JP7655084B2 - Refrigeration Cycle Equipment - Google Patents

Description

The present invention relates to a refrigeration cycle device in which the opening degree of the pressure reducing section is controlled by a control section.

Patent Document 1 describes a refrigeration cycle device that is applied to a vehicle air conditioning system. In this conventional technology, an evaporator exchanges heat between the refrigerant flowing out of an expansion valve and the air being blown into the vehicle cabin to cool the air being blown into the vehicle cabin.

The opening of the expansion valve is controlled by a control device so that the degree of superheat of the refrigerant flowing into the compressor approaches the target degree of superheat.

JP 2019-26111 A

According to the above conventional technology, there are cases where the refrigerant flowing into the compressor cannot be superheated, such as when the evaporator intake air temperature is low. If there is a large load fluctuation under such conditions, the refrigerant may dry out in the evaporator, causing the evaporator to lose its cooling capacity. Drying out refers to the excessive evaporation of the refrigerant in the evaporator, resulting in an excessively large area where only gas-phase refrigerant exists.

In view of the above, the present invention aims to suppress the drying out of refrigerant in the evaporator.

In order to achieve the above object, the refrigeration cycle device according to claim 1 comprises:
A compressor (11) that draws in, compresses, and discharges a refrigerant;
A heat dissipation section (12) that dissipates heat from the refrigerant;
a pressure reducing unit (14) capable of reducing the pressure of the refrigerant and adjusting a flow path opening degree so as to adjust a flow rate of the refrigerant;
an evaporation section (15) for allowing the refrigerant decompressed in the decompression section to absorb heat from air;
a refrigerant state detection unit (64, 66) for detecting a state of a refrigerant downstream of a refrigerant inlet of an evaporation unit and upstream of a suction port of a compressor;
a control unit (60) that controls an opening degree of the pressure reducing unit to a normal opening degree (EVN) that is an opening degree such that a superheat degree (SHE) of the refrigerant flowing out from the evaporator approaches a target superheat degree (SHEO), determines whether or not the refrigerant has dried out in the evaporation unit based on a state of the refrigerant detected by the refrigerant state detection unit, and, when it is determined that the refrigerant has dried out in the evaporation unit, makes the opening degree of the pressure reducing unit larger than the normal opening degree;
The refrigerant state detection unit is
a first detection unit (66) that detects a state of a refrigerant downstream of an outlet of the evaporator and upstream of a suction port of the compressor;
and a second detection unit (64) that detects a state of the refrigerant downstream of the inlet of the evaporator and upstream of the outlet of the evaporator,
The first detection unit detects the pressure (Psuc) of the refrigerant,
The second detection unit detects the temperature (Tefin) of the refrigerant,
The control unit calculates a saturation temperature (Tsat) of the refrigerant based on the pressure of the refrigerant detected by the first detection unit,
When the difference between the refrigerant temperature detected by the second detection unit and the saturation temperature exceeds a threshold value (α1), it is determined that the refrigerant has dried out in the evaporation unit ,
The control unit increases the threshold value as the flow rate of the refrigerant flowing into the evaporation unit increases .

This allows for an appropriate determination of whether or not the refrigerant has dried out in the evaporation section. If it is determined that the refrigerant has dried out in the evaporation section, the flow rate of the refrigerant flowing into the evaporation section can be increased, thereby preventing the refrigerant from drying out in the evaporator.

Note that the symbols in parentheses for each means described in this section and in the claims indicate the corresponding relationship with the specific means described in the embodiments described below.

1 is an overall configuration diagram of a refrigeration cycle device according to a first embodiment. FIG. 2 is a block diagram showing an electrical control unit of the refrigeration cycle device in the first embodiment. FIG. 5 is a flowchart showing a control process of a control program in the first embodiment. 5 is a graph showing a refrigerant temperature and a refrigerant pressure when no dryout occurs in the evaporator of the first embodiment. 5 is a graph showing a refrigerant temperature and a refrigerant pressure when dryout occurs in the evaporator of the first embodiment. 5 is a graph showing a refrigerant temperature and a refrigerant pressure when a refrigerant flow rate is large in the evaporator of the first embodiment. 5 is a graph showing a refrigerant temperature and a refrigerant pressure when an intake air temperature is low in the evaporator of the first embodiment. 5 is a graph showing the behavior of an expansion valve in the evaporator of the first embodiment when the intake air temperature is low. 10 is a flowchart showing a control process of a control program in a second embodiment. FIG. 11 is a control characteristic diagram used in the control process of the control program in the second embodiment.

