JP2002174462A - Cooling cycle for air conditioning apparatus and lubricating oil for cooling cycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cooling cycle for an air-conditioning apparatus and lubricating oil for cooling cycle, in which a stable operation can be performed by eliminating the problem of insufficient oil-returning to a compressor. SOLUTION: The cooling cycle for an air conditioning apparatus comprises a compressor 1, a gas cooler 2, a pressure-control valve 3, and an evaporator 4, which are serially connected each other by piping. The cooling cycle includes further a receiver vessel 5 for storing liquid refrigerant, penetrated by a pipe on the outlet side of the evaporator 4, and a communicating tub 5b allowing the lower part of the vessel 5 to communicate with the piping between the valve 3 and a throttling means. In the cooling cycle, CO2 refrigerant is used, and the used lubricating oil is incompatible with the refrigerant in the temperature range higher than -15 deg.C, and has a specific gravity greater than the density of saturated liquid refrigerant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a closed circuit,
The present invention relates to a cooling cycle for an air conditioner using a carbon dioxide refrigerant operated under supercritical conditions on the high side, and a lubricating oil used in the cooling cycle.

[0002]

2. Description of the Related Art In a supercritical vapor compression cycle, a technique for controlling a high side pressure by adjusting a circulating refrigerant has been proposed (for example, see Japanese Patent Publication No. Hei 7-18602). This supercritical vapor compression cycle includes a compressor 100 connected in series to a radiator 110, as shown in FIG.
A counter-flow heat exchanger 120 and a throttle valve 130 are provided. An evaporator 140 and a liquid separator (receiver) 160 are provided between the throttle valve 130 and the inlet 190 of the compressor 100.
And the low-pressure side of the countercurrent heat exchanger 120 are communicably connected. The receiver 160 is connected to the evaporator outlet 150, and the gas phase inlet of the receiver 160 is connected to the countercurrent heat exchanger 120. A liquid phase line (see dashed line) from the receiver 160 is connected to the suction line at any point between the point 170 and the point 180 after the countercurrent heat exchanger 120. The throttle valve 130
Adjusts the high side pressure by changing the remaining amount of liquid in the receiver 160. In the conventional example of FIG. 8, instead of the receiver,
An intermediate reservoir 250 having valves 230 and 240 on the inlet side and the outlet side, respectively, is connected in parallel with the throttle valve 130.

In recent years, as one of measures against CFCs in a refrigerant used in a vapor compression refrigeration cycle, a vapor compression refrigeration cycle using carbon dioxide (CO ₂ ) (hereinafter abbreviated as a CO ₂ cycle) has been proposed. Proposed. The operation of this CO ₂ cycle is basically the same as the operation of a conventional vapor compression refrigeration cycle using Freon.
That is, ABC- in FIG. 4 (CO ₂ Mollier diagram)
As shown by DA, CO ₂ in a gaseous state is compressed by a compressor (AB), and CO ₂ in a gaseous state in a high-temperature state is cooled by a radiator (gas cooler) (B). -C). Then, the pressure is reduced by a pressure reducer (CD) to evaporate the CO ₂ in a gas-liquid two-phase state (DA), and the external fluid is cooled by removing latent heat of evaporation from an external fluid such as air. .

Since the critical temperature of CO ₂ is about 31 ° C., which is lower than the critical point temperature of conventional CFCs, in summer or the like, the CO ₂ temperature on the radiator side becomes higher than the critical point temperature of CO _2. I will. That is, CO ₂ does not condense on the radiator outlet side (the line segment BC does not cross the saturated liquid line SL). Also,
State of the radiator outlet side (C point), the discharge pressure of the compressor is determined by the CO ₂ temperature at the radiator outlet side, CO ₂ temperature at the radiator outlet side, the radiator of the heat transfer capability and the outside air temperature (Which cannot be controlled), the temperature at the radiator outlet cannot be substantially controlled.
Therefore, the state of the radiator outlet side (point C) can be controlled by controlling the compressor discharge pressure (radiator outlet side pressure). That is, when the outside air temperature is high in summer or the like, in order to secure a sufficient cooling capacity (enthalpy difference), as shown by EFGHHE in FIG. High pressure is needed.

However, in order to increase the pressure on the outlet side of the radiator, the discharge pressure of the compressor must be increased as described above, so that the compression work of the compressor (the enthalpy change ΔL in the compression process) increases. . Therefore, the evaporation process (D-
The compression process (A) is based on the increase in the enthalpy change ΔI in A).
When the increase in the enthalpy change amount ΔL in −B) is large, the coefficient of performance of the CO ₂ cycle (COP = ΔI / ΔL)
Worsens. Therefore, for example, assuming that the CO ₂ temperature at the radiator outlet side is 40 ° C. and the relationship between the CO ₂ pressure at the radiator outlet side and the coefficient of performance is calculated using FIG. 4, as shown by the solid line in FIG. The coefficient of performance becomes maximum at the pressure P ₁ (about 10 MPa). Similarly, when the CO ₂ temperature at the radiator outlet side is 30 ° C., the coefficient of performance becomes the maximum at the pressure P ₂ (about 8.0 MPa) as shown by the broken line in FIG.

