JP4160415B2 - Method of detecting frost formation in refrigeration cycle using supercritical refrigerant and defrosting method using the method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for detecting frost formation in a refrigeration cycle in which heating and cooling are performed using a supercritical refrigerant, and a defrosting method using the method.
[0002]
[Prior art]
In recent air conditioners for vehicles, measures are taken to reduce the impact on the environment by heating and cooling using a refrigeration cycle using carbon dioxide, which is a supercritical fluid maintained above the gas-liquid critical temperature and pressure, as a refrigerant. It has been adopted.
[0003]
The refrigeration cycle generally includes a compressor that pressurizes supercritical refrigerant, a radiator (condenser) that exchanges heat between the pressurized refrigerant and outside air, an expansion valve that adiabatically expands the refrigerant cooled by the radiator, An internal heat exchanger that exchanges heat between the high-pressure refrigerant on the downstream side of the radiator and the low-pressure refrigerant on the downstream side of the heat absorber, particularly when carbon dioxide is used as the refrigerant. A device is provided.
[0004]
By the way, in such a refrigeration cycle, the heat absorber may be frosted on the heat absorber due to the outside air temperature or the outside air humidity to be heat exchanged with the heat absorber due to the introduction of the low-temperature refrigerant adiabatically expanded by the expansion valve. This frosting causes a decrease in the endothermic function.
[0005]
Therefore, when the heat absorber is frosted, the heat absorption function can be recovered by operating the refrigeration cycle in the defrost mode and defrosting the heat absorber. It needs to be detected.
[0006]
As a method for detecting the frosting state, the low pressure (evaporation pressure) of the refrigeration cycle is read, and it is determined whether or not the low pressure is lower than a preset pressure (for example, patent) Reference 1).
[0007]
[Patent Document 1]
JP-A-8-197937 (page 22, FIGS. 44 and 45)
[0008]
[Problems to be solved by the invention]
However, in such a conventional refrigeration cycle frost detection method, frost formation is detected only from the low pressure of the refrigeration cycle.
[0009]
In addition, the frost phenomenon is largely attributed to the amount of moisture (humidity) contained in the outside air, and when trying to construct a device that detects the frost phenomenon in combination with humidity detection, a sensor for accurately detecting the humidity. However, this humidity detection method cannot be expected.
[0010]
Therefore, in view of such conventional problems, the present invention pays attention to a unique phenomenon in which the discharge refrigerant temperature of the compressor rises and the discharge pressure decreases when the heat absorber frosts, and the frost formation phenomenon is simple and accurate. An object of the present invention is to provide a method for detecting frost formation in a refrigeration cycle and a defrost method using the method.
[0011]
[Means for Solving the Problems]
In order to achieve this object, the present invention uses a supercritical fluid as a refrigerant, a compressor that pressurizes the supercritical refrigerant, a radiator that exchanges heat between the pressurized refrigerant and the outside air, and a refrigerant that is cooled by the radiator. An expansion valve that adiabatically expands and a heat absorber that evaporates the refrigerant adiabatically expanded, and controls the throttle valve of the expansion valve in the throttle direction as the refrigerant temperature rises at the radiator outlet, It is characterized in that the frost formation state of the heat absorber is estimated using the rise rate of the refrigerant discharge refrigerant temperature and the drop rate of the compressor discharge pressure detected simultaneously.
[0012]
【The invention's effect】
According to the present invention having such a configuration, the rate of increase in the refrigerant discharge refrigerant temperature and the rate of decrease in the compressor discharge pressure are detected simultaneously to estimate the frost formation state of the heat absorber. The rise exceeding the predetermined value and the decrease of the discharge pressure below the predetermined value are caused by the expansion valve being controlled in the throttle direction as the refrigerant temperature rises when the heat sink is frosted. By utilizing the peculiar phenomenon, frost formation of the heat absorber can be detected easily and accurately.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0014]
1 to 5 show a method for detecting frost formation in a refrigeration cycle using a supercritical refrigerant according to the present invention and a defrost method using the method, and FIG. 1 is a schematic diagram showing an operation state in a cooling mode of the refrigeration cycle. FIG. 2, FIG. 2 is a schematic diagram showing the operating state of the refrigeration cycle in the heating mode, FIG. 3 is a schematic diagram showing the operating state of the refrigeration cycle in the dehumidifying mode, and FIG. 4 shows the operating state of the refrigeration cycle in the defrosting mode. FIG. 5 is an explanatory diagram showing a flowchart for executing the defrosting mode.
