U.S. patent application number 12/672744 was filed with the patent office on 2011-04-07 for pump bearing arrangement.
This patent application is currently assigned to OERLIKON LEYBOLD VACUUM GMBH. Invention is credited to Markus Henry, Rainer Hoelzer, Robert Stolle.
Application Number | 20110081231 12/672744 |
Document ID | / |
Family ID | 40227013 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110081231 |
Kind Code |
A1 |
Hoelzer; Rainer ; et
al. |
April 7, 2011 |
PUMP BEARING ARRANGEMENT
Abstract
A pump bearing arrangement, suitable particularly for rapidly
rotating pumps such as turbomolecular pumps, comprises a pump rotor
(10) con-nected to a rotor shaft. The rotor shaft (14) is supported
in a shaft housing (20) by two bearing arrangements (12). Each
bearing arrangement (12) has an inner bearing ring (16) connected
to the rotor shaft (14) and an outer bearing ring (22) connected to
the shaft housing (20). Bearing supports (24) are disposed between
the two bearing rings. At least one vibration element (26) is
provided between the outer bearing ring (22) and the shaft housing
(20), serving for damping and further having a thermal conductivity
of at least 0.3 W/mK for dissipating heat.
Inventors: |
Hoelzer; Rainer; (Huerth,
DE) ; Henry; Markus; (Koeln, DE) ; Stolle;
Robert; (Kaarst, DE) |
Assignee: |
OERLIKON LEYBOLD VACUUM
GMBH
KOELN
DE
|
Family ID: |
40227013 |
Appl. No.: |
12/672744 |
Filed: |
July 22, 2008 |
PCT Filed: |
July 22, 2008 |
PCT NO: |
PCT/EP2008/059593 |
371 Date: |
December 6, 2010 |
Current U.S.
Class: |
415/119 |
Current CPC
Class: |
F04D 19/042 20130101;
F04D 29/668 20130101; F16C 19/163 20130101; F16C 2360/45 20130101;
F16C 27/066 20130101; F04D 29/059 20130101; F16C 35/077
20130101 |
Class at
Publication: |
415/119 |
International
Class: |
F04D 29/66 20060101
F04D029/66; F04D 29/059 20060101 F04D029/059 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2007 |
DE |
10 2007 037 792.6 |
Claims
1. A pump bearing arrangement, particularly for rapidly rotating
pumps such e.g. as turbomolecular pumps, comprising a rotor shaft
connected to a pump rotor, and a shaft housing with the rotor shaft
supported therein via two bearing arrangements, each bearing
arrangement comprising an inner bearing ring, an outer bearing ring
and bearing supports arranged between said bearing rings, and a
vibration element for damping, arranged in abutment on the outer
bearing ring and the shaft housing and respectively the rotor
shaft, said vibration element further serving for heat dissipation,
wherein said vibration element has a thermal conductivity of at
least 0.3 W/mK.
2. The pump bearing arrangement according to claim 1, wherein the
thermal conductivity of the vibration elements is higher than 0.35
W/mK, preferably higher than 0.4 W/mK.
3. The pump bearing arrangement according to claim 1, wherein the
vibration element comprises an elastomeric material.
4. The pump bearing arrangement according to claim 1, wherein the
vibration element comprises silicone.
5. The pump bearing arrangement according to claim 1, wherein the
vibration element comprises Elastosil, preferably Elastosil
R840.
6. The pump bearing arrangement according to claim 1, wherein a gap
is formed between the outer bearing ring and the shaft housing.
7. The pump bearing arrangement according to claim 1, wherein the
vibration element is free of metal particles.
8. The pump bearing arrangement according to claim 1, wherein the
vibration element has a Shore A hardness of 40-85 Shore A.
9. The pump bearing arrangement according to claim 1, wherein the
vibration element has an annular shape.
10. The pump bearing arrangement according to claim 1, wherein the
vibration element has a rectangular or circular cross section.
11. The pump bearing arrangement according to claim 1, wherein, for
damping radial movements, the vibration element surrounds the outer
bearing ring.
12. The pump bearing arrangement according to claim 1, wherein the
vibration element is arranged in a groove provided in the shaft
housing.
13. The pump bearing arrangement according to claim 1, wherein a
plurality of vibration elements are provided.
14. Use of a vibration element in pump bearing arrangements,
particularly for rapidly rotating pumps, said vibration element
having a thermal conductivity of at least 0.3 W/mK.
15. Use according to claim 14, wherein the vibration element is
provided according to claim 1.
16. The pump bearing arrangement according to claim 1, wherein the
thermal conductivity of the vibration elements is higher than 0.4
W/mK, preferably higher than 0.4 W/mK.
17. A turbomolecular pump comprising: a pump rotor; a rotor shaft
connected to the pump rotor; a shaft housing; at least one bearing
arrangement which supports the rotor shaft in the shaft housing,
the bearing arrangement including: an outer bearing ring, an inner
bearing ring connected with the rotor shaft, rolling elements
between the inner and outer bearing rings, an elastomeric vibration
damping element having a thermal conductivity of at least 0.3 W/mK
disposed between the outer bearing ring and the shaft housing.
