JP6716036B2 - Refrigeration cycle equipment - Google Patents

Description

The present invention relates to a refrigeration cycle device in which oil return control is performed.

BACKGROUND ART Conventionally, there is known a refrigeration cycle device in which an oil separator is arranged between a compressor and a condenser in order to separate a gaseous refrigerant (gas refrigerant) discharged from a compressor and a lubricating oil. .. In the refrigeration cycle apparatus, when the amount of lubricating oil in the compressor is insufficient, control for returning lubricating oil from the oil separator to the compressor (oil return control) may be performed.

For example, in the refrigeration system disclosed in Japanese Patent Laid-Open No. 2015-38407 (Patent Document 1), the lubricating oil level in the compressor is lower than the reference position in order to sufficiently lubricate the compressor. When the output signal of the oil level sensor indicates, the opening/closing valve provided in the emergency oil return passage is opened, and the lubricating oil stored in the oil separator is returned to the compressor.

JP, 2005-38407, A

The density of the fluid has a density difference between the gas and the liquid with the liquid surface of the fluid, which is the interface between the gas and the liquid, as a boundary. By detecting that the density of the fluid at the reference position in the compressor or the oil separator changes by the density difference, it can be detected that the liquid level has passed the reference position. In the following, the detection of the liquid level means to detect that the liquid level has passed the reference position.

In the refrigeration cycle apparatus in operation, the fluid discharged from the compressor is usually composed of gas refrigerant and lubricating oil. In order to detect the liquid level of the fluid, the liquid level detection unit needs to have a resolution capable of detecting the density difference between the gas refrigerant and the lubricating oil.

In the refrigeration cycle device, due to insufficient vaporization of the liquid refrigerant (liquid refrigerant) in the evaporator, there is a phenomenon (liquid return) in which the liquid refrigerant flows out from the evaporator and the liquid refrigerant is sucked into the compressor. It may occur. When liquid return occurs, the fluid discharged from the compressor contains liquid refrigerant in addition to gas refrigerant and lubricating oil. When the liquid return occurs, in order to detect the liquid level of the fluid discharged from the compressor, it is necessary to detect the density difference between the gas refrigerant and the liquid containing the lubricating oil and the liquid refrigerant.

The density difference between the gas refrigerant and the liquid containing the lubricating oil and the liquid refrigerant may be smaller than the density difference between the gas refrigerant and the lubricating oil. When the liquid level of the fluid is detected using the liquid level detection unit that has the resolution capable of detecting the density difference between the gas refrigerant and the lubricating oil without assuming the liquid return, the liquid level detection unit Depending on the resolution, it may be difficult to detect the density difference between the gas refrigerant and the liquid containing the lubricating oil and the liquid refrigerant.

When the liquid return occurs, it may be difficult to detect the liquid level of the fluid discharged from the compressor. As a result, a situation may occur in which the lubricating oil is not returned from the oil separator to the compressor even though the compressor lacks the lubricating oil. If the operation of the compressor is continued in the state where the lubricating oil is insufficient, the possibility that the compressor will fail increases.

The present invention has been made to solve the above problems, and an object thereof is to suppress the occurrence of a shortage of lubricating oil in a compressor.

In the refrigeration cycle apparatus according to the present invention, the refrigerant circulates in the first circulation direction in the order of the compressor, the first heat exchanger, the expansion valve, and the second heat exchanger. The refrigeration cycle device includes an oil separator, a flow control valve, a bypass flow path, a liquid level detection unit, and a control device. The oil separator separates and stores the lubricating oil from the refrigerant from the compressor. The bypass passage moves the lubricating oil from the oil separator to the compressor via the flow control valve. The liquid level detection unit detects the liquid level in the compressor or the oil separator by utilizing the density difference between the lubricating oil and the vaporized refrigerant. The control device adjusts the opening degree of the flow control valve using the detection result of the liquid level. When a predetermined condition is satisfied, the control device increases the opening degree without using the detection result.

According to the refrigeration cycle apparatus of the present invention, when the predetermined condition is satisfied, the opening degree of the flow control valve is increased without using the liquid level detection result by the liquid level detection unit, and the oil separator Increase the lubricating oil returned to the compressor from. As a result, the shortage of lubricating oil in the compressor is suppressed, and the reliability of the refrigeration cycle device can be improved.

