Capacity controllable compressor apparatus

A capacity controllable compressor apparatus has a plurality of high-pressure chamber compressors which are connected in parallel to a common refrigerant suction pipe and a common refrigerant discharge pipe, and oil equalizing pipes through which oil sumps of the plurality of compressors are communicated with each other. One of the plurality of compressors is operated with its chamber kept at a higher internal pressure than other compressors. The compressor apparatus comprises an oil separator disposed to the common discharge pipe; device for returning lubricating oil separated by the oil separator to a suction side of one of the compressors operated with its chamber kept at a higher internal pressure; first control device disposed in the oil equalizing pipes so as to prevent the lubricating oil from flowing into one of the two compressors communicated with each other by the oil equalizing pipe, said one being made inoperative when the capacity of the compressor apparatus is controlled; and valve device disposed in a discharge pipe of the inoperative compressor so as to prevent refrigerant from flowing into the inoperative compressor.

SUMMARY OF THE INVENTION 
The present invention relates to a compressor apparatus having a plurality 
of parallel connected high-pressure chamber compressors and, more 
particularly, to a compressor apparatus which is capable of controlling 
its overall capacity by making inoperative that is, some of these 
high-pressure chamber compressors or by controlling the capacities of the 
compressors. 
It is preferable for an air conditioning equipment (or system) serving to 
effect air conditioning of a plurality of rooms, or a refrigerating device 
serving to cool a plurality of freezing rooms, or the like, that the 
capacity of a compressor apparatus used therein can be varied in 
accordance with a change in the number of rooms to be subjected to air 
conditioning or the number of freezing rooms to be cooled, respectively. 
This type of capacity controllable compressor apparatus has, as shown in 
FIG. 20, a plurality of parallel-connected compressors with their oil 
sumps connected with each other by means of oil equalizing pipes, so that 
the overall capacity thereof is controlled by making inoperative some of 
the compressors or by varying the capacities of the compressors. In this 
type of compressor apparatus, when all the compressors are operated, 
internal pressure in the chambers of all the compressors are not 
substantially equalized with each other due to the manufacturing variation 
among the individual compressors, pipes and the like. For this reason, the 
amount of lubricating oil of each compressor is not uniform, whereby 
nonuniform distribution of the lubricating oil among the compressors 
results. Meanwhile, when the capacity control is effected by making 
inoperative some of the compressors, there is a problem that a part of the 
high-pressure gas, such as a gas compressed by other compressor, flows 
into the inoperative compressor and is dissolved in the lubricating oil of 
a relatively low temperature in the chamber of the inoperative compressor 
resulting in a dilution of the lubricating oil thereat. Further, when the 
compressor is started again, the liquid refrigerant thus dissolved is 
compressed and there occurs a foaming which results in an undesirable 
increase in the amount of the oil being drawn into the compression space, 
so that the efficiency of the compressor is decreased. In addition, the 
internal pressure in the chamber of the inoperative compressor becomes 
slightly lower than the internal pressure in the chamber of the 
compressor(s) in operation, so that there is a problem in this case as 
well that the lubricating oil is distributed nonuniformly among the 
compressors. 
There has been made a proposal for solving the problem of nonuniform 
distribution of the lubricating oil in the compressor apparatus having a 
plurality of parallel-connected compressors, as disclosed in Japanese 
Patent Unexamined Publication No. 57-51982. This proposal, however, has a 
problem of lowering of the efficiency of each compressor because the 
pressures in the low-pressure chambers of the respective, 
parallel-connected compressors are differed by making use of the pressure 
loss in the intake pipe. In particular, since the suction pressure is 
decreased, the applicable range of the compressor apparatus is limited 
disadvantageously. This method is applicable to the low-pressure chamber 
compressor but it is not suitable for the high-pressure chamber compressor 
in which the chamber is kept at a high pressure as a whole. 
An object of the present invention is to provide a compressor apparatus 
which is free from non-uniform distribution of lubricating oil both when 
all compressors are operated and when a capacity control is effected by 
making inoperative some of the compressors. 
Another object of the present invention is to provide a compressor 
apparatus in which compressed gas is not dissolved in the lubricating oil 
when the capacity control is effected by making inoperative some of the 
compressors thereby preventing dilution of the lubricating oil. 
Still another object of the present invention is to provide a compressor 
apparatus which is free from the lowering of the efficiency of the 
compressor due to an increase in the amount of the oil drawn into the 
compression space attributable to compression and foaming of liquid 
refrigerant when the inoperative compressor is started again. 