Description
[0001] The invention relates to a pump bearing arrangement which is
suitable particularly for rapidly rotating pumps such as e.g.
turbomolecular pumps.
[0002] Pumps, such as e.g. turbomolecular pumps, comprise a pump
rotor connected to a rotor shaft. The rotor shaft is supported in a
shaft housing via two bearing arrangements. Said two bearing
arrangements usually comprise respectively one ball bearing. The
inner bearing rings and respectively bearing shells of the two ball
bearings are fixedly connected to the rotor shaft. The outer
bearing rings and respectively bearing shells are connected to the
shaft housing in the axial direction, or are arranged in abutment
e.g. on an annular projection of the shaft housing in the axial
direction. The two bearing arrangements are axially biased. In the
radial direction, the outer bearing rings are usually not arranged
in direct abutment on the shaft housing. Instead, an annular gap is
provided between the outer bearing rings and the shaft housing. In
a circular groove formed in the shaft housing and surrounding the
outer bearing ring, an O-ring is arranged, serving particularly as
a vibration element for damping and radially holding each of the
two bearing arrangements. As vibration elements, use is made e.g.
of O-rings manufactured from silicone. This, however, gives rise to
the problem that the heat dissipation effected via silicone O-rings
will be merely poor.
[0003] For improving the heat dissipation, it is known from DE 8
910 040 to fill said vibration element, such as e.g. the O-ring,
with metal powder and preferably copper powder. Particularly those
O-rings which comprise metal and respectively copper contents,
however, will tend to change their mechanical properties, which is
due to the compression of the copper elements occurring during
operation. This may affect the damping properties and the position
of the bearing arrangements. Admixture of metal or copper powder to
an elastomer further entails the risk that the distribution of the
particles will not be homogeneous. This will give rise to regions
with increased particle density, so-called nests, as well as
regions with reduced particle density. As a result, unpredictable
local variations of thermal conductivity will take place within the
O-ring. As a result, the elastic properties of the vibration
element will deteriorate. Especially in regions of increased
particle density, the stiffness and respectively elasticity of the
vibration element will be caused to vary. Pump bearing
arrangements, particularly those of fast-rotating pumps such as
e.g. turbomolecular pumps, are subjected to permanent vibration.
Thereby, vibrations of up to 1.5 kHz may occur. This can lead to a
decomposition or segregation of the metal and respectively copper
particles in the O-ring. This effect will lead to internal friction
of solids and a resultant considerable increase of temperature in
the vibration element. In case of such a decomposition or
segregation of the particles on the surface of the vibration
element, particles may happen to escape from the vibration element
and penetrate into the bearing. Such occurrences will reduce the
operating life of the bearing. Said decomposition or segregation
will further cause changes of the vibration properties as well as
local thermal over-stressing of the material. This may lead to
complete destruction or plastic deformation of the vibration
element.
[0004] Particularly in rotors of pump bearing arrangements for use
in fast-rotating units such as turbomolecular pumps, the problem
exists that the friction generated in the bearings will cause a
massive heat-up of the bearing arrangements. The temperatures
generated in such fast-rotating components cannot be sufficiently
dissipated by known vibration elements such as O-rings made of
silicone or O-rings including copper contents. This is the case
particularly in pump bearing arrangements for fast-rotating
turbomolecular pumps which typically are designed for a rotor speed
of 500 Hz-1.500 Hz, depending on the rotor diameter.
[0005] Heat dissipation from the bearing is difficult to achieve
particularly because the axial surfaces of the ball bearings used,
which preferably are angular-contact ball bearings, are small and
thus will contribute only little to heat dissipation. In the radial
direction, the outer bearing rings are usually arranged at a
distance from the shaft housing for allowing the axial bias to be
realized. Consequently, heat dissipation in the radial direction
will not be sufficient. Particularly since the bearings are
operated at low pressures of usually 1.times.10.sup.-3 to
10.sup.-10 mbar, heat dissipation in the radial direction is
extremely poor.
[0006] It is an object of the invention to provide a pump bearing
arrangement, particularly of the type suited for rapidly rotating
pumps, wherein the heat dissipation is improved.
[0007] According to the invention, the above object is achieved by
the features defined in claim 1.
[0008] As provided by the invention, the vibration element serving
for damping is designed and/or arranged to have a thermal
conductivity of at least 0.3 W/mK. The vibration element is located
between the bearing ring and the shaft housing. Preferably, the
vibration element surrounds the outer bearing ring and consequently
is arranged between the outer bearing ring and the shaft housing.
According to the invention, the vibration element thus fulfills two
functions, i.e. on the one hand, damping the movements of the
bearing ring and, on the other hand, dissipating the heat from the
bearing ring particularly into the shaft housing. This inventive
dual function of the vibration element makes it possible to realize
a good heat dissipation from the bearing. Thereby, the operating
life of the bearing is extended.