As described above, CO _{2 at the} radiator outlet side is
The temperature and the pressure at which the coefficient of performance is maximized are calculated, and the result is depicted in FIG. 5, as indicated by the thick solid line η _max (hereinafter, optimal control line) in FIG. Therefore, in order to operate the CO ₂ cycle efficiently, it is necessary to control the radiator outlet pressure and the radiator outlet CO ₂ temperature as indicated by the optimal control line η _max .

[0007]

In a vapor compression refrigeration cycle, lubrication of a compressor is performed by mixing lubricating oil into a refrigerant. In a conventional refrigeration cycle using a CFC refrigerant, lubricating oil having excellent compatibility with the CFC refrigerant has been used in order to smoothly return oil to the compressor. On the other hand, in the cooling cycle using CO ₂ as a refrigerant, in terms of compatibility with the CO ₂ refrigerant,
There was a problem that it was difficult to use the lubricating oil conventionally used.

An example of selection of a lubricating oil in a cooling cycle using CO ₂ is described in JP-A-11-94380. Japanese Patent Application Laid-Open No. H11-94380 discloses that a predetermined amount of lubricating oil for a compressor is used as lubricating oil for a compressor in order to prevent damage to the compressor and deterioration of the coefficient of performance due to suction of a liquid-phase refrigerant into the compressor together with lubricating oil. It is disclosed that the compatibility with the refrigerant at a pressure lower than the pressure is lower than the compatibility at a pressure higher than a predetermined pressure, and as a preferable lubricating oil, a polyalkyl group glycol-based oil or a polyvinyl ether-based oil is used. Are listed.

However, there is a lubricating oil which is chemically stable with respect to CO ₂ refrigerant in a temperature range required for use, has excellent compatibility with the refrigerant, and has good oil return to the compressor. do not do. And when the cooling cycle is operated using incompatible lubricating oil in the temperature range necessary for use of the CO ₂ refrigerant,
When a low-density lubricating oil is used, the density of the lubricating oil is lower than that of the liquid-phase CO ₂ refrigerant at a temperature lower than a certain temperature. As a result, when a liquid reservoir (receiver) is used in the CO ₂ cooling cycle, the liquid-phase CO ₂ refrigerant is placed in a lower layer inside the liquid reservoir.
The lubricating oil is in the upper layer, and instead of the lubricating oil, the liquid-phase CO ₂ refrigerant is discharged from the discharge port provided on the lower side of the liquid reservoir, and the lubricating oil stays in this liquid reservoir, causing a shortage of the lubricating oil in the compressor. There is a problem that leads to malfunction of the cooling cycle and deterioration of the cooling efficiency. Here compatibility (when the two-layer separation of a mixture of the refrigerating machine oil and refrigerant, the solution may be to or emulsion separated into two layers) two-layer separation is defined not to, CO ₂ for a temperature If there is an area where two layers are separated when refrigeration oil and refrigeration oil are tried at an arbitrary mixing ratio,
Defined as incompatible with O ₂ .

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cooling cycle for an air conditioner capable of resolving insufficient oil return to a compressor and performing stable operation.

[0011]

SUMMARY OF THE INVENTION A cooling cycle for an air conditioner according to the present invention is a compressor connected in series by piping so as to form a closed circuit operated at supercritical pressure on the high side of the vapor compression cycle. A radiator, a restrictor, and an evaporator, and are provided between the radiator and the restrictor, and the pressure at the radiator outlet side is set to a target pressure according to the refrigerant temperature at the radiator outlet side. A pressure control valve for controlling the pressure, a liquid reservoir for storing a liquid refrigerant, and penetrating the pipe on the evaporator outlet side, a lower portion of the liquid reservoir, the pressure control valve and the throttle. A communication pipe for communicating with the pipe between the means, wherein the refrigerant is CO ₂
And the lubricating oil is incompatible with the refrigerant in a temperature range higher than −15 ° C., and has a specific gravity greater than the liquid density of the saturated liquid refrigerant. In this cooling cycle for an air conditioner, an intercooler for exchanging heat between the liquid refrigerant passing through the radiator and the gas refrigerant passing through the evaporator is provided, and a pressure control valve is provided on an outlet pipe of the intercooler. Good as The lubricating oil has the following general formula (1): R- (EO) n- (PO) m-R (1) [wherein, R represents at least one of an alkyl group having 1 to 4 carbon atoms or one of: The other of the alkyl groups represents hydrogen;
(EO) indicates (CH ₂ CH ₂ O); (PO) indicates (CH
₂ CH (CH ₃ ) O); n and m are both 0
N / (m + n) = approximately 0.05 to 0.25], and at least one of both terminals of the compound is alkyl etherified or alkyl esterified. At least one selected from the group consisting of compounds may be used. Further, the lubricating oil has the following general formulas (2) to (5): R'-O- (EO) n- (PO) m-H (2) R'-O- (EO) n- (PO) m -R '(3) H-CO-O- (EO) n- (PO) m-H (4) H-CO-O- (EO) n- (PO) m-CO-H (5) [Formula In (2) to (5), R ′ represents an alkyl group having 1 to 4 carbon atoms; (EO) represents (CH ₂ CH ₂ O);
O) represents (CH ₂ CH (CH ₃ ) O); n and m are both non-zero integers, and n / (m + n) = 0.05
At least about 0.25] at least one selected from the group consisting of compounds represented by the formula:

