JP2016125749A - Refrigeration unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a refrigeration unit capable of suppressing exhaustion of a refrigerating machine oil in a multi-stage compression refrigeration cycle.SOLUTION: A first oil separator 31 disposed between a discharge side of a first compression portion at a low stage side and a suction side of a second compression portion, and for separating a refrigerating machine oil accompanying a passing refrigerant, has a first main body container 31a, a first lower oil return pipe 31b, and a first upper oil return pipe 31d, and a first discharge pipe 21b and a first outflow pipe 21c are connected thereto. The first lower oil return pipe 31d guides the separated refrigerating machine oil to the suction side of the second compression portion. The first outflow pipe 21c is extended to the external from a position upper than an upper end of the first lower oil return pipe 31b in the inside of the first main body container 31a. The first upper oil return pipe 31d is extended from a height position upper than the upper end of the first lower oil return pipe 31b and lower than a lower end of the first outflow pipe 21c in the inside of the first main body container 31a, and is joined to the first outflow pipe 21c.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a refrigeration apparatus.

  Conventionally, there is a refrigeration apparatus that performs a multi-stage compression refrigeration cycle and is provided with an oil separator for each stage compressor.

  For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2014-212293) discloses a refrigeration apparatus that performs a four-stage compression refrigeration cycle in which four compressors are connected in series, and is provided between each stage compressor and the uppermost stage. An oil separator is provided on each discharge side of the compressor. The oil separator provided on the discharge side of the compressor below the uppermost stage is configured to return the separated refrigeration oil to the suction side of the compressor on the upper stage. The oil separator provided on the discharge side of the uppermost compressor is configured to return the separated refrigeration oil to the suction side of the lowermost compressor.

  Here, in particular, in the oil separator provided between the uppermost and lowermost compressors, it becomes difficult to ensure a sufficient pressure difference with the return destination to which the separated refrigeration oil is returned. Machine oil may accumulate inside.

  If refrigeration oil accumulates in the oil separator in this way, it may be difficult to smoothly drive the sliding portion of the compressor.

  This invention is made | formed in view of the point mentioned above, The subject of this invention is providing the refrigeration apparatus which can suppress exhaustion of refrigerator oil in a multistage compression refrigeration cycle.

  The refrigeration apparatus according to the first aspect includes a refrigerant circuit and an intermediate oil separator. The refrigerant circuit is configured by connecting a low-stage compression section, a high-stage compression section, a radiator, a decompression section, and an evaporator. The high stage compression unit further compresses the refrigerant compressed by the low stage compression unit. The radiator dissipates the heat of the refrigerant. The evaporator evaporates the refrigerant. The intermediate oil separator is disposed between the discharge side of the low-stage compression unit and the suction side of the high-stage compression unit, and is configured to be able to separate the refrigerating machine oil accompanying the passing refrigerant. . The intermediate oil separator has a main body container, an introduction pipe, a lower oil return pipe, an outflow pipe, and an upper oil return pipe. The introduction pipe guides the refrigerant discharged from the lower stage compression section to the internal space of the main body container. The lower oil return pipe extends from the lower part of the inner space of the main body container to the outside in order to guide the refrigerating machine oil separated in the main body container to the suction side of the higher stage compression section. The outflow pipe extends to the outside from a position above the upper end of the lower oil return pipe in the internal space of the main body container in order to guide the refrigerant to the suction side of the higher stage compression section. The upper oil return pipe extends from a height position above the upper end of the lower oil return pipe in the internal space of the main body container and below the lower end of the outflow pipe, and joins the outflow pipe.

  Here, the joining position of the upper oil return pipe and the outflow pipe may be inside the main body container of the intermediate oil separator or outside the main body container of the intermediate oil separator. This is more preferable in that the effect of pumping refrigeration oil is high.

  In this refrigeration system, the lower oil return is not achieved because a sufficient differential pressure between the refrigerant pressure inside the main body container of the intermediate oil separator and the refrigerant pressure on the suction side of the high-stage compression unit that is the return destination of the refrigeration oil is not secured. Even in situations where the refrigeration oil cannot be sufficiently conveyed through the pipe, it is possible to send the refrigeration oil sucked by the upper oil return pipe to the outside of the intermediate oil separator by joining the refrigerant flowing through the outflow pipe. become. Thereby, it becomes possible to suppress the accumulation of refrigerating machine oil.

  The refrigeration apparatus according to the second aspect is the refrigeration apparatus according to the first aspect, wherein the inner diameter of the outflow pipe is larger than the inner diameter of the upper oil return pipe.

  In this refrigeration apparatus, the refrigerant that has flowed into the intermediate oil separator flows relatively vigorously through the outflow pipe having a larger inner diameter. And the upper oil return pipe whose inner diameter is smaller than the outflow pipe can pump the refrigeration oil separated in the intermediate oil separator by the venturi effect, join the refrigerant flowing through the outflow pipe, and send it out of the intermediate oil separator become. Thus, the upper oil return pipe having an inner diameter smaller than the outflow pipe can pump the refrigeration oil more efficiently.

  The refrigeration apparatus according to the third aspect is the refrigeration apparatus according to the first aspect or the second aspect, and the refrigerant circuit further includes a switching valve and an intercooler that radiates heat of the refrigerant. The switching valve can switch the cooling operation and the heating operation to be executed by the refrigerant circuit. In the cooling operation, the refrigerant discharged from the low-stage compression unit is guided to the suction side of the high-stage compression unit via the intermediate oil separator and the intermediate cooler. In the heating operation, the refrigerant discharged from the low-stage compression unit is guided to the suction side of the high-stage compression unit via the intermediate oil separator and not through the intermediate cooler.

  In this refrigeration apparatus, it is possible to increase cycle efficiency by using an intercooler during cooling operation. Further, during cooling operation, the refrigerant pressure loss occurs when the refrigerant passes through the intermediate cooler, so the refrigerant pressure inside the intermediate container of the intermediate oil separator and the high-stage compression unit that is the return destination of the refrigeration oil Since it is easy to ensure a sufficient differential pressure from the refrigerant pressure on the suction side, the refrigerating machine oil separated in the intermediate oil separator is easily sent to the suction side of the high-stage compression section. In contrast, during heating operation, the refrigerant discharged from the low-stage compression unit is guided to the suction side of the high-stage compression unit through the intermediate oil separator and not through the intermediate cooler. No pressure loss occurs when passing through the intermediate cooler during operation. For this reason, compared with the cooling operation during heating operation, the differential pressure between the refrigerant pressure inside the main body container of the intermediate oil separator and the refrigerant pressure on the suction side of the high-stage compression unit that is the return destination of the refrigeration oil is increased. It is difficult to secure enough. Thus, even if it is difficult to ensure the above-mentioned differential pressure during heating operation, this refrigeration apparatus has an upper oil return pipe, so that accumulation of refrigeration oil can be suppressed. Become.

  The refrigeration apparatus according to the fourth aspect is the refrigeration apparatus according to the third aspect, wherein the lower oil return pipe extends from the lower side of the internal space of the main body container to the outside, and then is placed in a higher stage via the flow path resistor. It is connected to the suction side of the side compression section. The passage resistance of the refrigerant by the flow path resistor is larger than the passage resistance of the refrigerant from the outflow pipe to the suction side of the high-stage compression unit.

  In this refrigeration apparatus, the lower oil return pipe through which the refrigeration oil flows mainly is provided with a flow path resistor having a passage resistance larger than the passage resistance of the refrigerant from the outflow pipe to the suction side of the high-stage compression section. For this reason, not only the refrigerating machine oil but also a large amount of refrigerant flows through the lower oil return pipe during the cooling operation, and it is possible to suppress the performance degradation caused by the inability to pass through the intermediate cooler.

  The refrigeration apparatus according to the fifth aspect is the refrigeration apparatus according to any one of the first to fourth aspects, and further includes a high stage oil separator. The high stage oil separator is provided on the discharge side of the high stage side compression unit, and is configured to be able to separate the refrigerating machine oil accompanied by the refrigerant passing therethrough. The high stage oil separator does not have a structure corresponding to the upper oil return pipe of the intermediate oil separator.

  For example, the high-stage oil separator has a configuration corresponding to each of the main body container, the inflow pipe, the outflow pipe, and the lower oil return pipe, but does not have an upper oil return pipe.

  In this refrigeration apparatus, the intermediate oil separator that allows the refrigerant discharged from the low-stage compression section to pass through and the high-stage oil separator that allows the refrigerant discharged from the high-stage compression section to pass through can be divided into different types. In addition, it is possible to suppress the accumulation of refrigeration oil in the intermediate oil separator, and the configuration of the high stage oil separator can be simplified.

  A refrigeration apparatus according to a sixth aspect is the refrigeration apparatus according to any one of the first to fifth aspects, further comprising a lower oil separator. The low-stage compression section has a first low-stage compression section on the low-stage side and a second low-stage compression section that further compresses the refrigerant compressed by the first low-stage compression section. . The lower oil separator is disposed between the discharge side of the first low-stage compression unit and the suction side of the second low-stage compression unit, and can separate the refrigerating machine oil accompanying the refrigerant passing therethrough. It is configured. The lower oil separator includes a lower main body container, a lower inlet pipe, a lower lower oil return pipe, a lower outlet pipe, and a lower upper oil return pipe. The lower stage introduction pipe guides the refrigerant discharged from the first lower stage compression section to the internal space of the lower stage main body container. The lower lower oil return pipe extends from the lower part of the inner space of the lower main body container to the outside in order to guide the refrigerating machine oil separated in the lower main body container to the suction side of the second lower stage compression section. The lower outlet pipe extends from a position above the upper end of the lower lower oil return pipe in the internal space of the lower main body container to guide the refrigerant to the suction side of the second lower-stage compression section. The lower upper oil return pipe extends from a height above the upper end of the lower lower oil return pipe in the internal space of the lower main body container and below the lower end of the lower outlet pipe, and joins the lower outlet pipe. Yes.

  In this refrigeration apparatus, the accumulation of refrigerating machine oil is suppressed even in a refrigeration apparatus configured with three compression sections, a first low-stage compression section, a second low-stage compression section, and a high-stage compression section. It becomes possible to do.

  The refrigeration apparatus according to the seventh aspect is the refrigeration apparatus according to any one of the first to sixth aspects, and the high-stage compression unit and the low-stage compression unit share a drive source. Here, as a case where the drive source is common, for example, the drive shaft is common, and both the high-stage compression unit and the low-stage compression unit are driven by the common drive shaft, and the high-stage compression unit And the lower stage compression section cannot be independently and freely driven.

  This refrigeration apparatus has a structure in which the discharge pressure and the suction pressure cannot be individually controlled due to the common drive source of the high-stage compression section and the low-stage compression section. Even if it is a case where the drive state of a low stage compression part cannot be controlled independently and the accumulation of refrigerating machine oil cannot be suppressed, the accumulation of refrigerating machine oil in the oil separator can be suppressed.

  In the refrigeration apparatus according to the first aspect, accumulation of refrigeration oil can be suppressed.

