VACUUM PUMP

Abstract

A vacuum pump includes a housing, a rotor located in the housing and having a shaft and pump-active elements supported on the shaft, a stator having pump-active elements and located in a separate housing part of the housing, for driving the pump, bearings for rotatably supporting the rotor shaft, and at least one vacuum chamber also located in the separate housing part.

Description

RELATED APPLICATIONS

This application is a continuation-in-part of patent application Ser. No. 11/786,692, filed on Apr. 11, 2007 and which claims priority of German Patent Application DE 10 2006 020 710.6 filed on May 4, 2006 and incorporated herein by reference thereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vacuum pump including a housing, a rotor located in the housing and having a shaft and pump-active elements supported on the shaft, a stator located in the housing and having pump-active elements, with the housing having a housing part for holding the pump-active elements of the stator, drive means for driving the pump and bearing means for rotatably supporting the rotor shaft.

2. Description of the Prior Art

Vacuum pumps form, together with vacuum chambers, vacuum systems with which numerous tasks can be performed. These tasks range from manufacturing monolithic layers through analyses of gases, and up to optical columns of high-resolution electronic microscopes. The technical developments put higher and higher requirements to the vacuum tightness and compactness of the vacuum systems.

In some common applications, so-called differential pumps are used. With differential pumps, a system is formed of vacuum pumps connected with each other, with separate vacuum chambers being held at different gas pressures.

A noticeable simplification of formation of a pump system for differential pumps is disclosed in German Patent DE-PS 43 31 589. Instead of a plurality of pumps, a single vacuum pump takes over evacuation of vacuum chambers.

European Patent EP-PS 1 090 231 discloses a vacuum pump with a double housing. An inner housing combines a rotor/stator region and a drive/bearing region of the pump. The inner housing is then pushed into an outer housing that is adapted to a particular use. However, the latter solution has serious drawbacks, a double housing is expensive as more parts are used than with a single-part housing. This increases both expenses associated with manufacturing of the housing components and expenses associated with the assembly of numerous components. The contact surfaces of the two housings must be machined with a high precision. The danger of a virtual leak increases with an increase of number of components needed for the housing. Between the two separate housings, seals must be provided which, because of their large number, increase the risk of leakage. For a double housing, additional space should be provided, which makes gas feeding more expensive. These problems are independent of the number of vacuum chambers provided in the vacuum system.

Accordingly, an object of the invention is a vacuum pump in which the problems, which are associated with a double housing, are eliminated.

Another object of the invention is a vacuum pump having a compact construction and requiring a small number of parts.

SUMMARY OF THE INVENTION

These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a vacuum pump in which the housing part which serves for holding pump-active stator elements, has at least one vacuum chamber. This noticeably reduces the number of necessary parts. A smaller number of flanges and other housing transition elements results in an increase of vacuum tightness and reduction of costs. Generally, a very compact unit is provided. Because a flange connection between the vacuum chamber and vacuum pump, which is necessary in the existing state of the art, is eliminated, the vacuum tightness is noticeably increased. This permits to achieve lower end pressures with the inventive vacuum pump.

A further reduction of the number of parts is achieved when the separate housing part further holds at least one component of bearings and drive means.

According to the invention, the inventive vacuum pump has a plurality of pumping stages with each of which a vacuum chamber is connected, with the vacuum chambers being also connected with each other. Thereby, a single component, such as a housing, is necessary for all chambers in the vacuum pump, which reduces costs and increases tightness. With the gas pressure in the respective chambers being different, a plurality of differential pumps are provided in a single vacuum pump.

According to the invention the bearing means includes a permanent magnet bearing for supporting an end of the rotor shaft. This bearing does not require lubrication and is wear-free and, thus, can be used in the high-vacuum region of a vacuum pump.

According to a further modification of the present invention, for production of the high vacuum, the pump-active rotor elements and the pump-active stator elements includes blades forming at least one high-vacuum pumping stage. This is particularly suitable for obtaining low pressures.

