U.S. patent application number 10/308819 was filed with the patent office on 2003-06-05 for vacuum pump.
Invention is credited to Kabasawa, Takashi, Miwata, Tooru, Nonaka, Manabu.
Application Number | 20030103847 10/308819 |
Document ID | / |
Family ID | 19179820 |
Filed Date | 2003-06-05 |
United States Patent
Application |
20030103847 |
Kind Code |
A1 |
Nonaka, Manabu ; et
al. |
June 5, 2003 |
Vacuum pump
Abstract
A multiple cylinder having a plurality of cylinders arranged
concentrically and a rotor shaft rotatably disposed on the center
axis of the multiple cylinder are provided in a pump casing. Each
of the cylinders that constitute the multiple cylinder has a
mounting portion, through which the cylinders are integrally fixed
to the rotor shaft.
Inventors: |
Nonaka, Manabu;
(Narashino-shi, JP) ; Miwata, Tooru;
(Narashino-shi, JP) ; Kabasawa, Takashi;
(Narashino-shi, JP) |
Correspondence
Address: |
ADAMS & WILKS
31st Floor
50 Broadway
New York
NY
10004
US
|
Family ID: |
19179820 |
Appl. No.: |
10/308819 |
Filed: |
December 3, 2002 |
Current U.S.
Class: |
417/203 |
Current CPC
Class: |
F04D 29/266 20130101;
F04D 19/044 20130101; F04D 19/046 20130101 |
Class at
Publication: |
417/203 |
International
Class: |
F04B 023/14 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 4, 2001 |
JP |
JP2001-370627 |
Claims
What is claimed is:
1. A vacuum pump comprising: a multiple cylinder having a plurality
of cylinders arranged concentrically; a rotor shaft rotatably
disposed on the center axis of said multiple cylinder; and a screw
pump stator having an exhaust passage of a thread-groove pump
between said screw pump stator and each of said cylinders; wherein
each of the cylinders constituting said multiple cylinder has a
mounting portion, through which said each cylinder is integrally
mounted to the rotor shaft.
2. A vacuum pump according to claim 1, wherein said rotor shaft has
a collar on the outer peripheral surface; each of the cylinders
constituting said multiple cylinder has a mounting portion to said
collar; and the mounting portion of said cylinder and the collar of
said rotor shaft are integrally joined.
3. A vacuum pump according to claim 2, wherein the mounting portion
of said outer cylinder is fixed to the surface of said collar and
the mounting portion of said inner cylinder is fixed to the back of
said collar.
4. A vacuum pump according to claim 2, wherein the mounting portion
of said inner cylinder is disposed on the surface of said collar,
on which the mounting portion of said outer cylinder is disposed
and both the mounting portions of the inner and outer cylinders are
fastened to said collar with bolts passing therethrough.
5. A vacuum pump according to claim 2, wherein said collar has a
shoulder; and wherein the mounting portion of the outer cylinder is
fastened to the upper step of the shoulder with bolts and the
mounting portion of the inner cylinder is fastened to the lower
step of the shoulder with other bolts.
6. A vacuum pump according to claim 1, wherein the outer periphery
of the end of said rotor shaft is tapered from the end face of the
rotor shaft to a mounting position for said outer cylinder and a
tapered hole to be fitted to the tapered portion of the rotor shaft
is opened in the mounting portion of said outer cylinder and
wherein said rotor shaft and said outer cylinder are integrally
joined by a counter joining structure in which said tapered hole
and said tapered section are fitted to-each other.
7. A vacuum pump according to claim 6, wherein a push ring which is
in contact with the periphery of the tapered hole of the mounting
portion of said outer cylinder is disposed at the end face of said
rotor shaft, said outer cylinder being fastened to said rotor shaft
with a bolt screwed into the end of the rotor shaft through a bolt
insertion hole of the push ring.
8. A vacuum pump according to claim 1, wherein the outer periphery
of the end of said rotor shaft is tapered from the end face of the
rotor shaft to a mounting position for said inner cylinder through
the mounting position for said outer cylinder and a tapered hole to
be fitted to the tapered portion of the rotor shaft is opened in
each of the mounting portion of said outer cylinder and the
mounting portion of said inner cylinder and wherein said rotor
shaft, said outer cylinder, and said inner cylinder are integrally
joined by a counter joining structure in which said tapered hole
and said tapered section are fitted to each other.