First Embodiment
A first embodiment will be described below with reference to the drawings. A vehicle air conditioner 1 shown in Fig. 1 is an air conditioner that adjusts the temperature of a vehicle interior space (in other words, a space to be air-conditioned) to an appropriate temperature. The vehicle air conditioner 1 has a refrigeration cycle device 10.

The refrigeration cycle device 10 is a vapor compression type refrigerator equipped with a compressor 11, a condenser 12, a receiver 13, an expansion valve 14, and an evaporator 15. In the refrigeration cycle device 10 of this embodiment, a fluorocarbon-based refrigerant is used as the refrigerant, and a subcritical refrigeration cycle is formed in which the high-pressure side refrigerant pressure does not exceed the critical pressure of the refrigerant.

A refrigerant circulation circuit is formed in the refrigeration cycle device 10. In the refrigerant circulation circuit, the refrigerant circulates through the compressor 11, condenser 12, receiver 13, expansion valve 14, evaporator 15, and compressor 11 in that order.

The compressor 11 is an electric compressor driven by power supplied from a battery, and draws in, compresses, and discharges the refrigerant from the refrigeration cycle device 10. The electric motor of the compressor 11 is controlled by the control device 60 shown in FIG. 2. The compressor 11 may be a variable displacement compressor driven by a belt.

The condenser 12 is a high-pressure side heat exchanger that dissipates heat from the high-pressure side refrigerant discharged from the compressor 11 to condense it. The condenser 12 condenses the high-pressure side refrigerant by exchanging heat between the high-pressure side refrigerant discharged from the compressor 11 and outside air. The condenser 12 may also condense the high-pressure side refrigerant by exchanging heat between the high-pressure side refrigerant discharged from the compressor 11 and cooling water.

The receiver 13 is a gas-liquid separation section that separates the high-pressure refrigerant flowing out from the condenser 12 into gas and liquid, and discharges the separated liquid-phase refrigerant downstream while storing excess refrigerant from the cycle.

The expansion valve 14 is a pressure reducing section that reduces the pressure and expands the liquid phase refrigerant that flows out of the receiver 13. The expansion valve 14 is an electric expansion valve. The electric expansion valve is an electric variable throttle mechanism that includes a valve body that is configured to change the throttle opening and an electric actuator that changes the opening of the valve body.

The expansion valve 14 is a refrigerant flow switching unit that switches between a state in which refrigerant flows through the evaporator 15 and a state in which refrigerant does not flow through the evaporator 15. The operation of the expansion valve 14 is controlled by a control signal output from the control device 60.

The evaporator 15 is an evaporator that evaporates the refrigerant by exchanging heat between the refrigerant flowing out from the expansion valve 14 and the air blown into the vehicle cabin. In the evaporator 15, the refrigerant absorbs heat from the air blown into the vehicle cabin. The evaporator 15 is an air cooler that cools the air blown into the vehicle cabin. The gas-phase refrigerant evaporated in the evaporator 15 is sucked into the compressor 11 and compressed.

The evaporator 15 is housed in an air conditioning casing 51 of the interior air conditioning unit 50. The interior air conditioning unit 50 is disposed inside an instrument panel (not shown) at the front of the vehicle interior. The air conditioning casing 51 is an air passage forming member that forms an air passage.

An inside/outside air switching box 52, an indoor blower 53, and a heater core 54 are arranged in the air conditioning casing 51. The inside/outside air switching box 52 is an inside/outside air switching section that switches between introducing inside air and outside air into the air passage in the air conditioning casing 51. The indoor blower 53 draws in the inside air and outside air that have been introduced into the air passage in the air conditioning casing 51 through the inside/outside air switching box 52 and blows them out. The operation of the indoor blower 53 is controlled by the control device 60.