  In the refrigeration apparatus according to the second aspect, the upper oil return pipe whose inner diameter is smaller than the outflow pipe can pump the refrigeration oil more efficiently.

  In the refrigeration apparatus according to the third aspect, it is possible to suppress accumulation of refrigeration oil even when it is difficult to ensure the differential pressure during heating operation.

  In the refrigeration apparatus according to the fourth aspect, it is possible to suppress performance degradation caused by the inability to pass through the intermediate cooler during cooling operation.

  In the refrigeration apparatus according to the fifth aspect, it is possible to suppress the accumulation of refrigeration oil in the intermediate oil separator, and the configuration of the high stage oil separator can be simplified.

  In the refrigeration apparatus according to the sixth aspect, even in the refrigeration apparatus configured to include three compression units, the first low-stage compression unit, the second low-stage compression unit, and the high-stage compression unit, It becomes possible to suppress accumulation.

  In the refrigeration apparatus according to the seventh aspect, the refrigeration oil in the oil separator can be controlled even when the drive states of the high-stage compression section and the low-stage compression section cannot be controlled independently to suppress the accumulation of refrigeration oil. The accumulation of can be suppressed.

It is a schematic block diagram of the air conditioning apparatus which concerns on one Embodiment of this invention. It is sectional drawing of the one part axial view of a four-stage compression part. It is side sectional drawing of a part of four-stage compression part. It is a schematic block diagram of a 1st oil separator. It is a schematic block diagram at the time of air_conditionaing | cooling operation of an air conditioning apparatus. FIG. 6 is a pressure-enthalpy diagram of the refrigeration cycle during the cooling operation of FIG. 5. It is a schematic block diagram at the time of the heating operation of an air conditioning apparatus. It is a pressure-enthalpy diagram of the refrigerating cycle at the time of heating operation of FIG.

  An air conditioner 1 that is a refrigeration apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

(1) Configuration of Air Conditioner FIG. 1, FIG. 5 and FIG. 7 are schematic configuration diagrams of the air conditioner 1. Among these, FIG. 6 represents the flow of the refrigerant circulating through the refrigerant circuit during the cooling operation, and FIG. 7 represents the flow of the refrigerant circulating through the refrigerant circuit during the heating operation.

  The air conditioner 1 is a refrigeration apparatus that performs a four-stage compression refrigeration cycle using a carbon dioxide refrigerant in a supercritical state. The air conditioner 1 includes an outdoor unit 11 that is a heat source unit, and a plurality of indoor units 12 and 13 that are utilization units (including the first indoor unit 12 and the second indoor unit 13), a liquid refrigerant communication pipe 14 and The apparatus is connected by the gas refrigerant communication pipe 15 and has a refrigerant circuit that switches between a cooling operation cycle and a heating operation cycle. 5 and 7, arrows shown along the refrigerant circuit piping represent the flow of the refrigerant.

  The refrigerant circuit of the air conditioner 1 mainly includes a four-stage compressor 20, a four-way switching valve group 25 (first to fourth four-way switching valves 26 to 29), an outdoor heat exchanger 40, and a first outdoor expansion valve 47. , Second outdoor expansion valve 48, bridge circuit 49, economizer circuit 50, liquid gas heat exchange circuit 60, expansion mechanism 70, separation gas pipe 80, receiver 81, supercooling circuit 90, first indoor heat exchanger 12a, second The indoor heat exchanger 13a, the first indoor expansion valve 12b, the second indoor expansion valve 13b, and the control unit 7 are provided. The outdoor heat exchanger 40 includes a first outdoor heat exchanger 41, a second outdoor heat exchanger 42, a third outdoor heat exchanger 43, and a fourth outdoor heat exchanger 44.

  Hereinafter, each component of the refrigerant circuit will be described in detail.

(1-1) Four-stage compressor The four-stage compressor 20 includes a first compression unit 21, a second compression unit 22, a third compression unit 23, a fourth compression unit 24, and a compressor drive motor ( (Not shown) is a hermetic compressor. A compressor drive motor drives the four compression parts 21-24 via a common drive shaft. That is, the four-stage compressor 20 has a uniaxial four-stage compression structure in which four compression units 21 to 24 are connected to a single drive shaft. In the four-stage compressor 20, the 1st compression part 21, the 2nd compression part 22, the 3rd compression part 23, and the 4th compression part 24 are pipe-connected in series in this order. The first compressor 21 sucks the refrigerant from the first suction pipe 21a and discharges the refrigerant to the first discharge pipe 21b. The first suction pipe 21a is provided with a suction pressure sensor 21p for detecting the suction pressure of the flowing refrigerant. The second compressor 22 sucks the refrigerant from the second suction pipe 22a and discharges the refrigerant to the second discharge pipe 22b. The third compressor 23 sucks the refrigerant from the third suction pipe 23a and discharges the refrigerant to the third discharge pipe 23b. The fourth compressor 24 sucks the refrigerant from the fourth suction pipe 24a and discharges the refrigerant to the fourth discharge pipe 24b. The fourth discharge pipe 24b is provided with a discharge pressure sensor 24p that detects the discharge pressure of the flowing refrigerant.

  The 1st compression part 21 is a compression mechanism of the lowest stage, and compresses the lowest pressure refrigerant which flows through a refrigerant circuit. The second compression unit 22 sucks and compresses the refrigerant compressed by the first compression unit 21. The third compression unit 23 sucks and compresses the refrigerant compressed by the second compression unit 22. The fourth compression unit 24 is the uppermost compression mechanism, and sucks and compresses the refrigerant compressed by the third compression unit 23. The refrigerant compressed by the fourth compressor 24 and discharged to the fourth discharge pipe 24b becomes the highest pressure refrigerant that flows through the refrigerant circuit.

  In addition, in this embodiment, each compression parts 21-24 are positive displacement type compression mechanisms, such as a rotary type and a scroll type. The compressor drive motor is inverter-controlled by the control unit 7.

  Although details are omitted, the third compression unit 23 and the fourth compression unit 24 of the four-stage compressor 20 of the present embodiment are, for example, as shown in FIG. It may be configured. That is, the piston 122, which is an integral part of the fixed cylinder 121, receives an action from a common drive source and performs an eccentric rotational movement so that the compression is performed simultaneously in the two compressed spaces. May be. In such a compressor, the inner gap between the cylinder 121 and the piston 122 and the outer gap between the cylinder 121 and the piston 122 cannot be adjusted independently, and the compression ratio is adjusted independently. It is a configuration that can not be. In addition, the specific structure of the compressor is described in, for example, Japanese Patent No. 4962855 (the entire contents of the document are incorporated herein by reference). Such a drive source is preferably shared by the first compression unit 21, the second compression unit 22, the third compression unit 23, and the fourth compression unit 24.

(1-2) Oil separator The first oil separator 31 and the second oil are provided at the downstream ends of the first discharge pipe 21b, the second discharge pipe 22b, the third discharge pipe 23b, and the fourth discharge pipe 24b, respectively. A separator 32, a third oil separator 33, and a fourth oil separator 34 are provided. The first to fourth oil separators 31, 32, 33 and 34 can separate the refrigeration oil as the lubricating oil contained in the refrigerant circulating in the refrigerant circuit and return it to a specific place.

  As shown in FIG. 4, the first oil separator 31 includes a first main body container 31a, a first lower oil return pipe 31b, and a first upper oil return pipe 31d. The first main body container 31a can separate the refrigerant flowing in and the refrigerating machine oil.

  A first discharge pipe 21b extending in a substantially horizontal direction is connected to the eccentric position above the first main body container 31a. The first lower oil return pipe 31b extends outward from the vicinity of the lower end of the first main body container 31a. The first lower oil return pipe 31b has an end opposite to the end on the inner side of the first main body container 31a connected to the middle of the second suction pipe 22a. A first capillary tube 31c as a flow path resistor is provided in the middle of the first lower oil return pipe 31b. The size (flow path resistance) of the flow path of the first capillary tube 31c is such that when the air conditioner 1 performs the cooling operation, the refrigerating machine oil can be sufficiently passed while suppressing the flow of the refrigerant excessively. Designed to. Note that the passage resistance of the refrigerant through the first capillary tube 31c is larger than the passage resistance of the refrigerant from the first outlet pipe 21c to the suction side of the second compression section 22 in both the cooling operation and the heating operation. Designed. Further, in the first main body container 31a, the first outflow pipe 21c extends upward from the position above the upper end of the first lower oil return pipe 31b and below the end of the first discharge pipe 21b. I'm out. One end of the first outflow pipe 21c is located near the center of the first main body container 31a, and the other end is connected to one of the ports of the first four-way switching valve 26 described later. The first upper oil return pipe 31d is radially outside from the position inside the first main body container 31a above the upper end of the first lower oil return pipe 31b and below the lower end of the first outflow pipe 21c. It is growing towards The first upper oil return pipe 31d extends to the outside outside in the radial direction of the first main body container 31a, then extends upward to the upper side of the first main body container 31a, bends toward the first outflow pipe 21c, The first outlet pipe 21c is joined above the one main body container 31a. Here, the inner diameter of the first outflow pipe 21c is larger than the inner diameter of the first upper oil return pipe 31d, and is not particularly limited. For example, the inner diameter of the first outflow pipe 21c is the first upper oil return pipe. You may be comprised so that it may become 2 times or more of the internal diameter of 31d.

  The second oil separator 32 is also the same as the first oil separator 31 shown in FIG. The second oil separator 32 includes a second main body container 32a, a second lower oil return pipe 32b, and a second upper oil return pipe 32d. A second discharge pipe 22b extending in a substantially horizontal direction is connected to the eccentric position above the second main body container 32a. The second lower oil return pipe 32b extends outward from the vicinity of the lower end of the second main body container 32a downward. The second lower oil return pipe 32b has an end opposite to the end on the inner side of the second main body container 32a connected to the middle of the third suction pipe 23a. A second capillary tube 32c as a flow path resistor is provided in the middle of the second lower oil return pipe 32b. With regard to the size of the flow path of the second capillary tube 32c (flow path resistance), when the air-conditioning apparatus 1 performs the cooling operation, it is possible to sufficiently pass the refrigerating machine oil while suppressing excessive flow of the refrigerant. Designed to be Note that the passage resistance of the refrigerant through the second capillary tube 32c is larger than the passage resistance of the refrigerant from the second outlet pipe 22c to the suction side of the third compression section 23 in both the cooling operation and the heating operation. Designed. Further, in the second main body container 32a, the second outflow pipe 22c extends upward from a position above the upper end of the second lower oil return pipe 32b and below the end of the second discharge pipe 22b. I'm out. One end of the second outflow pipe 22c is located in the vicinity of the center of the second main body container 32a, and the other end is connected to one of the ports of the second four-way switching valve 27 described later. The second upper oil return pipe 32d is radially outward from the position inside the second main body container 32a above the upper end of the second lower oil return pipe 32b and below the lower end of the second outflow pipe 22c. It is growing towards The second upper oil return pipe 32d extends to the outside outside in the radial direction of the second main body container 32a, then extends upward to the upper side of the second main body container 32a, bends toward the second outflow pipe 22c, The second main body container 32a is joined to the second outlet pipe 22c above. Here, the inner diameter of the second outflow pipe 22c is larger than the inner diameter of the second upper oil return pipe 32d, and is not particularly limited. For example, the inner diameter of the second outflow pipe 22c is the second upper oil return pipe. You may be comprised so that it may become 2 times or more of the internal diameter of 32d.

