JPH1163691A - Oil equalizing system for plural compressors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent oil amount insufficiency of a compressor of a low capacity side, by communicating one end of an oil equalizing bypass with the vicinity of standard oil level height of a shell of partial compressor, communicating many ends with a suction pipe of the other compressor, and providing a throttle on the way of the both ends. SOLUTION: Oil equalizing tube connecting pipes 2a to 2c are provided near standard oil level height of shells of a plurality of compressors 1a to 1c. An oil equalizing tube 3 communicates with one ends of the pipes 2a to 2c. A vapor liquid separator 6 having a gas refrigerant exhaust port 7 for exhausting only gas refrigerant is provided at a suction pipe 5a of an upstream side from suction branch parts 4a, 4b of the compressors 1a to 1c. One end of an oil equalizing bypass 9 closely communicates with standard oil level height of the shells of the partial compressors 1b, 1c. Many ends communicate with the pipe 5a of the other compressor 1a, and a throttle is formed on the way of the both ends. Thus, oil amount insufficiency of the compressor of low capacity side can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-pressure shell type oil equalizing system for a plurality of compressors.

[0002]

2. Description of the Related Art A conventional oil level control system for a plurality of compressors is disclosed in Japanese Utility Model Laid-Open Publication No. 4-19675.

Hereinafter, the oil equalizing system for a plurality of compressors will be described with reference to the drawings.

In FIG. 8, oil equalizing pipe connection pipes 2 are provided near the standard oil level of a plurality of shells of a low-pressure shell type compressor 1, and one end of each oil equalizing pipe connection pipe 2 communicates with an oil equalizing pipe 3. doing. Incidentally, three compressors 1 are connected in the conventional example, and the subscripts a, b, and c will be added to distinguish them.

[0005] Next, a method of controlling the oil amount of each compressor in the oil equalizing system of a plurality of compressors having the above configuration will be described.

First, when the amount of oil in the shell of the compressor 1 increases and the oil level increases, the pressure in the oil equalizing pipe connection pipe 2 of the compressor 1 increases. Further, when the amount of oil in the shell of the compressor 1 decreases and the oil level decreases, the pressure of the oil equalizing pipe connection pipe 2 of the compressor 1 decreases.

Therefore, for example, when the oil amount of the compressor 1a decreases due to oil forming at the time of starting, the oil level of the compressor 1a decreases, and the pressure of the oil equalizing pipe connection pipe 2a of the compressor 1a decreases. Oil equalizing pipe connection pipe 2b of compressors 1b and 1c,
It becomes lower than the pressure of 2c.

Therefore, the oil in the shells of the compressors 1b and 1c moves into the shell of the compressor 1a via the oil equalizing pipe 3, and
Insufficient oil amount of the compressor 1a can be prevented.

Further, when the oil amount of the compressor 1a increases due to an uneven return oil amount or the like, the oil level of the compressor 1a increases, and the pressure of the oil equalizing pipe connection pipe 2a of the compressor 1a decreases. Machine 1
It becomes higher than the pressure of the oil equalizing pipe connection pipes 2b and 2c of b and 1c.

Therefore, the oil in the shell of the compressor 1a moves through the oil equalizing pipe 3 into the shells of the compressors 1b and 1c.
Excessive oil amount of the compressor 1a can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

[0011]

However, in the above configuration, a plurality of compressors include compressors of different capacities, or a plurality of compressors include a variable capacity compressor. In this case, the pressure in the shell of the high-capacity compressor is low, and the pressure in the shell of the low-capacity compressor is high because each compressor is of the low-pressure shell type.

Therefore, until the oil level difference corresponding to the pressure difference in the shell between the compressors (for example, a pressure difference of 0.01 kg / cm ² corresponds to an oil level difference of 10 cm), the compression on the low capacity side is performed. The oil in the shell of the compressor moves through the oil equalizing pipe into the shell of the compressor on the higher capacity side.

At this time, even if the oil level of the compressor on the low-capacity side is lower than the position of the connecting pipe for the oil equalizing pipe, the oil stirred by the rotating parts in the shell of the compressor on the low-capacity side, or Since the oil that has fallen from the compression chamber floats in the form of a mist, the mist-like oil moves to the high-capacity compressor together with the refrigerant.

Therefore, even if the oil level of the compressor on the low-capacity side is lower than the position of the oil equalizing pipe connection pipe, the oil amount continues to decrease, and eventually the oil amount becomes insufficient, resulting in damage to the compressor.

As described above, when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a variable capacity compressor, There is a problem that the oil amount of the compressor is insufficient.

As a solution to this problem, a method is considered in which all compressors are stopped every predetermined time and oil is leveled. However, it is necessary to stop the compressors every several minutes to several tens of minutes. And the system is not stable. Therefore, there is a problem that the efficiency is lowered and the reliability of the system is lowered.

An object of the present invention is to solve the conventional problem, and an object of the present invention is to provide an oil equalizing system with a simple configuration when a plurality of low pressure shell type compressors are used in parallel.

[0018]

SUMMARY OF THE INVENTION The present invention provides an equalizing pipe connecting pipe near a standard oil level of a plurality of low pressure shell type shells, and an equalizing pipe connected to one end of each of the equalizing pipe connecting pipes. An oil pipe, a gas-liquid separator provided in a suction pipe upstream of a suction branch to each compressor and provided with a gas refrigerant discharge port for discharging only gas refrigerant, and communicating the gas refrigerant discharge port with the oil equalizing pipe; A communication pipe in which the pressure of the oil equalizing pipe is higher than the pressure in the shell of each compressor, one end of which communicates with the vicinity of the standard oil level of some of the compressor shells, and the other end of which is suctioned by another compressor. This is provided with an oil equalizing bypass which communicates with the pipe and has a throttle at an intermediate position at both ends.

Further, according to the present invention, an oil equalizing pipe connecting pipe is provided near a standard oil level of a plurality of low pressure shell type compressor shells, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connecting pipe is provided. A gas-liquid separator provided in a suction pipe upstream of a suction branch to the compressor and having a gas refrigerant discharge port for discharging only a gas refrigerant, and a gas refrigerant discharge port communicating with the oil equalizing pipe and the oil equalizing pipe Of the compressor is higher than the pressure in the shell of each compressor, one end communicates near the standard oil level of some compressor shells, and the other end communicates with the suction pipe of another compressor. And an equalizing oil bypass having a restriction in the middle of both ends,
Equipped with a two-way valve provided in the communication pipe, cooling, or
A two-way valve control means for closing the two-way valve for a fixed time when the continuous heating operation time is equal to or longer than a predetermined time.

