JP2017129310A - Refrigerating-cycle having a plurality of multiple stage compressors to be connected in parallel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To level the amount of lube oil within each housing while securing an injection amount in a configuration having a plurality of multiple stage compressors to be connected in parallel, and an injection circuit for supplying refrigerant gas with an intermediate pressure into respective housings of the multiple stage compressors.SOLUTION: A refrigerating-cycle 1 comprises: an oil leveling route 17 for connecting between housings 103A and 103B of a plurality of multiple stage compressors 11A and 11B; a plurality of gas injection circuits 20A and 20B for supplying gas refrigerant within a gas-liquid separator 14 to a corresponding housing of the multiple stage compressors; a plurality of bypass passages 30A and 30B for supplying the refrigerant extracted from a position between a chiller 12 and a first expansion valve 13 to a corresponding housing of the multiple stage compressors; bypass flow control valves 31A and 31B capable of changing the flow rate of at least any one of the bypass passages 20A and 20B of the plurality of multiple stage compressors; check valves 21A and 21B; and a control unit 40.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a refrigeration cycle including a plurality of multistage compressors connected in parallel and a circuit for supplying an intermediate-pressure refrigerant gas into the housing of each of the multistage compressors.

A refrigeration cycle having a gas injection circuit for supplying an intermediate-pressure refrigerant gas in a housing of a two-stage compressor having two compression mechanisms is known.
According to the two-stage compression and the injection of the intermediate pressure refrigerant, the compression efficiency can be ensured and the temperature of the refrigerant discharged from the compressor can be suppressed as compared with the case where the same refrigeration capacity is obtained by the first-stage compression.
Further, a refrigeration cycle including a plurality of two-stage compressors connected in parallel in order to widely change the refrigeration capacity is also known (Patent Document 1).

By the way, since the discharge amount and the return amount of the lubricant contained in the refrigerant gas from the compressor housing vary among a plurality of compressors connected in parallel, if the operation is continued for a long time, The lubricating oil is biased to some compressors depending on the operating conditions.
Therefore, an oil equalizing operation is performed in a timely manner in which housings of a plurality of compressors are connected by piping, a pressure difference is given between the housings, and lubricating oil is moved between the housings of the plurality of compressors according to the pressure difference.
In patent document 1, in order to give the pressure difference required for oil equalization, the gas injection circuit is utilized. In Patent Document 1, a flow rate adjusting valve is provided in each of the gas injection circuits that supply intermediate pressure refrigerant gas into a plurality of compressor housings. The lubricating oil in the housing is averaged between the housings.

Japanese Patent No. 5193011

In order to achieve oil leveling, it is possible to increase the rotational speed of some compressors and increase the pressure loss of refrigerant sucked into and discharged from the compressors, thereby giving a pressure difference between the housings of the multiple compressors. It is done.
However, it is possible to change the pressure in each housing and thereby provide a pressure difference between the housings by connecting in parallel a single-stage compressor in which only low-pressure refrigerant gas is supplied into the housing. Limited to cases.
If not only low-pressure refrigerant gas but also intermediate pressure gas from the gas injection circuit is supplied to each housing at the same flow rate, even if the number of rotations of some compressors is increased, the pressure in each housing Since it does not change so much, it is difficult to obtain the pressure difference between the housings necessary for moving the lubricating oil.
Therefore, it is conceivable to increase or decrease the supply amount of the intermediate-pressure refrigerant gas into the compressor housing by controlling the opening degree of the flow rate adjustment valve provided in each gas injection circuit as in Patent Document 1. However, if the supply amount of the intermediate pressure refrigerant gas is decreased, there is a possibility that a necessary injection amount (flow rate) cannot be secured.

  As described above, the present invention is necessary in a refrigeration cycle including a plurality of multistage compressors connected in parallel and a gas injection circuit for supplying a refrigerant gas having an intermediate pressure into the housing of each of the multistage compressors. The purpose is to average the lubricating oil in each housing while ensuring a sufficient injection amount.

The present invention is a refrigeration cycle comprising a plurality of multi-stage compressors connected in parallel, each having a housing containing a multi-stage compression mechanism including a low-stage compression mechanism and a high-stage compression mechanism. A multi-stage compressor, a cooler, a first pressure reducing unit, a gas-liquid separator, a second pressure reducing unit, and an evaporator are sequentially connected to form a refrigerant circuit, and a plurality of multi-stage compressor housings are connected to each other. A plurality of gas injection circuits for supplying an oil equalizing path, a gas refrigerant in the gas-liquid separator between a low-stage compression mechanism and a high-stage compression mechanism in a corresponding multi-stage compressor housing, and a cooler And a plurality of bypass paths for supplying the refrigerant extracted from between the first decompression sections between the low-stage compression mechanism and the high-stage compression mechanism in the corresponding multi-stage compressor housing, Each of the multistage compressor A bypass valve that can change the flow rate of at least one of the ipass paths, a check valve that is provided in the gas injection circuit and prevents the reverse flow of the gas refrigerant flowing into the housing, and a controller that controls the opening of the bypass valve And.
The “cooler” in the present invention lowers the temperature of the refrigerant and includes a condenser or a gas cooler.

