U.S. patent application number 12/159186 was filed with the patent office on 2010-09-16 for screw-type fluid machine.
This patent application is currently assigned to KABUSHIKI KAISHA TOYOTA JIDOSHOKKI. Invention is credited to Masahiro Inagaki, Kentaro Ishihara, Yuya Izawa, Ryosuke Koshizaka, Shinya Yamamoto.
Application Number | 20100233006 12/159186 |
Document ID | / |
Family ID | 38218027 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100233006 |
Kind Code |
A1 |
Yamamoto; Shinya ; et
al. |
September 16, 2010 |
SCREW-TYPE FLUID MACHINE
Abstract
A vacuum pump includes rotary shafts connected to a pair of
screw-type rotors, respectively, and a pair of shaft retainers
extending in the housing. Each shaft retainer supports the
corresponding rotary shaft by means of a proximal bearing portion
and a distal bearing portion. Each pair of the proximal and distal
bearing portions are fixed in the axial direction with respect to
the corresponding rotary shaft and shaft retainer. Lubricant oil is
stored in an oil storage space in a gear case attached to the
housing. A cooling water passage through which cooling water to
cool the lubricant oil passes is formed in the gear case. A
controller controls the flow rate of the cooling fluid, so that the
temperature of the lubricant oil in the oil storage space is kept
constant. With this configuration, when the bearing portions are
fixed in the axial direction with respect to the rotary shafts and
the shaft retainers, it is possible to prevent load from being
applied to the bearing portions in the axial direction.
Inventors: |
Yamamoto; Shinya;
(Kariya-shi, JP) ; Koshizaka; Ryosuke;
(Kariya-shi, JP) ; Ishihara; Kentaro; (Kariya-shi,
JP) ; Inagaki; Masahiro; (Kariya-shi, JP) ;
Izawa; Yuya; (Kariya-shi, JP) |
Correspondence
Address: |
KNOBLE, YOSHIDA & DUNLEAVY
EIGHT PENN CENTER, SUITE 1350, 1628 JOHN F KENNEDY BLVD
PHILADELPHIA
PA
19103
US
|
Assignee: |
KABUSHIKI KAISHA TOYOTA
JIDOSHOKKI
Kariya-shi, Aichi-ken
JP
|
Family ID: |
38218027 |
Appl. No.: |
12/159186 |
Filed: |
December 26, 2006 |
PCT Filed: |
December 26, 2006 |
PCT NO: |
PCT/JP2006/325864 |
371 Date: |
August 7, 2008 |
Current U.S.
Class: |
418/206.3 ;
418/206.7; 418/206.8 |
Current CPC
Class: |
F04C 18/16 20130101;
F04C 29/023 20130101; F04C 29/025 20130101; F04C 29/04 20130101;
F04C 2220/10 20130101 |
Class at
Publication: |
418/206.3 ;
418/206.7; 418/206.8 |
International
Class: |
F01C 1/18 20060101
F01C001/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2005 |
JP |
2005-372225 |
Claims
1. A screw-type fluid machine, comprising: a housing; a pair of
screw-type rotors accommodated in the housing and meshed with each
other; a pair of rotary shafts each coaxially coupled to one of the
rotors, each rotary shaft having an end portion protruding from the
housing; a pair of cylindrical shaft retainers extending in the
housing, each shaft retainer having a first end portion and a
second end portion, and having a through hole into which one of the
rotary shafts is inserted; first bearing portions each mounted in
the through hole at one of the first end portions; second bearing
portions each mounted in the through hole at one of the second end
portions, each pair of the first and second bearing portions
rotatably supporting the corresponding rotary shaft with respect to
the shaft retainer, and each pair of the first and second bearing
portions being fixed in the axial direction with respect to the
corresponding rotary shaft and the corresponding shaft retainer;
synchronous gears each provided at the end portion of one of the
rotary shafts protruding from the housing; a gear case in which the
synchronous gears are accommodated, the gear case defining an oil
storage space capable of storing lubricant oil and being connected
to the housing, a cooling portion for cooling the lubricant oil by
using a cooling fluid; and and a control portion for controlling
the flow rate of the cooling fluid so that the temperature of the
lubricant oil in the oil storage space is kept constant.
2. The screw-type fluid machine according to claim 1, wherein the
first and second bearing portions are each composed of a
combination of at least two roller bearings.
3. The screw-type fluid machine according to claim 2, wherein the
roller bearings include angular ball bearings.
4. The screw-type fluid machine according to claim 1, wherein the
cooling portion includes a cooling water passage extending in the
gear case so as to permit passage of the cooling fluid.
