Information
-
Patent Grant
-
6554594
-
Patent Number
6,554,594
-
Date Filed
Friday, December 7, 200122 years ago
-
Date Issued
Tuesday, April 29, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Denion; Thomas
- Trieu; Theresa
Agents
-
CPC
-
US Classifications
Field of Search
US
- 418 2066
- 418 104
- 418 79
-
International Classifications
-
Abstract
A vacuum pump has a housing accommodating a rotary shaft and a gas transferring assembly driven by the rotary shaft. The housing has an exhaust passage for exhausting gas outside the housing. The gas transferring assembly creates a vacuum. A lip seal for shaft seal is disposed between a pump chamber communicating with the exhaust passage and a region in which oil exists so as to slide relative to a circumferential surface of the rotary shaft. The lip seal has a back pressure surface in a back pressure region facing the pump chamber and a pressure surface facing the region in which the oil exists. A communicating passage in the housing intercommunicates the back pressure region and the exhaust passage for applying at least substantially the pressure in the exhaust passage to the back pressure surface.
Description
BACKGROUND OF THE INVENTION
The present invention relates to shaft seal structure for a vacuum pump that drives a gas transferring assembly due to rotation of a rotary shaft, generates vacuum action by transferring gas due to motion of the gas transferring assembly.
Japanese Unexamined Patent Publication No. 6-101674 discloses a vacuum pump that drives a gas transferring assembly due to rotation of a rotary shaft, generates vacuum action by transferring gas due to motion of the gas transferring assembly. This kind of vacuum pump has a plurality of rotary shafts that support each rotor or gas transferring assembly, and the rotary shafts are synchronously driven through a gear mechanism. The gear mechanism is lubricated by lubricant prepared in an oil bath in a gear case. The lubricant is also used for lubricating bearings which rotatably support the rotary shafts.
To prevent the lubricant in the oil bath from leaking into a pump chamber which accommodates the rotors in a housing, lip seals are disposed at the surfaces of the rotary shafts between the bearings and the housing.
An unwanted effect of the lip seal is that the large pressure difference between the two surfaces of the lip seal causes the lubricant in the gear case to leak into the pump chamber, with a consequent of deterioration of the durability of the lip seal and shortened lifetime of the lip seal.
A screw type vacuum pump disclosed in Japanese Unexamined Patent Publication No. 6-81788 is provided with an annular recess formed on a bottom end surface of a screw rotor, and a discharge port of the vacuum pump opens so as to wrap over a part of the recess as seen in an axial direction of a rotary shaft. Pressure in the discharge port is applied to a back surface of a lip seal via the recess. Thereby, the pressure difference between the two surfaces of the lip seal can be reduced.
However, in a roots pump, cocoon-shaped rotors are engaged with each other so that forming annular recesses at the rotors so as to communicate with a discharge port is difficult since the location of the discharge port is restricted within a limited space.
SUMMARY OF THE INVENTION
The present invention addresses the above-mentioned problems traceable to a pressure difference applied to surfaces of a lip seal by reducing the pressure difference. Accordingly, it is an object of the present invention to improve sealing performance and lengthen the lifetime of the lip seal by reducing pressure difference between the two surfaces of the lip seal.
According to the present invention, a vacuum pump has a housing accommodating a rotary shaft and a gas transferring assembly driven by the rotary shaft. The housing has an exhaust passage for exhausting gas outside the housing. The gas transferring assembly creates a vacuum. A lip seal for shaft seal is disposed between a pump chamber communicating with the exhaust passage and a region in which oil exists so as to slide relative to a circumferential surface of the rotary shaft. The lip seal has a back pressure surface in a back pressure region facing the pump chamber and a pressure surface facing the region in which the oil exists. A communicating passage in the housing intercommunicates the back pressure region and the exhaust passage for applying at least substantially the pressure in the exhaust passage to the back pressure surface. Thereby, at least substantially the pressure in the exhaust passage is applied to the back pressure surface of the lip seal. Accordingly, the difference between the pressures applied to the pressure surface and the back pressure surface is reduced.