  The third oil separator 33 is also the same as the first oil separator 31 shown in FIG. The third oil separator 33 includes a third main body container 33a, a third lower oil return pipe 33b, and a third upper oil return pipe 33d. A third discharge pipe 23b extending in a substantially horizontal direction is connected to the eccentric position above the third main body container 33a. The third lower oil return pipe 33b extends outward from the vicinity of the lower end of the third main body container 33a. The third lower oil return pipe 33b is connected to the middle of the fourth suction pipe 24a at the end opposite to the inner end of the third main body container 33a. A third capillary tube 33c as a flow path resistor is provided in the middle of the third lower oil return pipe 33b. With regard to the size of the flow path (flow path resistance) of the third capillary tube 33c as well, when the air-conditioning apparatus 1 performs the cooling operation, the refrigerating machine oil can be sufficiently passed while suppressing excessive flow of the refrigerant. Designed to be Note that the passage resistance of the refrigerant through the third capillary tube 331c is larger than the passage resistance of the refrigerant from the third outlet pipe 23c to the suction side of the fourth compression section 24 in both the cooling operation and the heating operation. Designed. Further, in the third main body container 33a, the third outflow pipe 23c extends upward from a position above the upper end of the third lower oil return pipe 33b and below the end of the third discharge pipe 23b. I'm out. One end of the third outflow pipe 23c is located in the vicinity of the center of the third main body container 33a, and the other end is connected to one of the ports of the third four-way switching valve 28 described later. The third upper oil return pipe 33d is radially outside from the position inside the third main body container 33a above the upper end of the third lower oil return pipe 33b and below the lower end of the third outlet pipe 23c. It is growing towards The third upper oil return pipe 33d extends to the outside outside in the radial direction of the third main body container 33a, then extends upward to the upper side of the third main body container 33a, bends to the third outlet pipe 23c side, The third main body container 33a is joined to the third outlet pipe 23c above. Here, the inner diameter of the third outlet pipe 23c is configured to be larger than the inner diameter of the third upper oil return pipe 33d, and is not particularly limited. For example, the inner diameter of the third outlet pipe 23c is the third upper oil return pipe. You may be comprised so that it may become 2 times or more of the internal diameter of 33d.

  The fourth oil separator 34 has a different structure from the first to third oil separators 31 to 33. The fourth oil separator 34 includes a fourth main body container 34a and a fourth lower oil return pipe 34b, but does not have a configuration corresponding to the first to third upper oil return pipes 31d to 33d. Above the fourth main body container 34a, a fourth discharge pipe 24b extending in a substantially horizontal direction is connected to an eccentric position. The fourth lower oil return pipe 34b extends outward from the vicinity of the lower end of the fourth main body container 34a. The fourth lower oil return pipe 34b has an end opposite to the inner end of the fourth main body container 34a connected to the middle of the first suction pipe 21a. A fourth capillary tube 34c as a flow path resistor is provided in the middle of the fourth lower oil return pipe 34b. The size (flow path resistance) of the flow path of the fourth capillary tube 34c is also designed so that refrigerating machine oil other than the refrigerant can flow mainly when the air conditioner 1 performs the cooling operation. Further, in the fourth main body container 34a, the fourth outflow pipe 24c extends upward from a position above the upper end of the fourth lower oil return pipe 34b and below the end of the fourth discharge pipe 24b. I'm out. One end of the fourth outflow pipe 24c is located near the center of the fourth main body container 34a, and the other end is connected to one of the ports of a fourth four-way switching valve 29 described later.

  With the above configuration, the refrigerating machine oil as the lubricating oil separated from the refrigerant in each of the first to fourth oil separators 31, 32, 33, 34 is returned to the four-stage compressor 20.

(1-3) Four-way switching valve group The four-way switching valve group 25 includes a first four-way switching valve 26, a second four-way switching valve 27, a third four-way switching valve 28, and a fourth four-way switching valve 29. It is configured. The four-way switching valve group 25 is provided for switching between the cooling operation cycle and the heating operation cycle by switching the direction of the refrigerant flow in the refrigerant circuit.

  The four ports of the first four-way selector valve 26 are connected to the first outlet pipe 21c, the second suction pipe 22a, the first pipe 41a, and the first liquid gas suction pipe 26a. The first pipe 41 a is a pipe connecting the first four-way switching valve 26 and the first outdoor heat exchanger 41. The first pipe 41a is provided with a third temperature sensor 41t for detecting the temperature of the refrigerant passing therethrough.

  The first liquid gas suction pipe 26a is a pipe that guides the low-pressure refrigerant to the first suction pipe 21a during the heating operation.

  The second four-way switching valve 27 is connected to the second outflow pipe 22c, the third suction pipe 23a, the second pipe 42a, and the first connection pipe 41d. The second pipe 42 a is a pipe connecting the second four-way switching valve 27 and the second outdoor heat exchanger 42. 41 d of 1st connection piping is connected with respect to the 5th piping 41b on the opposite side to the 1st piping 41a side of the 1st outdoor heat exchanger 41. As shown in FIG.

  The third four-way switching valve 28 is connected to the third outlet pipe 23c, the fourth suction pipe 24a, the third pipe 43a, and the second connection pipe 42d. The third pipe 43 a is a pipe connecting the third four-way switching valve 28 and the third outdoor heat exchanger 43. The second connection pipe 42d is connected to the sixth pipe 42b opposite to the second pipe 42a side of the second outdoor heat exchanger 42.

  The fourth four-way selector valve 29 is connected to the fourth outlet pipe 24 c, the gas refrigerant communication pipe 15, the fourth pipe 44 a, and the low pressure refrigerant pipe 19. The fourth pipe 44 a is a pipe connecting the fourth four-way switching valve 29 and the fourth outdoor heat exchanger 44. The fourth pipe 44a is provided with a second temperature sensor 44t2 for detecting the temperature of the refrigerant passing therethrough. The low-pressure refrigerant pipe 19 is connected to the opposite side of the liquid gas heat exchanger 61 from the first suction pipe 21a side.

  The four-way switching valve group 25 is controlled by the control unit 7 so that, during cooling operation, as shown in FIG. 5, a heat radiator (refrigerant of the refrigerant) that dissipates heat of the refrigerant compressed by the four-stage compressor 20. The outdoor heat exchanger 40 (first to fourth outdoor heat exchangers 41 to 44) functions as a cooler and passes through the expansion mechanism 70, the first indoor expansion valve 12b, and the second indoor expansion valve 13b. The first indoor heat exchanger 12a and the second indoor heat exchanger 13a function as the expanded refrigerant evaporator (refrigerant heater). Here, at the time of air_conditionaing | cooling operation, the 1st-4th outdoor heat exchangers 41-44 will be in the state mutually connected in series with respect to the refrigerant | coolant flow direction.

  Further, the four-way switching valve group 25 is controlled by the control unit 7 so that, during heating operation, as shown in FIG. 7, a radiator that radiates the heat of the refrigerant compressed by the four-stage compressor 20 ( The first indoor heat exchanger 12a and the second indoor heat exchanger 13a function as a refrigerant cooler, and have expanded through the expansion mechanism 70, the first outdoor expansion valve 47, and the second outdoor expansion valve 48. It will be in the switching state which functions the outdoor heat exchanger 40 (1st-4th outdoor heat exchanger 41-44) as a refrigerant | coolant evaporator (refrigerant | coolant of a refrigerant | coolant). Here, at the time of heating operation, the 1st-3rd outdoor heat exchangers 41-43 and the 4th outdoor heat exchanger 44 will be in the state mutually connected in parallel with respect to the refrigerant | coolant flow direction. The 3rd outdoor heat exchangers 41-43 will be in the state mutually connected in series in the refrigerant | coolant flow direction.

  That is, the four-way switching valve group 25 focuses only on the four-stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, the first indoor heat exchanger 12a, and the second indoor heat exchanger 13a as components of the refrigerant circuit. Then, a cooling operation cycle in which the refrigerant is circulated in the order of the four-stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, the first indoor heat exchanger 12a, and the second indoor heat exchanger 13a, and the four-stage compressor 20, It plays the role which switches the heating operation cycle which circulates a refrigerant | coolant in order of the 1st indoor heat exchanger 12a, the 2nd indoor heat exchanger 13a, the expansion mechanism 70, and the outdoor heat exchanger 40.

(1-4) Outdoor heat exchanger and intercooler tube As described above, the outdoor heat exchanger 40 includes the first outdoor heat exchanger 41, the second outdoor heat exchanger 42, the third outdoor heat exchanger 43, and the first outdoor heat exchanger 43. It is composed of four outdoor heat exchangers 44. During the cooling operation, the first to third outdoor heat exchangers 41 to 43 function as an intercooler that cools the refrigerant (intermediate pressure refrigerant) being compressed, and the fourth outdoor heat exchanger 44 cools the highest pressure refrigerant. It functions as a gas cooler (a radiator that dissipates the heat of the refrigerant). The fourth outdoor heat exchanger 44 has a larger capacity than the first to third outdoor heat exchangers 41 to 43. Further, during the heating operation, all of the first to fourth outdoor heat exchangers 41 to 44 function as low-pressure refrigerant evaporators (heaters).

  The first to fourth outdoor heat exchangers 41 to 44 are arranged in parallel and integrated as one outdoor heat exchanger 40. Water or air is supplied to the outdoor heat exchanger 40 as a cooling source or a heating source for exchanging heat with the refrigerant flowing inside. Here, air (outside air) is supplied to the outdoor heat exchanger 40 from a blower fan (not shown).

  A fifth pipe 41b is connected to the first outdoor heat exchanger 41 on the side opposite to the first pipe 41a. Apart from the first connection pipe 41d, a first intercooler pipe 41c connected to the second suction pipe 22a branches and extends from the fifth pipe 41b. A sixth pipe 42b is connected to the second outdoor heat exchanger 42 on the side opposite to the second pipe 42a. From the middle of the sixth pipe 42b, apart from the second connection pipe 42d, the second intercooler pipe 42c connected to the third suction pipe 23a branches and extends. A seventh pipe 43b is connected to the side of the third outdoor heat exchanger 43 opposite to the third pipe 43a. A common pipe 47a in which a first outdoor expansion valve 47 is provided in the middle is connected to the seventh pipe 43b. In addition to the common pipe 47a, a third intercooler pipe 43c connected to the fourth suction pipe 24a branches and extends from the seventh pipe 43b.

