Patent Publication Number: US-6699009-B2

Title: Vacuum pump

Description:
BACKGROUND OF INVENTION 
     1. Filed of the Invention 
     The present invention relates to a vacuum pump including a housing having a suction opening in its high-vacuum region, a gas outlet opening in its high pressure region, and an intermediate chamber adjoining the gas outlet opening, pump-active cooperating rotor and stator components arranged in the housing for pumping gases from the suction opening to the outlet opening, with an end of the pump-active components adjoining the high pressure region being connected with the gas outlet opening via the intermediate chamber. 
     2. Description of the Prior Art 
     Vacuum pumps of the type described above can be formed, e.g., as turbomolecular pumps, or as molecular pumps, such as Holweck pumps, or as a combination of both types of pumps. The present invention also extends to combination of pumps that discharge against atmospheric pressure after realizing high pressure such as, e.g. regenerative pumps. 
     Such vacuum pumps are formed, as a rule, of a number of stages having different configurations, with each stage including rotor and stator components. The delivered gas flows through these pump-active components. The field of application of these pumps extends to processes in which a large quantity of easily condensable gases is formed, e.g., such as chemical processes or processes associated with manufacturing of semiconductors. With these pumps, gases flow from a high-vacuum region to a pressure region, in which a laminar flow prevails or in which the gas is compressed to atmospheric pressure. This means that in this region of high pressures, a relatively large quantity of gas is being pumped. In case when these gases are easily condensable, which is particularly the case at low temperatures, a significant amount of deposition of liquid or a solid materials takes place. This deposition leads to corrosion and etching that can result in destruction of separate components of a pump or an entire pump. This is particularly critical for types of pumps, which were discussed above, because their optimal operation can only be obtained at their high rotational speeds with a very small distance between the stationary and rotatable parts. 
     It was suggested to prevent formation of undesirable deposits by heating the critical regions (DE-A-197 02 456, EP-A 0646 290). In the constructions described in these references, the critical regions are heated by feeding heat via large-surfaces. The drawback of this solution consists in that the pump components, which are not subjected to precipitation, become heated, e.g., such as the housing high-vacuum connections, bearings, the drive. This leads, in addition to a very high energy consumption, to further drawbacks such as undesirable expansion of components having very narrow tolerances, damage of the drive bearing parts, and to a danger of injury to personnel as a result of a contact with a heated part. 
     Accordingly, the object of the preset invention is to provide a vacuum pump in which only the components susceptible to precipitation are heated. 
     SUMMARY OF THE INVENTION 
     This and other objects of the present invention, which will become apparent hereinafter, are achieved by providing, in the intermediate chamber, heating means connected with stator components located in the pressure region by a connection having a high thermal conductibility, and by providing thermal resistance means for separating the heating means from the housing. 
     The present invention ensures that only the critical components, i.e., only those components, which are particularly susceptible to precipitation of condensable material, are heated. By providing thermal connections having a high thermal conductibility, the heat is specifically directed to critical points. Other components, e.g. the housing, high-vacuum connections, bearings, and the drive, are protected from heating by thermal insulation. The advantages of these measures consists in reduced energy consumption, prevention of an undesirable expansion of components with narrow tolerances, prevention of injury to the personnel as a result of contact with heated parts. By increasing the flow rate, the pump output can be increased. The small heat capacity of the heated parts and of the stator components in the region of high pressure results in a reduced time of heating and, thereby, in reduced power consumption. 
     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 
     In the Drawings: 
     Single FIGURE shows a cross-sectional view of a vacuum pump according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be explained in detail with reference to a turbomolecular pump that represents one type of a vacuum pump according to the present invention. 
     The turbomolecular pump, which is shown in the drawing figure, includes a housing  1  provided with a suction opening  2  in its high-vacuum region  8  and an outlet gas opening  3  in its forevacuum region  10 . The turbomolecular pump further includes a rotor shaft  4  which is supported in bearings  5  and  6  and is driven by a motor  7 . On the rotor shaft  4 , there are arranged rotor components  12  which have a pump-active structure and cooperate with stator components  14 , which likewise can have a pump-active structure, for producing a pumping effect. 
     The gases, which are delivered through the suction opening  2 , are fed by pump-active components to the gas outlet opening  3  through a forevacuum-side, intermediate chamber  18 . Accordingly to the present invention, the intermediate chamber  18  is provided with heating means  20  and is connected with fore vacuum-side stator components  24  via thermal connection with a high thermal conductibility. The thermal connection is produced by forming the stator components  24  of a material having a high thermal conductibility and by providing a large-surface contact therebetween. The intermediate chamber  18  of the housing  1  and the high vacuum-side, stator components  14  are separated from each other by thermal resistances  28 . Additionally, the gas outlet opening can likewise be provided with heating means  21  and be thermally separated from adjoining housing parts by thermal resistances  27 . 
     Because the present invention, being described with reference to the turbomolecular pump, extends to pumps and pump systems, which discharge against up to the atmospheric pressure, the term “fore-vacuum” includes high-pressure regions up to the atmospheric pressure. 
     Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof, and various modifications to 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 embodiment or details thereof, and the present invention includes all of variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.