SUMMARY OF THE INVENTION 
A capacity controllable compressor apparatus according to the present 
invention comprises: a plurality of high-pressure chamber compressors 
which are connected in parallel to a common refrigerant suction pipe and a 
common refrigerant discharge pipe having an oil separator, one of said 
compressors being operated with its chamber kept at a higher internal 
pressure than other compressors; means for returning lubricating oil 
separated by said oil separator to a suction side of one of said 
compressors operated with its chamber kept at a higher internal pressure; 
oil equalizing pipes through which oil sumps of said plurality of 
compressors are communicating with each other; first control means 
disposed in said oil equalizing pipes so as to prevent the lubricating oil 
from flowing into one of the two compressors communicating with each other 
by means of said oil equalizing pipe, and which said one of the two 
compressors is made inoperative when the capacity of the compressor 
apparatus is being controlled; and valve means disposed in a discharge 
pipe of said inoperative compressor so as to prevent refrigerant from 
flowing into said inoperative compressor. 
The first control means includes check valves disposed in the oil 
equalizing pipes or stop valves serving to close the oil equalizing pipes 
so as to prevent the lubricating oil from flowing into the inoperative 
compressor. 
The valve means includes a check valve disposed to prevent the refrigerant 
from flowing into the inoperative compressor. 
The lubricating oil return means includes an oil return pipe connected 
between the oil separator and a refrigerant suction pipe of the compressor 
operated with its chamber kept at a high internal pressure, and 
communication pipes each serving to communicate between adjacent 
refrigerant suction pipes of the plurality of compressors at a point 
downstream of a point where the oil return pipe is connected to the 
aforesaid refrigerant suction pipe. These communication pipes may be 
dispensed with. The oil return pipe may be connected with a space in the 
compressor operated with its chamber kept at a high internal pressure, the 
pressure in the space corresponding to an intermediate pressure obtained 
in the course of the compression stroke. 
In an embodiment, a plurality of oil return pipes are provided for 
connecting between the oil separator and spaces in the plurality of 
compressors, the pressure in each space corresponding to an intermediate 
pressure obtained in the course of the compression stroke. In this case, 
it is required to dispose stop valves for closing the oil return pipes. 
The internal pressure of the compressor may be increased by means of making 
larger the flow resistance of the discharge pipe of the compressor. 
Further, it is preferred that the oil equalizing pipe extends to project 
into the oil sump of the compressor located on the upstream side with 
respect to the flow of the lubricating oil. 
When all of the compressors are operating, the lubricating oil separated 
from the high-pressure gas refrigerant by the oil separator is returned to 
the compressor operated at an increased internal pressure and then 
supplied from this compressor to the other compressor. It is therefore 
possible to prevent the nonuniform distribution of the lubricating oil. 
When the capacity of the compressor apparatus is controlled by making 
inoperative some of the compressors, the lubricating oil is returned to 
the compressor which is operating at an increased internal pressure among 
the compressors in operation with the inoperative compressor isolated 
within the circuit, thereby preventing the high-pressure gas refrigerant 
and the lubricating oil from flowing into the inoperative compressor. It 
is therefore possible to prevent the nonuniform distribution of the 
lubricating oil and to prevent the compression of the liquid refrigerant 
and the occurrence of the foaming when the inoperative compressor is 
started again, thereby avoiding the lowering of the efficiency of the 
compressor apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Description will be given below of preferred embodiments of the compressor 
apparatus according to the present invention with reference to the 
accompanying drawings. 
FIG. 1 shows a first embodiment of the compressor apparatus according to 
the present invention. The compressor apparatus has three high-pressure 
chamber compressors 1, 2 and 3 which are connected in parallel to a common 
suction pipe 10 and a common discharge pipe 11. The compressors 1, 2 and 3 
are of the fixed capacity type. The compressor 1 is operated at a higher 
frequency than the other compressors 2 and 3. Further, the compressor 2 is 
operated at a higher frequency than the compressor 3. An oil sump 1b of 
the compressor 1 communicates with an oil sump 2b of the compressor 2 by 
means of an oil equalizing pipe 15a, and the oil sump 2b of the compressor 
2 communicates with an oil sump 3b of the compressor 3 by means of an oil 
equalizing pipe 15b. The oil equalizing pipes 15a and 15b are provided 
with check valves 22a and 22b, respectively, so that the check valves 22a 
and 22b permit lubricating oil to flow from the compressor 1 to the 
compressor 2 and from the compressor 2 to the compressor 3, respectively. 