  In the refrigeration cycle of the present invention, it is preferable that the bypass path causes the refrigerant extracted from between the cooler and the first decompression unit to flow into the gas injection circuit.

  In the refrigeration cycle of the present invention, the control unit can control the opening degree of the bypass valve at least during the oil leveling operation in which the lubricating oil is moved between the housings of the plurality of multistage compressors through the oil leveling path.

  The refrigeration cycle of the present invention preferably includes a discharge temperature sensor that detects a discharge temperature that is the temperature of the refrigerant discharged from the multistage compressor, and the control unit preferably controls the opening degree of the bypass valve using the discharge temperature. .

  In the refrigeration cycle of the present invention, the bypass valve is a flow rate adjustment valve capable of adjusting the flow rate, and is preferably provided in each of the plurality of bypass paths.

In the refrigeration cycle of the present invention, CO ₂ is preferably used as the refrigerant circulating in the refrigerant circuit.

  The refrigerant extracted from between the cooler and the first decompression unit to the bypass path is in a liquid or liquid phase dominant state and has a higher pressure than the gas refrigerant extracted from the gas-liquid separator. Therefore, by controlling the opening of the bypass valve and making a difference in the flow rate among the plurality of bypass paths, the pressure difference between the housings required to move the lubricating oil in the housing through the oil leveling path is realized. be able to. In the present invention, in order to obtain the pressure difference between the housings, it is necessary to reduce the flow rate of the gas refrigerant in a part of the plurality of gas injection circuits that supply the gas refrigerant extracted from the gas-liquid separator to the housing. Absent.

In the housing of the multistage compressor in the present invention, in addition to the low-temperature gas refrigerant extracted from the gas-liquid separator to the gas injection circuit, it is extracted from between the cooler and the first pressure reducing unit to the bypass path. Extra low-temperature refrigerant will be supplied.
Therefore, not only during oil leveling operation, but depending on the injection using only the gas injection circuit, the bypass path is not used in operating conditions where the temperature and pressure in the housing or the temperature of the refrigerant discharged from the compressor may exceed the upper limit. Can be used.
In other words, it is possible to prevent overheating of the refrigerant discharged from the compressor and excessive increase in the temperature and internal pressure of the housing while securing the necessary injection amount as a whole, including injection of low-temperature refrigerant through the bypass path. .

  Since a refrigerant having a higher density than the gas refrigerant flowing through the gas injection circuit flows in the bypass path in the present invention, the bypass valve has a flow control valve provided in the gas injection circuit when the flow rate of the gas injection circuit is increased or decreased. Also, those having a small diameter can be used. Therefore, the cost required for the valve can be suppressed.

It is a schematic diagram which shows the refrigerating cycle which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the refrigerating cycle which concerns on 2nd Embodiment of this invention. It is a schematic diagram which shows the refrigerating cycle which concerns on the modification of this invention. It is a schematic diagram which shows the refrigerating cycle which concerns on the other modification of this invention. It is a schematic diagram which shows the refrigerating cycle which concerns on a comparative example with embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[First Embodiment]
A refrigeration cycle 1 shown in FIG. 1 includes a refrigerant circuit 10 including two two-stage compressors 11A and 11B (hereinafter referred to as “compressors”) connected in parallel and a two-stage compressor 11A and 11B. An oil path 17, two gas injection circuits 20A and 20B, two bypass paths 30A and 30B prepared in correspondence with the two compressors 11A and 11B, and a control unit 40 that controls the overall operation of the refrigeration cycle 1. I have.
11A, 20A, and 30A, which are suffixed with “A”, correspond to each other. Similarly, the ones denoted by “B” at the end, such as 11B, 20B, and 30B, correspond to each other.

The refrigeration cycle 1 of the present embodiment can be used for, for example, a refrigeration apparatus, an air conditioner, a water heater, and the like.
The control unit 40 changes the refrigeration capacity by operating only one or both of the compressors 11A and 11B according to the heat load.

The refrigerant circuit 10 is configured by sequentially connecting the compressors 11A and 11B, the cooler 12, the first expansion valve 13, the gas-liquid separator 14, the second expansion valve 15, and the evaporator 16. Has been.
In the present embodiment, CO ₂ that is a natural refrigerant is used as the refrigerant circulating in the refrigerant circuit 10.
However, other refrigerants such as ammonia, propane, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), etc. can also be used.

The compressor 11A houses the low-stage compression mechanism 101 and the high-stage compression mechanism 102, an electric motor (not shown) that drives the compression mechanisms 101 and 102, and the compression mechanisms 101 and 102 and the electric motor in a sealed state. And a housing 103A. The compressors 11 </ b> A and 11 </ b> B are configured to have a variable compression capacity according to the rotation speed under the control of the control unit 40.
As the low-stage compression mechanism 101, a rotary piston type compression mechanism is employed in the present embodiment.
As the high-stage compression mechanism 102, a scroll-type compression mechanism is employed in the present embodiment.
The above is only an example, and the compression mechanisms 101 and 102 can be appropriately configured.

