Patent Publication Number: US-8992162-B2

Title: Multi-inlet vacuum pump

Description:
BACKGROUND 
     The present invention relates to a multi-inlet vacuum pump. 
     Multi-inlet vacuum pumps comprise, within a common housing, a plurality of pump devices provided e.g. as turbomolecular pumps, optionally in connection with a Holweck stage. Usually, the individual pump devices are carried by a common rotor shaft and are driven by a single electric motor. The pump housing comprises a main inlet through which a first fluid stream is sucked in by operation of the first pump device. Then, after passing through the first pump device, the first fluid stream will be conveyed in the direction of an outlet by the second pump device and, optionally, by further pump devices. Between the first and second pump devices, an intermediate inlet is provided for suctional intake of a second fluid stream by operation of the second pump device. The second pump device will thus convey the first and second fluid streams in the direction of the outlet. Optionally, a second intermediate inlet can be provided between the second pump device and a third pump device. By operation of the third pump device, also a corresponding third fluid stream is conveyed in the direction of the outlet, wherein all of said three fluid streams will be conveyed by the third pump device. 
     It is an object of the invention to provide a multi-inlet vacuum pump having a high suction capacity in said intermediate inlet. 
     SUMMARY 
     In a preferred embodiment of the invention, the first pump device comprises a rotor disk, preferably the last rotor disk when viewed in the conveying direction, which has an enlarged diameter. The diameter of the last rotor disk of the first pump device preferably corresponds to the diameter of the first rotor disk of the second pump device, it being particularly preferred that all of the rotor disks of the second pump device have the same diameter. By said enlargement of the diameter of the last rotor disk of the first pump device relative to the other rotor disks of the first pump device, there is effected, still within the first pump device, a radical deflection of the first conveying flow towards the outside. In the region of the intermediate inlet, the first conveying flow will thus already have been deflected. The intermediate inlet is preferably located between said larger-diametered last rotor disk of the first pump device and the first rotor disk of the second pump device. The larger diameter of the last vane of the first rotor stage is effective to improve the compression in the intermediate inlet in the direction towards the outlet and thus to prevent a backflow of the fluids from the intermediate inlet in the direction opposite to the conveying flow. Although this improvement of the compression could also be achieved by providing several stages which have the same rotor diameter as the first stage, this solution would be more expensive. 
     According to the invention, at least one rotor disk of the first rotor element has a diameter which is smaller than the diameter of the second rotor disks of the second rotor element. Thus, according to the invention, the diameter of the rotor disks within the first rotor element is stepped. According to the invention, the first rotor element thus comprises rotor disks with different diameters, wherein also a multiple stepping can be provided within the first rotor element. Preferably, when viewed in the flow direction, at least the first rotor disk of the first rotor element is configured with a smaller diameter than that of the rotor disks of the second rotor element. It is especially preferred that at least 50%, still more preferably at least 75% of the rotor disks of the first rotor element have a smaller diameter than the second rotor disks of the second rotor element. 
     With preference, it is not only the last rotor disk of the first pump device that has a larger diameter preferably identical to that of the rotor disks of the second pump device. Instead, for instance, it can also be provided that—when seen in flow direction—the last two or even more than the last two rotor disks of the first pump device have a larger diameter than the other rotor disks of the first pump device. Further, it is possible that at least the last two rotor disks of the first pump device have substantially the same diameter as the first rotor disk of the second pump device, while the rotor disks of the second pump device preferably all have the same diameter. Optionally, the diameter of the last rotor disks of the first pump device can increase in a step-wise manner. Thus, starting from the relatively small diameter of the first rotor disk of the first pump device, the diameter of the rotor disks becomes larger with stepped increases, until at least the last rotor disk has a diameter corresponding to the diameter of the rotor disks of the second pump devices. 
     Optionally, the multi-inlet vacuum pump can also comprise a plurality of intermediate inlets. For this purpose, a further pump device is arranged, when viewed in flow direction, upstream and/or downstream of the first and respectively the second pump device. Between mutually adjacent pump devices, respective intermediate inlets can be provided. It is of relevance for the invention that two mutually adjacent pump devices, which for the sake of brevity will be referred to hereunder as the first and second pump devices, are configured in the above described inventive manner. In a multi-inlet vacuum pump comprising a plurality of intermediate inlets, it is according to the invention also possible that, in the region of an intermediate inlet, the inventive configuration is provided a plurality of times. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described in greater detail hereunder by way of a preferred embodiment with reference to the accompanying drawing. 