One aspect of the lubricating oil of the present invention is -5.
℃ with incompatible and CO ₂ saturated liquid refrigerant at a higher temperature range than, CO ₂ than the liquid density of the saturated liquid refrigerant to provide a CO ₂ refrigeration cycle lubricating oil having a large specific gravity. Another aspect of the lubricating oil of the present invention, together with a CO ₂ saturated liquid refrigerant incompatible at higher temperature region than -15 ° C., has a specific gravity greater than the liquid density of the CO ₂ saturated liquid refrigerant CO _2. Provide lubricating oil for cooling cycle. The lubricating oil has the following general formula (1): R- (EO) n- (PO) m-R (1) [wherein, R represents at least one of an alkyl group having 1 to 4 carbon atoms or one of: The other of the alkyl groups represents hydrogen;
(EO) indicates (CH ₂ CH ₂ O); (PO) indicates (CH
₂ CH (CH ₃ ) O); n and m are both 0
N / (m + n) = approximately 0.05 to 0.25], and at least one of both terminals of the compound is alkyl etherified or alkyl esterified. At least one selected from the group consisting of compounds may be used. Further, the lubricating oil is
The following general formulas (2) to (5) R'-O- (EO) n- (PO) m-H (2) R'-O- (EO) n- (PO) m-R '(3) H-CO-O- (EO) n- (PO) m-H (4) H-CO-O- (EO) n- (PO) m-CO-H (5) [Formulas (2) to (5) )), R ′ represents an alkyl group having 1 to 4 carbon atoms; (EO) represents (CH ₂ CH ₂ O);
O) represents (CH ₂ CH (CH ₃ ) O); n and m are both non-zero integers, and n / (m + n) = 0.05
At least about 0.25] at least one selected from the group consisting of compounds represented by the formula:

[0013]

Next, an embodiment of the present invention will be described.
This will be described with reference to the drawings. FIG. 1 is for an air conditioner of the present invention.
FIG. 2 is a configuration diagram of an embodiment of a cooling cycle, and FIG.
FIG. 3 is a cross-sectional view showing details of a pressure control valve that has been used. Sky shown in Figure 1
Cooling cycle for air conditioner is applied to air conditioner for vehicle, for example.
CO _Two1 is a gaseous CO 2 cycle_TwoCompress
Compressor. The compressor 1 has a drive source (not shown) (for example,
(For example, an engine). 2 is compression
CO compressed by machine 1_TwoBy exchanging heat with the outside air
3 is a gas cooler (radiator) to be replaced.
Pressure control valve provided on the pipe on the outlet side of the intercooler 7
It is. This pressure control valve 3 is connected to the gas cooler 2 outlet side.
CO detected by the temperature sensing cylinder 11 described later_Twotemperature
(Refrigerant temperature) Gas cooler 2 outlet side pressure (this example)
Controls the high side pressure at the exit side of the intercooler 7)
I do. The pressure control valve 3 controls the high side pressure and
Also serves as a pressure reducer, and its structure and operation
Details will be described later. CO_TwoIs depressurized by the pressure control valve 3.
CO in low temperature and low pressure gas-liquid two-phase state_TwoAnd then
The pressure is reduced by the aperture resistance 4a (aperture means).

Reference numeral 4 denotes an evaporator (evaporator) serving as air cooling means in the vehicle compartment. When CO ₂ in a gas-liquid two-phase state is vaporized (evaporated) in the evaporator 4, it takes latent heat of evaporation from the air in the vehicle compartment. To cool the cabin air. Reference numeral 5 denotes a liquid storage container for storing a liquid refrigerant (liquid-phase CO ₂ refrigerant) 5a. A pipe 6 at the outlet side of the evaporator 4 penetrates vertically through the liquid storage container 5, and the liquid in the liquid storage container 5 The heat exchange between the refrigerant 5a and the liquid refrigerant in the pipe 6 is performed. The penetrating portion of the pipe 6 of the liquid reservoir 5 is sealed (not shown) so that the inside of the liquid reservoir 5 becomes a closed space. In order to increase the efficiency of the heat exchange, it is preferable that the pipe 6 on the outlet side of the evaporator 4 penetrate the liquid refrigerant 5a in the liquid reservoir 5 as in the present embodiment, but is not limited to this. The bottom of the liquid reservoir 5 communicates with a pipe 6 between the pressure control valve 3 and the throttle resistor 4a by a communication pipe 5b. The intercooler 7 is a countercurrent heat exchanger that exchanges heat between the liquid refrigerant that has passed through the gas cooler 2 and the gas refrigerant that has passed through the evaporator 4. The intercooler 7 increases the capacity of the vapor compression refrigeration cycle. Thus, the rise characteristic of the vehicle interior temperature is improved, and is not necessarily provided. When the intercooler 7 is not provided, it is preferable to provide the pressure control valve 3 in a pipe near the outlet of the gas cooler 2. The compressor 1, the gas cooler 2, the intercooler 7, the pressure control valve 3, the throttle resistor 4a and the evaporator 4 are connected by a pipe 6 to form a closed circuit (CO ₂ cycle). Reference numeral 8 denotes an oil separator that collects lubricating oil from refrigerant gas discharged from the compressor 1, and the collected lubricating oil is returned into the compressor 1 through an oil return pipe 9. Also, some lubricating oil circulates in the cycle with the flow of CO ₂ refrigerant,
It is returned to the compressor 1 again (oil return).