Either pressure in a highest pressure region in the pump chamber communicating with the exhaust passage or the pressure in the exhaust passage is applied to the back pressure surface of the lip seal via the communicating passage. This can reduce the difference between the pressures applied to the two surfaces of the lip seal, as compared with structure without the communicating passage.
The present invention has such a feature that a region to which substantially the same pressure as the exhaust passage is applied is the highest pressure region. The pressure in the highest pressure region is applied to the back pressure surface of the lip seal via the communicating passage.
The pressure in the highest pressure region is applied to the back pressure surface of the lip seal via the communicating passage. Such structure for applying the pressure in the highest pressure region to the back pressure surface via the communicating passage can reduce the pressure difference between the pressures applied to the two surfaces of the lip seal, as compared with structure without the communicating passage.
The present invention has the following feature that the housing forming the communicating passage includes a dividing wall. The dividing wall divides the region in which the oil exists and the pump chamber communicating with the exhaust passage. The rotary shaft extends through a bore in the dividing wall from the pump chamber into the region in which the oil exists.
The communicating passage is formed in the dividing wall. The pressure in the highest pressure region is applied to the back pressure surface of the lip seal via the communicating passage.
The present invention has such a feature that the dividing wall provides a wall surface defining the pump chamber. The communicating passage is a recessed channel in the wall surface. The channel extends to the dividing wall bore.
The pressure in the highest pressure region or the pressure in the exhaust passage is applied to the back pressure surface of the lip seal via the recess and a gap between the circumferential surface of the rotary shaft and the shaft hole.
The present invention further includes a first extending portion formed on the circumferential surface of the rotary shaft so as to reduce a gap between the circumferential surface of the rotary shaft and the shaft hole. The recess reaches the shaft hole so as to pass by a part of the extending portion.
The present invention further includes a second extending portion formed on the rear end surface of the rotor so as to reduce a gap between the rear end surface of the rotor and the dividing wall. The recess reaches the shaft hole so as to pass by a part of the second extending portion.
The first and second extending portions are efficient in applying the pressure in the highest pressure region or the pressure in the exhaust passage to the back pressure surface of the lip seal.
The present invention has the following feature that the region in which the oil exists is a region accommodating a bearing for rotatably supporting the rotary shaft.
The oil lubricating the bearing also lubricates the lip seal.
The present invention further includes a feature as follows. The vacuum pump is a roots pump. The gas transferring mechanism has a plurality of generally parallel rotary shafts. Each of the rotary shaft carries a rotor with adjacent rotors. The adjacent rotors are engaged with each other. A set of the engaged rotors is accommodated in either a plurality of the pump chambers or the single pump chamber.
Such vacuum pump as a roots pump is appropriate for applying the present invention.
The present invention has such a feature that a plurality of the rotary shafts is synchronously driven through a gear mechanism. The region in which the oil exists includes a region accommodating the gear mechanism.
The oil lubricating the gear mechanism also lubricates the lip seal.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
The invention together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
a
is a longitudinal cross-sectional view of a multi-stage roots pump according to a first embodiment of the present invention;
FIG. 1
b
is a cross-sectional view on the side of a lip seal
46
according to the first embodiment of the present invention;
FIG. 1
c
is a cross-sectional view on the side of a lip seal
45
according to the first embodiment of the present invention;
FIG. 2
a
is a cross-sectional end view, taken along the line I—I in
FIG. 1
;
FIG. 2
b
is a cross-sectional end view, taken along the line II—II in
FIG. 1
;
FIG. 3
a
is a cross-sectional end view, taken along the line III—III in
FIG. 1
;
FIG. 3
b
is a cross-sectional end view, taken along the line IV—IV in
FIG. 1
;
FIG. 4
a
is a cross-sectional view, taken along the line V—V in
FIG. 3
b;
FIG. 4
b
is a cross-sectional view, taken along the line VI—VI in
FIG. 3
b;
FIG. 5
a
is a longitudinal sectional view illustrating a rotary shaft
19
side according to a second embodiment of the present invention;
FIG. 5
b
is a longitudinal sectional view illustrating a rotary shaft
20
side according to the second embodiment of the present invention;
FIG. 6
a
is a cross-sectional end view according to a third embodiment of the present invention;
FIG. 6
b
is an enlarged partial cross-sectional view, taken along the line VII—VII in
FIG. 6
a;
FIG. 7
a
is a cross-sectional end view according to a fourth embodiment of the present invention;
FIG. 7
b
is an enlarged partial cross-sectional view, taken along the line VIII—VIII in
FIG. 7
a;
FIG. 8
a
is a longitudinal sectional view illustrating a rotary shaft
19
side according to an alternative embodiment of the present invention; and
FIG. 8
b
is a longitudinal sectional view illustrating a rotary shaft
20
side according to the alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will now be described with reference to
FIGS. 1 through 4
.