  The low-pressure refrigerant sucked into the low-stage compression mechanism 101 in the housing 103A through the suction port P1 is compressed to an intermediate pressure by the low-stage compression mechanism 101, and is in the housing 103A above the low-stage compression mechanism 101. It is discharged into the space. The refrigerant discharged from the low-stage compression mechanism 101 into the housing 103A and the refrigerant supplied from the gas injection circuit 20A into the housing 103A are sucked by the high-stage compression mechanism 102. Then, the high-pressure gas refrigerant compressed by the high-stage compression mechanism 102 is discharged from the discharge port P2 to the refrigerant circuit 10.

  Here, the “intermediate pressure” refers to the pressure of the refrigerant sucked into the low-stage compression mechanism 101 via the second expansion valve 15 and the evaporator 16, and the pressure of the refrigerant discharged from the high-stage compression mechanism 102. The pressure between. A relatively low pressure based on “intermediate pressure” is referred to as “low pressure”, and a relatively high pressure is referred to as “high pressure”.

  Similarly to the compressor 11A, the compressor 11B also includes a low-stage compression mechanism 101 and a high-stage compression mechanism 102, an electric motor (not shown) that drives the compression mechanisms 101 and 102, the compression mechanisms 101 and 102, and And a housing 103B that houses the electric motor in a sealed state.

Lubricating oil supplied to sliding parts such as the compression mechanisms 101 and 102 and motor bearings is stored in the bottoms of the housings 103A and 103B of the compressors 11A and 11B. In order to sufficiently supply the lubricating oil to the sliding portion to ensure reliability, it is necessary that a predetermined amount of lubricating oil is present in the housings 103A and 103B.
The lubricating oil in the housings 103A and 103B is discharged from the housings 103A and 103B in a state of being mixed with the refrigerant in the housings 103A and 103B, and returns to the housings 103A and 103B through the refrigerant circuit 10.
In order to ensure sufficient reliability, an oil return mechanism is provided as needed to separate the lubricating oil from the refrigerant discharged by the high-stage compression mechanism 102 and return it to the housings 103A and 103B.

Even when the same amount of lubricating oil is present in the housings 103A and 103B of the compressors 11A and 11B at the start of operation of the compressors 11A and 11B, the compressors 11A and 11B will continue to be operated. The amount of lubricating oil in the housings 103A and 103B is biased between.
This occurs due to a difference in discharge amount due to individual differences between the compressors 11A and 11B, a difference in resistance of the oil return mechanism, and the like.

In order to move the lubricating oil between the housing 103A of the compressor 11A and the housing 103B of the compressor 11B, and to secure a necessary amount of lubricating oil in each of the housings 103A and 103B, the housings 103A and 103B communicate with each other through the oil leveling path 17. Connected by.
The oil leveling path 17 connects the inside of the housing 103A of the compressor 11A and the inside of the housing 103B of the compressor 11B near the bottoms of the housings 103A and 103B.

The oil leveling path 17 is provided with an oil leveling valve 171 that opens and closes the oil leveling path 17.
The oil equalizing valve 171 is opened during the oil equalizing operation of the refrigeration cycle 1 performed in a timely manner. The oil leveling valve 171 is closed during operation other than during the leveling operation.
In this embodiment, in order to obtain a pressure difference necessary for moving the lubricating oil between the housings 103A and 103B of the compressors 11A and 11B through the oil equalization path 17 during the oil leveling operation, in this embodiment, bypass paths 30A and 30B described later are provided. A pressure can be introduced into the housings 103A and 103B through each.

  In the present embodiment, the first expansion valve 13, the gas-liquid separator 14, and the second expansion valve 15 are disposed between the cooler 12 and the evaporator 16. The high-temperature and high-pressure gas refrigerant discharged from the compressors 11 </ b> A and 11 </ b> B is liquefied by releasing heat in the cooler 12. The liquid refrigerant that has flowed out of the cooler 12 is made into a gas-liquid two-phase by depressurization in the first expansion valve 13 and is gas-liquid separated in the gas-liquid separator 14. The gas refrigerant in the gas-liquid separator 14 is supplied between the low-stage compression mechanism 101 and the high-stage compression mechanism 102 in the housings 103A and 103B of the compressors 11A and 11B through the gas injection circuits 20A and 20B. .

  In this embodiment, the intermediate pressure gas refrigerant is extracted from the gas-liquid separator 14 by the pipe 20 common to the gas injection circuits 20A and 20B, and then branched to the gas injection circuit 20A and the gas injection circuit 20B. .