  As shown in FIG. 1, the first intercooler pipe 41c, the second intercooler pipe 42c, and the third intercooler pipe 43c include a first intercooler check valve, a second intercooler check valve, and a second intercooler check valve, respectively. A third intercooler check valve is provided (reference numerals are omitted).

  An eighth pipe 44b is connected to the opposite side of the fourth outdoor heat exchanger 44 from the fourth pipe 44a. The eighth pipe 44b is connected between the second outdoor expansion valve 48 and the third check valve 49c in the bridge circuit 49 described later.

(1-5) First outdoor expansion valve and second outdoor expansion valve The first outdoor expansion valve 47 is provided in the middle of the common pipe 47a. The common pipe 47a joins with a supercooling refrigerant pipe 84 through which the supercooling refrigerant that has flowed out of the supercooling heat exchanger 91 described later flows, and between the second outdoor expansion valve 48 and the first check valve 49a of the bridge circuit 49. Connected to.

  During the cooling operation, the first outdoor expansion valve 47 and the second outdoor expansion valve 48 are closed under the control of the control unit 7. During the heating operation, the first outdoor expansion valve 47 and the second outdoor expansion valve 48 do not drift the refrigerant flow from the bridge circuit 49 to the first to fourth outdoor heat exchangers 41 to 44 under the control of the control unit 7. In this way, the opening degree is adjusted, and each plays a role as an expansion mechanism.

(1-6) Bridge Circuit The bridge circuit 49 includes a first check valve 49a, a second check valve 49b, a third check valve 49c, and a second outdoor expansion valve 48, which are connected in order. A circuit is formed in which the valve 49a and the second outdoor expansion valve 48 are connected. The first check valve 49a allows only the refrigerant flow toward the side opposite to the second outdoor expansion valve 48 side. The third check valve 49c allows only the refrigerant flow toward the side opposite to the second outdoor expansion valve 48 side. The second check valve 49b does not allow the refrigerant flow toward the first check valve 49a, but allows only the refrigerant flow toward the third check valve 49c.

  Between the first check valve 49a and the second outdoor expansion valve 48 of the bridge circuit 49, a pipe in which the common pipe 47a and the supercooling refrigerant pipe 84 are joined is connected. An eighth pipe 44 b extending from the fourth outdoor heat exchanger 44 is connected between the third check valve 49 c and the second outdoor expansion valve 48 of the bridge circuit 49. A liquid refrigerant communication pipe 14 extending from the first and second indoor units 12 and 13 is connected between the first check valve 49 a and the second check valve 49 b of the bridge circuit 49. A refrigerant pipe extending toward the economizer heat exchanger 51 side of the economizer circuit 50 is connected between the second check valve 49b and the third check valve 49c of the bridge circuit 49.

(1-7) Economizer circuit 50
The economizer circuit 50 is provided between the portion of the bridge circuit 49 between the second check valve 49 b and the third check valve 49 c and the liquid gas heat exchanger 61 or the expansion mechanism 70. The economizer circuit 50 includes an economizer heat exchanger 51, an economizer injection pipe 53, and an economizer expansion valve 52.

  The economizer injection pipe 53 branches and extends from a portion between the second check valve 49b and the third check valve 49c of the bridge circuit 49 and a portion in front of the economizer heat exchanger 51, The second intercooler pipe 42c is connected to the downstream side of the second intercooler check valve.

  The economizer expansion valve 52 is provided in the middle of the economizer injection pipe 53 and before flowing into the economizer heat exchanger 51 after branching.

  The economizer heat exchanger 51 is branched to the economizer injection valve 53 and expanded at the economizer expansion valve 52 by the high-pressure refrigerant exceeding the critical pressure from the bridge circuit 49 toward the liquid gas heat exchanger 61 or the expansion mechanism 70. Heat exchange is performed with the refrigerant having the pressure.

  The refrigerant expanded in the economizer expansion valve 52 and evaporated in the economizer heat exchanger 51 is merged with the refrigerant flowing through the second intercooler pipe 42c, whereby the refrigerant sucked into the third compressor 23 from the third suction pipe 23a. Cool down.

(1-8) Liquid-gas heat exchange circuit The liquid-gas heat exchange circuit 60 is provided between the economizer heat exchanger 51 and the expansion mechanism 70, and includes the liquid-gas heat exchanger 61 and the first liquid-gas on-off valve 62. And a second liquid gas on-off valve 63.

  In the liquid gas heat exchanger 61, a high-pressure refrigerant that exceeds a critical pressure from the bridge circuit 49 toward the expansion mechanism 70, a low-pressure refrigerant that flows through the supercooling injection pipe 93, and a low-pressure refrigerant that flows through the low-pressure refrigerant pipe 19 are merged. Heat exchange is performed with the merged refrigerant that is the low-pressure refrigerant merged at 65. The liquid gas heat exchanger 61 may be referred to as an internal heat exchanger. The merged refrigerant that is the low-pressure refrigerant merged at the merge point 65 flows through the first suction pipe 21 a after passing through the liquid gas heat exchanger 61. The first liquid gas suction pipe 26a described above is connected to the first suction pipe 21a.

  In addition, the low-pressure refrigerant | coolant which flows through the supercooling injection piping 93, and the low-pressure refrigerant | coolant which flows through the low pressure refrigerant | coolant piping 19 join at the junction 65, and the confluence | merging which detects the refrigerant | coolant temperature of the merged refrigerant | coolant which is flowing toward the liquid gas heat exchanger 61 is detected. A refrigerant temperature sensor 64t is provided on the low-pressure refrigerant inlet side of the liquid gas heat exchanger 61.

  The second liquid gas on-off valve 63 is an on-off valve provided in the middle of the refrigerant pipe connecting the one end side and the other end side of the liquid gas heat exchanger 61.

  The first liquid gas on-off valve 62 is located between the economizer heat exchanger 51 and the liquid gas heat exchanger 61 and is connected to a refrigerant pipe connecting the one end side and the other end side of the liquid gas heat exchanger 61. It is an on-off valve provided on the liquid gas heat exchanger 61 side.

  During the cooling operation, in order to perform heat exchange in the liquid gas heat exchanger 61, the control unit 7 closes the second liquid gas on-off valve 63 while opening the first liquid gas on-off valve 62, The refrigerant that has passed through the economizer heat exchanger 51 is passed through the liquid gas heat exchanger 61. On the other hand, during heating operation, in order not to perform heat exchange in the liquid gas heat exchanger 61, the control unit 7 opens the second liquid gas on / off valve 63 while closing the first liquid gas on / off valve 62. Thus, the refrigerant that has passed through the economizer heat exchanger 51 is sent to the expansion mechanism 70 without passing through the liquid gas heat exchanger 61.

(1-9) Expansion Mechanism The expansion mechanism 70 depressurizes and expands the high-pressure refrigerant flowing from the economizer heat exchanger 51 or the liquid gas heat exchanger 61, and receives the intermediate-pressure refrigerant in the gas-liquid two-phase state as a receiver 81. To flow. That is, during the cooling operation, the expansion mechanism 70 includes the first and second indoor heat exchangers functioning as low-pressure refrigerant evaporators from the outdoor fourth outdoor heat exchanger 44 functioning as a high-pressure refrigerant gas cooler (heat radiator). The refrigerant sent to 12a and 13a is decompressed. Further, during the heating operation, the expansion mechanism 70 is a refrigerant sent from the first and second indoor heat exchangers 12a and 13a functioning as a high-pressure refrigerant radiator to the outdoor heat exchanger 40 functioning as a low-pressure refrigerant evaporator. The pressure is reduced.

  The expansion mechanism 70 is configured by connecting an expander 71 and a third outdoor expansion valve 72 in parallel. The expander 71 plays a role of recovering the throttle loss in the decompression process of the refrigerant as effective work (energy).

  An intermediate temperature sensor 70t is provided between the expansion mechanism 70 and the receiver 81 for the refrigerant temperature. Since the intermediate temperature sensor 70t detects the saturation temperature of the intermediate pressure, the control unit 7 can grasp the intermediate pressure that is the equivalent saturation pressure from the detected temperature of the intermediate temperature sensor 70t.

(1-10) Receiver The receiver 81 causes the gas-liquid two-phase intermediate pressure refrigerant that has exited the expansion mechanism 70 to flow into the internal space from the ceiling surface, and is separated into liquid refrigerant and gas refrigerant.

  The liquid refrigerant separated in the receiver 81 is sent to the supercooling circuit 90 via the liquid refrigerant outlet pipe 83 extending from below the receiver 81.

  The gas refrigerant separated in the receiver 81 is joined to the refrigerant flowing in a supercooling injection pipe 93 of a supercooling circuit 90 described later via a separation gas pipe 80 extending from above the receiver 81. A separation gas expansion valve 82 is provided in the middle of the separation gas pipe 80. The refrigerant flowing through the separation gas pipe 80 is a gas refrigerant from which the liquid refrigerant has been separated in the receiver 81 and is reduced in pressure by the separation gas expansion valve 82 to become a low-pressure gas-rich refrigerant, and then the supercooling injection pipe 93. Sent to.

(1-11) Supercooling Circuit The supercooling circuit 90 is provided between the receiver 81 and the portion of the bridge circuit 49 between the first check valve 49a and the second outdoor expansion valve 48. The supercooling circuit 90 includes a supercooling heat exchanger 91, a supercooling injection pipe 93, and a supercooling expansion valve 92.

  The refrigerant that has flowed through the liquid refrigerant outlet pipe 83 extending from the receiver 81 is divided into a refrigerant that is directed to the supercooling heat exchanger 91 and a refrigerant that is divided and flows through the supercooling injection pipe 93. The supercooling injection pipe 93 branches off from the middle of the liquid refrigerant outlet pipe 83 and is connected to the low pressure refrigerant pipe 19 at the junction 65. A supercooling expansion valve 92 is provided in the middle of the supercooling injection pipe 93 and between the part branched from the liquid refrigerant outlet pipe 83 and the part to which the separation gas pipe 80 is connected.

  During the cooling operation, the control unit 7 controls the supercooling expansion valve 92 and the separation gas expansion valve 82, and the refrigerant is decompressed by the supercooling expansion valve 92 of the supercooling injection pipe 93 to be in a gas-liquid two-phase state. Then, the refrigerant decompressed in the separation gas expansion valve 82 of the separation gas pipe 80 is merged, flows through the supercooling injection pipe 93, and flows into the supercooling heat exchanger 91. In the supercooling heat exchanger 91, a low-pressure gas refrigerant that flows through the supercooling injection pipe 93 and an intermediate-pressure liquid refrigerant that is sent from the liquid refrigerant outlet pipe 83 and proceeds to the supercooling refrigerant pipe 84. Heat exchange. The refrigerant flowing from the supercooling heat exchanger 91 to the supercooling refrigerant pipe 84 is in a state where the degree of supercooling is increased. The supercooling refrigerant pipe 84 is provided with a supercooling temperature sensor 90t for detecting the temperature of the refrigerant passing therethrough. The refrigerant that flows through the supercooling injection pipe 93 and has passed through the supercooling heat exchanger 91 is in a superheated state and is sent toward the junction 65 of the low-pressure refrigerant pipe 19.