FIG. 3 is a functional block diagram showing the configuration of the refrigeration cycle device according to the first embodiment. It is a figure which shows the state in which the lubricating oil in a compressor is insufficient in the refrigeration cycle apparatus of FIG. 3 is a flowchart showing an example of a flow of processing for oil return control by liquid level detection, which is performed in the refrigeration cycle device of FIG. 1. It is a figure which shows an example of a structure of a self-heating sensor. It is a figure which shows together the characteristic of the self-heating sensor when the surrounding fluid is lubricating oil, and the characteristic of the self-heating sensor when the surrounding fluid is a gas refrigerant. It is a functional block diagram which shows a structure when the defrost mode is started in the refrigeration cycle apparatus of FIG. It is a functional block diagram which shows a structure when the defrost mode is complete|finished in the refrigerating-cycle apparatus of FIG. Characteristics of the self-heating sensor when the surrounding fluid is lubricating oil, characteristics of the self-heating sensor when the surrounding fluid is gas refrigerant, and characteristics of the self-heating sensor when the surrounding fluid is liquid containing lubricating oil and liquid refrigerant It is a figure which also shows the characteristic of. It is a figure which shows the correspondence of environmental temperature and a sensor voltage difference. 5 is a flowchart showing an example of the flow of processing for oil return control in the first embodiment. 11 is a flowchart showing an example of the flow of processing of oil return control which is not shown in FIG. 10 and which does not depend on liquid level detection. FIG. 7 is a functional block diagram showing a configuration of a refrigeration cycle device according to Modification 1 of Embodiment 1. 13 is a flowchart showing an example of the flow of processing for oil return control by liquid level detection, which is performed in the refrigeration cycle apparatus of FIG. 12. 7 is a functional block diagram showing a configuration of a refrigeration cycle device according to Modification 2 of Embodiment 1. FIG. 9 is a flowchart showing an example of the flow of processing for oil return control that does not depend on liquid level detection in the second embodiment. 16 is a flowchart showing an example of the flow of processing for oil return control that does not depend on liquid level detection in the third embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and the description thereof will not be repeated in principle.

Embodiment 1.
FIG. 1 is a functional block diagram showing the configuration of the refrigeration cycle device 100 according to the first embodiment. The operation modes of the refrigeration cycle apparatus 100 include a heating mode, a cooling mode, and a defrosting mode. In FIG. 1, the flow of the refrigerant in the heating mode is shown.

As shown in FIG. 1, the refrigeration cycle apparatus 100 includes a compressor 1, an oil separator 2, a four-way valve 3, a heat exchanger 4 arranged indoors, an expansion valve 5, and heat arranged outdoors. The exchanger 6, the on-off valve 7, the bypass flow path 8, the liquid level detection unit 10, and the control device 30 are provided. In the heating mode, the refrigerant circulates through the compressor 1, the oil separator 2, the heat exchanger 4, the expansion valve 5, and the heat exchanger 6 in this order.

The compressor 1 adiabatically compresses the low-pressure gas refrigerant and discharges the high-pressure gas refrigerant to the oil separator 2. Lubricating oil LB1 is stored inside the compressor 1 in order to suppress wear and frictional heat caused by direct metal contact with each other in a mechanism for adiabatic compression of a gas refrigerant. Lubricating oil LB1 is discharged from the compressor 1 together with the refrigerant.

The oil separator 2 is connected between the compressor 1 and the heat exchanger 4, and separates and stores the lubricating oil LB1 from the gas refrigerant from the compressor 1. Examples of the type of the oil separator 2 include a centrifugal type, a perforated plate type, a wire mesh type, and a demister type.

If the lubricating oil LB1 discharged from the compressor 1 is circulated as it is, the pressure loss increases and the heat transfer performance of the heat exchangers 4 and 6 deteriorates, so that the performance of the refrigeration cycle apparatus 100 may deteriorate. In addition, the lubricating oil LB1 which is generally higher in viscosity than the refrigerant takes longer than the refrigerant until it returns to the compressor 1 after being discharged from the compressor 1. When the amount of the lubricating oil LB1 sucked into the compressor 1 is smaller than the amount of the lubricating oil LB1 discharged from the compressor 1, the amount of the lubricating oil LB1 inside the compressor 1 decreases, and the amount of the lubricating oil LB1 inside the compressor 1 decreases. The amount of the lubricating oil LB1 may fall below the required amount. By temporarily storing the lubricating oil LB1 discharged from the compressor 1 in the oil separator 2, it is possible to suppress the amount of the lubricating oil LB1 flowing out to the heat exchanger 4 and thereafter, and the lubricating oil in the compressor 1 can be suppressed. The lubricating oil LB1 can be returned when the LB1 is insufficient.

In the heating mode, the four-way valve 3 forms a flow path so that the refrigerant circulates in the order of the compressor 1, the oil separator 2, the heat exchanger 4, the expansion valve 5, and the heat exchanger 6 as shown in FIG. To do. In the cooling mode and the defrosting mode, a flow path is formed so that the refrigerant circulates through the compressor 1, the oil separator 2, the heat exchanger 6, the expansion valve 5, and the heat exchanger 4 in this order. In the cooling mode and the defrosting mode, the refrigerant circulates through the compressor 1, the oil separator 2, the heat exchanger 6, the expansion valve 5, and the heat exchanger 4 in this order.