The heater core 54 is disposed downstream of the evaporator 15 in the air passage in the air conditioning casing 51. The heater core 54 is an air heater that heats the air being blown into the vehicle cabin by exchanging heat between the high-temperature coolant and the air being blown into the vehicle cabin. The high-temperature coolant is heated by a heating heat source such as the driving engine or an electric heater. The high-temperature coolant may be heated by the condenser 12.

An air mix door 55 is disposed between the evaporator 15 and the heater core 54 in the air passage in the air conditioning casing 51. The air mix door 55 adjusts the ratio of the amount of cold air that passes through the evaporator 15 and flows into the heater core 54 and the amount of cold air that flows through the cold air bypass passage 56.

The cold air bypass passage 56 is an air passage through which the cold air that has passed through the evaporator 15 flows by bypassing the heater core 54. The rotating shaft of the air mix door 55 is driven by a servo motor 57. The operation of the servo motor for the air mix door is controlled by the control device 60.

The air mix door 55 may be a sliding door that slides in a direction substantially perpendicular to the air flow. The sliding door may be a plate-shaped door made of a rigid body, or a film door made of a flexible film material.

The conditioned air, whose temperature has been adjusted by the air mix door 55, is blown out into the vehicle cabin from an air outlet 58 formed in the air conditioning casing 51.

The control device 60 shown in FIG. 2 is composed of a well-known microcomputer including a CPU, ROM, RAM, etc., and its peripheral circuits. The control device 60 performs various calculations and processing based on a control program stored in the ROM. Various controlled devices are connected to the output side of the control device 60. The control device 60 is a control unit that controls the operation of the various controlled devices.

The devices controlled by the control device 60 include the compressor 11, the expansion valve 14, the indoor blower 53, and the servo motor 57 for the air mix door.

The software and hardware of the control device 60 that controls the electric motor of the compressor 11 is a refrigerant discharge capacity control unit. The software and hardware of the control device 60 that controls the expansion valve 14 is a throttling control unit.

The software and hardware of the control device 60 that controls the indoor blower 53 is the air blowing capacity control section. The software and hardware of the control device 60 that controls the servo motor 57 for the air mix door is the air volume ratio control section.

A variety of control sensors are connected to the input side of the control device 60. The various control sensors include an inside air temperature sensor 61, an outside air temperature sensor 62, a solar radiation sensor 63, an evaporator temperature sensor 64, an intake refrigerant temperature sensor 65, an intake refrigerant pressure sensor 66, and a high-temperature coolant temperature sensor 67.

The interior air temperature sensor 61 detects the interior temperature Tr. The exterior air temperature sensor 62 detects the exterior air temperature Tam. The solar radiation sensor 63 detects the amount of solar radiation Ts inside the vehicle.

The evaporator temperature sensor 64 is an evaporator temperature detection unit that detects the refrigerant evaporation temperature (evaporator temperature) Tefin in the evaporator 15. Specifically, the evaporator temperature sensor 64 detects the temperature of the heat exchange fins of the evaporator 15.

The evaporator temperature sensor 64 is disposed in a region of the evaporator 15 where liquid-phase refrigerant is present when dryout is not occurring. For example, the evaporator temperature sensor 64 is disposed in a portion of the evaporator 15 upstream of the refrigerant flow.

The intake refrigerant temperature sensor 65 is an intake refrigerant temperature detection unit that detects the intake refrigerant temperature Tsuc of the refrigerant being drawn into the compressor 11. In other words, the intake refrigerant temperature sensor 65 detects the temperature of the refrigerant on the outlet side of the evaporator 15.

The suction refrigerant pressure sensor 66 is a suction refrigerant temperature detection unit that detects the suction refrigerant pressure Psuc of the refrigerant being suctioned into the compressor 11. In other words, the suction refrigerant pressure sensor 66 detects the pressure of the refrigerant on the outlet side of the evaporator 15.

The intake refrigerant temperature sensor 65 and the intake refrigerant pressure sensor 66 are disposed in an area where superheated refrigerant is present when no dryout occurs in the evaporator 15. For example, the intake refrigerant temperature sensor 65 and the intake refrigerant pressure sensor 66 are disposed in the refrigerant piping between the evaporator 15 and the compressor 11.