Further, the present invention provides an oil equalizing pipe connecting pipe near a standard oil level of a plurality of low pressure shell type compressor shells, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connecting pipe. A gas-liquid separator provided in a suction pipe upstream of a suction branch to the compressor and having a gas refrigerant discharge port for discharging only a gas refrigerant, and a gas refrigerant discharge port communicating with the oil equalizing pipe and the oil equalizing pipe Of the compressor is higher than the pressure in the shell of each compressor, one end communicates near the standard oil level of some compressor shells, and the other end communicates with the suction pipe of another compressor. And an equalizing oil bypass having a restriction in the middle of both ends,
A two-way valve provided in the communication pipe, and a differential pressure detecting device that detects a differential pressure between a shell upper part and a shell lower part of each compressor,
When the differential pressure between the upper shell and the lower shell detected by the differential pressure detector of at least one compressor is less than a predetermined lower differential pressure, the two-way valve is closed, and then the differential pressure of all the compressors is reduced. A two-way valve control means for opening the two-way valve when a differential pressure between the upper shell portion and the lower shell portion detected by the detecting device is equal to or higher than a predetermined reference differential pressure.

The present invention also provides an oil equalizing pipe connecting pipe near the standard oil level of a plurality of low pressure shell type compressor shells, and one end of each oil equalizing pipe connecting pipe. A gas-liquid separator provided in a suction pipe upstream of a suction branch to the compressor and having a gas refrigerant discharge port for discharging only a gas refrigerant, and a gas refrigerant discharge port communicating with the oil equalizing pipe and the oil equalizing pipe Of the compressor is higher than the pressure in the shell of each compressor, one end communicates near the standard oil level of some compressor shells, and the other end communicates with the suction pipe of another compressor. And an equalizing oil bypass having a restriction in the middle of both ends,
A two-way valve provided in the communication pipe, and an oil level detector for detecting the oil level of each compressor, and oil detected by the oil level detector of at least one compressor. When the surface height becomes less than a predetermined lower limit oil level, the two-way valve is closed, and thereafter, the oil level detected by the oil level detectors of all the compressors is equal to a predetermined reference oil level. If it is not less than this, a two-way valve control means for opening the two-way valve is provided.

According to the present invention, the amount of oil in the shell of each compressor can be surely controlled to an appropriate amount regardless of the combination of compressors of any capacity and usage conditions.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is characterized in that a plurality of low pressure shell type compressors are provided with oil equalizing pipe connection pipes in the vicinity of a standard oil level of the shell, and each of the oil equalizing pipe connection pipes is provided. An oil equalizing pipe communicating with one end of the gas refrigerant, a gas-liquid separator provided in a suction pipe upstream of a suction branch to each compressor, and having a gas refrigerant discharge port for discharging only gas refrigerant, and the gas refrigerant discharge port And a communication pipe in which the pressure of the oil equalization pipe is higher than the pressure in the shell of each compressor, and one end of the communication pipe near the standard oil level of some of the compressor shells. The compressor is provided with an oil equalizing bypass which communicates with the suction pipe of another compressor and has a throttle in the middle of both ends.

Therefore, even if a plurality of compressors include compressors of different capacities, or a plurality of compressors include a variable capacity compressor, during operation of the compressor, Oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, and the shortage of oil in the low-capacity compressor can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe.

At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the differential pressure between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor through the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, a high-capacity compressor has a larger oil supply amount to a compression chamber than a low-capacity compressor, and therefore has a higher oil content of the discharged refrigerant than a low-capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal.

Accordingly, in the compressor on the high capacity side, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high capacity side compressor, the low pressure side compressor with high pressure is provided. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

Further, the oil temperature is low due to low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases.

Accordingly, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass is reduced, and continuous operation for a long time (for example, 3
(0 hours), the oil amount of the high-capacity compressor decreases.

However, when all the compressors are stopped, the pressure inside the refrigeration cycle is equalized, and the oil moves through the oil equalizing pipes so that the oil level of each compressor becomes equal, and the compression on the high capacity side is stopped. Insufficient oil level of the machine can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

The invention according to claim 2 of the present invention provides
An oil equalizing pipe connection pipe is provided near the standard oil level of the shell of the plurality of low-pressure shell type compressors, and an oil equalizing pipe communicating one end of each of the oil equalizing pipe connection pipes, and an upstream of a suction branch to each compressor. A gas-liquid separator provided in the suction pipe on the side and having a gas refrigerant discharge port for discharging only the gas refrigerant, communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe in the shell of each compressor. With one end communicating near the standard oil level of some compressor shells, one end communicating with the suction pipe of another compressor, and a restrictor in the middle of both ends. A two-way valve control means for equipping a two-way valve provided in the communication pipe with the equalizing oil bypass, and for closing the two-way valve for a predetermined time when the continuous operation time of cooling or heating is equal to or longer than a predetermined time; It is provided with.

Accordingly, even when a plurality of compressors include compressors having different capacities, or when a plurality of compressors include a compressor of a variable capacity type, the above-described operation is performed during the operation of the compressor. During the period in which the two-way valve is open, the oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil amount of the compressor on the low capacity side is prevented. Shortage can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe.

At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, the compressor on the high capacity side has a larger oil supply amount to the compression chamber than the compressor on the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor on the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal.

Therefore, in the compressor of the high capacity side, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases.

Accordingly, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass is reduced, and continuous operation for a long time (for example, 3
(0 hours), the oil amount of the high-capacity compressor decreases.

However, when the continuous operation time of the cooling or the heating exceeds a predetermined time (for example, 20 hours), the two-way valve is closed for a predetermined time (for example, 5 minutes). At the time of closing, oil moves from the compressor on the low-capacity side where the pressure in the shell is high to the compressor on the high-capacity side where the pressure in the shell is low through the oil equalizing pipe, and the high-capacity compressor continues to operate for a long time Insufficient oil amount during operation can be prevented. in this way,
The oil amount of each compressor can be controlled to an appropriate amount.

The invention according to claim 3 of the present invention provides:
An oil equalizing pipe connection pipe is provided near the standard oil level of the shell of the plurality of low-pressure shell type compressors, and an oil equalizing pipe communicating one end of each of the oil equalizing pipe connection pipes, and an upstream of a suction branch to each compressor. A gas-liquid separator provided in the suction pipe on the side and having a gas refrigerant discharge port for discharging only the gas refrigerant, communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe in the shell of each compressor. With one end communicating near the standard oil level of some compressor shells, one end communicating with the suction pipe of another compressor, and a restrictor in the middle of both ends. An oil bypass, a two-way valve provided in the communication pipe, and a differential pressure detecting device for detecting a differential pressure between a shell upper part and a shell lower part of each compressor, wherein the differential pressure detection of at least one compressor is provided. The differential pressure between the upper shell and lower shell detected by the device is lower than the specified lower differential pressure. The two-way valve is closed, and thereafter, when the differential pressure between the upper shell and the lower shell detected by the differential pressure detecting devices of all the compressors becomes equal to or higher than a predetermined reference differential pressure, the two-way valve is opened. It is provided with a direction valve control means.