9. A vacuum pump according to claim 8, wherein a screw part is
provided at the periphery of the end of said rotor shaft and at a
position slightly higher than the mounting position for said inner
cylinder and said inner cylinder is fastened to said rotor shaft
with a nut on said screw part tightened from above the mounting
portion of said inner cylinder.
10. A vacuum pump according to claim 1, wherein a plurality of
rotor blades and stator blades are alternately provided on the
outer periphery of the outer cylinder of said cylinders, said rotor
blades being integrated with the outer peripheral surface of the
outer cylinder and said stator blades being fixed to the inner
surface of a pump casing.
11. A vacuum pump according to claim 1, wherein: said multiple
cylinder includes a pair of inner and outer cylinders arranged
concentrically; said screw pump stator includes a first screw-pump
stator arranged at a position facing the outer peripheral surface
of said outer cylinder and a second screw-pump stator arranged
between said outer cylinder and said inner cylinder; said exhaust
passage of the thread-groove pump includes a first gas-exhaust
passage provided between said first screw-pump stator and said
outer cylinder, a second gas-exhaust passage provided between said
outer cylinder and said second screw-pump stator, and a third
gas-exhaust passage provided between said second screw-pump stator
and said inner cylinder, said first gas-exhaust passage and said
second gas-exhaust passage being communicated under said outer
cylinder and said second gas exhaust passage and said third gas
exhaust passage being communicated above said second screw-pump
stator.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a vacuum pump used for a
semiconductor manufacturing apparatus, an electron microscope, a
surface analysis apparatus, a mass spectrograph, a particle
accelerator, an atomic fusion experimental apparatus and so on.
[0003] 2. Description of the Related Art
[0004] Pumps (hereinafter, referred to as compound-type vacuum
pumps) that combine a turbo-molecular pump and a thread-groove pump
are well known as this type of vacuum pump. Such compound-type
vacuum pumps employ a structure in which a series of exhaust
passages R1, R2, and R3 of the thread-groove pump are turned back
in order to increase the pump compression ratio and miniaturize the
whole pump, as shown in FIGS. 6 and 7.
[0005] In order to obtain a turn-back structure of the exhaust
passages R1, R2, and R3 of the thread-groove pump, the
compound-type vacuum pumps shown in FIGS. 6 and 7 have a structure
in which a substantially lower half of a rotor (rotation body) 70
which functions as a thread-groove pump has a multiple cylinder 2
composed of two cylinders 4 and 5, and screw pump stators 21 and 22
with a thread groove are disposed on the outside of the outer
cylinder 4 and between the outer and inner cylinders 4 and 5,
respectively. In the compound-type vacuum pump shown in FIGS. 6 and
7, since the upper half of the rotor 70 works as a turbo-molecular
pump, a plurality of rotor blades 18 is integrally formed on the
outer peripheral surface of the upper part of the rotor 70.
[0006] Here, both the rotors 70 of the compound-type vacuum pumps
shown in FIGS. 6 and 7 have a structure of the multiple cylinder 2
and the rotor blades 18. However, the rotor 70 of the compound-type
vacuum pump shown in FIG. 6 is formed such that the multiple
cylinder 2 and the rotor blades 18 are cut out from one rotor
forming material. The rotor 70 of the compound-type vacuum pump
shown in FIG. 7 is formed such that two cylinders 4 and 5 are
joined later to the vicinity of the lowermost rotor blade 18 by
adhesive bonding or shrink fitting.
[0007] However, for manufacturing the rotor 70 having the structure
of the multiple cylinder 2 and the rotor blades 18, by the method
of cutting out the multiple cylinder 2 and the rotor blades 18 from
one rotor forming material as described above, the cutting shape is
too difficult to form the rotor 70 because of complication of its
shape, thus causing an increase in the cost of the whole pump.
