WO2001063185A1

WO2001063185A1 - Refrigerating cycle

Info

Publication number: WO2001063185A1
Application number: PCT/JP2000/001081
Authority: WO
Inventors: Nobuhiko Suzuki
Original assignee: Zexel Valeo Climate Control Corporation
Priority date: 2000-02-25
Filing date: 2000-02-25
Publication date: 2001-08-30

Abstract

A refrigerating cycle including a compressor, a radiator, an expander, an evaporator, and an internal heat exchanger for heat exchange between a refrigerant flowing out of the evaporator and the refrigerant in the supercritical zone, the supercritical fluid being used as a refrigerant, wherein the expander (5) is provided with a pressure reducing regulating valve (14) whose degree of opening is adjusted by the refrigerant temperature and refrigerant pressure on the inflow side, and a relief valve (15) that establishes communication between the inflow side and outflow side of the expander (5) when the refrigerant pressure on the inflow side exceeds a predetermined pressure. The pressure reducing regulating valve (14) is placed in a passageway through which the refrigerant flowing into the expander (5) flows to the relief valve (15). The relief valve (15) may be provided with the pressure reducing regulating valve so that when the refrigerant pressure on the inflow side exceeds a predetermined pressure, the relief valve is displaced integrally with the regulating valve to open the valve. This prevents an abnormal rise in pressure that occurs when the compressor is started from a high load stoppage state.

Description

Specification

Refrigeration cycle technology

The present invention relates to a refrigeration cycle using a supercritical refrigerant, for example, carbon dioxide (C 0 ₂ ) as a refrigerant. Background art

As a non-CFC refrigeration cycle that replaces the refrigeration cycle, a refrigeration cycle disclosed in Japanese Patent Publication No. 7-18602 is known. This refrigeration cycle is composed of at least a compressor, a cooling device, a throttling means, and an evaporator. Ethylene (C ₂ H ₄ ), diborane

(B 2 He), nitrogen (C ₂ He), nitric oxide (N ₂₀ ), carbon dioxide

(C 0 ₂ ) is used, and among them, carbon dioxide (C〇 ₂ ) is mainly used.

However, carbon dioxide (C 0 ₂₎ the refrigeration cycle using, since the critical point is lower and approximately 3 1. 1 ° C, such as summer and scorching sun the temperature inside the engine room reaches 6 0 ° C or more on At such a high load, even if the refrigeration cycle is stopped, the refrigerant in the cycle is in a supercritical state beyond the critical point.

When the compressor is started in such a state, the high-pressure pressure rapidly reacts and rapidly rises simultaneously with the start of the compressor because the refrigerant in the cycle is in a critical state. On the other hand, even when the compressor starts and the refrigerant starts to circulate, the refrigerant temperature at the inlet of the expansion valve does not react as quickly as the pressure and does not drop sharply. Moreover, since the temperature sensor and the expansion valve temperature sensing portion have their own heat capacity, the decrease in the refrigerant temperature is further delayed. For this reason, when the compressor is started, the expansion valve is kept closed, and high-pressure pressure cannot be released through the expansion valve, so that a burst is likely to occur on the cycle (the rupture disk is not safe). The bursting of the rupture disk occurs with the device installed, and the operation of the cycle is stopped by the operation of the high-pressure cut switch).

In order to prevent such inconvenience, the applicant has set up a relief valve that connects the high-pressure line and the low-pressure line when the high-pressure line reaches a predetermined pressure or higher, so that the high-pressure pressure does not exceed the predetermined pressure. We are considering a configuration that will

However, even if a relief valve is provided, if the high-pressure line and low-pressure line can be connected in front of the expansion valve, the refrigerant will be relieved before reaching the expansion valve if the high-pressure line exceeds a predetermined pressure. Since the refrigerant is bypassed to the low-pressure line via the valve, it is not possible to supply sufficient cold refrigerant to the expansion valve, and the closed state of the expansion valve may not be released.

Therefore, the main object of the present invention is to prevent an abnormal increase in pressure that occurs when the compressor is started from a high load stop state in a refrigeration cycle using a supercritical fluid as a refrigerant. Another object is to promote cooling of the expansion device at start-up, release the blockage of the expansion device after the compressor starts, and ensure accurate startup of the cycle. Disclosure of the invention

In order to achieve the above object, a refrigeration cycle according to the present invention includes a compressor that pressurizes a refrigerant to a supercritical region, a radiator that cools the refrigerant that has reached the supercritical region, and a radiator that cools the refrigerant. An expansion device for decompressing the refrigerant later, an evaporator for evaporating the refrigerant decompressed by the expansion device, and an internal heat exchanger for exchanging heat between the refrigerant flowing out of the evaporator and the refrigerant in the supercritical region. Equipment A pressure-reducing control valve that controls an opening degree of the expansion device based on a refrigerant temperature and a refrigerant pressure on an inflow side; and a decompression control valve when the refrigerant pressure on the inflow side becomes a predetermined pressure or more. A relief valve communicating with the outflow side is provided, and the pressure reducing control valve is provided on a path through which the refrigerant flowing into the expansion device reaches the relief valve.