[0015]
The refrigeration cycle of this embodiment shows a case where it is applied to a vehicle air conditioner, and uses carbon dioxide gas (CO ₂ ) as a supercritical fluid as a refrigerant. As shown in FIGS. , The compressor 2 for pressurizing the refrigerant, the sub-gas cooler 3 functioning as a sub-radiator for exchanging heat between the pressurized refrigerant and the outside air, the external heat exchanger 4 as a radiator, and the sub-gas cooler 3 and the external heat exchanger A first expansion valve 5 for adiabatic expansion of the refrigerant cooled at 4, an evaporator 6 as a heat absorber for evaporating the adiabatic expansion refrigerant, a high-pressure refrigerant downstream of the external heat exchanger 4, and a low-pressure refrigerant downstream of the evaporator 6 And an internal heat exchanger 7 for exchanging heat between them.
[0016]
The sub-gas cooler 3 is housed in the air conditioning duct 8 and introduces the pressurized refrigerant of the compressor 2 through the passage P1, and uses heat generated by the pressurized refrigerant as a heating heat source to exchange heat with the conditioned air in the air conditioning duct 8. At the same time, the switching door 9 switches between the heating passage 8 a through which the conditioned air passes through the sub gas cooler 3 and the bypass passage 8 b that bypasses the sub gas cooler 3.
[0017]
The external heat exchanger 4 introduces the refrigerant that has passed through the sub-gas cooler 3 through the passage P2, and is arranged in front of the engine room (not shown) so as to exchange heat with the outside air by a radiator fan (not shown). It has become.
[0018]
The first expansion valve 5 introduces the refrigerant that has passed through the external heat exchanger 4 through the passage P3, and has a variable throttle function by a throttle valve (not shown) to control the throttle amount. Control is performed so that the throttle valve is throttled as the outlet temperature of the external heat exchanger 4 rises, but when the outlet temperature rises beyond the normal control range (frosting state described later). Is forcibly controlled to open the throttle valve.
[0019]
The evaporator 6 is provided in the low-pressure passage P4 on the downstream side of the first expansion valve 5 and introduces the refrigerant adiabatically expanded by the first expansion valve 5 and on the upstream side of the sub-gas cooler 3 in the air conditioning duct 8. It is housed and becomes a cooling heat source by exchanging heat between the air-conditioning duct 8 and the conditioned air passing therethrough.
[0020]
The internal heat exchanger 7 flows into the first expansion valve 5 by exchanging heat between the high-pressure refrigerant in the high temperature state downstream of the external heat exchanger 4 and the cooled low-pressure refrigerant that has passed through the evaporator 6. The temperature of the refrigerant can be lowered and the refrigerant sucked into the compressor 2 can be warmed.
[0021]
In the low-pressure passage P4, an accumulator 10 is provided between the evaporator 6 and the internal heat exchanger 7, and the refrigerant passing through the evaporator 6 is gas-liquid separated by this accumulator 10, and only the gas-phase refrigerant is converted into the internal heat exchanger 7. It is allowed to pass through and be sucked into the compressor 2.
[0022]
A passage P2 connecting the sub-gas cooler 3 and the external heat exchanger 4 is provided with a three-way valve 11. By switching the three-way valve 11, a path (first switching position) for connecting the external heat exchanger 4 to the passage P2 is provided. The external heat exchanger 4 is switched to a path (second switching position) communicating with the return path P5 communicating with the upstream side of the accumulator 10 on the downstream side of the evaporator 6.
[0023]
In addition, the upstream side of the passage P2 with respect to the three-way valve 11 and the passage P3 communicate with each other via the first bypass passage P6 provided with the electromagnetic valve 12, and the first side of the passage P2 downstream of the internal heat exchanger 7. The upstream side of the expansion valve 5 and the outlet side of the external heat exchanger 4 are communicated with each other via a second bypass passage P7 provided with a second expansion valve 13.
[0024]
In the passage P3, a first check valve 14 that allows refrigerant to pass from the external heat exchanger 4 toward the internal heat exchanger 7 between the external heat exchanger 4 and the communication portion of the first bypass passage P6. And a second check valve 15 that allows passage of refrigerant in the direction of the heat exchanger 4 in the downstream of the second expansion valve 13 in the second bypass passage P7, and in the return passage P5 Is provided with a third check valve 16 that allows passage of refrigerant in the return direction from the external heat exchanger 4 to the compressor 2.