Here, an example of the pressure control valve will be described in detail. As shown in FIG. 2, the valve body 12 of the pressure control valve 3
The (valve casing) is arranged between the intercooler 7 and the throttle resistor 4a (each shown in FIG. 1) in a refrigerant passage 7 (in this example, a CO ₂ passage) formed by the pipe 6. Further, the valve body 12 is disposed so as to partition the refrigerant passage 7 into an upstream space 7a and a downstream space 7b, and within both orthogonal ends of the valve body 12, an upstream space 7a of the refrigerant passage 7 is provided. And a second partition 14 which is a boundary with the downstream space 7b. The first partition 13 and the second partition 14 have a first valve port. 13a (opening) and second valve port 1
4a (openings) are respectively formed.

The inner space 12a of the valve body 12 is provided with an expandable container 17 made of bellows for forming a closed space 17a, and the expandable container 17 is provided in accordance with a pressure difference between the inside and the outside of the closed space 17a. Axial direction (arrow A in FIG. 1)
(Vertical direction indicated by the direction). This telescopic container 1
7 is fixed to the inner wall of the valve body 12, and a valve stem 16 a having a valve 16 at the distal end is provided in the hollow shaft portion 17 b of the telescopic container 17 in the axial direction (arrow A).
Direction). This valve 16 is fixed to the tip of the telescopic container 17 and the second partition 14
And the valve port 14a. The valve stem 16a is movable in mechanical cooperation with the expansion and contraction of the telescopic container 17, and there is no pressure difference between the inside and outside of the closed space 17a of the telescopic container 17,
When the telescopic container 17 is in a no-load state, the valve 16 closes the second valve port 14a.

Reference numeral 15 is provided in the valve body 12 and
A check valve for opening and closing the first valve port 13a is shown, and the check valve 15 is configured such that the pressure in the upstream space 7a is
The first valve port 13a is opened when the internal pressure of the second internal space 12a becomes larger than the internal pressure by a predetermined amount. The check valve 21 is connected to the first valve port 13a by a biasing means (not shown) (for example, a coil spring).
, And a predetermined initial load is always applied to the check valve 15. This initial load is the predetermined amount.

The closed space 17a of the telescopic container 17 communicates with the temperature sensing tube 11 via the capillary tube 10 (tube member). The temperature sensing tube 11 is accommodated in the large diameter portion 6 a of the pipe 6 near the outlet of the gas cooler 2, and detects the temperature of the refrigerant in the pipe 6 and transmits the detected temperature to the telescopic container 17.
In addition, the temperature-sensitive cylinder 11 is provided in the pipe 6 in consideration of good thermal responsiveness of the temperature-sensitive cylinder 11, but is not limited thereto, and may be provided in close contact with the outer surface of the pipe 6. The communication pipe 19 (small pipe) communicates the inner space 12 a of the valve body 12 with a middle part of the capillary tube 10. The communication pipe 19 is provided with a closing valve 18. When the closing valve 18 is closed, the inner space 12a of the valve body 12 and the telescopic container 1
The closed space 17a of 7 is cut off and becomes an independent space. The cooling cycle for an air conditioner of this example is a CO ₂ cycle using carbon dioxide as a refrigerant, and a refrigerant gas (CO 2) is stored in the valve body 12, the telescopic container 17, the temperature-sensitive tube 11, and the capillary tube 10. ₂ ) in a state where the valve 16 and the check valve 15 are respectively closed, and the temperature of the refrigerant gas falls within a predetermined range from a saturated liquid density at 0 ° C. to a saturated liquid density at a critical point of the refrigerant. Each is enclosed at a density.

Next, the method of use and operation of the pressure control valve 3 will be described. First, at the time of initial setting, the closing valve 18
Is opened, C is introduced into the valve body 12 through the first valve port 13a.
By introducing O ₂ gas, through which CO ₂ communicating pipe 19 and the capillary tube 10 a portion of the gas is introduced into the expansion vessel 17 sealed space 17a and the temperature sensitive cylinder 11, the introduction is complete reverse The stop valve 15 automatically closes and the close valve 18 closes, so that the inner space 12a of the valve body 12 and the closed space 17a of the telescopic container 17 become
The spaces are isolated from each other and have no internal pressure difference. As a result, the pressure in the closed space 17a of the shrinkable container 17 becomes a pressure corresponding to the temperature of the thermosensitive cylinder 11, and the pressure corresponding to the valve body 12 is maintained outside the shrinkable container 17, so that the pressure shrinks unless a large temperature difference occurs. Since the pressure difference between the inside and the outside of the container 17 does not increase, the shrinkable container 17 is not excessively deformed, and there is no possibility that the elastic restoring force is reduced or broken. Assuming that the CO ₂ temperature at the outlet of the intercooler 7 is 40 ± 1 ° C., the CO
The pressure of the _two gases is preferably set to 10.5 ± 0.5 MPa.