As shown in
FIG. 1
a
, a multi-stage roots pump
11
has a rotor housing
12
, a front housing
13
and a rear housing
14
. The front housing
13
is coupled to the rotor housing
12
on its front end. The end plate
36
is coupled to the front housing
13
. The rear housing
14
is coupled to the rotor housing
12
on its rear end. The rotor housing
12
, the front housing
13
and the rear housing
14
constitute a housing of the roots pump. The rotor housing
12
is constituted of a cylinder block
15
and a plurality of partition walls
16
. As shown in
FIG. 2
b
, the cylinder block
15
is constituted of a pair of block pieces
17
,
18
and each of the partition walls
16
is constituted of a pair of wall pieces
161
,
162
. As shown in
FIG. 1
a
, a space between the front housing
13
and a frontmost partition wall
16
, spaces between the partition walls
16
, and a space between the rear housing
14
and a rearmost partition wall
16
are defined as pump chambers
39
,
40
,
41
,
42
,
43
, respectively.
A pair of rotary shafts
19
,
20
are rotatably supported by the front housing
13
and the rear housing
14
via radial bearings
21
,
37
,
22
,
38
, respectively. Both the rotary shafts
19
,
20
are disposed in parallel with each other. The rotary shafts
19
,
20
extend through the partition walls
16
.
A plurality of rotors
23
,
24
,
25
,
26
,
27
is integrally formed with the rotary shaft
19
. Also, the same number of rotors
28
,
29
,
30
,
31
,
32
is integrally formed with the rotary shaft
20
. The rotors
23
through
32
are congruously formed as seen in a direction of axes
191
,
201
of the rotary shafts
19
,
20
. Thickness of the rotors
23
,
24
,
25
,
26
,
27
become thinner in this order. Also, thickness of the rotors
28
,
29
,
30
,
31
,
32
become thinner in this order. A pair of the rotors
23
,
28
is accommodated in the pump chamber
39
so as to engage with each other. A pair of the rotors
24
,
29
is accommodated in the pump chamber
40
so as to engage with each other. A pair of the rotors
25
,
30
is accommodated in the pump chamber
41
so as to engage with each other. A pair of the rotors
26
,
31
is accommodated in the pump chamber
42
so as to engage with each other. A pair of the rotors
27
,
32
is accommodated in the pump chamber
43
so as to engage with each other. The inside of the pump chambers
39
through
43
are not lubricated. Therefore, each of the rotors
23
through
32
is not kept in slide contact with the cylinder block
15
, the partition walls
16
, the front housing
13
and the rear housing
14
. Also, a pair of the rotors engaging with each other does not keep in slide contact with each other.
As shown in
FIG. 2
a
, the rotors
23
,
28
define a suction region
391
and a high pressure region
392
in the pump chamber
39
. Pressure in the high pressure region
392
is higher than pressure in the suction region
391
. Likewise, the rotors
24
,
29
, the rotors
25
,
30
and the rotors
26
,
31
define a suction region like as the suction region
391
and a high pressure region like as the high pressure region
392
in the pump chambers
40
,
41
,
42
, respectively. As shown in
FIG. 3
a
, the rotors
27
,
32
define a suction region
431
like as the suction region
391
, and a high pressure region
432
like as the high pressure region
392
in the pump chamber
43
.