5. The screw-type fluid machine according to claim 1, further
including oil feed portions each driven by one of the rotary shafts
so that the shaft retainers and the rotary shafts are cooled by
using lubricant oil in the oil storage space.
6. The screw-type fluid machine according to claim 5, wherein a
space is provided between the inner circumferential surface of each
shaft retainer and the outer circumferential surface of the
corresponding rotary shaft, an oil feed passage having an inlet
opening to the end portion of the rotary shaft and an outlet
communicating with the space is formed at each rotary shaft,
wherein the oil feed portion is a pump provided at the end portion
of each of the rotary shafts, and the pump supplies lubricant oil
existing in the oil storage space to the inlet of the oil feed
passage of the corresponding rotary shaft.
7. The screw-type fluid machine according to claim 1, further
comprising a flow rate changing portion for controlling the flow
rate of the cooling fluid and a temperature sensor provided in the
oil storage space for detecting the temperature of the lubricant
oil, wherein the control portion controls the flow late changing
portion in accordance with the temperature detected by the
temperature sensor.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a screw-type fluid machine
such as a vacuum pump, that is used in, for example, a
semiconductor manufacturing process.
BACKGROUND OF THE INVENTION
[0002] For example, a screw-type vacuum pump described in Patent
Document 1 has been known as a screw-type fluid machine. The
screw-type vacuum pump according to Patent Document 1 includes a
pair of screw-shaped rotors, which are adjacent to and meshed with
each other, in the casing. Each rotor has a rotary shaft. The
rotary shafts are supported with respect to the casing, which
operates as a shaft retainer, with upper bearings and lower
bearings.
[0003] A synchronous gear is fixed to each rotary shaft, and the
synchronous gears are meshed with each other. A lubricant oil
passage extending in the axial direction is formed in the interior
of the each rotary shaft, and the lubricant oil passage functions
as a centrifugal pump. The lubricant oil passage has an inlet open
to the lower end of the rotary shaft and an outlet open to the
circumferential surface of the rotary shaft above the upper
bearing. A heat exchanger is provided near the inlet of the
lubricant oil passage. Lubricant oil is stored in the casing, and
the lower end of the rotary shaft is immersed in the lubricant oil
stored therein. Further, a cooling water pipe is provided in the
casing, and heat exchange takes place between the cooling water and
the lubricant oil in the heat exchanger.
[0004] As the vacuum pump is driven, the centrifugal pump draws up
lubricant oil stored in the casing. The lubricant oil is subjected
to heat exchange and cooled down by the heat exchanger when being
drawn up by the centrifugal pump. The lubricant oil thus drawn up
comes out through the outlet of the lubricant oil passage and flows
down to the upper bearing to cool the upper bearing. After that,
the lubricant oil flows down from the upper bearing along the
rotary shaft and is again stored in the casing. With such
circulation of the lubricant oil, the upper and lower bearings, the
rotary shaft, and other members, are cooled. If the rotary shaft is
thermally expanded due to, for example, load is applied to the
bearings, by which the rotary shaft is supported with respect to
the casing, in the axial direction. However, since the bearings and
rotary shafts are cooled by the lubricant oil, such thermal
expansion is suppressed, and the load on the bearings is
reduced.
[0005] However, by only cooling the lubricant oil merely using the
heat exchanger, it is impossible to finely adjust the temperature
of the lubricant oil in accordance with the running state of the
vacuum pump. Therefore, practically, the thermal expansion of the
rotary shaft cannot be sufficiently suppressed, and it is not
possible to sufficiently suppress the load applied to the bearings
in the axial direction.
[0006] If the bearings are provided between the casing and the
rotary shaft so as to allow displacement of the rotary shaft in the
axial direction with respect to the casing, load resulting from
thermal expansion of the rotary shafts can be prevented from being
applied to the bearings in the axial direction. However, when such
a configuration is used, it is impossible to prevent the rotary
shafts from being subjected to lateral sway and longitudinal sway,
which likely to result in vibrations and noises.
Patent Document 1: Japanese Laid-Open Patent Publication No.
4-314991
SUMMARY OF THE INVENTION
[0007] It is an objective of the present invention to provide a
screw-type fluid machine capable of preventing load from being
applied to bearings in the axial direction even when the bearings
are fixed in the axial direction with respect to rotary shafts and
a shaft retainer.