Therefore, even when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a compressor of a variable capacity type, the above-described operation is performed during the operation of the compressor. During the period in which the two-way valve is open, the oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil amount of the compressor on the low capacity side is prevented. Shortage can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connecting pipe.

At this time, the amount of the refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows.

Therefore, it is possible to prevent the shortage of the oil amount of some of the compressors due to the difference between the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor through the oil equalizing pipe. .

In general, the compressor on the high capacity side has a larger amount of oil supply to the compression chamber than the compressor on the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor on the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure side compressor with high pressure is provided. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

Also, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases.

Accordingly, the amount of oil supplied to the compressor on the high capacity side due to the oil equalization bypass is reduced, and continuous operation for a long time (for example, 3
(0 hours), the oil amount of the high-capacity compressor decreases.

However, when the differential pressure between the upper shell portion and the lower shell portion detected by the differential pressure detecting device of at least one compressor is less than a predetermined lower limit differential pressure (for example, 0.003 kg / cm ² ), In order to close the two-way valve until the differential pressure between the upper shell and the lower shell detected by the differential pressure detecting devices of all the compressors becomes equal to or higher than a predetermined reference differential pressure (for example, 0.006 kg / cm ² ), When the two-way valve is closed, the oil moves from the high-pressure side compressor having a high pressure in the shell to the high-capacity side compressor having a low pressure in the shell via the oil equalizing pipe, and the high-capacity side Insufficient oil amount during long-time continuous operation of the compressor can be prevented.

Further, since the shortage of the oil amount of each compressor is detected from the differential pressure between the upper shell and the lower shell, the oil discharge amount and the oil return amount of the compressor due to the difference in the operating conditions are not affected. The two-way valve can be controlled with high accuracy.

Therefore, whether the closing of the two-way valve is too late,
Alternatively, the opening after the closing of the two-way valve is too early, the amount of oil in the compressor on the high capacity side is insufficient, and the closing of the two-way valve is too early, or after the closing of the two-way valve. Insufficient oil amount of the compressor on the low capacity side due to the opening being too slow can be prevented.
Thus, the oil amount of each compressor can be controlled to an appropriate amount.

The invention according to claim 4 of the present invention provides
An oil equalizing pipe connection pipe is provided near the standard oil level of the shell of the plurality of low-pressure shell type compressors, and an oil equalizing pipe communicating one end of each of the oil equalizing pipe connection pipes, and an upstream of a suction branch to each compressor. A gas-liquid separator provided in the suction pipe on the side and having a gas refrigerant discharge port for discharging only the gas refrigerant, communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe in the shell of each compressor. With one end communicating near the standard oil level of some compressor shells, one end communicating with the suction pipe of another compressor, and a restrictor in the middle of both ends. An oil level bypass, a two-way valve provided in the communication pipe, and an oil level detector for detecting the oil level of each compressor, wherein the oil level detection of at least one compressor is provided. When the oil level detected by the device is less than a predetermined lower limit oil level, the two-way valve is closed. Thereafter, a two-way valve control means for opening the two-way valve when the oil level detected by the oil level detectors of all the compressors is equal to or higher than a predetermined reference oil level is provided. .

Accordingly, even when a plurality of compressors include compressors having different capacities, or when a plurality of compressors include a compressor of a variable capacity type, the above-described operation is performed during the operation of the compressor. During the period in which the two-way valve is open, the oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil amount of the compressor on the low capacity side is prevented. Shortage can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe. At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the difference between the oil equalizing pipe and the shell of each compressor. It is proportional to the square root of pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, the compressor on the high capacity side has a larger amount of oil supply to the compression chamber than the compressor on the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor on the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is communicated with the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

Also, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases.

Accordingly, the amount of oil supplied to the compressor on the high capacity side due to the oil equalization bypass is reduced, and continuous operation for a long time (for example, 3
(0 hours), the oil amount of the high-capacity compressor decreases.

However, when the oil level detected by the oil level detector of at least one of the compressors is less than a predetermined lower limit oil level (for example, 3 cm), thereafter, all of the compressors In order to close the two-way valve until the oil level detected by the oil level detector reaches a predetermined reference oil level (for example, 6 cm), the shell is closed when the two-way valve is closed. The oil moves from the low-capacity compressor with a high internal pressure to the high-capacity compressor with a low internal pressure in the shell via the oil equalizing pipe, and the oil during the long-time continuous operation of the high-capacity compressor Insufficient quantity can be prevented.

Further, in order to detect the shortage of the oil amount of each compressor from the oil level, the oil discharge amount and the oil return amount of the compressor due to the difference in the operating conditions, and the pressure in the shell of the compressor are reduced. The two-way valve can be accurately controlled without being affected by variations in distribution.

Therefore, whether the closing of the two-way valve is too late,
Alternatively, the opening after the closing of the two-way valve is too early, the oil amount of the compressor on the high capacity side is insufficient, and the closing after the closing of the two-way valve is too early, or Insufficient oil amount of the compressor on the low capacity side because the opening after closing is too slow can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

[0073]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The same parts as those in the related art are denoted by the same reference numerals, and detailed description thereof will be omitted.

(Embodiment 1) Embodiment 1 of the present invention will be described with reference to FIG.

FIG. 1 is a structural diagram of an oil equalizing system for a plurality of compressors according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 6 denotes a suction pipe 5 o upstream of the suction branch portion 4 to each compressor 1.
And a gas refrigerant outlet 7 for discharging only gas refrigerant
8 is a communication pipe which communicates the gas refrigerant discharge port 7 with the oil equalizing pipe 3, wherein the pressure of the oil equalizing pipe 3 is higher than the pressure in the shell of each compressor 1, and 9 is a communication pipe. One end communicates with the shells of the compressors 2b and 2c, the other end communicates with the suction pipe 5a of the compressor 2a, and an oil-equalizing bypass having a restriction in the middle of both ends. Note that three compressors 1 are connected in this embodiment, and the subscripts a, b, and c will be added to distinguish them.

Next, a method for controlling the oil amount of each compressor in the oil equalizing system for a plurality of compressors having the above configuration will be described.
Here, it is assumed that the plurality of compressors include compressors having different capacities or a compressor of a variable capacity system, and the compressor 1a has a lower capacity than the compressors 1b and 1c. Suppose there is.

First, during the operation of the compressor 1, the pressure of the oil equalizing pipe 3 that is connected to the gas refrigerant outlet 7 by the communication pipe 8 becomes higher than the pressure in the shell of the compressor 1. Therefore,
From the low-capacity compressor 1a to the high-capacity compressor 1b, 1c
The oil does not move to

When all the compressors 1 are stopped, the pressure in the cycle is equalized, and the oil can be moved between the compressors 1 through the oil equalizing pipe 3. The oil amount is adjusted so that the oil level is equal.

