U.S. patent application number 12/952568 was filed with the patent office on 2011-05-26 for vacuum pump.
This patent application is currently assigned to OERLIKON LEYBOLD VACUUM GmbH. Invention is credited to Christian Beyer, Heinz Englaender, Markus Henry, Rainer Hoelzer, Heinz-Dieter Odendahl.
Application Number | 20110123328 12/952568 |
Document ID | / |
Family ID | 43545260 |
Filed Date | 2011-05-26 |
United States Patent
Application |
20110123328 |
Kind Code |
A1 |
Henry; Markus ; et
al. |
May 26, 2011 |
VACUUM PUMP
Abstract
A vacuum pump, particularly a turbomolecular pump or multi-inlet
pump, comprises a rotor shaft (12) carrying at least one rotor
means (14). The rotor shaft (12) is supported on the pressure side
by a bearing assembly (56) and on the suction-side by a further
bearing assembly (30). According to the invention, the suction-side
bearing assembly (30) comprises an electromagnetic bearing (32,34).
Further according to the invention, the pressure-side bearing
assembly (56) comprises a ball bearing (58) so that the rotor shaft
(12) can be given the largest possible length. The rolling bearing
(58) is preferably biased by the electromagnetic bearing
(32,34).
Inventors: |
Henry; Markus; (Koeln,
DE) ; Beyer; Christian; (Koeln, DE) ;
Englaender; Heinz; (Linnich, DE) ; Hoelzer;
Rainer; (Huerth, DE) ; Odendahl; Heinz-Dieter;
(Koeln, DE) |
Assignee: |
OERLIKON LEYBOLD VACUUM
GmbH
Koeln
DE
|
Family ID: |
43545260 |
Appl. No.: |
12/952568 |
Filed: |
November 23, 2010 |
Current U.S.
Class: |
415/229 |
Current CPC
Class: |
F04D 29/058 20130101;
F04D 29/0563 20130101; F04D 19/048 20130101; F16C 32/0402 20130101;
F16C 2360/45 20130101; F04D 19/042 20130101; F04D 29/059
20130101 |
Class at
Publication: |
415/229 |
International
Class: |
F04D 29/04 20060101
F04D029/04 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 26, 2009 |
DE |
10 2009 055 888.8 |
Claims
1. A vacuum pump, particularly a turbomolecular pump or multi-inlet
turbomolecular pump, said vacuum pump comprising: a rotor shaft
carrying at least one rotor means, and a pressure-side bearing
assembly and a suction-side bearing assembly supporting said rotor
shaft, said suction-side bearing assembly comprising an
electromagnetic bearing which radially supports the rotor shaft,
and said pressure-side bearing assembly comprising a rolling
bearing which axially and radially supports said rotor shaft.
2. The vacuum pump according to claim 1, wherein the suction-side
bearing assembly serves exclusively for radial support.
3. The vacuum pump according to claim 1, further including a
biasing assembly which axially biases said rolling bearing.
4. The vacuum pump according to claim 3, wherein said biasing
assembly is formed by the suction-side bearing assembly.
5. The vacuum pump according to claim 3, wherein said biasing
assembly is formed by an electric motor which drives the rotor
shaft.
6. The vacuum pump according to claim 3, wherein said biasing
assembly is formed by a separate magnet.
7. The vacuum pump according to claim 1, wherein at least one of
the suction-side bearing assembly and the pressure-side bearing
assembly is arranged at an end of the rotor shaft.
8. The vacuum pump according to claim 1, wherein all rotors are
arranged between said bearing assemblies.
9. The vacuum pump according to claim 1, wherein the rotor shaft
between the two bearing assemblies has a length of at least 170 mm,
with a rotor diameter of 100 to 140 mm.
10. The vacuum pump according to claim 1, wherein the rotor shaft
has a length between the two bearing assemblies that is larger than
or equal to a diameter of the at least one rotor.
11. The vacuum pump according to claim 1, wherein at least the
suction side end of the rotor shaft has a reduced diameter.
12. The vacuum pump according to claim 1, wherein the suction-side
bearing assembly is arranged within a cartridge closed on the
suction side.
13. The vacuum pump according to claim 1, wherein the suction-side
bearing assembly is arranged in a high vacuum region in which the
pressure is less than 10.sup.-5 mbar.
14. The vacuum pump according to claim 6, wherein the separate
magnet is a permanent magnet arranged in the region of the rolling
bearing.
15. The vacuum pump according to claim 9, wherein the rotor shaft
has a length of at least 220 mm.
