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 
       [0001]    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 
       [0002]    1. Field of the Invention 
         [0003]    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. 
         [0004]    2. Description of the Prior Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    Accordingly, an object of the invention is a vacuum pump in which the problems, which are associated with a double housing, are eliminated. 
         [0010]    Another object of the invention is a vacuum pump having a compact construction and requiring a small number of parts. 
       SUMMARY OF THE INVENTION 
       [0011]    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. 
         [0012]    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. 
         [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    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. 
         [0019]    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. 
         [0020]    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 
         [0021]    The drawings show: 
           [0022]      FIG. 1  a cross-sectional view of a first embodiment of a vacuum pump according to the present invention; 
           [0023]      FIG. 2  a cross-sectional view of a second embodiment of a vacuum pump according to the present invention; and 
           [0024]      FIG. 3  a cross-sectional view of a third embodiment of a vacuum pump according to the present invention. 
           [0025]      FIG. 4  a schematic view illustrating mounting of stator elements and spacers on a rotor shaft; 
           [0026]      FIG. 5  a plan view of a spacer; and 
           [0027]      FIG. 6  a plan view of a stator element. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    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. 
         [0029]    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. 
         [0030]    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. 
         [0031]    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. 
         [0032]    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 . 
         [0033]    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. 
         [0034]    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. 
         [0035]    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. 
         [0036]    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. 
         [0037]    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. 
         [0038]    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.