U.S. patent application number 11/786358 was filed with the patent office on 2008-10-16 for vacuum pumps with auxiliary pumping stages.
This patent application is currently assigned to Varian S.p.A.. Invention is credited to Marsbed Hablanian.
Application Number | 20080253903 11/786358 |
Document ID | / |
Family ID | 39853881 |
Filed Date | 2008-10-16 |
United States Patent
Application |
20080253903 |
Kind Code |
A1 |
Hablanian; Marsbed |
October 16, 2008 |
Vacuum pumps with auxiliary pumping stages
Abstract
Vacuum pumping apparatus includes a housing, one or more primary
pumping stages disposed in the housing, a motor coupled to the
primary pumping stages, the motor including at least one stationary
surface and at least one moving surface when the motor is
energized, the stationary and moving surfaces of the motor defining
an auxiliary pumping stage coupled in series with the primary
pumping stages to pump gas through a pumping channel between the
stationary and moving surfaces of the motor, the housing having a
first exhaust port between the primary pumping stages and the
auxiliary pumping stage, and a second exhaust port at an outlet of
the auxiliary pumping stage, and a valve connected in series with
the first exhaust port and configured to close when an inlet
pressure of the vacuum pumping apparatus is below a predetermined
pressure.
Inventors: |
Hablanian; Marsbed;
(Wellesley, MA) |
Correspondence
Address: |
Varian Inc.;Legal Department
3120 Hansen Way D-102
Palo Alto
CA
94304
US
|
Assignee: |
Varian S.p.A.
|
Family ID: |
39853881 |
Appl. No.: |
11/786358 |
Filed: |
April 11, 2007 |
Current U.S.
Class: |
417/245 |
Current CPC
Class: |
F04D 25/0606 20130101;
F04D 19/046 20130101; F04D 19/042 20130101; F04D 29/522
20130101 |
Class at
Publication: |
417/245 |
International
Class: |
F04B 5/00 20060101
F04B005/00 |
Claims
1. Vacuum pumping apparatus comprising: a housing; one or more
primary pumping stages disposed in the housing; a motor coupled to
the primary pumping stages, the motor including at least one
stationary surface and at least one moving surface when the motor
is energized, the stationary and moving surfaces of the motor
defining an auxiliary pumping stage coupled in series with the
primary pumping stages to pump gas through a pumping channel
between the stationary and moving surfaces of the motor; the
housing having a first exhaust port between the primary pumping
stages and the auxiliary pumping stage, and a second exhaust port
at an outlet of the auxiliary pumping stage; and a valve connected
in series with the first exhaust port and configured to close when
an inlet pressure of the vacuum pumping apparatus is below a
predetermined pressure.
2. Vacuum pumping apparatus as defined in claim 1, wherein the
motor includes a stator and a rotor and wherein the stationary and
moving surfaces comprise stator and rotor surfaces,
respectively.
3. Vacuum pumping apparatus as defined in claim 1, wherein the
motor includes a bearing preload nut and wherein the stationary and
moving surfaces comprise housing and bearing preload nut surfaces,
respectively.
4. Vacuum pumping apparatus as defined in claim 1, wherein the
motor includes a shaft and wherein the stationary and moving
surfaces comprise housing and shaft surfaces, respectively.
5. Vacuum pumping apparatus as defined in claim 1, wherein the
auxiliary pumping stage comprises a screw-type pumping stage
6. Vacuum pumping apparatus as defined in claim 1, wherein the
auxiliary pumping stage comprises a molecular drag stage.
7. Vacuum pumping apparatus as defined in claim 2, wherein the
auxiliary pumping stage includes a helical groove in the rotor.
8. Vacuum pumping apparatus as defined in claim 2, wherein the
auxiliary pumping stage includes a helical groove in the
stator.
9. Vacuum pumping apparatus as defined in claim 1, wherein the
primary pumping stages comprise one or more turbomolecular pumping
stages.
10. Vacuum pumping apparatus as defined in claim 1, wherein the
primary pumping stages include one or more molecular drag pumping
stages.
11. Vacuum pumping apparatus as defined in claim 1, wherein the
primary pumping stages include one or more turbomolecular pumping
stages and one or more molecular drag pumping stages.
