Housing for a turbo-molecular vacuum pump

Abstract

A housing for a turbo-molecular vacuum pump comprising a body having an inlet disposed at a high vacuum side to be connected with a chamber to be evacuated; an inlet flange element integrally built with the body along a perimeter of the inlet, wherein by the inlet flange element a flange surface is provided to be in contact with the chamber to be evacuated, a circumferential groove in the inlet flange element to allow flexible deformation of the flange element upon connecting to the chamber to be evacuated.

Description

[0001] HOUSING FOR A TURBO-MOLECULAR VACUUM PUMP

[0002] The present invention relates to a housing for a turbo-molecular vacuum pump and a turbo-molecular vacuum pump comprising such a housing.

[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 order to connect a vacuum pump to a chamber to be evacuated, common vacuum pumps comprise a flange that is clamped or bolted to a corresponding flange of the chamber to be evacuated. However, by the clamping or bolting relative high forces are introduced into the housing of the vacuum pump which may cause deformation of the housing. Consequently, required accuracy of positioning components within the vacuum pump may compromised. This may in particular affect the bearings, wherein already minimal changes of the axial distance of the two bearings can lead to an increase bearing preload, reducing efficiency of the vacuum pump and further may also reduce the lifetime due to increased wear. This in particular applies if a bearing support of the vacuum pump is placed in close proximity to the inlet flange. Thus, in order to avoid deterioration of the vacuum pump, a certain distance between the inlet bearing support and the inlet flange needs to be maintained to avoid deflection of the inlet flange upon clamping or bolting from being transferred to the inlet bearing support. Hence, the overall size of the vacuum pump cannot be further reduced.

[0005] It is an object of the present invention to provide a turbo-molecular pump and a housing for a turbo-molecular pump which can be built more compact while maintaining theperformance and operating the turbo-molecular pump more reliable without increase of power consumption.

[0006] The problem is solved by a housing for a turbo-molecular pump according to claim 1 and a turbo-molecular pump according to claim 14.

[0007] According to the present invention, a housing for a turbo-molecular pump (TMP) is provided comprising a body having an inlet disposed at a high vacuum side of the turbo-molecular vacuum pump and which is connectable to a chamber to be evacuated. Hence, the inlet defines an opening in the housing of the TMP through which a gaseous medium can enter the TMP from the chamber to be evacuated by the pumping action of the TMP. Further, the housing comprises an inlet flange element integrally built with a body along a perimeter of the inlet, wherein by the inlet flange element a flange surface is provided to be in contact with the chamber to be evacuated. The flange surface may by an axially facing surface that comes in direct contact with the chamber to be sealed and may also be used as sealing surface. Thus, the inlet flange element may form the opening in the housing and may provide its shape. In addition, the inlet flange element or at least a part of the inlet flange element may be the most axial part of the housing. The inlet flange element may extend from the body in an axial direction to terminate with the flange surface or may at least partially overlap with the body in the axial direction. Therein, here and in the following, the axial direction is the axial direction of the housing, i.e. coinciding with the axis of rotation of the TMP. Consequently, the inlet flange element enables secure fastening of the housing of the TMP to the chamber to be evacuated. In particular, the inlet flange element of the housing is connected to a corresponding flange of the chamber to be evacuated.

[0008] The housing further comprises a circumferential groove in the inlet flange element to allow flexible deformation of the flange element upon connecting to the chamber to be evacuated. Thus, by the circumferential groove torsional movement of the inlet flange element upon clamping the inlet flange element to a corresponding flange of the chamber to be evacuated is decoupled from the body of the housing, thereby reducing deformation of the body and any parts connected to the body such as bearings of the TMP. Hence, any deformation of the inlet flange element by the clamping force of the inlet flange element is not transmitted for example to any bearing support. Thus, a bearing position of the TMP can be maintainedwith a higher accuracy and unwanted axial movement during operating, which otherwise would result in reduced operation performance and increased power consumption, can be avoided. Since the circumferential groove is inserted into the inlet flange element itself, the clamping force is directly compensated where it is induced and consequently, it is possible to position the low pressure I high vacuum bearing support close to the inlet, reducing the size of the TMP. Therein, the depth of the circumferential groove is sufficient to prevent axial movement of the inlet flange element to be transferred to the body, thereby decoupling the inlet flange element and the body of the housing.