The evaporator temperature sensor 64 and the suction refrigerant pressure sensor 66 are refrigerant state detection units that detect the state of the refrigerant downstream of the refrigerant inlet of the expansion valve 14 and upstream of the suction port of the compressor 11. More preferably, the evaporator temperature sensor 64 and the suction refrigerant pressure sensor 66 detect the state of the refrigerant downstream of the refrigerant inlet of the evaporator 15 and upstream of the suction port of the compressor 11.

The suction refrigerant pressure sensor 66 is a first detection unit that detects the state of the refrigerant downstream of the outlet of the evaporator 15 and upstream of the suction port of the compressor 11. The evaporator temperature sensor 64 is a second detection unit that detects the state of the refrigerant downstream of the inlet of the evaporator 15 and upstream of the outlet of the evaporator 15.

The high-temperature coolant temperature sensor 67 detects the temperature TW of the high-temperature coolant flowing into the heater core 54. For example, the high-temperature coolant temperature sensor 67 detects the temperature of the coolant flowing out from the condenser 12.

Various operation switches (not shown) are connected to the input side of the control device 60. The various operation switches are provided on an operation panel 70 and are operated by the occupant. The operation panel 70 is located near the instrument panel at the front of the vehicle interior. Operation signals from the various operation switches are input to the control device 60.

The various operation switches include an auto switch, an air conditioner switch, a temperature setting switch, etc. The auto switch is a switch that sets and cancels the automatic control operation of the vehicle air conditioner 1. The air conditioner switch is a switch that sets whether or not the air is cooled by the interior air conditioning unit 50. The temperature setting switch is a switch that sets the set temperature inside the vehicle cabin.

Next, the operation of the above configuration will be described. Below, the operation when the auto switch on the operation panel 70 is turned on by the occupant will be described. When the air conditioner switch on the operation panel 70 is turned on by the occupant, the control device 60 executes the air conditioning control program.

In the air conditioning control program, the rotation speed Nc of the compressor 11, the opening SW of the air mix door 55, and the throttling opening EV of the expansion valve 14 are determined. The rotation speed of the compressor 11 is determined by a feedback control method based on the deviation between the target evaporator temperature TEO and the evaporator temperature Tefin detected by the evaporator temperature sensor 64 so that the evaporator temperature Tefin approaches the target evaporator temperature TEO. The target evaporator temperature TEO is determined by referring to a control map stored in the control device 60 based on the target blowing temperature TAO. In the control map of this embodiment, the target evaporator temperature TEO is determined so that it increases as the target blowing temperature TAO increases.

The target outlet temperature TAO is a target temperature of the air to be blown into the vehicle compartment. The control device 60 calculates the target outlet temperature TAO based on the following formula F1.
TAO=Kset×Tset-Kr×Tr-Kam×Tam-Ks×Ts+C…(F1)
In this formula, Tset is the vehicle interior set temperature set by the temperature setting switch on the operation panel 70, Tr is the inside air temperature detected by the inside air temperature sensor 61, Tam is the outside air temperature detected by the outside air temperature sensor 62, and Ts is the amount of solar radiation detected by the solar radiation sensor 63. Kset, Kr, Kam, and Ks are control gains, and C is a correction constant.

The opening degree SW of the air mix door 55 is determined so that the conditioned air whose temperature has been adjusted by the air mix door 55 reaches the target blowing temperature TAO. Specifically, the opening degree of the air mix door 55 is determined based on the target blowing temperature TAO, the evaporator temperature Tefin, the temperature TW of the high-temperature coolant flowing into the heater core 54, etc.

The throttle opening EV of the expansion valve 14 is determined by the control process shown in the flowchart of FIG. 3. First, in step S100, the throttle opening EVN of the expansion valve 14 during normal control (hereinafter referred to as normal opening) is determined by a feedback control method based on the deviation between the target superheat degree SHEO of the refrigerant on the outlet side of the evaporator 15 and the superheat degree SHE of the refrigerant on the outlet side of the evaporator 15 so that the superheat degree SHE approaches the target superheat degree SHEO. For example, the target superheat degree SHEO is a predetermined constant (5°C in this embodiment).