[0008] By the method of joining the two cylinders 4 and 5 to the
vicinity of the lowermost rotor blade 18 later by adhesive bonding
or shrink fitting, as described above, it is difficult to ensure
the durability of the joint section, requiring high processing
accuracy, thus leading to a higher cost of the whole pump. Also,
the periphery of the joint sections of the cylinders 4 and 5, that
is, the vicinity of the lowermost rotor blade 18 has a large
displacement especially by a centrifugal force during the operation
of the pump; moreover, the vicinity of the lowermost rotor blade 18
has a displacement by thermal expansion due to the heat of
compression that generates during the operation of the pump, so
that the areas for mounting the cylinders 4 and 5 change to cause
an unstable mounting state of the cylinders 4 and 5. Accordingly,
the center of rotation of the cylinders 4 and 5 tends to deviate
from the center axis of rotation of a rotor shaft 8 and the rotor
blades 18, in other words, off-core of the rotor blades 18 is
likely to occur. Such off-core of the rotor blades 18 increases an
imbalance of the rotor 70 to cause vibration and a decrease in the
life and damage to a shaft bearing for supporting the rotor 70.
[0009] Particularly, when the cylinders 4 and 5 and the rotor
blades 18 are made of different types of materials, the phase
difference due to the difference in coefficient of thermal
expansion, modulus of elasticity, and Poisson's ratio between the
different types of materials causes a further unstable mounting
state of the cylinders 4 and 5, particularly causes imbalance of
the rotor 70.
SUMMARY OF THE INVENTION
[0010] The present invention has been made to solve the above
problems and the object thereof is to prevent imbalance of a
rotation body during the operation of the pump and to provide a
highly-reliable low-cost vacuum pump capable of obtaining a stable
operation for a long period of time.
[0011] In order to achieve the above object, the present invention
comprises: a multiple cylinder having a plurality of cylinders
arranged concentrically; a rotor shaft rotatably disposed on the
center axis of said multiple cylinder; and a screw pump stator
having an exhaust passage of a thread-groove pump between it and
each of said cylinders; wherein each of the cylinders constituting
the multiple cylinder has a mounting portion, through which each
cylinder is integrally mounted to the rotor shaft.
[0012] In the present invention, preferably, the rotor shaft has a
collar on the outer peripheral surface; each of the cylinders
constituting the multiple cylinder has a mounting portion to the
collar; and the mounting portions of the cylinders and the collar
of the rotor shaft are integrally joined.
[0013] In the above arrangement having the collar on the outer
peripheral surface of the rotor shaft, preferably, the mounting
portion of the outer cylinder is fixed to the surface of the collar
and the mounting portion of the inner cylinder is fixed to the back
of the collar.
[0014] In the above arrangement having the collar on the outer
peripheral surface of the rotor shaft, preferably, the mounting
portion of the inner cylinder is disposed on the surface of the
collar, on which the mounting portion of the outer cylinder is
disposed; and both the mounting portions of the inner and outer
cylinders are fastened to the collar with bolts passing
therethrough.
[0015] In the above arrangement having the collar on the outer
peripheral surface of the rotor shaft, preferably, the collar has a
shoulder; wherein the mounting portion of the outer cylinder is
fastened to the upper step of the shoulder with bolts; and the
mounting portion of the inner cylinder is fastened to the lower
step of the shoulder with other bolts.
[0016] In the present invention, preferably, the outer periphery of
the end of the rotor shaft is tapered from the end face of the
rotor shaft to a mounting position for the outer cylinder; and a
tapered hole to be fitted to the tapered portion of the rotor shaft
is opened in the mounting portion of the outer cylinder; wherein
the rotor shaft and the outer cylinder are integrally joined by a
counter joining structure in which the tapered hole and the tapered
section are fitted to each other.
[0017] In the above arrangement in which the outer cylinder is
fixed to the rotor shaft, preferably, a push ring which is in
contact with the periphery of the tapered hole of the mounting
portion of the outer cylinder is disposed at the end face of the
rotor shaft and wherein the outer cylinder is fastened to the rotor
shaft with a bolt screwed into the end of the rotor shaft through a
bolt insertion hole of the push ring.