According to this embodiment, even when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a variable capacity compressor,
During the operation of the compressor, the oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, so that the low-capacity compressor can be prevented from running out of oil.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connecting pipe.

At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the differential pressure between the oil equalizing pipe and the shell of each compressor, and the amount of oil returned is also the same between the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor is different from the ratio of the amount of oil returned from the communication pipe of each compressor through the oil leveling pipe.
Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows.
Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor via the oil equalizing pipe.

In general, the high-capacity compressor has a larger oil supply amount to the compression chamber than the low-capacity compressor, so that the oil content of the discharged refrigerant is larger than that of the low-capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure side compressor with high pressure is provided. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases.

Accordingly, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass is reduced, and continuous operation for a long time (for example, 3
(0 hours), the oil amount of the high-capacity compressor decreases.

However, when all the compressors are stopped, the pressure inside the refrigeration cycle is equalized, and the oil moves through the oil equalizing pipes so that the oil level of each compressor becomes equal. Insufficient oil level of the machine can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

(Embodiment 2) Embodiment 2 of the present invention will be described with reference to FIGS.

FIG. 2 is a structural view of an oil equalizing system for a plurality of compressors according to a second embodiment of the present invention. In FIG. 2, reference numeral 6 denotes a suction pipe 5o upstream of a suction branch portion 4 to each compressor 1.
And a gas refrigerant outlet 7 for discharging only gas refrigerant
Is a communication pipe which communicates the gas refrigerant discharge port 7 with the oil equalizing pipe 3, and has a pressure of the oil equalizing pipe 3 higher than the pressure in the shell of each compressor 1, and 9 is a communication pipe. One end communicates with the shells of the compressors 2b and 2c, the other end communicates with the suction pipe 5a of the compressor 2a, and an oil-equalizing bypass having a restriction in the middle of both ends. It is a two-way valve. Here, the two-way valve control means 12 closes the two-way valve 11 for a fixed time when the continuous operation time of cooling or heating reaches a predetermined time. In this embodiment, three compressors 1 are connected.
b and c will be added.

FIG. 3 is a flowchart showing a method for controlling the two-way valve 11 of the oil equalizing system for a plurality of compressors according to the second embodiment of the present invention.

As shown in FIG. 3, first, in step 1, the continuous operation time _Tr for cooling or heating is detected. Step 2
In continuous operation time detected in step 1 T _r is a predetermined upper limit continuous operation time T _ro (e.g., 10 hours) Return to step 1 is less than, Step 3 When it is a predetermined upper limit continuous operation time T _ro more Proceed to.

In step 3, the two-way valve 11 is closed.
In step 4, the closing time T _v of the two-way valve 11 is detected.

In step 5, if the two-way valve closing time T _v detected in step 4 is shorter than a predetermined upper limit two-way valve closing time T _vo (for example, 5 minutes), the process returns to step 4, and the predetermined upper limit two-way valve closing time T _vo is returned. If it is longer than the valve closing time _Tvo , the process proceeds to step 6.

In step 6, the two-way valve 11 is opened.
In step 7, the continuous operation time _Tr is returned to 0, and the process returns to step 1.

Next, a method of controlling the oil amount of each compressor in the oil equalizing system for a plurality of compressors having the above-described configuration will be described.
Here, it is assumed that the plurality of compressors include compressors having different capacities or a compressor of a variable capacity system, and the compressor 1a has a lower capacity than the compressors 1b and 1c. Suppose there is.

First, when the compressor 1 starts operating, since the two-way valve 11 is open, the pressure of the oil equalizing pipe 3 that is connected to the gas refrigerant discharge port 7 by the communication pipe 10 is reduced.
Higher than the pressure in the shell. Therefore, the oil does not move from the low-capacity compressor 1a to the high-capacity compressors 1b and 1c.

When the continuous operation time of cooling or heating reaches a predetermined time, the two-way valve 10 is closed, and the compressor 1a on the low-capacity side where the pressure in the shell is high is changed from the oil equalizing pipe 3 to
, The compressor 1b on the high capacity side where the pressure in the shell is low
The oil moves to 1c. Then, after a certain period of time has elapsed after the two-way valve 11 is closed, the two-way valve is opened, and the movement of oil through the oil equalizing pipe 3 is eliminated.

According to this embodiment, even when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a variable capacity compressor,
During the period when the two-way valve is open during operation of the compressor, oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, and the low-capacity compressor is not operated. Insufficient oil amount of the compressor on the side can be prevented. Further, when oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe via the oil equalizing pipe connection pipe.

At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

[0103] In general, the compressor on the high capacity side has a larger amount of oil supply to the compression chamber than the compressor on the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor on the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, when the multi-end is connected to the integral low pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high capacity side compressor, the low pressure side compressor with high pressure is provided. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases.

However, when the continuous operation time of the cooling or the heating exceeds a predetermined time (for example, 20 hours), the two-way valve is closed for a predetermined time (for example, 5 minutes). At the time of closing, oil moves from the compressor on the low-capacity side where the pressure in the shell is high to the compressor on the high-capacity side where the pressure in the shell is low through the oil equalizing pipe, and the high-capacity compressor continues to operate for a long time Insufficient oil amount during operation can be prevented. in this way,
The oil amount of each compressor can be controlled to an appropriate amount.

(Embodiment 3) Embodiment 3 of the present invention will be described with reference to FIGS.

FIG. 4 is a structural diagram of an oil equalizing system for a plurality of compressors according to the third embodiment of the present invention. In FIG. 5, reference numeral 6 denotes a suction pipe 5o upstream of a suction branch portion 4 to each compressor 1.
And a gas refrigerant outlet 7 for discharging only gas refrigerant
Is a communication pipe which communicates the gas refrigerant discharge port 7 with the oil equalizing pipe 3, and has a pressure of the oil equalizing pipe 3 higher than the pressure in the shell of each compressor 1, and 9 is a communication pipe. One end communicates with the shells of the compressors 2b and 2c, the other end communicates with the suction pipe 5a of the compressor 2a, and an oil-equalizing bypass having a throttle at both ends. A two-way valve 14 is a differential pressure detecting device (for example, a differential pressure sensor or two pressure sensors) that detects a differential pressure between the upper shell portion and the lower shell portion of the compressor 1.

Here, the two-way valve control means 13 operates the two-way valve when the differential pressure between the upper shell portion and the lower shell portion of the at least one compressor 1 detected by the differential pressure detecting device 14 becomes lower than a predetermined lower limit differential pressure. The two-way valve 11 is opened when the differential pressure between the upper shell portion and the lower shell portion detected by the differential pressure detecting devices 14 of all the compressors 1 exceeds a predetermined reference differential pressure.
Note that three compressors 2 are connected in this embodiment, and the subscripts a, b, and c are attached to distinguish them.