16. The vacuum pump according to claim 9, wherein the rotor
diameter is about 130 mm.
17. The vacuum pump according to claim 11, wherein the suction side
end of the rotor shaft is smaller than or equal to 0.66 times a
root of a rotor diameter of the at least one rotor.
18. The vacuum pump according to claim 17, wherein the suction side
end of the rotor shaft has a reduced diameter smaller than 6
mm.
19. The vacuum pump according to claim 1, wherein the suction-side
bearing assembly is arranged in a high vacuum region in which the
pressure is less than 10.sup.-10 mbar.
20. A turbomolecular vacuum pump comprising: a housing having a
suction inlet adjacent a suction-side and an outlet adjacent a
pressure-side; a rotor shaft; at least one rotor supported by the
rotor shaft and at least one stator supported by the housing; an
electromagnetic bearing assembly supporting a suction-end of the
rotor shaft in an interior of the housing and adjacent a
suction-side of the housing, the suction-side bearing assembly
including: a magnetic bearing element affixed to and rotating with
the rotor shaft, a coil mounted into the housing, and an isolation
structure which vacuum isolates the coil from the interior of the
housing; and a rolling bearing supporting a pressure-end of the
rotor shaft in the interior of the housing adjacent the
pressure-side of the housing.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to a vacuum pump, particularly
a turbomolecular pump or multi-inlet turbomolecular pump.
[0003] 2. Description of the Prior Art
[0004] Turbomolecular pumps comprise a rotor means including at
least one rotor having a plurality of rotor disks. Arranged between
said rotor disks are stator disks held by stator rings. Said rotor
means is arranged on a fast-rotating rotor shaft. Turbomolecular
pumps have an inlet on the suction side and an outlet on the
pressure side. At said suction-side inlet, final pressures of
optionally less than 10.sup.-10 mbar can be generated. Said
pressure-side pump outlet is often connected to additional
pre-vacuum pumps.
[0005] Multi-inlet pumps comprise, in addition to a suction-side
main inlet, at least one intermediate inlet. Normally, the rotor
array of a multi-inlet pump comprises two pump stages which are
formed e.g. as turbomolecular stages, said intermediate inlet being
arranged between the two pump stages. Often, a further pump stage
such as, e.g., a Holweck stage, is arranged downstream of the
turbomolecular stages in the conveying direction. Multi-inlet pumps
make it possible to generate different pressure levels at said main
inlet and said at least one intermediate inlet.
[0006] Particularly in fast-rotating vacuum pumps such as, e.g.,
turbomolecular pumps and multi-inlet pumps, support of the rotor
shaft on the pressure side, e.g. in regions where no low pressures
prevail, can be provided via electromagnetic bearings. In known
vacuum pumps, such electromagnetic bearings are used in pressure
ranges up to 120 mbar. Further, it is known to support the rotor
shaft in the high vacuum range by use of passive magnet
bearings.
[0007] For support of a vacuum pump on the suction side, use of
electromagnetic bearings is not a common practice, which is due to
the low pressures prevailing in this region; notably, the coil
bodies and sensor devices used in electromagnetic bearings are
components with large surfaces and numerous hollow spaces.
Consequently, because of the continuous outgassing, it is not
possible or at least possible only with difficulties to reach the
desired final pressure. Further, it is known to use permanent
magnetic bearings in the high vacuum region.
[0008] For electromagnetic support of the whole rotor shaft, it is
proposed in DE 20 2005 019 644 to arrange the two electromagnetic
bearings within a cartridge. In said cartridge, the rotor shaft is
arranged together with the bearings and the electric motor. The
cartridge is open substantially in the direction of the pressure
side so that, within the cartridge, there will prevail atmospheric
pressure or at least a relatively high pressure acting onto the
pressure side of the pump. The rotor shaft comprises an extension
projecting out of the cartridge and carrying the rotor means. Thus,
the rotor means is fastened on a cantilevered end of the shaft.
Consequently, the constructional length of the pump is limited.
Further, as a result of the attachment of the rotor means on said
cantilevered shaft end, high forces will occur at the bearing
sites, thus entailing the need to provide correspondingly complex
electromagnetic bearings. Further still, this type of
constructional design is subjected to massive restrictions due to
the rotor-dynamic behavior since particularly low inherent
frequencies will occur.