A suction pipe 7 of the compressor 1 communicates with a suction pipe 8 of 
the compressor 2 by means of a communication pipe 17a, and the suction 
pipe 8 of the compressor 2 communicates with a suction pipe 9 of the 
compressor 3 by means of a communication pipe 17b. Discharge pipes 4 and 5 
are provided with check valves 20a and 20b, respectively, so as to prevent 
the backward flowed or reverse flow) of compressed gas. The common 
discharge pipe 11 is provided with an oil separator 16 for separating the 
lubricating oil from the high pressure gas, which is a high-pressure gas 
refrigerant, in this embodiment, discharged from each of the compressors. 
An oil return pipe 18 is connected to the oil separator 16 for returning 
the lubricating oil thus separated to the compressors. The oil return pipe 
18 is connected to the suction pipe 7 of the compressor 1 at a point 
upstream of a point where the communication pipe 17a is connected to the 
suction pipe 7. A check valve 21a is disposed in the suction pipe 7 at a 
point downstream of the point of connection of the communication pipe 17a 
so as to prevent the refrigerant from flowing out of the compressor 1. 
Likewise, a check valve 21b is disposed in the suction pipe 8 of the 
compressor 2. 
A condenser 12 is connected to the oil separator 16. A plurality of 
parallel-connected evaporators 14 are connected to the condenser 12 
through decompression devices 13. Each of the evaporators 14 is connected 
to the common suction pipe 10, thus completing a refrigerating cycle. 
In the case when the high-pressure chamber compressors 1, 2 and 3 are 
operated simultaneously, the compressor 1 is operated at a higher 
frequency, that is, with a larger capacity, than the other compressor 2, 3 
so that the velocity of the refrigerant flowing through the discharge pipe 
4 of the compressor 1 becomes higher than that of the refrigerant flowing 
through the discharge pipes 5, 6 of the other compressors 2, 3. 
Consequently, the pressure loss in the discharge pipe 4 becomes greater 
than that in the discharge pipes 5, 6. Since the pressure is equalized in 
the common discharge pipe 11 to which the respective discharge pipes 4, 5 
and 6 are connected, the internal pressure of the chamber of the 
compressor 1 is increased by an amount corresponding to a difference in 
the pressure loss. The high-pressure gas refrigerant containing the 
lubricating oil is discharged from the respective compressors 1, 2 and 3 
to be separated from the lubricating oil by means of the oil separator 16 
and is then fed to the condenser 12 through the common discharge pipe 11. 
The lubricating oil thus separated is returned through the oil return pipe 
18 and a decompression device 19 to the suction pipe 7 of the compressor 
1. The lubricating oil is then returned to the respective compressors 1, 2 
and 3 through the suction pipe 7 and the communication pipes 17a and 17b. 
Further, the lubricating oil gathered in the oil sump 1b of the compressor 
1 is supplied to the compressors 2 and 3 through the oil equalizing pipes 
15a and 15b due to a difference in the internal pressure between the 
compressors 1 and 2. Since the oil equalizing pipes 15a and 15b are 
extended so as to project into the oil sumps of the compressors located on 
the upstream side as shown in FIG. 1, when an oil level 25 in the 
compressor on the upstream side is lowered below an opening of the oil 
equalizing pipe 15a or 15b, the returned lubricating oil is prevented from 
being supplied to the compressor on the downstream side by flowing down 
along the chamber wall of the compressor, thus making it possible to keep 
the oil level 25 in the compressor on the upstream side at a regular 
position. It is therefore possible to prevent the nonuniform distribution 
of the lubricating oil. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 1 is made inoperative, the high-pressure gas 
refrigerant discharged through the discharge pipes 5 and 6 of the 
compressors 2 and 3 is prevented from flowing into the compressor 1 by 
means of the check valve 20a disposed in the discharge pipe 4 of the 
compressor 1. The lubricating oil separated from the high-pressure gas 
refrigerant by means of the oil separator 16 is returned to the suction 
pipe 7 of the compressor 1 through the oil return pipe 18 and the 
decompression device 19. Since the inside of the compressor 1 is kept at a 