Therefore, if the pressure rises when the compressor starts, the relief valve provided in the expansion device opens, and the high pressure line from the compressor discharge side to the expansion valve and the high pressure line from the expansion valve to the compressor suction side Communicates with the low-pressure line, allowing the pressure in the high-pressure line to escape to the low-pressure line at once. In addition, since the pressure reducing valve is provided on the path through which the refrigerant flowing into the expansion device reaches the relief valve, even when the refrigerant in the high pressure line flows to the low pressure line via the relief valve, the pressure of the refrigerant can be reduced. Since the gas flows around the valve, cooling of the pressure reducing control valve is promoted, and a situation in which the expansion device is closed after starting can be avoided.

When the expansion device is provided with a pressure reducing valve and a relief valve, the pressure reducing valve is provided in the relief valve, and when the refrigerant pressure on the inflow side becomes equal to or higher than a predetermined pressure, the relief valve is adjusted. The valve may be opened by being displaced integrally with the valve.

According to such a configuration, if there is a pressure increase at the time of starting the compressor, the relief valve provided in the expansion device opens integrally with the control valve, and the high-pressure line and the low-pressure line communicate with each other. Pressure can be released to the low pressure line at once. In addition, since the pressure reducing valve is provided in the relief valve, even when the refrigerant in the high pressure line flows to the low pressure line through the relief valve, the refrigerant flows around the pressure reducing valve. Cooling of the pressure reducing valve is promoted, and the situation where the expansion device is closed after starting can be avoided. Further, the refrigerant discharge amount of the compressor may be changed, and when starting the compressor, the refrigerant discharge amount of the compressor may be controlled so that the refrigerant pressure in the high-pressure line is equal to or lower than a predetermined pressure. Since the high pressure increases when the compressor is started, controlling the compressor displacement prevents the pressure at the start from exceeding the burst pressure.

The high pressure control at the time of such a start is an electric type in which the degree of opening of the expansion device can be arbitrarily controlled by an external control signal, and the refrigerant pressure of the high pressure line is set to a predetermined pressure or less when the compressor is started. It can also be realized by controlling the amount of pressure reduction by the expansion device. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a configuration example of a refrigeration cycle according to the present invention. FIG. 2 is a characteristic diagram showing an optimal control region of the refrigeration cycle shown in FIG. FIG. 3 is a diagram showing an expansion device used in the refrigeration cycle shown in FIG. FIG. 4 is a diagram showing another expansion device used in the refrigeration cycle shown in FIG. FIG. 5 is a flowchart showing an example of a control operation of the discharge capacity when the compressor is started under a high load. FIG. 6 is a flowchart showing an example of the control operation of the expansion device when starting the compressor at a high load. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

In FIG. 1, a refrigeration cycle 1 includes a compressor 2 for compressing the refrigerant, a radiator 3 for cooling the refrigerant, an internal heat exchanger 4 for exchanging heat between the high-pressure line and the low-pressure line, and a decompression of the refrigerant. Expansion device 5, evaporator for evaporating and evaporating refrigerant 6. It has an accumulator 7 for gas-liquid separation of the refrigerant flowing out of the evaporator. In this cycle, the discharge side of the compressor 2 is connected to the high-pressure passage 4a of the internal heat exchanger 4 via the radiator 3, and the discharge side of the high-pressure passage 4a is connected to the expansion device 5, The path from the discharge side of 2 to the expansion device 5 is a high-pressure line 8. The outlet side of the expansion device 5 is connected to an evaporator 6, and the outlet side of the evaporator 6 is connected to a low-pressure passage 4b of the internal heat exchanger 4 via an accumulator. The outflow side of the low-pressure passage 4 b is connected to the suction side of the compressor 2, and the path from the outflow side of the expansion device 5 to the compressor 2 is a low-pressure line 9.