[0009] Preferably, the circumferential groove extends along the complete perimeter of the inlet flange element.

[0010] Preferably, the circumferential groove is a continuous groove and thus uninterrupted along its extension and in particular along the complete perimeter. Hence, by a continuous groove flexibility can be efficiently introduced to decouple deformation of the flange from the bearing position.

[0011] Preferably, the circumferential groove is not arranged in the flange surface and / or may be separate from the flange surface.

[0012] Preferably, the circumferential groove is empty or in particular completely filled by a grouting material such as a softer metal or vacuum stable plastic. Thereby, the flexibility introduced by the groove can be adapted to the needs of the specific application.

[0013] Preferably, the groove does not contain a sealing element. Thus, the circumferential groove according to the present invention is an additional feature separate from and distinct of any groove of the vacuum pump housing containing a sealing element, such as an O-ring. Further, the circumferential groove is not used as recess for a clamp of an ISO-K flange (that is usually open in a direction opposite to the flange surface). Further, the groove is not a semi-circular indentation in the radial direction which is present in conventional ISO-K flanges.Preferably, in the area of the circumferential groove, the inlet flange element comprises a reduced radial thickness. In particular, the material in the area of the circumferential groove is reduced by more than 20 %, more preferably more than 50% and preferably more than 66%. In particular, the depths of the circumferential groove may be between 80%-10% of the maximum thickness of the inlet flange element in the direction of the circumferential groove, preferably between 50%-20% and more preferably 33%. Thus, by the area of reduced radial thickness, sufficient flexibility is induced in the inlet flange element to allow deformation of the inlet flange while preventing deformation of the body of the housing by decoupling the inlet flange element and the body of the housing.

[0014] Preferably, in the area of the circumferential groove, the inlet flange element comprises reduced stiffness. Due to the induced circumferential groove, a flexibility is induced in the inlet flange element by reducing the stiffness of the inlet flange element allowing flexible deformation upon clamping the inlet flange element to a corresponding flange of the chamber to be evacuated.

[0015] Preferably, the housing comprises more than one circumferential groove. Therein, more than one circumferential groove may be inserted into the inlet flange element at different positions. Alternatively or additionally, one or more further grooves may be arranged in the body adjacent to the inlet flange element.

[0016] Preferably, the circumferential groove extends in the radial direction. In particular, the circumferential groove extends only in the radial direction. Alternatively, the circumferential groove extends in the axial direction. In particular, the circumferential groove extends only in the axial direction. Consequently, by either the extension of the circumferential groove in the radial direction or the axial direction, a tailored flexibility of the inlet flange element can be induced to allow desired deformation of the inlet flange element upon clamping the inlet flange element to a corresponding flange.

[0017] Preferably, the circumferential groove extends at an angle relative to the axial axis of the housing. Consequently, the circumferential groove extends partially in a radial direction as well as partially in an axial direction. Preferably, the circumferential groove extends at an angle of between 10° and 80° and more preferably between 20° and 70°. In particular, thecircumferential groove extends in an angle of 45° relative to the axial axis of the housing. In addition to a tailored flexibility of the inlet flange element, an angled circumferential groove may also allow for easy manufacture of the circumferential groove due to an improved accessibility via the inlet of the housing compared to a pure radial circumferential groove.

[0018] Preferably, the circumferential groove has a depth of more than 3mm and preferably more than 5mm. It has been shown by the inventors of the present invention that these dimensions of the depths of the circumferential groove are sufficient in order to induce the necessary flexibility of the inlet flange element and prevent transfer of any unwanted deformation of the inlet flange element to the body of the housing. Therein, at the same time sufficient strength of the housing is maintained.

[0019] Preferably, the circumferential groove is arranged at an inner radius of the flange element, i.e. at a radially inner surface. Consequently, the circumferential groove is arranged at an inward-facing radial surface inside the housing and may extend in a radially outward direction. Alternatively, the groove is arranged at an outer radius of the flange element, i.e. and radially outer surface, which allows simple manufacturing from the outside of the housing. In particular, the circumferential groove is arranged at an outward-facing radial surface outside the housing and may extend in a radially inward direction.

[0020] Preferably, the circumferential groove has a substantial rectangular cross-section. Alternatively, the circumferential groove has a substantially U-shaped cross-section. In particular, the cross-section of the circumferential groove has a shape of a milling tool used for inserting the circumferential groove. Consequently, inducing or manufacture of the circumferential groove can be performed by a single milling, reducing the time for manufacture of the housing.

