JP6286844B2 - Air conditioner - Google Patents

Description

  The present invention relates to an air conditioner.

  Conventionally, chlorofluorocarbon refrigerant (CFC) has been used as a refrigerant used in air-conditioning equipment using a refrigeration cycle, but instead of chlorofluorocarbon regulations, instead of chlorofluorocarbon refrigerant, an alternative to R410A or the like having a small ozone destruction coefficient Fluorocarbon refrigerant has been used. At present, efforts to reduce greenhouse gases are also promoting the use of alternative CFC refrigerants with low global warming potential (GWP). In such a flow, the R32 refrigerant has an ozone depletion coefficient of 0 and a global warming coefficient of about 1/3 that of R410A, so that it is expected to be used for an air conditioner.

  When the R32 refrigerant is used, the refrigerant temperature (refrigerant discharge temperature) at the discharge port of the compressor is about 15 ° C. to 20 ° C. higher than when other refrigerants are used. For example, there is a high possibility that the seal member or the like will be thermally deteriorated. Therefore, Patent Document 1 prevents the thermal deterioration of each part of the compressor by controlling the dryness of the refrigerant sucked into the compressor within the range of 0.75 to 0.85 and lowering the refrigerant discharge temperature. The technology is disclosed. That is, the refrigerant discharge temperature is lowered by reducing the suction superheat degree. For this reason, the thermal deterioration of the compressor is unlikely to occur, and the reliability of the compressor when the R32 refrigerant is used is improved.

  Patent Document 2 discloses an air conditioner configured to control the circulation rate of the lubricating oil for lubricating the compressor to the refrigerant circuit within a range of 0 to 1% when using R32. By controlling the circulation rate of the lubricating oil to the refrigerant circuit within the above range, the refrigeration efficiency (COP) is improved when the R32 refrigerant is used.

JP 2001-194015 A Japanese Patent No. 3468174

(Problems to be solved by the invention)
According to the air conditioner described in Patent Document 1, since the dryness of the refrigerant at the suction port of the compressor is set to less than 1 in order to prevent an increase in the refrigerant discharge temperature, the wet refrigerant is sucked into the compressor. . Lubricating oil for lubricating the compressor is also sucked into the compressor. Therefore, when refrigerant having a dryness of less than 1 is sucked into the compressor, the lubricating oil is diluted with liquid refrigerant (or vapor refrigerant). In addition, the viscosity of the lubricating oil decreases and the lubricating ability decreases. Moreover, since the non-evaporated refrigerant is sucked into the compressor, the refrigeration efficiency is lowered.

  According to the air conditioner described in Patent Document 2, the efficiency is improved by controlling the oil circulation rate to improve the heat transfer rate in the heat transfer tube in the heat exchanger, but the oil circulation rate is controlled. In this case, the temperature of the refrigerant sucked into the compressor (refrigerant suction temperature) and the temperature of the refrigerant discharged from the compressor (refrigerant discharge temperature) are not observed. For this reason, there may be a case where there is too little circulating lubricating oil and the refrigerant sucked into the compressor is not sufficiently heated by the lubricating oil. Then, the refrigerant suction temperature is lowered, and the dryness of the refrigerant becomes less than 1, which may cause the above problem.

  An object of the present invention is to provide an air conditioner in which, when an R32 refrigerant is used, an increase in the refrigerant discharge temperature can be suppressed without making the dryness of the refrigerant sucked into the compressor less than 1.

(Means for solving the problem)
The present invention has a suction port and a discharge port, operates by receiving power from a drive source, sucks refrigerant mixed with lubricating oil from the suction port, compresses the sucked refrigerant and discharges it from the discharge port a machine, an oil separator of the refrigerant discharged from the discharge port is separated into a gas refrigerant and a lubricating oil, an indoor heat exchanger, an outdoor heat exchanger, and inhalation pipe connected to the suction port, the suction pipe are connected, and an oil return pipe for flowing the separated lubricating oil by the oil separator to the suction pipe, e Preparations and oil flow control device for controlling the flow rate of lubricating oil flowing in the oIL back in the pipe, and during the heating, room The heat exchanger serves as a condenser that condenses the gas refrigerant separated by the oil separator, while the outdoor heat exchanger serves as an evaporator that evaporates the refrigerant flowing out of the condenser. On the other hand, the outdoor heat exchanger becomes the condenser, the suction pipe sucks the refrigerant flowing out of the evaporator into the suction port of the compressor, and the oil flow control device detects the temperature of the refrigerant discharged from the discharge port. Lubricating oil flowing in the oil return pipe when the refrigerant discharge temperature is higher than a predetermined upper limit discharge temperature and when the superheat degree of the refrigerant at the suction port is smaller than a predetermined lower limit value of the superheat degree The flow rate of the lubricating oil flowing in the oil return pipe is controlled so that the flow rate of the indoor heat exchanger is increased so that the heat exchange temperature difference that is the absolute value of the difference between the target heat exchange temperature and the heat exchange temperature of the indoor heat exchanger is Provided is an air conditioner that controls the flow rate of lubricating oil flowing in the oil return pipe so that the heat exchange temperature difference is reduced when the difference is larger than a predetermined upper limit heat exchange temperature difference .

  In this case, the upper limit discharge temperature is preferably set in advance as a temperature lower by a predetermined temperature than the upper limit temperature limit (heat resistance temperature) at which each component of the compressor does not cause thermal degradation. In particular, the upper limit discharge temperature is preferably set in advance as a temperature lower by 10 to 15 ° C. than the heat resistant temperature.

  According to the present invention, when the refrigerant discharge temperature is higher than the upper limit discharge temperature, the flow rate of the lubricating oil flowing in the oil return pipe increases. As the flow rate of the lubricating oil flowing through the oil return pipe increases, the flow rate of the lubricating oil drawn into the compressor also increases. The temperature of the lubricating oil sucked into the compressor is lower than the temperature of the refrigerant compressed by the compressor. For this reason, the lubricating oil has not only a lubricating action for lubricating the compressor, but also a cooling action for cooling the compressor and the refrigerant compressed by the compressor. Therefore, if the flow rate of the lubricating oil sucked into the compressor increases, cooling of the compressor and the refrigerant compressed by the compressor is promoted. Thus, by increasing the flow rate of the lubricating oil sucked into the compressor to promote cooling of the discharged refrigerant, an excessive increase in the refrigerant discharge temperature can be suppressed even when the R32 refrigerant is used. Further, since the lubricating oil is used for cooling the refrigerant, it is not necessary to make the dryness of the refrigerant less than 1.

