Note: Descriptions are shown in the official language in which they were submitted.
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A multi-stage friction vacuum pump
The invention refers to a multi-stage friction vacuum pump with at least one
axially compressing turbo-compressor stage having a rotor rotating about its
axis and comprising rotor discs projecting between stationary stator discs.
Turbomolecular pumps belong in the group of friction vacuum pumps with
which a high vacuum can be created, for example for recipients used in semi-
conductor manufacturing or for mass spectrometers. A multi-stage friction
vacuum pump described in DE 100 04 271 A1 (Leybold Vakuum AG) com-
prises one or a plurality of turbo-compressor stages each formed by a rotor
with radially projecting rotor discs and a stator with radially projecting
stator
discs. The rotor discs and the stator discs mesh in a comb-like manner with
little space between them. They cause a molecular flow axial to the rotor
axis.
In addition to the turbo-compressor stage, a circular compressor stage may be
provided which comprises a rotor with axially projecting rotor blades arranged
on a circular line and a stator with axially protruding stator blades arranged
on
a circular line. The rotor blades and the stator blades mesh alternately and
cause a molecular flow that is directed either radially inward or radially out-
ward, depending on the sense of rotation and the angle of attack of the
blades.
It is the object of the invention to provide a multi-stage friction vacuum
pump
with at least one turbo-compressor stage, wherein the stages are arranged in
series in the flow path and which is to yield higher compression.
The multi-stage friction vacuum pump of the present invention has the fea-
tures of claim 1. The vacuum pump comprises a turbo-compressor stage and a
circular compressor stage arranged downstream in the flow path. Whereas the
turbo-compressor stage is suited to generate a high vacuum, the downstream
circular compressor stage serves to effect a pressure increase. As a conse-
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quence, since the gas volume is reduced by compression, the circular com-
pressor stage can have small dimensions. The circular compressor stage has a
small axial dimension since it is flown through mainly in the radial
direction.
The overall dimensions of the friction pump are not significantly increased by
the circular compressor stage, but the compression is clearly intensified with
respect to single-stage friction vacuum pumps. The present combination of an
upstream turbo-compressor stage and a downstream circular compressor
stage offers the advantage of requiring little space while having a high com-
pression capacity.
According to a preferred embodiment of the invention, the turbo-compressor
stage and the circular compressor stage are integrated in a common combina-
tion of rotor and stator. This means that the rotors of both compressor stages
are formed by a single combined rotor and the stators of both compressor
stages are also formed by a single combined stator. Thus, the dimensions and
the weight can be reduced further.
The present friction vacuum pump is preferably designed as a multiple inlet
pump. It comprises at least two axially spaced, serially compressing turbo-
compressor stages between which an intermediate inlet is located. A circular
compressor stage is arranged on the compressor side of the first turbo-
compressor stage and/or the second turbo-compressor stage. Such a pump is
particularly suited for use in the context of mass spectrometers. Due to the
increased gas flow at the intermediate inlet to which the analyzing means of
the mass spectrometer is connected, the gas flow at the intermediate inlet is
increased without a negative effect on the pressure at the high vacuum inlet.
The increase in the gas flow at the intermediate inlet means an increased sen-
sitivity of the mass spectrometer.
Depending on the compression ratio, different types and structures may be
used for the circular compressor stages, such as described in DE 100 94 271
A1.
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The following is a detailed description of embodiments of the invention with
reference to the drawings. These embodiments should not be seen as limiting
the scope of protection of the present invention. Rather, this scope is
defined
by the claims and the equivalents thereof.
In the Figures:
Fig. 1 illustrates a longitudinal section through a friction vacuum pump
of the present invention,
Fig. 2 is an illustration of the circular compressor stage,
Figs. 3 and 4 are longitudinal sections through different embodiments of
circular compressor stages.
The friction vacuum pump illustrated in Figure 1 comprises a housing 10 of
substantially cylindrical design, which has a high vacuum port HV at one end.