[0021] Preferably, the circumferential groove has depth larger than the width of the circumferential groove. In order to maintain structural stability of the housing while still decoupling movement of the inlet flange element from the body of the housing, it has been found to be beneficial that the depth is larger than the width of the circumferential groove. Therein, the depth may correspond the extension of the circumferential groove away from the respectivesurface of the housing, and the width may correspond to the extension of the groove along this surface.

[0022] Preferably, the housing comprises a bearing support member arranged in the inlet to receive a bearing of a rotor shaft, wherein the bearing support member is connected to the body and / or the inlet flange element by struts extending substantially radially from the body to the bearing support member. This is also known as a “bearing spider”. Therein, the bearing support member is located in the center of the inlet. The struts are connected to the body and may overlap at least partially with the inlet flange element on a side of the circumferential groove opposite to the flange surface. In other words, the circumferential groove may be arranged axially next to the struts in a direction towards the flange surface. Hence, deformation of the inlet flange element is also decoupled from the struts holding the bearing support member and thus, positioning accuracy of the bearing by the bearing support member is not affected by the clamping force applied to the inlet flange element.

[0023] Preferably, an axial surface of the bearing support member coincides with the flange surface of the inlet flange element.

[0024] Preferably, the circumferential groove extends across the struts. Thus, when following the circumferential groove along its perimeter, it is not interrupted at the positions of the struts but may be continuously formed.

[0025] Preferably, the circumferential groove extends into the struts. Hence, the circumferential groove is at least partially inserted into the struts to also allow flexibility of the struts to decouple deformation of the flange from the accuracy of positioning of the bearing support.

[0026] Preferably, an inner surface of the groove is built by the struts. Thus, while apart from the struts, the circumferential groove may be partially open, at the struts, the circumferential groove may comprise an additional inner surface provided by the struts.

[0027] In an aspect of the present invention, a turbo-molecular vacuum pump is provided comprising a housing as described before.Preferably, the vacuum pump comprises a first bearing built as permanent magnetic bearing and arrange at the inlet end of a rotor shaft, i.e. a first end of the rotor shaft. In particular, the first bearing may be supported and connected to the housing by the bearing support member of the housing. Alternatively or additionally, the vacuum pump comprises a second bearing arranged towards a second end of the rotor shaft being opposite to the first end. Therein, the second bearing may also be built as permanent magnetic bearing. Consequently, all radial bearings of the vacuum pump are provided by permanent magnetic bearings and the rotor shaft is fully magnetically levitated.

[0028] Preferably, the vacuum pump comprises an active axial bearing preferably arranged at an end of the rotor shaft opposite to the inlet and i. e. the second end of the rotor shaft.

[0029] Preferably, the vacuum pump comprises an eddy current damper in order to damp or reduce vibrations of the rotor assembly. Therein, in particular, the eddy current damper may be integrated in the active axial bearing at the second end of the roto shaft.

[0030] In the following, the present invention is described, by way of example only, with reference to the accompanying figures.

[0031] The figures show:

[0032] Fig. 1 a housing for a turbo-molecular pump according to the present invention,

[0033] Fig. 2 a detailed sectional view of the housing of a turbo-molecular pump according to a first embodiment of the present invention and

[0034] Fig. 3 a detailed sectional view of the housing of a turbo-molecular pump according to a second embodiment of the present invention.

[0035] Greater control of tolerance stack up is required to maintain clearances between the rotor and stator during pump operation. Therefore, the accurate position of bearings on the drive shaft or rotor shaft becomes more critical. A bearing spider can be used to locate the bearing with a high degree of accuracy when a bearing is provided on the vacuum side of the rotor.It has been understood that a relatively high level of accurate positioning can be achieved by integrating the bearing spider with the pump body such that the bearing spider and pump body are formed from a single piece of material.

[0036] Commercial considerations are increasing the push to reduce pump size, which has resulted (in some circumstances, depending on the pump's application) in the rotor being placed as near to the pump inlet as practically possible. As a result, the point at which a bearing spider joins the pump body can be coincidental or overlapping with an inlet flange element.

