U.S. patent number 3,859,815 [Application Number 05/448,874] was granted by the patent office on 1975-01-14 for two-stage compression apparatus.
This patent grant is currently assigned to Kabushiki Kaisha Maekawa Seisakusho. Invention is credited to Keisuke Kasahara.
United States Patent |
3,859,815 |
Kasahara |
January 14, 1975 |
TWO-STAGE COMPRESSION APPARATUS
Abstract
Two-stage compression apparatus comprises a first compressor for
low compression stage and a second compressor for high compression
stage. Each of the compressors is composed of a screw compressor of
an oil injection type. A single electric motor is provided for
driving both compressors. The motor is enclosed within a confined
atmosphere which is on the one hand communicated with the exhaust
side of the first compressor and on the other hand communicated
with the suction side of the second compressor.
Inventors: |
Kasahara; Keisuke (Tokyo,
JA) |
Assignee: |
Kabushiki Kaisha Maekawa
Seisakusho (Tokyo, JA)
|
Family
ID: |
14650769 |
Appl.
No.: |
05/448,874 |
Filed: |
March 7, 1974 |
Foreign Application Priority Data
|
|
|
|
|
Oct 12, 1973 [JA] |
|
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48-114955 |
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Current U.S.
Class: |
62/197; 417/371;
62/469; 62/505; 418/97 |
Current CPC
Class: |
F25B
1/10 (20130101); F25B 31/006 (20130101); F25B
2400/13 (20130101); F25B 2600/2509 (20130101) |
Current International
Class: |
F25B
31/00 (20060101); F25B 1/10 (20060101); F25b
031/00 () |
Field of
Search: |
;62/192,193,468,469,505,196,197 ;310/53,52,54 ;417/371,423
;418/97,98,99 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Perlin; Meyer
Attorney, Agent or Firm: Stevens, Davis, Miller &
Mosher
Claims
What is claimed is:
1. Two-stage compression apparatus comprising an oil injection type
of a screw compressor for low compression stage, an oil injection
type of a screw compressor for high compression stage, an electric
motor for driving both of said compressors, and means for defining
a sealed atmosphere around said electric motor, said atmosphere
being communicated with a gas exhaust outlet of said compressor for
low compression stage and a gas suction inlet of said compressor
for high compression stage.
2. Two-stage compression apparatus as set forth in claim 1, wherein
said atmosphere is communicated with a portion of a liquid gas
conduit through a temperature responsive expansion valve which is
operated in dependence upon variations in temperature of exhaust
gas from said compressor for high compression stage.
3. Two-stage compression apparatus as set forth in claim 2, further
comprising a supercooler disposed between said sealed atmosphere
and said expansion valve.
4. Two-stage compression apparatus as set forth in claim 1, wherein
said means for defining a sealed atmosphere is formed by a
fluid-tightly closed enclosure.
5. Two-stage compression apparatus as set forth in claim 1, wherein
said means for defining a sealed atmosphere is formed by a jacket
provided around the periphery of the housing of said motor.
6. Two-stage compression apparatus as set forth in claim 1, wherein
said compressors for low and high compression stages are coaxially
arranged with interposition of said motor.
7. Two-stage compression apparatus as set forth in claim 1, wherein
said motor has a single output shaft.
Description
BACKGROUND OF INVENTION
The present invention relates to a two-stage compression apparatus
wherein the necessity of using an intermediate cooler is
evaded.
In hitherto known two-stage compression apparatus, an intermediate
cooler is provided between a compressor for high compression stage
and the other compressor for low compression stage. These
compressors are driven by respective electric motors which are
adapted to be cooled by suction gas of the associated compressors.
Thus, the conventional two-stage compression apparatus are complex,
very volumious and expensive.
Accordingly, an object of the present invention is to eliminate the
drawbacks of the conventional compression apparatus as above
mentioned.
Another object of this invention is to provide an improved
two-stage compression apparatus in which a single motor is used for
driving both compressors for the high and low compression
stages.
To this end, according to the present invention, screw compressors
of oil injection type are employed to cool the primary compressed
gas by a large quantity of oil injected into the compressor so as
to make the use of the conventionally employed intermediate cooler
unnecessary. The electric motor for driving both compressors is
enclosed within a confined atmosphere into which the primary
compressed gas is supplied from the low stage compressor to effect
the cooling of the electric motor. In the apparatus according to
the invention, undesirable effect such as lowering of the
compression efficiency due to the re-expansion of the suction gas
as seen in the conventional apparatus can be substantially
suppressed.