In the housing wall an intermediate inlet ZE1 is provided that is open to the
side. The intermediate inlet ZE1 is bridged by webs 18 that connect the stator
parts with each other.
In the front portion 10a of the housing 10, a first turbo-compressor stage 11
formed by a stator 12 and a rotor 13 is arranged. The stator 12 has a
plurality
of stator discs 15 directed radially inward from a circumferential wall 14.
The
rotor 13 has a plurality of rotor discs 16 projecting radially outward between
the stator discs 15. A drive 17 including a fast rotating electric motor
drives
the rotor 13 at a number of rotations between 30,000 and 60,000 rpm.
A second turbo-compressor stage 21 is arranged on the compressor side of
the first turbo-compressor stage 11 and has its inlet connected with the inter-
mediate inlet ZE1. The turbo-compressor stage 21 is formed by a stator 22
and a rotor 23. The stator 22 comprises a plurality of stator discs 25
directed
radially inward from a circumferential wall 22. The rotor 23 comprises a
plural-
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ity of rotor discs 26 projecting radially outward between the stator discs 25.
The rotors 13 and 23 are fixedly interconnected and are driven together by the
drive 17.
In the housing 10, a further compressor stage 30 follows the second turbo-
compressor stage 21, this further compressor stage being additionally con-
nected with an intermediate inlet ZE2. For example, the compressor stage 30
is a Holweck stage or another molecular pump, for example a Gaede pump, a
Siegbahn pump, an Englander pump or a side channel pump.
In the present embodiment, a circular compressor stage 33 is provided follow-
ing the first turbo-compressor stage 11. It comprises a rotor disc 34 which is
a
part of the rotor 13 of the turbo-compressor stage 11, and a stator disc 32
which is a part of the stator 12. The rotor disc 34 comprises rotor blades 35
arranged on concentric circles, and the stator disc 32 comprises stator blades
36 also arranged on concentric circles and engaging in gaps between the rotor
circles, as is illustrated in Figure 2. The stator blades and the rotor blades
are
inclined oppositely with respect to the radial direction. Depending on the
sense
of rotation of the rotor, the circular compressor stage 33 conveys either ra-
dially outward or radially inward. In the present embodiment, the conveying
direction is indicated by the arrow 37. The gas transport passes from the high
vacuum inlet HV through the turbo-compressor stage 11 and radially inward
from the circumference thereof through the circular compressor stage 33 and
from there through a gap 38 to the intermediate inlet ZE1. From the interme-
diate inlet ZE1, the turbo-compressor stage 21 conveys the gas to the com-
pressor stage 30. The second intermediate inlet ZE2 also opens into the com-
pressor stage 30. The compressor stage 30 conveys to an outlet (not illus-
trated).
One of the rotor discs 16 of the turbo compressor stage 11 is the supporting
disc for the rotor blades of the circular compressor stage 33. The stator disc
of
the circular compressor disc simultaneously forms the end wall of the pres-
sure-side end of the turbo-compressor stage 11.
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It is a special advantage that the circular compressor stage 33 is quasi inte-
grated in the turbo-compressor stage 11. The only additional effort required
are the rotor and stator blades 35, 36 additionally provided at the rotor and
the stator of the turbo compressor stage.
As an alternative to the present embodiment, a circular compressor stage 33
may also be provided behind the second turbo-compressor stage 21. The cir-
cular compressor stage arranged on the pressure side of the respective turbo-
compressor stage and integrated in the turbo-compressor stage increases the
gas flow on the pressure side. For a mass spectrometer connected thereto,
this means an increase in sensitivity.
Figure 3 illustrates the gas flow 40 through the circular compressor stage 33
flowing radially from the outside inward.
In the embodiment of Figure 4, the blade surface of the rotor disc 34 is coni-
cal. The rotor blades 35 have an axial length that decreases as the radius of
the circular path decreases.
It is also possible to use a circular compressor stage with a plurality of
discs
and alternately outward and inward directed flow paths, as is generally illus-
trated in Figure 7 of DE 100 04 271 A1.