FIG. 5 is a flowchart showing a method for controlling the two-way valve 11 of the oil equalizing system for a plurality of compressors according to the third embodiment of the present invention.

As shown in FIG. 5, first, at step 11, the differential pressure detecting device 14 detects the differential pressure P between the upper part and the lower part of the shell of the compressor 1. In step 12, if the differential pressure P detected in step 11 of at least one of the compressors 1 is equal to or higher than a predetermined lower limit differential pressure Pl (for example, 0.003 kg / cm ² ), the process returns to step 11 and returns to the predetermined lower limit. If it is less than the differential pressure Pl, the process proceeds to step S13.

In step 13, the two-way valve 11 is closed. In step 14, the differential pressure detecting device 14 detects the differential pressure P between the upper part and the lower part of the shell of the compressor 1.

In step 15, when the differential pressure P detected in step 14 of all the compressors 1 is less than a predetermined reference differential pressure Ps (for example, 0.006 kg / cm ² ), the process returns to step 14 and returns to step 14. If it is equal to or higher than the reference differential pressure Ps, the process proceeds to step S16. In step 16, the two-way valve 11 is opened,
Return to step 1.

Next, a method for controlling the oil amount of each compressor in the oil equalizing system for a plurality of compressors having the above configuration will be described.
Here, it is assumed that the plurality of compressors include compressors having different capacities or a compressor of a variable capacity system, and the compressor 1a has a lower capacity than the compressors 1b and 1c. Suppose there is.

First, when the compressor 1 starts operating, since the two-way valve 11 is open, the pressure of the oil equalizing pipe 3 connected to the gas refrigerant discharge port 7 by the communication pipe 10 is reduced.
Higher than the pressure in the shell. Therefore, the oil does not move from the low-capacity compressor 1a to the high-capacity compressors 1b and 1c.

When the oil amount of the compressor decreases, the oil level decreases, the differential pressure between the upper shell and the lower shell decreases, and when the oil amount of the compressor increases, the oil level decreases. As a result, the pressure difference between the upper shell and the lower shell increases.

Accordingly, when the amount of oil in the compressors 1b and 1c decreases and the pressure difference between the upper shell and the lower shell becomes less than the lower limit pressure, the two-way valve 11 is closed, and the pressure in the shell is high and the low capacity side is high. Moves from the compressor 1a through the oil equalizing pipe 3 to the compressors 1b and 1c on the high capacity side where the pressure in the shell is low.

When the amount of oil in the compressors 1b and 1c increases and the differential pressure between the upper shell and the lower shell exceeds the standard differential pressure, the two-way valve 11 is opened to move the oil through the oil equalizing pipe 3. lose.

According to this embodiment, even when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a variable capacity compressor,
During the period when the two-way valve is open during operation of the compressor, oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, and the low-capacity compressor is not operated. Insufficient oil amount of the compressor on the side can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe.

At this time, the amount of the refrigerant distributed to each compressor is proportional to the square root of the differential pressure between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure.

Therefore, the ratio of the amount of oil discharged from each compressor differs from the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

[0124] In general, the high-capacity compressor has a larger amount of oil supply to the compression chamber than the low-capacity compressor, so that the oil content of the discharged refrigerant is larger than that of the low-capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalization bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalization bypass decreases.

Accordingly, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass is reduced, and continuous operation for a long time (for example,
(0 hours), the oil amount of the high-capacity compressor decreases. However, when the differential pressure between the upper shell portion and the lower shell portion detected by the differential pressure detecting device of at least one compressor is less than a predetermined lower limit differential pressure (for example, 0.003 kg / cm ² ), thereafter, all the compressions are performed. The two-way valve is closed until the differential pressure between the upper shell portion and the lower shell portion detected by the differential pressure detecting device of the machine is equal to or higher than a predetermined reference differential pressure (for example, 0.006 kg / cm ² ). When the valve is closed,
The oil moves from the low-capacity compressor having a high pressure in the shell to the high-capacity compressor having a low pressure in the shell via the oil equalizing pipe, and the high-capacity compressor operates continuously for a long time. Oil shortage can be prevented.

Further, since the shortage of the oil amount of each compressor is detected from the pressure difference between the upper shell and the lower shell, the oil discharge amount and the oil return amount of the compressor due to the difference in the operating conditions are not affected. The two-way valve can be controlled with high accuracy.

Therefore, the closing of the two-way valve is too slow or
Alternatively, the opening after the closing of the two-way valve is too early, the amount of oil in the compressor on the high capacity side is insufficient, and the closing of the two-way valve is too early, or after the closing of the two-way valve. Insufficient oil amount of the compressor on the low capacity side due to the opening being too slow can be prevented.
Thus, the oil amount of each compressor can be controlled to an appropriate amount.

Embodiment 4 Embodiment 4 of the present invention will be described with reference to FIGS.

FIG. 6 is a structural view of an oil equalizing system for a plurality of compressors according to a fourth embodiment of the present invention. In FIG. 6, reference numeral 6 denotes a suction pipe 5o upstream of a suction branch portion 4 to each compressor 1.
And a gas refrigerant outlet 7 for discharging only gas refrigerant
Is a communication pipe which communicates the gas refrigerant discharge port 7 with the oil equalizing pipe 3 and makes the pressure of the oil equalizing pipe 3 higher than the pressure in the shell of each compressor 1; One end communicates with the shells of the compressors 2b and 2c, the other end communicates with the suction pipe 5a of the compressor 2a, and an oil-equalizing bypass having a restriction in the middle of both ends. A two-way valve 16 is an oil level detector (for example, a plurality of float switches) for detecting the oil level of the compressor 1.

Here, the two-way valve control means 15 operates the two-way valve when the oil level detected by the oil level detector 16 of at least one of the compressors 1 becomes less than a predetermined lower limit oil level. 11 and then the oil level detectors 1 of all the compressors 1
When the oil level detected by 6 becomes equal to or higher than a predetermined reference oil level, the two-way valve 11 is opened. Note that three compressors 1 are connected in this embodiment, and the subscripts a, b, and c will be added to distinguish them.

FIG. 7 is a flowchart showing a method for controlling the two-way valve 11 of the oil equalizing system for a plurality of compressors according to the fourth embodiment of the present invention.

Referring to FIG. 7, first, at step 21, the oil level detector 16 detects the oil level H of the compressor 2. In step 22, the oil level H detected in step 21 of at least one of the compressors 1 is equal to a predetermined lower limit oil level Ho.
(For example, 3 cm) or more, return to step 21;
If it is less than the predetermined lower limit oil level Ho, the process proceeds to step 23.

In Step 23, the two-way valve 11 is closed. In step 24, the oil level detector 16 detects the oil level H of the compressor 1.