  During the heating operation, the control unit 7 closes the supercooling expansion valve 92 so that the part connected to the liquid refrigerant outlet pipe 83 and the part connected to the separation gas pipe 80 in the supercooling injection pipe 93. Although no refrigerant flows between them, the intermediate-pressure liquid refrigerant flowing through the liquid refrigerant outlet pipe 83 of the receiver 81 and the low-pressure refrigerant decompressed by the separation gas expansion valve 82 are heated in the supercooling heat exchanger 91. Will be exchanged.

(1-12) Indoor Heat Exchanger The first indoor heat exchanger 12a is provided in the first indoor unit 12. The second indoor heat exchanger 13 a is provided in the second indoor unit 13.

  The first indoor heat exchanger 12a and the second indoor heat exchanger 13a function as a refrigerant evaporator during the cooling operation, and function as a refrigerant cooler during the heating operation. Water and air are flown through these first indoor heat exchanger 12a and second indoor heat exchanger 13a as a cooling object or a heating object that exchanges heat with the refrigerant flowing inside. Here, room air from each indoor blower fan (not shown) flows to the first indoor heat exchanger 12a and the second indoor heat exchanger 13a, and cooled or heated conditioned air is supplied to the room. The air volume of each indoor fan is individually controlled for load processing required in the air-conditioning target space.

  One end of the first indoor heat exchanger 12a is connected to the first indoor expansion valve 12b. One end of the second indoor heat exchanger 13a is connected to the second indoor expansion valve 13b. The other end of the first indoor heat exchanger 12a and the other end of the second indoor heat exchanger 13a are joined, and the joined portion is connected to the gas refrigerant communication pipe 15.

(1-13) Indoor Expansion Valve The first indoor expansion valve 12b is provided in the first indoor unit 12. The first indoor expansion valve 12b adjusts the amount of refrigerant flowing to the first indoor heat exchanger 12a, and performs decompression and expansion of the refrigerant. The first indoor expansion valve 12b is disposed between the liquid refrigerant communication pipe 14 and the first indoor heat exchanger 12a.

  The second indoor expansion valve 13 b is provided in the second indoor unit 13. The second indoor expansion valve 13b adjusts the amount of refrigerant flowing to the second indoor heat exchanger 13a, and performs decompression / expansion of the refrigerant. The second indoor expansion valve 13b is disposed between the liquid refrigerant communication pipe 14 and the second indoor heat exchanger 13a.

(1-14) Control Unit The control unit 7 is configured by connecting each control board on which electronic components of the outdoor unit 11, the first indoor unit 12, and the second indoor unit 13 are connected by a communication line. The compressor drive motor of the four-stage compressor 20, the four-way switching valve group 25, the expansion valves 12b, 13b, 47, 48, 52, 72, 82, 92 and the like are connected. The control unit 7 controls the rotational speed of the compressor drive motor, adjusts the opening degree of the expansion valve, and ventilates the room based on information such as the indoor set temperature input from the outside, measured values of a temperature sensor and a pressure sensor (not shown), and the like. Adjust the air volume of fans and outdoor fans.

  The control unit 7 has a cooling operation mode and a heating operation mode, and selectively performs one of the operations.

(2) Operation of Air Conditioner The operation of the air conditioner 1 will be described with reference to FIGS.

  6 and 8 are pressure-enthalpy diagrams (ph diagrams) of the refrigeration cycle in the cooling operation and the heating operation, respectively. In each of these drawings, the curves indicated by the one-dot chain line that protrudes upward are the saturated liquid line and the dry saturated vapor line of the refrigerant. Moreover, in each figure, the point which the English letter on the refrigerating cycle was attached | subjected represents the pressure and enthalpy of the refrigerant | coolant in the point represented by the same alphabetical character in FIG. For example, the refrigerant at point B in FIG. 5 is in the state of pressure and enthalpy at point B in FIG. In addition, each operation control in the cooling operation and the heating operation of the air conditioner 1 is performed by the control unit 7.

(2-1) Operation in the cooling operation mode During the cooling operation, the four-way switching valve group 25 is switched to the connected state shown in FIG. 5, and the refrigerant moves in the direction of the arrow along the refrigerant pipe shown in FIG. 5. The four-stage compressor 20, the outdoor heat exchanger 40, the expansion mechanism 70, the first indoor heat exchanger 12a, and the second indoor heat exchanger 13a are circulated in the refrigerant circuit in this order. Hereinafter, operation | movement of the air conditioning apparatus 1 at the time of air_conditionaing | cooling operation is demonstrated, referring FIG. 5 and FIG.

  The low-pressure gas refrigerant (point A) sucked into the four-stage compressor 20 from the first suction pipe 21a is compressed by the first compression section 21 and discharged to the first discharge pipe 21b (point B). The discharged refrigerant flows into the first main body container 31a of the first oil separator 31 through the first discharge pipe 21b. The refrigerating machine oil entrained by the refrigerant is separated in the first main body container 31a, gathered downward, and sent to the middle of the second suction pipe 22a via the first lower oil return pipe 31b. Here, the size (flow path resistance) of the first capillary tube 31c provided in the middle of the first lower oil return pipe 31b is such that refrigerating machine oil other than the refrigerant flows mainly during the cooling operation. Therefore, the refrigerant in the first main body container 31a is suppressed from flowing excessively to the first lower oil return pipe 31b side, and flows mainly to the first outlet pipe 21c side. The refrigerant that has flowed through the first outflow pipe 21c passes through the first four-way switching valve 26 and is cooled by the first outdoor heat exchanger 41 that functions as an intercooler (intermediate cooler), and then the first intercooler pipe. It flows into the second suction pipe 22a through 41c (point C). In this way, during cooling operation, pressure loss occurs when the refrigerant flows through the first outdoor heat exchanger 41 that functions as an intercooler (intermediate cooler). Therefore, the first main body container 31a and the second suction pipe The pressure difference between the first main body container 31a and the refrigerating machine oil separated in the first main body container 31a is easily returned to the second suction pipe 22a via the first lower oil return pipe 31b. Therefore, during the cooling operation, it is difficult for a large amount of refrigerating machine oil to be accumulated in the first main body container 31a, and it is difficult for the refrigerating machine oil to accumulate to the height position of the lower end of the first upper oil return pipe 31d. The state where the oil return pipe 31d directly sucks only the refrigerating machine oil can be avoided.

  The refrigerant sucked into the second compression part 22 from the second suction pipe 22a is compressed and discharged to the second discharge pipe 22b (point D). The discharged refrigerant flows into the second main body container 32a of the second oil separator 32 through the second discharge pipe 22b. The refrigerating machine oil entrained by the refrigerant is separated in the second main body container 32a, gathered downward, and sent to the middle of the third suction pipe 23a via the second lower oil return pipe 32b. Here, similarly to the first lower oil return pipe 31b, the refrigerant in the second main body container 32a is suppressed from flowing excessively to the second lower oil return pipe 32b side, and mainly flows to the second outflow pipe 22c side. . The state of the second oil separator 32 is the same as that of the first oil separator 31. The same is true in that it is easy to ensure a sufficient pressure difference between the second main body container 32a and the third suction pipe 23a. The refrigerant that has flowed through the second outflow pipe 22c passes through the second four-way switching valve 27 and is cooled by the second outdoor heat exchanger 42 that functions as an intercooler (intermediate cooler), and then the second intercooler pipe. It flows through 42c (point E). The refrigerant flowing through the second intercooler pipe 42c merges with the intermediate pressure refrigerant (point L) that is heat-exchanged in the economizer heat exchanger 51 and flows through the injection pipe 53, and then flows into the third suction pipe 23a (point). F).

  The refrigerant sucked into the third compression section 23 from the third suction pipe 23a is compressed and discharged to the third discharge pipe 23b (point G). The discharged refrigerant flows into the third main body container 33a of the third oil separator 33 through the third discharge pipe 23b. The refrigerating machine oil entrained by the refrigerant is separated in the third main body container 33a, gathered downward, and sent to the middle of the fourth suction pipe 24a via the third lower oil return pipe 33b. Here, similarly to the first lower oil return pipe 31b, the refrigerant in the third main body container 33a is suppressed from flowing excessively to the third lower oil return pipe 33b side, and flows mainly to the third outflow pipe 23c side. . The state of the third oil separator 33 is the same as that of the first and second oil separators 31 and 32. The same is true in that it is easy to ensure a sufficient pressure difference between the third main body container 33a and the fourth suction pipe 24a. The refrigerant that has flowed through the third outlet pipe 23c passes through the third four-way switching valve 28, is cooled by the third outdoor heat exchanger 43 that functions as an intercooler, and then passes through the third intercooler pipe 43c. 4 Flows into the suction pipe 24a (point H).

  The refrigerant sucked into the fourth compression section 24 from the fourth suction pipe 24a is compressed and discharged to the fourth discharge pipe 24b (point I). The discharged high-pressure refrigerant flows into the fourth main body container 34a of the fourth oil separator 34 through the fourth discharge pipe 24b. The refrigerating machine oil entrained by the refrigerant is separated in the fourth main body container 34a, gathered downward, and sent to the middle of the first suction pipe 21a via the fourth lower oil return pipe 34b. Since a sufficient differential pressure is ensured between the fourth main body container 34a and the first suction pipe 21a, the refrigerating machine oil captured by the fourth main body container 34a is easy to return to the four-stage compressor 20, and other parts. The outflow to can be suppressed. Note that the high-pressure refrigerant discharged from the fourth compression unit 24 is in a supercritical state exceeding the critical pressure. This supercritical refrigerant passes through the fourth outlet pipe 24 c and the fourth four-way switching valve 29, is cooled by the fourth outdoor heat exchanger 44 that functions as a gas cooler, and is supplied to the third check valve 49 c of the bridge circuit 49. And flows to the economizer heat exchanger 51 (point J).

  A part of the high-pressure refrigerant that has passed through the third check valve 49 c of the bridge circuit 49 branches into the economizer injection pipe 53 and is decompressed by the economizer expansion valve 52. The intermediate pressure refrigerant (point K) that has been reduced from the supercritical state to a pressure lower than the critical pressure in the economizer expansion valve 52 to be in a gas-liquid two-phase state is replaced with another refrigerant (bridge) in the economizer heat exchanger 51. Heat exchange with the high-pressure refrigerant (point J) exceeding the critical pressure from the circuit 49 toward the liquid gas heat exchanger 61 results in an intermediate-pressure gas refrigerant (point L). This intermediate-pressure gas refrigerant (point L) flows from the injection pipe 53 into the second intercooler pipe 42c as described above.

  Here, the control unit 7 opens the first liquid gas on-off valve 62 in order to cause the refrigerant to flow through the liquid gas heat exchanger circuit 60 during the cooling operation and to perform heat exchange in the liquid gas heat exchanger 61, The second liquid gas on-off valve 63 is closed.