[0009] Further, e.g. from U.S. Pat. No. 6,416,290, it is known to
provide a suction-side rotor on a cantilevered end of the rotor
shaft. Thus, in the flow direction, the suction-side bearing is
arranged behind the first rotor and consequently is not exposed to
the very low pressures on the high vacuum side. Since, relative to
the suction-side bearing, the attachment of the rotor is thus
provided outside the bearing on a cantilevered end of the shaft,
high forces and moments will occur in the bearings.
[0010] In turbomolecular pumps and particularly in multi-inlet
pumps, it is desirable that the length of the rotor shaft is as
large as possible so as to increase the overall pump performance
and, optionally, to provide a larger number of intermediate inlets.
With known bearing arrangements, the length of the rotor shaft is
restricted because of machine-dynamic limitations. Presently, if
the production and operating costs of a turbomolecular pump or a
multi-inlet pump are to remain within a reasonable range, the
maximum rotor length should be about 170 mm, with a rotor diameter
of about 130 mm and a shaft diameter of about 8 mm.
[0011] It is an object of the invention to provide a vacuum pump,
particularly a turbomolecular pump or a multi-inlet pump, wherein
the rotor shaft has a larger length.
SUMMARY
[0012] In accordance with one aspect, a vacuum pump of the
invention comprises a rotor shaft carrying a rotor means, said
rotor means optionally comprising a plurality of rotors or other
suction or pump devices. Said rotor shaft is normally supported via
two bearing assemblies, notably a pressure-side bearing assembly
and a suction-side bearing assembly. The suction-side bearing
assembly is an electromagnetic bearing for radial support of the
rotor shaft. Thus, with the aid of said electromagnetic bearing,
there is effected exclusively a biaxial support of the rotor shaft.
Herein, support in the axial direction is preferably not effected
by the electromagnetic bearing. Further, the pressure-side bearing
assembly is designed as a rolling bearing, particularly as a ball
bearing. Use is made of such a rolling bearing, or the rolling
bearing is arranged in such a manner, that the rolling bearing
provides both axial and radial support, i.e. triaxial support of
the shaft. The bearing assembly makes it possible to provide a long
rotor shaft which will meet the high requirements to the quality
and particularly also to the useful life of turbomolecular pumps or
multi-inlet pumps. Particularly, such an arrangement has the
advantage that a shaft which is supported on the shaft ends can be
stiffened between the bearings as desired, without the necessity to
give consideration to mating clearances for adequate bearings. The
high stiffness of the shaft has the beneficial effect that the
bending-critical inherent frequencies are shifted far away from the
nominal frequency of the pump. Since bearings which are operated
near the inherent frequencies of the shaft will be subjected to
additional dynamic stresses, operation at frequencies far away from
the inherent frequencies has a favorable influence on the useful
life of the bearings.
[0013] The provision of an electromagnetic bearing on the suction
side has the advantage that a contamination of the process gases
will be avoided even at low pressures. If one were to use ball
bearings with lubricants on the high vacuum side, the low pressures
would cause an outgassing of the lubricant and thus lead to
contamination of the process gases.
[0014] According to a particularly preferred embodiment, the
suction-side bearing assembly serves exclusively for radial
support. Thus, the rotor shaft is preferably not axially supported
on the suction side. However, the electromagnetic bearing provided
on the suction side preferably can also be used for biasing the
rolling bearing located on the pressure side. This can be
accomplished by a slight axial offset of the component parts of the
electromagnetic bearing. Effecting the biasing of the rolling
bearing with the aid of the suction-side electromagnetic bearing
advantageously obviates the need for a separate biasing means so
that no separate component need be provided. Instead, the biasing
means is realized by the electromagnetic bearing.
[0015] Further, it is possible to realize the biasing of the
rolling bearing with the aid of an electric motor. Preferably, said
electric motor is arranged to act directly on the rotor shaft so
that the rotor shaft will be directly driven by the electric motor.
Thus, by a corresponding axial offset between the magnet and the
coils of the electric motor, it is possible to generate a bias. For
generating the bias by use of the electromagnetic bearing, this
provision has the advantage that no additional component part will
be necessitated.
[0016] Another possibility resides in the providing separate
biasing means. Such a biasing means can be designed e.g. in the
form of a magnet preferably arranged in the region of the rolling
bearing. With preference, this magnet is a permanent magnet which
thus will generate a clearly defined biasing force.