In addition, the oil flow control device is configured so that the flow rate of the lubricating oil flowing in the oil return pipe increases when the superheat degree of the refrigerant at the suction port of the compressor is smaller than a predetermined superheat degree lower limit value. that controls the flow rate of lubricating oil flowing in the pipe. In this case, the lower limit value of the superheat degree is preferably 3 ° C. or higher.

  When the degree of superheat of the refrigerant at the suction port of the compressor is small, there is a high possibility that the dryness of the refrigerant drawn into the compressor is locally less than 1. In the present invention, the flow rate of the lubricating oil flowing through the oil return pipe is increased when the superheat degree is smaller than the lower limit value of the superheat degree. The temperature of the lubricating oil sucked into the compressor suction port from the oil return pipe is higher than the temperature of the refrigerant sucked into the compressor. For this reason, the lubricating oil has not only a lubricating action for lubricating the compressor, but also a heating action for heating the refrigerant sucked into the compressor. Therefore, if the flow rate of the lubricating oil sucked into the compressor is increased, heating of the refrigerant sucked into the compressor is promoted. In this way, by increasing the flow rate of the lubricating oil to promote the heating of the suction refrigerant, the degree of superheat is increased, and the dryness of the refrigerant sucked into the compressor can be maintained at 1 or more.

  Moreover, the air conditioner of this invention is good to provide the oil return flow control valve which is interposed in the middle of the oil return piping and can adjust an opening degree. The oil flow rate control device may control the flow rate of the lubricating oil flowing through the oil return pipe by controlling the opening of the oil return flow rate control valve. According to this, the flow rate of the lubricating oil flowing through the oil return pipe can be controlled by the oil flow control device controlling the opening degree of the oil return flow control valve.

It is the schematic which shows the structure of the air conditioner which concerns on 1st Embodiment. It is a flowchart which shows the opening degree control routine which the control apparatus which concerns on 1st Embodiment performs. It is a figure which shows the refrigerating cycle represented on the ph diagram. It is a block diagram which shows the function structure of the control apparatus which concerns on 2nd Embodiment. It is a flowchart which shows the heat exchange temperature comparison routine which the heat exchange temperature difference output part of the control apparatus which concerns on 2nd Embodiment performs. It is a flowchart which shows the superheat degree comparison routine which the superheat degree output part of the control apparatus which concerns on 2nd Embodiment performs. It is a flowchart which shows the discharge temperature comparison routine which the discharge temperature difference output part of the control apparatus which concerns on 2nd Embodiment performs. It is a flowchart which shows the opening degree control routine which the opening degree control part of the control apparatus which concerns on 2nd Embodiment performs.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram illustrating a configuration of an air conditioner 1 according to the first embodiment. The air conditioner 1 is an engine-driven air conditioner that is driven by a gas engine. As shown in FIG. 1, the air conditioner 1 includes a gas engine 11, a compressor 12, an oil separator 13, an indoor heat exchanger 14 installed indoors, and an outdoor heat exchanger 15 installed outdoor. An expansion valve 16 for expanding the refrigerant, a four-way switching valve 17, an accumulator 18 for separating the refrigerant from gas and liquid, and a control device 19.

  The compressor 12 operates by receiving power from the gas engine 11. The compressor 12 has a suction port 12a and a discharge port 12b. The compressor 12 sucks refrigerant from the suction port 12a and compresses the sucked refrigerant and discharges it from the discharge port 12b. In this embodiment, R32 refrigerant is used as the refrigerant.

  One end of the discharge pipe 121 is connected to the discharge port 12 b of the compressor 12. The other end of the discharge pipe 121 is connected to the refrigerant inlet 131 of the oil separator 13. The oil separator 13 flows in the refrigerant from the refrigerant inlet 131 and separates the lubricating oil from the flowed refrigerant. The separated oil is discharged from the oil discharge port 133. The refrigerant from which the oil has been separated is discharged from the refrigerant discharge port 132. Further, one end of the suction pipe 122 is connected to the suction port 12 a of the compressor 12.

  One end of the first pipe 21 is connected to the refrigerant outlet 132 of the oil separator 13. The other end of the first pipe 21 is connected to the four-way switching valve 17. As shown in FIG. 1, the four-way switching valve 17 has four ports (a first port 171, a second port 172, a third port 173, and a fourth port 174). The four-way switching valve 17 includes a heating connection state in which the first port 171 is connected to the second port 172 and the third port 173 is connected to the fourth port 174, the first port 171 is connected to the third port 173, and The connection state can be switched to the cooling connection state in which the second port 172 is connected to the fourth port 174. The first pipe 21 described above is connected to the first port 171 of the four-way switching valve 17. One end of the second pipe 22 is connected to the second port 172. One end of the third pipe 23 is connected to the third port 173, and one end of the fourth pipe 24 is connected to the fourth port 174.

  The indoor heat exchanger 14 is connected to the other end of the second pipe 22. The outdoor heat exchanger 15 is connected to the other end of the third pipe 23. The indoor heat exchanger 14 and the outdoor heat exchanger 15 are connected by an intermediate pipe 25. The indoor heat exchanger 14 allows the refrigerant to flow into the inside from the second pipe 22 or the intermediate pipe 25 and also causes the refrigerant and the ambient air to exchange heat. The outdoor heat exchanger 15 allows the refrigerant to flow into the inside from the intermediate pipe 25 or the third pipe 23, and exchanges heat between the flowed refrigerant and the outside air. As can be seen from FIG. 1, the expansion valve 16 is interposed in the middle of the intermediate pipe 25. The expansion valve 16 expands the refrigerant passing therethrough.

  The other end of the fourth pipe 24 is connected to the refrigerant inlet 181 of the accumulator 18. The accumulator 18 gas-liquid separates the refrigerant that has flowed from the refrigerant inlet 181 and discharges the separated gas refrigerant from the refrigerant outlet 182. The other end of the suction pipe 122 is connected to the refrigerant discharge port 182.

  One end of the oil return pipe 26 is connected to the oil discharge port 133 of the oil separator 13. An oil return flow control valve 31 having a variable opening is interposed in the middle of the oil return pipe 26. The other end of the oil return pipe 26 communicates with the suction pipe 122.

  A discharge temperature sensor 41 is attached to the discharge pipe 121. The discharge temperature sensor 41 detects the temperature of the refrigerant discharged from the compressor 12 and flowing through the discharge pipe 121 (refrigerant discharge temperature Td). A suction temperature sensor 42 and a suction pressure sensor 43 are attached to the suction pipe 122. The suction temperature sensor 42 detects the temperature of the refrigerant that flows through the suction pipe 122 and is sucked into the compressor 12 (refrigerant suction temperature Ts). The suction pressure sensor 43 detects the pressure of the refrigerant (refrigerant suction pressure Ps) that flows through the suction pipe 122 and is sucked into the compressor 12. Further, a heat exchange temperature sensor 44 is attached to the indoor heat exchanger 14. The heat exchange temperature sensor 44 detects the temperature of the refrigerant flowing in the indoor heat exchanger 14 (heat exchange temperature Th). In addition, a temperature sensor and a pressure sensor may be attached to other parts.