The heat exchanger 4 functions as a condenser in the heating mode. In the heat exchanger 4, the gas refrigerant from the compressor 1 releases condensation heat and condenses. The liquid refrigerant RL1 is stored in the heat exchanger 4 in the heating mode. The heat exchanger 4 functions as an evaporator in the cooling mode and the defrosting mode.

The expansion valve 5 adiabatically expands the liquid refrigerant to reduce the pressure, and causes the liquid refrigerant to flow out as wet vapor in a gas-liquid two-phase state. As the expansion valve 5, for example, an electronically controlled expansion valve (LEV: Linear Expansion Valve) can be used.

The heat exchanger 6 functions as an evaporator in the heating mode. The moist steam from the expansion valve 5 absorbs heat of vaporization from the outside air and vaporizes. The heat exchanger 4 functions as a condenser in the cooling mode and the defrosting mode.

The bypass passage 8 moves the lubricating oil LB1 from the oil separator 2 to the compressor 1 via the opening/closing valve 7. The bypass passage 8 connects the discharge port of the oil separator 2 and the suction port of the compressor 1.

The liquid level detection unit 10 detects the liquid level in the oil separator 2. The liquid level detection unit 10 includes a temperature sensor 11 and a self-heating sensor 12. The self-heating sensor 12 is arranged at the reference position SP1 inside the oil separator 2. The self-heating sensor 12 detects a voltage value according to the density of the fluid around the reference position SP1 (ambient fluid). The temperature sensor 11 detects the temperature of the surrounding fluid (environmental temperature). The liquid level detection unit 10 may include a capacitance type sensor and detect a capacitance value according to the density of the surrounding fluid. The configuration of the self-heating sensor 12 and the liquid level detection mechanism of the liquid level detection unit 10 will be described in detail later.

The control device 30 controls the opening/closing of the opening/closing valve 7 by using the detection result of the liquid level from the liquid level detection unit 10 to return the lubricating oil LB1 stored in the oil separator 2 to the compressor 1 (return). Oil control). The oil return control is performed when the lubricating oil LB1 in the compressor 1 is insufficient. The larger the amount of lubricating oil LB1 stored in the oil separator 2, the smaller the amount of lubricating oil LB1 stored in the compressor 1. In the refrigeration cycle apparatus 100, the case where the liquid level of the lubricating oil LB1 in the oil separator 2 is higher than the reference position SP1 is the case where the lubricating oil LB1 in the compressor 1 is insufficient. In FIG. 1, since the liquid level of the lubricating oil LB1 in the oil separator 2 is lower than the reference position SP1, the lubricating oil LB1 in the compressor 1 is not insufficient and the oil return control is not performed.

The control device 30 controls the drive frequency of the compressor 1 to control the amount of refrigerant discharged by the compressor 1 per unit time. The control device 30 controls the four-way valve 3 to switch the circulation direction of the refrigerant. The control device 30 acquires the temperature of the compressor 1 from the temperature sensor 21.

FIG. 2 is a diagram showing a state in which the lubricating oil LB1 in the compressor 1 is insufficient in the refrigeration cycle device 100 of FIG. As shown in FIG. 2, the liquid level of the lubricating oil LB1 in the oil separator 2 is higher than the reference position SP1. In this case, the control device 30 performs oil return control by detecting the liquid level.

FIG. 3 is a flowchart showing an example of the flow of processing for oil return control by liquid level detection, which is performed in the refrigeration cycle apparatus 100 of FIG. Hereinafter, the step is simply described as S.

As shown in FIG. 3, the control device 30 determines in S101 whether the liquid level of the lubricating oil LB1 in the oil separator 2 is higher than the reference position SP1. When the liquid level of lubricating oil LB1 in oil separator 2 is higher than reference position SP1 (YES in S101), control device 30 advances the process to S102. The control device 30 opens the open/close valve 7 in S102 and advances the process to S103. After waiting the reference time in S103, control device 30 advances the process to S104. The reference time is a time required for the reference amount of the lubricating oil LB1 to move from the oil separator 2 to the compressor 1, and can be appropriately determined by an actual machine experiment or simulation. The control device 30 closes the on-off valve in S104 and then ends the oil return control by the liquid level detection. When the liquid level of the lubricating oil LB1 in the oil separator 2 is equal to or lower than the reference position SP1 (NO in S101), the control device 30 ends the oil return control by the liquid level detection.