[0018] In the present invention, preferably, the outer periphery of
the end of the rotor shaft is tapered from the end face of the
rotor shaft to a mounting position for the inner cylinder through
the mounting position for the outer cylinder; and a tapered hole to
be fitted to the tapered portion of the rotor shaft is opened in
each of the mounting portion of the outer cylinder and the mounting
portion of the inner cylinder; wherein the rotor shaft, the outer
cylinder, and the inner cylinder are integrally joined by a counter
joining structure in which the tapered hole and the tapered section
are fitted to each other.
[0019] In the above arrangement in which the inner cylinder is
fixed to the rotor shaft, preferably, a screw part is provided at
the periphery of the end of the rotor shaft and at a position
slightly higher than the mounting position for the inner cylinder;
and the inner cylinder is fastened to the rotor shaft with a nut on
the screw part tightened from above the mounting portion of the
inner cylinder.
[0020] In the present invention, preferably, a plurality of rotor
blades and stator blades are alternately provided on the outer
periphery of the outer cylinder of the cylinders; wherein the rotor
blades are integrated with the outer peripheral surface of the
outer cylinder; and the stator blades are fixed to the inner
surface of a pump casing.
[0021] In the present invention, preferably, the multiple cylinder
includes a pair of inner and outer cylinders arranged
concentrically; the screw pump stator includes a first screw-pump
stator arranged at a position facing the outer peripheral surface
of the outer cylinder and a second screw-pump stator arranged
between the outer cylinder and the inner cylinder; the exhaust
passage of the thread-groove pump includes a first gas-exhaust
passage provided between the first screw-pump stator and the outer
cylinder, a second gas-exhaust passage provided between the outer
cylinder and the second screw-pump stator, and a third gas-exhaust
passage provided between the second screw-pump stator and the inner
cylinder; wherein the first gas-exhaust passage and the second
gas-exhaust passage communicate under the outer cylinder; and the
second gas exhaust passage and the third gas exhaust passage
communicate above the second screw-pump stator.
BRIEF DESCRIPTION OF THE DRABLADES
[0022] FIG. 1 is a sectional view of an embodiment of a vacuum pump
according to the present invention;
[0023] FIG. 2 is a sectional view of a second embodiment of a
vacuum pump according to the present invention;
[0024] FIG. 3 is a sectional view of a third embodiment of a vacuum
pump according to the present invention;
[0025] FIG. 4 is a sectional view of a forth embodiment of a vacuum
pump according to the present invention;
[0026] FIG. 5 is a sectional view of a fifth embodiment of a vacuum
pump according to the present invention;
[0027] FIG. 6 is a sectional view of a conventional vacuum pump;
and
[0028] FIG. 7 is a sectional view of another conventional vacuum
pump.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Referring to FIGS. 1 to 5, embodiments of a compound-type
vacuum pump incorporating a vacuum pump according to the present
invention will be described hereinbelow.
[0030] A compound-type vacuum pump shown in FIG. 1 includes a
multiple cylinder 2 as a rotation body in a cylindrical pump casing
1. The multiple cylinder 2 is arranged so that the upper end
thereof faces a gas suction port 3 at the upper part of the pump
casing 1.
[0031] In this embodiment, the multiple cylinder 2 has a
double-cylindrical structure in which two cylinders 4 and 5 are
arranged concentrically. A rotor shaft 8 is provided so as to be
rotatably erected on the center axis of the multiple cylinder 2
having the inner and outer pair of cylinders 4 and 5 through a
radial bearing 6 and a thrust bearing 7.
[0032] The rotor shaft 8 has a collar 9 on the upper peripheral
surface integrally. On the other hand, the two cylinders 4 and 5
constituting the multiple cylinder 2 have mounting portions 10 and
11 to the collar 9 at the respective upper parts thereof. By
integrally joining the respective mounting portions 10 and 11 of
the cylinders 4 and 5 and the collar 9 of the rotor shaft 8, the
two cylinders 4 and 5 are integrally secured to the rotor shaft
8.
[0033] Several types of joining structures of the cylinders 4 and 5
and the rotor shaft 8 may be provided; however, this embodiment
employs, as a joining structure, a structure in which mounting
holes 10a and 11a are opened in respective mounting portions 10 and
11 of the inner and outer cylinders 4 and 5, through which the
respective mounting portions 10 and 11 of the inner and outer
cylinders 4 and 5 are mounted to the rotor shaft 8, and in which
the mounting portion 10 of the outer cylinder 4 is fastened to the
surface of the collar 9 with bolts 12, and the mounting portion 11
of the inner cylinder 5 is fastened to the back of the collar 9
with the other bolts 13.