The above and other objects as well as novel features and
advantages of the present invention will become more apparent from
the following description on preferred embodiments. The description
makes reference to drawings.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a flow-diagram showing schematically an embodiment of a
two-stage compression apparatus according to the invention; and
FIGS. 2 to 4 show various modifications of the apparatus of FIG. 1
in similar views.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Now referring to FIG. 1 which shows an embodiment of a two-stage
compression refrigerator according to the invention, reference
numeral 1 generally indicates an oil injection type of screw
compressor for the low compression stage, to which an oil injection
type screw compressor 2 for the high compression stage is coaxially
arranged with interposition of a sealed type electric motor 3. It
will be noted that the compressors 1 and 2 are connected to the
shaft of the motor 3 at both ends thereof. The motor 3 has a
fluid-tightly closed housing or enclosure 4 defining therein a
hollow chamber with which an exhaust outlet 5 of the low stage
compressor 1 and a suction inlet 6 of the high stage compressor 2
are communicated. The high stage compressor 2 has an exhaust outlet
17 from which an exhaust conduit 9 extends to a condenser 11 by way
of an oil separator 10. A liquid conduit 8 from the condenser 11 is
connected to an evaporator 14 through a liquid receptacle or
collector 12 and an expansion valve 13. Further, a gas suction
conduit 15 is led from the evaporator 14 and communicated with the
suction inlet 16 of the low stage compressor 1. Additionally, an
oil conduit 18 led from the coil separator 10 is communicated with
an oil cooler 20 by way of an oil pump 19. The oil cooler 20 has a
cooled oil conduit 21 which is connected to an oil injection
opening 22 formed in the low stage compressor 1 at the position
where gas compression has begun and to a lubricating orifice 23 for
bearing portions on the one hand and connected on the other hand to
a lubricating orifice 24 for bearing portions of the high stage
compressor 2. A liquid conduit 25 is branched from the liquid
conduit 8 and communicated with the interior of the sealed housing
4 through a temperature responsive expansion valve 7, which is
adapted to be controlled by a temperature sensing member 26
disposed in contact with the gas exhaust conduit 9 or the sealed
housing 4 of the motor 3.
Next, the operation of the above described apparatus will be
explained.
Gas sucked into the low stage compressor 1 through the suction
opening 16 is subjected to compression under cooling by a large
quantity of cooling oil injected from the injecting orifice 22. The
gas-oil mixture is then discharged into the hollow interior of the
fluid-tightly sealed housing 4 of the motor at a temperature in the
range from about 40.degree. to about 50.degree.C and at a pressure
ranging from about 1 Kg/cm.sup.2 to about 5 Kg/cm.sup.2 to thereby
cool the electric motor 3, and then fed to the suction opening 6 of
the high stage compressor 2. From the gas-oil mixture derived from
the high stage compressor of a pressure of about 6 to 1.5
Kg/cm.sup.2 and temperature of about 50.degree. to 70.degree.C, oil
is separated by the oil separator 10. The oil thus obtained is,
after having been cooled by the oil cooler 20, supplied to both the
low and high stage compressors 1 and 2 at about 30.degree.C and
used again for the cooling, sealing and lubrication. The gas got
free from oil in turn is condensed by the condenser 11, collected
at the liquid collector 12 and, after having been subjected to
adiabatic expansion at the expansion valve 13, used for cooling the
heat load 14. Subsequently, the gas is sucked into the suction
inlet 16 of the low stage compressor 1 through the gas suction
conduit 15. When the temperature within the hollow interior of the
enclosure or sealed housing 4 of the motor 3 is increased as caused
by any possible variations in operating conditions of the oil
cooler 20, the temperature sensor 26 detects such increment in the
temperature and opens the temperature responsive expansion valve 7,
whereby coolant is subjected to the adiabatic expansion in the
housing 4 and used for cooling the exhaust gas from the low stage
compressor and hence the electric motor 3.