FIG. 4 is a diagram showing an example of the configuration of the self-heating sensor 12. The self-heating sensor 12 includes electrodes 121 and 122 and a resistance element 123. The resistance element 123 is installed between the electrode 121 and the electrode 122. The resistance element 123 includes a thermistor having a characteristic (negative temperature characteristic) that the resistance value monotonously decreases as the temperature of the resistance element 123 rises. The resistance element 123 may be any element whose resistance value changes with a change in temperature, and is, for example, a thermistor having a characteristic (positive temperature characteristic) in which the resistance value monotonously increases with a rise in temperature of the resistance element 123. It may be. The self-heating sensor 12 outputs a voltage between the electrodes 121 and 122. The voltage between electrodes 121 and 122 varies with ambient temperature and the density of the surrounding fluid.

The density of the lubricating oil LB1 is higher than the density of the gas refrigerant. The higher the density of the fluid, the higher the thermal conductivity of the fluid. The heat generated in the resistance element 123 when the reference current flows through the resistance element 123 is more easily transferred to the surrounding fluid when the surrounding fluid is the lubricating oil LB1 than when the surrounding fluid is the gas refrigerant. The amount of heat radiated from the resistance element 123 to the surrounding fluid when the reference current flows through the resistance element 123 is larger when the surrounding fluid is the lubricating oil LB1 than when the surrounding fluid is the gas refrigerant. Of the heat quantity generated in the resistance element 123 when the reference current flows through the resistance element 123, the heat quantity remaining in the resistance element 123 without moving to the surrounding fluid is smaller as the heat radiation quantity from the resistance element 123 to the surrounding fluid is larger. .. Therefore, the temperature change of the resistance element 123 when the reference current flows through the resistance element 123 is smaller when the surrounding fluid is the lubricating oil LB1 than when the surrounding fluid is the gas refrigerant. The change in the resistance value of the resistance element 123 is smaller as the temperature change of the resistance element 123 is smaller. Therefore, the change in the resistance value of the resistance element 123 is smaller when the surrounding fluid is the lubricating oil LB1 than when the surrounding fluid is the gas refrigerant. The smaller the change in the resistance value of the resistance element 123, the smaller the change in the voltage between the electrodes 121 and 122 (the output value of the self-heating sensor 12). Therefore, the change in the output value of the self-heating sensor 12 when the reference current flows through the resistance element 123 is smaller when the surrounding fluid is the lubricating oil LB1 than when the surrounding fluid is the gas refrigerant.

FIG. 5 is a diagram showing the characteristics VC1 of the self-heating sensor 12 when the surrounding fluid is the lubricating oil LB1 and the characteristics VC2 of the self-heating sensor 12 when the surrounding fluid is a gas refrigerant. The characteristics VC1 and VC2 are represented as a relationship between the environmental temperature Tatm and the output value (sensor voltage) Vs of the self-heating sensor 12. In FIG. 5, the voltage V1so is the sensor voltage Vs when the ambient temperature is T1 and the surrounding fluid is the lubricating oil LB1. The voltage V1sg is the sensor voltage Vs when the ambient temperature is T1 and the surrounding fluid is a gas refrigerant. As shown in FIG. 5, when the environmental temperature Tatm is T1, the density difference between the lubricating oil LB1 and the gas refrigerant is detected as the sensor voltage difference ΔV1s between the voltages V1so and V1sg. Therefore, when the ambient fluid changes from the gas refrigerant to the lubricating oil LB1, or when the lubricating oil LB1 changes to the gas refrigerant, the sensor voltage difference ΔV1s changes in the sensor voltage Vs. In the refrigeration cycle apparatus 100, a threshold value is determined according to the environmental temperature Tatm, and it is determined that the liquid level is detected when the change in the sensor voltage Vs exceeds the threshold value.

When the sensor voltage Vs decreases more than the threshold value, it means that the surrounding fluid has changed from the lubricating oil LB1 to the gas refrigerant. In this case, the liquid level in the oil separator 2 is below the reference position SP1 as shown in FIG. 1, and the lubricating oil in the compressor 1 is not insufficient. Conversely, when the sensor voltage Vs increases above the threshold value, it means that the surrounding fluid has changed from the gas refrigerant to the lubricating oil LB1. Since the liquid level in the oil separator 2 is above the reference position SP1 as shown in FIG. 2, the lubricating oil LB1 in the compressor 1 is insufficient and the oil return control is performed.

In the refrigeration cycle device 100 in operation, the fluid discharged from the compressor 1 is usually composed of a gas refrigerant and a lubricating oil LB1. In order to detect the liquid level of the fluid, the self-heating sensor 12 needs to have a resolution capable of detecting the density difference between the gas refrigerant and the lubricating oil LB1.