[0017] It is particularly preferred that the suction-side bearing
assembly and/or the pressure-side bearing assembly are each
arranged at a respective end of the rotor shaft. Thus, according to
a preferred embodiment, the rotor shaft is not cantilevered on
either of the two sides. Particularly in the region of the high
vacuum, no cantilevered arrangement of the rotor shaft exists. This
is possible due to the inventive arrangement and design of the
bearings. In non-cantilevered shafts, merely relatively low forces
and moments will occur in the bearings of the rotor shaft of a
turbomolecular pump or a multi-inlet pump. Thereby, a rotor shaft
of a smaller diameter can be provided particularly in the region of
the electromagnetic bearing. Especially, this has the advantage
that a relatively small catch bearing can be provided, thereby
reducing the costs. Thus, in this preferred embodiment, all rotor
assemblies are arranged between the bearings. At the most, the
rotor assemblies may cover the bearings in the axial direction, but
the rotor assemblies are always connected to the rotor shaft
between the bearing assemblies.
[0018] Due to the inventive configuration of the bearing
assemblies, it is rendered possible to realize rotor shafts having
a length of more than 200 mm with a rotor diameter of about 130 mm,
for use in turbomolecular pumps or multi-inlet pumps.
[0019] The electromagnetic bearing of the suction-side bearing
assembly is preferably arranged within a cartridge. Thereby, it is
made possible to arrange particularly the coil of the bearing in a
region where the pressure is higher than the minimal pressure
prevailing on the suction side.
[0020] The suction-side bearing assembly can be arranged in a high
vacuum region and thus be subjected to low pressures. Further, the
suction-side bearing assembly is an electromagnetic bearing. A high
vacuum herein is understood to be a pressure of less than 10.sup.-3
mbar, preferably less than 10.sup.-5 mbar and most preferably less
than 10.sup.-10 mbar.
[0021] Particularly if the electromagnetic bearing is arranged in
the region of very low pressures as occurring on the suction side,
i.e. in the inlet region of a turbomolecular pump, it is provided
according to an especially preferred embodiment that the coil of
the electromagnetic bearing is arranged within a
pressure-encapsulated recess. By arranging the coil within a
pressure-encapsulated recess, it is safeguarded that the coil
itself is not located immediately in the high vacuum region.
Thereby, the disadvantage is avoided that, due to the numerous
hollow spaces within the coil, the resultant continuous outgassing
would make it impossible or very difficult to reach the final
pressure. By the inventive provision of an electromagnetic bearing
in the high vacuum region, it is rendered possible to support the
rotor shaft in the end regions of the shaft.
[0022] According to a particularly preferred embodiment, said
recess is arranged in a housing element, i.e. preferably in a
stationary element connected to the housing. An opening of the
recess is preferably oriented in the direction of the rotor shaft.
Particularly, the opening has a circular shape and fully surrounds
the rotor shaft. Thus, an annular coil of a solenoid can be
arranged in the recess. In such an arrangement, the electric feed
lines preferably can be guided into the recess through the housing
and not from the sides of the opening of the recess that is
provided in the direction of the rotor shaft.
[0023] For pressure encapsulation, i.e. for sealing the recess, it
would also be possible, for instance, to cast synthetic resin or
the like into the recess after placing the coil in the recess. In
case of very low pressures, however, the use of synthetic resin has
the disadvantage of causing an outgassing of e.g. softening agents
in the high vacuum, which in turn may adulterate the results of an
analysis, for instance. According to a preferred embodiment of the
invention, the opening of the recess is tightly closed by a
preferably tubular closing element. The opening, preferably facing
inwardly in the direction of the rotor shaft, can thus be closed in
a simple manner by a tubular closure element. In case of a
preferably circular recess, the opening of the recess corresponds
to the inner peripheral surface of the circular cylinder.
Preferably, the closure element can be sealingly connected to the
housing element via sealing elements such as e.g. O-rings.
BRIEF DESCRIPTION OF THE DRAWING
[0024] A full and enabling disclosure of the present invention,
including the best mode thereof, enabling one of ordinary skill in
the art to carry out the invention, is set forth in greater detail
in the following description, including reference to the
accompanying drawing in which the sole
[0025] FIG. 1 is a schematic sectional view of a multi-inlet pump
comprising a bearing assembly according to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0026] A multi-inlet pump, as schematically illustrated in FIG. 1,
comprises a rotor shaft 12 arranged in a housing 10. Said rotor
shaft 12 carries a plurality of rotor means 14. Each of said rotor
means 14 comprises a plurality of rotor disks 16. Between said
rotor disks 16, stator disks 18 are arranged. A suction side 22 of
the pump forms the high vacuum connection so that a medium will be
sucked in the direction marked by arrow 24. Normally, an outlet 26
of the turbomolecular pump, i.e. the pressure side 28, is connected
to a pre-vacuum pump.
