JP6495048B2 - Oil return circuit and oil return method for refrigeration cycle - Google Patents

Description

  The present invention relates to an oil return circuit and an oil return method for a refrigeration cycle using an R32 refrigerant having a low global warming potential (hereinafter referred to as GWP) or a mixed refrigerant rich in R32 refrigerant (hereinafter simply referred to as R32 refrigerant). It is.

  R32 refrigerant has an ozone depletion potential (ODP) of zero and GWP is about 1/3 lower than that of R410A refrigerant, so it can contribute to the reduction of environmental load. Used as a refrigerant. However, the R32 refrigerant has a tendency that the discharge gas temperature rises by 10 to 20 ° C. compared to the R410A refrigerant, and the discharge gas temperature tends to rise as the pressure ratio between the suction pressure and the discharge pressure increases. The oil temperature in the compressor rises due to the return oil. As a result, the oil viscosity decreases, so the allowable operating range or conditions must be limited in comparison with the R410A refrigerant.

  Therefore, an oil separator is provided in the discharge circuit of the compressor, and at the time of cooling, the refrigerant containing the oil discharged from the compressor is directly cooled by the cooler from the oil separator via the first bypass flow path, and then compressed. It is returned to the housing of the machine, where oil is separated and only the refrigerant is circulated to the condenser via the second bypass flow path to suppress an increase in the oil temperature in the compressor. During heating, the oil separator The refrigerant is separated from the oil, and the refrigerant is circulated through the condenser for heating, and the oil is cooled through the first bypass channel and the cooler, and then returned to the compressor. Japanese Patent Application Laid-Open No. H10-228667 provides a device that suppresses a decrease in capability.

  On the other hand, in the refrigeration cycle using R410A refrigerant or the like, conventionally, an oil separator is provided in the discharge circuit of the compressor, and after the oil contained in the refrigerant gas is separated by the oil separator, the refrigerant is circulated to the condenser. The separated oil is returned to the compressor or the suction circuit of the compressor by an oil return circuit, or an oil cooler is provided in the oil return circuit, and the oil is cooled as necessary. The thing etc. which were made to return to the side are provided by patent document 2-5.

JP 2014-85104 A JP-A-6-337171 JP-A-11-83204 JP 2005-214515 A JP 2006-170570 A

  However, the above-mentioned Patent Document 1 must have not only a high-pressure atmosphere inside the compressor housing but also an oil separation function, and a compressor with a direct suction and direct discharge structure. In addition, the first bypass channel and the second bypass channel must each be a high-pressure gas pipe having a relatively large diameter, which complicates and increases the cost of the compressor structure and the surrounding pipe structure. There is a problem that it cannot be applied to a refrigeration cycle using a compressor of a type.

  On the other hand, in the case of using a low pressure housing type compressor in which the inside of the housing is in a low pressure atmosphere, as shown in Patent Document 2-5, only the oil separated by the oil separator is compressed via the oil return circuit. Can be returned to the side. At this time, by returning the oil to the suction circuit of the compressor, the oil can be cooled with the low-pressure refrigerant gas, the oil temperature can be lowered, and the compressor can be returned, but in this case, the oil and the refrigerant gas are remixed, There is a problem that the oil must be separated again in the compressor and the oil separation efficiency decreases, that is, the oil circulation rate increases, that is, the oil circulation rate increases.

  In addition, an oil cooler is provided in the oil return circuit, and the oil cooled there is directly returned to the oil sump of the compressor housing. However, in this case, the oil is always cooled by the oil cooler. Therefore, in the case of using a refrigerant as a cooling heat source in the oil cooler, there are problems such as affecting the performance and performance of the refrigeration cycle.

  The present invention has been made in view of such circumstances, and even when an R32 refrigerant whose discharge gas temperature is high is used, an increase in the oil temperature in the compressor is suppressed, and an allowable operation equivalent to that of the R410A refrigerant is performed. An object of the present invention is to provide an oil return circuit and an oil return method for a refrigeration cycle that can ensure a range or conditions and can suppress an increase in oil circulation rate and an effect on the performance and performance of the refrigeration cycle. .