In the refrigeration cycle apparatus 100, liquid return may occur. Examples of the cases where the liquid return occurs include the case where the defrost mode is started (FIG. 6), the case where the defrost mode is ended (FIG. 7), the case where the heating mode is started (FIG. 7), and the four-way valve. The case where the circulation direction of the refrigerant is switched by 3 (FIGS. 6 and 7) can be mentioned.

As shown in FIG. 6, when the heating mode is interrupted and the defrosting mode is started, the circulation direction of the refrigerant is switched by the four-way valve 3. In the defrosting mode, the frost attached to the heat exchanger 6 that functions as an evaporator in the heating mode is dissolved and removed by the heat of condensation of the refrigerant. In the defrosting mode of the refrigeration cycle apparatus 100, reverse cycle defrosting is performed. The heat exchanger 4 that functions as a condenser in the heating mode functions as an evaporator in the defrosting mode. At the start of the defrosting mode, the liquid refrigerant RL1 is stored in the heat exchanger 4 that functions as a condenser in the heating mode. For a while after the defrosting mode starts, the liquid refrigerant RL1 flows into the compressor 1 from the heat exchanger 4, so that liquid return occurs.

When the defrosting mode ends and the heating mode restarts, the circulation direction of the refrigerant is switched by the four-way valve 3 as shown in FIG. 7. The liquid refrigerant is stored in the heat exchanger 6 that functions as a condenser in the defrosting mode. For a while after the heating mode is restarted, the liquid refrigerant RL1 flows into the compressor 1 from the heat exchanger 6, so that liquid return occurs.

While the refrigeration cycle apparatus 100 is stopped, in the heat exchanger 6 arranged outdoors, the gas refrigerant is cooled to become a liquid refrigerant, and the liquid refrigerant is stored in the heat exchanger 6 as shown in FIG. 7. To be done. The lower the outside air temperature, the larger the amount of liquid refrigerant stored in the heat exchanger 6. When the refrigeration cycle apparatus 100 is activated with the operation mode set to the heating mode, the liquid refrigerant RL1 flows from the heat exchanger 6 into the compressor 1 for a while after the heating mode is started, so that liquid return occurs. ..

When a liquid return occurs, the fluid discharged from the compressor 1 contains a liquid refrigerant in addition to the gas refrigerant and the lubricating oil LB1. When the liquid return occurs, in order to detect the liquid level of the fluid discharged from the compressor 1, it is necessary to detect the density difference between the gas refrigerant and the liquid containing the lubricating oil LB1 and the liquid refrigerant.

FIG. 8 shows the characteristic VC1 of the self-heating sensor 12 when the surrounding fluid is the lubricating oil LB1, the characteristic VC2 of the self-heating sensor 12 when the surrounding fluid is a gas refrigerant, and the surrounding fluid is the lubricating oil LB1 and the liquid refrigerant. It is a figure which also shows the characteristic VC3 of the self-heating sensor 12 when it is a liquid containing. Characteristics VC1 and VC2, sensor voltages V1so and V1sg, sensor voltage difference ΔV1s, and environmental temperature T1 shown in FIG. 8 are characteristics VC1 and VC2, sensor voltages V1so and V1sg, sensor voltage difference ΔV1s, and environment It is similar to the temperature T1. In FIG. 8, the sensor voltage V1sm is the sensor voltage Vs when the ambient temperature is T1 and the surrounding fluid is a liquid including the lubricating oil LB1 and the liquid refrigerant. The sensor voltage difference ΔV2s is the difference between the sensor voltages V1sm and V1sg.

When the density of the liquid refrigerant is smaller than that of the lubricating oil LB1, the density difference between the gas refrigerant and the liquid containing the lubricating oil LB1 and the liquid refrigerant is smaller than the density difference between the gas refrigerant and the lubricating oil LB1. As a result, as shown in FIG. 8, the sensor voltage difference ΔV2s representing the density difference between the gas refrigerant and the liquid containing the lubricating oil LB1 and the liquid refrigerant is equal to the sensor voltage difference representing the density difference between the gas refrigerant and the lubricating oil LB1. It is smaller than the difference ΔV1s.

FIG. 9 is a diagram showing a correspondence relationship between the environmental temperature Tatm and the sensor voltage difference ΔV1s and a correspondence relationship between the environmental temperature Tatm and the sensor voltage difference ΔV2s. In FIG. 9, the sensor voltage difference ΔVrs represents the change (resolution) in the voltage value that can be detected by the self-heating sensor 12. A change (difference) in voltage value smaller than the sensor voltage difference ΔVrs cannot be detected by the self-heating sensor 12. The range of the environmental temperatures T2 to T4 (T2<T4) represents the range of temperatures assumed during the operation of the refrigeration cycle apparatus 100.