[0037] The inlet flange element can be formed integrally with the pump body typically comprises a standard arrangement that cooperates with standard clamping tools. A high vacuum seal is often used between a flange surface and another surface that engages the flange surface.

[0038] Application of a clamping force to the inlet flange can cause the inlet flange element to distort by relatively very small amounts. These distortions are typically insufficient to compromise the vacuum seal that is formed at the flange. As such, until now, the distortion of the inlet flange has been acceptable and of no undue concern.

[0039] However, it has been noticed by the inventors that these distortions now have an effect on the bearing spider. This undesirable effect is especially noticeable when the bearing spider and pump body are integral with one another and joined at the inlet flange. The torsional moment applied to the flange by the clamp is transmitted to the bearing spider causing the central portion of the bearing spider to become displaced by an undesirable amount. This in turn causes the bearing itself to become displaced such that accurate placement of the rotor is no longer achievable to the now desired amount. As a result, pump failure may occur if the rotor is not located accurately because the rotor and stator clash during operation. The problem is compounded if the bearing spider comprises magnetic bearings that have bearing components which do not make physical contact with one another, but rather rely on magnetic forces of attraction and repulsion.Figure 1 shows a pump housing 10 having a bearing spider with a bearing support member 14 on the vacuum side of a rotor (not shown for clarity). An inlet flange element 12 forms the inlet 18 of the pump.

[0040] The outlet is located at the bottom end of the pump housing 10. The pump body 20 forms a housing in which the pump components, including a rotor, stator, motor, drive shaft and other components are located.

[0041] The bearing spider is integrally formed on the inside of the body 20 at a location co-located or overlapping with the inlet flange element 12, which is also integrally formed with the body 20. The bearing spider comprises three spokes or struts 16 that extend radially out from the bearing support member 14 located coaxially with the axis of rotation. Thus, during pump operation, the bearing spider together with its bearing support member 14 is located in a region of high vacuum on the inlet side of the rotor, i.e. a first end of the rotor. As a result, it is typical to use passive magnetic bearings because they are best suited to operating in high vacuum pressure environments, in certain applications.

[0042] Fig. 2 shows a detailed view of the inlet area of the housing 10. Therein, same or similar elements are indicated by the same reference signs. As shown in Fig. 2, the circumferential groove 22 in the inlet flange element 12 extends along the complete perimeter around the inlet opening 18 of the housing 10. The circumferential groove 22 may have a width W and a depth D as indicated in Fig. 3. Therein, in the embodiment of Fig. 2, the circumferential groove extends in an angled direction having an angle a with respect to the direction 21 corresponding to the axial axis of the housing 10, i.e. the axial axis of the TMP corresponding to the axis of rotation of the TMP. Therein, the circumferential groove 22 may be II-shaped in particular in the area of the struts, or may be partially open, i.e. shown an L-shape. Thus, the circumferential groove 22 may be partially inserted into the struts and an inner surface 29 may be provided by the struts.

[0043] As shown in Figs. 2 and 3, by the inlet flange element 12 a recess 15 is provided open in a direction opposite to the inlet, wherein a clamp can be inserted into the recess in order to clamp the vacuum pump or housing 10 to a corresponding flange of the chamber to be evacuated. Therein, the housing 10 is in contact with the corresponding flange via the flangesurface 28. The flange element 12 may additionally or alternatively comprises a semi-circular indentation 13 of an ISO-K flange at the outer side of the flange element.

[0044] Further, as shown in Figs. 2 and 3, a top surface 26 of the struts and in particular the bearing support member 14 is positioned slightly below a flange surface 28 and axially corresponding to the inlet flange element 12. Consequently, the circumferential groove separates the inlet flange element 12 from the struts 16 directly connected to the body 20 of the housing 10 or at least overlapping in its axial position. Thereby, deformation of the inlet flange element 12 upon clamping the inlet flange element 12 to a corresponding flange of a chamber to be evacuated, is not transferred to the spider. Hence, the bearing support member 14 can be positioned close to the inlet 18 of the vacuum pump, reducing the axial extension of the vacuum pump.

