U.S. patent application number 12/994245 was filed with the patent office on 2011-06-09 for multi-stage vacuum pump.
This patent application is currently assigned to OBERLIKON LEYBOLD VACUUM GmbH. Invention is credited to Markus Henry, Peter Klingner.
Application Number | 20110135506 12/994245 |
Document ID | / |
Family ID | 40873510 |
Filed Date | 2011-06-09 |
United States Patent
Application |
20110135506 |
Kind Code |
A1 |
Henry; Markus ; et
al. |
June 9, 2011 |
MULTI-STAGE VACUUM PUMP
Abstract
A multi-stage vacuum pump includes a plurality of rotor elements
(14, 16) disposed on a common shaft (10) in a pump housing (12) for
configuring multiple pump stages (18, 24, 26). The shaft is driven
by an electric motor (40). An inner bearing element (42) is
disposed between two rotor elements (14, 16) such that a
mechanically favorable bearing arrangement is implemented using a
simple configuration of the bearing elements (42, 44) as roller
bearings. This is possible in particular due to the separation into
two rotor elements (14, 16).
Inventors: |
Henry; Markus; (Koeln,
DE) ; Klingner; Peter; (Koeln, DE) |
Assignee: |
OBERLIKON LEYBOLD VACUUM
GmbH
KOELN
DE
|
Family ID: |
40873510 |
Appl. No.: |
12/994245 |
Filed: |
May 5, 2009 |
PCT Filed: |
May 5, 2009 |
PCT NO: |
PCT/EP09/55397 |
371 Date: |
November 23, 2010 |
Current U.S.
Class: |
417/245 |
Current CPC
Class: |
F04D 17/168 20130101;
F04D 29/059 20130101; F04D 19/04 20130101 |
Class at
Publication: |
417/245 |
International
Class: |
F04B 5/00 20060101
F04B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 23, 2008 |
DE |
10 2008 024 764.2 |
Claims
1. A multi-stage vacuum pump, comprising: a plurality of rotor
elements arranged on a common shaft in a pump housing to form a
plurality of pump stages, a drive element for driving said shaft,
and an inner bearing element arranged between two rotor
elements.
2. The multi-stage vacuum pump according to claim 1, wherein said
inner bearing element is fixed via a holding element comprising at
least one throughflow opening.
3. The multi-stage vacuum pump according to claim 2, wherein said
inner bearing element is connected to the pump housing via said
holding element.
4. The multi-stage vacuum pump according to claim 2, wherein said
holding element is substantially round.
5. The multi-stage vacuum pump according to claim 2, wherein said
holding element is arranged between two rotor elements.
6. The multi-stage vacuum pump according claim 1, wherein, along
the axial direction, said inner bearing element is arranged at
least partially within a rotor element.
7. The multi-stage vacuum pump according to claim 1, wherein a
rotor element is arranged between said inner bearing element and an
outer bearing element.
8. The multi-stage vacuum pump according to claim 7, wherein said
outer bearing element is arranged between two rotor elements.
9. The multi-stage vacuum pump according to claim 7, wherein said
inner bearing element and/or said outer bearing element are
configured as rolling bearings.
10. The multi-stage vacuum pump according to claim 9, wherein said
rolling bearing is grease-lubricated.
11. The multi-stage vacuum pump according to claim 2, wherein the
holding element defines a plurality of throughflow openings which
are shaped as partial ring segments.
12. The multi-stage vacuum pump according to claim 7, wherein the
rotor element is tightly connected to the shaft.
13. The multi-stage vacuum pump according to claim 8, wherein the
outer bearing element is fixed via a holding element comprising
throughflow openings.
14. The multi-stage vacuum pump according to claim 9, wherein the
inner bearing element and/or the outer bearing element are roller
bearings.
15. A multi-stage vacuum pump comprising: a pump housing which
defines at least a first inlet and a second inlet and an outlet; a
drive shaft; a first rotor element mounted to the drive shaft and
configured to draw gas into the housing through the first inlet; a
second rotor mounted to the drive shaft and configured to draw gas
into the housing through the second inlet and to push the gas drawn
into the housing through the first and second inlets out the
outlet; a first bearing mounted to the shaft on an opposite side of
the first rotor element from the first inlet to rotatably support
the shaft in the housing; a second bearing mounted to the shaft on
a side of the second rotor element facing the outlet to rotatably
support the shaft in the housing; and a motor mounted around the
shaft between the first and second bearings to rotate the shaft and
the first and second rotor elements.
Description
[0001] The invention relates to a multi-stage vacuum pump.