  The high-pressure refrigerant (point M) that has exchanged heat with the intermediate pressure refrigerant that has exited the economizer expansion valve 52 and has exited the economizer heat exchanger 51 in a state in which the temperature has further decreased, opens the first liquid gas on-off valve 62 in the open state. Passes through the liquid gas heat exchanger 61 and flows to the expansion mechanism 70 (point N). In the liquid gas heat exchanger 61, the high-pressure refrigerant (point M) exceeding the critical pressure that has passed through the economizer heat exchanger 51 flows from the low-pressure refrigerant pipe 19 to the first suction pipe 21a and the supercooled injection pipe. The high-pressure refrigerant (point N) is cooled by heat exchange between the low-pressure refrigerant flowing through the refrigerant 93 and the merged refrigerant joined together.

  The high-pressure refrigerant (point N) exiting the liquid gas heat exchanger 61 is branched into two, one flows toward the expander 71 of the expansion mechanism 70 and the other flows to the third outdoor expansion valve 72 of the expansion mechanism 70. It flows toward. In the third outdoor expansion valve 72, an intermediate pressure refrigerant (point O1) is obtained by reducing the pressure from the supercritical state to a pressure equal to or lower than the critical pressure. Also, in the expander 71, the pressure is reduced from the supercritical state to a pressure equal to or lower than the critical pressure, thereby becoming an intermediate pressure refrigerant (point O2). These intermediate pressure refrigerant (point O1) and intermediate pressure refrigerant (point O2) flow into the internal space of the receiver 81 after joining (point P). The gas-liquid two-phase intermediate pressure refrigerant flowing into the receiver 81 is separated into liquid refrigerant and gas refrigerant in the internal space of the receiver 81.

  The liquid refrigerant (point Q) separated by the receiver 81 flows through the liquid refrigerant outlet pipe 83. A part of the refrigerant flowing through the liquid refrigerant outlet pipe 83 passes through the supercooling heat exchanger 91 and enters a supercooled state (point W), and passes through the supercooled refrigerant pipe 84 and the first check valve 49a of the bridge circuit 49. Then, it is sent to the first indoor expansion valve 12b and the second indoor expansion valve 13b via the liquid refrigerant communication pipe 14. The other part of the refrigerant flowing through the liquid refrigerant outlet pipe 83 branches before flowing into the supercooling heat exchanger 91 and flows through the supercooling injection pipe 93. The refrigerant flowing through the supercooling injection pipe 93 is decompressed by the supercooling expansion valve 92 and becomes a low-pressure refrigerant in a gas-liquid two-phase state (point R).

  The gas refrigerant (point S) separated by the receiver 81 flows through the separation gas pipe 80. The refrigerant flowing through the separation gas pipe 80 is decompressed by the separation gas expansion valve 82 on the way, and becomes a low-pressure refrigerant (point T). The low-pressure refrigerant (point T) depressurized by the separation gas expansion valve 82 further flows through the separation gas pipe 80, and in the supercooling injection pipe 93 downstream of the supercooling expansion valve 92 and supercooling heat exchange. Join the upstream portion of the vessel 91 (point U).

  In the supercooling heat exchanger 91, the liquid refrigerant (point Q) separated by the receiver 81 and the gas-liquid two-phase low-pressure refrigerant (point U) joined to the supercooling injection pipe 93 via the separation gas pipe 80 and It is cooled by exchanging heat between the two, and it becomes a state with a degree of supercooling by being cooled (point W). On the other hand, the low-pressure refrigerant (point U) in the gas-liquid two-phase state joined to the supercooling injection pipe 93 via the separation gas pipe 80 is liquid refrigerant (point U) separated by the receiver 81 in the supercooling heat exchanger 91. Q) is heated (point V, where point V illustrates an overheated state, but may become wet depending on operating conditions and transient conditions).

  The refrigerant flowing into the first indoor unit 12 and the second indoor unit 13 from the liquid refrigerant communication pipe 14 expands when passing through the first indoor expansion valve 12b and the second indoor expansion valve 13b, and is a gas-liquid two-phase low pressure. It becomes a refrigerant (point X) and flows into the first indoor heat exchanger 12a and the second indoor heat exchanger 13a. This low-pressure refrigerant takes heat from the indoor air in the first indoor heat exchanger 12a and the second indoor heat exchanger 13a and becomes a superheated low-pressure gas refrigerant (point Y). The low-pressure refrigerant that has exited the first indoor unit 12 and the second indoor unit 13 flows to the low-pressure refrigerant pipe 19 via the gas refrigerant communication pipe 15 and the fourth four-way switching valve 29.

  The low-pressure refrigerant (point Y) that returns from the first indoor unit 12 or the second indoor unit 13 and flows through the low-pressure refrigerant pipe 19 and the low-pressure refrigerant (point V) that flows from the supercooling injection pipe 93 are merged point 65. At the point (Z) and returns to the four-stage compressor 20 from the first suction pipe 21a through the low pressure side of the liquid gas heat exchanger 61. Here, in the liquid gas heat exchanger 61, a low-pressure refrigerant (point Z) that goes to the first suction pipe 21a of the four-stage compressor 20 and a high-pressure that goes to the expansion mechanism 70 after passing through the economizer heat exchanger 51. Heat exchange is performed with the refrigerant (point M).

  As described above, the refrigerant circulates in the refrigerant circuit, whereby the air conditioner 1 performs the cooling operation cycle.

(2-2) Operation in the heating operation mode During the heating operation, the four-way switching valve group 25 is switched to the connected state, and the refrigerant moves in the direction of the arrow along the refrigerant pipe shown in FIG. 20, the 1st indoor heat exchanger 12a, the 2nd indoor heat exchanger 13a, the expansion mechanism 70, and the outdoor heat exchanger 40 are circulated in the refrigerant circuit in this order. Hereinafter, operation | movement of the air conditioning apparatus 1 at the time of heating operation is demonstrated, referring FIG. 7 and FIG.

  The low-pressure gas refrigerant (point A) sucked into the four-stage compressor 20 from the first suction pipe 21a is compressed by the first compression section 21 and discharged to the first discharge pipe 21b (point B). The discharged refrigerant flows into the first main body container 31a of the first oil separator 31 through the first discharge pipe 21b. The refrigerant that has flowed into the first main body container 31a flows toward the first outflow pipe 21c. The refrigerant that has flowed through the first outflow pipe 21c passes through the first four-way switching valve 26 and flows into the second suction pipe 22a without passing through the first outdoor heat exchanger 41 (point C). Here, the refrigerating machine oil separated and collected in the first main body container 31a is sent to the middle of the second suction pipe 22a via the first lower oil return pipe 31b. However, the size (flow path resistance) of the first capillary tube 31c provided in the middle of the first lower oil return pipe 31b is such that refrigerating machine oil other than the refrigerant flows mainly during the cooling operation. Since the refrigerant does not flow to the first outdoor heat exchanger 41 that functions as an intercooler (intermediate cooler) during heating operation, the refrigerant does not flow, so no pressure loss occurs. And the second suction pipe 22a cannot secure a sufficient pressure difference, and the refrigerating machine oil separated by the first oil separator 31 is unlikely to flow through the first lower oil return pipe 31b. For this reason, refrigeration oil may accumulate in the 1st main body container 31a. Even if the refrigeration oil accumulates in the first main body container 31a in this way, when the oil level of the refrigeration oil reaches the vicinity of the inlet height of the first upper oil return pipe 31d, the refrigeration oil becomes the first upper oil return pipe 31d. Can be sent to the second compression section 22 via the first four-way switching valve 26 and the second suction pipe 22a. Thereby, the situation where refrigerating machine oil accumulates too much in the 1st main body container 31a can be avoided also at the time of heating operation.

  The refrigerant sucked into the second compression part 22 from the second suction pipe 22a is compressed and discharged to the second discharge pipe 22b (point D). The discharged refrigerant flows into the second main body container 32a of the second oil separator 32 through the second discharge pipe 22b. The refrigerant that has flowed into the second main body container 32a flows toward the second outflow pipe 22c. The refrigerant that has flowed through the second outflow pipe 22c passes through the second four-way switching valve 27 and flows through the third suction pipe 23a without passing through the second outdoor heat exchanger 42. In addition, since the refrigerant | coolant (point L) of the intermediate pressure which heat-exchanges in the economizer heat exchanger 51 and flows through the injection piping 53 also flows in into the 3rd suction pipe 23a, the temperature of a refrigerant | coolant falls (point F). . Here, the refrigerating machine oil separated and collected in the second main body container 32a is sent to the middle of the third suction pipe 23a via the second lower oil return pipe 32b. Here, similarly to the first oil separator 31, the size of the flow path (flow path resistance) of the second capillary tube 32c provided in the middle of the second lower oil return pipe 32b performs the cooling operation. At this time, it is designed to be small so that refrigerating machine oil other than the refrigerant can flow, and the pressure does not flow through the second outdoor heat exchanger 42 that functions as an intercooler (intercooler) during heating operation. Since no loss occurs, a sufficient pressure difference between the second main body container 32a and the third suction pipe 23a cannot be ensured, and the refrigerating machine oil separated by the second oil separator 32 is the second lower oil. It is difficult to flow through the return pipe 32b. For this reason, refrigeration oil may accumulate in the 2nd main body container 32a. Even if the refrigeration oil accumulates in the second main body container 32a in this way, when the oil level of the refrigeration oil reaches the vicinity of the inlet height of the second upper oil return pipe 32d, the refrigeration oil becomes the second upper oil return pipe 32d. Can be sent to the third compression section 23 via the second four-way switching valve 27 and the third suction pipe 23a. Thereby, the situation where refrigerating machine oil accumulates too much in the 2nd main body container 32a can be avoided also at the time of heating operation.

  The refrigerant sucked into the third compression section 23 from the third suction pipe 23a is compressed and discharged to the third discharge pipe 23b (point G). The discharged refrigerant flows into the third main body container 33a of the third oil separator 33 through the third discharge pipe 23b. The refrigerant that has flowed into the third main body container 33a flows toward the third outlet pipe 23c. The refrigerant that has flowed through the third outflow pipe 23c passes through the third four-way switching valve 28 and flows into the fourth suction pipe 24a without passing through the third outdoor heat exchanger 43 (point H). Here, the refrigerating machine oil separated and collected in the third main body container 33a is sent to the middle of the fourth suction pipe 24a via the third lower oil return pipe 33b. Here, similarly to the first and second oil separators 31 and 32, the size of the flow path (flow path resistance) of the third capillary tube 33c provided in the middle of the third lower oil return pipe 33b is as follows. In the cooling operation, it is designed to be small so that refrigeration oil other than the refrigerant can flow mainly, and in the heating operation, the refrigerant is supplied to the third outdoor heat exchanger 43 that functions as an intercooler (intermediate cooler). Since there is no pressure loss because it does not flow, a sufficient pressure difference cannot be secured between the third main body container 33a and the fourth suction pipe 24a, and the refrigerating machine oil separated by the third oil separator 33 is , It is difficult to flow through the third lower oil return pipe 33b. For this reason, refrigeration oil may accumulate in the 3rd main body container 33a. Even if the refrigeration oil accumulates in the third main body container 33a in this way, when the oil level of the refrigeration oil reaches the vicinity of the inlet height of the third upper oil return pipe 33d, the refrigeration oil becomes the third upper oil return pipe 33d. Can be sucked up by the Venturi effect and sent to the fourth compression section 24 via the third four-way switching valve 28 and the fourth suction pipe 24a. Thereby, the situation where refrigerating machine oil accumulates too much in the 3rd main body container 33a can be avoided also at the time of heating operation.