In this refrigeration cycle 1, C 0 ₂ as refrigerant, the compressor 2 and is used as it can adjust the discharge volume, the refrigerant compressed by the compressor 2, as supercritical refrigerant of high temperature and high pressure It enters the radiator 3 where it is radiated and cooled. Thereafter, the heat is exchanged with the low-temperature refrigerant flowing out of the evaporator in the internal heat exchanger 4 to be further cooled and sent to the expansion device 5 without being liquefied. Then, the pressure is reduced in the expansion device 5 to become low-temperature and low-pressure wet steam, and heat exchange with the air passing therethrough in the evaporator 6 to become gaseous. It is heated by heat exchange and returned to the compressor 2.

In the refrigeration cycle 1 described above, the refrigerant temperature T [° C.] on the inflow side of the expansion device 5 and the refrigerant pressure P [MPa] on the inflow side of the expansion device 5 in the normal operation state It is set to be the area shown in the sand in the figure. In this region, the range of the refrigerant temperature and the refrigerant pressure on the inflow side of the expansion device at which good C 0 P is obtained under various operating conditions is determined by the simulation, and more specifically, T = 2.41P + 4.886 (shown by line C) and と = 2.52 2-7.41 (shown by line D). If the cycle is operated in this range, the cooling capacity Is the priority control.

In the figure, line A has a preferred control line for a cycle in which the compressor has a constant discharge capacity without the internal heat exchanger 4, and line B has the internal heat exchanger 4. 2 shows preferred control lines for a cycle in which the displacement of the compressor is constant without being adjusted. The X mark is a refrigeration cycle that uses existing efficiency components, and plots the location where the maximum coefficient of performance can be obtained under various conditions. This is a refrigeration cycle using the above components, and plots the locations where the maximum coefficient of performance can be obtained under various conditions, and the range covering both of these distributions is the above sandy region .

Means for setting the refrigerant temperature and the refrigerant pressure on the inflow side of the expansion device 5 to such ranges include not only adjusting the discharge capacity of the compressor 2 but also controlling the opening degree by an external control signal. In the case of using an electric expansion device that performs expansion, by adjusting the valve opening so that the refrigerant temperature and the refrigerant pressure at the inflow side of the expansion device are set to target values within the region, it is also possible to use an equalizing type expansion device. In the case of a dilatation device, it is advisable to adjust the amount of gas to be charged, and in the case of an expansion device using bimetal, it is advisable to adjust the material by selecting the material.

Among these, the case where the expansion device 5 shown in FIG. 3 is used will be described. The expansion device 5 is provided with a housing 10, an inflow passage 11 communicating with the high-pressure passage 4 a of the internal heat exchanger 4, and an evaporator 5. An outflow passageway 12 leading to 6 and a high-pressure space 13 opening these passageways are provided, and the high-pressure space 13 houses a pressure-reducing control valve 14 and a relief valve 15. The outflow passageway 12 is divided into two branches and opens into the high-pressure space 13, and the openings thereof seat the valve bodies 16 and 17 of the pressure reduction control valve 14 and the relief valve 15. Valve seats 18 and 19 are provided. The pressure reducing control valve 14 is composed of a valve body 16 and a bellows 21 joined to a rod 20 of the valve body 16, and a bellows 2 is accommodated by a spring 22 housed in the bellows. 1 is urged in the direction of extension, that is, the valve element 16 is seated on the valve seat 18. The valve opening pressure of the pressure reducing control valve 14 and the movement of the valve element 16 are adjusted by adjusting the spring pressure with an adjusting plug 23 screwed tightly into the housing 10 or inside the bellows. It is adjusted by adjusting the amount of gas to be filled.The pressure reducing control valve 14 is responsive to the pressure of the high pressure space 13 and the temperature of the refrigerant around the bellows, and controls the area shown in FIG. Characteristics are obtained.

Similarly, the relief valve 15 includes a valve element 17 and a bellows 25 joined to a rod 24 of the valve element 17. The inside of the bellows 25 is formed as a bellows 25. It is opened to the atmosphere through a through hole 27 of an adjusting plug 26 that is integrally screwed into the housing 10 in an airtight manner, and is set at atmospheric pressure. Also, when the opening pressure of the relief valve 15 is adjusted by adjusting the amount of screwing of the control plug 26, and the pressure in the high-pressure space becomes slightly lower than the maximum operating pressure of the cycle. Then, the bellows 25 contracts, and the relief valve 15 is opened.

The relief valve 15 is located at a position farther from the high-pressure passage 11 than the pressure-reducing valve 14. In other words, the pressure-reducing valve 14 allows the refrigerant that has flowed in to the relief valve 15. When the relief valve 15 is opened, the refrigerant flows around the bellows of the pressure reducing control valve 14.