According to a further development of the present invention, the at least one vacuum chamber has an opening, and the vacuum pump further includes a releasable cover for closing the opening, and at least two seals for sealing the opening. The opening provides for an easy access to the vacuum chamber so that, e.g., maintenance becomes possible, or the components located in the vacuum chamber, e.g., of some experiment, can be very easily replaced. The opening-sealing seals insure the vacuum tightness.

The arrangement discussed above can be further improved by providing an annular channel between the two seals and in which vacuum is produced. Thereby, the pressure drop between the atmospheric pressure and vacuum takes place in stages, which reduces forces acting on the seals. Because the leakage rate of a leak depends on the pressure difference between the inner and outer sides, and the stagewise pressure drops means a smaller pressure difference across a seal, smaller leaks play a smaller role. By measuring the power consumption of a pump used for producing vacuum, leakage at the seals can be determined.

According to further development of the present invention, there is provided a push-in or insertable module in which at least one of the vacuum chambers is located. The insertable module is pushed in a bore formed in the vacuum pump housing and is retained there. Thereby, it is possible to replace the vacuum chamber system of the inventive vacuum pump and adapt it to other requirements. In addition, it is possible to have the vacuum chambers and the vacuum pump produced by different manufactures. This reduces costs because manufacturing steps take place parallel with each other and respective professional skills and knowledge are optimally used.

According to a further advantageous embodiment of the present invention, for producing vacuum in the annular channel, there is provided a connection conduit integrated in the housing between the annular channel and one of pumping stages and gas outlet channel.

The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show:

FIG. 1 a cross-sectional view of a first embodiment of a vacuum pump according to the present invention;

FIG. 2 a cross-sectional view of a second embodiment of a vacuum pump according to the present invention; and

FIG. 3 a cross-sectional view of a third embodiment of a vacuum pump according to the present invention.

FIG. 4 a schematic view illustrating mounting of stator elements and spacers on a rotor shaft;

FIG. 5 a plan view of a spacer; and

FIG. 6 a plan view of a stator element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vacuum pump 1 according to the present invention, a first embodiment of which is shown in FIG. 1, has an upper housing part 2 and a lower housing part 3. A shaft 4 is supported at one of its ends by bearing means 8 and at its another opposite end by a permanent magnetic bearing 17. The permanent magnetic bearing 17 is located at a high-vacuum side of the pump system and is secured thereat by a support structure 16. The pump system includes pump-active rotor elements 5 supported on the shaft 4, and stationary pump-active stator elements 6. In the embodiment shown in the drawings, rotor and stator elements are formed as blade-carrying discs, whereby a vacuum pump in accordance with a known constructional principle of turbomolecular pumps is formed. However, the present invention is not limited to this type of a vacuum pump, rather it is applicable to a combination of different types in accordance with a pressure region that should be obtained. E.g., the invention is applicable to Holweck stages and the like. The stator has, in addition to pump-active stator elements 6, spacers 7 which determine the axial distance of the stator elements from each other. Both the stator elements 5 and the spacer elements 7 are formed of two semi-circular elements 6′ and 7′, as shown in FIGS. 5 and 4, respectively. However, if the inner diameter of the spacer is smaller than the outer diameter of the rotor it can be formed as a single spacer ring.

During assembly of the vacuum pump, the related semi-circular elements 6′ of the stator elements 6 and the semi-circular elements 7′ of the spacers 7 are positioned around the rotor shaft 4 with the rotor elements 5 already mounted thereon. The stator elements 6 and the spacers 7 are mounted on the shaft 4, starting from the region of the shaft 4 behind the first rotor element 5 and up. Firstly, a spacer 7 is mounted on the rotor shaft 4, then a stator element 6 is mounted around the shaft 4, with the rim of the stator element 6 being supported on the rim of the spacer 7. A respective rotor element 5 extends into the circular space defined by a spacer 7. The sequence of mounting of the stator elements 6 and the spacers 7 is shown in FIG. 4, with the end or assembled position shown with dash lines. When all of the stator elements 6 are mounted around the shaft 4, the support structure 16 for the magnetic bearing 17 is mounted on the shaft 4, as shown with arrow A. Finally, the upper housing part 2 is pushed over the support structure 16 and the stack of the stator elements 6. The upper housing part 2 secures the stator elements 6 around the shaft 4 and holds them in their predetermined position.