  In the refrigeration cycle 1, the low-stage compression mechanism 101 and the high-stage compression mechanism are used for the purpose of suppressing the temperature of the refrigerant discharged from the compressors 11A and 11B, improving the compression efficiency, lowering the internal pressure of the housings 103A and 103B, and the like. A low-temperature intermediate-pressure gas refrigerant is supplied between the gas injection circuit 20A and the gas injection circuit 20B.

The injection gas refrigerant extracted from the gas-liquid separator 14 to the gas injection circuits 20 </ b> A and 20 </ b> B has not undergone pressure reduction by the second expansion valve 15 and heat absorption by the evaporator 16.
The pressure of the injection gas refrigerant corresponds to an intermediate pressure. Since the temperature of the injection gas refrigerant is lower than the temperature of the refrigerant in the housings 103A and 103B, the injection gas refrigerant is sucked into the high-stage compression mechanism 102 together with the refrigerant in the housings 103A and 103B and compressed. The temperature of the refrigerant discharged from the stage side compression mechanism 102 is suppressed.

In particular, when CO ₂ that tends to increase the maximum temperature and the maximum pressure of the refrigerant in the refrigeration cycle 1 is used as the refrigerant, the injection of the intermediate pressure / low temperature refrigerant is effective.
Considering the temperature at which the motor coils in the housings 103A and 103B can be used, maintaining the quality of the lubricating oil, the efficiency of the refrigeration cycle, etc., the temperature and pressure in the housings 103A and 103B and the discharge by the injection of the intermediate pressure / low temperature refrigerant It is necessary to keep the temperature of the refrigerant below the allowable limit. For this purpose, it is necessary to secure an injection amount (injection flow rate) that is greater than or equal to a predetermined value.

Next, the bypass paths 30A and 30B, which are the main features of the present embodiment, will be described.
The bypass paths 30A and 30B connect between the cooler 12 and the first expansion valve 13 and the corresponding gas injection circuits 20A and 20B.
By the bypass paths 30A and 30B, the refrigerant that has passed through the cooler 12 flows into the gas injection circuits 20A and 20B without being passed through the first expansion valve 13 and the gas-liquid separator 14 (bypassed), and the gas injection circuits 20A and 20B. 20B is supplied between the low-stage compression mechanism 101 and the high-stage compression mechanism 102 in the housings 103A and 103B.

  By ensuring the required injection amount, the bypass paths 30A and 30B satisfy the temperature of the discharged refrigerant, the internal pressure of the housings 103A and 103B, the cycle efficiency, and the like, and the pressure difference between the housings 103A and 103B necessary for oil leveling. In order to obtain the above, the refrigeration cycle 1 is provided.

The bypass refrigerant extracted from between the cooler 12 and the first expansion valve 13 to the bypass paths 30 </ b> A and 30 </ b> B has a low temperature because it passes through the cooler 12. Further, since the bypass refrigerant does not pass through the first expansion valve 13, it is in a liquid or liquid phase dominant state, and has a pressure higher than that of the gas refrigerant extracted from the gas-liquid separator 14 to the gas injection circuits 20A and 20B. Is expensive. By supplying the bypass refrigerant into the housings 103A and 103B, the pressure for moving the lubricating oil between the housings 103A and 103B while keeping the temperature of the discharged refrigerant and the internal pressure of the housings 103A and 103B low below an allowable value. A difference can be obtained.
The low-temperature refrigerant supplied into the housings 103A and 103B through the bypass paths 30A and 30B is a small amount with respect to the gas discharged into the housings 103A and 103B by the low-stage compression mechanism 101, and is mixed with the discharged gas. Sometimes it evaporates and is sucked into the higher stage compression mechanism 102.
Since a bypass refrigerant having a pressure higher than that of the gas refrigerant extracted from the gas-liquid separator 14 flows in, the gas injection circuit 20A is provided with a check valve 21A, and the gas injection circuit 20B is provided with a check valve 21B. It has been. By these check valves 21A and 21B, it is possible to prevent the reverse flow of the refrigerant flowing through the gas injection circuits 20A and 20B toward the housings 103A and 103B, respectively.

The bypass path 30A is provided with a bypass flow rate adjustment valve 31A capable of adjusting the flow rate, and the bypass path 30B is provided with a bypass flow rate adjustment valve 31B capable of adjusting the flow rate.
By operating the opening degree of each of the bypass flow rate adjusting valves 31A and 31B by the control unit 40 during the oil leveling operation, the pressure in the housings 103A and 103B of the compressors 11A and 11B is changed, and between the housings 103A and 103B. A pressure difference can be given.

Hereinafter, the effects of the bypass paths 30A and 30B of the present embodiment are compared with the case where the flow rate of the gas refrigerant extracted from the gas-liquid separator 14 to the gas injection circuits 20A and 20B is adjusted (comparative example). Will be explained.
A comparative example is a refrigerant cycle as shown in FIG.
In the refrigeration cycle shown in FIG. 5, the gas injection circuit 20A is provided with a flow rate adjustment valve 91A, and the gas injection circuit 20B is provided with a flow rate adjustment valve 91B.
It is considered that a pressure difference necessary for oil leveling is given between the housings 103A and 103B by controlling the opening degree of the flow rate adjusting valves 91A and 91B by the control unit 90 during the oil leveling operation.