As shown in FIG. 9, the sensor voltage difference ΔV1s exceeds the resolution ΔVrs in the range of the environmental temperatures T2 to T4. However, the sensor voltage difference ΔV2s becomes lower than the resolution ΔVrs when the environmental temperature becomes higher than T3 (T2<T3<T4). When the liquid return occurs within the range of the environmental temperature T3 to T4, it becomes difficult for the self-heating sensor 12 to detect the liquid level in the oil separator 2. As a result, a situation may occur in which the oil return control is not performed despite the lack of lubricating oil in the compressor 1. If the operation of the compressor 1 is continued in the state where the lubricating oil is insufficient, the possibility that the compressor 1 will fail increases.

Therefore, in the refrigeration cycle apparatus 100, when the liquid level detection unit 10 may have difficulty in detecting the liquid level due to the liquid refrigerant being sucked into the compressor 1 (when a predetermined condition is satisfied), The oil return control is performed without using the result of liquid level detection by the liquid level detection unit 10. As a result, the shortage of the lubricating oil LB1 in the compressor 1 is suppressed, and the reliability of the refrigeration cycle device 100 can be improved. The predetermined condition is a condition that is defined in advance as a condition in which liquid return is likely to occur. The liquid return refers to, for example, when the liquid level is difficult to be detected by the liquid level detection unit 10 due to the liquid refrigerant being sucked into the compressor 1, or the amount of the liquid refrigerant sucked into the compressor 1 per unit time is a standard. It can be considered to be larger than the quantity.

FIG. 10 is a flowchart showing an example of the flow of processing for oil return control in the first embodiment. The processing shown in FIG. 9 is performed at regular time intervals by a main routine (not shown). The predetermined conditions include a condition that the defrosting mode has been started, a condition that the defrosting mode has ended, and a condition that the heating mode has been started. The predetermined condition may include a condition that the circulation direction of the refrigerant has been switched instead of the condition that the defrost mode has started and the condition that the defrost mode has ended.

As shown in FIG. 10, control device 30 determines whether or not a predetermined condition is satisfied in S10. If the predetermined condition is satisfied (YES in S10), control device 30 advances the process to S200. After performing the oil return control without using the liquid level detection result of the liquid level detection unit 10 in S200, the control device 30 returns the process to the main routine. If the predetermined condition is not satisfied (NO in S10), control device 30 advances the process to S100. After performing the oil return control using the liquid level detection result of the liquid level detection unit 10 in S100, the control device 30 returns the process to the main routine. The process of oil return control by liquid level detection shown in S100 is the same as the process shown in FIG.

FIG. 11 is a flowchart showing an example of the flow of processing for oil return control that does not depend on liquid level detection in FIG. As shown in FIG. 11, the control device 30 opens the opening/closing valve 7 in S201, and advances the processing to S202. The control device 30 determines whether or not a reference time has elapsed since the opening/closing valve 7 was opened in S202. The reference time is a time required for the reference amount of the lubricating oil LB1 to move from the oil separator 2 to the compressor 1, and can be appropriately determined by an actual machine experiment or simulation. When the reference time has elapsed since the opening/closing valve 7 was opened (YES in S202), the control device 30 closes the opening/closing valve 7 in S203, and then returns the process to the main routine. When the reference time has not elapsed after opening the opening/closing valve 7 (NO in S202), control device 30 returns the process to S202.

As described above, according to the refrigeration cycle apparatus according to the first embodiment, when the liquid level of the refrigerant in the compressor exceeds the reference liquid amount and the liquid level detection unit may have difficulty in detecting the liquid level, The opening degree of the on-off valve is increased without using the information from the section to increase the amount of lubricating oil returned from the oil separator to the compressor. As a result, the lack of lubricating oil in the compressor is less likely to occur, and the reliability of the refrigeration cycle device can be improved.

Modification 1 of the first embodiment.
In the first embodiment, the case where the liquid level detection unit detects the liquid level in the oil separator has been described. In the refrigeration cycle apparatus according to the present invention, the liquid level detection unit 20 may detect the liquid level in the compressor 1 as in the refrigeration cycle apparatus 100A shown in FIG.

As shown in FIG. 12, the liquid level detection unit 20 detects the liquid level in the compressor 1. The liquid level detection unit 20 includes a temperature sensor 21 and a self-heating sensor 22. The self-heating sensor 22 is arranged at the reference position SP2 inside the compressor 1. The self-heating sensor 22 detects a voltage value according to the density of the fluid around the reference position SP2. The temperature sensor 21 detects the environmental temperature. The control device 30A performs oil return control using the detection result of the liquid level from the liquid level detection unit 20.