12. Vacuum pumping apparatus as defined in claim 1, wherein the
valve is automatically closed when the inlet pressure of the vacuum
pumping apparatus is below the predetermined pressure.
13. Vacuum pumping apparatus as defined in claim 1, further
comprising a roughing vacuum pump coupled to the first exhaust
port.
14. A method for operating vacuum pumping apparatus of the type
including a housing, one or more primary pumping stages disposed in
the housing and a motor to operate the primary pumping stages, the
motor including at least one stationary surface and at least one
moving surface when the motor is energized, the method comprising:
defining an auxiliary pumping stage, coupled in series with the
primary pumping stages, to pump gas through a pumping channel
between the stationary and moving surfaces of the motor; exhausting
gas from the vacuum pumping apparatus through a first exhaust port
between the primary pumping stages and the auxiliary pumping stage
when an inlet pressure of the vacuum pumping apparatus is above a
predetermined pressure; and exhausting gas from the vacuum pumping
apparatus through a second exhaust port at an outlet of the
auxiliary pumping stage when an inlet pressure of the vacuum
pumping apparatus is below the predetermined pressure.
15. The method as defined in claim 14, further comprising
automatically closing a valve coupled to the first exhaust when the
inlet pressure of the vacuum pumping apparatus is below the
predetermined pressure.
16. The method as defined in claim 14, wherein the motor includes a
stator and a rotor and wherein the stationary and moving surfaces
comprise stator and rotor surfaces, respectively.
17. The method as defined in claim 14, wherein the motor includes a
bearing preload nut and wherein the stationary and moving surfaces
comprise housing and bearing preload nut surfaces,
respectively.
18. The method as defined in claim 14, wherein the motor includes a
shaft and wherein the stationary and moving surfaces comprise
housing and shaft surfaces, respectively.
Description
FIELD OF THE INVENTION
[0001] This invention relates to high vacuum pumps and, more
particularly, to high vacuum pumps and methods for vacuum pumping
that include one or more auxiliary pumping stages. The invention
relates to vacuum pumps of the type which incorporate an electric
motor, such as for example turbomolecular pumps, molecular drag
pumps and hybrid pumps.
BACKGROUND OF THE INVENTION
[0002] Conventional turbomolecular vacuum pumps include a housing
having an inlet port, an interior chamber containing a plurality of
axial pumping stages, and an exhaust port. The exhaust port is
typically attached to a roughing vacuum pump. Each axial pumping
stage includes a stator having inclined blades and a rotor having
inclined blades. The rotor and stator blades are inclined in
opposite directions. The rotor blades are rotated at high speed by
a motor to pump gas between the inlet port and the exhaust port. A
typical turbomolecular vacuum pump may include six to twelve axial
pumping stages.
[0003] Variations of the conventional turbomolecular vacuum pump,
often referred to as hybrid turbomolecular vacuum pumps, have been
disclosed in the prior art. In one prior art configuration, one or
more of the axial pumping stages are replaced with molecular drag
stages which form a molecular drag compressor. This configuration
is disclosed in U.S. Pat. No. 5,238,362, issued Aug. 24, 1993 to
Casaro et al. A hybrid vacuum pump including an axial
turbomolecular compressor and a molecular drag compressor in a
common housing is sold by Varian, Inc. Molecular drag stages and
regenerative stages for hybrid vacuum pumps are disclosed in U.S.
Pat. No. 5,358,373, issued Oct. 25, 1994 to Hablanian. Other hybrid
vacuum pumps are disclosed in U.S. Pat. No. 5,074,747, issued Dec.
24, 1991 to Ikegami et al., U.S. Pat. No. 5,848,873, issued Dec.
15, 1998 to Schofield; and U.S. Pat. No. 6,135,709, issued Oct. 24,
2000 to Stones.
[0004] Molecular drag compressors include a rotating disk and a
stator. The stator defines a tangential flow channel and an inlet
and an outlet for the tangential flow channel. A stationary baffle,
often called a stripper, disposed in the tangential flow channel
separates the inlet and the outlet. As is known in the art, the
momentum of the rotating disk is transferred to the gas molecules
within the tangential flow channel, thereby directing the molecules
toward the outlet.