Referring to FIG. 2 which shows another embodiment of the
invention, a supercooler 31 is disposed in a liquid conduit 8 at
the upstream side of an expansion valve 13. The supercooler 31 has
a heat exchanger 32 which is communicated with the liquid conduit
8. A conduit 25 is branched from the liquid conduit 8 and
communicated with the super-cooler 31 by way of an automatic
expansion valve 7 of a temperature responsible type. The
supercooler 31 has additionally a gas conduit 33 which opens into
the hollow interior of the motor housing 4. The remaining
arrangement as well as the operation of the apparatus shown in FIG.
2 are same as those of the hereinbefore described apparatus shown
in FIG. 1.
Referring to FIG. 3 which shows still another embodiment of the
invention wherein a radial type of electric motor 3 having a
coolant jacket is employed, the housing 4 of electric motor 3 is
provided with a jacket 28 around the periphery thereof so as to
form a tightly closed hollow chamber 27, the interior of which is
communicated with an exhaust or discharging conduit 29 extending
from the outlet 5 of the low stage compressor 1. Besides, a suction
conduit 30 led from the hollow chamber 27 is connected to the
suction inlet 6 of the high stage compressor 2. A branch conduit 25
branched from the liquid conduit 8 is additionally communicated
with the hollow chamber 27 of the jacket 28 by way of a temperature
responsive expansion valve 7 which in turn has a temperature
sensing member 26 for detecting the temperature of exhaust gas from
the high stage compressor 2. The remaining arrangement of the
apparatus is same as that of the embodiment shown in FIG. 1. In
operation, the cooled exhaust gas from the compressor 1 is supplied
to the hollow chamber 27 formed by the jacket 28 to thereby cool
the electric motor 3.
The embodiment shown in FIG. 4 is different from the one shown in
FIG. 3 only in the respect that the electric motor of a cooling
jacket type has a single output shaft.
As is apparent from the foregoing description, according to the
present invention, the electric motor 3 for driving the compressors
is cooled by the exhaust gas discharged from the low stage
compressor and introduced into the sealed atmosphere enclosing the
motor 3. Thus, it is possible to use a single electric motor for
driving both compressors of the high and low stages in contrast to
the hitherto known apparatus wherein an electric driving motor is
required for each compressor and cooled by gas derived from the
suction side of the respective associated compressor. Further,
because the electric motor 3 is cooled by the discharged gas from
the low compression stage, there may arise no such undesirable
possibility that the efficiency of the compressor being lowered due
to re-expansion of the suction gas, which can not be evaded in the
conventional apparatus. Since the compressors for the low and high
compression stages are both composed of the screw compressors of
oil injection type and the exhaust gas from the low stage
compressor is cooled by a large amount of coolant oil injected from
the oil injecting orifice 22, an intermediate cooler is not
required. Furthermore, owing to this feature, the temperature of
the atmosphere enclosing the electric motor 3 or the temperature
within the exhaust gas conduit 9 can be arbitrarily adjusted by
controlling the quantity of oil injected into the low stage
compressor 1. Because the gas sucked into the high stage compressor
is mixed with a considerable amount of oil, the tendency of the
re-expansion of gas due to its heat absorption can be substantially
suppressed.
According to another feature of the invention, the liquid conduit 8
is partially communicated with the sealed atmosphere enclosing the
electric motor by way of the temperature responsive valve 7. This
arrangement provides an additional advantage that, even when the
temperature of the atmosphere enclosing the motor or of the exhaust
gas from the high stage compressor should be increased as caused by
fault of the oil cooler or for any other reasons, the temperature
sensing member will respond to the increase in the temperature to
automatically open the expansion valve 7 to thereby add the coolant
into the enclosing atmosphere, whereby the increased temperature is
automatically lowered.
Although the invention has been described with reference to
embodiments in which the invention is applied to a refrigerator, it
should be appreciated that the invention is more useful for the
application to compress a permanent gas such as helium, nitrogen
etc., because the apparatus according to the invention can be
constructed in a compacted form wherein a single electric motor is
used for driving both the high and low stage compressors and no
intermediate coolers are required due to the fact that the electric
motor is cooled at a moderate temperature. The invention therefore
is never restricted to the illustrated embodiments. Those skilled
in the art may make many changes and modifications in the form of
the invention without departing from the spirit and scope of the
invention.
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