  The control device 19 is configured by a microcomputer having a CPU, a ROM, a RAM, and the like, and performs control related to the operation of the air conditioner 1 (for example, the rotational speed control of the gas engine 11). The control device 19 is electrically connected to each sensor (discharge temperature sensor 41, suction temperature sensor 42, suction pressure sensor 43, heat exchange temperature sensor 44, etc.), and inputs information detected by these sensors. To do. The control device 19 is also electrically connected to the oil return flow control valve 31 and controls the opening degree of the oil return flow control valve 31 based on information input from each sensor.

  Next, the air conditioning operation (heating operation, cooling operation) of the air conditioner 1 will be briefly described. First, the heating operation will be described. During heating, the four-way switching valve 17 is brought into a heating connection state. When the gas engine 11 is driven and the compressor 12 is activated during heating, the compressor 12 sucks in the low-pressure gas refrigerant mixed with lubricating oil from the suction port 12a and compresses the gas refrigerant inside. At this time, the lubricating oil lubricates the compressor 12. Then, the compressed high-pressure gas refrigerant is discharged from the discharge port 12b together with the lubricating oil.

  The high-pressure gas refrigerant and the lubricating oil discharged from the discharge port 12 b flow through the discharge pipe 121 and further flow into the oil separator 13 from the refrigerant inlet 131 of the oil separator 13. The oil separator 13 separates the lubricating oil from the high pressure gas refrigerant. The lubricating oil separated by the oil separator 13 flows from the oil discharge port 133 of the oil separator 13 into the oil return pipe 26 and further flows into the suction pipe 122. Then, the air is sucked into the compressor 12 again from the suction port 12 a of the compressor 12. In this way, the lubricating oil repeatedly lubricates the compressor 12.

  The high-pressure gas refrigerant from which the lubricating oil has been separated by the oil separator 13 exits the oil separator 13 from the refrigerant discharge port 132 and flows through the first pipe 21, and enters the four-way switching valve 17 from the first port 171 of the four-way switching valve 17. . During heating, the first port 171 of the four-way switching valve 17 is connected to the second port 172, and the second port 172 is connected to the second pipe 22, so that the four-way switching valve 17 enters from the first port 171. The high-pressure gas refrigerant exits the four-way switching valve 17 from the second port 172, flows in the second pipe 22, and then flows into the indoor heat exchanger 14 ahead. The high-pressure gas refrigerant that has flowed into the indoor heat exchanger 14 discharges heat to the indoor air and condenses while circulating in the indoor heat exchanger 14. At this time, the indoor air is warmed by the heat discharged from the high-pressure gas refrigerant, and the room is heated.

  The refrigerant that has exhausted heat to the indoor air and has condensed is partially liquefied and flows out of the indoor heat exchanger 14 and flows through the intermediate pipe 25. Then, after being expanded by the expansion valve 16, the pressure is reduced so as to be easily evaporated, and then flows into the outdoor heat exchanger 15. The refrigerant flowing into the outdoor heat exchanger 15 evaporates by taking heat from the outside air while flowing through the outdoor heat exchanger 15.

  A part of the refrigerant evaporated by taking the heat of the outside air is vaporized and flows out of the outdoor heat exchanger 15 and flows through the third pipe 23. Then, the four-way switching valve 17 enters from the third port 173. During heating, the third port 173 of the four-way selector valve 17 is connected to the fourth port 174, and the fourth port 174 is connected to the fourth pipe 24. Therefore, the four-way selector valve 17 enters from the third port 173. The refrigerant flows from the fourth port 174 through the four-way switching valve 17 to the fourth pipe 24. The refrigerant flowing through the fourth pipe 24 is introduced into the accumulator 18 from the refrigerant inlet 181 of the accumulator 18. In the accumulator 18, the refrigerant is separated into a liquid refrigerant and a low-pressure gas refrigerant. Only the low-pressure gas refrigerant is discharged from the refrigerant discharge port 182 of the accumulator 18 and flows to the suction pipe 122. The refrigerant in the suction pipe 122 merges with the lubricating oil flowing from the oil return pipe 26 and is sucked into the compressor 12 from the suction port 12a of the compressor 12 together with the lubricating oil.

  Next, the cooling operation will be described. During cooling, the four-way switching valve 17 is brought into a cooling connection state. When the gas engine 11 is driven and the compressor 12 is activated during cooling, the compressor 12 sucks in the low-pressure gas refrigerant mixed with lubricating oil from the suction port 12a and compresses the gas refrigerant inside. At this time, the lubricating oil lubricates the compressor 12. Then, the compressed high-pressure gas refrigerant is discharged from the discharge port 12b together with the lubricating oil.

  The high-pressure gas refrigerant and lubricating oil discharged from the discharge port 12 b flow through the discharge pipe 121 and further flow into the oil separator 13 from the refrigerant inlet 131 of the oil separator 13. The lubricating oil separated by the oil separator 13 flows into the oil return pipe 26 from the oil discharge port 133 of the oil separator, and further flows into the suction pipe 122. Then, the air is sucked into the compressor 12 again from the suction port 12 a of the compressor 12.

  The high-pressure gas refrigerant from which the lubricating oil has been separated by the oil separator 13 exits the oil separator 13 from the refrigerant discharge port 132 and flows through the first pipe 21, and enters the four-way switching valve 17 from the first port 171 of the four-way switching valve 17. . During cooling, the first port 171 of the four-way switching valve 17 is connected to the third port 173, and the third port 173 is connected to the third pipe 23, so that the four-way switching valve 17 enters the first port 171. The gas refrigerant exits the four-way switching valve 17 from the third port 173, flows through the third pipe 23, and further flows into the outdoor heat exchanger 15 ahead. The high-pressure gas refrigerant that has flowed into the outdoor heat exchanger 15 discharges heat to the outside air and condenses while circulating in the outdoor heat exchanger 15.

  A part of the refrigerant that is condensed by discharging heat to the outside air is liquefied and flows out of the outdoor heat exchanger 15 and flows through the intermediate pipe 25. Then, the pressure is reduced so as to be easily evaporated by expanding with the expansion valve 16, and then flows into the indoor heat exchanger 14. The refrigerant flowing into the indoor heat exchanger 14 takes the heat of the indoor air and evaporates while flowing through the indoor heat exchanger 14. At this time, the refrigerant removes heat from the room air, thereby cooling the room air and cooling the room.