In order to solve the above-described problems, the oil return circuit and oil return method of the refrigeration cycle of the present invention employ the following means.
That is, an oil return circuit of a refrigeration cycle according to the present invention includes a compressor in which a housing having an oil sump is in a low pressure atmosphere, and the cycle is filled with an R32 refrigerant or an R32 rich mixed refrigerant. An oil separator provided in a discharge circuit from the compressor; and an oil return circuit that decompresses the oil separated by the oil separator and returns the oil to the oil reservoir in the housing. The circuit is a parallel circuit of a direct circuit that returns the oil directly from the oil separator to the oil reservoir and a cooling circuit that cools and returns the oil by an oil cooler, and the oil viscosity inside the compressor is changed to the refrigeration cycle. the pressure of the refrigerant in the suction circuit, is calculated on the basis of the detected value of the oil temperature in the sump the oil, when it falls below a preset threshold, the said oil return circuit straight Switching from the circuit to the cooling circuit, characterized in that it comprises a fluid temperature control unit which back the temperature cooled below a predetermined temperature of the return oil.

According to the present invention, the oil return circuit is provided with an oil return circuit that decompresses the oil separated by the oil separator provided in the discharge circuit from the compressor and returns the oil to the oil sump in the housing. It is a parallel circuit of a direct circuit that directly returns from the oil separator to the oil reservoir and a cooling circuit that is cooled and returned by the oil cooler. The oil viscosity inside the compressor, the refrigerant pressure in the suction circuit of the refrigeration cycle, and the oil Calculated based on the detected value of the oil temperature in the reservoir, and when it falls below a preset threshold, the oil return circuit is switched directly from the circuit to the cooling circuit, and the temperature of the return oil is cooled below a predetermined temperature. Therefore, even if the discharge gas temperature may rise due to the use of R32 refrigerant or R32 rich mixed refrigerant, the oil viscosity inside the compressor is adjusted in the intake circuit of the refrigeration cycle. Above And pressure medium, calculated based on the detected value of the oil temperature in the oil reservoir, it is time to below a preset threshold, the oil return oil cooler oil is switched directly from the circuit of the circuit in the cooling circuit The oil temperature rise in the compressor can be limited to a specified value or less by cooling by the above, cooling to a predetermined temperature or lower, and returning the oil pool in the housing of the compressor. Therefore, an increase in the oil temperature inside the compressor can be suppressed, and an allowable operation range or condition equivalent to that of the R410A refrigerant can be ensured. In addition, since the oil separated by the oil separator can be directly returned to the oil sump in the housing, remixing with the refrigerant gas can be prevented, and an increase in the oil circulation rate due to rising oil can be suppressed. It is sufficient to cool the oil only when necessary, and the influence on the capacity and performance of the refrigeration cycle can be minimized.

  Further, the oil return circuit of the refrigeration cycle of the present invention is the oil return circuit of the refrigeration cycle, wherein the compressor is a low-pressure housing type scroll compressor of either a closed type or an open type, The oil reservoir is filled with any one of PVE oil, POE oil, PAG oil, or a mixed oil containing them as a main component.

  According to the present invention, the compressor is either a closed type or an open type low-pressure housing type scroll compressor, and any one of PVE oil, POE oil, PAG oil or the like is placed in an oil reservoir inside the housing. Since it is filled with the mixed oil as the main component, the low-pressure refrigerant gas from the refrigeration cycle side is sucked into the housing, the refrigerant is sucked in, compressed, and discharged into the discharge chamber. PVE oil (polyvinyl ether oil), POE oil (polyol ester oil), PAG oil (polyalkylene glycol oil) or Refrigeration cycle using R32 refrigerant or R32 rich mixed refrigerant by filling these mixed oils Configure, the refrigeration cycle can be operated to secure the R410A refrigerant contrast equivalent allowable operating range or conditions. Therefore, it is possible to reliably eliminate the poor lubrication caused by the decrease in the oil viscosity due to the increase in the oil temperature in the compressor. In addition, when the compressor is an open type compressor, it is possible to prevent oil from being sludged by preventing the oil from becoming sludge due to the increase in the sliding portion temperature at the shaft seal portion due to the mechanical seal or lip seal. There is an effect such as being able to.

Furthermore, the oil return method of the refrigeration cycle according to the present invention includes an oil in a discharge circuit of the compressor of the refrigeration cycle that includes a low-pressure housing type compressor and is filled with R32 refrigerant or R32 rich mixed refrigerant. In the oil return method of the refrigeration cycle in which a separator is provided and the oil separated by the oil separator is returned to the oil reservoir in the compressor housing through an oil return circuit, the oil viscosity inside the compressor is when it falls below the pressure of the refrigerant in the suction circuit of the refrigeration cycle, is calculated on the basis of the detected value of the oil temperature in the sump the oil, a threshold which the calculation detection value is set in advance, provided in the oil return circuit The oil temperature inside the compressor is limited to a specified value or less by cooling the return oil temperature below a predetermined temperature with an oil cooler.

