Abstract:
A friction vacuum pump ( 1 ) comprises a fixed element ( 7 ) bearing rows of stator blades ( 3 ) and a rotating element ( 6 ) bearing rows of rotor blades ( 2 ). The rows of stator blades and rotor blades are arranged concentrically with respect to an axis of rotation ( 4 ) of the rotating element ( 6 ) and mesh with each other. In order to create in the axial direct a short friction pump, the elements ( 6, 7 ) bearing the rows of rotor blades and stator blades extend in a substantially radial manner and the longitudinal axes of the blades ( 2, 3 ) extend in a substantially axial manner.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a friction vacuum pump comprising a fixed element bearing rows of stator blades and a rotating element bearing rows of rotor blades whereby the rows of stator blades and rotor blades are arranged concentrically with respect to the axis of rotation of the rotating element and engage with each other. 
   Turbomolecular vacuum pumps are a kind of friction pump, see for example U.S. Pat. No. 5,577,883. They are designed just like a turbine with rows of rotor and stator blades. Stator and rotor are substantially cylindrical in shape and are arranged coaxially with respect to the rotational axis of the rotating component. The longitudinal axes of the stator and rotor blades which engage in alternating fashion, extend radially so that a substantially axial direction for the pumping action results. One or several pairs of a row of rotor blades and a row of stator blades form a pump stage. The pumping properties (pumping capacity, compression) of a pump stage are adjusted through the design of the blades, preferably through their angle of incidence. 
   In the instance of turbomolecular vacuum pumps according to the state-of-the-art, there exists a minimum requirement for the number of pump stages, which can not be reduced any further. Thus turbomolecular vacuum pumps according to the state-of-the-art have to be relatively long, in particular since the drive motor contributes further to the axial length. Moreover, in the instance of the known turbomolecular vacuum pumps only one component—commonly the rotor—can be made of a single piece, whereas the other component—commonly the stator—needs consist of a multitude of components in order to be able to assemble the engaging rows of stator blades. 
   It is the task of the present invention to create a turbomolecular vacuum pump of the aforementioned kind which is significantly shorter in the axial direction. 
   This task is solved by the present invention through characterising features of the patent claims. 
   SUMMARY OF THE INVENTION 
   The present invention allows the manufacture of friction pumps, the axial length of which—disregarding the drive motor—does not significantly extend beyond the length of the stator and rotor blades. Since the blades extend axially, both rotor and stator may be made of a single part respectively. 
   It is expedient to operate radially pumping pumps of the kind according to the present invention, in such a manner that the pumped gases flow from outside to inside. Here the utilisation of the differing circumferential speeds of the blades offers an advantage, since corresponding to the pressure range the frictional losses can be reduced. Moreover, the losses owing to backflowing gas can be much reduced in the direction of the pumping action compared to the axial compressor, since the stator may be manufactured as a single part and since no tolerances will add owing to a multitude of components needing to be joined. Equally the losses due to backflowing gas flowing around the tips of the blades are minimised, since here too the slots can be reduced significantly by aligning the carriers. 
   A further advantage exists in that the detailed rotor disks can be manufactured on lathes or erosion machines. Both techniques are relatively cost-effective. With the attainable reduction in the number of parts, the present invention represents a true alternative in meeting today&#39;s pressure on prices. 
   Moreover, it is expedient to combine known axially compressing turbomolecular vacuum pumps with radially compressing friction vacuum pumps designed according to the present invention. Pump systems of this kind allow the placement of the drive motor on the high vacuum side without the need for the motor and the bearings to consist of high-vacuum capable materials. Finally, there result advantages relating to the bearing arrangement for the rotating component. Long rotors require, in particular when they are to be suspended in a cantilevered manner, relatively involved bearings which in the instance of the relatively short rotors in the friction vacuum pumps according to the present invention are no longer necessary. 
   Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
       FIG. 1  depicts a radial section through the blades of a friction vacuum pump according to the present invention, 
       FIGS. 2 to 4  depict axial sections through different embodiments, 
       FIGS. 5 and 6  depict sections through a double-flow embodiment, 
       FIG. 7  depicts a section through a multi-stage solution, 
       FIG. 8  depicts a combination of a radially pumping pump stage with axially pumping friction pumping stages as well as, and 
       FIGS. 9 to 11  depict combined friction vacuum pumps for multi-chamber systems. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  depicts an embodiment of a friction pump  1  according to the present invention, in which the longitudinal axes of blades  2 ,  3  extend parallel to a rotational axis  4  of the rotating component. They are arranged in concentric rows about the rotational axis  4 . The rows of rotor blades  2  and the rows of stator blades  3  alternate. They engage into each other and have changing angles of incidence in the direction of flow (arrow  16 ) in a basically known manner. 