[0008] In order to achieve the above objective and in accordance
with one aspect of the present invention, a screw-type fluid
machine is provided that includes a housing, a pair of screw-shaped
rotors which are accommodated in the housing and are meshed with
each other, a pair of rotary shafts which are connected to both
rotors so as to become coaxial with the rotors respectively, and a
pair of cylindrical shaft retainers extending in the housing. Each
rotary shaft has an end portion protruding from the housing. Each
shaft retainer has a first end portion and a second end portion,
and also has a through hole into which one of the rotary shafts is
inserted. The first bearing is mounted in the through hole at the
first end portion, and the second bearing is mounted in the through
hole at the second end portion. Each pair of the first and second
bearings supports the corresponding rotary shaft rotatably with
respect to the shaft retainer. The first and second bearings are
fixed in the axial direction with respect to the corresponding
rotary shafts and the shaft retainers. Synchronous gears are
provided at the end portions of both rotary shafts protruding from
the housing, respectively. A gear case accommodates the synchronous
gears, and the gear case defines an oil reservoir space in which
lubricant oil can be stored. The gear case is connected to the
housing. A cooling portion cools down the lubricant oil using a
cooling fluid. A control portion controls the flow rate of the
cooling fluid so that the temperature of lubricant oil in the oil
reservoir space is kept constant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a longitudinally cross-sectional view of a vacuum
pump according to one embodiment of the present invention;
[0010] FIG. 2 is a cross-sectional view taken along line A-A of the
vacuum pump of FIG. 1;
[0011] FIG. 3 is an enlarged view showing a major portion of a
proximal bearing portion and a distal bearing portion in the vacuum
pump of FIG. 1;
[0012] FIG. 4 is a cross-sectional view taken along line B-B of the
vacuum pump of FIG. 1; and
[0013] FIG. 5 is an enlarged sectional view of an oil feed pump in
the vacuum pump of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] One embodiment according to the present invention will now
be described, with reference to FIGS. 1 to 5. As shown in FIG. 1, a
screw-type fluid machine according to the present embodiment is a
screw-type vacuum pump 10 which is vertically placed and used for
semiconductor manufacturing (hereinafter simply referred to as a
"vacuum pump"). The vacuum pump 10 has a housing 14 having an upper
housing member 11, a rotor housing member 12, and a lower housing
member 13. The housing 14 forms the shell of the vacuum pump
10.
[0015] In detail, the upper housing member 11 is connected to the
upper end of the rotor housing member 12, and the lower housing
member 13 is connected to the lower end of the rotor housing member
12. A suction port 15 to draw in a compressive fluid is formed in
the upper housing member 11 so as to communicate with the interior
of the housing 14. The lower housing member 13 is provided with a
discharge port 16 to discharge the compressive fluid. The discharge
port 16 communicates with the interior of the housing 14. Also, the
lower housing member 13 is provided with an extension part 13a
caused to extend sideways, and a drive motor 17 operating as a
drive source is installed on the extension part 13a. Furthermore, a
gear case 18 to cover the lower housing member 13 including the
extension part 13a from downward thereof is connected to the lower
housing member 13.
[0016] As shown in FIG. 2, a screw-type male rotor 21 and a
screw-type female rotor 31, which are meshed with each other, are
accommodated in the housing 14. An operation chamber is formed by
the rotors 21, 31 and the housing 14. The male rotor 21 has an
insertion hole 22 extending from the discharge port 16 toward the
suction port 15 and an connection hole 23, the diameter of which is
smaller than that of the insertion hole 22, extending upward from
the upper end of the insertion hole 22. A rotary shaft 25 passing
through the lower housing member 13 is inserted into the connection
hole 23. The male rotor 21 and the rotary shaft 25 are connected to
each other by using a stop plate 26 and a connection bolt 27.
Accordingly, the male rotor 21 and the rotary shaft 25 rotate
integrally. Similarly, the female rotor 31 shown in FIG. 2 is
provided with an insertion hole 32 and a connection hole 33, and is
connected to a rotary shaft 35 by using a stop plate 36 and a
connection bolt 37. Each of the respective rotors 21 and 31 is
coaxial with the corresponding one of the rotary shafts 25 and
35.
[0017] The lower housing member 13 has a pair of cylindrical shaft
retainers 28, 38 extending upward, and as shown in FIG. 2, the
proximal portions of the shaft retainers 28, 38 are linked with
each other and integrated. In this embodiment, the shaft retainers
28, 38 are fixed to the lower housing member 13 by fixing bolts 41.
The shaft retainer 28 is inserted into the insertion hole 22 of the
male rotor 21, and a slight space is formed between the outer
circumferential surface of the shaft retainer 28 and the
inner-circumferential surface of the insertion hole 22. The shaft
retainer 38 is inserted into the insertion hole 32 of the female
rotor 31, and a slight space is also formed between the outer
circumferential surface of the shaft retainer 38 and the inner
circumferential surface of the insertion hole 32.