As shown in
FIG. 1
a
, a gear case
33
is coupled to the rear housing
14
. The rotary shafts
19
,
20
extend through the gear case
33
and protrude their rear ends into the gear case
33
. A pair of gears
34
,
35
secured to the respective rear ends of the rotary shafts
19
,
20
is engaged with each other. An electric motor M is installed to the gear case
33
. Driving force of the electric motor M is transmitted to the rotary shaft
19
through a coupling
44
, and the rotary shaft
19
is rotated by the electric motor M in a direction of an arrow R
1
in
FIGS. 2
a
,
2
b
and
3
a
. Rotation of the rotary shaft
19
is transmitted to the rotary shaft
20
through a pair of the gears
34
,
35
, and the rotary shaft
20
is rotated in a direction of an arrow R
2
(a counter direction relative to the direction in which the rotary shaft
19
rotates) as shown in
FIGS. 2
a
,
2
b
and
3
a
. Namely, the rotary shafts
19
,
20
are synchronously rotated through the gears
34
,
35
.
As shown in
FIG. 2
b
, passages
163
are formed within the partition walls
16
, and inlets
164
and outlets
165
of the passage
163
are formed in the partition walls
16
, respectively. The coadjacent pump chambers
39
,
40
,
41
,
42
,
43
are intercommunicated via the passages
163
.
As shown in
FIG. 2
a
, an intake port
181
is formed in the block piece
18
so as to communicate with the suction region
391
in the pump chamber
39
. As shown in
FIG. 3
a
, an exhaust port
171
is formed in the block piece
17
so as to communicate with the high pressure region
432
in the pump chamber
43
. Gas introduced from the intake port
181
into the suction region
391
in the pump chamber
39
is transferred to the high pressure region
392
due to rotation of the rotors
23
,
28
. The gas transferred to the high pressure region
392
is compressed, so that pressure in the high pressure region
392
is higher than pressure in the suction region
391
. The gas in the high pressure region
392
is transferred to the suction region in the coadjacent pump chamber
40
via the frontmost inlet
164
of the frontmost partition wall
16
, the frontmost passage
163
and the frontmost outlet
165
. Likewise, the gas is transferred in order of reducing volume, that is, in order of the pump chambers
40
,
41
,
42
,
43
. The gas transferred into the suction region
431
in the pump chamber
43
is transferred into the high pressure region
432
due to rotation of the rotors
27
,
32
, and is exhausted outside via the exhaust port
171
. The rotors
23
through
32
are gas transferring assemblies.
The exhaust port
171
is an exhaust passage exhausting the gas outside the housing. The pump chamber
43
is a rearmost pump chamber communicating with the exhaust port
171
, or the exhaust passage. Pressure in the high pressure region
432
in the rearmost pump chamber
43
is the highest among the pump chambers
39
through
43
. The exhaust port
171
communicates with the highest high pressure region
432
defined by the rotors
27
,
32
in the pump chamber
43
.
As shown in
FIG. 4
a
, a seal chamber
47
is defined around the rotary shaft
19
between the radial bearing
37
and the rotor
27
. The lip seal
45
is accommodated in the seal chamber
47
. As shown in
FIG. 4
b
, a seal chamber
48
is defined around the rotary shaft
20
between the radial bearing
38
and the rotor
32
. The lip seal
46
is accommodated in the seal chamber
48
.