According to the present invention, in the oil return method of the refrigeration cycle, the oil separated by the oil separator provided in the discharge circuit of the compressor is returned to the oil sump in the housing of the compressor via the oil return circuit. the interior of the oil viscosity, the pressure of the refrigerant in the suction circuit of the refrigeration cycle, when calculated on the basis of the detected value of the oil temperature in the oil sump, below the threshold for the calculation detection value is set in advance, the oil return The temperature of the return oil is cooled to a predetermined temperature or lower by an oil cooler provided in the circuit so as to limit the increase in the oil temperature inside the compressor to a predetermined value or less. Even if the discharge gas temperature may rise due to the use of a rich refrigerant mixture, the oil viscosity inside the compressor is determined based on the detected values of the refrigerant pressure in the suction circuit of the refrigeration cycle and the oil temperature in the oil reservoir. There was calculated, when below the threshold the calculation detection value is preset, the temperature of the oil return oil cooler provided in the oil return circuit is cooled below a predetermined temperature of the compressor within the housing By returning the oil sump, the oil temperature rise inside the compressor can be limited to a specified value or less. Therefore, an increase in the oil temperature inside the compressor can be suppressed, and an allowable operation range or condition equivalent to that of the R410A refrigerant can be ensured. In addition, since the oil separated by the oil separator can be returned directly to the oil sump in the housing, remixing with the refrigerant gas can be prevented, and an increase in the oil circulation rate due to oil rising can be suppressed, The oil need only be cooled when necessary, and the impact on the capacity and performance of the refrigeration cycle can be minimized.

Furthermore, the oil return method of the refrigeration cycle according to the present invention is the oil return method of the refrigeration cycle, wherein the oil return circuit directly returns the oil from the oil separator to the oil reservoir, and an oil cooler. When the calculated value of the viscosity of the oil inside the compressor falls below the threshold, the oil return circuit is changed from the direct circuit to the cooling circuit. Switching, the temperature of the return oil is cooled to a predetermined temperature or less by the oil cooler and returned.

According to the present invention, the oil return circuit is a parallel circuit of a direct circuit that returns the oil directly from the oil separator to the oil reservoir and a cooling circuit that cools and returns the oil by the oil cooler. When the calculated viscosity value falls below the threshold value, the oil return circuit is switched directly from the circuit to the cooling circuit, and the temperature of the return oil is cooled back below the predetermined temperature by the oil cooler. If the calculated value of oil viscosity on threshold than returns the oil directly oil sump from the oil separator through the direct circuit, when the calculated value is below the threshold value, the oil in the oil cooler cooling circuit It can be cooled below a predetermined temperature and returned to the oil sump. Therefore, the oil temperature rise inside the compressor can be reliably limited to the specified value or less, and the oil can be cooled only by the oil cooler when necessary, minimizing the influence on the capacity and performance of the refrigeration cycle. be able to.

According to the oil return circuit and the oil return method of the refrigeration cycle of the present invention, even when the discharge gas temperature may be increased by using the R32 refrigerant or the R32 rich mixed refrigerant, the oil viscosity inside the compressor is detected, When it falls below a preset threshold, the oil return circuit is switched directly from the circuit to the cooling circuit, the oil is cooled by the oil cooler, cooled below the predetermined temperature, and the oil pool in the compressor housing is returned. As a result, the increase in the oil temperature inside the compressor can be limited to a specified value or less, so that the increase in the oil temperature inside the compressor can be suppressed, and an allowable operation range or condition equivalent to the R410A refrigerant can be ensured. In addition, since the oil separated by the oil separator can be directly returned to the oil sump inside the compressor, remixing with the refrigerant gas can be prevented, and an increase in the oil circulation rate due to rising oil can be suppressed. It is sufficient to cool the oil only when necessary, and the influence on the capacity and performance of the refrigeration cycle can be minimized.