The pressures in the housings 103A and 103B change based on the flow rates of the gas injection circuits 20A and 20B according to the opening degree of the flow rate adjusting valves 91A and 91B.
For example, when the flow rate is reduced by the flow rate adjusting valve 91A, the pressure in the housing 103A of the compressor 11A becomes relatively small, and when the flow rate is increased by the flow rate adjusting valve 91A, the pressure in the housing 103B of the compressor 11B is reduced. It becomes relatively large. If it does so, lubricating oil will move through the oil equalization path | route 17 according to the pressure difference between housing 103A, 103B of compressor 11A, 11B.

  In the comparative example, in order to realize a pressure difference between the housings 103A and 103B necessary for oil leveling, a difference is given to the flow rate of the injection refrigerant supplied to the housings 103A and 103B between the compressor 11A and the compressor 11B. There is a need. Therefore, it is necessary to reduce the flow rate of one of the gas injection circuits 20A and 20B, and there is a possibility that a necessary injection amount cannot be ensured for the compressor 11A with the reduced flow rate.

Unlike the above comparative example, in this embodiment (FIG. 1), there is no difference in the flow rate of the gas refrigerant extracted from the gas-liquid separator 14 to the gas injection circuits 20A and 20B, and the bypass flow rate. A pressure difference is given between the housings 103A and 103B by the flow rate difference between the bypass passages 30A and 30B adjusted by the adjusting valves 31A and 31B.
The flow rate of the refrigerant extracted to the bypass paths 30A and 30B is sufficient as long as it is necessary to move the lubricating oil between the housings 103A and 103B.
As described above, the refrigerant extracted into the bypass passages 30A and 30B from between the cooler 12 and the first expansion valve 13 is in a liquid or liquid phase dominant state and extracted from the gas-liquid separator 14. Since the pressure is higher than that of the gas refrigerant, if a small amount is extracted into the bypass passages 30A and 30B, the oil equalization passage 17 is set to the maximum when one of the bypass flow rate adjusting valves 31A and 31B is fully opened and the other is fully closed. A pressure difference between the housings 103A and 103B necessary for the movement of the lubricating oil can be ensured.

  In addition, since the refrigerant flowing through the bypass paths 30A and 30B is in a liquid or liquid phase dominant state and has a higher density than the gas refrigerant, the bypass flow rate adjusting valves 31A and 31B of the bypass paths 30A and 30B include a gas injection circuit 20A. , 20B flow regulating valves 91A, 91B (FIG. 5) can be used. Therefore, in this embodiment, the cost which a flow volume adjustment valve requires with respect to a comparative example can be held down.

The control by the control unit 40 during the oil leveling operation will be described.
The operation of the refrigeration cycle 1 is continued for a long time, and the refrigeration cycle 1 is performed at an appropriate timing at which there may be a deviation in the lubricating oil between the housing 103A of the compressor 11A and the housing 103B of the compressor 11B. Is transferred to the oil leveling operation by the control unit 40.

The control unit 40 of the present embodiment integrates the amount of lubricating oil that has flowed out of the housings 103A and 103B in accordance with the operating conditions, and estimates the state of unevenness of the lubricating oil between the housings 103A and 103B. 1 is shifted to oil leveling operation. Specifically, the oil equalizing valve 171 is opened and the opening degree of the bypass flow rate adjusting valves 31A and 31B is set. Every time the oil leveling operation is performed, the accumulated amount of the lubricating oil that has flowed out is reset.
The oil leveling operation may be performed every predetermined operation duration time.

  The pressure difference according to the direction in which the lubricating oil moves from the housing 103A of the compressor 11A to the housing 103B of the compressor 11B, and conversely, the inside of the housing 103A of the compressor 11A from the housing 103B of the compressor 11B. A pressure difference corresponding to the direction in which the lubricating oil moves is applied to the housings 103A and 103B of the compressors 11A and 11B. Then, even if it is unclear which housing 103A, 103B of compressor 11A, 11B has a lot of lubricating oil or which housing 103A, 103B has little lubricating oil, the lubricating oil in housings 103A, 103B Can be averaged.

Therefore, the control unit 40 first determines that the opening degree of the bypass flow rate adjustment valve 31A is larger than the opening degree of the bypass flow rate adjustment valve 31B so that the pressure of the housing 103A of the compressor 11A> the pressure of the housing 103B of the compressor 11B. The opening degree of each of the bypass flow rate adjusting valves 31A and 31B is set so as to increase. Thereafter, the bypass flow rate adjustment is performed so that the opening degree of the bypass flow rate adjustment valve 31B is larger than the opening degree of the bypass flow rate adjustment valve 31A so that the pressure of the housing 103A of the compressor 11A <the pressure of the housing 103B of the compressor 11B. The respective opening degrees of the valves 31A and 31B are set.
Then, the lubricating oil is averaged between the housings 103A and 103B of the compressors 11A and 11B regardless of the state of unevenness of the lubricating oil in the respective housings 103A and 103B before the oil leveling operation.