[0025]
And the refrigerating cycle 1 comprised in this way is operate | moving in air_conditioning | cooling mode, heating mode, and dehumidification mode as shown in FIGS. 1-3, Furthermore, when the evaporator 6 is frosted, As shown in FIG. 4, the operation is performed in the defrosting mode. In the schematic diagrams of FIGS. 1 to 4, a path through which the refrigerant flows is shown by a solid line, and a path through which the refrigerant is not supplied is shown by a broken line.
[0026]
<Cooling mode>
The operation of the refrigeration cycle 1 in the cooling mode is performed by switching the three-way valve 11 to the first switching position as shown in FIG. Gas cooler 3 → (three-way valve 11) → external heat exchanger 4 → internal heat exchanger 7 → first expansion valve 5 → evaporator 6 → accumulator 10 → internal heat exchanger 7 This constitutes a circulation path.
[0027]
In the air conditioning duct 8, the inflow side of the conditioned air of the sub gas cooler 3 is blocked by the switching door 9, so that only the cooling air that has passed through the evaporator 6 passes through the bypass passage 8 a and blows out into the vehicle interior (not shown). It has become.
[0028]
<Heating mode>
The operation in the heating mode of the refrigeration cycle 1 is a state in which the first expansion valve 5 is shut off as shown in FIG. 2, the three-way valve 11 is switched to the second switching position, and the electromagnetic valve 12 is set in the communication state. Then, the pressurized refrigerant of the compressor 2 is changed to the sub gas cooler 3 → (electromagnetic valve 12) → internal heat exchanger 7 → second expansion valve 13 → external heat exchanger 4 → (three-way valve 11) → accumulator 10 → internal heat exchange. A circulation path is formed in which the compressor 2 sucks after passing through the container 7 in this order.
[0029]
In the air conditioning duct 8, the opening degree of the bypass passage 8 b is adjusted by the switching door 9, and the conditioned air passes through the heating passage 8 a of the subgas cooler 3 and the throttled bypass passage 8 b to adjust the temperature of the heating air. It is designed to blow out into the vehicle compartment outside the figure. In this case, the evaporator 6 is not functioning.
[0030]
<Dehumidification mode>
The operation of the refrigeration cycle 1 in the dehumidifying mode is performed by opening the first expansion valve 5 as shown in FIG. 3 and supplying the pressurized refrigerant of the compressor 2 to the sub-gas cooler 3 with the electromagnetic valve 12 set to the communication state. → (Electromagnetic valve 12) → Internal heat exchanger 7 → First expansion valve 5 → Evaporator 6 → Accumulator 10 → Internal heat exchanger 7 In this order, a circulation path is formed in which the compressor 2 sucks the refrigerant.
[0031]
In the air conditioning duct 8, the opening degree of the bypass passage 8 b is adjusted by the switching door 9, and the cooling air that has passed through the evaporator 6 passes through the heating passage 8 a of the sub-gas cooler 3 to form a cooling / heating mixed air (temperature-conditioned air). This air-cooled mixed air is blown out into the passenger compartment outside the figure.
[0032]
<Defrost mode>
The operation in the defrosting mode of the refrigeration cycle 1 is executed when the external heat exchanger 4 is defrosted to detect the defrosting state and defrost, and the three-way valve 11 is turned on as shown in FIG. While switching to the first switching position and with the solenoid valve 12 set to the shut-off state, the pressurized refrigerant of the compressor 2 is sub-gas cooler 3 → (three-way valve 11) → external heat exchanger 4 → internal heat exchanger 7 → After passing through the first expansion valve 5 → the evaporator 6 → the accumulator 10 → the internal heat exchanger 7 in this order, a circulation path is formed in which the compressor 2 is made to suck.
[0033]
That is, the refrigerant circulation path in the defrost mode is the same as that in the cooling mode, and the switching position of the switching door 9 in the air conditioning duct 8 is different. This switching door 9 blocks the bypass passage 8b as in the dehumidification mode. Then, the cooling air that has passed through the evaporator 6 passes through the heating passage 8a of the sub-gas cooler 3 to form a cooling / heating mixed air (temperature-conditioned air), and this temperature-conditioned air is blown out into the vehicle interior (not shown). Of course, even in this case, the opening degree of the bypass passage 8b can be adjusted by the switching door 9.