At the end of the initial setting, the first valve port 13a and the second valve port 14a are closed by the check valve 15 and the valve 16, respectively. When the compressor 1 is started to operate the CO ₂ cycle, when the pressure in the upstream space 7 a of the pressure control valve 3 becomes larger than the internal pressure of the valve body 12, the check valve 15 moves and the first valve port 13 a is closed. Open, whereby CO ₂ gas flows into the valve body 12. When the internal pressure of the valve body 12 becomes larger than the internal pressure of the contraction container 17, the valve 16 moves to open the second valve port 14a, and CO ₂ circulates in the pipe 6.
At this time, due to the heat conduction of the enclosed CO ₂ gas, the temperature in the telescopic container 17 is linked with the temperature in the temperature-sensitive cylinder 11,
It becomes almost equal to the gas cooler 2 outlet temperature. Therefore, the internal pressure of the telescopic container 17 is a balance pressure of the temperature of the circulating CO ₂ . When the internal pressure of the valve body 12 is larger than the balance pressure, the second valve port 14a is in an open state, and when the internal pressure of the valve body 12 is smaller than the balance pressure, the second valve port 14 is in a closed state, Thus, the balance pressure corresponding to the temperature on the outlet side of the gas cooler 2 is automatically controlled so as to be substantially equal to the internal pressure of the valve body 12. That is, the pressure at the outlet of the intercooler 7 is controlled according to the CO ₂ temperature at the outlet of the gas cooler 2.

Specifically, for example, the temperature on the outlet side of the gas cooler 2 is 40 ° C. and the outlet pressure of the gas cooler 2 is about 1
When the pressure is 0.7 MPa or less, since the pressure control valve 3 is closed, the outlet pressure of the radiator 2 is increased by the flow rate of CO ₂ flowing from the compressor 1 (b′− in FIG. 4).
c ′ → b ″ −c ″). When the outlet pressure of the radiator 2 exceeds about 10.7MPa (B-C), since the pressure control valve 3 opens, CO ₂ is a gas-liquid two-phase from the supercritical and gas phase at a reduced pressure The state changes to (C-D),
It flows into the evaporator 4. After evaporating in the evaporator 4 (DA), the air is cooled and then returned to the intercooler 7 again. At this time, since the outlet pressure of the radiator 2 decreases again, the pressure control valve 3 closes again.

That is, the CO ₂ cycle is to increase the temperature of the outlet side of the radiator 2 to a predetermined pressure by closing the pressure control valve 3 and then reduce and evaporate the CO ₂ to cool the air. It is. As described above, the pressure control valve 3 according to the present embodiment opens after the pressure on the outlet side of the radiator 2 is raised to a predetermined pressure, and the control characteristic thereof is as follows. Greatly depends on the pressure characteristics of the enclosed space. Incidentally, as is apparent from FIG. 4, the isopycnic line of 600 kg / cm ³ in the supercritical region substantially coincides with the above-mentioned optimal control line η _max . Therefore, the pressure control valve 3 according to the present embodiment increases the outlet pressure of the radiator 2 to a pressure substantially along the optimal control line η _max , thereby efficiently operating the CO ₂ cycle even in the supercritical region. be able to. And below supercritical pressure, 600kg
/ M ³ , the deviation from the optimum control line η _max is large, but the internal pressure of the enclosed space is the saturation liquid line S
It varies along L. Practically, it is desirable to seal the inside of the closed space in a range from a saturated liquid density at a CO ₂ temperature of 0 ° C. to a saturated liquid density at a critical point of CO ₂ .

Next, automatic adjustment of the amount of circulating refrigerant, which is a feature of the present embodiment, will be described. First, when the refrigerant temperature at the outlet of the gas cooler 2 decreases, the pressure control valve 3 is opened as described above in order to reduce the high side pressure so that the coefficient of performance of the supercritical vapor compression cycle is maximized. The pressure control valve 3 and the throttle resistance 4a
The refrigerant pressure during the rise increases. Thereby, a part of the refrigerant in the pipe 6 between the pressure control valve 3 and the throttle resistor 4a is
b flows into the liquid reservoir 5 and, as a result, the refrigerant circulation amount of the cycle automatically decreases. On the other hand, gas cooler 2
When the outlet-side refrigerant temperature increases, the opening of the pressure control valve 3 decreases as described above in order to increase the high side pressure so that the coefficient of performance of the supercritical vapor compression cycle is maximized. The pressure control valve 3 and the throttle resistance 4
The pressure of the refrigerant in the pipe 6 between “a” and “a” decreases. As a result, the refrigerant in the liquid reservoir 5 passes through the communication pipe 5b and passes through the pressure control valve 3
Then, the refrigerant flows into the pipe 6 between the throttle resistor 4a, and as a result, the refrigerant circulation amount of the cycle automatically increases.