As shown in
FIG. 1
c
, the lip seal
45
is constituted of a ring-shaped metal retainer
49
and a lip seal ring
51
, which is made of elastic resin such as rubber, supported by the metal retainer
49
so as to cover a part of the metal retainer
49
with the lip seal ring
51
. As shown in
FIG. 1
b
, the lip seal
46
is constituted of a ring-shaped metal retainer
50
and a lip seal ring
52
, which is made of elastic resin such as rubber, supported by the metal retainer
50
so as to cover a part of the metal retainer
50
with the lip seal ring
52
. An inner circumferential surface of the lip seal ring
51
of the lip seal
45
accommodated in the seal chamber
47
contacts with an outer circumferential surface
192
of the rotary shaft
19
. An inner circumferential surface of the lip seal ring
52
of the lip seal
46
accommodated in the seal chamber
48
contacts with an outer circumferential surface
202
of the rotary shaft
20
.
The lip seal
45
divides the seal chamber
47
into a back pressure chamber
53
facing to the pump chamber
43
and an oil chamber
471
facing to the radial bearing
37
. The lip seal
46
divides the seal chamber
48
into a back pressure chamber
54
facing to the pump chamber
43
and an oil chamber
481
facing to the radial bearing
38
. The back pressure chambers
53
,
54
are back pressure regions in the present embodiment. The back pressure chamber
53
is defined between the lip seal ring
51
and the pump chamber
43
. The back pressure chamber
54
is defined between the lip seal ring
52
and the pump chamber
43
. The oil chambers
471
,
481
communicates with a gear chamber
331
via gaps
371
,
381
between rings within the radial bearings
37
,
38
and chambers
144
,
145
of the radial bearings
37
,
38
, respectively (shown in
FIG. 1
a
).
As shown in
FIGS. 4
a
,
4
b
, lubricant Y is prepared in the gear chamber
331
in the gear case
33
. The lubricant Y lubricates the gears
34
,
35
. The gears
34
,
35
constituting the gear mechanism are accommodated in the gear chamber
331
in the gear case
33
. The gear chamber
331
is a region in which oil exists, and the region is sealed so as not to communicate with the outside of the housing of the multi-stage roots pump
11
. The chambers
144
,
145
of the radial bearings
37
,
38
communicating with the gear chamber
331
are also the region in which the oil exists. The lubricant Y prepared in the gear chamber
331
is swashed due to rotation of the gears
34
,
35
, and lubricates the radial bearings
37
,
38
. The lubricant Y also passes through the gaps
371
,
381
between the rings within the radial bearings
37
,
38
, and flows into the oil chambers
471
,
481
. The lubricant Y lubricates the lip seal rings
51
,
52
of the lip seals
45
,
46
. The lip seal rings
51
,
52
of the lip seals
45
,
46
prevent the lubricant Y from leaking from the oil chambers
471
,
481
along the outer circumferential surfaces
192
,
202
of the rotary shafts
19
,
20
into the back pressure chambers
53
,
54
.
As shown in
FIG. 3
b
, a wall surface
141
of the rear housing
14
defines the pump chamber
43
, and recesses
55
,
56
for applying pressure in an exhaust passage are formed on the wall surface
141
. The recess
55
communicates with the highest compression chamber
432
which varies its volume in accordance with the rotation of the rotors
27
,
32
. The recess
55
also communicates with a shaft hole
142
for extending the rotary shaft
19
through the rear housing
14
(shown in
FIG. 4
a
). The recess
56
communicates with the highest compression chamber
432
, and communicates with a shaft hole
143
for extending the rotary shaft
20
through the rear housing
14
(shown in
FIG. 4
b
). The gear chamber
331
, or the region in which the oil exists, and the rearmost pump chamber
43
communicating with the exhaust port
171
are divided by the rear housing
14
as a dividing wall, and the rotary shafts
19
,
20
extend through the rear housing
14
so as to protrude their rear ends into the gear chamber
331
.
The following advantageous effect can be obtained in the first embodiment.
(1-1) A small gap is provided between the outer circumferential surface
192
of the rotary shaft
19
and the shaft hole
142
, and another small gap is provided between the rotors
27
,
32
and the wall as surface
141
of the rear housing
14
. Therefore, pressure in the rearmost pump chamber
43
is applied to the back pressure chamber
53
via the small gaps. Likewise, a small gap is also provided between the outer circumferential surface
202
of the rotary shaft
20
and the shaft hole
143
. Therefore, pressure in the rearmost pump chamber
43
is also applied to the back pressure chamber
54
.