  In the present embodiment, it is allowed to contribute to the realization of the pressure difference between the housings 103A and 103B by increasing the number of revolutions of the compressors 11A and 11B and increasing the pressure loss of the refrigerant sucked and discharged. Is done.

  By the way, if the bypass flow rate adjusting valves 31A and 31B are open, the corresponding bypass paths 30A and 30B are open. Therefore, the cooler 12 is provided in the housings 103A and 103B through the open bypass paths 30A and 30B. And a low-temperature refrigerant extracted from between the first expansion valve 13 and the first expansion valve 13. Low-temperature gas refrigerant is supplied to the housings 103A and 103B through the gas injection circuits 20A and 20B. In addition, extra low-temperature refrigerant is supplied through the open bypass paths 30A and 30B. .

Therefore, depending on the gas injection using only the gas injection circuits 20A and 20B, the temperature and pressure in the housings 103A and 103B and the temperature of the refrigerant discharged from the compressors 11A and 11B may exceed the upper limit. Bypass paths 30A and 30B can be used.
The control unit 40 of the present embodiment performs the injection of the low-temperature refrigerant through the bypass paths 30A and 30B by controlling the opening degree of the bypass flow rate adjusting valves 31A and 31B, not only during the oil leveling operation.

The controller 40 uses the temperature of the refrigerant discharged from the compressors 11A and 11B as an index when controlling the opening degree of each of the bypass flow rate adjusting valves 31A and 31B.
For this purpose, the refrigerant circuit 10 includes a temperature sensor 32A that detects the temperature of the refrigerant discharged from the compressor 11A and a temperature sensor 32B that detects the temperature of the refrigerant discharged from the compressor 11B.
Hereinafter, the temperature of the refrigerant discharged from the compressors 11A and 11B is referred to as “discharge temperature”.

  As shown in FIG. 1, the control unit 40 determines whether or not the discharge temperature acquisition unit 41 that acquires the discharge temperature from the temperature sensors 32A and 32B and the discharge temperature detected by the temperature sensors 32A and 32B exceeds a predetermined threshold value. And a degree-of-opening setting unit 43 that sets the degree of opening of the bypass flow rate adjusting valves 31A and 31B according to the result of determination by the determination unit 42.

A flow of control by the control unit 40 will be described.
The discharge temperature acquisition unit 41 of the control unit 40 acquires the discharge temperatures detected by the temperature sensors 32A and 32B, respectively.
Next, the determination unit 42 of the control unit 40 determines whether or not the acquired discharge temperatures of the compressors 11A and 11B exceed a predetermined threshold value.
The opening degree setting unit 43 of the control unit 40 is connected to the compressor housing (one or both of 103A and 103B) corresponding to the discharge temperature exceeding the threshold when the discharge temperature exceeds the threshold. The bypass flow rate adjustment valve (one or both of 31A and 31B) in the bypass path is opened at a predetermined opening.

For example, if the discharge temperature of the compressor 11A exceeds the threshold value, the opening degree setting unit 43 supplies the low-temperature refrigerant into the housing 103A of the compressor 11A by opening the bypass flow rate adjustment valve 31A. The refrigerant is compressed by the high-stage compression mechanism 102 together with the refrigerant in the housing 103A, so that the discharge temperature of the compressor 11A is suppressed.
If the discharge temperature of the compressor 11B exceeds the threshold value, the opening degree setting unit 43 opens the bypass flow rate adjustment valve 31B to supply low-temperature refrigerant into the housing 103B of the compressor 11B, and the compressor 11B. Suppresses the discharge temperature.
As the deviation of the discharge temperature from the threshold temperature is larger, it is preferable to set the bypass flow rate adjusting valves 31A and 31B to a larger opening. Thereby, the discharge temperature can be quickly suppressed below the threshold value.
When the discharge temperature is equal to or lower than the threshold value, it is not necessary to open the bypass flow rate adjustment valves 31A and 31B in order to suppress the discharge temperature.

As described above, by controlling the opening degree of the bypass flow rate adjusting valves 31A and 31B using the discharge temperature, the temperature and the internal pressure of the housings 103A and 103B can be suppressed to an allowable value or less as well as the discharge temperature.
The bypass flow rate adjusting valves 31A and 31B may be controlled using detected values such as the temperature and internal pressure of the housings 103A and 103B instead of the discharge temperature, or at a predetermined opening determined according to the operating conditions. it can.