When the amount of the refrigerant flowing out of the evaporator 4 is reduced and the capacity of the cycle is insufficient, the refrigerant flowing out of the evaporator 4 is in a heated state, and when the refrigerant passes through the inside of the liquid reservoir 5, The liquid refrigerant is heated, and when the pressure of the liquid refrigerant becomes equal to or higher than the saturation pressure, the communication pipe 5
b, a pipe 6 between the pressure control valve 3 and the throttle resistor 4a
As a result, the amount of circulating refrigerant in the cycle increases, and the capacity increases. On the other hand, when the amount of the refrigerant flowing out of the evaporator 4 increases and the capacity of the cycle is excessive, the refrigerant flowing out of the evaporator 4 cools the liquid refrigerant therein when passing through the liquid reservoir 5, When the pressure of the refrigerant drops below the saturation pressure, part of the refrigerant in the pipe 6 between the pressure control valve and the throttle resistor 4a flows into the liquid reservoir 5 through the communication pipe 5b, and as a result, The refrigerant circulation amount is reduced, and the capacity is reduced.

According to this embodiment, the radiator outlet side pressure (high side pressure) corresponding to the refrigerant temperature at the radiator outlet
Is controlled to the target value, so that the cooling efficiency of the radiator is improved. In addition, the amount of circulating refrigerant is automatically adjusted in accordance with the adjustment of the high side pressure (the larger the high side pressure, the larger the amount of circulating refrigerant is required), and the time and effort of manually adjusting the opening degree of the throttle valve as in the conventional case. Can be omitted. In addition, by providing an intercooler for exchanging heat between the liquid refrigerant passing through the radiator and the gas refrigerant passing through the evaporator, the response speed to the requirement for increasing the capacity of the cooling cycle for the air conditioner is improved. be able to.

According to the present invention, in a cooling cycle for an air conditioner using CO ₂ as a refrigerant as described above, it is immiscible with a CO ₂ refrigerant in a temperature range higher than −5 ° C. or in a temperature range higher than −15 ° C. With saturated liquid refrigerant (saturated liquid phase CO
_The lubricating oil having a specific gravity larger than the liquid density of ( ₂ refrigerant) is used in a state where it coexists in the refrigerant in the system.

This lubricating oil has the following general formula (1): R- (EO) n- (PO) m-R (1) wherein R is at least one of an alkyl group having 1 to 4 carbon atoms. Or one represents the alkyl group and the other represents hydrogen;
(EO) indicates (CH ₂ CH ₂ O); (PO) indicates (CH
₂ CH (CH ₃ ) O); n and m are both 0
N / (m + n) = approximately 0.05 to 0.25], and at least one of both terminals of the compound is alkyl etherified or alkyl esterified. At least one selected from the group consisting of compounds is used.

Further preferred lubricating oils are represented by the following general formulas (2) to (5): R'-O- (EO) n- (PO) m-H (2) R'-O- (EO) n- ( PO) m-R '(3) H-CO-O- (EO) n- (PO) m-H (4) H-CO-O- (EO) n- (PO) m-CO-H (5 [In the formulas (2) to (5), R ′ represents an alkyl group having 1 to 4 carbon atoms; (EO) represents (CH ₂ CH ₂ O);
O) represents (CH ₂ CH (CH ₃ ) O); n and m are both non-zero integers, and n / (m + n) = 0.05
At a rate of about 0.25].

When the lubricating oil is introduced into the cooling system shown in FIG. 1 and the system is driven, the liquid storage container 5 (so that the temperature of the liquid storage container 5 during the operation of the system is -15 ° C. or higher). The liquid phase CO ₂ refrigerant and the lubricating oil flow into the system because there is no need to lower the temperature in the system below from the viewpoint of cooling the human body), and the lubricating oil and the CO ₂ refrigerant are incompatible, that is, Even in the two-liquid separation state, the lubricating oil having a high specific gravity is in the lower layer, and the CO ₂ refrigerant having a low specific gravity is in the upper layer. As a result, the lower layer lubricating oil and the refrigerant are transferred from the communication pipe 5 b connected to the lower end of the liquid reservoir 5 to the pressure control valve 3.
And it flows out to the pipe 6 between the throttle resistors 4a. Thereafter, the lubricating oil is returned (oil return) to the compressor 1 again along with the flow of CO ₂ . Therefore, it is possible to prevent the compressor from being damaged due to lack of oil. The terminal-modified polyalkylene glycol represented by the above formulas (1) to (5) is different from a polyalkylene glycol whose terminal is not modified (PAG; general formula HO- (EO) n- (PO) m-H). , C
The incompatibility with the O ₂ refrigerant increases. When a refrigerating machine oil having high incompatibility is used, CO on a sealing surface sealed with the refrigerating machine oil (for example, a sealing surface of a compression chamber of the compressor 1) is used.
_2. Leakage passing through the refrigerating machine oil can be reduced. Therefore, the performance of the compressor can be improved. The present invention actively utilizes the incompatibility by devising the reconstitution of the refrigerating machine oil which is usually used for compatibility in terms of reconstitution.