When the recesses
55
,
56
are not provided for the rear housing
14
, pressure in the suction region
431
applied to the back pressure chamber
53
,
54
is substantially the same as the pressure in the highest high pressure region
432
applied to the back pressure region
53
,
54
. The pressure applied to the back pressure surfaces
53
,
54
of the lip seal rings
51
,
52
is intermediate pressure relative to the pressure in the suction region
431
and the pressure in the highest high pressure region
432
, and is expressed as follows.
P
b
=(
P
2
+
P
1
)/2
P
b
denotes the pressure applied to the back pressure surfaces
512
,
522
of the lip seal rings
51
,
52
. P
1
denotes the pressure in the suction region
431
in the rearmost pump chamber
43
. P
2
(>P
1
) denotes the pressure in the highest high pressure region
432
. On the other hand, pressures in the oil chambers
471
, is
481
communicating with the gear chamber
331
do not up vary because motion of the rotors
23
through
32
does not act in the oil chambers
471
,
481
. Therefore, in those are substantially the same as atmospheric pressure (about 1000 Torr). Substantially the same as atmospheric pressure is applied to pressure surfaces
511
,
521
of the lip seal rings
51
,
52
. Accordingly, pressure differences between the two surfaces of the lip seal rings
51
,
52
are P
diff.
(Torr) expressed as follows.
P
diff.
=1000−(
P
2
+
P
1
)/2
P
diff.
denotes the pressure difference.
The recesses
55
,
56
in the present embodiment help the pressure in the highest high pressure region
432
to be applied to the back pressure chamber
53
,
54
. That is, the pressure in the highest pressure region
432
applied to the back pressure chambers
53
,
54
via the recesses
55
,
56
is much higher than the pressure in the suction region
431
applied to the back pressure chambers
53
,
54
. Accordingly, the pressures in the back pressure chambers
53
,
54
are much higher than the above-mentioned P
b
(Torr), and the pressure difference between the two surfaces of the lip seal rings
51
,
52
is much lower than the above-mentioned P
diff.
. Consequently, such structure having the recesses
55
,
56
further prevents the lubricant Y from leaking from the oil chambers
471
,
481
into the back pressure chambers
53
,
54
, and sealing performance of the lip seal rings
51
,
52
improves. Besides, durability of the lip seal rings
51
,
52
also improves, and lifetime of the lip seal rings
51
,
52
may be lengthened.
(1-2) As the cross sections of the recesses
55
,
56
expand, the pressure in the highest high pressure region
432
applied to the back pressure chambers
53
,
54
via the recesses
55
,
56
also increases. The recesses
55
,
56
having desired cross sections can easily be formed, and are appropriate for applying the pressure in the highest high pressure region
432
to the back pressure chambers
53
,
54
.
(1-3) The recesses
55
,
56
are formed on the wall surface
141
of the rear housing
14
constituting a part of a circumferential wall defining the pump chamber
43
. The shaft holes
142
,
143
for extending the rotary shafts
19
,
20
through the rear housing
14
are bored through the wall surface
141
, and the highest high pressure region
432
constituting a part of the pump chamber
43
is in the vicinity of the wall surface
141
. Accordingly, forming passages on the wall surface
141
for applying the pressure in the exhaust passage so as to intercommunicate the shaft holes
142
,
143
and the highest high pressure region
432
is easy. Namely, the wall surface
141
is appropriate for forming the passages for applying the pressure in the exhaust passage so as to intercommunicate the shaft holes
142
,
143
and the highest high pressure region
432
.
(1-4) The lubricant Y is not used in the pump chambers
39
through
43
in the dry pump such as the roots pump
11
. The roots pump
11
that may not use the lubricant Y in the pump chambers
39
through
43
is appropriate for applying the present invention.
A second embodiment of the present invention will now be described with reference to
FIGS. 5
a
,
5
b
. The same reference numerals denote the same components in the first embodiment.