  The refrigerant that has evaporated the heat of the indoor air partially vaporized and flows out of the indoor heat exchanger 14 and flows through the second pipe 22. Then, the four-way switching valve 17 enters from the second port 172. During cooling, the second port 172 of the four-way switching valve 17 is connected to the fourth port 174, and the fourth port 174 is connected to the fourth pipe 24, so that the four-way switching valve 17 enters the third port 173. The refrigerant flows from the fourth port 174 through the four-way switching valve 17 to the fourth pipe 24. The refrigerant flowing through the fourth pipe 24 is introduced into the accumulator 18 from the refrigerant inlet 181 of the accumulator 18. In the accumulator 18, the refrigerant is separated into a liquid refrigerant and a low-pressure gas refrigerant. Only the low-pressure gas refrigerant is discharged from the refrigerant discharge port 182 of the accumulator 18 and flows to the suction pipe 122. The refrigerant in the suction pipe 122 merges with the lubricating oil flowing from the oil return pipe 26 and is sucked into the compressor 12 from the suction port 12a of the compressor 12 together with the lubricating oil.

  Thus, during heating, the indoor heat exchanger 14 becomes a condenser and the outdoor heat exchanger 15 becomes an evaporator. On the other hand, during cooling, the outdoor heat exchanger 15 serves as a condenser, and the indoor heat exchanger 14 serves as an evaporator. A portion where the refrigerant discharged from the discharge port 12b of the compressor 12 flows until it is sucked into the suction port 12a of the compressor 12 is called a refrigerant circuit. Therefore, the refrigerant discharged from the compressor 12 flows through the refrigerant circuit and returns to the compressor 12. Air conditioning (cooling and heating) is performed by the refrigerant flowing through the refrigerant circuit.

  During the operation of the air conditioner 1, the control device 19 controls the opening degree of the oil return flow control valve 31. FIG. 2 is a flowchart showing an opening control routine executed by the control device 19 to control the opening of the oil return flow control valve 31 during the air conditioning operation.

  The opening degree control routine shown in FIG. 2 is repeatedly executed every predetermined short time. When this opening degree control routine is activated, the control device 19 first sets the refrigerant discharge temperature Td detected by the discharge temperature sensor 41 at the step 11 in FIG. 2 (hereinafter, step is abbreviated as S) to the upper limit discharge temperature Td0. It is judged whether it is higher than. The upper limit discharge temperature Td0 is determined in advance as a value lower than the heat resistance temperature of each component of the compressor 12 by a predetermined temperature. For example, when it is predicted that each component of the compressor 12 will be thermally deteriorated at 80 ° C. (when the heat resistant temperature of the compressor 12 is 80 ° C.), the upper limit discharge temperature Td0 is 70 ° C. lower by about 10 ° C. than 80 ° C. Can be set to a degree. Therefore, when the refrigerant discharge temperature Td is higher than the upper limit discharge temperature Td0, the possibility that each component of the compressor 12 is thermally deteriorated by the heat of the refrigerant is increased.

  When it is determined in S11 that the refrigerant discharge temperature Td is higher than the upper limit discharge temperature Td0 (S11: Yes), the control device 19 proceeds to S12 and outputs an opening increase signal to the oil return flow control valve 31. Thereby, the opening degree of the oil return flow control valve 31 is increased. When the opening degree of the oil return flow control valve 31 increases, the flow rate of the lubricating oil flowing through the oil return pipe 26 increases. When the oil return flow control valve 31 is already fully open, the fully open state is maintained (the same applies hereinafter). The control device 19 thereafter ends this routine.

  Further, when it is determined in S11 that the refrigerant discharge temperature Td is equal to or lower than the upper limit discharge temperature Td0 (S11: No), the control device 19 proceeds to S13 and calculates the superheat degree Tk. The degree of superheat Tk represents the difference between the temperature of the refrigerant sucked into the compressor 12 and the saturated vapor temperature. The refrigerant suction temperature Ts detected by the suction temperature sensor 42 and the refrigerant suction pressure Ps detected by the suction pressure sensor 43. Calculated based on Specifically, the degree of superheat Tk is calculated from the difference (Ts−T (Ps)) between the refrigerant suction temperature Ts and the saturated vapor temperature T (Ps) of the R32 refrigerant at the refrigerant suction pressure Ps.

  Next, the control device 19 determines whether or not the calculated superheat degree Tk is less than the superheat degree lower limit value Tk0 (S14). The superheat lower limit value Tk0 is determined in advance as a threshold value indicating whether or not the superheat degree is small. When the superheat degree Tk is close to 0 or is a negative value (in short, when the superheat degree Tk is small), there is a high possibility that the refrigerant sucked into the compressor 12 is moist. The wet operation of the compressor 12 is not preferable in terms of reliability because it may cause dilution of the lubricating oil or liquid compression, and also means that the non-evaporated refrigerant has returned to the compressor 12, so that the efficiency is also improved. It is not preferable. For this reason, the superheat lower limit value Tk0 is determined in advance as a value at which there is no possibility that all the refrigerant sucked into the compressor 12 is moist. Therefore, when the superheat degree Tk is less than the superheat degree lower limit value Tk0, the possibility that the refrigerant sucked into the compressor 12 is wet is increased. The superheat lower limit value Tk0 is preferably about 3 ° C., for example.

  When it is determined in S14 that the superheat degree Tk is less than the superheat degree lower limit value Tk0 (S14: Yes), the control device 19 proceeds to S12 and outputs an opening degree increase signal to the oil return flow control valve 31. Thereby, the opening degree of the oil return flow control valve 31 is increased, and the flow rate of the lubricating oil flowing through the oil return pipe 26 is increased. The control device 19 thereafter ends this routine.

  Further, when it is determined in S14 that the superheat degree Tk is equal to or higher than the superheat degree lower limit value Tk0 (S14: No), the control device 19 proceeds to S15, and the target heat exchange temperature Th * and the heat exchange temperature sensor 44 are used. The absolute value of the difference from the detected heat exchange temperature Th is calculated as the heat exchange temperature difference ΔTh. The target heat exchange temperature Th * is a target value of the temperature of the refrigerant flowing in the indoor heat exchanger 14 that is required for the indoor heat exchanger 14 to exhibit the capacity corresponding to the air conditioning load. The target heat exchange temperature Th * is calculated based on, for example, the set temperature of the indoor space, the indoor temperature, the air conditioning load, the state of the refrigerant in the refrigerant circuit, and the like. Therefore, the heat exchange temperature difference ΔTh represents a deviation between the target and the current state. When the heat exchange temperature difference ΔTh is large, it indicates that the capacity of the indoor heat exchanger 14 needs to be controlled.