[0034] In this embodiment, the radial bearing 6 and the thrust
bearing 7 that support the rotor shaft 8 are magnetic bearings,
with which the rotor shaft 8 is supported in the radial direction
and the thrust direction.
[0035] The rotor shaft 8 is driven to rotate by a drive motor 14.
The drive motor 14 of this embodiment has a structure in which a
motor stator 16 is mounted to a motor stator column 15 provided
inside the multiple cylinder 2 and a motor rotor 17 is mounted on
the peripheral surface of the rotor shaft 8 which faces the motor
stator 16.
[0036] In the compound-type vacuum pump shown in FIG. 1, the
substantially upper half of the multiple cylinder 2 functions as a
turbo-molecular pump and the substantially lower half of the
multiple cylinder 2 functions as a thread-groove pump.
[0037] First, the structure of the substantially upper half of the
multiple cylinder 2 that functions as a turbo-molecular pump will
be described.
[0038] A plurality of worked rotor blades 18 and stator blades 19
are provided on the upper outer periphery of the multiple cylinder
2, that is, on the upper outer periphery of the outer cylinder 4 of
the inner and outer pair of cylinders 4 and 5. The rotor blades 18
and the stator blades 19 are alternately arranged along the center
axis of rotation of the multiple cylinder 2.
[0039] More specifically, the multiple cylinder 2 has, at the upper
outer periphery, the stator blades 19 between the upper and lower
rotor blades 18, or has the rotor blades 18 between the upper and
lower stator blades 19.
[0040] The rotor blades 18 are integrated with the upper outer
peripheral surface of the outer cylinder 4 by integral processing
with the outer cylinder 4, and can be rotated integrally with the
inner and outer cylinders 4 and 5. The stator blades 19 are fixed
to the inner surface of the pump casing 1 through spacers 20.
[0041] In the compound-type vacuum pump of this embodiment, when
the multiple cylinder 2 is rotated with the rotor shaft 8, the gas
molecules are exhausted from the gas suction port 3 at the upper
part of the pump casing 1 toward the lowermost rotor blade 18 and
stator blade 19 at the substantially upper half of the multiple
cylinder 2 by the interaction of the rotor blades 18 and the stator
blades 19. The exhaust gas is sequentially fed to the next stage,
that is, to the substantially lower half of the multiple cylinder 2
functioning as a thread-groove pump.
[0042] Next, in the multiple vacuum cylinder shown in FIG. 1, the
structure of the substantially lower half of the multiple cylinder
2 functioning as the thread-groove pump will be described.
[0043] While the multiple cylinder 2 is constituted by a pair of
inner and outer cylinders 4 and 5, as described above, a first
screw-pump stator 21 is disposed at a position which faces the
outer peripheral surface of the outer cylinder 4, and a second
screw-pump stator 22 is disposed between the outer cylinder 4 and
the inner cylinder 5. Both the first and second screw-pump stators
21 and 22 are shaped like a cylinder similar to the cylinders 4 and
5 constituting the multiple cylinder 2.
[0044] The first screw-pump stator 21 has a thread groove 23 at the
inner surface, that is, a surface facing the outer peripheral
surface of the outer cylinder 4. The second screw-pump stator 22
has thread grooves 23 at the inner and outer surfaces, that is, a
surface facing the inner peripheral surface of the outer cylinder 4
and a surface facing the outer peripheral surface of the inner
cylinder 5.
[0045] A first gas-exhaust passage R1 is provided between the first
screw-pump stator 21 and the outer cylinder 4; a second gas-exhaust
passage R2 is provided between the outer cylinder 4 and the second
screw-pump stator 22; and a third gas-exhaust passage R3 is
provided between the second screw-pump stator 22 and the inner
cylinder 5. The first gas-exhaust passage R1 and the second
gas-exhaust passage R2 communicate with each other at the lower end
of the outer cylinder 4; and the second gas-exhaust passage R2 and
the third gas-exhaust passage R3 are communicated with each other
at the upper end of the second screw-pump stator 22.