FIG. 13 is a flowchart showing an example of the flow of processing for oil return control by liquid level detection, which is performed in the refrigeration cycle apparatus 100A shown in FIG. As shown in FIG. 13, the control device 30A determines in S121 whether the liquid level of the lubricating oil LB1 in the compressor 1 is lower than the reference position SP2. When the liquid level of the lubricating oil LB1 in the compressor 1 is lower than the reference position SP2 (YES in S121), the control device 30A performs the oil return control in S102 to S104 as in the first embodiment to perform the main processing. Return to routine. When the liquid level of the lubricating oil LB1 in the compressor 1 is equal to or higher than the reference position SP2 (NO in S121), the process is returned to the main routine.

Modification 2 of Embodiment 1.
In the first embodiment, the refrigeration cycle device including the four-way valve as the flow path switching device and performing the reverse cycle defrost in the defrosting mode has been described. The refrigeration cycle apparatus according to the present invention does not have to include the four-way valve unlike the refrigeration cycle apparatus 100B shown in FIG. In the defrosting mode of the refrigeration cycle apparatus 100B, the defrosting operation (off cycle defrost) with the compressor 1 stopped is performed by the controller 30B. In the off-cycle defrost, for example, the heat exchanger 6 (evaporator) is heated by a heater (not shown), so that the frost generated in the heat exchanger 6 is melted and removed. In the refrigeration cycle apparatus 100B, the predetermined conditions under which the oil return control without liquid level detection is performed by the control device 30B include a condition that the heating mode is started and a condition that the defrost mode is ended. Be done.

As described above, also with the refrigeration cycle apparatus according to Modification 1 and Modification 2 of Embodiment 1, the same effect as that of Embodiment 1 can be obtained.

Embodiment 2.
In the first embodiment, the termination condition indicating that the reference amount of lubricating oil has moved from the oil separator to the compressor is the condition that the reference time has elapsed since the opening/closing valve 7 was opened (S202 in FIG. 11). Since the reference time is a fixed value, even if the reference amount of lubricating oil moves from the oil separator to the compressor, the opening/closing valve 7 cannot be closed unless the reference time has elapsed. If the on-off valve 7 remains open in the state where the amount of lubricating oil in the oil separator is sufficiently reduced, even the gas refrigerant discharged from the compressor to the oil separator can be returned to the compressor. When a part of the gas refrigerant discharged from the compressor is returned to the compressor from the oil separator, the amount of the gas refrigerant flowing into the heat exchanger functioning as the condenser decreases. As a result, the amount of refrigerant circulating in the refrigeration cycle apparatus (the amount of circulating refrigerant) decreases while repeating the phase change, and the performance of the refrigeration cycle apparatus deteriorates. On the other hand, in oil return control by detecting the liquid level, the amount of lubricating oil in the oil separator is detected because the reference level of lubricating oil is transferred from the oil separator to the compressor by detecting the liquid level. It is unlikely that the on-off valve 7 is left open even though it has been sufficiently reduced.

When the liquid return is eliminated while the oil return control is not performed by the liquid level detection, it is desirable to close the opening/closing valve 7 as soon as possible and shift to the oil return control by the liquid level detection. Therefore, in the second embodiment, the condition that the temperature inside the compressor is higher than the reference temperature is adopted as the condition for ending the oil return control that does not depend on the liquid level detection. Other than this, the configuration of the second embodiment is similar to that of the first embodiment, and therefore the description will not be repeated.

When the liquid returns, the temperature of the liquid refrigerant is lower than that of the gas refrigerant, so that the temperature of the compressor 1 temporarily drops. The temperature of the compressor 1 rises as the amount of liquid refrigerant flowing into the compressor 1 decreases. Therefore, when the temperature of the compressor 1 becomes higher than the reference temperature, it can be determined that the liquid return has disappeared. When the temperature rise rate of the compressor 1 (value obtained by dividing the temperature change by the time interval) exceeds the reference value, it may be determined that the liquid return has been eliminated.

As described above, according to the refrigeration cycle device according to the second embodiment, the same effect as that of the first embodiment can be obtained. Further, in the second embodiment, when it is determined that the liquid return has been eliminated, the oil return control that does not depend on the liquid level detection ends. As a result, it is possible to suppress the decrease in the amount of circulating refrigerant, and thus it is possible to suppress the performance deterioration of the refrigeration cycle apparatus.

Embodiment 3.
When the termination condition of the oil return control not based on the liquid level detection is satisfied and the on-off valve 7 is closed, the pressure of the high-pressure side refrigerant (condensing pressure) from the compressor to the expansion valve rises, and the performance of the refrigeration cycle device And safety may be reduced. Therefore, in the third embodiment, after the condition for ending the oil return control that does not depend on the liquid level detection is satisfied and the on-off valve 7 is closed, the drive frequency of the compressor is reduced to the reference value, and the unit of the compressor is reduced. The discharge amount per time is reduced to the reference discharge amount. By reducing the discharge amount of the compressor per unit time, the pressure of the high-pressure side refrigerant can be reduced.