  After calculating the heat exchange temperature difference ΔTh in S15, the control device 19 determines whether the calculated heat exchange temperature difference ΔTh is greater than the upper limit heat exchange temperature difference ΔTh0 (S16). The upper limit heat exchange temperature difference ΔTh0 can be arbitrarily set as a threshold value indicating whether or not the heat exchange temperature difference ΔTh is large. The upper limit heat exchange temperature difference ΔTh0 can be set in advance to about 5 ° C., for example.

  When it is determined in S16 that the heat exchange temperature difference ΔTh is equal to or less than the upper limit heat exchange temperature difference ΔTh0 (S16: No), the control device 19 ends this routine. On the other hand, when it is determined that the heat exchange temperature difference ΔTh is larger than the upper limit heat exchange temperature difference ΔTh0 (S16: Yes), the control device 19 proceeds to S17 and performs heat exchange so that the heat exchange temperature difference ΔTh is reduced. Based on the temperature difference ΔTh, a target opening degree α * that is a target value of the opening degree of the oil return flow control valve 31 is calculated. When the opening degree of the oil return flow control valve 31 is increased, the flow rate (circulation oil flow rate) of lubricating oil flowing out into the refrigerant circuit and circulating through the refrigerant circuit increases. When the circulating oil flow rate is increased, the flow rate of the refrigerant flowing in the refrigerant circuit is relatively reduced, and thus the air conditioning capability exhibited by the indoor heat exchanger 14 is reduced. On the other hand, when the opening degree of the oil return flow control valve 31 is decreased, the circulating oil flow rate is decreased. When the circulating oil flow rate decreases, the flow rate of the refrigerant flowing in the refrigerant circuit relatively increases, so that the air conditioning capability exhibited by the indoor heat exchanger 14 increases. Based on this, the control device 19 calculates the target opening degree α * based on the heat exchange temperature difference ΔTh in S17.

  In the calculation of S17, for example, when the heat exchange temperature Th is lower than the target heat exchange temperature Th * during the heating operation, the capacity of the indoor heat exchanger 14 needs to be increased. The target opening α * is calculated so that the opening decreases. Further, during the heating operation, when the heat exchange temperature Th is higher than the target heat exchange temperature Th *, it is necessary to reduce the capacity of the indoor heat exchanger 14, so the opening degree of the oil return flow control valve 31 increases. Thus, the target opening degree α * is calculated. Further, during the cooling operation, when the heat exchange temperature Th is higher than the target heat exchange temperature Th *, it is necessary to increase the capacity of the indoor heat exchanger 14, and therefore the opening degree of the oil return flow control valve 31 decreases. Thus, the target opening degree α * is calculated. Further, during the cooling operation, when the heat exchange temperature Th is lower than the target heat exchange temperature Th *, it is necessary to reduce the capacity of the indoor heat exchanger 14, so the opening degree of the oil return flow control valve 31 increases. Thus, the target opening degree α * is calculated.

  After calculating the target opening α * in S17, the control device 19 outputs a control amount (for example, an opening change amount) corresponding to the calculated target opening α * to the oil return flow control valve 31. Thereby, the opening degree of the oil return flow control valve 31 is controlled. The control device 19 thereafter ends this routine.

  When the control device 19 executes the opening degree control routine described above, when the refrigerant discharge temperature Td is larger than the upper limit discharge temperature Td0 and when the superheat degree Tk is smaller than the superheat degree lower limit value Tk0, the oil The opening degree of the return flow control valve 31 increases. Therefore, the flow rate of the lubricating oil in the oil return pipe 26 is controlled to increase. Further, when the refrigerant discharge temperature Td is not more than the upper limit discharge temperature Td0, the superheat degree Tk is not less than the superheat degree lower limit value Tk0, and the heat exchange temperature difference ΔTh is larger than the upper limit heat exchange temperature difference ΔTh0, heat exchange is performed. The opening degree of the oil return flow control valve 31 is controlled by the control device 19 based on the temperature difference ΔTh.

  FIG. 3 is a diagram showing the refrigeration cycle represented on the ph diagram when the air conditioner 1 according to the present embodiment is operated. In FIG. 3, the state of the low-pressure gas refrigerant sucked into the compressor 12 is represented by a position indicated by a point A. The refrigerant in the state represented by the position indicated by point A is compressed by the compressor 12, thereby changing to a high-temperature and high-pressure gas refrigerant represented by the position indicated by point B. The refrigerant in the state represented by the position indicated by the point B is represented by the position indicated by the point C by being condensed by the condenser (the indoor heat exchanger 14 during heating and the outdoor heat exchanger 15 during cooling). Changes to low-temperature and high-pressure liquid refrigerant. The refrigerant in the state represented by the position indicated by the point C is expanded when passing through the expansion valve 16, thereby changing to a low-temperature low-pressure liquid refrigerant represented by the position indicated by the point D. And the refrigerant | coolant of the state represented by the position shown at the point D is evaporated in the evaporator (the outdoor heat exchanger 15 at the time of heating, the indoor heat exchanger 14 at the time of cooling), and is in the position shown to the point A. It changes to the low-temperature gas refrigerant represented. The air-conditioning operation is continued by repeating such a refrigeration cycle.

  The refrigerant temperature at the point B in FIG. 3 is detected by the discharge temperature sensor 41 as the refrigerant discharge temperature Td. If the refrigerant discharge temperature Td is too high, each component of the compressor 12 (particularly, a resin component such as a seal member) is thermally deteriorated, so that the reliability of the compressor 12 is lowered. In this regard, in this embodiment, when the refrigerant discharge temperature Td exceeds the upper limit discharge temperature Td0, the opening degree of the oil return flow control valve 31 is increased and the flow rate of the lubricating oil flowing in the oil return pipe 26 is reduced. Increasing. For this reason, the flow rate of the lubricating oil sucked into the compressor 12 increases. Here, the temperature of the lubricating oil sucked into the compressor 12 is lower than the temperature of the refrigerant compressed by the compressor 12. For this reason, the lubricating oil has a cooling action for cooling the compressor 12 and the refrigerant compressed by the compressor 12 in addition to a lubricating action for lubricating the compressor 12. Therefore, when the flow rate of the lubricating oil sucked into the compressor 12 increases, cooling of the high-temperature gas refrigerant compressed by the compressor 12 and the compressor 12 by the lubricating oil is promoted. As a result, the state of the refrigerant discharged from the compressor 12 shifts from the state represented by the point B to the left in FIG. 3 and changes to the state represented by the point B ′. That is, the refrigerant discharge temperature Td decreases. In this way, by increasing the return amount of the lubricating oil and suppressing the excessive increase in the refrigerant discharge temperature Td, the thermal deterioration of the compressor 12 is prevented even when the R32 refrigerant is used. As a result, the compressor 12 reliability is improved.