[0034]
Therefore, in this embodiment, in order to automatically operate the defrost mode, it is necessary to automatically detect the frost formation of the external heat exchanger 4, and as this frost detection method, the discharge refrigerant temperature of the compressor 2 detected simultaneously. The increase rate of (Td) and the decrease rate of the discharge pressure (Pd) of the compressor 2 are used to estimate the frost formation state. The increase rate of the discharge refrigerant temperature (Td) and the discharge pressure ( When the reduction rate of Pd) exceeds a predetermined value, the operation in the dehumidifying mode is executed.
[0035]
That is, when the refrigeration cycle 1 of the present embodiment is actually operated, when the external heat exchanger 4 is frosted, the frost is defrosted through the following phenomena (1) to (6).
[0036]
(1) Since the heat absorption amount of the low-pressure refrigerant passing through the external heat exchanger 4 decreases, the refrigerant circulation flow rate in the refrigeration cycle 1 decreases.
[0037]
(2) As a result, the heat absorption performance on the low-pressure side by the internal heat exchanger 7 is lowered, so that the degree of heating of the refrigerant sucked by the compressor 2 is increased, and the discharge refrigerant temperature (Td) of the compressor 2 is increased accordingly. .
[0038]
(3) As a result, the outlet refrigerant temperature of the sub gas cooler 3 rises, so that the throttle valve of the second expansion valve 13 is controlled in the direction in which the pressure rises, that is, the throttle direction.
[0039]
(4) As the throttle amount of the second expansion valve 13 is increased, the refrigerant circulation amount is further reduced, and accordingly, the refrigerant discharge amount of the compressor 2 is reduced, so that the discharge pressure (Pd) is lowered.
[0040]
(5) Accordingly, in the refrigeration cycle 1, the operations (1) to (4) are repeated, and the discharge refrigerant temperature (Td) of the compressor 2 continues to rise, while the discharge pressure (Pd) of the compressor 2 increases. It will continue to decline.
[0041]
(6) Then, the refrigerant discharge temperature (Td) of the compressor 2 exceeds a predetermined value set in advance, that is, a predetermined value appearing at the time of frost formation, and accordingly, the discharge pressure (Pd) of the compressor 2 is below a predetermined value. In this case, the heating mode is switched to the defrosting mode regardless of the rise in the outlet temperature of the sub gas cooler 3.
[0042]
An example of the defrost control by the refrigeration cycle 1 will be described with reference to the flowchart of FIG. (Reading optional set values, outside air temperature, indoor temperature, solar radiation, etc.) by the occupant and cooling control (cooling mode) in step S3 during cooling, and DEF / SW (dehumidification switch), wiper in step S4 during heating It is determined whether or not the dehumidifying operation (dehumidifying mode) is performed by reading the SW, outside air temperature, and the like.
[0043]
If NO is determined in step S4, the occupant set value, the outside air temperature, the room temperature, the solar radiation, etc. are read in step S6, and the operation in the heating mode is executed. In the operation state in this heating mode, step S7 is 2 is read to determine whether or not the protection operation is to be executed. If NO, the process returns to step S6. If YES, the operation state of the air conditioning fan (not shown) is determined by step S8. Determine if is normal.
[0044]
If it is determined that the air conditioning fan is operating abnormally, the process proceeds to protection control in step S9. If the air conditioning fan is normal, the relationship between the discharge pressure Pd of the compressor 2 and the discharge refrigerant temperature Td is determined in step S10. If it is within the normal calculation range set in advance, the process proceeds to step S9 to shift to protection control, and outside the calculation range where the discharge pressure Pd is equal to or lower than the predetermined value and the discharge refrigerant temperature Td exceeds the predetermined value. If yes, the process proceeds to step S11 to determine whether or not the outside air temperature read in step S6 is within a set value.
[0045]
If the outside air temperature is equal to or higher than the set value, even if the discharge pressure Pd and the discharge refrigerant temperature Td are abnormal, the process proceeds to protection control in step S9 because it is caused by the abnormality of the outside air temperature. At the same time, if the outside air temperature is equal to or lower than the set value, it is determined that the discharge pressure Pd and the discharge refrigerant temperature Td are truly abnormal, and the process proceeds to step S12. The refrigeration cycle 1 is switched to the defrost mode and the defrost mode is performed in step S13. Execute the operation.
[0046]
At this time, in the defrosting mode operation in step S13, a time necessary for defrosting is set in advance by a timer, and the defrosting mode is executed only for this set time, and when this set time elapses. It returns to step S4.