It is a refrigerant circuit figure containing the oil return circuit of the refrigerating cycle concerning one embodiment of the present invention. It is a longitudinal cross-sectional view of the low pressure housing type compressor applied to the said refrigerating cycle.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a refrigerant circuit diagram including an oil return circuit of a refrigeration cycle according to an embodiment of the present invention. FIG. 2 is a longitudinal sectional view of a low-pressure housing type compressor applied to the refrigeration cycle. It is shown.
Here, the refrigeration cycle 1 is filled with R32 refrigerant or R32 rich mixed refrigerant (hereinafter simply referred to as R32 refrigerant) as a refrigerant, and includes a four-way switching valve 4 for cooling and heating by switching the refrigerant circulation direction. However, it may be a refrigeration or a single heat pump cycle.

The refrigeration cycle 1 is provided with a low pressure housing type compressor 2, an oil separator 3 provided in a discharge circuit 13A of the compressor 2, a four-way switching valve 4 for switching the refrigerant circulation direction, and a blower 5. The outdoor heat exchanger 6, the heating electronic expansion valve 7, the receiver 8, the cooling electronic expansion valve 9, the indoor heat exchanger 11 provided with the blower 10, and the compressor 2. The accumulator 12 provided in the suction circuit 13B is constituted by a closed cycle refrigerant circuit in which the refrigerant pipe 13 is sequentially connected.

  As shown in FIG. 2, the compressor 2 is a hermetic electric scroll compressor 2. This hermetic electric scroll compressor 2 includes a vertically long cylindrical housing 14 having a hermetically sealed structure constituting an outer shell, and a compressor in which a scroll compression mechanism 15 is incorporated in an upper portion inside the housing 14. ing. As is well known, the scroll compression mechanism 15 includes a pair of fixed scrolls 16 and a turning scroll 17 and is incorporated through a bearing member 18 fixedly installed in the housing 14. The high-pressure refrigerant gas compressed by the scroll compression mechanism 15 is discharged into the discharge chamber 19 and sent to the discharge circuit 13A on the refrigeration cycle 1 side through the discharge pipe 20.

  In the housing 14, a motor 21 including a stator 22 and a rotor 23 is fixedly installed below the scroll compression mechanism 15. A drive shaft 24 is integrally coupled to the rotor 23 of the motor 21, and a crank pin provided at the upper end of the drive shaft 24 is connected to the back surface of the orbiting scroll 17 of the scroll compression mechanism 15. The scroll compression mechanism 15 can be driven by being connected via a bearing.

  The upper end side of the drive shaft 24 is supported by a bearing member 18, and the lower end portion is supported by a bearing member 25 installed at a lower portion in the housing 14. An oil supply pump 26 is provided between the lower end portion of the drive shaft 24 and the bearing member 25, and lubricating oil (oil) filled in an oil reservoir 27 at the inner bottom portion of the housing 14 is provided in the drive shaft 24. The sliding portion of the scroll compression mechanism 15 can be supplied with oil through the oil supply hole 28. The hermetic electric scroll compressor 2 provided with such an oil supply mechanism is well known.

  The compressor 2 does not have to be the sealed electric scroll compressor 2 as described above, and may be an open type scroll compressor having an oil sump inside the housing, or other type other than the scroll compressor. It may be a compressor. The lubricating oil (oil) filled in the oil reservoir 27 in the housing 14 is PVE oil (polyvinyl ether-based oil), POE oil (polyol ester-based oil), PAG oil (compatible with R32 refrigerant) Polyalkylene glycol oil) or a mixed oil containing them as a main component, and an oil having a viscosity at 40 ° C. of about 20 to 150 cP is used.

  Further, in the present embodiment, a suction pipe 29 is provided on the outer peripheral portion of the housing 14 so as to open in a space portion between the motor 21 and the scroll compression mechanism 15, and the refrigeration cycle is provided via the suction pipe 29. It is connected to the suction circuit 13B on the one side. Thus, the hermetic electric scroll compressor 2 is a low pressure housing type compressor 2 in which the inside of the housing 14 has a low pressure atmosphere.

  Further, as shown in FIG. 1, in the housing 14 of the hermetic electric scroll compressor 2, the oil separated by the oil separator 3 provided in the discharge circuit 13A on the refrigeration cycle 1 side is compressed. An oil return circuit 31 for returning to the oil reservoir 27 on the second side is connected. The oil return circuit 31 includes a direct circuit 32 for returning the oil separated by the oil separator 3 directly to the oil sump 27 via the electromagnetic valve 33 and the cupilary tube 34 for pressure reduction and flow rate adjustment. It is connected in parallel, and is constituted by a parallel circuit with a cooling circuit 35 that returns oil from the oil separator 3 to the oil sump 27 through a solenoid valve 36, an oil cooler 37, and a pressure reduction and flow rate adjusting capillary tube 38. ing.