The difference between the third embodiment and the first embodiment is that the drive frequency of the compressor is reduced to the reference value after the termination condition of the oil return control not based on the liquid level detection is satisfied and the opening/closing valve 7 is closed. Is. Since the other configurations are similar, the description will not be repeated.

FIG. 16 is a flowchart showing an example of the flow of processing for oil return control that does not depend on liquid level detection in the third embodiment. As shown in FIG. 16, after opening the on-off valve in S201 (S201), the control device waits for the reference time to elapse (S202) and then closes the on-off valve (S203). After that, the control device reduces the drive frequency of the compressor 1 to the reference value in S204, and then returns the process to the main routine.

As described above, according to the refrigeration cycle device according to the third embodiment, the same effect as that of the first embodiment can be obtained. Further, in the third embodiment, the drive frequency of the compressor is reduced to the reference value after the termination condition of the oil return control that does not depend on the liquid level detection is satisfied and the open/close valve is closed. As a result, it is possible to suppress an increase in the pressure on the high pressure side of the refrigeration cycle apparatus, and it is possible to suppress deterioration of the performance and safety of the refrigeration cycle apparatus.

It is also planned that the respective embodiments disclosed this time are appropriately combined and implemented within a range that does not contradict. The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

1 compressor, 2 oil separator, 3 four-way valve, 4, 6 heat exchanger, 5 expansion valve, 7 on-off valve, 8 bypass flow passage, 10, 20 liquid level detection unit 11, 21 temperature sensor, 12, 22 Self-heating sensor, 30, 30A, 30B control device, 100, 100A, 100B refrigeration cycle device, 121, 122 electrode, 123 resistance element, LB1 lubricating oil.

Claims (12)

A refrigeration cycle apparatus in which a refrigerant circulates in a first circulation direction in the order of a compressor, a first heat exchanger, an expansion valve, and a second heat exchanger,
An oil separator configured to separate and store lubricating oil from the refrigerant from the compressor,
A flow control valve,
From the oil separator to the compressor via the flow control valve, a bypass flow path configured to move the lubricating oil,
Utilizing the density difference between the lubricating oil and the vaporized refrigerant, a liquid level detection unit configured to detect the liquid level in the compressor or the oil separator,
Using the detection result of the liquid level, a control device configured to adjust the opening of the flow control valve,
The control device is configured to increase the opening degree without using the detection result when a predetermined condition is satisfied ,
The operation mode of the refrigeration cycle device includes a heating mode and a defrosting mode,
The predetermined conditions include a refrigeration cycle apparatus including a condition that the defrosting mode has ended . Before SL predetermined condition, further comprising a condition that the heating mode is started, the refrigeration cycle apparatus according to claim 1. Circulation direction before Symbol refrigerant, a first circulation direction, further comprising a configured flow path switching unit to switch between a reverse direction of the second circulation direction from the first circulation direction,
The control device is configured to control the flow path switching device to set the circulation direction to the first circulation direction in the heating mode and to the second circulation direction in the defrosting mode. The refrigeration cycle apparatus according to claim 2, which is present. Said predetermined conditions further includes a condition that the defrost mode is initiated, the refrigeration cycle apparatus according to claim 3. The refrigeration cycle apparatus according to claim 3, wherein the predetermined condition further includes a condition that the circulation direction has been switched. In the case where the predetermined condition is satisfied, the control device, after increasing the opening degree, has an end condition indicating that the reference amount of the lubricating oil has moved from the oil separator to the compressor. The refrigeration cycle apparatus according to any one of claims 1 to 5 , which is configured to reduce the opening when it is satisfied. The refrigeration cycle apparatus according to claim 6 , wherein the termination condition includes a condition that a reference time has elapsed after the increase of the opening degree is completed. The refrigeration cycle apparatus according to claim 6 , wherein the termination condition includes a condition that a temperature inside the compressor is higher than a reference temperature. The control device, after reduction of the opening has been completed, either the discharge amount per unit of the compressor time and is configured to reduce to the reference discharge amount, claims 6 to claim 8 1 The refrigeration cycle apparatus according to item. The liquid level detection unit is configured to detect the liquid level in the oil separator,
The control device is configured to increase the opening degree when the liquid level is higher than a reference position in the oil separator when the predetermined condition is not satisfied. The refrigeration cycle apparatus according to claim 9 . The liquid level detection unit is configured to detect a liquid level in the compressor,
The control device is configured to increase the opening degree when the liquid level is lower than a reference position in the compressor when the predetermined condition is not satisfied. The refrigeration cycle apparatus according to any one of 9 above. The liquid level detecting unit includes a self-heating type sensors, the refrigeration cycle apparatus according to any one of claims 1 to 11.

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