[0009] With particular preference, said at least one vibration
element has a thermal conductivity of at least 0.35 W/mK and more
preferably at least 0.4 W/mK. Preferably, the vibration element
comprises an elastomeric material or is made of elastomeric
material. Tests have shown that the material Elastosil R840 is
especially well-suited for use in the realization of the
invention.
[0010] With particular preference, use is made of a
quasi-homogeneous material for the at least one vibration element.
In this case, the inventive thermal conductivity of the material is
guaranteed not by admixture of particles such as e.g. metal or
copper powder but, instead, by the elastomeric material itself.
Herein, the properties of the material are influenced particularly
by the length and the structure of the macromolecules. In this
regard, it is preferred to select a material in which the vibration
and heat-conductivity properties are substantially identical in all
spatial directions and which, particularly, is not susceptible to
material decomposition even in case of large temperature influences
and temperature variations, especially in the range of 4.degree. C.
to 120.degree. C. Even when pumps, particularly fast-rotating pumps
such as turbomolecular pumps, are subjected to high vibration
stresses up to 1.5 kHz, said material which is preferred according
to the invention will still remain elastic. Particularly within the
frequencies normally occurring in this application field,
especially in the range from 1 Hz to 4 kHz, the material is
permanently vibration-proof so that no changes of the material
properties will occur.
[0011] Preferably, the material to be used comprises a silicone
rubber mass.
[0012] Particularly, a plural number of vibration elements can be
provided for each bearing arrangement. Preferably, two annular
vibration elements are provided, surrounding the outer bearing ring
so as to take up radial forces. Further, for axial damping,
vibration elements--preferably again of an annular shape--can be
provided also in the axial direction.
[0013] According to a preferred embodiment, the vibration elements,
which preferably are of a rectangular or circular cross-sectional
shape, are respectively arranged in a groove. Preferably, said
groove is arranged in the shaft housing, with the vibration element
preferably extending beyond the groove so that there will always be
a gap formed between the shaft housing and the bearing ring.
[0014] The vibration element preferably has a Shore A hardness of
40-80 Shore A.
[0015] The invention further relates to the use of a vibration
element having a thermal conductivity of at least 0.3 W/mK in pump
bearing arrangements. Herein, the vibration element is preferably
designed in the above described manner.
[0016] The invention will be explained in greater detail hereunder
by way of a preferred embodiment with reference to the accompanying
drawing.
[0017] The FIGURE shows a schematic lateral view of an upper and
respectively rotor-side bearing arrangement according to the
invention.
[0018] A preferred embodiment of the bearing arrangement 12
arranged in an upper position, i.e. facing toward a rotor 10, is
illustrated in the FIGURE. Rotor 10 is connected to a rotor shaft
14 for common rotation therewith. Arranged on rotor shaft 14 for
common rotation therewith is an inner bearing shell 16 of a grooved
ball bearing, which is held in position by the rotor and the shaft
stub 18.
[0019] The upper bearing arrangement 12 is arranged in a shaft
housing 20 which in the illustrated embodiment has a substantially
cylindrical shape. An outer bearing ring 22 is arranged internally
of shaft housing 20. Between said two bearing rings 16,22, bearing
bodies in the form of balls are arranged.
[0020] In the first embodiment, outer bearing ring 22 is connected
to shaft housing 20 by two radial vibration elements 26 formed as
elastic O-rings. Further provided is an axial vibration element 28,
preferably also formed as an elastic O-ring. Said two radial
vibration elements 26 are respectively arranged in an edge region
of outer bearing ring 22 in a respective groove 30. Said groove 30
is provided in shaft housing 20. The depth of groove 30 is smaller
than the diameter of said O-rings 26 so that the latter projects
beyond an inner side 32 of shaft housing 20 and are located in
abutment on outer bearing ring 22.
[0021] The axial vibration element 28 is arranged in an axial
annular groove 34 which also is provided in shaft housing 20. Also
here, the depth of groove 34 is smaller than the diameter of O-ring
28 so that the latter projects in the direction of outer bearing
ring 22. Between axial vibration element 28 and outer bearing ring
22, a force transmission element 36 is provided. Said force
transmission element 36 particularly has the function of a friction
damper. A further function of force transmission element 36 resides
in allowing for movement of outer bearing ring 22 in the radial
direction without causing shear forces or radial forces to act on
axial vibration element 28. At least, the corresponding forces that
occur can be significantly reduced.
[0022] Between the two radial vibration elements 26, a venting bore
38 formed as a transverse bore can be provided.
[0023] The annular vibration elements 26,28 provided in the
illustrated embodiment serve for heat dissipation from the bearing
arrangement 12. The heat, generated especially by the rolling
friction of the balls 24, is thus dissipated via outer bearing ring
22 as well as via vibration elements 26,28 into shaft housing 20.
For this purpose, vibration elements 26,28 have a good thermal
conductivity, preferably higher than 0.3 W/mK.
[0024] In addition to the illustrated upper bearing arrangement 12,
a further ball bearing is provided to support the lower end of
rotor shaft 14. Said two bearings are tensioned for providing an
axial bias in the longitudinal direction of rotor shaft 14.
* * * * *