In step 25, if the oil level H detected in step 24 of all the compressors 1 is less than the predetermined reference oil level Hs (for example, 6 cm), the process returns to step 24, and the processing returns to step 24. If the oil level is higher than Hs, step 26
Proceed to. In step 26, the two-way valve 11 is opened, and the process returns to step 21.

Next, a method for controlling the oil amount of each compressor in the oil equalizing system for a plurality of compressors having the above configuration will be described.
Here, it is assumed that the plurality of compressors include compressors having different capacities or a compressor of a variable capacity system, and the compressor 1a has a lower capacity than the compressors 1b and 1c. Suppose there is.

First, when the compressor 1 starts operating, the two-way valve 11 is opened, so that the communication pipe 10 communicates with the gas refrigerant discharge port 7 of the gas-liquid separator 6 on the upstream side of the suction branch section 4. The pressure in the oil equalizing pipe 3 is higher than the pressure in the shell of the compressor 1.

Therefore, no oil flows out of the compressor 1a on the low capacity side to the oil equalizing pipe connection pipe 2a. Further, when the oil amount of the compressors 1b and 1c decreases and the oil level becomes lower than the lower limit oil level, the two-way valve 11 is closed, and the pressure in the shell is higher. The oil moves through the oil equalizing pipe 3 to the compressors 1b and 1c on the high capacity side where the pressure in the shell is low. When the oil amount of the compressors 1b and 1c increases and the oil level becomes equal to or higher than the standard oil level, the two-way valve 11 is opened, and the movement of the oil through the oil level pipe 3 is eliminated.

According to this embodiment, even when a plurality of compressors include compressors of different capacities, or when a plurality of compressors include a variable capacity compressor,
During the period when the two-way valve is open during operation of the compressor, oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, and the low-capacity compressor is not operated. Insufficient oil amount of the compressor on the side can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe.

At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the differential pressure between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the same as that of the oil equalizing pipe and the shell of each compressor. Is proportional to the square root of the differential pressure. Therefore, the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe are different. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, the compressor of the high capacity side has a larger oil supply amount to the compression chamber than the compressor of the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor of the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases.

However, when the oil level detected by the oil level detector of at least one of the compressors is less than a predetermined lower limit oil level (for example, 3 cm), thereafter, all the compressors In order to close the two-way valve until the oil level detected by the oil level detector reaches a predetermined reference oil level (for example, 6 cm), the shell is closed when the two-way valve is closed. The oil moves from the low-capacity compressor with a high internal pressure to the high-capacity compressor with a low internal pressure in the shell via the oil equalizing pipe, and the oil during the long-time continuous operation of the high-capacity compressor Insufficient quantity can be prevented.

Further, in order to detect the shortage of the oil amount of each compressor from the oil level, the oil discharge amount and the oil return amount of the compressor due to the difference in operating conditions, and the pressure inside the shell of the compressor are reduced. The two-way valve can be accurately controlled without being affected by variations in distribution.

Therefore, whether the closing of the two-way valve is too late,
Alternatively, the opening after the closing of the two-way valve is too early, the oil amount of the compressor on the high capacity side is insufficient, and the closing after the closing of the two-way valve is too early, or Insufficient oil amount of the compressor on the low capacity side because the opening after closing is too slow can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

[0150]

As described above, the invention according to claim 1 is
An oil equalization pipe connection pipe is provided near the standard oil level of the shell of the plurality of low pressure shell type compressors, and an oil equalization pipe communicating one end of each of the oil equalization pipe connection pipes, and an upstream of a suction branch portion to each compressor. A gas-liquid separator provided in the suction pipe on the side and having a gas refrigerant discharge port for discharging only the gas refrigerant, communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe in the shell of each compressor. With one end communicating near the standard oil level of some compressor shells, one end communicating with the suction pipe of another compressor, and a restrictor in the middle of both ends. It is equipped with a leveling oil bypass.

Accordingly, even when a plurality of compressors include compressors having different capacities, or when a plurality of compressors include a compressor of a variable capacity type, even if the compressor is in operation, In addition, the oil does not move from the shell of the low-capacity compressor to the high-capacity compressor via the oil equalizing pipe, and the shortage of the oil in the low-capacity compressor can be prevented.

If oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connecting pipe. At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the differential pressure between the oil equalizing pipe and the shell of each compressor, and the amount of oil returned is also the differential pressure between the oil equalizing pipe and the shell of each compressor. It is proportional to the square root of. Therefore, the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe are different. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows.
Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor via the oil equalizing pipe.

[0154] In general, the compressor on the high capacity side has a larger amount of oil supply to the compression chamber than the compressor on the low capacity side, so that the oil content of the discharged refrigerant is larger than that of the compressor on the low capacity side. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases. However, when all the compressors are stopped, the pressure inside the refrigeration cycle is equalized, and the oil moves through the oil equalizing pipe so that the oil level of each compressor becomes equal,
Insufficient oil amount of the compressor on the high capacity side can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

Further, according to the invention of claim 2, a plurality of low pressure shell type compressors are provided with oil equalizing pipe connecting pipes near the standard oil level of the shell, and one end of each of the oil equalizing pipe connecting pipes is connected. Oil equalizing pipe, a gas-liquid separator provided in a suction pipe upstream of a suction branch to each compressor, and having a gas refrigerant outlet for discharging only gas refrigerant, the gas refrigerant outlet and the oil equalizing pipe A communication pipe in which the pressure of the oil equalizing pipe is higher than the pressure in the shell of each compressor, one end of which communicates with the vicinity of the standard oil level of some of the compressor shells, and the other end of which is connected to the other compressor. Equipped with a two-way valve provided in the communication pipe, and an equalizing oil bypass having a restriction in the middle of both ends communicating with the suction pipe, and when the continuous operation time of cooling or heating becomes a predetermined time or more, the constant With two-way valve control means for closing the two-way valve only for a time. That.

Thus, even when a plurality of compressors include compressors of different capacities, or a plurality of compressors include a variable capacity compressor, the operation of the compressor during operation of the compressor may be reduced. During the period in which the two-way valve is open, oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil of the compressor on the low capacity side is prevented. Insufficient quantity can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe via the oil equalizing pipe connection pipe. At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the difference between the oil equalizing pipe and the shell of each compressor. It is proportional to the square root of pressure. Therefore, the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe are different. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, the higher capacity compressor has a larger oil supply to the compression chamber than the lower capacity compressor, so that the oil content of the discharged refrigerant is larger than that of the low capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is communicated with the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

Further, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases.

However, when the continuous operation time of the cooling or the heating exceeds a predetermined time (for example, 20 hours), the two-way valve is closed for a predetermined time (for example, 5 minutes). At the time of closing, oil moves from the compressor on the low-capacity side where the pressure in the shell is high to the compressor on the high-capacity side where the pressure in the shell is low through the oil equalizing pipe, and the high-capacity compressor continues to operate for a long time Insufficient oil amount during operation can be prevented. in this way,
The oil amount of each compressor can be controlled to an appropriate amount.

