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.

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.

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.