[0046] In the compound-type vacuum pump of this embodiment, when
the multiple cylinder 2 is rotated with the rotor shaft 8, the
substantially lower half of the multiple cylinder 2 functions as a
thread-groove pump. More specifically, a gas is exhausted by the
relative motion between the two cylinders 4 and 5 and the thread
grooves 23 of the screw pump stators 21 and 22. The flow of the gas
to be exhausted will be described as follow:
[0047] The exhaust gas first flows into the first gas-exhaust
passage R1 from the lowermost rotor blade 18 and stator blade 19
and flows therein downwardly in the drawing. The downward flowing
gas is 180.degree. reversed at the lower end of the outer cylinder
4, and then flows into the second gas-exhaust passage R2, and flows
therein upwardly in the drawing. Subsequently, the upward flowing
gas is 180.degree. reversed at the upper end of the second
screw-pump stator 22, then flows into the third gas-exhaust passage
R3, and flows therein downwardly in the drawing, and finally flows
from the lower end of the inner cylinder 5 to a gas exhaust port 24
for discharge.
[0048] In the compound-type vacuum pump of this embodiment, while
the substantially lower half of the multiple cylinder 2 functions
as a thread-groove pump, as described above, the series of gas
exhaust passages (R1, R2, and R3) of this thread-groove pump turn
over at the upper and lower points, that is, at the lower end of
the outer cylinder 4 and the upper end of the second screw-pump
stator 22.
[0049] The gas suction port 3 at the upper part of the pump casing
1 connects to a high vacuum vessel including a process chamber of a
semiconductor manufacturing apparatus, and the gas exhaust port 24
at the lower part of the pump casing 1 is set so as to communicate
with an auxiliary pump (not shown). Therefore, the compound-type
vacuum pump of this embodiment is constructed such that the
turbo-molecular-pump functioning section that performs evacuation
by the interaction between the rotor blades 18 and the stator
blades 19 is positioned on a high vacuum side, and the
thread-groove-pump functioning section that performs evacuation by
the interaction between the inner and outer cylinders 4 and 5 and
the thread grooves 23 is positioned on the auxiliary pump side (not
shown).
[0050] Referring to FIG. 1, the use example and operation of the
compound-type vacuum pump of this embodiment, constructed as
described above, will be described. The arrows in the drawing
indicate the flow direction of the exhaust gas in the pump.
[0051] The compound-type vacuum pump in this drawing can be used,
for example, as a means for evacuating the inside of a process
chamber of the semiconductor manufacturing apparatus, in which the
gas suction port 3 of the pump casing 1 connects to the process
chamber.
[0052] In the compound-type vacuum pump connected as described
above, when the auxiliary pump (not shown) connected to the gas
exhaust port 24 is activated to evacuate the process chamber to a
predetermined vacuum level and an operation start switch is then
turned on, the drive motor 14 is activated to rotate the multiple
cylinder 2 and the rotor blades 18 integrally with the rotor shaft
8.
[0053] In this case, in the evacuating operation for the gas
molecules in the turbo-molecular-pump functioning section, the
uppermost rotor blade 18, which is rotating at a high speed,
applies a momentum in the direction of the gas exhaust port 24 to
gas molecules injected through the gas suction port 3, and the gas
molecules having the downward momentum are carried to the stator
blades 19 and are fed to the next lower rotor blade 18. By
repeating the application of momentum, the gas molecules are
carried from the gas suction port 3 toward the lowermost stator
blade 19 for discharge.
[0054] The gas molecules that have reached the lowermost stator
blade 19, as described above, are carried toward the gas discharge
port 24 through the gas exhaust passages (R1, R2, and R3), where
the gas molecules are compressed from a intermediate flow to a
viscous flow by the relative movement between the cylinders 4 and 5
and the thread grooves 23. The compressed gas is discharged from
the gas exhaust port 24 to the exterior of the pump through the
auxiliary pump (not shown).