[0005] Another type of molecular drag compressor includes a
cylindrical drum that rotates within a housing having a cylindrical
interior wall in close proximity to the rotating drum. The outer
surface of the cylindrical drum is provided with a helical groove.
As the drum rotates, gas is pumped through the groove by molecular
drag.
[0006] A vacuum pump which utilizes an inverted motor to achieve a
compact structure is disclosed in U.S. Pat. No. 6,179,573, issued
Jan. 30, 2001 to Hablanian. This patent also discloses a vacuum
pump structure wherein the rotor of the motor is provided with a
molecular drag groove and gas is pumped through the molecular drag
groove when the rotor is rotated at high speed.
[0007] Known vacuum pump structures have certain drawbacks,
including but not limited to the need for a roughing vacuum pump in
many applications and limited efficiency under certain operating
conditions. Accordingly, there is a need for improved vacuum
pumping methods and apparatus, particularly in regard to increasing
the maximum compression ratio of the pump.
SUMMARY OF THE INVENTION
[0008] According to a first aspect of the invention, vacuum pumping
apparatus comprises a housing, one or more primary pumping stages
disposed in the housing, a motor coupled to the primary pumping
stages, the motor including at least one stationary surface and at
least one moving surface when the motor is energized, the
stationary and moving surfaces of the motor defining an auxiliary
pumping stage coupled in series with the primary pumping stages to
pump gas through a pumping channel between the stationary and
moving surfaces of the motor, the housing having a first exhaust
port between the primary pumping stages and the auxiliary pumping
stage, and a second exhaust port at an outlet of the auxiliary
pumping stage, and a valve connected in series with the first
exhaust port and configured to close when an inlet pressure of the
vacuum pumping apparatus is below a predetermined pressure.
[0009] According to a second aspect of the invention, a method is
provided for operating vacuum pumping apparatus of the type
including a housing, one or more primary pumping stages disposed in
the housing and a motor to operate the primary pumping stages, the
motor including at least one stationary surface and at least one
moving surface when the motor is energized. The method comprises
defining an auxiliary pumping stage, coupled in series with the
primary pumping stages, to pump gas through a pumping channel
between the stationary and moving surfaces of the motor, exhausting
gas from the vacuum pumping apparatus through a first exhaust port
between the primary pumping stages and the auxiliary pumping stage
when an inlet pressure of the vacuum pumping apparatus is above a
predetermined pressure, and exhausting gas from the vacuum pumping
apparatus through a second exhaust port at an outlet of the
auxiliary pumping stage when an inlet pressure of the vacuum
pumping apparatus is below the predetermined pressure. Thus, in
accordance with embodiments of the invention, close-proximity
rotating and stationary surfaces are utilized to provide auxiliary
pumping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] For a better understanding of the present invention,
reference is made to the accompanying drawings, which are
incorporated herein by reference and in which:
[0011] FIG. 1 is an elevation view, partly in cross-section, of a
prior art vacuum pump;
[0012] FIG. 2 is a cross-sectional diagram of a vacuum pump in
accordance with a first embodiment of the invention;
[0013] FIG. 3 is a partial cross-sectional view of the vacuum pump
motor, configured for vacuum pumping;
[0014] FIG. 4 is a partial cross-sectional view of the lower end of
the vacuum pump, showing a bearing preload nut used for vacuum
pumping;
[0015] FIG. 5 is a partial cross-sectional view of the vacuum pump,
showing a shaft extension used for vacuum pumping; and
[0016] FIG. 6 is a block diagram of vacuum pumping apparatus in
accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] A prior art high vacuum pump is shown in FIG. 1. An upper
housing 10 defines an interior chamber 12 having an inlet port 14.
The housing 10 includes a vacuum flange 18 for sealing the inlet
port 14 to a vacuum chamber (not shown) to be evacuated. A motor
housing 15 includes an exhaust port 16. The exhaust port 16 is
typically connected to a roughing vacuum pump (not shown). In cases
where the vacuum pump is capable of exhausting to atmospheric
pressure, the roughing vacuum pump is not required. Located within
housing 10 is an axial turbomolecular compressor 20, which
typically includes several axial turbomolecular stages, and a
molecular drag compressor 22, which typically includes several
molecular drag stages. Each stage of the axial turbomolecular
compressor 20 includes a rotor 24 and a stator 26. Each rotor and
stator has inclined blades as is known in the art. Each stage of
the molecular drag compressor 22 includes a rotor disk 30 and a
stator 32. The rotor 24 of each turbomolecular stage and the rotor
30 of each molecular drag stage are attached to a drive shaft 34.