[0002] Multi-stage vacuum pumps are configured e.g. as multi-inlet
vacuum pumps having at least two inlets and one outlet. Said inlets
are connected to different vacuum stages of the multi-inlet pump,
wherein a different vacuum is generated at each inlet. Normally, in
such an arrangement, the highest vacuum is generated by the inlet
connected to the first stage of the multi-inlet pump, the second
highest vacuum is generated by the inlet connected to the second
stage, and so forth. Such vacuum pumps with a plurality of vacuum
stages comprise, within a housing, a shaft which is driven by an
electric motor, the latter being normally arranged around said
shaft.
[0003] From the state of the art, there are known various types of
bearing arrangements for said shaft. Particularly, it is known to
support the shaft via two ball bearings, the electric motor being
arranged between said two ball bearings. In the direction of the
first stage, the shaft comprises a shaft extension. On said shaft
extension, the rotor element is arranged. Thus, the rotor is
arranged on the projecting shaft extension and accordingly is
supported in a cantilevered manner. Since all of the forces acting
on the rotor will be transmitted to the shaft at the cantilevered
end of the shaft, the bearings are subjected to high stresses.
Further, in shafts supported in this manner, the length of the
shaft is limited because, otherwise, it would not be possible
anymore to take up the occurring forces in the bearings, or one
would have to use extremely complex and expensive bearings. A
further disadvantage of this bearing arrangement resides in the
relatively small bearing spacing.
[0004] In another bearing arrangement of a similar type, the
electric motor is not arranged between the two bearings but
externally of the bearing. Also here, the rotor is arranged on the
cantilevered extension of the shaft and thus again has the
disadvantages of a cantilevered bearing arrangement. This will
cause an unfavorable position of the center of gravity and, as a
result, high stresses acting on the bearing.
[0005] Further, from DE 603 13 493, it is known to support the
shaft on both of its ends. Because of the large bearing spacing
resulting from such an arrangement, the forces occurring in the
bearings can be equalized and reduced. However, the bearing
arranged on the suction side of the pump, i.e. in the region of the
first stage, has to be designed as a magnetic bearing, which is of
necessity due to the low pressure existing in this region.
According to the state of the art, a grease-lubricated ball bearing
is unsuited for use in this region because the low pressure would
then cause the grease to be sucked out from the bearing. As usually
the case in magnetic bearings, there is additionally provided a
further ball bearing serving as a retainer bearing, while this
bearing, however, is not used for take-up of forces but only as an
emergency bearing. Due to the required provision of a permanent
magnetic bearing and additionally of a retainer bearing, this type
of bearing arrangement is expensive. Further, it is required to
provide a star-shaped holding element for the permanent magnetic
bearing, said holding element comprising flow passage openings.
Since this star-shaped bearing shield is located in the region of
the high vacuum stage, conductance losses will occur on extremely
unfavorable sites in the course of the flow. Such occurrences will
cause a deterioration of the maximum performance of the vacuum
pump.
[0006] It is an object of the invention to provide an inexpensive
and effective bearing arrangement for multi-stage vacuum pumps
which particularly also allows for a reduction of the
constructional length of the pump.
[0007] According to the invention, the above object is achieved by
the features defined in claim 1.
[0008] As provided by the invention, the rotor is divided into at
least two rotor elements. Thus, the two rotor elements are arranged
separately from each other, and particularly are connected to the
shaft separately from each other. Herein, depending on the
configuration of the multi-stage vacuum pump and particularly on
the arrangement of the inlets, one or also a plurality of stages
can be provided per rotor element. By the inventive division of the
rotor into two rotor elements, it is possible to arrange an inner
bearing element, usually a rolling bearing such as a ball bearing,
between the two rotor elements. Preferably, for this reason, one of
the two rotor elements, particularly the rotor element forming or
including the high vacuum stage, is arranged externally of the
inner bearing element. The rotor element is thus arranged on a
shaft extension which is projecting relative to the inner bearing
element. Since, however, in contrast to the state of the art, it is
not the whole rotor but only one of at least two rotor elements
that is arranged on the cantilevered end of the shaft, the forces
and moments introduced into the shaft at the cantilevered end
thereof will be considerably smaller. The second rotor element can
be arranged e.g. between an inner bearing element and an outer
bearing element and particularly be fixedly connected to the
shaft.
[0009] Since, according to the invention, the inner bearing element
is preferably not arranged in the region of the high vacuum but
instead is arranged within the outer rotor element comprising the
high vacuum stage, the bearing will not be subjected to the
extremely low pressures which prevail in the region of the high
vacuum. This offers the inventive advantage that especially
grease-lubricated bearings such as e.g. ball bearings can be used.
Particularly, the provision of a ball bearing has the advantage
that ball bearings have a distinctly smaller constructional size.