[0018] A through hole 29 extending in the axial direction is formed
at the center of the shaft retainer 28, and the rotary shaft 25 for
the male rotor 21 is inserted into the through hole 29. A pair of
upper and lower bearing portions 42, 43 consisting of roller
bearings are provided between the rotary shaft 25 and the shaft
retainer 28. The bearing portions 42, 43 are disposed at the upper
and lower parts of the shaft retainer 28. In this embodiment, the
upper bearing portion 42 is a distal bearing portion or a second
bearing portion, and the lower roller bearing 43 is a proximal
bearing portion or a first bearing portion. An upper large diameter
hole 29a having a larger diameter than the diameter of the through
hole 29 is formed at the upper end portion (the second end portion)
of the shaft retainer 28, continuous to the through hole 29. The
distal bearing portion 42 is disposed in the upper large diameter
hole 29a. Also, the portion between the distal bearing 42 and the
proximal bearing 43 at the rotary shaft 25 has a slightly larger
diameter than that of the upper and lower parts of the rotary shaft
25. As shown in FIG. 3, the portion of the rotary shaft 25, the
diameter of which changes, forms a distal step portion 25a and a
proximal step portion 25b.
[0019] As shown in FIGS. 1 and 2, a sealing member 30 is located
between the rotary shaft 25 and the shaft retainer 28 at a position
above the distal bearing portion 42. A lower large diameter hole
29b having a larger diameter than that of the through hole 29 is
provided at the lower end portion (the first end portion) of the
shaft retainer 28, continuous to the through hole 29. The proximal
bearing portion 43 is disposed in the lower large diameter hole
29b.
[0020] These bearing portions 42, 43 are provided to rotatably
support the rotary shaft 25 with respect to the shaft retainer 28.
In the embodiment, each of the distal bearing portion 42 and the
proximal bearing portion 43 is structured by stacking two roller
bearings each one being a single row.
[0021] A further detailed description will now be given of the
distal bearing portion 42. The distal bearing portion 42 is
composed of a combination of two angular ball bearings 42a, 42b. As
shown in FIG. 3, both bearings 42a, 42b are disposed in the upper
large diameter hole 29a in a state of Duplex Back-to-back. The
outer rings of both bearings 42a, 42b are pressure-fitted to the
upper large diameter hole 29a and fixed to the shaft retainer 28.
In addition, the inner rings of both bearings 42a, 42b are
pressure-fitted to the rotary shaft 25.
[0022] The inner ring of the angular ball bearing 42b is pressed
against the distal step portion 25a of the rotary shaft 25, and the
inner ring of the angular ball bearing 42a is pressed against the
inner ring of the angular ball bearing 42b by a nut 49a screwed in
the rotary shaft 25. As a result, the rolling elements of the
angular ball bearings 42a, 42b are in contact with the inner and
outer rings without any space in either of the axial direction or
the radial direction.
[0023] On the other hand, as shown in FIG. 3, the angular ball
bearings 43a, 43b are disposed at the lower large diameter hole 29b
at the proximal bearing portion 43 in a state of Duplex
Back-to-back. The outer rings of the bearings 43a, 43b are
pressure-fitted to the lower large diameter hole 29b and are fixed
to the shaft retainer 28. The inner ring of the angular ball
bearing 43a is pressed against the proximal step portion 25b of the
rotary shaft 25, and the inner ring of the angular ball bearing 43b
is pressed against the inner ring of the angular ball bearing 43a
by a nut 49b screwed in the rotary shaft 25. Therefore, the rolling
elements of the angular ball bearings 43a, 43b are in contact with
the inner and outer rings without any space in either of the axial
direction or the radial direction.
[0024] Since the distal bearing portions 42 and the proximal
bearing portions 43 are each composed of two angular ball bearings
in the state of Duplex Back-to-back, the rotary shaft 25 does not
move in the axial direction and the radial direction with respect
to the shaft retainer 28. That is, the distal bearing portion 42
and the proximal bearing portion 43 are fixed in the axial
direction by means of nuts 49a, 49b and the step portions 25a,
25b.
[0025] These angular ball bearings 42a, 42b, 43a, 43b secure a
slight space between the outer circumferential surface of the
rotary shaft 25 and the inner circumferential surface of the
through hole 29 of the shaft retainer 28. The space forms a
lubricant oil recovery passage 48 (hereinafter, simply referred to
as an oil recovery passage 48). The oil recovery passage 48 causes
lubricant oil 62, which is a cooling medium, to be brought into
contact with the rotary shaft 25 and the shaft retainer 28, which
are objects to be cooled down. The oil recovery passage 48 is also
a passage that supplies lubricant oil 62 to the gear case 18.