  Moreover, when the superheat degree Tk of the refrigerant | coolant represented by the position of the point A of FIG. 3 is near 0, or when it is a negative value, there exists a possibility that the refrigerant | coolant suck | inhaled by the compressor 12 may be moist. When wet refrigerant is sucked into the compressor 12, the lubricating oil sucked into the compressor 12 together with the refrigerant is diluted with liquid refrigerant, and the viscosity of the lubricating oil is reduced. For this reason, the lubricating performance of the lubricating oil is deteriorated. In addition, when a damp refrigerant is sucked into the compressor 12, there is a concern about the occurrence of liquid compression and the reliability of the device is lowered. Furthermore, the liquid refrigerant which has not been evaporated is sucked into the compressor 12, and the efficiency of the refrigeration cycle is poor. In this regard, in the present embodiment, when the superheat degree Tk is less than the superheat degree lower limit value Tk0 (that is, when the superheat degree Tk is small), the opening degree of the oil return flow control valve 31 is increased and the oil return pipe is increased. The flow rate of the lubricating oil flowing through 26 is increased. For this reason, the flow rate of the lubricating oil sucked into the compressor 12 is increased. Here, the temperature of the lubricating oil sucked into the compressor 12 is higher than the temperature of the refrigerant before being compressed by the compressor 12, that is, the refrigerant sucked into the compressor 12. Therefore, the lubricating oil has not only a lubricating action for lubricating the compressor 12 but also a heating action for heating the refrigerant sucked into the compressor 12. Therefore, when the flow rate of the lubricating oil sucked into the compressor 12 increases, heating of the low-temperature gas refrigerant before being sucked into the compressor 12 and compressed by the lubricating oil is promoted. Therefore, the refrigerant sucked into the compressor 12 shifts from the state represented by the position of the point A to the right in FIG. 3 and changes to the state represented by the position of the point A ′. That is, the refrigerant suction temperature Ts rises and the superheat degree Tk is increased accordingly. In this way, by increasing the return amount of the lubricating oil and promoting the heating of the refrigerant sucked into the compressor 12, the suction of the moist refrigerant into the compressor 12 is prevented. As a result, the dryness of the refrigerant sucked into the compressor 12 can be maintained at 1 or more, and the compressor 12 is protected.

  Further, when the refrigerant discharge temperature Td is equal to or lower than the upper limit discharge temperature and the superheat degree Tk is equal to or higher than the lower limit value Tk0, the heat exchange temperature difference ΔTh is equal to or higher than the upper limit heat exchange temperature difference ΔTh0. The opening degree of the oil return flow control valve 31 is controlled so that the difference ΔTh becomes small. In this way, by controlling the opening of the oil return flow control valve 31 and controlling the flow rate of the lubricating oil flowing in the refrigerant circuit, the capacity of the indoor heat exchanger 14 is corrected to the capacity corresponding to the required air conditioning load. be able to.

(Second Embodiment)
Next, a second embodiment will be described. This embodiment is different in the configuration of the control device 19 described in the first embodiment and the opening control method of the oil return flow control valve 31 by the control device 19, and the other parts are the same as those in the first embodiment. Therefore, the same parts are denoted by the same reference numerals, and a specific description thereof is omitted.

  FIG. 4 is a block diagram illustrating a functional configuration of the control device 19 according to the second embodiment. As shown in FIG. 4, the control device 19 according to the second embodiment includes a heat exchange temperature difference output unit 191, a superheat degree output unit 192, a discharge temperature difference output unit 193, and an opening degree control unit 194. .

  The heat exchange temperature difference output unit 191 inputs the heat exchange temperature Th and executes a heat exchange temperature difference output processing routine shown in FIG. The superheat degree output unit 192 inputs the refrigerant suction temperature Ts from the suction temperature sensor 42 and the refrigerant suction pressure Ps from the suction pressure sensor 43, and executes a superheat degree output processing routine shown in FIG. The discharge temperature difference output unit 193 receives the refrigerant discharge temperature Td from the discharge temperature sensor 41 and executes a discharge temperature difference output processing routine shown in FIG. The opening degree control unit 194 controls the opening degree of the oil return flow control valve 31 by executing an opening degree control routine shown in FIG.

  When the heat exchange temperature difference output processing routine shown in FIG. 5 is started, the heat exchange temperature difference output unit 191 first calculates the absolute value of the difference between the target heat exchange temperature Th * and the heat exchange temperature Th in S21 of FIG. Calculated as the heat exchange temperature difference ΔTh. Next, the calculated heat exchange temperature difference ΔTh and the upper limit heat exchange temperature difference ΔTh0 are compared to determine whether the heat exchange temperature difference ΔTh is larger than the upper limit heat exchange temperature difference ΔTh0 (S22). When the heat exchange temperature difference ΔTh is equal to or less than the upper limit heat exchange temperature difference ΔTh0 (S22: No), this routine is finished. On the other hand, when the heat exchange temperature difference ΔTh is larger than the upper limit heat exchange temperature difference ΔTh0 (S22: Yes), a signal indicating the calculated heat exchange temperature difference ΔTh is output to the opening degree control unit 194 (S23). Thereafter, the heat exchange temperature difference output unit 191 ends this routine.

  When the superheat degree output processing routine shown in FIG. 6 is started, the superheat degree output unit 192 first calculates the superheat degree Tk based on the inputted refrigerant suction temperature Ts and refrigerant suction pressure Ps in S31 of FIG. . Next, the calculated superheat degree Tk and the superheat degree lower limit value Tk0 are compared, and it is determined whether or not the superheat degree Tk is less than the superheat degree lower limit value Tk0 (S32). When the superheat degree Tk is equal to or higher than the superheat degree lower limit value Tk0 (S32: No), this routine is finished. On the other hand, when the superheat degree Tk is less than the superheat degree lower limit value Tk0 (S32: Yes), a signal indicating the calculated superheat degree Tk is output to the opening degree control unit 194. Thereafter, the superheat degree output unit 192 ends this routine.

  When the discharge temperature difference output processing routine shown in FIG. 7 is started, the discharge temperature difference output unit 193 first compares the input refrigerant discharge temperature Td with the upper limit discharge temperature Td0 in S41 of FIG. It is determined whether the temperature Td is higher than the upper limit discharge temperature Td0. When the refrigerant discharge temperature Td is equal to or lower than the upper limit discharge temperature Td0 (S41: No), this routine ends. On the other hand, when the refrigerant discharge temperature Td is higher than the upper limit discharge temperature Td0 (S41: Yes), the discharge temperature difference output unit 193 determines the difference (Td−Td0) between the refrigerant discharge temperature Td and the upper limit discharge temperature Td0 as the discharge temperature difference ΔTd. (S42), and a signal representing the calculated discharge temperature difference ΔTd is output to the opening degree control unit 194 (S43). Thereafter, the discharge temperature difference output unit 193 ends this routine.