Passages
57
,
58
for applying the pressure in the exhaust passage communicating with the highest high pressure region
432
are directly connected with the back pressure chambers
53
,
54
bored through the rear housing
14
. The same advantageous effects as the paragraphs (1-1) and (1-4) in the first embodiment can be obtained in the second embodiment.
A third embodiment of the present invention will now be described with reference to
FIGS. 6
a
,
6
b
. The same reference numerals denote the same components in the first embodiment.
Gaps G
1
are provided between the outer circumferential surfaces
192
,
202
of the rotary shafts
19
,
20
and the shaft holes
142
,
143
, respectively. Annular extending portions
193
,
203
as first extending portions in the present invention are formed on the circumferential surfaces
192
,
202
of the rotary shafts
19
,
20
in the vicinity of the rotors
27
,
32
, respectively. Ends
551
,
561
of the recesses
55
,
56
for applying the pressure in the exhaust passage are hooked or crank-shaped so as to connect with the gaps G
1
. In other words, the recesses
55
,
56
pass by a part of the extending portions
193
,
203
, and reach the shaft holes
142
,
143
. The cross sections of the recesses
55
,
56
connecting with the gaps G
1
are same as the cross sections of the recesses
55
,
56
in the first embodiment.
The drive shafts
19
,
20
are provided with the extending portions
193
,
203
, so that the gaps to between the outer circumferential surfaces
192
,
202
of the rotary shafts
19
,
20
and the shaft holes
142
,
143
become narrow. Thereby, the cross sections of passages between the suction region
431
and the gaps G
1
become much smaller than those between the highest high pressure region
432
and the gaps G
1
. Therefore, the pressure in the suction region
431
applied to the back pressure chambers
53
,
54
is smaller than that of the first embodiment, and the pressure in the highest compression chamber
432
applied to the back pressure chambers
53
,
54
is relatively larger. Consequently, such structure having the extending portions
193
,
203
further prevents the lubricant Y from leaking from the oil chambers
471
,
481
into the back pressure chambers
53
,
54
, and the sealing performance of the lip seal rings
51
,
52
further improves, as compared with that of the first embodiment. Besides, the durability of the lip seal rings
51
,
52
further improves, and the lifetime of the lip seal rings
51
,
52
may be lengthened.
A fourth embodiment of the present invention will now be described with reference to
FIGS. 7
a
,
7
b
. The same reference numerals denote the same components in the third embodiment.
Gaps G
2
are provided between rear ends
271
,
321
of the rotors
27
,
32
and the wall surface
141
of the rear housing
14
. Annular extending portions
272
,
322
as second extending portions are formed on the rear end surfaces
271
,
321
of the rotors
27
,
32
. The extending portions
272
,
322
function as well as the extending portions
193
,
203
in the third embodiment.
The present invention is not limited to the embodiments described above, but may be modified into examples as follows.
(1) The exhaust port
171
and the back pressure chambers
53
,
54
are directly intercommunicated via passages for applying the pressure in the exhaust passage.
(2) As shown in
FIGS. 8
a
,
8
b
, a pair of lip seal rings
51
,
61
is disposed in series between the rearmost pump chamber
43
and the gear chamber
331
. Likewise, a pair of lip seal rings
52
,
62
is disposed in series between the rearmost pump chamber
43
and the gear chamber
331
. A back pressure chamber
53
is defined between the lip seal rings
51
,
61
. Another back pressure chamber
54
is defined between the lip seal rings
52
,
62
. The highest pressure region
432
in the rearmost pump chamber
43
and the back pressure chambers
53
,
54
are intercommunicated via the passages for applying the pressure in the exhaust passage same as those of the second embodiment.
(3) The present invention may be applied to a roots pump that is provided with a single pump chamber.
(4) The present invention may be applied to a is vacuum pump other than a roots pump.