Further, the provision of a preferably grease-lubricated ball
bearing in this region advantageously obviates the need for an
additional emergency bearing. In magnetic bearings, such an
emergency bearing would be positively required because, otherwise,
no emergency running properties would be guaranteed in case of
failure of the magnetic bearing.
[0010] Especially due to the relatively large bearing spacing, the
forces acting on the bearing will distribute more favorably. This
is of advantage under the aspect of rotor dynamics. Further,
possible angular deviations of the shaft will be smaller, resulting
in advantages for the mechanics of the bearing. Due to the benefit
of reduced angular deviations, smaller gaps can be realized so that
the efficiency of the pump can be improved and higher final
pressures can be achieved. According to a particularly preferred
embodiment, the inner bearing element is fixed via a holding
element. Said holding element is formed with at least one
throughflow opening. For fixing the bearing in position,
particularly for fixing the outer bearing shell in case of rolling
bearings, the holding element is preferably connected to the pump
housing. With special preference, the holding element comprises a
plurality of throughflow openings and particularly has a
star-shaped configuration. The individual throughflow openings,
preferably arranged in a regular pattern and preferably having
identical shapes, are with preference configured as partial ring
segments. Since, when viewed in the conveying direction, the inner
bearing element is arranged within the rotor element comprising the
high vacuum stage, the medium will flow through the throughflow
openings only when exiting from the high vacuum stage and
respectively when entering the next stage. The conductance losses
caused by the holding element will thus be distinctly lower than in
case of an arrangement wherein such a holding element is provided
in the region of the high vacuum stage, i.e. in the gas-entrance
region of the high vacuum stage.
[0011] According to a particularly preferred embodiment, at least
two rotor elements are provided, wherein both the inner bearing
element and the holding element are arranged between these two
rotor elements.
[0012] According to a further particularly preferred embodiment,
the inner bearing element is--along the axial direction--at least
partially arranged within a rotor element. Particularly, this rotor
element is the rotor element comprising the high vacuum stage.
Since also in this embodiment the rotor element as seen in flow
direction is arranged before the inner bearing element, the inner
bearing element is also herein arranged between two rotor elements,
particularly between the two fastening regions of the rotor
elements to the shaft. Due to the resultant, at least partial
covering of the inner bearing element by a part of the rotor
element in the axial direction, the cantilevered shaft extension
can be made shorter. This will further improve the bearing
mechanics.
[0013] Preferably, an outer bearing element is arranged in such a
manner that, between the two bearing elements, a rotor element is
arranged, the latter particularly being fixedly connected to the
shaft. Thus, when two rotor elements are provided, the outer
bearing element is preferably arranged outside of the rotor element
forming the lowest stage. In this arrangement, it is particularly
preferred that the drive unit is arranged between the outer bearing
element and the rotor element forming the lowest vacuum stage. This
has the advantage of allowing for a very large bearing spacing
between the two bearing elements, resulting in improved bearing
mechanics.
[0014] In embodiments comprising e.g. three or more inlets and a
corresponding number of vacuum stages, it is preferred that the
outer bearing element is arranged between two rotor elements. These
will preferably be the two rotor elements forming the lowest vacuum
stages, while, optionally, a given rotor element can also form a
plurality of vacuum stages.
[0015] Particularly in case of a multi-stage vacuum pump with more
than two inlets and in case of the herein preferred arrangement of
the outer bearing element between two rotor elements, the outer
bearing element is fixed by a holding element. Said holding element
is preferably provided with through openings and is designed
corresponding to the holding element of the inner bearing
element.
[0016] The inner bearing element is preferably designed as a
rolling bearing. It is, however, also possible to provide a
magnetic bearing, particularly a permanent magnetic bearing, while
optionally also a retainer bearing can be provided.
[0017] According to a particularly preferred embodiment, the
multi-stage vacuum pump of the invention is a vacuum pump of the
multi-inlet type. This pump is provided, apart from the main inlet,
with at least one additional inlet. Preferably, each of said
additional inlets is arranged between two adjacent vacuum pumps. In
usual multi-inlet vacuum pumps, a pressure of 1.times.10.sup.-5
mbar to 1.times.10.sup.-9 mbar can be generated on the high vacuum
side. At a first intermediate inlet, a pressure of
1.times.10.sup.-2 mbar to 1.times.10.sup.-5 mbar can be reached. In
case that a second intermediate inlet is provided, a pressure of
1.times.10.sup.-2 mbar to 5.times.10.sup.-1 mbar can be reached
thereat.
[0018] The invention will be explained in greater detail hereunder
by way of preferred embodiments.
