 200 is connected to the rotor shaft 13. In particular, connection between the carrier element 200 and the rotor shaft 13 is provided by an interference fit.Therein, the carrier element 200 carries the motor magnet 202 and the one or more ring magnets 206 of the first permanent magnetic bearing 42. Thus, neither the motor magnet 202 nor the one or more ring magnets 206 are directly connected to the rotor shaft 13 but are instead indirectly connected to the rotor shaft 13 via the carrier element 200. Therein, by the carrier element 200 a recessed portion 212 is provided providing a recess 208, i.e. a bell-shaped section. Therein, the one or more ring magnets 206 are arranged and connected to the carrier element 200 inside the recess 208 to an inner surface of the carrier element 200, i.e. a radially inward facing surface. Thus, the one or more permanent ring magnets 206 are arranged at the maximum diameter of the carrier element and facing in the radial inner direction. As shown in Figures 3A, 3B a support element 214 reaches into the recess 208 and carries the static ring magnets 216 of the first permanent magnetic bearing 42.

[0049] Furthermore, the motor magnet 202 is arranged at an outer surface of the carrier element 200. In particular, the outer radial surface of the motor magnet 202 flushes with an outer radial surface of the carrier element 200. Therein, the axial position of the motor magnet 202 may be defined by the carrier element 200 and a stopper element 204. The stopper element 204 may be built as separate part or may be integrally formed with the carrier element 200. Alternatively, no additional stopper element 204 is provided and axial positioning of the motor magnet 202 may be provided by a respective axial abutment surface of the rotor shaft 13. In addition and as further elucidated in Figures 3A and 3B, the carrier element may be surrounded by a reinforcement element 210. Therein, as shown in Figure 3A, the reinforcement element 210 may extend over the complete axial length of the carrier element 200 or at least the substantial axial length of the carrier element 200. In the embodiment of Figure 3A, the reinforcement element 210 may extend only along the axial extension of the motor magnets 202 in order to protect the motor magnets 202 from radial forces exerted upon fast rotation of the rotor shaft 13. Preferably, the reinforcement element 210 is made from a metal or fiber reinforced material.

[0050] Although shown in Figures 3A, 3B that the carrier element 200 is connected to the rotor shaft 13 via two axial abutment surfaces or shoulders only one shoulder would be sufficient in order to fully define the axial position of the carrier element 200. Hence, one reduction ofthe diameter of the rotor shaft 13 can be omitted in order to maintain a large diameter of the rotor shaft 13 up to the second end 19 of the rotor shaft 13.

[0051] Preferably, the carrier element 200 can be made from a different material than the rotor shaft 13 providing different properties. In particular, the carrier element may be made from a Mu-metal or a steel in order to shield the magnetic stray fields generated by the first magnetic bearing.

[0052] By use of an intermediate carrier element 200 carrying the rotated ring magnets 206 of the first permanent magnetic bearing 42 together with the motor magnet 202, a larger diameter of the rotor shaft 13 can be maintained on the second end 19 improving rotodynamic behaviors. At the same time the same reinforcement element 210 can be used for the motor magnets 200 as well as the rotated ring magnets 206 of the first bearing 42. Further, by the use of the carrier element 200 the first permanent magnetic bearing 42 can be arranged in the middle of the rotor shaft 13 and thus can be compactly arranged within the molecular drag stage 22. At the same time, an active axial bearing as well as a damper can be arranged at the second end 19 of the rotor shaft 13. Hence, a compact and size reduced turbo-molecular pump can be provided.

[0053] In addition, it is possible to pre-assemble the carrier subassembly including the carrier element 200, the rotated ring magnet 206 and the motor magnet 202. If a reinforcement element 210 is implemented, this can be also included into the carrier subassembly pre-assembled prior to assembly of these components to the rotor shaft 13.Reference List:

[0054] 10 vacuum pump

[0055] 12 housing

[0056] 13 rotor shaft

[0057] 14 inlet

[0058] 16 outlet

[0059] 17 first end

[0060] 18 second permanent magnetic bearing 19 second end

[0061] 20 turbo-molecular pumping stage

[0062] 22 molecular drag stage

[0063] 24 stator vanes

[0064] 26 vane

[0065] 28 threaded stator

[0066] 30 cylinder

[0067] 40 electromotor

[0068] 42 first permanent magnetic bearing 44 axial bearing assembly

[0069] 200 carrier element

[0070] 202 motor magnet

[0071] 204 stopper element

[0072] 206 rotated ring magnets

[0073] 208 recess

[0074] 210 reinforcement element

[0075] 212 recessed portion

[0076] 214 support element

[0077] 216 static ring magnets

[0078] 218 motor stator

Claims

CLAIMS1. Vacuum pump, in particular turbomolecular vacuum pump, comprising:a housing defining a pump chamber,a rotor assembly arranged in the pump chamber comprising a rotor shaft and at least one rotor element connected to the rotor shaft,an electromotor for rotating the rotor assembly, comprising a motor stator and a motor magnet rotated with the rotor assembly, anda first bearing rotatably supporting the rotor shaft and built as a permanent magnetic bearing, comprising one or more static ring magnets and one or more rotated ring magnets radially next to the static ring magnets,wherein the rotor assembly comprises a carrier element built as separate element from the rotor shaft, the carrier element is connected to and rotated with the rotor shaft of the rotor assembly, andwherein the motor magnet and the one or more rotated ring magnets are connected to the carrier element.

2. Vacuum pump according to claim 1, wherein the motor magnet and / or the one or more rotated ring magnets are connected to the carrier element by an interference fit.

3. Vacuum pump according to claim 1 or 2, wherein the carrier element is a single piece.

4. Vacuum pump according to any of claims 1 to 3, wherein the carrier element and the rotor shaft are in contact with each other at one axial abutment surface.

5. Vacuum pump according to any of claims 1 to 4, wherein by the carrier element a recessed portion is provided, wherein the rotated ring magnets are arranged at an inner surface of the recessed portion.

6. Vacuum pump according to any of claims 1 to 5, wherein the motor magnet is arranged at an outer surface of the carrier element.

7. Vacuum pump according to any of claims 1 to 6, wherein the motor magnet and the recessed portion are flush at their radially outer surface.

8. Vacuum pump according to any of claims 1 to 7, wherein the motor magnet comprises a sleeve, wherein the sleeve preferably extends over the recessed portion of the carrier element.

9. Vacuum pump according to any of claims 1 to 8, wherein the carrier element is made from a material different than the rotor shaft.

10. Vacuum pump according to any of claims 1 to 9, wherein the vacuum pump further comprises a second bearing built as permanent magnetic bearing and arranged at an inlet end of the rotor shaft.

11. Vacuum pump according to any of claims 1 to 10, wherein the vacuum pump comprises an active axial bearing preferably arranged at an end of the rotor shaft opposite to the inlet end.

12. Method of assembly of a rotor assembly for a vacuum pump including the steps of:providing a rotor shaft;connecting one or more rotor elements to the rotor shaft; andproviding a carrier element subassembly independent from the rotor shaft and the one or more rotor elements, wherein providing the carrier element subassembly includes:providing a carrier element;connecting a motor magnet to the carrier element;connecting one or more ring magnets to the carrier element; and connecting the carrier element subassembly to the rotor shaft.

13. Method of claim 12, wherein the carrier element subassembly is built according to any of claims 2 to 8.

14. Method of assembly of a vacuum pump in particular a turbomolecular vacuum pump including:providing a rotor assembly according to the method of claims 12 or 13; and - providing a housing of the vacuum pump and inserting the rotor assembly.

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