According to the present invention described above, the housing of the vacuum pump is provided with the passage communicating with the exhaust passage. The pressure in the exhaust passage or substantially the same pressure as the pressure in the exhaust passage is applied to the back pressure surface of the lip seal ring via the passage. Therefore, the vacuum pump ensures the sealing performance, and the lifetime of the lip seal may be lengthened.
Therefore the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein but may be modified within the scope of the appended claims.
Claims
- 1. A shaft seal structure for a vacuum pump, comprising:a housing accommodating a rotary shaft and a gas transferring assembly driven by the rotary shaft, the housing having an exhaust passage for exhausting gas outside the housing, the gas transferring assembly creating a vacuum; a lip seal for shaft seal disposed between a pump, chamber communicating with said exhaust passage and a region in which oil exists so as to slide relative to a circumferential surface of the rotary shaft, and having a back pressure surface in a back pressure region facing the pump chamber, and a pressure surface facing the region in which the oil exists; and a communicating passage in the housing intercommunicating the back pressure region and said exhaust passage for applying at least substantially the pressure in said exhaust passage to the back pressure surface.
- 2. A shaft seal structure for a vacuum pump according to claim 1, wherein:at least substantially the pressure in said exhaust passage is pressure in a highest pressure region in the pump chamber communicating with said exhaust passage; and said communicating passage applies the pressure in the highest pressure region to the back pressure surface of said lip seal.
- 3. A shaft seal structure for a vacuum pump according to claim 1, wherein:the housing forming said communicating passage includes a dividing wall; said region in which the oil exists and the pump chamber communicating with said exhaust passage are divided by the dividing wall; and the rotary shaft extends through a bore in the dividing wall from the pump chamber communicating with said exhaust passage to said region in which the oil exists.
- 4. A shaft seal structure for a vacuum pump according to claim 3, wherein:the dividing wall provides a wall surface defining said pump chamber; said communicating passage is a recessed channel in the wall surface; and said channel extends to the dividing wall bore.
- 5. A shaft seal structure for a vacuum pump according to claim 4 further comprising:a first extending portion formed on the circumferential surface of the rotary shaft so as to reduce a gap between the circumferential surface of the rotary shaft and the shaft hole; and wherein said recess reaches the shaft hole so as to pass by a part of said first extending portion.
- 6. A shaft seal structure for a vacuum pump according to claim 4 further comprising:a second extending portion formed on the rear end surface of the rotor so as to reduce a gap between the rear end surface of the rotor and the dividing wall; and wherein said recess reaches the shaft hole so as to pass by a part of said second extending portion.
- 7. A shaft seal structure for a vacuum pump according to claim 1, wherein said region in which the oil exists is a region accommodating a bearing for rotatably supporting the rotary shaft.
- 8. A shaft seal structure for a vacuum pump according to claim 1, wherein the vacuum pump is a roots pump, wherein the gas transferring mechanism comprises:a plurality of generally parallel rotary shafts, each carrying a rotor, with adjacent rotors being engaged with each other; and a set of the engaged rotors is accommodated in either a plurality of pump chambers or a single pump chamber.
- 9. A shaft seal structure for a vacuum pump according to claim 8, wherein:a plurality of the rotary shafts is synchronously driven through a gear mechanism; and said region in which the oil exists includes a region accommodating the gear mechanism.
- 10. A shaft seal structure for a vacuum pump according to claim 1, wherein:a pair of said lip seals disposed between the pump chamber and the region in which the oil exists so as to slide relative to the circumferential surface of the rotary shaft; and said communicating passage for applying at least substantially the pressure in said exhaust passage to the back pressure surface opposed to the pressure surface of said lip seal disposed in the vicinity of the region in which the oil exists.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2001-015350 |
Jan 2001 |
JP |
|
US Referenced Citations (4)
Foreign Referenced Citations (6)
Number |
Date |
Country |
427973 |
May 1991 |
EP |
2175956 |
Dec 1986 |
GB |
63277877 |
Nov 1988 |
JP |
04314992 |
Nov 1992 |
JP |
6-081788 |
Mar 1994 |
JP |
6-101674 |
Apr 1994 |
JP |