     FIGS. 2 to 4  depict an embodiment in which the blades  2 ,  3  are components of rotating and fixed carriers respectively,  6  and  7 . In the design example according to  FIG. 2  the rotating carrier  6  and the fixed carrier  7  have the shape of a disk. In the embodiment in accordance with  FIG. 3 , the surface on the blade side of the stator disk  7  is designed to be cone-shaped in such a manner that the distance between the two disks  6 ,  7  decreases from outside to inside. Also the length of the blades  2 ,  3  decreases from outside to inside. 
   In the embodiment in accordance with  FIG. 4 , the fixed carrier  7  has the shape of a funnel so that the distance between the carriers  6  and  7  decreases from inside to outside. The length of the blades  2 ,  3  is adapted to this change in distance. 
   In the embodiment of  FIG. 4 , the fixed carrier  7  is part of a casing  8  of pump  1 . It includes the carrier  7  with connecting port  9  as well as of a flat, pot-shaped casing section  11  which at its rim is flanged to carrier  7 . A bottom  12  of the casing section  11  extends parallel to rotor disk  6 . Said bottom carries the drive motor  13 , the shaft  14  which engages the rotor disk  6  through an opening in the bottom  12 . Moreover, there is provided at the casing section  12  a further connecting port  15 . 
   Vacuum pumps are preferably operated such that the pumping chamber decreases in the direction in which the gases are pumped. Friction vacuum pumps  1  according to the present invention offer this property already when the gases are being pumped from outside to inside (c.f. the arrows  16  drawn in to  FIGS. 1 to 3 ). The design of the fixed carrier  7  in accordance with drawing  FIG. 3  even strengthens this property. Also the width of the blades  2 ,  3  may decrease from outside to inside (c.f.  FIG. 1  in particular). 
   Of course, operation of the friction pumps is possible in the reverse pumping direction. To this end only the direction of rotation for rotor  6  needs to be reversed. An example of a friction pump  1  being operated in this manner is depicted in  FIG. 4  (arrows  18 ). The connecting flange  9  forms the inlet, the connecting flange  15  the outlet of the pump. To change the direction of the pumped gases, the pump chamber is modified such that the distance of the carriers  6 ,  7  and thus the lengths of the blades  2 ,  3  decrease from inside to outside. 
   Depicted in  FIGS. 5 and 6  is a double-flow embodiment of a friction vacuum pump  1  according to the present invention. An inner group of rows of blades pumps the gases radially towards the outside (arrows  21 ), an outer group of rows of blades from outside to inside (arrows  22 ). The connection ports  9  and  15  are inlet ports. Between the two groups, the stator disk  7  is equipped with a connection port  23  having the function of an outlet. By reversing the direction of rotation there results a further configuration (one intake port, two discharge ports), as may be utilised for leak detectors, the operation of which is based on the counter flow principle. Finally there also exists the option of designing the friction pump  1  according to the present invention as multiple-flow pump, i.e. with several groups of blades, which—compared to their neighboring groups of blades in each instance—have an opposing direction for the pumping action. 
   In the design example according to  FIG. 7 , several radially pumping pump stages are located axially in the casing  8  over each other. The rotating system comprises two rotor disks  6 , which each carry on both sides rotor blades  2 . The casing  8  and a carrier  25  affixed to the casing, said carrier being located between the two rotor disks  6 , carry the corresponding stator blades  3 . 
   Drawn in arrows  27  indicate that the connection port  9  has the function of an inlet and that the subsequent radially compressing stages (four, in all) pump from inside to outside and from outside to inside in alternating fashion. The outlet is designated as  26 . It is located inside and surrounds the drive shaft  14  so that in this area no sealing agents are required. By adapting the length of the blades from the inlet to the outlet (decrease) it is again possible to influence the volume of the pump chamber. 
     FIG. 8  depicts an option in which radially compressing friction vacuum pump  1  according to the present invention may be combined with an axially compressing friction pump  31  according to the state-of-the-art. The friction pump  31  consists of a turbomolecular pumping stage  32  located on the intake side and a molecular pumping stage  33  located on the delivery side, said molecular pump being designed as a Holweck pump (as depicted) or as a Gaede, Siegbahn, Engländer or side channel pump. 