The described method of assembly of the stator elements 6 does not form part of the present invention and is adduced in order to clarify how a one-piece housing part including both a vacuum chamber and pump-active elements can be used.

In the housing part 3, in addition to bearing means 8, there is provided drive means 9, e.g., electrical coils which cooperate with permanent magnets arranged on the shaft 4, setting the shaft in rapid rotation. The bearing means 8 can be formed as a ball bearing, magnetic bearing, or gas bearing. The lower housing part 3 also includes a gas outlet channel 30 leading to a gas outlet union. When the vacuum pump itself is not compressed to the atmospheric pressure, a forevacuum pump is connected with this gas outlet union.

Also are arranged in the upper housing part 2, a first vacuum chamber 20 and a second vacuum chamber 21, with a lower pressure being produced in the first vacuum chamber 20 than in the second vacuum chamber 21.

The first vacuum chamber 20 is directly connected with the first pumping stage 22 of the pump system. The second vacuum chamber 21 is connected by a suction channel 10 with an intermediate inlet 18. Through the intermediate inlet 18, gas can be fed to the second pumping stage 23. Thus, gas from the first vacuum chamber 20 is fed into both the first pumping stage 22 and the second pumping stage 23 and is compressed there, whereas gas from the second vacuum chamber 21 is compressed only in the second pumping stage 23. This principle can be expanded further by providing further vacuum chambers in the upper housing part 2. The further vacuum chambers can be connected with further intermediate inlets of the pump system. Likewise, one of the chambers can be connected with the gas outlet channel 30 by a channel formed in the housing. The first and second vacuum chambers 20 and 21 are connected with each other by a connection passage 25. The passage 25 can be formed as a bore in the upper housing part 2 or as a throttle. The second vacuum chamber 21 has an opening 26 through which, e.g., a to-be-analyzed gas or a particle stream can flow in.

The upper housing part 2 has an opening that can be closed by a cover 11 and which is connected with the first vacuum chamber. The cover 11 permits to monitor components which are located in the first vacuum chamber 20. Around this opening, two seals are provided, with a first seal 12 surrounding the opening and the second seal 13 surrounding the first seal 12. An annular channel 14 is provided between the seals 12 and 13 and in which vacuum is produced. For producing the vacuum, there is provided a connection conduit 15 that opens either in one of the pumping stages of the vacuum pump or in the gas outlet channel 30. When the connection conduit opens not in front of the first pumping stage but at the other location of the pump system, the vacuum, which is produced between the two seals 12 and 13, is between the pressure in the first vacuum chamber 20 and the pressure of the vacuum pump environment. Thereby, the load, which act on separate seals, is noticeably reduced as the pressure drop across a respective seal is smaller. Measurement of drive power of the pump or the pumping stage necessary for producing the vacuum permits to make a conclusion about leakage and whether the seals are defective.

The vacuum pump according to the first embodiment has a further advantage achieved with the present invention, namely, when all of vacuum conduits between the chambers, chambers and pumping stages, and to the annular channel in the housing are integrated, only one forevacuum flange is necessary. Additional expensive conduits, which should be attached later, are eliminated.