Of the above-mentioned terminal-modified polyalkylene glycols, the compounds represented by the formulas (2) and (3) have a structure in which both terminals or one terminal of the polyalkylene glycol are etherified. The compounds represented by (4) and (5) have a structure in which both terminals or one terminal of polyalkylene glycol are esterified. Compounds in which the terminal of polyalkylene glycol is modified have a terminal structure (alkylation, etherification or esterification) and the number of modifications (both terminal modification or one terminal modification)
The solubility, the lubricity and the hygroscopicity in the CO ₂ refrigerant change depending on the difference. In general, compounds in which both terminals are alkylated or etherified are less soluble in CO ₂ refrigerant than compounds in which the terminals are esterified and compounds in which only one terminal has been modified, have good incompatibility, and have good hygroscopicity. descend. The viscosity of the lubricating oil mainly depends on the molecular weight. Suitable lubricating oils for the cooling cycle of the present invention have a viscosity VG of 50 to 150 and a weight average molecular weight of 1,000 to 2,000.
Are preferred.

In the above-mentioned example, the present invention is applied to a cooling cycle in which a liquid CO ₂ refrigerant is stored as shown in FIG. 1 and a liquid reservoir 5 is provided through a pipe on the outlet side of the evaporator 4. Is described, but the lubricating oil of the present invention is not limited to this, and can be applied to various types of cooling cycles. When used in various types of cooling cycles, it is possible to control the temperature not to be lower than -5 ° C depending on the position of the liquid reservoir during the cycle. Hereinafter, the effects of the present invention will be clarified by examples.

[0032]

EXAMPLES Various lubricating oils of the following AD were prepared, and CO ₂
The specific gravity in the temperature range shown in FIG. 3 was measured together with the refrigerant.
The results are shown in FIG. A: polyol ester-based lubricating oil (manufactured by Nisseki Mitsubishi Co., Ltd.) B: terminally etherified polyalkylene glycol (viscosity VG100, average molecular weight 2,000) used in the present invention C: alkylbenzene-based lubricating oil (Matsumura Sekiyu KK; product) D: Mineral oil-based lubricating oil (manufactured by Nippon Sun Oil Co., Ltd .; trade name SUNISO 5)
GS)

As can be seen from FIG.
Among the lubricating oils, the specific gravity of the lubricating oil B used in the present invention is the highest, and at least in the temperature range higher than -15 ° C.
₂ Greater than the specific gravity of the refrigerant. Therefore, the lubricating oil of the present invention is always heavier than the CO ₂ refrigerant at a higher temperature range than -15 ° C., after entering the liquid reservoir container 5 together with CO ₂ refrigerant, to always present below the CO ₂ refrigerant I understand. On the other hand, other lubricating oils A, C, and D are in a temperature range higher than -15 ° C,
There is a temperature range which makes the specific gravity less than the specific gravity of the CO ₂ refrigerant, the when the temperature range into the liquid reservoir container 5 together with CO ₂ refrigerant, CO ₂ refrigerant is in a lower layer, the lubricating oil is retained turned upper It turns out that the oil return worsens.

The lubricating oil B of the present invention was introduced as a lubricating oil into the cooling cycle shown in FIG. 1, and the cooling cycle was operated to perform a performance verification test. As a result, it was found that the use of the lubricating oil B enables stable driving for a long period without causing poor oil return.

[0035]

As described above, the present invention provides CO ₂
Is used as a refrigerant, and is incompatible with the refrigerant in a temperature range higher than −15 ° C. in a cooling cycle for an air conditioner equipped with a liquid storage container, and has a specific gravity greater than the liquid density of the saturated liquid refrigerant. When the lubricating oil flows into the liquid storage container together with the CO ₂ refrigerant, the two are separated, and the lubricating oil is always in the lower layer of the CO ₂ refrigerant in the container. It flows out of the communication pipe provided at the lower part of the container and is surely returned to the compressor, so that the oil return is good. Therefore, according to the present invention, there is provided a cooling cycle for an air conditioner using a CO ₂ refrigerant that can be operated stably without lubricating oil remaining in a liquid reservoir and causing insufficient lubrication of a compressor, and the cooling cycle. Suitable lubricating oil can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of a cooling cycle for an air conditioner of the present invention.

FIG. 2 is a sectional view showing details of a pressure control valve shown in FIG. 1;

FIG. 3 is a graph showing the relationship between the density of various lubricating oils and the CO ₂ refrigerant.

FIG. 4 is a graph for explaining the operation of a vapor compression refrigeration cycle.

FIG. 5 is a CO ₂ Mollier diagram.

FIG. 6 is a graph showing a relationship between a coefficient of performance (COP) and a radiator outlet pressure.

FIG. 7 is a configuration diagram of an example of a conventional vapor compression refrigeration cycle.