   The friction pumps  1  and  31  are located in a joint, approximately cylindrically-shaped casing  35  with an inlet  36  at the side. A shaft  39  supported by bearings at both face sides (bearings  37 ,  38 ) carries the respective rotating components of the pumping stages (rotor disk  6  of the radially compressing pump  1 , rotor  41  of the turbomolecular pumping stage  32 , cylinder  42  of the Holweck pumping stage  33 ). The side inlet  36  of the combined pump opens out between the radially compressing pumping stage  1  and the axially compressing pump  31 . The outlet  44  of the combined pump is located on the delivery side of the molecular pumping stage  33 . The drawn in arrows  45  and  46  indicate that the radially compressing pump stage  1  takes in the gases which are to be pumped in the area of its periphery, and that the axially compressing pump  31 —as is common—takes in the gases in the area of its high-vacuum side. The gases being pumped by pump stage  1  pass via a bypass  47  directly to the intake side of the Holweck pumping stage  33 . 
   The special characteristic of the solution in accordance with drawing  FIG. 8  is, that the drive motor  48  is located at the high-vacuum side of the axially pumping pump  31  (and not as is common on the delivery side of the Holweck pumping stage  33 ). In that the radially compressing pumping stage  1  is located between the inlet  36  and the drive motor  48 , a relatively high pressure (1×10 −2  mbar, for example) can be maintained in the motor chamber  49 . The use of high-vacuum capable materials in motor chamber  49  is not required. Moreover, the radially pumping pump stage  1  supports the pumping capacity of the turbomolecular pumping stage  32  without significantly increasing the length of the pump  31 . 
     FIGS. 9 to 11  depict embodiments of combined friction pumps for deployment in connection with multi-chamber systems, a two-chamber system in this instance. These are, for example, analytical instruments with several chambers which need to be evacuated down to different pressures. Thus the distance of the intake ports is given, which in the instance of the state-of-the art frequently results in the requirement for relatively long cantilevered rotor systems which in turn require involved bearing systems. 
   All embodiments in accordance with  FIGS. 9 to 11  have two side inlets  36 ,  36 ′. These are separated by at least one radially compressing pumping stage  1 . The inlet  36  “sees” in each instance, as also in the embodiment according to drawing  FIG. 8 , the inlet areas of an axially pumping friction pump  31  as well as a friction pump  1  pumping radially from outside to inside. 
   In the embodiment in accordance with  FIG. 9 , the outlet of the radially pumping pump  1  opens out into the inlet area of a second turbomolecular pumping stage  32 ′ to which the second inlet  36 ′ is connected. The pump  1  has the effect that the pressure at inlet  36  is lower than at inlet  36 ′. The drive motor  48  is located on the delivery side of the turbomolecular pumping stage  32 ′. Said delivery side is linked via a bypass  47  to the suction side of the molecular pumping stage  33 . 
   If pumping of a partial flow from the inlet  36  into the area of the inlet  36 ′ is not desired, a further axially compressing friction vacuum pump  1 ′ may be provided for separating the inlets  36 ,  36 ′ ( FIG. 10 ). It pumps a partial flow of the gases entering into the inlet  36 ′. The outlets of the two friction pumps  1  and  1 ′ are linked to the bypass  47 . 
   The embodiment in accordance with  FIG. 11  has instead of the turbomolecular pumping stage  32 ′, a further axially pumping friction pump  1 ″. This solution may be employed when the amount of gas is not great. 
   In the embodiments in accordance with  FIGS. 9 to 11 , there are provided in each instance two high-vacuum pump systems  32 ,  32 ′,  1 ″ each connected with an inlet  36  and  36 ′. The selected arrangement also permits the arrangement of further high-vacuum pumps on the common shaft  39  and to separate their inlets each by radially pumping pump stages designed in accordance with the present invention. Through bypasses, both the high-vacuum pumping stages, generally turbomolecular pumping stages and also the outlets of the radially pumping pump stages can be linked each to a joint molecular pumping stage. 
   The presented examples demonstrate that the combination and the sequence of the pumping stages can be selected at will, and can be adapted to the specific application requirements. The arrangement of the pumping stages allows for more compact designs with bearings at both shaft ends. Thus the shafts can be made as stiff as needed. This results in designs which are unproblematic as to the rotor dynamics, and which also exhibit a good balancing characteristic. In that almost any number of stages can be attached to the shaft just like the components of a modular system, it is easier to implement a high-vacuum pump which compresses against the atmosphere. 
   The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will 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.