[0055] The compound-type vacuum pump of this embodiment employs a
structure in which the two cylinders 4 and 5 constituting the
multiple cylinder 2 have the mounting portions 10 and 11,
respectively, with which the cylinders 4 and 5 are integrally fixed
to the rotor shaft 8. Therefore, when manufacturing the rotation
body (rotor) of the multiple cylinder 2 constituted by the outer
cylinder 4 with the rotor blades 18 and the inner cylinder 5
without the rotor blades 18, there is no need to cut out the
multiple-cylindrical structure portion and the rotor blades 18 from
one rotor forming material, but after the outer cylinder 4 with the
rotor blades 18 and the inner cylinder 5 without the rotor blades
18 have been formed, the outer and inner cylinders 4 and 5 may be
combined concentrically and fixed to the rotor shaft 8. Therefore,
the processing is simplified as compared with the conventional art,
thus reducing the cost of the whole pump.
[0056] During the operation of the pump, the displacement of the
rotor shaft 8 due to the heat of compression of the pump is smaller
than that of the rotor blades 18 and so on. Since this embodiment
employs a structure in which the cylinders 4 and 5 are mounted to
the rotor shaft 8 having a small displacement, the load applied to
the mounting portions of the cylinders 4 and 5 is small, so that
the cylinders 4 and 5 can be maintained in stable positions for a
long period of time, thus preventing problems due to an unstable
mounting state, for example, deviation of the rotational center
axes of the rotor blades 18 integrated with the outer cylinder 4
from the geometrical central axes of the rotor shaft 8 and the
rotor blades 18, so-called off-core of the rotor blades 18, and
resultant imbalance of the multiple cylinder 2, providing a
high-reliable vacuum pump capable of obtaining a stable operation
for a long period of time.
[0057] The joining structure of the cylinders 4 and 5 and the rotor
shaft 8 may be other structures shown in FIGS. 2 to 5 in addition
to that of the above-described embodiment shown in FIG. 1, which
can also provide similar advantages.
[0058] In the joining structure of FIG. 2, the mounting portion 11
of the inner cylinder 5 is arranged on the surface of the collar 9,
on which the mounting portion 10 of the outer cylinder 4 is
arranged, and the mounting portions 10 and 11 of the outer and
inner cylinders 4 and 5 are fastened to the collar 9 of the rotor
shaft 8 with bolts 12 that pass through the mounting portions 10
and 11.
[0059] In the joining structure of FIG. 3, the collar 9 has a
shoulder 25, to an upper step 25a of which the mounting portion 10
of the outer cylinder 4 is fastened with the bolts 12, and to a
lower step 25b of which the mounting portion 11 of the inner
cylinder 5 is fastened with the other bolts 13.
[0060] The joining structure of FIG. 4 is a center lock structure
in which the mounting portion 10 of the outer cylinder 4 is
fastened to the end center of the rotor shaft 8 with the bolt 12.
In the center lock structure, the outer periphery of the end of the
rotor shaft 8 is tapered from the end face to the position of
mounting the outer cylinder 4; a tapered hole 27 to be fitted on a
tapered portion 26 of the rotor shaft 8 is opened in the mounting
portion 10 of the outer cylinder 4; and the rotor shaft 8 and the
outer cylinder 4 are joined in one by a counter lock structure in
which the tapered hole 27 and the tapered portion 26 are fitted to
each other.
[0061] In the joining structure of FIG. 4, for fixing the outer
cylinder 4 to the rotor shaft 8, the mounting portion 10 of the
outer cylinder 4 is mounted to the outer-cylinder-4 mounting
position of the rotor shaft 8 through the tapered hole 27 of the
mounting portion 10 of the outer cylinder 4, then the push ring 28
that is in contact with the periphery of the tapered hole 27 of the
mounting portion 10 is arranged at the end face of the rotor shaft
8, and the bolt 12 may be screwed into the end of the rotor shaft 8
through a bolt insertion hole of the push ring 28. Thus, the
driving torque is applied to the mounting portion 10 of the outer
cylinder 4 through the push ring 28, and a wedge effect is produced
between the tapered portion 26 and the tapered hole 27, thereby
firmly fastening the outer cylinder 4 to the rotor shaft 8.
[0062] In the joining structure of FIG. 4, the inner cylinder 5
does not employ the center lock structure as in the outer cylinder
4, but adopts a structure in which the mounting portion 11 of the
cylinder 5 is fastened to the collar 9 on the peripheral surface of
the rotor shaft 8 with the bolts 13.