  The cooling source for cooling the oil by the oil cooler 37 includes a high-pressure liquid refrigerant circulated in the refrigerant circuit of the refrigeration cycle 1, a gas-liquid two-phase refrigerant decompressed by an expansion valve, a low-pressure gas refrigerant, etc. It is possible to employ a refrigerant cooling method in which a part is used for cooling by heat exchange with the refrigerant or an air cooling method in which cooling is performed by air cooling using the blower 5 attached to the outdoor heat exchanger 6. .

Further, the oil return circuit 31 limits at least one of the refrigerant discharge temperature, the oil temperature in the compressor 2 and the oil viscosity in order to limit the oil temperature rise in the housing 14 of the compressor 2 to a specified value or less. When the detected discharge temperature or oil temperature exceeds a preset threshold value, or when the detected oil viscosity falls below a preset threshold value, the oil return circuit 31 is directly The circuit 32 is switched to the cooling circuit 35 so that the temperature of the return oil can be cooled to a predetermined temperature or less and returned to the oil sump 27.

That is, the oil return circuit 31 is at least one of a detection value of the discharge temperature sensor 39 provided in the discharge circuit 13A of the refrigeration cycle 1 and a detection value of the oil temperature sensor 40 provided at the housing bottom of the compressor 2. When one exceeds a preset threshold value, or the oil viscosity calculated based on the detection value of the low pressure sensor 41 and the oil temperature sensor 40 provided in the suction circuit 13B of the refrigeration cycle 1 is An oil temperature control unit 42 that controls opening and closing of the solenoid valves 33 and 36 and switches the oil return circuit 31 directly from the circuit 32 to the cooling circuit 35 when it falls below the set threshold value, and returns oil from the oil separator 3. The oil cooler 37 is used to cool the water back to a predetermined temperature or lower.

With the configuration described above, according to the present embodiment, the following operational effects can be obtained.
In the refrigeration cycle 1, the high-temperature and high-pressure refrigerant gas discharged from the compressor 2 is circulated to the outdoor heat exchanger 6 side by the four-way switching valve 4, and the outdoor heat exchanger 6 is a condenser and indoor heat exchange. Cooling operation is performed by causing the vessel 11 to function as an evaporator, and high-temperature and high-pressure refrigerant gas is circulated to the indoor heat exchanger 11 side by the four-way switching valve 4, and the indoor heat exchanger 11 is a condenser and outdoor heat. Heating operation can be performed by making the exchanger 6 function as an evaporator.

  During this time, the oil contained in the refrigerant gas discharged from the compressor 2 is separated by the oil separator 3 provided in the discharge circuit 13A, and is a sealed electric type that is a low-pressure housing type via the oil return circuit 31. The oil is returned to the oil reservoir 27 of the scroll compressor 2. The oil return circuit 31 is a parallel circuit of a direct circuit 32 that returns oil directly to the oil reservoir 27 and a cooling circuit 35 that cools the oil by the oil cooler 37 and returns it to the oil reservoir 27, and is thus discharged from the compressor 2. When the refrigerant discharge temperature rises and the oil temperature inside the compressor 2 may exceed a preset threshold, this is detected and the oil return circuit 31 is switched directly from the circuit 32 to the cooling circuit 35. The return oil can be cooled to a predetermined temperature or lower by the oil cooler 37 and returned to the oil reservoir 27.

That is, at least one of the discharge temperature of the refrigerant discharged from the compressor 2, the oil temperature or the oil viscosity inside the compressor 2, the oil temperature control unit 42 discharges the temperature sensor 39, the oil temperature sensor 40, and the low pressure sensor. When the detected discharge temperature or oil temperature exceeds a preset threshold value, or when the detected oil viscosity falls below a preset threshold value, By switching the valve 33 from open to closed and the electromagnetic valve 36 from closed to open, the oil return circuit 31 is switched directly from the circuit 32 to the cooling circuit 35, and the temperature of the return oil is cooled below a predetermined temperature and returned to the oil reservoir 27. The oil temperature inside the compressor 2 functions so as to be limited to a specified value or less.