Further, according to the third aspect of the present invention, the oil equalizing pipe connection pipes are provided near the standard oil level of a plurality of low pressure shell type compressor shells, and one end of each oil equalizing pipe connection pipe is connected. Oil equalizing pipe, a gas-liquid separator provided in a suction pipe upstream of a suction branch to each compressor, and having a gas refrigerant outlet for discharging only gas refrigerant, the gas refrigerant outlet and the oil equalizing pipe A communication pipe in which the pressure of the oil equalizing pipe is higher than the pressure in the shell of each compressor, one end of which communicates with the vicinity of the standard oil level of some of the compressor shells, and the other end of which is connected to the other compressor. An oil-equalizing bypass communicating with the suction pipe and having throttles at both ends thereof, a two-way valve provided in the communication pipe, and a differential pressure detecting device for detecting a differential pressure between a shell upper part and a shell lower part of each compressor. And a shell detected by the differential pressure detecting device of at least one compressor. When the differential pressure between the upper portion and the lower portion of the shell is less than a predetermined lower limit differential pressure, the two-way valve is closed, and thereafter, the differential pressure between the upper shell portion and the lower shell portion detected by the differential pressure detecting devices of all the compressors is equal to a predetermined value. It is provided with a two-way valve control means for opening the two-way valve when the pressure becomes equal to or higher than a reference differential pressure.

Accordingly, even when a plurality of compressors include compressors of different capacities, or a plurality of compressors include a compressor of a variable capacity type, the operation of the compressor is not affected. During the period in which the two-way valve is open, oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil of the compressor on the low capacity side is prevented. Insufficient quantity can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe. At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the difference between the oil equalizing pipe and the shell of each compressor. It is proportional to the square root of pressure. Therefore, the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe are different. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

In general, the high-capacity compressor has a larger amount of oil supply to the compression chamber than the low-capacity compressor, so that the oil content of the discharged refrigerant is larger than that of the low-capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalization bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the low-pressure high-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

Further, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases.

However, if the differential pressure between the upper shell and the lower shell detected by the differential pressure detecting device of at least one compressor is lower than a predetermined lower differential pressure (for example, 0.003 kg / cm ² ), then In order to close the two-way valve until the differential pressure between the upper shell and the lower shell detected by the differential pressure detecting devices of all the compressors becomes equal to or higher than a predetermined reference differential pressure (for example, 0.006 kg / cm ² ), When the two-way valve is closed, the oil moves from the high-pressure side compressor having a high pressure in the shell to the high-capacity side compressor having a low pressure in the shell via the oil equalizing pipe, and the high-capacity side Insufficient oil amount during long-time continuous operation of the compressor can be prevented.

Further, since the shortage of the oil amount of each compressor is detected from the differential pressure between the upper shell and the lower shell, the oil discharge amount and the oil return amount of the compressor due to the difference in the operating conditions are not affected. The two-way valve can be controlled with high accuracy. Therefore,
The closing of the two-way valve is too slow or the opening of the two-way valve after closing is too early, and the oil volume of the compressor on the high capacity side is insufficient, and the closing of the two-way valve is too early. Or
Insufficient oil amount of the compressor on the low capacity side because the opening after the closing of the two-way valve is too slow can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

Further, in the invention according to claim 4, a plurality of low pressure shell type compressors are provided with oil equalizing pipe connecting pipes near the standard oil level of the shell, and one end of each of the oil equalizing pipe connecting pipes is connected. Oil equalizing pipe, a gas-liquid separator provided in a suction pipe upstream of a suction branch to each compressor, and having a gas refrigerant outlet for discharging only gas refrigerant, the gas refrigerant outlet and the oil equalizing pipe A communication pipe in which the pressure of the oil equalizing pipe is higher than the pressure in the shell of each compressor, one end of which communicates with the vicinity of the standard oil level of some of the compressor shells, and the other end of which is connected to the other compressor. Equipped with an oil level bypass communicating with the suction pipe, and having a throttle in the middle of both ends, a two-way valve provided on the communication pipe, and an oil level detector for detecting the oil level of each compressor. The oil level detected by the oil level detector of at least one compressor is a predetermined level. When the oil level is lower than the oil level limit, the two-way valve is closed. Thereafter, when the oil level height detected by the oil level detectors of all the compressors becomes equal to or higher than a predetermined reference oil level, the two-way valve is closed. It has two-way valve control means for opening the one-way valve.

Thus, even when a plurality of compressors include compressors of different capacities, or a plurality of compressors include a variable capacity compressor, the operation of During the period in which the two-way valve is open, oil does not move from the shell of the compressor on the low capacity side to the compressor on the high capacity side via the oil equalizing pipe, and the oil of the compressor on the low capacity side is prevented. Insufficient quantity can be prevented.

When oil is contained in the refrigerant flowing through the communication pipe, the oil is returned to the compressors together with the refrigerant from the oil equalizing pipe through the oil equalizing pipe connection pipe. At this time, the amount of refrigerant distributed to each compressor is proportional to the square root of the pressure difference between the oil equalizing pipe and the shell of each compressor, and the oil return amount is also the difference between the oil equalizing pipe and the shell of each compressor. It is proportional to the square root of pressure. Therefore, the ratio of the amount of oil discharged from each compressor and the ratio of the amount of oil returned from the communication pipe of each compressor via the oil equalizing pipe are different. Therefore, in some compressors, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, only the gas refrigerant separated by the gas-liquid separator flows from the suction pipe to the communication pipe, and no oil flows. Therefore, it is possible to prevent the shortage of the oil amount of some compressors due to the difference between the ratio of the discharge oil amount of each compressor and the ratio of the oil return amount from the communication pipe of each compressor through the oil equalizing pipe.

[0178] In general, the high-capacity compressor has a larger amount of oil supply to the compression chamber than the low-capacity compressor, so that the oil content of the discharged refrigerant is larger than that of the low-capacity compressor. In contrast, the oil content of the refrigerant distributed from the suction pipe to each compressor via the suction branch portion is equal. Therefore, in the high-capacity compressor, the returned oil amount is smaller than the discharged oil amount, and the oil amount decreases.

However, if the multi-end is connected to the integral low-pressure side compressor shell of the oil equalizing bypass and the multi-end is connected to the suction pipe of the high-capacity side compressor, the high-pressure low-pressure side compressor is high. The oil moves from the shell to the suction pipe on the high-capacity side where the pressure is low, so that the shortage of oil in the compressor on the high-capacity side can be prevented.