  The refrigerant sucked into the fourth compression section 24 from the fourth suction pipe 24a is compressed and discharged to the fourth discharge pipe 24b (point I). The discharged high-pressure refrigerant flows into the fourth main body container 34a of the fourth oil separator 34 through the fourth discharge pipe 24b. The refrigerating machine oil entrained by the refrigerant is separated in the fourth main body container 34a, gathered downward, and sent to the middle of the first suction pipe 21a via the fourth lower oil return pipe 34b. Since a sufficient differential pressure is ensured between the fourth main body container 34a and the first suction pipe 21a, the refrigerating machine oil captured by the fourth main body container 34a is easy to return to the four-stage compressor 20, and other parts. The outflow to can be suppressed. Note that the high-pressure refrigerant discharged from the fourth compression unit 24 is in a supercritical state exceeding the critical pressure. This supercritical refrigerant passes through the fourth four-way switching valve 29 and flows into the first indoor unit 12 and the second indoor unit 13 via the gas refrigerant communication pipe 15 (point Y).

  The high-pressure refrigerant that has entered the first indoor unit 12 and the second indoor unit 13 from the gas refrigerant communication pipe 15 is converted into room air by the first indoor heat exchanger 12a and the second indoor heat exchanger 13a that function as a refrigerant radiator. Dissipates heat and warms indoor air. When the high-pressure refrigerant (point X) whose temperature has decreased due to heat exchange in the first indoor heat exchanger 12a or the second indoor heat exchanger 13a passes through the first indoor expansion valve 12b or the second indoor expansion valve 13b. The pressure is slightly reduced and flows through the liquid refrigerant communication pipe 14 to the bridge circuit 49 of the outdoor unit 11. In the bridge circuit 49, it passes through the second check valve 49b and goes to the economizer heat exchanger 51 (point J).

  Part of the high-pressure refrigerant (point J) that has passed through the second check valve 49 b of the bridge circuit 49 branches into the economizer injection pipe 53 and is decompressed by the economizer expansion valve 52. The intermediate pressure refrigerant (point K), which has been decompressed by the economizer expansion valve 52 and is in a gas-liquid two-phase state, is converted into another refrigerant (from the bridge circuit 49 to the liquid gas heat exchanger 61) in the economizer heat exchanger 51. It exchanges heat with the high-pressure refrigerant (point J) heading to become an intermediate-pressure gas refrigerant (point L). This intermediate-pressure gas refrigerant (point L) flows from the injection pipe 53 into the second intercooler pipe 42c as described above.

  Here, the control unit 7 closes the first liquid gas on-off valve 62 in order to prevent the refrigerant from flowing through the liquid gas heat exchanger circuit 60 during the heating operation and to prevent heat exchange in the liquid gas heat exchanger 61. The second liquid gas on-off valve 63 is opened.

  The high pressure refrigerant (point M) that has exchanged heat with the intermediate pressure refrigerant that has exited the economizer expansion valve 52 and has exited the economizer heat exchanger 51 in a state where the temperature has further decreased does not flow through the liquid gas heat exchanger 61. It passes through the second liquid gas on-off valve 63 and flows to the expansion mechanism 70 (point N).

  The high-pressure refrigerant (point N) flowing into the expansion mechanism 70 is branched into two, one flows toward the expander 71 of the expansion mechanism 70 and the other flows toward the third outdoor expansion valve 72 of the expansion mechanism 70. . In the third outdoor expansion valve 72, an intermediate pressure refrigerant (point O1) is obtained by reducing the pressure from the supercritical state to a pressure equal to or lower than the critical pressure. Also, in the expander 71, the pressure is reduced from the supercritical state to a pressure equal to or lower than the critical pressure, thereby becoming an intermediate pressure refrigerant (point O2). These intermediate pressure refrigerant (point O1) and intermediate pressure refrigerant (point O2) flow into the internal space of the receiver 81 after joining (point P). The gas-liquid two-phase intermediate pressure refrigerant flowing into the receiver 81 is separated into liquid refrigerant and gas refrigerant in the internal space of the receiver 81.

  The liquid refrigerant (point Q) separated by the receiver 81 flows through the liquid refrigerant outlet pipe 83. All of the refrigerant flowing through the liquid refrigerant outlet pipe 83 passes through the supercooling heat exchanger 91 to be in a supercooled state (point W), passes through the supercooled refrigerant pipe 84 and the bridge circuit 49, and goes to the outdoor heat exchanger 40. Sent.

  During the heating operation, the control unit 7 controls the supercooling expansion valve 92 to be fully closed, so that the refrigerant flowing through the liquid refrigerant outlet pipe 83 is not diverted toward the supercooled injection pipe 93.

  The gas refrigerant (point S) separated by the receiver 81 flows through the separation gas pipe 80. The refrigerant flowing through the separation gas pipe 80 is decompressed by the separation gas expansion valve 82 on the way, and becomes a low-pressure refrigerant (point T). The low-pressure refrigerant (point T) depressurized by the separation gas expansion valve 82 further flows through the separation gas pipe 80, and in the supercooling injection pipe 93 downstream of the supercooling expansion valve 92 and supercooling heat exchange. It flows into the portion upstream of the vessel 91 (point U).

  In the supercooling heat exchanger 91, between the intermediate-pressure refrigerant (point Q) flowing from the liquid refrigerant outlet pipe 83 of the receiver 81 and the low-pressure refrigerant (points T and U) decompressed by the separation gas expansion valve 82. Heat exchange takes place. By this heat exchange, the low-pressure refrigerant (points T and U) flowing through the supercooling injection pipe 93 evaporates to become superheated low-pressure refrigerant (point V) and flows toward the junction 65. The intermediate pressure refrigerant (point Q) flowing from the liquid refrigerant outlet pipe 83 of the receiver 81 is deprived of heat and becomes an intermediate pressure refrigerant (point W) with supercooling, and is bridged via the supercooling refrigerant pipe 84. It flows toward 49.

  The refrigerant flowing in the supercooled refrigerant pipe 84 toward the bridge circuit 49 is separated so that a part flows through the common pipe 47 a before the bridge circuit 49, and the other part is the second outdoor expansion valve 48 of the bridge circuit 49. Pass through.

  The refrigerant flowing through the common pipe 47a is reduced in pressure by the first outdoor expansion valve 47 to become a low-pressure refrigerant (point WX), and flows to the seventh pipe 43b. The refrigerant that has passed through the seventh pipe 43b partially evaporates in the third outdoor heat exchanger 43, passes through the third pipe 43a, the third four-way selector valve 28, and the second connection pipe 42d, and passes through the sixth pipe 42b. It flows toward. Part of the refrigerant that has passed through the sixth pipe 42b evaporates in the second outdoor heat exchanger 42, passes through the second pipe 42a, the second four-way switching valve 27, and the first connection pipe 41d, and passes through the fifth pipe. It flows toward 41b. The refrigerant that has passed through the fifth pipe 41b is further evaporated in the first outdoor heat exchanger 41 to become a superheated low-pressure gas refrigerant, and the first pipe 41a, the first four-way switching valve 26, and the first liquid gas suction. It passes through the pipe 26a (point XY) and joins the first suction pipe 21a. That is, these first to third outdoor heat exchangers 41 to 43 are connected to each other in series to evaporate the refrigerant that passes therethrough.

  The refrigerant (point VW) decompressed after passing through the second outdoor expansion valve 48 of the bridge circuit 49 evaporates in the fourth outdoor heat exchanger 44 after flowing through the eighth pipe 44b, and is overheated and low-pressure gas. It becomes a refrigerant and flows toward the low-pressure refrigerant pipe 19 through the fourth pipe 44 a and the fourth four-way switching valve 29.

  At this time, the control unit 7 adjusts the valve openings of the first outdoor expansion valve 47 and the second outdoor expansion valve 48 according to the capacity of each heat exchanger and the amount of pressure loss, so that the fourth outdoor heat The refrigerant is prevented from drifting to any one of the heat exchangers of the exchanger 44 and the first to third outdoor heat exchangers 41 to 43.

  The low-pressure gas refrigerant flowing through the low-pressure refrigerant pipe 19 joins the low-pressure gas refrigerant (point V) flowing through the supercooled injection pipe 93 at the junction 65 (point Z), and then the low-pressure side of the liquid gas heat exchanger 61 Flowing. Note that, during the heating operation, the refrigerant does not flow on the high-pressure side of the liquid gas heat exchanger 61, so heat exchange here is not performed.

  The low-pressure gas refrigerant that has passed through the low-pressure side of the liquid gas heat exchanger 61 joins the refrigerant (point XY) flowing through the first liquid gas suction pipe 26a, and then the four-stage compressor 20 through the first suction pipe 21a. (Point A).

As described above, the refrigerant circulates in the refrigerant circuit, whereby the air conditioner 1 performs the heating operation cycle.

(3) Features of the air conditioner (3-1)
In the air conditioner 1, the first to third oil separators 31 to 33 are provided with first to third upper oil return pipes 31d to 33d. For this reason, even if the refrigerating machine oil in the first to third main body containers 31a to 33a increases, the first to third outflows are made using the venturi effect in the first to third upper oil return pipes 31d to 33d. Refrigerating machine oil can be sent out to the tubes 21c to 23c. Thereby, accumulation of the refrigeration oil in the first to third oil separators 31 to 33 can be suppressed, and the exhaustion of the refrigeration oil in the four-stage compressor 20 can be suppressed.

  Here, the inner diameters of the first to third upper oil return pipes 31d to 33d are configured to be smaller than the inner diameters of the first to third outflow pipes 21c to 23c. For this reason, the refrigerant flows vigorously in the first to third outlet pipes 21c to 23c, and the venturi effect in the first to third upper oil return pipes 31d to 33d is easily obtained.

(3-2)
Moreover, in the air conditioning apparatus 1, since the 1st-3rd outdoor heat exchangers 41-43 function as an intermediate cooler at the time of air_conditionaing | cooling operation, it is possible to improve cycle efficiency. During the cooling operation, the first to third lower oil return pipes 31b to 33b are used for the refrigerating machine oil by using the pressure loss in the first to third outdoor heat exchangers 41 to 43 that function as intermediate coolers. Can be returned efficiently. Here, excessive refrigerant does not flow through the first to third lower oil return pipes 31b to 33b due to the pressure loss generated in the first to third outdoor heat exchangers 41 to 43 during the cooling operation. In addition, the first to third capillary tubes 31c to 33c can be designed to be small. Thereby, a refrigerant | coolant can be efficiently flowed through the 1st-3rd outdoor heat exchangers 41-43 which function as an intercooler at the time of air_conditionaing | cooling operation, and it can fully improve cycle efficiency.