[0026] On the other hand, a long conduit 44 extending along the
axis of the rotary shaft 25 is formed in the rotary shaft 25. The
long conduit 44 reaches the underside of the distal bearing portion
42 from the lower end of the rotary shaft 25. A short conduit 45
extending in the radial direction of the rotary shaft 25 is formed
in the rotary shaft 25 below the distal bearing portion 42. The
upper end of the long conduit 44 is located below the distal
bearing portion 42, and is connected to the short conduit 45. The
short conduit 45 is made open to the circumferential surface of the
rotary shaft 25 at a position below the distal bearing portion 42
so as to communicate with the oil recovery passage 48. The long
conduit 44 and the short conduit 45 compose an oil feed passage 46
that supplies lubricant oil 62 to the oil recovery passage 48. The
oil feed passage 46 and the oil recovery passage 48 compose an oil
circulation passage.
[0027] In the above, a description has been given of respective
elements such as the shaft retainer 28 at the male rotor 21, rotary
shaft 25, bearing portions 42, 43. Respective elements at the
female rotor 31 basically have the same configuration as those at
the male rotor 21. That is, as shown in FIG. 2, the rotary shaft 35
is inserted into the through hole 39 of the shaft retainer 38. The
shaft retainer 38 is provided with an upper large diameter hole 39a
and a lower large diameter hole 39b as in the shaft retainer 28. A
distal bearing portion 52 and a proximal bearing portion 53 are
disposed in the upper large diameter hole 39a and the lower large
diameter hole 39b, respectively. The bearing portions 52, 53 are
disposed between the rotary shaft 35 and the shaft retainer 38.
[0028] A distal bearing portion 52 is composed of two angular ball
bearings 52a, 52b in a state of Duplex Back-to-back as in the
distal bearing portion 42 of the male rotor 21, and is pushed down
by a nut 59a. Further, a sealing member 40 is disposed at a
position above the distal bearing portion 52. The proximal bearing
portion 53 is composed of two angular ball bearings 53a, 53b in a
state of Duplex Back-to-back as in the proximal bearing portion 43
of the male rotor 21, and is pushed upward by a nut 59b.
[0029] In addition, an oil feed passage 56 composed of a long
conduit 54 and a short conduit 55 is formed in the rotary shaft 35
of the female rotor 31. Further, a space that forms an oil recovery
passage 58 is formed between the rotary shaft 35 and the shaft
retainer 38. The axial diameters of the rotary shafts 25, 35 are
identical to each other, and the distal bearing portions 42, 52 and
the proximal bearing portions 43, 53 use angular ball bearings of
the same specification.
[0030] A detailed description will now be given of the male rotor
21. As shown in FIG. 4, the male rotor 21 has five teeth 24, and
these teeth 24 are disposed equidistant in the circumferential
direction of the male rotor 21. Also, the teeth 24 spirally extend
from the upper end of the male rotor 21 to the lower end thereof.
And, as shown in FIG. 2, the teeth 24 are formed so that the lead
angle decreases from the upper end toward the lower end.
[0031] On the other hand, tooth grooves 34 in the female rotor 31
are formed so as to correspond to the teeth 24 of the male rotor 21
as shown in FIG. 4, and the number of the tooth grooves 34 is six.
That is, since the number of the teeth 24 of the male rotor 21 is
fewer than the number of the tooth grooves 34 of the female rotor
31, the rotation speed of the male rotor 21 becomes faster than
that of the female rotor 31 when both rotors 21 and 31
synchronously rotate, and the rotation speed of the female rotor 31
becomes lower than that of the male rotor 21. Such screw-type
rotors 21 and 31 are called a gradual change type.
[0032] As shown in FIGS. 1 and 2, the rotary shaft 25 of the male
rotor 21 extends so as to pass through the lower housing member 13,
and the lower end of the rotary shaft 25 is positioned in the gear
case 18. The portion located in the gear case 18 of the rotary
shaft 25 is provided with a synchronous gear 47. On the other hand,
the rotary shaft 35 of the female rotor 31 extends so as to pass
through the lower housing member 13 as well, and the lower end of
the rotary shaft 35 is positioned in the gear case 18. The portion
located in the gear case 18 of the rotary shaft 35 is provided with
a synchronous gear 57. Both synchronous gears 47, 57 are meshed
with each other.
[0033] As shown in FIG. 1, the synchronous gear 47 at the male
rotor 21 is meshed with an intermediate gear 50 secured in the gear
case 18. The intermediate gear 50 is meshed with a drive gear 20
attached to the drive shaft 19 of the drive motor 17 in the gear
case 18. An oil storage chamber 61 that composes an oil reservoir
space is formed at the lower part of the gear case 18, and
lubricant oil 62 is stored in the oil storage chamber 61.