high internal pressure by means of the check valve 21a, the lubricating 
oil thus returned is not allowed to flow into the compressor 1, instead it 
is directed to the suction pipe 8 of the compressor 2 through the 
communication pipe 17a. The lubricating oil is then returned to the 
compressors 2 and 3 through the suction pipe 8 and the communication pipe 
17b. Further, the lubricating oil gathered in the oil sump 2b of the 
compressor 2 is supplied through the oil equalizing pipe 15b to the 
compressor 3 due to a difference in the internal pressure between the 
compressors 2 and 3. The lubricating oil in the compressor 2 is prevented 
from being supplied to the compressor 1 by means of the check valve 22a of 
the oil equalizing pipe 15a. Since the oil equalizing pipe 15b is extended 
so as to project into the oil sump of the compressor 2 located on the 
upstream side as shown in FIG. 1, when the oil level 25 in the compressor 
2 on the upstream side is lowered below the opening of the oil equalizing 
pipe 15b, the returned lubricating oil is prevented from being supplied to 
the compressor 3 on the downstream side by flowing down along the chamber 
wall of the compressor 2, thus making it possible to keep the oil level 25 
in the compressor 2 on the upstream side at a regular position. It is 
therefore possible to prevent the lubricating oil from being nonuniformly 
distributed between the compressors 2 and 3 and to keep the quantity of 
the lubricating oil in the oil sump of the compressor 1 at a regular 
quantity. Further, since the high-pressure gas refrigerant discharged from 
the compressors 2 and 3 is prevented from flowing into the compressor 1, 
there is no possibility that the refrigerant dissolves in the lubricating 
oil in the compressor 1 to dilute the lubricating oil. In addition, even 
when the compressor 1 is started again, there is no compression of a 
liquid refrigerant and no occurrence of the foaming, thereby preventing 
the lowering of the efficiency of the compressor apparatus. 
Also when the compressor apparatus is operated in a capacity controlling 
mode in which the compressor 3 alone is operated while the compressors 1 
and 2 are made inoperative, the high-pressure gas refrigerant discharged 
from the compressor 3 is prevented from flowing into the compressors 1 and 
2 by means of the check valves 20a and 20b in the same manner as mentioned 
above. Further, the lubricating oil separated by means of the oil 
separator 16 is returned through the oil return pipe 18 while being 
prevented from flowing into the compressors 1 and 2 by means of the check 
valves 21a and 21b. Consequently, it is possible, in this case as well, to 
prevent dilution of the lubricating oil, compression and foaming of the 
liquid refrigerant. 
FIG. 2 shows a second embodiment of the compressor apparatus according to 
the present invention. In this embodiment, two high-pressure chamber 
compressors 1 and 2 are connected in parallel, and the compressor 1 is 
operated at a higher frequency than the compressor 2. An oil equalizing 
pipe 15 is provided with a stop valve 23 which serves to close the oil 
equalizing pipe 15, in place of the check valves 22a and 22b. Other 
arrangements are identical with those of the first embodiment so that 
explanation thereof will be omitted. 
In case that the two compressors 1 and 2 are operated simultaneously, the 
stop valve 23 disposed in the oil equalizing pipe 15 is opened. The 
compressor 1 is operated at a higher frequency, that is, with a larger 
capacity, than the compressor 2 so that the velocity of the refrigerant 
flowing through the discharge pipe 4 of the compressor 1 becomes higher 
than that of the refrigerant flowing through the discharge pipe 5 of the 
compressor 2. Consequently, the pressure loss in the discharge pipe 4 
becomes greater than that in the discharge pipe 5. Since the pressure is 
equalized in the common discharge pipe 11 to which the respective 
discharge pipes 4 and 5 are connected, the internal pressure of the 
chamber of the compressor 1 is increased by an amount corresponding to a 
difference in the pressure loss. The high-pressure gas refrigerant 
containing the lubricating oil is discharged from the respective 
compressors 1 and 2 to be separated from the lubricating oil by means of 
the oil separator 16 and is then fed to the condenser (not shown in FIG. 