The degree of superheat SHE is calculated based on the intake refrigerant pressure Psuc detected by the intake refrigerant pressure sensor 66 and the intake refrigerant temperature Tsuc detected by the intake refrigerant temperature sensor 65.

In the next step S110, it is determined whether the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1. The evaporator outlet saturation temperature Tsat is calculated based on the suction refrigerant pressure Psuc detected by the suction refrigerant pressure sensor 66. The threshold value α1 is a positive value that is appropriately determined by the control device 60.

If it is determined that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin does not exceed the threshold value α1, it is considered that dryout has not occurred in the evaporator 15. If it is determined that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1, it is considered that dryout has occurred in the evaporator 15.

In other words, as shown in FIG. 4, when dryout does not occur in the evaporator 15, the evaporator temperature sensor 64 detects the temperature of a refrigerant that does not have a degree of superheat, and the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin falls below the threshold value α1.

As shown in FIG. 5, when dryout occurs in the evaporator 15, the evaporator temperature sensor 64 detects the temperature of the refrigerant with a degree of superheat, and the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1.

The threshold value α1 is set to a larger value as the flow rate of the refrigerant flowing into the evaporator 15 increases. As shown in FIG. 6, a large refrigerant flow rate results in a large pressure loss, which creates a pressure difference between the inlet and outlet sides of the evaporator 15. This is to suppress erroneous judgments caused by this pressure difference.

If it is determined in step S110 that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin does not exceed the threshold value α1, proceed to step S120. If it is determined in step S110 that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1, proceed to step S130.

In step S120, since it is assumed that dryout has not occurred in the evaporator 15, the normal opening EVN determined in step S100 is set as the throttling opening EV of the expansion valve 14, and the process proceeds to step S140.

In step S130, since it is considered that dryout has occurred in the evaporator 15, the throttle opening EV of the expansion valve 14 is set to an opening EVD (hereinafter referred to as the dryout opening) that is greater than the normal opening EVN determined in step S100, and the process proceeds to step S140. For example, the dryout opening EVD is the opening (100%) when the expansion valve 14 is fully open. The dryout opening EVD may be a predetermined amount greater than the normal opening EVN.

In step S140, a control signal or control voltage is output to the expansion valve 14 so that the expansion valve 14 throttle opening EV determined in steps S120 and S130 is obtained, and the process returns to step S100.

As a result, in the refrigeration cycle device 10, the state of the refrigerant circulating through the cycle changes as follows: That is, the high-pressure refrigerant discharged from the compressor 11 flows into the condenser 12 and dissipates heat. As a result, the refrigerant is cooled and condensed in the condenser 12.

The refrigerant flowing out of the condenser 12 is separated into gas and liquid in the receiver 13. The liquid-phase refrigerant separated in the receiver 13 flows into the expansion valve 14, where it is reduced in pressure and expanded until it becomes a low-pressure refrigerant. The low-pressure refrigerant reduced in pressure by the expansion valve 14 flows into the evaporator 15, where it absorbs heat from the air being blown into the vehicle cabin and evaporates. This cools the air being blown into the vehicle cabin.

The refrigerant that flows out of the evaporator 15 then flows to the suction side of the compressor 11 and is compressed again by the compressor 11.

In this way, the refrigeration cycle device 10 can make the low-pressure refrigerant absorb heat from the air in the evaporator 15 and blow the cooled air into the vehicle cabin. This allows the vehicle cabin to be cooled.

If dryout occurs in the evaporator 15, the throttle opening EV of the expansion valve 14 is increased from the normal opening EVN in step S130, so that the flow rate of the refrigerant flowing into the evaporator 15 can be increased. This allows the dryout to be quickly resolved.

In this embodiment, the detection values of the evaporator temperature sensor 64 and the suction refrigerant pressure sensor 66 are feedback controlled, so it is not affected by the tolerance of the expansion valve 14 itself and can be used appropriately even at low openings. Furthermore, the degree of superheat can be easily controlled at the outlet of the evaporation section 15, and a gas-liquid separation mechanism (a so-called accumulator) is not required between the outlet of the evaporation section 15 and the suction port of the compressor 11, so that the suction pressure loss can be reduced, improving performance and efficiency while also reducing manufacturing costs.