       The FIGURE shows a schematic longitudinal sectional view of a preferred embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The FIGURE illustrates that part of a multi-inlet vacuum pump which is of relevance for the invention. Said part of the overall pump comprises a first pump device  10  and a further or second pump device  12 , both of them arranged in a common housing  14 . Additionally, a third pump device such as e.g. a Holweck stage, can be provided in said housing on the right-hand side in the FIGURE. 
     Said first pump device  10  comprises a rotor element  18  arranged on a rotor shaft  16 . In the illustrated embodiment, rotor element  18  comprises four radially extending rotor disks  20  having identical outer diameters as well as one rotor disk  21  having a larger outer diameter. Said rotor disks  20 , 21  comprise rotor vanes for conveyance of a fluid, particularly gas. Between adjacent rotor disks  20 , stationary stator disks  22  are arranged. Said stator disks  22  are fixedly held in housing  14 , e.g. with the aid of rings. 
     On rotor shaft  16 , which in the illustrated embodiment is supported by two bearings  24 , there is further mounted a further or second rotor element  26  of second pump device  12 . In the illustrated embodiment, said second rotor element  26  comprises five rotor disks  28 . Between the rotor disks  28 , stator disks  30  are arranged which again are fastened in a stationary manner to housing  14 , optionally with the aid of stator rings. Also said rotor disks  28  comprise vanes for conveyance of fluid, which vanes are arranged in an outer region which in the FIGURE is shown without hatching. 
     The first pump device  10  will suck in the gas via a main inlet  32  of housing  14 . In this manner, a first fluid flow  34  will be generated in the direction of the second pump device  12 , i.e. in the conveying direction  36 . The conveying direction  36  corresponds to the main conveying direction from the main inlet  32  towards an outlet which is provided, in the conveying direction, downstream of the last pump device, i.e.—in the FIGURE—on the right-hand side in the housing. 
     Further, housing  14  is provided with an intermediate inlet  38 . Intermediate inlet  38  is arranged in housing  14  between first pump device  10  and second pump device  12 . By intermediate inlet  38 , a second fluid flow  40  is generated, again in the conveying direction  36 . Said second fluid flow  40  is conveyed in the direction of the pump outlet by operation of the second pump device  12  and, optionally, a further pump device arranged downstream thereof. In multi-inlet vacuum pumps related to the exemplary embodiment illustrated herein, a high vacuum exists at the main inlet  32  and a slightly lower vacuum exists at the intermediate inlet  38 . To make it possible to obtain the highest possible suction performance, i.e. to generate a low vacuum also on intermediate inlet  38 , it is provided in the illustrated embodiment that the radius of the rotor disks  28  of second pump device  12  is larger than the radius of the rotor disks  20  of first pump device  10 . 
     According to the invention, the first pump device  10  comprises an additional rotor disk  21 , being the last rotor disk in the conveying direction  36 , which has a larger outer diameter than the rotor disks  20 . Thereby, the first fluid flow  34 , after passing through the first rotor disks  20 , will by radially outwardly deflected (arrow  42 ) by rotor disk  21 . In the region of the vanes (non-hatched area) of rotor disk  21 , the first fluid flow will pass through rotor disk  21  (arrow  44 ). 
     The last rotor disk  21  of first pump device  10  has an outer diameter which substantially corresponds to the outer diameter of rotor disk  28  of second pump device  12 . Thus, it is guaranteed, in spite of the different diameters of the rotor disks in relation to the entire multi-inlet vacuum pump, that the first fluid flow  34  and the second fluid flow  40  will be united as desired. 
     The two rotor elements  18 , 26  are mounted on a common shaft  16  and are driven by a common electric motor  25 . 
     According to the invention, it is further possible to provide a multi-inlet vacuum pump comprising a plurality of intermediate inlets wherein at least one of said intermediate inlets is configured in the manner described above with reference to the Figure. Preferably, a plurality of intermediate inlets are configured as provided by the invention. Irrespective of the configuration of the individual intermediate inlets, it can also be possible that, with respect to the embodiment shown in the Figure, at least one further pump device is arranged upstream of the first pump device  10  in the flow direction  36 . Further at least one further pump device can be provided downstream of the second pump device  12  in the flow direction  36 . 
     The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.