2). The lubricating oil thus separated is returned through the oil return 
pipe 18 and the decompression device 19 to the suction pipe 7 of the 
compressor 1. The lubricating oil is then returned to the respective 
compressors 1 and 2 through the suction pipe 7 and the communication pipe 
17. Further, the lubricating oil gathered in the oil sump 1b of the 
compressor 1 is supplied to the compressor 2 through the oil equalizing 
pipe 15 due to a difference in the internal pressure between the 
compressors 1 and 2. Since the oil equalizing pipe 15 is extended so as to 
project into the oil sump 1b of the compressor 1 located on the upstream 
side similarly to the first embodiment, when the oil level 25 in the 
compressor 1 on the upstream side is lowered below the opening of the oil 
equalizing pipe 15, the returned lubricating oil is prevented from being 
supplied to the compressor 2 on the downstream side by flowing down along 
the chamber wall of the compressor, thus making it possible to keep the 
oil level 25 in the compressor 1 on the upstream side at a regular 
position. It is therefore possible to prevent the nonuniform distribution 
of the lubricating oil. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 1 is made inoperative, the high-pressure gas 
refrigerant discharged through the discharge pipe 5 of the compressor 2 is 
prevented from flowing into the compressor 1 by means of the check valve 
20 disposed in the discharge pipe 4 of the compressor 1. The lubricating 
oil separated from the high-pressure gas refrigerant by means of the oil 
separator 16 is returned to the suction pipe 7 of the compressor 1 through 
the oil return pipe 18 and the decompression device 19. Since the inside 
of the compressor 1 is kept at a high internal pressure by means of the 
check valve 21, the lubricating oil thus returned is not allowed to flow 
into the compressor 1 but made to return to the suction pipe 8 of the 
compressor 2 through the communication pipe 17. The lubricating oil is 
then returned to the compressor 2 through the suction pipe 8 and the 
communication pipe 17. The lubricating oil in the compressor 2 is 
prevented from being supplied to the compressor 1 by closing the stop 
valve 23 of the oil equalizing pipe 15. It is therefore possible to keep 
the lubricating oil in the compressor 2 in the normal state. Further, 
since the high-pressure gas refrigerant discharged from the compressor 2 
is prevented from flowing into the compressor 1, there is no possibility 
that the refrigerant dissolves in the lubricating oil in the compressor 1 
to dilute the lubricating oil. In addition, even when the compressor 1 is 
started again, there is no compression of the liquid refrigerant and no 
occurrence of foaming, thereby preventing the lowering of the efficiency 
of the compressor apparatus. 
FIG. 3 shows a third embodiment of the compressor apparatus according to 
the present invention. In the third embodiment, a check valve 24 is 
disposed, in addition, in the discharge pipe 5 of the compressor 2 of the 
second embodiment so as to prevent the high-pressure gas refrigerant from 
flowing into the compressor 2. Other arrangements are identical with those 
of the second embodiment so that explanation thereof will be omitted. 
Functions effected when the two compressors 1 and 2 are operated 
simultaneously and when the compressor 1 is made inoperative in the 
capacity controlling mode are identical with those in the second 
embodiment so that explanation thereof will be omitted. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 2 is made inoperative, the high-pressure gas 
refrigerant discharged through the discharge pipe 4 of the compressor 1 is 
prevented from flowing into the compressor 1 by means of the check valve 
24 disposed in the discharge pipe 5 of the compressor 2. The lubricating 
oil separated from the high-pressure gas refrigerant by means of the oil 
separator 16 is returned to the suction pipe 7 of the compressor 1 through 
the oil return pipe 18 and the decompression device 19 by which the 
pressure of the lubricating oil is reduced to a suction pressure level. 
Since the inside of a chamber 2a of the compressor 2 is kept at a high 
pressure, the returned lubricating oil kept at the suction pressure is 
scarcely allowed to flow into the compressor 2 through the communication 
pipe 17 so as to be returned to the compressor 1. The lubricating oil in 
the compressor 1 is prevented from being supplied to the compressor 2 by 
closing the stop valve 23 of the oil equalizing pipe 15. It is therefore 
possible to keep the lubricating oil in the compressor 1 in the normal 
state. Further since the high-pressure gas refrigerant discharged from the 
compressor 1 is prevented from flowing into the compressor 2, there is no 
possibility that the refrigerant dissolves in the lubricating oil in the 
compressor 2 to dilute the lubricating oil. In addition, even when the 
compressor 2 is started again, there is no compression of the liquid 
refrigerant and no occurrence of the foaming, thereby preventing the 
lowering of the efficiency of the compressor apparatus. In this 
embodiment, since it is possible to stop either of the compressors 1 and 
2, the lifetime of the compressor apparatus can be extended. 