Whether or not dryout has occurred in the evaporator 15 is determined based on the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin, so that it is possible to appropriately determine whether or not dryout has occurred in the evaporator 15 even under conditions where the temperature of the air flowing into the evaporator 15 is low, as shown in Figure 7.

When the temperature of the air flowing into the evaporator 15 is low and sufficient superheat cannot be obtained even by reducing the opening of the expansion valve 14, the behavior of the expansion valve 14 repeatedly increases and decreases the opening as shown in FIG. 8. In other words, the opening of the expansion valve 14 fluctuates. Therefore, even if the temperature of the air flowing into the evaporator 15 is low, the superheat can be appropriately feedback-controlled.

In this embodiment, in the normal control of the expansion valve 14, the control device 60 controls the opening of the expansion valve 14 to a normal opening such that the superheat degree SHE of the refrigerant flowing out of the evaporator 15 approaches the target superheat degree SHEO. The control device 60 determines whether the refrigerant has dried out in the evaporator 15 based on the refrigerant temperature Tefin detected by the evaporator temperature sensor 64 and the refrigerant pressure Psuc detected by the suction refrigerant pressure sensor 66. If the control device 60 determines that the refrigerant has dried out in the evaporator 15, it increases the opening of the expansion valve 14 beyond the normal opening.

This allows appropriate determination of whether or not the refrigerant has dried out in the evaporator 15. If it is determined that the refrigerant has dried out in the evaporator 15, the flow rate of the refrigerant flowing into the evaporator 15 can be increased, thereby preventing the refrigerant from drying out in the evaporator 15.

In this embodiment, a suction refrigerant pressure sensor 66 is provided as a first detection unit that detects the state of the refrigerant downstream of the outlet of the evaporator 15 and upstream of the suction port of the compressor 11, and an evaporator temperature sensor 64 is provided as a second detection unit that detects the state of the refrigerant downstream of the inlet of the evaporator 15 and upstream of the outlet of the evaporator 15. This makes it possible to appropriately determine whether the refrigerant has dried out in the evaporator 15.

In this embodiment, the control device 60 calculates the saturation temperature Tsat of the refrigerant based on the refrigerant pressure Psuc detected by the suction refrigerant pressure sensor 66, and if the difference between the refrigerant temperature Tefin detected by the evaporator temperature sensor 64 and the saturation temperature Tsat exceeds the threshold value α1, it determines that the refrigerant has dried out in the evaporator 15.

This makes it possible to properly determine whether the refrigerant has dried out in the evaporator 15, even when the intake air temperature of the evaporator 15 is low.

In this embodiment, the control device 60 increases the threshold value α1 as the flow rate of the refrigerant flowing into the evaporator 15 increases. This allows for a more appropriate determination of dryout, taking into account the pressure loss of the refrigerant in the evaporator 15.

In this embodiment, the above-mentioned expansion valve control is applied to the refrigeration cycle device 10 that has a receiver 13 downstream of the condenser 12 and upstream of the expansion valve 14, making it easier to use the expansion valve 14 by slightly closing it. As a result, the phenomenon in which liquid-phase refrigerant is sucked into the compressor 11 (so-called liquid backflow) can be suppressed.

In this embodiment, when the control device 60 determines that the refrigerant has dried out in the evaporator 15, it increases the opening of the expansion valve 14 beyond its normal opening, and then controls the expansion valve 14 to return to its normal opening. As a result, after the dryout is resolved, the expansion valve 14 can be normally controlled to appropriately control the refrigeration cycle device 10.

In this embodiment, the control device 60 determines the superheat degree SHE of the refrigerant on the outlet side of the evaporator 15 based on the deviation between the target superheat degree SHEO and the superheat degree SHE of the refrigerant on the outlet side of the evaporator 15 so that the superheat degree SHE approaches the target superheat degree SHEO. This allows the superheat degree SHE to be appropriately controlled during normal control.

Second Embodiment
In the above first embodiment, in the control process for determining the throttle opening EV of the expansion valve 14, if the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1, the dryout opening EVD is determined as the throttle opening EV of the expansion valve 14.