[0045] In the following, Fig. 3 shows another embodiment of the housing 10 of the TMP. Therein, same or similar elements are indicated by the same reference signs. In addition to the circumferential groove 22 in the inlet flange element 12, in the embodiment of Fig. 3, an additional circumferential groove 24 is located in the body 20 from the outside providing further flexibility of the inlet flange element 12 upon clamping to a chamber to be evacuated. Therein, the additional circumferential groove 24 may be located directly adjacent to the inlet flange element 12 and in particular below the connection point of the struts 16 with the body 20 or overlapping with the connection point of the struts 16.Reference List:

[0046] 10 housing

[0047] 12 inlet flange element

[0048] 14 bearing support member

[0049] 15 recess

[0050] 16 struts

[0051] 18 inlet

[0052] 20 body

[0053] 21 direction

[0054] 22 circumferential groove

[0055] 24 additional circumferential groove 26 top surface

[0056] 28 flange surface

Claims

CLAIMS1. A housing for a turbo-molecular vacuum pump comprising:a body having an inlet disposed at a high vacuum side for connection to a chamber to be evacuated;an inlet flange element integrally built with the body along a perimeter of the inlet, the inlet flange element comprising a flange surface for contacting the chamber to be evacuated, anda circumferential groove in the inlet flange element to allow flexible deformation of the flange element upon connection to the chamber to be evacuated.

2. Housing according to claim 1 , wherein the circumferential groove extends along the complete perimeter of the inlet flange element.

3. Housing according to claim 1 or 2, wherein the circumferential groove is a continuous groove.

4. Housing according to any of claims 1 to 3, wherein the circumferential groove is not arranged in the flange surface and / or may be separate from the flange surface.

5. Housing according to any of claims 1 to 4, wherein in the area of the circumferential groove the flange comprises a reduced radial thickness.

6. Housing according to claim 5, wherein the radial thickness is reduced by more than 20% and preferably by more than 50% by the circumferential groove.

7. Housing according to any of claims 1 to 6, wherein in the area of the circumferential groove the inlet flange element comprises a reduced stiffness.

8. Housing according to any of claims 1 to 7, wherein the circumferential groove extends in the radial direction.

9. Housing according to claim 8, wherein the circumferential groove extends only in the radial direction.

10. Housing according to any of claims 1 to 8, wherein the circumferential groove extends in the axial direction.

11. Housing according to claim 10, wherein the circumferential groove extends only in the axial direction.

12. Housing according to any of claims 1 to 11, wherein the circumferential groove extends at an angle relative to an axial axis of the housing.

13. Housing according to claim 12, wherein the circumferential groove extends at an angle of between 10° and 80° and preferably between 20° and 70° relative to the axial direction of the housing.

14. Housing according to any of claims 1 to 13, wherein the circumferential groove is open towards the inlet of the housing.

15. Housing according to any of claims 1 to 14, wherein the circumferential groove has a depth of more than 3mm and preferably more than 5mm.

16. Housing according to any of claims 1 to 15, wherein the depths of the circumferential groove may be between 10%-80% of the maximum thickness of the inlet flange element in the direction of the circumferential groove and preferably between 20%-50%.

17. Housing according to any of claims 1 to 16, wherein the circumferential groove is arranged at an radially inner surface of the flange element.

18. Housing according to any of claims 1 to 17, wherein the circumferential groove is arranged at an radially outer surface of the flange element or the body.

19. Housing according to any of claims 1 to 18, wherein the circumferential groove has a substantially rectangular cross-section or a substantially U-shaped cross-section.

20. Housing according to any of claims 1 to 19, wherein a cross-section of the circumferential groove has the shape of a milling tool used for generating the circumferential groove.

21. Housing according to any of claims 1 to 20, wherein the circumferential groove has a depth larger than a width of the circumferential groove.

22. Housing according to any of claims 1 to 21 , wherein the housing comprises a bearing support member arranged at the inlet to receive a bearing of a rotor shaft, wherein the bearing support member is connected to the body by struts extending substantially radially, wherein the struts are connected to the body on a side of the circumferential groove opposite to the flange surface.

23. Housing according to claim 22, wherein the circumferential groove extends across the struts and / or into the struts.

24. Housing according to any of claims 1 to 23, wherein the circumferential groove is empty.

25. Housing according to any of claims 1 to 23, wherein the circumferential groove is at least partially filled by a grouting material.

26. Housing according to any of claims 1 to 24, wherein the flange surface comprises a recess to accommodate a sealing element such as an O-ring, wherein the circumferential groove is separate of and distinct from the recess.

27. Turbomolecular vacuum pump comprising a housing according to any of claims 1 to 26.

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