The drive shaft 34 is rotated at high speed by a motor located in
motor housing 15.
[0018] A high vacuum pump in accordance with a first embodiment of
the invention is shown in FIG. 2. An upper housing 110 defines an
interior chamber 112 having inlet port 114. Upper housing 110
includes a vacuum flange 118 for sealing the inlet port to a vacuum
chamber (not shown) to be evacuated. A motor housing 115 includes a
first exhaust port 116 and a second exhaust port 128. The upper
housing 110 and the motor housing 115 may be implemented as a
single, integral pump housing or as two housing elements which are
fastened together and sealed vacuum tight to form a pump
housing.
[0019] Located within upper housing 110 may be an axial
turbomolecular compressor 120, which typically includes several
axial turbomolecular stages, and a molecular drag compressor 122,
which typically includes several molecular drag stages. The pumping
stages of axial turbomolecular compressor 120 and molecular drag
compressor 122 constitute primary pumping stages of the vacuum
pump. Each stage of the axial turbomolecular compressor 120
includes a rotor and a stator. Each rotor and stator has inclined
blades as is known in the art. Each stage of the molecular drag
compressor 122 includes a rotor disk and a stator. The rotor of
each turbomolecular stage and the rotor disk of each molecular drag
stage are attached to a drive shaft 134. The drive shaft 134 is
rotated at high speed by a motor 140 located in motor housing
115.
[0020] Motor 140 includes a rotor 150 positioned on a central axis
152 and a stator 154 including stationary motor windings 160
disposed around rotor 150. Rotor 150 includes drive shaft 134 and a
magnetic element 162 disposed on drive shaft 134. Drive shaft 134
is mounted for rotation in bearings 164 and 166. When motor
windings 160 are energized, rotor 150 rotates about axis 152.
[0021] Motor 140 includes stationary surfaces and, when energized,
moving surfaces in close proximity to the stationary surfaces. The
stationary surfaces include surfaces of motor housing 115 and
stator 154. Moving surfaces include surfaces of rotor 150 and drive
shaft 134. The motor can be configured to provide auxiliary vacuum
pumping to supplement the primary pumping stages of turbomolecular
compressor 120 and molecular drag compressor 122. Auxiliary vacuum
pumping is achieved by configuring selected surfaces of the motor
140 to perform vacuum pumping. This is achieved by providing a
pumping channel in the moving surface or in the stationary surface,
in regions of the motor where the stationary and moving surfaces
are in close proximity.
[0022] As best shown in FIG. 3, rotating magnetic element 162 has a
generally cylindrical outer surface, and stationary motor windings
160 have a generally cylindrical inner surface in close proximity
to magnetic element 162. The cylindrical outer surface of magnetic
element 162 or the cylindrical inner surface of motor windings 160
may be provided with a pumping channel 180. In one embodiment,
molecular drag pumping channel 180 has a helical configuration as
shown in FIG. 3. When rotor 150 is rotated at high speed, gas is
pumped from an inlet region 184 through pumping channel 180 to
second exhaust port 128 (FIG. 2). The pumping channel 180 between
magnetic element 162 and motor windings 160 defines an auxiliary
pumping stage 182 that is connected in series with the primary
pumping stages of turbomolecular compressor 120 and molecular drag
compressor 122. Gas is pumped from the outlet of the primary
pumping stages through auxiliary pumping stage 182 to second
exhaust port 128. The pumping channel 180 can have a variety of
configurations within the scope of the invention. As noted above,
pumping channel 180 may be formed on the outer surface of rotor 150
or on the inner surface of stator 154 of motor 140. In one
embodiment, the pumping channel 180 has a helical configuration on
the outer surface of rotor 180, as shown in the FIG. 3. In another
embodiment, pumping channel 180 may be formed as multiple
circumferential grooves in the rotor 150. The circumferential
grooves are interconnected by axial passages, and a baffle or
stripper is provided in each channel to separate the inlet and the
outlet. In further embodiments, two or more pumping channels are
provided in parallel.