(3-3)
Further, in the air conditioner 1, during the heating operation, since the refrigerant does not flow to the first to third outdoor heat exchangers 41 to 43, a pressure loss is generated in the first to third outdoor heat exchangers 41 to 43. However, it becomes difficult to flow a sufficient amount of refrigerating machine oil to the first to third lower oil return pipes 31b to 33b using the differential pressure. In particular, so that excessive refrigerant does not flow through the first to third lower oil return pipes 31b to 33b due to pressure loss generated in the first to third outdoor heat exchangers 41 to 43 during the cooling operation. Since each of the first to third capillary tubes 31c to 33c is designed to be small, a sufficient amount of refrigerating machine oil is supplied to the first to third lower oil return pipes 31b to 33b during the heating operation in which the differential pressure is difficult to use. It becomes difficult to flow.

  On the other hand, in the first to third oil separators 31 to 33 of the air conditioner 1, since the first to third upper oil return pipes 31d to 33d are provided, even the first to third main bodies are provided. Even if the refrigerating machine oil accumulates in the containers 31a to 33a, an excessive amount of the first to third main body containers 31a to 33a is utilized by utilizing the venturi effect in the first to third upper oil return pipes 31d to 33d. Refrigerating machine oil can be prevented from accumulating.

  In addition, even if the 1st-3rd upper oil return pipes 31d-33d may suck | inhale much refrigeration oil at the time of heating operation, a refrigerant | coolant is the 1st-3rd outdoor heat exchanger 41 at the time of heating operation. Since it is immediately sucked into the upper compression section without being sent to -43, it is possible to avoid the refrigeration oil from sleeping in the first to third outdoor heat exchangers 41 to 43.

(3-4)
Further, in the air conditioner 1, the first to third upper oil return pipes 31d to 33d are employed only in the first to third oil separators 31 to 33, and the first to third oil separators 31 to 33d employ the first to third oil separators 31 to 33d. No pipes corresponding to the third upper oil return pipes 31d to 33d are provided.

  Thereby, in 1st-3rd main body containers 31a-33a, the outflow of the refrigerating machine oil from the 4th oil separator 34 to other parts other than the four-stage compressor 20 is suppressed, suppressing the accumulation of refrigerating machine oil. It is possible to make it.

(4) Modification (4-1) Modification A
In the said embodiment, in the 1st-3rd oil separators 31-33, the connection position of the 1st-3rd upper oil return pipes 31d-33d and the 1st-3rd outflow pipes 21c-23c is 1st-3rd. The case of being outside the third main body containers 31a to 33a has been described as an example.

  However, the connection positions of the first to third upper oil return pipes 31d to 33d and the first to third outlet pipes 21c to 23c may be inside the first to third main body containers 31a to 33a. In this case, it is preferable that the first to third upper oil return pipes 31d to 33d join at a position as far as possible from the lower ends of the first to third outflow pipes 21c to 23c.

(4-2) Modification B
In the above embodiment, the air conditioner 1 that performs a four-stage compression refrigeration cycle has been described as an example.

  However, the refrigeration cycle is not limited to one that performs four-stage compression, and may be, for example, two-stage compression or three-stage compression. For example, in an air conditioner that performs a two-stage compression refrigeration cycle, an upper oil return pipe may be employed in an oil separator provided between the first-stage discharge side and the second-stage suction side. it can. Further, for example, in the case of an air conditioner that performs a three-stage compression refrigeration cycle, between the first-stage discharge side and the second-stage suction side, the second-stage discharge side, and the third-stage suction side An upper oil return pipe can also be employed in an oil separator provided between at least one of the two.

1 Air conditioning equipment (refrigeration equipment)
7 Controller 12a First indoor heat exchanger (evaporator)
13a Second indoor heat exchanger (evaporator)
20 Four-stage compressor 21 First compression section (low-stage compression section, first low-stage compression section)
21b First discharge pipe (introducing pipe, lower introducing pipe)
21c 1st outflow pipe (outflow pipe, lower outflow pipe)
22 2nd compression part (low stage compression part, high stage compression part, 1st low stage compression part, 2nd low stage compression part)
22b Second discharge pipe (introducing pipe, lower introducing pipe)
22c 2nd outflow pipe (outflow pipe, lower stage outflow pipe)
23 3rd compression part (low stage compression part, high stage compression part, 2nd low stage compression part)
23b 3rd discharge pipe 23c 3rd outflow pipe (outflow pipe)
24 4th compression part (high stage side compression part)
25 Four-way switching valve group 26 First four-way switching valve (switching valve)
27 Second four-way switching valve (switching valve)
28 3rd four way switching valve (switching valve)
29 4th four way switching valve 31 1st oil separator (intermediate oil separator, lower oil separator)
31a First main body container (main body container, lower main body container)
31b First lower oil return pipe (lower oil return pipe, lower lower oil return pipe)
31c First capillary tube (flow path resistor)
31d First upper oil return pipe (upper oil return pipe, lower upper oil return pipe)
32 Second oil separator (intermediate oil separator, lower oil separator)
32a Second main body container (main body container, lower main body container)
32b Second lower oil return pipe (lower oil return pipe, lower lower oil return pipe)
32c Second capillary tube (flow path resistor)
32d Second upper oil return pipe (upper oil return pipe, lower upper oil return pipe)
33 Third oil separator (intermediate oil separator)
33a Third main body container (main body container)
33b Third lower oil return pipe (lower oil return pipe)
33c Third capillary tube (flow path resistor)
33d Third upper oil return pipe (upper oil return pipe)
34 4th oil separator (high stage oil separator)
40 outdoor heat exchanger 41 first outdoor heat exchanger (intermediate cooler)
42 Second outdoor heat exchanger (intercooler)
43 Third outdoor heat exchanger (intercooler)
44 4th outdoor heat exchanger (heat radiator)
47 first outdoor expansion valve 48 second outdoor expansion valve 49 bridge circuit 50 economizer circuit 51 economizer heat exchanger 52 economizer expansion valve 53 economizer injection piping 60 liquid gas heat exchange circuit 61 liquid gas heat exchanger 62 first liquid gas on-off valve 63 Second liquid gas on-off valve 70 Expansion mechanism (decompression unit)
DESCRIPTION OF SYMBOLS 71 Expander 72 Expansion valve 80 Separation gas piping 81 Receiver 82 Separation gas expansion valve 83 Liquid refrigerant outlet pipe 90 Supercooling circuit 91 Supercooling heat exchanger 92 Supercooling expansion valve 93 Supercooling injection piping

JP 2014-2111293 A

Claims (7)

Low-stage compression section (21, 22, 23),
A high-stage compression section (22, 23, 24) for further compressing the refrigerant compressed by the low-stage compression section,
A radiator (44) for dissipating the heat of the refrigerant,
A decompression unit (70), and evaporators (12a, 13a) for evaporating the refrigerant,
A refrigerant circuit configured by being connected,
Refrigerating machine oil that is disposed between the discharge side of the low-stage compression section (21, 22, 23) and the suction side of the high-stage compression section (22, 23, 24) and that is accompanied by the passing refrigerant. A separable intermediate oil separator (31, 32, 33);
With
The intermediate oil separator is
A body container (31a, 32a, 33a);
An introduction pipe (21b, 22b, 23b) for guiding the refrigerant discharged from the low-stage compression section to the internal space of the main body container;
A lower oil return pipe extending from the lower side of the inner space of the main body container to the outside in order to guide the refrigerating machine oil separated in the main body container to the suction side of the higher stage compression section (22, 23, 24). 31b, 32b, 33b),
In order to guide the refrigerant to the suction side of the high-stage compression section (22, 23, 24), it extends to the outside from a position in the internal space of the main body container and above the upper end of the lower oil return pipe. Outlet pipes (21c, 22c, 23c),
An upper oil return pipe extending from a height above the upper end of the lower oil return pipe in the internal space of the main body container and below the lower end of the outflow pipe and joining the outflow pipe ( 31d, 32d, 33d)
have,
Refrigeration equipment (1). The inner diameter of the outflow pipe is larger than the inner diameter of the upper oil return pipe,
The refrigeration apparatus according to claim 1. The refrigerant circuit further includes an intermediate cooler (41, 42, 43) for dissipating heat of the refrigerant, and a switching valve (26, 27, 28),
The switching valve includes a cooling operation for guiding the refrigerant discharged from the low-stage compression unit to the suction side of the high-stage compression unit via the intermediate oil separator and the intermediate cooler; and the low-stage side The refrigerant circuit is switched between a heating operation in which the refrigerant discharged from the compression section is guided to the suction side of the high-stage compression section without passing through the intermediate cooler while passing through the intermediate oil separator. Is possible,
The refrigeration apparatus according to claim 1 or 2. The lower oil return pipe extends from the lower side of the internal space of the main body container to the outside, and is then connected to the suction side of the higher stage compression unit via a flow path resistor (31c, 32c, 33c). And
The passage resistance of the refrigerant by the flow path resistor is larger than the passage resistance of the refrigerant from the outflow pipe to the suction side of the higher stage compression section (22, 23, 24).
The refrigeration apparatus according to claim 3. A high-stage oil separator (34) provided on the discharge side of the high-stage compression section and capable of separating the refrigerating machine oil accompanying the passing refrigerant;
The high stage oil separator does not have a structure corresponding to the upper oil return pipe of the intermediate oil separator.
The refrigeration apparatus according to any one of claims 1 to 4. The low stage compression section (21, 22, 23) further compresses the refrigerant compressed by the first low stage compression section (21, 22) and the first low stage compression section. A second low-stage compression section (22, 23),
A lower oil separator (31, disposed between a discharge side of the first low-stage compression unit and a suction side of the second low-stage compression unit and capable of separating the refrigerating machine oil accompanying the passing refrigerant. 32),
The lower oil separator is
Lower body containers (31a, 32a);
Lower introduction pipes (21b, 22b) for guiding the refrigerant discharged from the first lower stage compression section to the internal space of the lower body container;
A lower lower oil return pipe (31b, extending from the lower side of the inner space of the lower main body container to the outside in order to guide the refrigerating machine oil separated in the lower main body container to the suction side of the second lower stage compression section 32b)
In order to guide the refrigerant to the suction side of the second lower stage compression section, the lower stage outflow extends from the position above the upper end of the lower lower oil return pipe in the inner space of the lower body container to the outside. Tubes (21c, 22c);
A lower stage extending from a height above the upper end of the lower lower oil return pipe in the internal space of the lower main body container and below the lower end of the lower outlet pipe, and joined to the lower outlet pipe Upper oil return pipes (31d, 32d);
have,
The refrigeration apparatus according to any one of claims 1 to 5. The high-stage compression unit and the low-stage compression unit have a common drive source.
The refrigeration apparatus according to any one of claims 1 to 6.

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