Here, an example of setting the threshold will be described.
When the combination of refrigerant and refrigerating machine oil is R410A / PVE oil A, R32 / PVE oil B, for example, when HP / LP = 3.8 / 1.8 [MPa], SH = 10 [deg],
(1) Since the refrigerant discharge temperature is 85 ° C. for R410A and 100 ° C. for R32, the threshold is set to 90 ° C., for example.
(2) Since the compressor internal oil temperature is 70 ° C. for R410A and 85 ° C. for R32, the threshold is set to 75 ° C., for example.
(3) oil viscosity, since the R410A / PVE oil A in ^8mm 2 / s, R32 / PVE oil B in ^{6 mm} 2 / s, setting the threshold for example, 7.5 mm ² / s.

As described above, the refrigerant discharge temperature, the compressor oil temperature, and the oil viscosity threshold are set, and when the detected value of the discharge temperature or oil temperature exceeds the threshold via the oil temperature control unit 42, or the oil viscosity When the detected value falls below the threshold value, the oil return circuit 31 is switched directly from the circuit 32 to the cooling circuit 35, the return oil is cooled by the oil cooler 37, and the temperature is lowered by about 15 degrees and returned to the oil sump 27. By doing so, the oil temperature can be reduced to the same temperature as that of the R410A refrigerant, the oil viscosity can be made comparable to that of the R410A refrigerant, and an allowable operation range or condition equivalent to that of the R410A refrigerant can be ensured.

  The oil viscosity is known to depend on the solubility in the refrigerant determined by the pressure and temperature. As described above, the temperature and pressure are measured by the oil temperature sensor 40 and the low pressure sensor 41, and the temperature is used as a parameter. It can be grasped by obtaining the solubility from the pressure / solubility characteristic diagram.

As described above, by using the R32 refrigerant instead of the R410A refrigerant, even if the discharge gas temperature of the refrigerant discharged from the compressor 2 may increase, the refrigerant discharge temperature, the oil temperature in the compressor 2 Or at least one of the oil viscosities is detected, and when the detected discharge temperature or oil temperature exceeds a preset threshold value, or the detected oil viscosity falls below a preset threshold value The oil return circuit 31 is switched from the direct circuit 32 for returning oil directly from the oil separator 3 to the oil reservoir 27 of the compressor 2 to the cooling circuit 35 side for cooling the oil by the oil cooler 37 and returning it to the oil reservoir 27. Then, the oil is cooled by the oil cooler 37, cooled to a predetermined temperature or lower, and the oil sump 27 in the housing 14 of the compressor 2 is returned to restrict the oil temperature rise in the compressor 2 to a specified value or lower. it can.

  Therefore, an increase in the oil temperature in the compressor 2 can be suppressed, and an allowable operation range or condition equivalent to the R410A refrigerant can be ensured. Further, since the oil separated by the oil separator 3 can be directly returned to the oil reservoir 27 in the housing 14 of the compressor 2, remixing with the refrigerant gas can be prevented, and the oil circulation rate can be increased by rising oil. In addition to being able to suppress, it is sufficient to cool the oil only when necessary, and the influence on the capacity and performance of the refrigeration cycle 1 can be minimized.

  Further, the compressor 2 is a scroll compressor 2 of either a closed type or an open type low pressure housing type, and any one of PVE oil, POE oil, PAG oil or the like is added to an oil reservoir 27 in the housing 14. It is supposed to be filled with a mixed oil whose main component is. For this reason, the low-pressure refrigerant gas from the refrigeration cycle 1 side is sucked into the housing 14, the refrigerant is sucked in, compressed, and discharged into the discharge chamber 19. The scroll compressor 2 is applied as it is, and the refrigeration cycle 1 using the R32 refrigerant is constituted by filling PVE oil, POE oil, PAG oil or a mixed oil thereof suitable for the refrigerant. It is possible to operate while ensuring an allowable operation range or condition equivalent to that of the R410A refrigerant.

  As a result, concerns such as poor lubrication due to a decrease in oil viscosity due to an increase in the oil temperature in the compressor 2 can be reliably resolved. In particular, when the compressor 2 is an open type compressor, oil sludge due to an increase in the sliding portion temperature at the shaft seal portion due to a mechanical seal or a lip seal is suppressed, and refrigerant leakage is prevented. An effect such as prevention can be expected.