[0034] A cylindrical projection 63 is formed at the portion of the
bottom plate 18a of the gear case 18, which is opposite to the
lower end of the rotary shaft 25. As shown in FIG. 5, the
projection 63 defines a circular hole 63a having a bottom. A
trochoidal oil feed pump 70 operating as an oil feed portion is
disposed in the circular hole 63a. The oil feed pump 70 includes an
outer rotor 72 consisting of an inner-toothed gear and an inner
rotor 71 consisting of an outer-toothed gear. The inner rotor 71 is
disposed inside the outer rotor 72. The outer circumferential
surface of the outer rotor 72 is rotatably fitted to the inner
circumferential surface of the circular hole 63a. The lower end of
the rotary shaft 25 is fitted in and fixed in the through hole 71a
of the inner rotor 71.
[0035] The inner rotor 71 is eccentric with respect to the outer
rotor 72. When the inner rotor 71 rotates, the outer rotor 72 also
rotates therewith. An opening at the upper end of the cylindrical
projection 63 is blocked by an upper cover 73, and the upper cover
73 covers the inner rotor 71 and the outer rotor 72. In addition,
the oil feed pump 70 has an oil suction portion 75 and an oil
discharge portion 76. The oil suction portion 75 communicates with
the oil storage chamber 61. The oil discharge portion 76
communicates with the oil feed passage 46 of the rotary shaft 25
via a guide passage 77 formed on the bottom of the circular hole
63a.
[0036] As the rotary shaft 25 rotates, lubricant oil 62 stored in
the oil storage chamber 61 is drawn in the oil feed pump 70 through
the oil suction portion 75, in detail, drawn in a space between the
rotors 71 and 72. The lubricant oil is conveyed through the space
between the rotors 71 and 72 and reaches the oil discharge portion
76. The oil is then fed from the oil discharge portion 76 to the
oil feed passage 46 through the guide passage 77.
[0037] On the other hand, as shown in FIG. 2, a cylindrical
projection 64 is formed at the portion of the bottom plate portion
18a of the gear case 18, which is opposite to the lower end of the
rotary shaft 35. The projection 64 defines the circular hole 64a
having a bottom. A trochoidal oil feed pump 80 operating as an oil
feed device is disposed in the circular hole 64a. Although the
structure of the oil feed pump 80 is not illustrated in detail, the
structure is equivalent to the oil feed pump 70. That is, the oil
feed pump 80 includes an inner rotor 81 and an outer rotor 82. The
outer circumferential surface of the outer rotor 82 is rotatably
fitted to the inner circumferential surface of the circular hole
64a, and the inner rotor 81 is linked with the rotary shaft 35. The
inner rotor 81 and the outer rotor 82 are covered by an upper cover
83. Also, although not illustrated, the oil feed pump 80 has an oil
suction portion communicating with the oil storage chamber 61 and
an oil discharge portion communicating with the oil feed passage 56
through a guide passage 87. When the inner rotor 81 rotates
together with the rotary shaft 35, the outer rotor 82 rotates,
accordingly, and the lubricant oil 62 in the oil storage chamber 61
is fed to the oil feed passage 56 through the oil suction portion,
a space between both rotors 81 and 82, the oil discharge portion,
and the guide passage 87.
[0038] In addition, the vacuum pump 10 according to the present
embodiment has a configuration to cool the lubricant oil 62 stored
in the gear case 18. That is, a plurality of cooling water passages
88 through which cooling water operating as a cooling fluid passes
are formed in the bottom plate portion 18a of the gear case 18. The
cooling water passages 88 extend so as to pass through the bottom
plate 18a. Since cooling water is caused to pass through the
cooling water passage 88, the lubricant oil 62 stored in the gear
case 18 is then cooled. The cooling water passages 88 function as a
cooling portion to cool down the lubricant oil 62 by using the
cooling fluid.
[0039] As shown in FIG. 1, the upstream part of the cooling water
passage 88 is connected to an upstream pipe 89 provided with a
solenoid valve 91 as a flow rate changing portion, and the
downstream part of the cooling water passage 88 is connected to a
downstream pipe 90. The solenoid valve 91 is controlled so as to
open and close the upstream pipe 89 by a controller 92 operating as
a control portion. The controller 92 is connected to a temperature
sensor 93 that directly measures the temperature of the lubricant
oil 62 in the gear case 18. The temperature sensor 93 is disposed
in the gear case 18, that is, in the oil storage chamber 61. The
controller 92 controls the solenoid valve 91 based on detection
signals from the temperature sensor 93 so that the temperature of
the lubricant oil 62 in the gear case 18 is maintained to be
constant.