FIGS. 4 and 5 show respectively fourth and fifth embodiments of the 
compressor apparatus according to the present invention. The fourth and 
fifth embodiments are modifications of the second and third embodiments, 
respectively, in which a throttle 26 serving to increase the flow 
resistance of the pipe is disposed in the discharge pipe 4. Instead of 
disposing the throttle 26, the length and/or the diameter of the pipe may 
be adjusted to increase the flow resistance. By making larger the flow 
resistance of the discharge pipe 4 than that of the discharge pipe 5, the 
internal pressure of the chamber 1a of the compressor 1 becomes higher 
than that of the compressor 2. 
Functions are identical with those in the second and third embodiments, 
respectively, so that explanation thereof will be omitted. 
In these embodiments, since the compressors 1 and 2 can be operated at the 
same frequency, the construction of the compressor apparatus can be 
simplified. 
FIGS. 6 and 7 show respectively sixth and seventh embodiments of the 
compressor apparatus according to the present invention. The sixth and 
seventh embodiments are different from the second and third embodiments in 
that compressors 27 and 28 are used in place of the compressors 1 and 2. 
The compressor 27 has a larger capacity than the compressor 28. 
Functions are identical with those in the second and third embodiments, 
respectively, so that explanation thereof will be omitted. 
In these embodiments as well, since the compressors 27 and 28 can be 
operated at the same frequency, the construction of the compressor 
apparatus can be simplified. 
FIGS. 8 to 13 show respectively eighth to thirteenth embodiments of the 
compressor apparatus according to the present invention. In these 
embodiments, only the compressors 2 and 28 are enabled to be made 
inoperative. 
The eighth embodiment is a modification of the third embodiment, in which 
the communication pipe 17, the check valve 21 and the check valve 20 of 
the discharge pipe 4 of the compressor 1 are dispensed with. The 
compressors 1 and 2 are fixed capacity type high-pressure chamber 
compressors, and the compressor 1 is operated at a high frequency. 
When the compressors 1 and 2 are operated simultaneously, the stop valve 23 
disposed in the oil equalizing pipe 15 is opened. The high-pressure gas 
refrigerant containing the lubricating oil is discharged from the 
respective compressors 1 and 2 to be separated from the lubricating oil by 
means of the oil separator 16 and is then fed to the condenser which is 
not shown. The lubricating oil thus separated is returned through the oil 
return pipe 18 and the decompression device 19 to the suction pipe 7 of 
the compressor 1. The lubricating oil is then returned to the compressor 1 
through the suction pipe 7. Further, the lubricating oil gathered in the 
oil sump 1b of the compressor 1 is supplied through the oil equalizing 
pipe 15 to the compressor 2 due to a difference in the internal pressure 
between the compressors 1 and 2. Since the oil equalizing pipe 15 is 
extended so as to project into the oil sump 1b of the compressor 1 located 
on the upstream side come similarly to the first embodiment, when the oil 
level 25 in the compressor 1 on the upstream side is lowered below the 
opening of the oil equalizing pipe 15, the returned lubricating oil is 
prevented from being supplied to the compressor 2 on the downstream side 
by flowing down along the chamber wall of the compressor, thus making it 
possible to keep the oil level 25 in the compressor 1 on the upstream side 
at a regular position. It is therefore possible to prevent the nonuniform 
distribution of the lubricating oil between the compressors 1 and 2. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 2 is made inoperative, the high-pressure gas 
refrigerant discharged through the discharge pipe 4 of the compressor 1 is 
prevented from flowing into the compressor 2 by means of the check valve 
24 disposed in the discharge pipe 5 of the compressor 2. The lubricating 
oil separated from the high-pressure gas refrigerant by means of the oil 
separator 16 is returned to the suction pipe 7 of the compressor 1 through 
the oil return pipe 18 and the decompression device 19 and is then 
returned to the compressor 1. The lubricating oil in the compressor 1 is 
prevented from being supplied to the compressor 2 by closing the stop 
valve 23 of the oil equalizing pipe 15. It is therefore possible to keep 
the lubricating oil in the compressor 2 in the normal state. Further, 
since the high-pressure gas refrigerant discharged from the compressor 1 
is prevented from flowing into the compressor 2 by means of the check 
valve 24, there is no possibility that the refrigerant dissolves in the 
lubricating oil in the compressor 2 to dilute the lubricating oil. In 
addition, even when the compressor 2 is started again, there is no 
compression of the liquid refrigerant and no occurrence of the foaming, 
thereby preventing the lowering of the efficiency of the compressor 
apparatus. 