Further, the oil return circuit 31 is a parallel circuit of a direct circuit 32 that directly returns the oil separated by the oil separator 3 from the oil separator 3 to the oil reservoir 27 and a cooling circuit 35 that is cooled and returned by the oil cooler 37. cage, the discharge temperature of the refrigerant, when at least one of one detection value of the oil temperature in the compressor 2 exceeds the threshold value, or when the detected value of the oil viscosity is below the threshold value, the oil returning circuit 31 directly By switching from the circuit 32 to the cooling circuit 35, the oil cooler 37 cools and returns the temperature of the return oil to a predetermined temperature or lower, so that the increase in the oil temperature inside the compressor 2 is reliably reduced to a predetermined value or less. In addition to being limited, it is only necessary to cool the oil with the oil cooler 37 when necessary, and the influence on the capacity and performance of the refrigeration cycle 1 can be minimized.

  In addition, this invention is not limited to the invention concerning the said embodiment, In the range which does not deviate from the summary, it can change suitably. For example, in the above-described embodiment, the discharge temperature sensor 39, the oil temperature sensor 40, and the low pressure sensor 41 are provided to detect the refrigerant discharge temperature, the oil temperature in the compressor 2, or the oil viscosity. As the sensor, sensors provided for controlling the operation of the refrigeration cycle 1 may be used and the solenoid valves 33 and 36 may be controlled using the detected values, and there is no need to newly install a sensor.

1 Refrigeration cycle 2 Compressor (sealed electric scroll compressor)
3 Oil separator 13A Discharge circuit 14 Housing 27 Oil reservoir 31 Oil return circuit 32 Direct circuit 33, 36 Solenoid valve 34, 38 Capillary tube 35 Cooling circuit 37 Oil cooler 39 Discharge temperature sensor 40 Oil temperature sensor 41 Low pressure sensor 42 Oil Temperature control unit

Claims (4)

A refrigeration cycle provided with a compressor having a low pressure atmosphere inside the housing having an oil reservoir, the cycle being filled with an R32 refrigerant or an R32 rich mixed refrigerant;
An oil separator provided in a discharge circuit from the compressor;
An oil return circuit that decompresses the oil separated by the oil separator and returns it to the oil reservoir in the housing;
The oil return circuit is a parallel circuit of a direct circuit that returns the oil directly from the oil separator to the oil reservoir and a cooling circuit that cools and returns the oil by an oil cooler,
When the oil viscosity inside the compressor is calculated based on the detected values of the refrigerant pressure in the suction circuit of the refrigeration cycle and the oil temperature in the oil reservoir, and when it falls below a preset threshold value An oil return circuit for a refrigeration cycle, comprising an oil temperature control unit that switches the oil return circuit from the direct circuit to the cooling circuit and cools the return oil to a predetermined temperature or lower.   The compressor is a hermetic type or open type low-pressure housing type scroll compressor, and the oil reservoir inside the housing is one of PVE oil, POE oil, PAG oil, or a main component thereof. The oil return circuit of the refrigeration cycle according to claim 1, wherein the mixed oil is filled. An oil separator is provided in the discharge circuit of the compressor of the refrigeration cycle having a low-pressure housing type compressor and filled with R32 refrigerant or R32 rich mixed refrigerant in the cycle, and the oil separated by the oil separator In the oil return method of the refrigeration cycle that returns the oil to the oil sump in the housing of the compressor through an oil return circuit,
The oil viscosity inside the compressor is calculated based on the detected value of the pressure of the refrigerant in the suction circuit of the refrigeration cycle and the oil temperature in the oil reservoir,
When below the threshold the calculation detection value is set in advance, by returning to cooling the oil return temperature oil return oil cooler provided in the circuit below a predetermined temperature,
An oil return method for a refrigeration cycle, wherein an increase in oil temperature inside the compressor is limited to a specified value or less. The oil return circuit is a parallel circuit of a direct circuit for returning the oil directly from the oil separator to the oil sump, and a cooling circuit for cooling back by an oil cooler;
When the calculated value of the viscosity of the oil inside the compressor is below the threshold value, switches the oil return circuit to the cooling circuit from the direct circuit, the temperature of the oil return through the oil cooler below a predetermined temperature 4. The oil return method for a refrigeration cycle according to claim 3, wherein the oil is returned by cooling.

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