[0027] The bearing assembly 30 arranged on the suction side
comprises an electromagnetic bearing. This bearing comprises a coil
32 of a solenoid, and a bearing element 34 fixedly rotating
together with rotor shaft 12, said bearing element being realized
in the form of a so-called bearing plate. Said coil 32 is arranged
in a recess 38 of a housing element 40. In the illustrated
embodiment, said recess 38 has the shape of a circular cylinder.
Recess 38 surrounds rotor shaft 12 in an end region of the shaft.
Recess 38 is closed by a tubular closure element 42 and by sealing
elements 44 preferably formed as O-rings. Thus, recess 38 is
pressure-encapsulated. Consequently, within recess 38, there does
not prevail the high vacuum existing in region 22. Thereby, it is
avoided that the numerous hollow spaces located within the coil
would make it difficult or even impossible to reach the final
pressure.
[0028] Additionally, the illustrated suction-side bearing assembly
30 comprises a mechanical catch bearing 20 formed e.g. as a ball
bearing. This catch bearing 20 is arranged in said housing element
40 and has a small distance to a shaft pin of shaft 12. Catch
bearing 20 substantially serves for assuring emergency running
features in case of failure of the electromagnetic bearing. In the
illustrated embodiment, housing element 40 is pot-shaped and
surrounds a suction-side end region of rotor shaft 12.
[0029] In the illustrated embodiment, the bearing assembly 56
arranged on the pressure side 28 is formed as a rolling bearing,
particularly as a ball bearing 58. Said ball bearing 58 is designed
and respectively is connected to a housing cover 60 in such a
manner that the ball bearing 58 is able to take up both axial and
radial forces.
[0030] Thus, the suction-side bearing assembly 30 serves
exclusively for radial support of shaft 12, while the pressure-side
bearing assembly 56 serves for axial and radial support of shaft
12.
[0031] With particular preference, it is provided that a radial
bias is exerted on bearing 58. This bias can be generated with the
aid of the suction-side bearing assembly 30 configured as an
electromagnetic bearing. A corresponding bias can be generated
already by a slight axial offset between coil 32 and bearing
element 34. It is also possible to generate an axial bias of
bearing assembly 56 with the aid of an electric motor 62. This
motor 62, which in the illustrated embodiment is supported by said
housing cover 60, comprises e.g. a permanent magnet 64 connected to
rotor shaft 12, and a coil assembly 66. Also the axial offset
between said permanent magnet 64 and said coil assembly 66 is
suited to realize the bias of ball bearing 58.
[0032] In case of a multi-inlet pump, rotor shaft 12, being at both
of its end regions supported by said bearing assemblies 30 and 56,
comprises a plurality of condenser stages 76,78,80. In the
illustrated embodiment, the first two condenser stages 76,78 are
realized in the form of turbomolecular pumps, each them comprising
a rotor 14 with rotor disks 16. Between said rotor disks 16, stator
disks 18 are arranged. The two rotors 14 are arranged with a mutual
distance on rotor shaft 12. Between the two rotors 14, housing 10
is provided with an inlet opening 82 which is the intermediate
inlet.
[0033] The illustrated multi-inlet pump further comprises a main
inlet 84 which is the high vacuum inlet. Via main inlet 84, the
suctioned gas will flow in the direction marked by arrow 24. In the
region of said intermediate inlet 82, an additional suctional
intake of medium is performed via the intermediate inlet as
indicated by arrow 86, and the suctioned medium will be conveyed
towards the right-hand side in FIG. 1.
[0034] The third condenser stage 80 will then convey the medium, as
marked by arrow 86, in the direction of the pressure side 28 and
respectively the outlet 26. Normally, a pre-vacuum pump is
connected to outlet 26. The third condenser stage 80 can comprise
e.g. a Holweck stage or the like.
[0035] By the inventive configuration of the suction-side bearing
assembly 30, it is rendered possible to provide the two bearing
assemblies 56,30 at the shaft ends so that a maximum bearing
spacing can be realized.
[0036] Although the invention has been described and illustrated
with reference to specific illustrative embodiments thereof, it is
not intended that the invention be limited to those illustrative
embodiments. Those skilled in the art will recognize that
variations and modifications can be made without departing from the
true scope of the invention as defined by the claims that follow.
It is therefore intended to include within the invention all such
variations and modifications as fall within the scope of the
appended claims and equivalents thereof.
* * * * *