[0063] In the joining structure of FIG. 5, both the inner and outer
cylinders employ the center lock structure. In this structure, the
outer periphery of the end of the rotor shaft 8 is tapered between
the end face thereof to the mounting position for the inner
cylinder 5 through the mounting position for the outer cylinder 4;
the tapered hole 27 to be fitted on the tapered portion 26 of the
rotor shaft 8 is opened in the mounting portion 11 of the inner
cylinder 5; and the rotor shaft 8 and the inner cylinder 5 are
joined in one by the counter lock structure in which the tapered
hole 27 and the tapered portion 26 are fitted to each other. The
outer periphery of the end of the rotor shaft 8 has a screw part 30
at a position slightly higher than the mounting position for the
inner cylinder 5, onto which a nut 31 is fitted.
[0064] In the joining structure of FIG. 5, for fixing the inner
cylinder 5 to the rotor shaft 8, the mounting portion 11 of the
inner cylinder 5 is mounted to the inner-cylinder-5 mounting
position of the rotor shaft 8 through the tapered hole 27 of the
mounting portion 10 of the inner cylinder 5, then the nut 31 on the
screw part 30 may be fastened from above the mounting portion 11.
Thus, the fastening force of the nut 31 causes a wedge effect
between the tapered portion 26 and the tapered hole 27, thereby
firmly fastening the inner cylinder 5 to the rotor shaft 8. Since
the center lock structure of the outer cylinder 4 is similar to
that of the example shown in FIG. 4, a specific description thereof
will be omitted.
[0065] In the above embodiments, while examples of forming the
thread grooves 23 in the screw pump stators 21 and 22 were
described, alternatively, the thread grooves 23 may be formed in
the cylinders 4 and 5.
[0066] In the above embodiments, while examples of employing the
multiple cylinder 2 composed of the two cylinders 4 and 5 were
described, the present invention can be applied to a multiple
cylinder having two or more cylinders arranged concentrically, and
the number of the cylinders constituting the multiple cylinder is
not limited to two.
[0067] In the above embodiments, examples of a so-called
compound-type vacuum pump in which the upper half of the multiple
cylinder 2 functions as a turbo-molecular pump and the lower half
functions as a thread-groove pump were described; however, the
present invention can also be applied to a vacuum pump having a
structure in which the whole multiple cylinder 2 functions as a
turbo-molecular pump, in other words, the rotor blades 18 are
provided over the whole peripheral surface of the outer cylinder 4,
that is a so-called blade vacuum pump, and to a vacuum pump having
only a function of a thread-groove pump without the rotor blades 18
over the peripheral surface of the outer cylinder 4.
[0068] As described above, according to the present invention, each
of a plurality of cylinders that constitute a multiple cylinder has
a mounting portion, through which the cylinders are integrally
fixed to a rotor shaft. Therefore, for example, when a rotation
body (rotor) of a multiple cylinder constituted by an outer
cylinder with rotor blades and an inner cylinder without the rotor
blades is manufactured, there is no need to cut out the
multiple-cylindrical structure portion and the rotor blades from
one rotor forming material; but all that is needed is to form the
outer cylinder with the rotor blades and the inner cylinder without
the rotor blades separately, then combine the outer and inner
cylinders concentrically, and fix it to the rotor shaft. Therefore,
the processing is simplified as compared with the conventional art,
thus reducing the cost of the whole pump.
[0069] During the operation of the pump, the displacement of the
rotor shaft due to the heat of compression of the pump is smaller
than those of the rotor blades and so on. According to the present
invention, since the cylinders are fixed to the rotor shaft having
a small displacement, the load applied to the fixing sections of
the cylinders is small, so that the cylinders can be maintained in
stable positions for a long period of time, thus preventing
problems due to an unstable mounting state, for example, the
deviation of the center axes of rotation of the rotor blades 18,
which are provided at the outer cylinder constituting the multiple
cylinder, from the geometrical central axes of the rotor shaft and
the rotor blades, so-called off-core of the rotor blades, and
resultant imbalance of the multiple cylinder, thus providing a
high-reliable vacuum pump capable of obtaining a stable operation
for a long period of time.
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