In this embodiment, as shown in FIG. 9, in the control process for determining the throttling opening EV of the expansion valve 14, if the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1 and the refrigerant flow rate Gr is below the threshold value β1, the dry-out opening EVD is determined as the throttling opening EV of the expansion valve 14.

In this embodiment, the throttling opening degree EV of the expansion valve 14 is determined by the control process shown in the flowchart of FIG. 9. First, in step S200, similar to step S100 in the first embodiment, the normal opening degree EVN of the expansion valve 14 is determined by a feedback control method based on the deviation between the target superheat degree SHEO of the refrigerant on the outlet side of the evaporator 15 and the superheat degree SHE of the refrigerant on the outlet side of the evaporator 15 so that the superheat degree SHE approaches the target superheat degree SHEO. For example, the target superheat degree SHEO is a predetermined constant (5°C in this embodiment).

In the next step S210, it is determined whether the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1 and whether the refrigerant flow rate Gr is below the threshold value β1. The refrigerant flow rate Gr is calculated based on the suction refrigerant pressure Psuc detected by the suction refrigerant pressure sensor 66 and the rotation speed of the compressor 11, etc. The refrigerant flow rate Gr may be detected by the refrigerant flow rate sensor. The threshold value β1 is stored in advance in the control device 60.

That is, in step S210, it is determined whether or not the area is within the shaded region in FIG. 10 (hereinafter, the dryout opening region). The dryout opening region is a part of the region where dryout occurs (the region above the solid line in FIG. 10).

If it is determined in step S210 that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin does not exceed the threshold value α1 or that the refrigerant flow rate does not fall below the threshold value β1 (i.e., it is determined that the dryout opening area in FIG. 10 is not present), proceed to step S220. If it is determined in step S210 that the temperature difference obtained by subtracting the evaporator outlet saturation temperature Tsat from the evaporator temperature Tefin exceeds the threshold value α1 and that the refrigerant flow rate Gr falls below the threshold value β1 (i.e., it is determined that the dryout opening area in FIG. 10 is present), proceed to step S230.

In step S220, similar to step S120 in the first embodiment, the normal opening EVN determined in step S200 is determined as the throttling opening EV of the expansion valve 14, and the process proceeds to step S240. When the temperature difference does not exceed the threshold value α1, the amount of heat exchange in the evaporator 15 is small to begin with, so even if dryout occurs in the evaporator 15, it is considered that the performance degradation due to dryout is small. When the refrigerant flow rate is not below the threshold value β1, even if dryout occurs in the evaporator 15 and the refrigerant flow rate decreases, the performance degradation does not become a major problem.

In step S230, since it is considered that dryout has occurred in the evaporator 15, similarly to step S130 in the first embodiment, the throttle opening EV of the expansion valve 14 is determined to be a dryout opening EVD that is greater than the normal opening EVN determined in step S200, and the process proceeds to step S240. For example, the dryout opening EVD is the opening (100%) when the expansion valve 14 is fully open. The dryout opening EVD may be a predetermined amount greater than the normal opening EVN.

In step S240, similar to step S240 in the first embodiment described above, a control signal or control voltage is output to the expansion valve 14 so that the throttle opening EV of the expansion valve 14 determined in steps S220 and S230 is obtained, and the process returns to step S200.

As a result, similar to the first embodiment described above, if dryout occurs in the evaporator 15, the throttle opening EV of the expansion valve 14 is made larger than the normal opening EVN in step S230, so that the flow rate of the refrigerant flowing into the evaporator 15 can be increased. This allows the dryout to be quickly resolved.

In this embodiment, the region in which the throttling opening EV of the expansion valve 14 is determined to the dry-out opening EVD is limited to the low refrigerant flow rate region, which simplifies control and reduces design labor.

Other Embodiments
The above embodiment can be modified in various ways, for example, as follows.

(1) In the above embodiment of the refrigeration cycle device 10, a fluorocarbon-based refrigerant is used as the refrigerant, but the type of refrigerant is not limited to this, and natural refrigerants such as carbon dioxide or hydrocarbon-based refrigerants may also be used.