  Further, when the opening degree control routine shown in FIG. 8 is started, the opening degree control unit 194 first, in S51 of FIG. 8, a signal indicating the heat exchange temperature difference ΔTh and a signal indicating the degree of superheat Tk during a predetermined time. Then, it is determined whether any one or two of the signals indicating the discharge temperature difference ΔTd, or all of these signals are input. If no signal is input (S51: No), this routine is terminated. On the other hand, when at least one signal is input (S51: Yes), the opening degree control unit 194 advances the process to S52, and the maximum temperature difference among the temperature differences represented by the input one or more signals. Is selected, and the temperature difference represented by the selected signal is set to the maximum temperature difference ΔTmax.

  Next, the opening degree control unit 194 performs feedback control of the opening degree of the oil return flow rate control valve 31 based on the maximum temperature difference ΔTmax set in S52 (S53). In this case, when the set maximum temperature difference ΔTmax is the superheat degree Tk or the discharge temperature difference ΔTd, an opening degree increase signal is output to the oil return flow control valve 31. Thereby, the opening degree of the oil return flow control valve 31 is increased, and the flow rate of the lubricating oil flowing in the oil return pipe 26 is increased. When the set maximum temperature difference is the heat exchange temperature difference ΔTh, the opening degree of the oil return flow control valve 31 is controlled so that the heat exchange temperature difference ΔTh becomes small.

  In the opening degree control in the present embodiment, when the maximum temperature difference ΔTmax is the discharge temperature difference ΔTd, the flow rate of the lubricating oil flowing in the oil return pipe 26 is controlled to increase. For this reason, the flow rate of the lubricating oil sucked into the compressor 12 increases, and cooling of the refrigerant discharged from the compressor 12 by the lubricating oil is promoted. Thereby, the rise in the refrigerant discharge temperature Td is suppressed, and the compressor 12 is prevented from being deteriorated by the heat of the refrigerant. Even when the maximum temperature difference ΔTmax is the degree of superheat Tk, the flow rate of the lubricating oil flowing through the oil return pipe 26 is controlled to increase. For this reason, the flow rate of the lubricating oil sucked into the compressor 12 increases, and the heating of the refrigerant sucked into the compressor 12 by the lubricating oil is promoted. As a result, the degree of superheat Tk is increased, and the compressor 12 is prevented from sucking wet refrigerant. When the maximum temperature difference ΔTmax is the heat exchange temperature difference ΔTh, the opening degree of the oil return flow rate control valve 31 is controlled so that the heat exchange temperature difference ΔTh becomes small. Thereby, the capability of the indoor heat exchanger 14 is corrected to the capability commensurate with the air conditioning load.

  As described above, the air conditioner 1 according to the first and second embodiments includes the compressor 12, the oil separator 13, and the condenser (the indoor heat exchanger 14 during heating and the outdoor heat exchanger 15 during cooling). And an evaporator (outdoor heat exchanger 15 during heating, indoor heat exchanger 14 during cooling), a suction pipe 122, an oil return pipe 26, and a control device 19. The compressor 12 has a suction port 12a and a discharge port 12b, operates by receiving power from the gas engine 11 as a driving source, and sucks R32 refrigerant mixed with lubricating oil from the suction port 12a and sucks the refrigerant. Is compressed and discharged from the discharge port 12b. The oil separator 13 separates the refrigerant discharged from the discharge port 12b of the compressor 12 into gas refrigerant and lubricating oil. The condenser condenses the gas refrigerant separated by the oil separator 13. The evaporator is a steam that evaporates the refrigerant flowing out of the condenser. The suction pipe 122 is connected to the suction port 12 a of the compressor 12 and sucks the gas refrigerant flowing out of the evaporator and passing through the accumulator into the suction port 12 a of the compressor 12. The oil return pipe 26 is connected to the suction pipe 122 and allows the lubricating oil separated by the oil separator 13 to flow into the suction pipe 122. Then, the control device 19 detects the lubricating oil flowing in the oil return pipe 26 when the refrigerant discharge temperature Td, which is the temperature of the refrigerant discharged from the discharge port 12b of the compressor 12, is higher than the predetermined upper limit discharge temperature Td0. The flow rate of the lubricating oil flowing in the oil return pipe 26 is controlled so that the flow rate of the oil increases.

  According to the first and second embodiments, the control device 19 determines that the lubricating oil flows so that the flow rate of the lubricating oil flowing in the oil return pipe 26 increases when the refrigerant discharge temperature Td is higher than the upper limit discharge temperature Td0. To control the flow rate. For this reason, cooling with the lubricating oil of the refrigerant (discharge refrigerant) compressed by the compressor 12 is promoted. By promoting the cooling by the lubricating oil, an excessive increase in the refrigerant discharge temperature Td can be suppressed even when the R32 refrigerant is used, and deterioration of each component of the compressor 12 due to the heat of the refrigerant can be prevented. it can. Further, since the lubricating oil is used for cooling the refrigerant to lower the refrigerant discharge temperature, it is not necessary to make the degree of dryness of the refrigerant less than 1 in order to lower the refrigerant discharge temperature.

  In addition, the control device 19 increases the flow rate of the lubricating oil flowing in the oil return pipe 26 when the superheat degree Tk of the refrigerant at the suction port 12a of the compressor 12 is smaller than a predetermined superheat degree lower limit value Tk0. In addition, the flow rate of the lubricating oil flowing through the oil return pipe 26 is controlled. For this reason, heating of the refrigerant sucked into the compressor 12 by the lubricating oil is promoted. By promoting the heating with such lubricating oil, the decrease in the degree of superheat Tk can be suppressed, the dryness of the refrigerant sucked into the compressor 12 can be maintained at 1 or more, and the wet operation is prevented to prevent the compressor. 12 can be protected.

  The air conditioner 1 according to the first and second embodiments includes an oil return flow control valve 31 that is interposed in the middle of the oil return pipe 26 and can adjust the opening degree. The control device 19 controls the flow rate of the lubricating oil flowing through the oil return pipe 26 by controlling the opening degree of the oil return flow rate control valve 31. According to this, the control device 19 can control the flow rate of the lubricating oil in the oil return pipe 26 relatively easily by controlling the opening degree of the oil return flow rate control valve 31.