The ninth embodiment is a modification of the eighth embodiment, in which 
the oil return pipe 18 is connected with a space 1c in the compressor 1, 
the pressure in the space 1c corresponding to an intermediate pressure 
obtained in the course of the compression stroke. In this embodiment, in 
addition to the functions and effects which are identical with those of 
the eighth embodiment, since the lubricating oil of low temperature is 
injected into the space of the intermediate pressure in which a high 
temperature has been reached due to compression, the efficiency of the 
compressor can be increased owing to the cooling effect of the lubricating 
oil. 
The tenth and eleventh embodiments are modifications of the eighth and 
ninth embodiments, respectively, in which the throttle 26 is disposed in 
the discharge pipe 4 of the compressor 1 instead of operating the 
compressor 1 at a high frequency. Instead of disposing the throttle 26, 
the length and/or the diameter of the pipe may be adjusted to increase the 
flow resistance. By making larger the flow resistance of the discharge 
pipe 4 than that of the discharge pipe 5, the internal pressure of the 
chamber 1a of the compressor 1 becomes higher than that of the compressor 
2. 
In these embodiments, the same functions and effects as those of the eighth 
and ninth embodiments can be attained, respectively. 
The twelfth and thirteenth embodiments are modifications of the eighth and 
ninth embodiments, respectively, in which the compressors 27 and 28 are 
used in place of the compressors 1 and 2. The compressor 27 has a larger 
capacity and a higher internal pressure than the compressor 28. 
In these embodiments, the same functions and effects as those of the eighth 
and ninth embodiments can be attained, respectively. Further, since it is 
possible to operate the compressors 27 and 28 at the same frequency, the 
construction of the compressor apparatus can be simplified. 
FIGS. 14 to 19 show respectively fourteenth to nineteenth embodiments of 
the compressor apparatus according to the present invention. In these 
embodiments, the parallel-connected high-pressure chamber compressors 1 
and 2 are both enabled to be made inoperative for the purpose of 
controlling the capacity. 
The fourteenth embodiment is a modification of the eighth embodiment, in 
which the check valve 20 is disposed in the discharge pipe 4 of the 
compressor 1 so as to prevent the high-pressure gas refrigerant from 
flowing into the compressor 1, an oil return pipe 32 is connected between 
the oil separator 16 and the suction pipe 8 of the compressor 2, the oil 
return pipe 32 is provided with a stop valve 30 serving to close the oil 
return pipe 32 and a decompression device 31, and the oil return pipe 18 
is provided with a stop valve 29 serving to close the oil return pipe 18. 
Further, the oil equalizing pipe 15 through which the oil sumps 1b and 2b 
of the compressors 1 and 2 are connected with each other is extended so as 
to project into both of the oil sumps 1b and 2b. The compressor 1 is 
operated at a higher frequency, that is, with a larger capacity, than the 
compressor 2. 
When the compressors 1 and 2 are operated simultaneously, the stop valve 23 
disposed in the oil equalizing pipe 15 is opened, the stop valve 30 of the 
oil return pipe 32 is closed, and the stop valve 29 of the oil return pipe 
18 is opened. The high-pressure gas refrigerant containing the lubricating 
oil is discharged from the respective compressors 1 and 2 to be separated 
from the lubricating oil by means of the oil separator 16 and is then fed 
to the condenser which is not shown. The lubricating oil thus separated is 
returned through the oil return pipe 18 and the decompression device 19 to 
the suction pipe 7 of the compressor 1. The lubricating oil is then 
returned to the compressor 1 through the suction pipe 7. Further, the 
lubricating oil gathered in the oil sump 1b of the compressor 1 is 
supplied through the oil equalizing pipe 15 to the compressor 2 due to a 
difference in the internal pressure between the compressors 1 and 2. Since 
the oil equalizing pipe 15 is extended so as to project into the oil sump 
1b of the compressor 1 located on the upstream side, similarly to the 
first embodiment, when the oil level 25 in the compressor 1 on the 
upstream side is lowered below the opening of the oil equalizing pipe 15, 
the returned lubricating oil is prevented from being supplied to the 
compressor 2 on the downstream side by flowing down along the chamber wall 
of the compressor 1, thus making it possible to keep the oil level 25 in 
the compressor 1 on the upstream side at a regular position. It is 
therefore possible to prevent the nonuniform distribution of the 
lubricating oil between the compressors 1 and 2. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 2 is made inoperative, the stop valves 23 and 30 are 
closed. The high-pressure gas refrigerant discharged through the discharge 
pipe 4 of the compressor 1 is prevented from flowing into the compressor 2 
by means of the check valve 24 disposed in the discharge pipe 5 of the 
compressor 2. The lubricating oil separated from the high-pressure gas 
refrigerant by means of the oil separator 16 is returned to the suction 
pipe 7 of the compressor 1 through the oil return pipe 18 and the 
decompression device 19 and is then returned to the compressor 1. The 
lubricating oil in the compressor 1 is prevented from being supplied to 
the compressor 2 by the closing of the stop valve 23 of the oil equalizing 
pipe 15. It is therefore possible to keep the lubricating oil in the 
compressor 2 in the normal state. Further, since the high-pressure gas 
refrigerant discharged from the compressor 1 is prevented from flowing 
into the compressor 2 by means of the check valve 24, there is no 
possibility for the refrigerant to be dissolved in the lubricating oil in 
the compressor 2 and thereby undesirably dilute the lubricating oil 
thereat. In addition, even when the compressor 2 is started again, that is 
becomes operational, there is no compression of the liquid refrigerant and 
no occurrence of the foaming, thereby preventing the lowering of the 
efficiency of the compressor apparatus. 