As described above, in the present embodiment, the refrigerant having a higher pressure than the gas refrigerant extracted from the gas-liquid separator 14 and supplied to the housings 103A and 103B passes through the bypass passages 30A and 30B. , 103B, and the flow rate of each of the bypass paths 20A, 20B is given a difference by controlling the opening degree of the bypass flow rate adjusting valves 31A, 31B.
With this configuration, at the time of the oil leveling operation, the pressure difference can be given between the housings 103A and 103B of the compressor 11A and the compressor 11B to achieve the leveling.
Further, not only during the oil leveling operation, the compressor 11A, while ensuring the necessary injection amount as a whole, together with the injection through the gas injection circuits 20A, 20B, by injection of the low-temperature refrigerant through the bypass paths 30A, 30B. It is possible to prevent the refrigerant discharged from 11B from being overheated and the temperatures and internal pressures of the housings 103A and 103B from becoming excessive.

  In the present embodiment, the flow rates of the bypass paths 30A and 30B can be adjusted to appropriate flow rates by the bypass flow rate adjusting valves 31A and 31B, respectively, according to the discharge temperatures of the compressors 11A and 11B. Therefore, for example, the bypass flow rate adjusting valves 31A and 31B are controlled so that the opening degree increases as the deviation of the discharge temperature from the threshold value increases, and the discharge temperature deviating from the threshold value quickly falls below the threshold value. It becomes possible to control the temperature appropriately.

  Furthermore, in this embodiment, the piping for injection is united downstream from the inflow positions of the bypass paths 30A and 30B to the gas injection circuits 20A and 20B, and the injection port P3 that receives the injection refrigerant is housed. It is only necessary to provide one for each of 103A and 103B. Therefore, compared with the case where the gas injection circuit 20A and the bypass path 30A (or the gas injection circuit 20B and the bypass path 30B) are individually configured, weight and cost can be suppressed.

  It is also possible to use an on / off valve instead of the flow rate adjusting valves 21A and 31B. For example, ON / OFF valves arranged in the bypass paths 30A, 30B are intermittently turned ON / OFF, the ON ratio per unit time is changed, or a plurality of ON / OFF valves are connected in parallel to each of the bypass paths 30A, 30B. By providing and changing the ON / OFF number ratio of these on / off valves, the same function as the flow rate adjusting valve can be realized.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG.
The second embodiment shows a more basic circuit for supplying a refrigerant having a temperature lower than that of the injection gas refrigerant to the housings 103A and 103B of the compressors 11A and 11B.
In the refrigeration cycle 2 shown in FIG. 2, the bypass paths 30A and 30B are not connected to the gas injection circuits 20A and 20B, but are directly connected to the housings 103A and 103B.
The check valves 21A and 21B provided in the gas injection circuits 20A and 20B prevent the refrigerant from flowing back in the gas injection circuits 20A and 20B. Also by the configuration shown in FIG. 2, the opening degree of the bypass flow rate adjusting valves 31A and 31B is controlled by the control unit 40 to give a flow rate difference to the bypass paths 30A and 30B, so that between the housings 103A and 103B necessary for oil leveling. A pressure difference can be obtained.
Further, even under severe operating conditions with respect to the allowable value such as the discharge temperature, the injection refrigerant necessary to prevent overheating is secured by the injection refrigerant supplied into the housings 103A and 103B through the bypass paths 30A and 30B, respectively. be able to.

The refrigeration cycle 3 shown in FIG. 3 includes a pressure sensor 33A that detects the pressure of the injection refrigerant flowing into the injection port P3 of the housing 103A of the compressor 11A, and an injection that flows into the injection port P3 of the housing 103B of the compressor 11B. And a pressure sensor 33B for detecting the pressure of the refrigerant.
The control unit 40 can control the opening degree of the bypass flow rate adjusting valves 31A and 31B based on the pressures detected by the pressure sensors 33A and 33B so that a necessary and sufficient flow rate difference is applied to the bypass paths 30A and 30B. it can. By doing so, the pressure difference between the housings 103A and 103B necessary for oil leveling can be obtained more reliably.

  Further, in order to more appropriately control the discharge temperature and the like of the compressors 11A and 11B, the control unit 40 uses the pressure detected by the pressure sensors 33A and 33B in addition to the discharge temperature detected by the temperature sensors 32A and 32B. Thus, the opening degree of the corresponding bypass flow rate adjusting valves 31A, 31B can be controlled.

  In the refrigeration cycle 2 shown in FIG. 2, pressure sensors 33A and 33B may be provided in the vicinity of the injection port P3 ′ into which the injection refrigerant from the bypass paths 30A and 30B flows. Also in that case, the opening degree of the bypass flow rate adjusting valves 31A and 31B can be controlled by the control unit 40 using the pressure detected by the pressure sensors 33A and 33B.