  Further, according to the first and second embodiments, the control device 19 allows the oil return so that the heat exchange temperature difference ΔTh becomes smaller when the heat exchange temperature difference ΔTh is larger than the upper limit heat exchange temperature difference ΔTh0. The opening degree of the flow control valve 31 is controlled. Thereby, the capability of the indoor heat exchanger 14 is corrected to the capability commensurate with the air conditioning load.

  Further, according to the first embodiment, the priority is set to the start condition for controlling the opening degree of the oil return flow control valve 31. Specifically, the discharge temperature condition that the refrigerant discharge temperature Td is greater than the upper limit discharge temperature Td0 is the first priority, and the superheat condition that the superheat degree Tk is less than the superheat degree lower limit Tk0 is the second priority. . Furthermore, the heat exchange temperature condition that the heat exchange temperature difference is larger than the upper limit heat exchange temperature difference ΔTh0 is the third priority. When the first priority discharge temperature condition is satisfied, the opening degree of the oil return flow control valve 31 is controlled (increased) regardless of whether other start conditions are satisfied or not. In addition, when the first priority discharge temperature condition is not satisfied and the second priority superheat condition is satisfied, the oil is set regardless of whether the third priority heat exchange temperature condition is satisfied or not. The opening degree of the return flow control valve 31 is controlled (increased). Since the discharge temperature condition has the highest priority, an excessive increase in the refrigerant discharge temperature Td is preferentially suppressed. For this reason, the reliability of the compressor 12, especially when the R32 refrigerant is used, can be improved.

  Further, according to the second embodiment, the opening degree of the oil return flow control valve 31 is controlled based on the start condition that requires the most control. Specifically, the discharge temperature difference ΔTd, the heat exchange temperature difference ΔTh, and the degree of superheat Tk are compared, and the opening degree of the oil return flow control valve 31 is controlled based on the largest temperature difference. Thereby, the capability of the indoor heat exchanger 14 can be optimally corrected while ensuring the reliability of the compressor 12.

DESCRIPTION OF SYMBOLS 1 ... Air conditioner, 11 ... Gas engine (drive source), 12 ... Compressor, 12a ... Inlet, 12b ... Discharge port, 13 ... Oil separator, 131 ... Refrigerant inlet, 132 ... Refrigerant outlet, 133 ... Oil exhaust Outlet, 14 ... indoor heat exchanger (condenser, evaporator), 15 ... outdoor heat exchanger (evaporator, condenser), 16 ... expansion valve, 17 ... four-way switching valve, 18 ... accumulator, 19 ... control device ( Oil flow control device), 191 ... heat exchange temperature difference output unit, 192 ... superheat degree output unit, 193 ... discharge temperature difference output unit, 194 ... opening control unit, 21 ... first piping, 22 ... second piping, 23 3rd piping, 24 ... 4th piping, 25 ... Intermediate piping, 26 ... Oil return piping, 31 ... Oil return flow control valve, 121 ... Discharge piping, 122 ... Suction piping, Td ... Refrigerant discharge temperature, Td0 ... Upper limit discharge Temperature, Tk ... degree of superheat, Tk ... superheat lower limit value

Claims (4)

A compressor that has a suction port and a discharge port, operates by receiving power from a drive source, sucks refrigerant mixed with lubricating oil from the suction port, compresses the sucked refrigerant, and discharges the refrigerant from the discharge port; ,
An oil separator that separates the refrigerant discharged from the discharge port into a gas refrigerant and lubricating oil;
An indoor heat exchanger,
An outdoor heat exchanger,
And inhalation pipe connected to the suction port,
An oil return pipe that is connected to the suction pipe and flows lubricating oil separated by the oil separator into the suction pipe;
An oil flow control device for controlling the flow rate of lubricating oil flowing in the oil return pipe;
With
During heating, the indoor heat exchanger becomes a condenser that condenses the gas refrigerant separated by the oil separator, while the outdoor heat exchanger becomes an evaporator that evaporates the refrigerant flowing out of the condenser, and during cooling, While the indoor heat exchanger becomes the evaporator, the outdoor heat exchanger becomes the condenser,
The suction pipe sucks the refrigerant flowing out of the evaporator into the suction port of the compressor,
In the oil flow control device, when the refrigerant discharge temperature, which is the temperature of the refrigerant discharged from the discharge port, is higher than a predetermined upper limit discharge temperature, and the degree of superheat at which the superheat degree of the refrigerant at the suction port is predetermined The flow rate of the lubricating oil flowing in the oil return pipe is controlled so that the flow rate of the lubricating oil flowing in the oil return pipe increases when the value is smaller than the lower limit value, and the target heat exchange temperature of the indoor heat exchanger is controlled. When the heat exchange temperature difference, which is the absolute value of the difference between the heat exchange temperature and the heat exchange temperature, is larger than a predetermined upper limit heat exchange temperature difference, the lubricating oil flows in the oil return pipe so as to reduce the heat exchange temperature difference. To control the flow rate of
Air conditioner. The air conditioner according to claim 1,
In the oil flow control device, when the refrigerant discharge temperature is higher than the upper limit discharge temperature, and when the refrigerant discharge temperature is equal to or lower than the upper limit discharge temperature and the degree of superheat is smaller than the lower limit value of the superheat degree. In addition, the flow rate of the lubricating oil flowing through the oil return pipe is controlled so that the flow rate of the lubricating oil flowing through the oil return pipe increases, the refrigerant discharge temperature is equal to or lower than the upper limit discharge temperature, and the degree of superheat Is the lower limit value of the superheat degree, and when the heat exchange temperature difference is larger than the upper limit heat exchange temperature, the flow rate of the lubricating oil flowing in the oil return pipe so that the heat exchange temperature difference becomes smaller To control the
Air conditioner. The air conditioner according to claim 1,
The oil flow rate control device includes a discharge temperature difference that is a temperature difference between the refrigerant discharge temperature and the upper limit discharge temperature when the refrigerant discharge temperature is higher than the upper limit discharge temperature, and the superheat degree is lower than the lower limit value of the superheat degree. In the case where the maximum temperature difference among the heat exchange temperature differences in the case where the heat exchange temperature difference is larger than the upper limit heat exchange temperature difference is the discharge temperature difference or the superheat degree. The flow rate of the lubricating oil flowing through the oil return pipe is controlled so that the flow rate of the lubricating oil flowing through the oil return pipe increases, and the heat difference is detected when the maximum temperature difference is the heat exchange temperature difference. Controlling the flow rate of the lubricating oil flowing in the oil return pipe so that the exchange temperature difference becomes small,
Air conditioner. The air conditioner according to any one of claims 1 to 3,
An oil return flow control valve that is interposed in the middle of the oil return pipe and can adjust the opening degree,
The oil flow control device is an air conditioner that controls a flow rate of lubricating oil flowing through the oil return pipe by controlling an opening degree of the oil return flow control valve.

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