FIG. 8 is a configuration diagram of another embodiment of a conventional vapor compression refrigeration cycle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compressor 2 Gas cooler (radiator) 3 Pressure control valve 4 Evaporator (evaporator) 4a Throttle resistance (throttle means) 5 Liquid reservoir 5b Communication pipe 6 Pipe (refrigerant passage) 7 Refrigerant passage (intercooler) 7a Upstream space (Upstream passage) 7b Downstream space (downstream passage) 10 Capillary tube 11 Thermosensitive cylinder 12 Valve body 13a First valve port 14a Second valve port 15 Check valve 16 Valve 17 Bellows (telescopic container) 18 Closed Valve 19 communication pipe

Continued on the front page (72) Inventor Mami Takeuchi 1 Nagoya Laboratory, Iwazuka-cho, Nakamura-ku, Nagoya-shi, Aichi, Japan Inside Nagoya Research Laboratory, Mitsubishi Heavy Industries, Ltd. Address: Nagoya Research Laboratory, Mitsubishi Heavy Industries, Ltd. (72) Norihisa Doroguchi, No. 1, Iwazuka-cho, Nakamura-ku, Nagoya-shi, Aichi Prefecture Inside Nagoya Research Laboratory, Mitsubishi Heavy Industries, Ltd. 3-1-1, Machi-cho, Mitsubishi Heavy Industries, Ltd.

Claims (8)

[Claims] A compressor, a radiator, a throttling means, and an evaporator connected in series by piping so as to form a closed circuit operated at a supercritical pressure on the high side of the vapor compression cycle; and A pressure control valve provided between the radiator and the throttling means for controlling the pressure at the radiator outlet side to a target pressure in accordance with the refrigerant temperature at the radiator outlet side; And a liquid storage container penetrated through the pipe on the evaporator outlet side; and a communication pipe for communicating the lower part of the liquid storage container with the pipe between the pressure control valve and the throttle means. , Wherein the refrigerant is CO ₂ , and the lubricating oil is incompatible with the refrigerant in a temperature range higher than −15 ° C., and a liquid density of the saturated liquid refrigerant. Have a higher specific gravity than A cooling cycle for an air conditioner. 2. An intercooler for exchanging heat between the liquid refrigerant passing through the radiator and the gas refrigerant passing through the evaporator, wherein the pressure control valve is provided on an outlet pipe of the intercooler. The cooling cycle for an air conditioner according to claim 1. 3. The lubricating oil has the following general formula (1): R- (EO) n- (PO) m-R (1) [wherein, at least one of R has 1 to 4 carbon atoms. An alkyl group or one of which represents the alkyl group and the other represents hydrogen;
(EO) indicates (CH ₂ CH ₂ O); (PO) indicates (CH
₂ CH (CH ₃ ) O); n and m are both 0
N / (m + n) = approximately 0.05 to 0.25], and at least one of both terminals of the compound is alkyl etherified or alkyl esterified. The cooling cycle for an air conditioner according to claim 1 or 2, wherein the cooling cycle is at least one selected from the group consisting of compounds. 4. The lubricating oil according to the following general formula (2)
(5) R'-O- (EO) n- (PO) m-H (2) R'-O- (EO) n- (PO) m-R '(3) H-CO-O- (EO) ) N- (PO) m-H (4) H-CO-O- (EO) n- (PO) m-CO-H (5) [In the formulas (2) to (5), R 'is a carbon atom. (EO) represents (CH ₂ CH ₂ O);
O) represents (CH ₂ CH (CH ₃ ) O); n and m are both non-zero integers, and n / (m + n) = 0.05
At least one selected from the group consisting of compounds represented by the formula (1): With 5. is a CO ₂ saturated liquid refrigerant incompatible at higher temperature range than -5 ° C., characterized in that it has a specific gravity greater than the liquid density of the CO ₂ saturated liquid refrigerant CO ₂
Lubricating oil for cooling cycle. With 6. is a CO ₂ saturated liquid refrigerant incompatible at higher temperature region than -15 ° C., characterized in that it has a specific gravity greater than the liquid density of the CO ₂ saturated liquid refrigerant CO
Lubricating oil for ₂ cooling cycles. 7. The lubricating oil is represented by the following general formula (1): R- (EO) n- (PO) mR (1) wherein R is at least one having 1 to 4 carbon atoms. An alkyl group or one of which represents the alkyl group and the other represents hydrogen;
(EO) indicates (CH ₂ CH ₂ O); (PO) indicates (CH
₂ CH (CH ₃ ) O); n and m are both 0
N / (m + n) = approximately 0.05 to 0.25], and at least one of both terminals of the compound is alkyl etherified or alkyl esterified. The lubricating oil for a CO ₂ cooling cycle according to claim 5, wherein the lubricating oil is at least one selected from the group consisting of compounds. 8. The lubricating oil according to the following general formula (2)
(5) R'-O- (EO) n- (PO) m-H (2) R'-O- (EO) n- (PO) m-R '(3) H-CO-O- (EO) ) N- (PO) m-H (4) H-CO-O- (EO) n- (PO) m-CO-H (5) [In the formulas (2) to (5), R 'is a carbon atom. (EO) represents (CH ₂ CH ₂ O);
O) represents (CH ₂ CH (CH ₃ ) O); n and m are both non-zero integers, and n / (m + n) = 0.05
Claim 5 or 6 CO ₂ cooling cycle lubricating oil, wherein the from the group consisting of compounds represented by a is] ratio of about 0.25 is at least one selected.