[0019] In the drawings, the following is shown:
[0020] FIG. 1 is a cross-sectional schematic diagram of a first
embodiment comprising two rotor elements,
[0021] FIG. 2 is a cross-sectional schematic diagram of a first
embodiment comprising three rotor elements, and
[0022] FIG. 3 is a schematic plan view of a holding element.
[0023] In the strongly simplified schematic representation of a
first embodiment of the multi-stage vacuum pump of the invention
(FIG. 1), a shaft 12 is arranged in a pump housing 10. Said shaft
12 carries the rotor elements 14,16 which according to the
invention are separated or detached from each other. Said rotor
elements are fixedly connected to shaft 12.
[0024] In the illustrated embodiment, rotor element 14 forms a
first vacuum stage 18 in which the highest vacuum is generated. The
gas which is to be conveyed is suctioned via a first inlet opening
20. In the illustrated embodiment, the first vacuum stage is a
vacuum stage formed by a turbomolecular pump. A stator 22 connected
to housing 10 cooperates with said rotor 14.
[0025] The second rotor element 16 in the illustrated embodiment is
arranged to form two vacuum stages 24,26. Also the second vacuum
stage 24 is formed by a turbomolecular pump while, also herein, a
stator 28 is connected to housing 10. The third stage 26 is a
Holweck stage wherein the helical extension 30 is arranged in
engagement with a corresponding helical recess. The second vacuum
stage 24 will suction the medium through an inlet opening 34, and
the third vacuum stage 26 will suction the medium through an inlet
opening 36. The suctioned medium will be conveyed by from all three
stages 18,24,26 to the discharge opening 38.
[0026] In the illustrated embodiment, an electric motor 40 for
driving said shaft 12 is located in the region of the third stage.
As provided according to a preferred embodiment, said electric
motor 40 is arranged to surround shaft 12. In the axial direction,
said Holweck stage preferably surrounds the electric motor 40.
[0027] Support of shaft 12 is realized by an inner bearing element
42 and an outer bearing element 44. Said inner bearing element 42
is arranged between the two rotor elements 14,16. In case that the
inner bearing element 42 is a rolling bearing, an inner bearing
ring is e.g. pressed onto shaft 12. An outer bearing ring is fixed
via a holding element 46. Said holding element 46, shown in plan
view in FIG. 3, comprises a plurality of through openings 48 formed
as partial ring segments and particularly arranged in a regular
configuration, for passage therethrough of the medium conveyed by
the first stage 18.
[0028] In the illustrated embodiment, outer bearing element 44 is
arranged outside the lowest, i.e. third stage 26. Also bearing
element 44 preferably is designed as a rolling bearing.
[0029] Along the axial direction 50, the inner bearing element of
the illustrated embodiment is arranged within rotor element 14. For
this purpose, rotor element 14 comprises a recess 52 having a
substantially circular cross section.
[0030] In the context of the second preferred embodiment,
constructional components similar to or identical with those
described above are designated with the same reference numerals.
For ease of survey, no pump housing is illustrated. The gas flow is
indicated by arrows 54, 56, 58, 60. An alternative gas flow is
indicated by arrows 62, 64, 56, 58, 60.
[0031] In the embodiment shown in FIG. 2, three rotor elements 14,
66, 68 are provided on the shaft 64. In the illustrated embodiment
(FIG. 2), all rotor elements 14, 66, 68 are shown as rotor elements
of molecular pumps while, of course, the rotor elements can also be
of a different type. Further, also in this embodiment, single rotor
elements can form a plurality of stages.
[0032] As in the embodiment shown in FIG. 1, the inner bearing
element 42 is arranged between two rotor elements 14,66 and again
is fixed or connected to the housing by a holding element 46 (FIG.
3). In the illustrated embodiment, the drive motor 40 is arranged
between the two rotor elements 14,66.
[0033] The second, i.e. outer bearing element 44 is arranged
between the two rotor elements 66,68 (FIG. 2) and, in the
illustrated embodiment, is fixed via a holding element 46.
[0034] Via a first flow path which is indicated by the arrows 54,
56, 58, 60, the flow will successively pass through the individual
pump stages formed by the rotor elements 14, 66, 68.
[0035] Within the second flow path which is indicated by arrows 62,
64, 56, 58, 60, there is additionally performed a suctional intake
of gas through a further inlet opening in the direction marked by
arrow 62. Via a bypass or connection channel (arrow 64), the gas
which is sucked both in the direction of arrow 62 and in the
direction of arrow 54 will be conveyed to the next stage (rotor
element 66).
[0036] The arrows 54, 62, 56 and 68 correspond to inlet openings
and outlet openings, respectively. Arrow 60 corresponds to the
discharge opening.
* * * * *