In addition to the above, as long as the gist of the present invention is not deviated, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.
Instead of the bypass flow rate adjustment valves 31A and 31B of the refrigeration cycle 1 in FIG. 1, on / off valves can be used. For example, the controller 40 opens the on / off valve corresponding to the bypass path 30A and closes the on / off valve corresponding to the bypass path 30B, thereby moving the lubricant between the housings 103A and 103B of the compressors 11A and 11B. A necessary pressure difference can be provided.
Further, if the discharge temperature from the compressors 11A and 11B exceeds a threshold value, the restriction of the discharge temperature and the like is protected by opening an on / off valve of a bypass path corresponding to the compressor whose discharge temperature exceeds the threshold value. be able to.

In the refrigeration cycle of the present invention, it is sufficient if the oil can be leveled between the housings 103A and 103B of the compressor while at least securing the injection amount. The discharge temperature limitation may not be necessary in the case of a compressor operated at a constant speed or from the viewpoint of displacement.
Therefore, in the refrigeration cycle of the present invention, the bypass valve can be provided only in the bypass paths 30A and 30B corresponding to the respective housings of the plurality of compressors, and the flow rate needs to be changed. , 30B need not be provided with a bypass valve.
For example, as in the refrigeration cycle 4 shown in FIG. 4, the flow rates of the bypass paths 30A and 30B are made different from each other by giving a difference in the diameters of the bypass paths 30A and 30B, and only the bypass path 30A having a large flow rate is turned on / off. 35 can be provided.
In the above configuration, a pressure difference for oil equalization can be given between the housings 103A and 103B by opening the on / off valve 35 or closing the on / off valve 35.

  The refrigeration cycles 1, 2 and 3 described above are configured to include two compressors 11A and 11B connected in parallel, but are configured to include three or more compressors connected in parallel. Also good. Also in this case, the housings of the plurality of compressors are connected to each other by an oil equalizing path. And the opening degree of the bypass valve of the bypass path prepared for each compressor is controlled. For example, when a bypass valve corresponding to one of the three compressors is opened at a predetermined opening degree and the bypass valves corresponding to the remaining two compressors are closed, the housing having a relatively high pressure, Lubricating oil can be moved to a relatively low pressure housing.

1, 2, 3, 4 Refrigeration cycle 10 Refrigerant circuit 11A, 11B Compressor (multistage compressor)
12 cooler 13 1st expansion valve (1st decompression part)
14 Gas-liquid separator 15 Expansion valve (second decompression unit)
16 Evaporator 17 Oil equalizing path 20A, 20B Gas injection circuit 21A, 21B Check valve 30A, 30B Bypass path 31A, 31B Bypass flow rate adjusting valve (bypass valve)
32A, 32B Temperature sensor (Discharge temperature sensor)
33A, 33B Pressure sensor 35 On-off valve 40 Control unit 41 Discharge temperature acquisition unit 42 Determination unit 43 Opening setting unit 90 Control unit 91A, 91B Flow rate adjustment valve 101 Low stage compression mechanism 102 High stage compression mechanism 103A, 103B Housing 171 Oil leveling valve P1 Suction port P2 Discharge port P3 Injection port

Claims (6)

A refrigeration cycle comprising a plurality of multistage compressors connected in parallel, each having a housing containing a multistage compression mechanism including a low stage compression mechanism and a high stage compression mechanism,
A refrigerant circuit is configured by sequentially connecting the plurality of multistage compressors, a cooler, a first decompression unit, a gas-liquid separator, a second decompression unit, and an evaporator,
An oil equalizing path connecting the housings of the plurality of multistage compressors;
A plurality of gas injection circuits for supplying gas refrigerant in the gas-liquid separator between the low-stage compression mechanism and the high-stage compression mechanism in the housing of the corresponding multistage compressor;
A plurality of refrigerants extracted from between the cooler and the first pressure reducing unit are supplied between the low-stage compression mechanism and the high-stage compression mechanism in the housing of the corresponding multistage compressor. A bypass path,
A bypass valve capable of changing the flow rate of at least one of the bypass paths of each of the plurality of multistage compressors;
A check valve provided in the gas injection circuit for preventing a back flow of the gas refrigerant flowing into the housing;
A control unit for controlling the opening degree of the bypass valve,
A refrigeration cycle characterized by that. The bypass path is
Allowing the refrigerant extracted from between the cooler and the first decompression section to flow into the gas injection circuit;
The refrigeration cycle according to claim 1. The controller is
At least during oil leveling operation in which lubricating oil is moved between the housings of each of the plurality of multistage compressors through the oil leveling path,
Controlling the opening of the bypass valve;
The refrigeration cycle according to claim 1 or 2, characterized in that. A discharge temperature sensor that detects a discharge temperature that is a temperature of refrigerant discharged from the multistage compressor;
The controller is
Control the opening of the bypass valve using the discharge temperature,
The refrigeration cycle according to any one of claims 1 to 3, wherein The bypass valve is
This is a flow control valve that can adjust the flow rate.
Provided in each of the plurality of bypass paths;
The refrigeration cycle according to any one of claims 1 to 4, wherein CO ₂ is used as a refrigerant circulating in the refrigerant circuit,
The refrigeration cycle according to any one of claims 1 to 5, wherein:

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