[0040] Next, a description is given of operations of the vacuum
pump 10 according to the embodiment. When the drive motor 17 is
rotated, rotation of the drive motor 17 is transmitted to the
synchronous gear 47 of the male rotor 21 via the drive gear 20 and
the intermediate gear 50. Thus, the synchronous gears 47, 57 rotate
in synchronization with each other, and the rotors 21, 31 rotate
along with the rotary shafts 25, 35. Since the rotors 21 and 31
rotate in a state where the teeth 24 of the male rotor 21 are
engaged with the tooth grooves 34 of the female rotor 31, a
compressive fluid is drawn in the operation chamber through the
suction port 15. The compressive fluid drawn in the operation
chamber is conveyed to the discharge port 16 while being compressed
by the rotors 21 and 31, and is discharged through the discharge
port 16. If the suction port 15 is connected to a closed space such
as a chamber or a vessel, the closed space can be made in a vacuum
state.
[0041] When the vacuum pump 10 is operating, the rotary shafts 25,
35 are caused to rotate at a high speed in directions opposed to
each other. Oil feed pumps 70, 80 secured at the end portion of the
rotary shaft 25, 35 draw in lubricant oil 62 stored in the oil
storage chamber 61 through respective oil suction portions and
discharge the same through the respective oil discharge portions.
Discharged lubricant oil 62 flows into the lower ends of the long
conduits 44, 54 of the rotary shafts 25, 35 through the guide
passages 77, 87 communicating with the respective oil discharge
portions, and reaches the underside of the distal bearing portions
42, 52, passing through the short conduits 45, 55.
[0042] When the lubricant oil 62 that has reached the underside of
the distal bearing portions 42, 52 passes through the oil recovery
passages 48, 58 and is oriented downward, it cools the rotary
shafts 25, 35 and the shaft retainers 28, 38. By the rotary shafts
25, 35 and the shaft retainers 28, 38 being cooled down, a
difference in the temperature between the rotary shafts 25, 35 and
the shaft retainers 28, 38 is suppressed. The lubricant oil 62 is
recovered in the oil storage chamber 61 in the gear case 18 after
having cooled the rotary shafts 25, 35 and the shaft retainers 28,
38. And, the lubricant oil 62 is conveyed from the oil storage
chamber 61 to the oil feed pump 70, 80 again, and the same action
as above is repeated. Further, the lubricant oil 62 lubricates the
synchronous gears 47, 57 via the synchronous gears 47, 57 on the
way of being recovered into the oil storage chamber 61.
[0043] Also, the lubricant oil 62 stored in the gear case 18 is
cooled by cooling water passing through the cooling water passage
88. That is, in the present embodiment, the lubricant oil 62 is
cooled by using cooling water so that the temperature of the
lubricant oil 62 supplied for cooling by actions of the oil feed
pumps 70, 80 is kept constant. In detail, the controller 92
monitors the temperature of the lubricant oil 62 by means of the
temperature sensor 93, and controls the solenoid valve 91 so that
the temperature of the lubricant oil 62 is maintained at a preset
cooling temperature. The controller 92 opens and closes the
solenoid valve 91 in accordance with the temperature of the
lubricant oil 62, which is detected by the temperature sensor 93,
and adjusts the flow of the cooling water in the cooling water
passage 88. That is, the controller 92 opens the solenoid valve 91
when the temperature of the lubricant oil 62 is likely to rise, and
prevents the temperature rise of the lubricant oil 62 in the gear
case 18 by causing cooling water to flow through the cooling water
passages 88. In addition, the controller 92 closes the solenoid
valve 91 when the temperature of the lubricant oil 62 is likely to
lower, and does not cool the lubricant oil 62 by cooling water by
not causing the cooling water to flow through the cooling water
passages 88. In this case, the temperature of the lubricant oil 62
stored in the oil storage chamber 61 is prevented from being
lowered than the preset cooling temperature.
[0044] By causing the lubricant oil 62, which is kept at a constant
temperature, to pass through the oil recovery passages 48, 58, a
difference in temperature between the rotary shafts 25, 35 and the
shaft retainers 28, 38 can be preferably suppressed, and thermal
expansion of the rotary shafts 25, 35 is prevented from occurring.
Therefore, it is possible to reliably prevent load generated by
thermal expansion of the rotary shafts 25, 35 from being applied to
the bearings 42a, 42b, 43a, 43b, 52a, 52b, 53a, and 53b in the
axial direction.
[0045] The vacuum pump 10 according to the present embodiment has
the following advantages.
[0046] (1) The controller 92 controls the solenoid valve 91 based
on a detection result of the temperature of lubricant oil 62 by the
temperature sensor 93. Therefore, the flow rate of cooling water is
adjusted so that the lubricant oil 62 stored in the oil storage
chamber 61 is kept at a constant temperature. By causing the
lubricant oil 62, the temperature of which is kept constant, to
pass through the oil recovery passages 48, 58, it is possible to
cool the rotary shafts 25, 35 and the shaft retainers 28, 38.