[0047]
In the frost formation detection method of the refrigeration cycle 1 of the present embodiment with the above configuration, the rate of increase in the discharge refrigerant temperature Td of the compressor 2 and the rate of decrease in the discharge pressure Pd of the compressor 2 are detected simultaneously. The frosting state of the heat exchanger 4 is estimated, and the increase of the discharge refrigerant temperature Td exceeding a predetermined value and the decrease of the discharge pressure Pd to a predetermined value or less are frosted on the external heat exchanger 4. This is a unique phenomenon that occurs when the second expansion valve 13 is controlled in the throttle direction as the refrigerant temperature at the outlet of the sub gas cooler 3 rises. By utilizing this unique phenomenon, the external heat exchanger 4 frost formation can be detected easily and accurately.
[0048]
In addition, when executing the frost detection method according to the present embodiment, a temperature sensor and a pressure sensor are installed at the outlet of the compressor 2. However, these temperature sensors and pressure sensors are relatively inexpensive, so that they are newly installed. When doing this, or particularly when using an existing sensor, it is possible to reduce the cost of the apparatus.
[0049]
Furthermore, in the defrosting method of the refrigeration cycle 1 of the present embodiment, the discharge refrigerant temperature Td and the discharge pressure Pd of the compressor 2 are simultaneously detected using the frost detection method, and the discharge refrigerant temperature Td appears at the time of frost formation. The heating mode is switched to the defrosting mode when the predetermined value is exceeded and the discharge pressure Pd becomes a predetermined value or less as the discharge refrigerant temperature Td rises.
[0050]
By the way, although the frost formation detection method of the refrigerating cycle using the supercritical refrigerant of the present invention and the defrost method using the method have been described by taking the above embodiment as an example, the present invention is not limited to this embodiment. Various other embodiments can be adopted without departing from the scope of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an operation state in a cooling mode of a refrigeration cycle in one embodiment of the present invention.
FIG. 2 is a schematic diagram showing an operation state in a heating mode of a refrigeration cycle in one embodiment of the present invention.
FIG. 3 is a schematic diagram showing an operation state in a dehumidifying mode of a refrigeration cycle in one embodiment of the present invention.
FIG. 4 is a schematic diagram showing an operation state in a defrosting mode of a refrigeration cycle in one embodiment of the present invention.
FIG. 5 is an explanatory diagram showing a flowchart for executing a defrosting mode in one embodiment of the present invention.
[Explanation of symbols]
1 Refrigeration cycle 2 Compressor 3 Subgas cooler 4 External heat exchanger (heat radiator)
5 First expansion valve (expansion valve)
6 Evaporator (heat absorber)
7 Internal heat exchanger

Claims (2)

Using a supercritical fluid as the refrigerant, the compressor (2) for pressurizing the supercritical refrigerant, the radiator (4) for exchanging heat between the pressurized refrigerant and the outside air, and the refrigerant cooled by the radiator (4) are insulated. An expansion valve (5) that expands and a heat absorber (6) that evaporates the adiabatically expanded refrigerant, and the throttle valve of the expansion valve (5) is throttled as the refrigerant temperature rises at the radiator (4) outlet. A refrigeration cycle (1) for controlling
The frosting state of the heat absorber (6) is estimated by using the rate of increase in the refrigerant temperature discharged from the compressor (2) and the rate of decrease in the discharge pressure of the compressor (2) detected simultaneously. A method for detecting frost formation in a refrigeration cycle using a critical refrigerant. Using a supercritical fluid as the refrigerant, the compressor (2) for pressurizing the supercritical refrigerant, the radiator (4) for exchanging heat between the pressurized refrigerant and the outside air, and the refrigerant cooled by the radiator (4) are insulated. An expansion valve (5) that expands and a heat absorber (6) that evaporates the adiabatically expanded refrigerant, and the throttle valve of the expansion valve (5) is throttled as the refrigerant temperature rises at the radiator (4) outlet. A refrigeration cycle (1) for controlling
The discharge refrigerant temperature and discharge pressure of the compressor (2) are detected at the same time, the discharge refrigerant temperature exceeds a predetermined value appearing at the time of frost formation, and the discharge pressure becomes lower than the predetermined value as the discharge refrigerant temperature increases. In this case, the defrosting method for a refrigeration cycle using a supercritical refrigerant is controlled such that the throttle valve of the expansion valve (5) is opened.

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