In addition, the refrigeration cycle device 10 in the above embodiment constitutes a subcritical refrigeration cycle in which the high-pressure side refrigerant pressure does not exceed the critical pressure of the refrigerant, but it may also constitute a supercritical refrigeration cycle in which the high-pressure side refrigerant pressure exceeds the critical pressure of the refrigerant.

(2) In the above embodiment, the evaporator 15 exchanges heat between the refrigerant and air (in other words, gas), but is not limited thereto, and may exchange heat between the refrigerant and cooling water (in other words, liquid). An object to be cooled, such as a battery, may be in thermally conductive contact with the evaporator 15, and the object to be cooled may be cooled by the refrigerant flowing through the evaporator 15.

(3) The refrigeration cycle device 10 of the above embodiment is applied to a vehicle air conditioner, but the application of the refrigeration cycle device 10 is not limited to this, and it may be applied to a battery cooling device, a stationary air conditioner, a refrigeration/freezing device, etc.

11 Compressor 12 Condenser (heat dissipation section)
14 Expansion valve (pressure reducing section)
15 Evaporator (evaporation section)
60 Control device (control unit)
64 Evaporator temperature sensor (refrigerant state detection unit, second detection unit)
66 Suction refrigerant pressure sensor (refrigerant state detection unit, first detection unit)

Claims (5)

A compressor (11) that draws in, compresses, and discharges a refrigerant;
A heat dissipation section (12) that dissipates heat from the refrigerant;
a pressure reducing unit (14) capable of reducing the pressure of the refrigerant and adjusting a flow path opening degree so as to adjust a flow rate of the refrigerant;
an evaporation section (15) for absorbing heat from air into the refrigerant decompressed in the decompression section;
a refrigerant state detection unit (64, 66) for detecting a state of the refrigerant downstream of a refrigerant inlet of the pressure reducing unit and upstream of a suction port of the compressor;
a control unit (60) that controls an opening degree of the pressure reducing unit to a normal opening degree (EVN) that is an opening degree such that a superheat degree (SHE) of the refrigerant flowing out from the evaporation unit approaches a target superheat degree (SHEO), determines whether or not the refrigerant has dried out in the evaporation unit based on a state of the refrigerant detected by the refrigerant state detection unit, and, when it is determined that the refrigerant has dried out in the evaporation unit, sets the opening degree of the pressure reducing unit to a value larger than the normal opening degree;
The refrigerant state detection unit is
a first detection unit (66) that detects a state of the refrigerant downstream of an outlet of the evaporator and upstream of a suction port of the compressor;
a second detection unit (64) that detects a state of the refrigerant downstream of an inlet of the evaporator and upstream of an outlet of the evaporator,
The first detection unit detects a pressure (Psuc) of the refrigerant,
The second detection unit detects the temperature (Tefin) of the refrigerant,
The control unit calculates a saturation temperature (Tsat) of the refrigerant based on the pressure of the refrigerant detected by the first detection unit,
When a difference between the temperature of the refrigerant detected by the second detection unit and the saturation temperature exceeds a threshold value (α1), it is determined that the refrigerant has dried out in the evaporation unit ,
The control unit sets the threshold value to a larger value as the flow rate of the refrigerant flowing into the evaporation unit increases . The refrigeration cycle device according to claim 1, wherein the refrigerant state detection unit detects the state of the refrigerant downstream of the refrigerant inlet of the evaporator and upstream of the suction port of the compressor. 3. The refrigeration cycle apparatus according to claim 1, further comprising a liquid storage section (13) downstream of the heat dissipation section and upstream of the pressure reduction section, the liquid storage section separating the refrigerant into gas and liquid and storing surplus refrigerant. 4. The refrigeration cycle apparatus according to claim 1, wherein when the control unit determines that the refrigerant has dried out in the evaporator , the control unit controls the pressure reducing unit to increase an opening degree of the pressure reducing unit beyond the normal opening degree and then to return the opening degree to the normal opening degree. 5. The refrigeration cycle device according to claim 1, wherein the control unit determines the superheat degree of the refrigerant flowing out of the evaporation unit based on a deviation between the target superheat degree and the superheat degree of the refrigerant flowing out of the evaporation unit so that the superheat degree of the refrigerant flowing out of the evaporation unit approaches the target superheat degree.

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