In addition, the oil temperature is low under low outside air temperature conditions, etc.
When the oil viscosity increases, or when the resistance of the throttle of the oil equalizing bypass increases due to clogging of foreign matter or the like, the amount of oil moving through the oil equalizing bypass decreases. Therefore, the amount of oil supplied to the high-capacity compressor due to the oil equalization bypass decreases, and if the continuous operation (for example, 30 hours) is continued for a long time, the oil amount of the high-capacity compressor decreases.

However, when the oil level detected by the oil level detector of at least one of the compressors becomes less than a predetermined lower limit oil level (for example, 3 cm), thereafter, all of the compressors In order to close the two-way valve until the oil level detected by the oil level detector reaches a predetermined reference oil level (for example, 6 cm), the shell is closed when the two-way valve is closed. The oil moves from the low-capacity compressor with a high internal pressure to the high-capacity compressor with a low internal pressure in the shell via the oil equalizing pipe, and the oil during the long-time continuous operation of the high-capacity compressor Insufficient quantity can be prevented.

Further, in order to detect the shortage of the oil amount of each compressor from the oil level, the oil discharge amount and the oil return amount of the compressor due to the difference in the operating conditions, and the pressure in the shell of the compressor are reduced. The two-way valve can be accurately controlled without being affected by variations in distribution.

Therefore, whether the closing of the two-way valve is too late,
Alternatively, the opening after the closing of the two-way valve is too early, the oil amount of the compressor on the high capacity side is insufficient, and the closing after the closing of the two-way valve is too early, or Insufficient oil amount of the compressor on the low capacity side because the opening after closing is too slow can be prevented. Thus, the oil amount of each compressor can be controlled to an appropriate amount.

[Brief description of the drawings]

FIG. 1 is a structural diagram of an oil equalizing system for a plurality of compressors according to a first embodiment of the present invention.

FIG. 2 is a structural diagram of an oil equalizing system for a plurality of compressors according to a second embodiment of the present invention.

FIG. 3 is a flowchart illustrating a control method of a two-way valve of the oil equalizing system for a plurality of compressors according to the second embodiment of the present invention.

FIG. 4 is a structural diagram of an oil equalizing system for a plurality of compressors according to a third embodiment of the present invention.

FIG. 5 is a flowchart illustrating a control method of a two-way valve of the oil equalizing system for a plurality of compressors according to the third embodiment of the present invention.

FIG. 6 is a structural diagram of an oil equalizing system for a plurality of compressors according to a fourth embodiment of the present invention.

FIG. 7 is a flowchart illustrating a control method of a two-way valve of the oil equalizing system for a plurality of compressors according to the fourth embodiment of the present invention.

FIG. 8 is a structural diagram of a conventional oil equalizing system for a plurality of compressors.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 compressor 2 equalizing pipe connection pipe 3 equalizing pipe 4 suction branch section 5 suction pipe 6 gas-liquid separator 7 gas refrigerant outlet 8, 10 communication pipe 9 equalizing bypass 11 two-way valve 12, 13, 15 two-way valve control Means 14 Differential pressure detecting device 16 Oil level detecting device

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michimi Kusaka 4-5-2-5 Takaidahondori, Higashiosaka-shi, Osaka Matsushita Refrigeration Co., Ltd.

Claims (4)

[Claims] An oil equalizing pipe connecting pipe is provided near a standard oil level of a shell of a plurality of low pressure shell type compressors, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connecting pipe is connected to each compressor. A gas-liquid separator provided in the suction pipe upstream of the suction branch portion and having a gas refrigerant discharge port for discharging only the gas refrigerant, and communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe by A communicating pipe that is higher than the pressure in the compressor shell;
A plurality of compressors having one end communicating with the vicinity of a standard oil level of a shell of a part of the compressor, the other end communicating with a suction pipe of another compressor, and an oil-equalizing bypass having a throttle in the middle of both ends. Oil leveling system. 2. An oil equalizing pipe connection pipe is provided near a standard oil level of a shell of a plurality of low-pressure shell type compressors, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connection pipe is connected to each compressor. A gas-liquid separator provided in the suction pipe upstream of the suction branch portion and having a gas refrigerant discharge port for discharging only the gas refrigerant, and communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe by A communicating pipe that is higher than the pressure in the compressor shell;
One end communicates with the vicinity of the standard oil level of the shell of some compressors, the other end communicates with the suction pipe of another compressor, and the oil equalizing bypass having a throttle on the way at both ends, and the communication pipe. Equipped with a two-way valve provided, when the continuous operation time of cooling or heating is equal to or more than a predetermined time, the two-way valve control means for closing the two-way valve for a fixed time, oil equalization of a plurality of compressors system. 3. An oil equalizing pipe connection pipe is provided near a standard oil level of a plurality of low pressure shell type compressor shells, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connection pipe is connected to each compressor. A gas-liquid separator provided in the suction pipe upstream of the suction branch portion and having a gas refrigerant discharge port for discharging only the gas refrigerant, and communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe by A communicating pipe that is higher than the pressure in the compressor shell;
One end communicates with the vicinity of the standard oil level of the shell of some compressors, the other end communicates with the suction pipe of another compressor, and the oil equalizing bypass having a throttle on the way at both ends, and the communication pipe. A two-way valve provided, a differential pressure detecting device for detecting a differential pressure between a shell upper portion and a shell lower portion of each compressor, and a shell upper portion and a shell lower portion detected by the differential pressure detecting device of at least one compressor. When the differential pressure is less than a predetermined lower limit differential pressure, the two-way valve is closed, and then the differential pressure between the upper shell and the lower shell detected by the differential pressure detectors of all the compressors is equal to or higher than a predetermined reference differential pressure. And a two-way valve control means for opening the two-way valve. 4. An oil equalizing pipe connecting pipe is provided near a standard oil level of a plurality of low pressure shell type compressor shells, and an oil equalizing pipe communicating with one end of each oil equalizing pipe connecting pipe is connected to each compressor. A gas-liquid separator provided in the suction pipe upstream of the suction branch portion and having a gas refrigerant discharge port for discharging only the gas refrigerant, and communicating the gas refrigerant discharge port with the oil equalizing pipe, and controlling the pressure of the oil equalizing pipe by A communicating pipe that is higher than the pressure in the compressor shell;
One end communicates with the vicinity of the standard oil level of the shell of some compressors, the other end communicates with the suction pipe of another compressor, and the oil equalizing bypass having a throttle on the way at both ends, and the communication pipe. A two-way valve provided, and an oil level detector for detecting the oil level of each compressor, wherein the oil level detected by the oil level detector of at least one of the compressors is When the oil level is less than a predetermined lower limit oil level, the two-way valve is closed, and thereafter, when the oil level detected by the oil level detectors of all the compressors is equal to or more than a predetermined reference oil level. An oil equalizing system for a plurality of compressors, comprising a two-way valve control unit that opens the two-way valve.