In the vacuum pump according to a second embodiment, which is shown in FIG. 2, the invention is applied to a three-chamber system. There are provided in the upper housing part 2 of the vacuum pump a first chamber 31 in which a high vacuum is produced, a second chamber 32 in which a medium vacuum is produced, and a third chamber 33. The third vacuum chamber 33 is retained at a forevacuum level. The third vacuum chamber 33 is connected via a forevacuum inlet 37 with the gas outlet channel 30 of the vacuum pump. A middle inlet 36 connects the second vacuum chamber 32 with the pumping system of the vacuum pump. A high vacuum inlet 35 connects the first vacuum chamber 31 with the pump system. Gas, which reaches the pump system through the high vacuum inlet 35 should flow over all of the parts of the pump system. The stationary components, stator discs 6 and spacers 7 should only be mounted on the shaft 4 and retained in their positions in the upper housing part 2. Without the upper housing part 2, this mounting of stationary components is not possible, and remaining pump components themselves are not operational. As a rule, it is necessary to optimize conductance between the chambers and the respective parts of the pump system. A parameter which permits to achieve optimization, is angle α between the rotor axis 40 and the chamber axis 41. This parameter can vary between 0°, i.e., with parallel arrangement, and 90°, i.e., with a mutually perpendicular arrangement.

A third embodiment of a vacuum pump according to the present invention is shown in FIG. 3. The third embodiment differs from the second embodiment by the vacuum chambers. At least one of the vacuum chambers, here, two vacuum chambers 32 and 33 are arranged in an insertable module 44. This module 44 is inserted through a bore formed in the upper housing part 2 of the vacuum pump 1 and is secured in the upper housing part 2. To provide for servicing or exchange of the module, the module 44 can be releasably secured, e.g., with screws. Seals 45 seal the module 44 against the housing 2. The vacuum chambers 32, 33 are connected with each other as the chambers 32 and 31 that is formed in the upper housing part 2. All or, as shown in FIG. 3, only some of the chambers can be provided in the insertable module. Suction channels 42, 43 connect the vacuum chambers 32, 33 with different parts of the pump system of the vacuum pump, so that different pressure can be produced in the vacuum chambers.

Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is therefore not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A vacuum pump, comprising an upper one-piece housing part and a lower housing part connectable with each other and forming together a vacuum pump housing; a rotor shaft extending in the upper housing part and the lower housing part; bearing means located in at least one of the upper housing part and the lower housing part for supporting the rotor shaft for rotation; drive means for driving the rotor shaft and located in the lower housing part; pump-active rotor elements secured on a portion of the rotor shaft extending in the upper housing part; pump-active stator elements located in the upper housing part and securable thereby, the pump-active stator elements and the pump-active rotor elements forming together pumping means for producing a pumping action; and at least one vacuum chamber located in the upper housing part and communicating with the pumping means.

2. A vacuum pump according to claim 1, wherein the bearing means comprises a permanent magnet bearing for supporting one end of the rotor shaft.

3. A vacuum pump according to claim 1, wherein the at least one vacuum chamber has an opening, the vacuum pump further comprising a releasable cover for closing the opening, and at least two seals for sealing the opening.

4. A vacuum pump according to claim 3, comprising an annular channel arranged between the at least two seals and in which vacuum is produced.

5. A vacuum pump according to claim 4, wherein the pumping means forms at least two pumping stages, and the vacuum pump further comprises a gas outlet channel, and a connection conduit integrated in the housing and connecting the annular channel with the gas outlet channel or one of the at least two pumping stages.

6. A vacuum pump according to claim 1, further comprising at least one further vacuum chamber, at least one of the at least one and further vacuum chambers being located in an insertable module.

7. A vacuum pump according to claim 1, comprising at least one further vacuum chamber, and wherein the pumping means forms at least two pumping stages, and the at least one vacuum chamber and the at least one further vacuum chamber are directly connected with each other and each of the at least one vacuum chamber and the at least one further vacuum chamber is connected with a respective one of the two pumping stages.

8. A vacuum pump according to claim 7, wherein the gas pressure in the at least one and at least one further vacuum chambers is not the same.