When the compressor apparatus is operated in a capacity controlling mode in 
which the compressor 1 is made inoperative, the stop valves 23 and 29 are 
closed. The high-pressure gas refrigerant discharged through the discharge 
pipe 5 of the compressor 2 is prevented from flowing into the compressor 1 
by means of the check valve 20 disposed in the discharge pipe 4 of the 
compressor 1. The lubricating oil separated from the high-pressure gas 
refrigerant by means of the oil separator 16 is returned to the suction 
pipe 8 of the compressor 2 through the oil return pipe 32 and the 
decompression device 31 and is then returned to the compressor 2. The 
lubricating oil in the compressor 2 is prevented from being supplied to 
the compressor 1 by the closing of the stop valve 23 of the oil equalizing 
pipe 15. It is therefore possible to keep the lubricating oil in the 
compressor 1 in the normal state. Further, since the high-pressure gas 
refrigerant discharged from the compressor 2 is prevented from flowing 
into the compressor 1 by means of the check valve 20, there is no 
possibility for the refrigerant to be dissolved in the lubricating oil in 
the compressor 1 to dilute the lubricating oil thereat. In addition, even 
when the compressor 1 is started again, that is becomes operational, there 
is no compression of the liquid refrigerant and no occurrence of the 
foaming, thereby preventing the lowering of the efficiency of the 
compressor apparatus. Furthermore, since the compressor to be made 
inoperative for controlling the capacity is not specified, the lifetime of 
the compressor apparatus can be extended. 
The fifteenth embodiment is a modification of the fourteenth embodiment, in 
which the oil return pipes 18 and 32 are connected with spaces 1c and 2c 
in the compressors 1 and 2, respectively, the pressure in each space 2c, 
2c corresponding to an intermediate pressure obtained in the course of the 
compression stroke. In this embodiment, in addition to the functions and 
effects which are identical with those of the fourteenth embodiment, since 
the lubricating oil of low temperature is injected into the space of the 
intermediate pressure in which a high temperature has been reached due to 
compression, the efficiency of the compressor can be increased owing to 
the cooling effect of the lubricating oil. 
The sixteenth and seventeenth embodiments are modifications of the 
fourteenth and fifteenth embodiments, respectively, in which the 
compressors 27 and 28 are used in place of the compressors 1 and 2, and 
the compressor 27 has a larger capacity and a higher internal pressure 
than the compressor 28. 
In these embodiments, the same functions and effects as those of the 
fourteenth and fifteenth embodiments can be obtained, respectively. 
Further, since it is possible to operate the compressors 27 and 28 at the 
same frequency, the construction of the compressor apparatus can be 
simplified. 
The eighteenth and nineteenth embodiments are modifications of the 
fourteenth and fifteenth embodiments, respectively, in which variable 
capacity type high-pressure chamber compressors 33 and 34 are used in 
place of the fixed capacity type high-pressure chamber compressors 1 and 
2. 
In these embodiments, the same functions and effects as those in the 
fourteenth and fifteenth embodiments can be obtained, respectively. 
Further, since the capacities of the compressors 33 and 34 are variable, 
the capacity of the compressor apparatus can be controlled continuously.