[0023] A further embodiment of the auxiliary pumping stage is
described with reference to FIG. 4. Motor 140 includes bearing
preload nut 170 secured to drive shaft 134 in order to maintain
bearing 164 in a desired position on drive shaft 134. The bearing
preload nut 170 rotates about axis 152 during motor operation.
Motor housing 115 or other stationary component of motor 140 may be
positioned in close proximity to bearing preload nut 170. A moving
outer surface of bearing preload nut 170 or a stationary inner
surface of motor housing 115 adjacent to bearing preload nut 170
may be provided with a pumping channel 210. The configuration of
bearing preload nut 170, adjacent motor housing 115 and pumping
channel 210 defines an auxiliary pumping stage 212. Gas is pumped
from an inlet region 214 through pumping channel 210 to second
exhaust port 128. As described above, pumping channel 210 may have
a variety of configurations within the scope of the invention.
[0024] As shown in FIG. 5, drive shaft 134 at the bottom of the
vacuum pump may be utilized to provide additional pumping capacity.
The drive shaft 134 may be extended, if necessary to provide
sufficient length. A drive shaft extension 134a is positioned in
close proximity to motor housing 115 or other stationary component
of motor 140. A moving outer surface of drive shaft extension 134a
or a stationary inner surface of motor housing 115 adjacent to
drive shaft extension 134a is provided with a pumping channel 220
to form an auxiliary pumping stage 222. Gas is pumped from an inlet
region 224 through pumping channel 220 to second exhaust port 128.
As described above, pumping channel 220 may have a variety of
configurations within the scope of the invention.
[0025] The auxiliary pumping stage configurations shown in FIGS.
3-5 and described above may be utilized separately or in any
combination in a particular vacuum pump. For example, a first
configuration may utilize only the rotor and the stator of the
motor to form an auxiliary pumping stage, whereas a second
configuration may utilize the rotor and stator; the bearing preload
nut and motor housing; and the drive shaft extension and motor
housing to form several auxiliary pumping stages.
[0026] The auxiliary pumping stage may have a small mass flow
capacity as a result of the limited volume between the stationary
and moving components of the motor. The conductance through the
auxiliary pumping stage may not be sufficient for rough pumping of
the vacuum chamber. A configuration for overcoming this drawback is
shown in FIG. 6. First exhaust 116 is coupled through a valve 250
to a roughing vacuum pump 252. Second exhaust 128 is coupled
directly to roughing vacuum pump 252. Valve 250 may be opened when
the pressure at inlet port 114 is above a predetermined level,
thereby bypassing the secondary pumping stage for rough vacuum
pumping. When the pressure at inlet port 114 is below the
predetermined pressure level, valve 250 is closed, and all gas is
exhausted through second exhaust port 128. When the pressure level
at inlet port 114 is below the predetermined pressure level, a
small mass flow is sufficient to maintain the desired pressure
level. Control of valve 250 may be manual or automatic in response
to pressure sensing at inlet port 114.
[0027] The vacuum pump shown in FIG. 2 is described as having
primary pumping stages including turbomolecular compressor 120 and
molecular drag compressor 122. However, the primary pumping stages
of the vacuum pump can have any configuration that is driven by a
motor. For example, the primary pumping stages may include only
turbomolecular stages or only molecular drag stages. Furthermore,
the primary pumping stages may include regenerative centrifugal
stages or may have any hybrid configuration known in the art or yet
to be developed. In each case, the primary pumping stages are used
in combination with one or more auxiliary pumping stages associated
with the stationary and moving surfaces of the motor.
[0028] Having thus described several aspects of at least one
embodiment of this invention, it is to be appreciated various
alterations, modifications, and improvements will readily occur to
those skilled in the art. Such alterations, modifications, and
improvements are intended to be part of this disclosure, and are
intended to be within the spirit and scope of the invention.
Accordingly, the foregoing description and drawings are by way of
example only.
* * * * *