Consequently, it is possible to prevent a difference in temperature
from occurring between the rotary shaft 25 and the shaft retainer
28 and to prevent a difference in temperature from occurring
between the rotary shaft 35 and the shaft retainer 38.
[0047] (2) The angular ball bearings 42a, 42b, 43a, 43b, 52a, 52b,
53a, and 53b are fixed immovably in the axial direction with
respect to the rotary shafts 25, 35 and the shaft retainers 28, 38.
However, in the present embodiment, by preventing a difference in
temperature from occurring between the rotary shafts 25, 35 and the
shaft retainers 28, 38, thermal expansion that results in
displacement of the rotary shafts 25, 35 in the axial direction
with respect to the shaft retainers 28, 38 is prevented from
occurring. Accordingly, it becomes possible to reliably prevent
load from being applied to the bearings 42a, 42b, 43a, 43b, 52a,
52b, 53a, and 53b in the axial direction.
[0048] (3) Since load is prevented from being applied to the
respective bearings 42a, 42b, 43a, 43b, 52a, 52b, 53a, and 53b, the
reliability of the respective bearings is improved, and the power
consumption of the vacuum pump 10 is reduced.
[0049] (4) Since load is prevented from being applied to the
respective bearings 42a, 42b, 43a, 43b, 52a, 52b, 53a, and 53b, the
distance between the distal bearing portions 42, 52 and the
proximal bearing portions 43, 53 can be increased. That is, the
configuration adds the flexibility of the arrangement of the
bearing portions 43 and 53 with respect to the rotary shafts 25,
35.
[0050] (5) Since the bearings 42a, 42b, 43a, 43b, 52a, 52b, 53a,
and 53b are fixed at the rotary shafts 25, 35 and the shaft
retainers 28, 38, it is possible to prevent the rotary shafts 25,
35 from swaying in the horizontal and vertical directions. It is
thus possible to prevent vibrations and noise in the vacuum pump 10
regardless of the rotation speed of the rotary shafts 25, 35.
[0051] (6) Since lubricant oil 62 is supplied into the oil recovery
passages 48, 58 at the lower side of the distal bearing portions
42, 52, the lubricant oil 62 supplied to the oil recovery passages
48, 58 is hardly influenced by sliding heat of the distal bearing
portions 42, 52. It thus becomes easy to control the temperature of
the lubricant oil 62 in the oil recovery passages 48, 58.
[0052] (7) Since the lubricant oil 62 passes through the
synchronous gears 47, 57 on the way of being recovered into the oil
storage chamber 61, the synchronous gears 47, 57 can also be
lubricated.
[0053] The present invention is not to be limited to the foregoing
embodiment, but may be modified as follows within the scope of the
invention.
[0054] A gear pump may be adopted for the oil feed pumps 70, 80
instead of a trochoidal pump.
[0055] The lead angle of the teeth of the male rotor and the tooth
grooves of the female rotor may be fixed.
[0056] In the above-described embodiment, the respective bearing
portions are composed of two angular ball bearings in a state of
Duplex Back-to-back. However, these may be composed by a
combination thereof in a state of Duplex Face-to-face or by a
combination thereof in a state of Duplex Tandem. Further, the
respective bearing portions are not limited to angular ball
bearings, but may be composed of ordinal deep groove type roller
bearings. Still further, the number of the roller bearings is not
specifically limited, and the respective bearing portions may be
composed of three or more roller bearings. Also, in order to
prevent horizontal sway of the rotary shafts with respect to the
shaft retainers, it is preferable that angular ball bearings be
combined at the backs thereof.
[0057] A thermostat may be used instead of an open/close type
solenoid valve 91, or a flow rate control valve which is capable of
adjusting the opening degree based on proportional control may be
adopted.
[0058] The short conduits 45, 55 may be provided at the upper side
of the distal bearing portions 42, 52, and lubricant oil may be
supplied from the upper side of the distal bearing portions 42, 52.
In this case, the lubricant oil is influenced by the sliding heat
of the distal bearing portions 42, 52. Thus, if the lubricant oil
is cooled with such influence taken into consideration, the
advantages almost equivalent to those of the above-described
embodiment are obtained.
[0059] The shaft retainer 28 of the male rotor 21 and the shaft
retainer 38 of the female rotor 31 may be composed of completely
separate members. In this case, it becomes easy to manufacture the
shaft retainers 28, 38.
[0060] The screw-type fluid machine according to the present
invention is not limited to a screw-type vacuum pump, but may be
applicable to a screw-type compressor.
* * * * *