In the above configuration, at high load, even if the refrigeration cycle 1 is stopped, the refrigerant in the cycle is in a supercritical state, and when the compressor 2 starts rotating, the pressure in the high-pressure line 8 increases, This pressure wave spreads throughout the high-pressure line and immediately reaches the high-pressure space 13 of the expansion device 5. Pressure reducing valve 1 4 The valve is in a closed state because of high load, but the relief valve 15 opens when the pressure in the high-pressure space 13 exceeds a predetermined pressure. The high pressure escapes to the low pressure line 9 at a stretch via the circumstance, and a pressure rise that may cause a burst can be avoided.

Also, at the time of such pressure relief, the refrigerant cooled by the radiator 3 and the internal heat exchanger 4 passes around the bellows of the pressure-reducing control valve 14, so that the velocity 21 Cooling can be promoted to open the pressure reducing control valve 14, and after the high pressure drops below a predetermined pressure and the relief valve 15 closes, pressure reduction is performed by the pressure reducing valve 14. A capacity control is performed to balance between the refrigerant pressure and the refrigerant temperature as shown by the sandy region in FIG. That is, according to the above configuration, at the time of starting, pressure control is performed prior to performance control to avoid an abnormal rise in pressure, and thereafter, it is possible to smoothly shift to performance control for obtaining good cooling performance.

FIG. 4 shows another example of the structure of the expansion device 5. In the expansion device 5, the housing 10 has an inflow passage 11 communicating with the high-pressure passage 4 a of the internal heat exchanger 4 and an evaporator 6. And a high-pressure space 13 where these passages are opened, and the high-pressure space 13 houses the pressure-reducing control valve 14 and the relief valve 15. Is the same as The difference is that the outflow passage 1 2 opens into the high-pressure space 13 without being divided into two branches, and this opening is used as the valve seat 31 on which the valve element 30 of the relief valve 15 is seated. The point 4 is that it is provided inside the relief valve 15.

The high-pressure space 13 is defined as a low-pressure space 33 set to atmospheric pressure or vacuum by a diaphragm 32 held in a housing. The relief valve 15 has a hollow valve element 30 disposed in the high-pressure space 13, and this valve element 30 is fixed to the diaphragm 32 and receives a spring received in the low-pressure space 33. The valve body 30 is seated by the spring 3 5 which is mounted between 3 and 4 3 1 To a predetermined pressure. Therefore, the relief valve 15 opens when the high pressure exceeds a predetermined pressure.

Also, the valve body 30 of the relief valve 15 has a large number of inflow holes 36 communicating with the inside and outside, formed on the side wall, and an outflow hole 37 formed at a position aligned with the outflow passage 12. I have. The pressure-reducing control valve 14 is composed of a valve body 39 seated on the periphery of the outflow hole 37 as a toilet seat 38 and a bellows 41 joined to a mouth 40 of the valve body. The bellows 41 is urged by the spring 42 stored in the rose in the direction in which the bellows 41 is extended, that is, the valve element 39 is seated on the valve seat 38. The valve opening pressure of the pressure reducing control valve 14 and the movement of the valve body are adjusted by adjusting the spring pressure and the amount of gas sealed inside the bellows. In response to the pressure and the refrigerant temperature around the nozzle, the control characteristics in the region shown in FIG. 2 are obtained.

The valve opening pressure of the relief valve 15 is set to a predetermined pressure slightly lower than the maximum operating pressure of the cycle, and does not open during the normal operation of the pressure reducing control valve 14. The valve is opened only when the temperature rises abnormally.

In such a configuration, when the compressor 2 starts to rotate and the pressure in the high-pressure line 8 rises and exceeds the opening pressure of the relief valve 15, the relief valve 15 opens and the relief valve 15 opens. The pressure quickly escapes to the low pressure line 9 via 15. For this reason, even when the compressor is started under a high load, it is possible to avoid a sudden and sudden increase in pressure.

At the time of pressure relief, the refrigerant cooled by the radiator 3 and the internal heat exchanger 4 not only flows around the relief valve 14 but also flows into the inlet hole 36 formed in the valve body 30. The pressure is also supplied to the inside of the valve body through the valve, so that the bellows 41 can be cooled and the pressure reducing control valve 14 can be opened. After the pressure becomes lower than the constant pressure and the relief valve 15 is closed, the pressure is adjusted by the pressure reducing control valve 14 to balance the refrigerant pressure and the refrigerant temperature as indicated by the sandy region in FIG. Capability control is performed.

That is, according to the above configuration, at the time of starting, pressure control is performed prior to performance control to avoid an abnormal rise in pressure, and thereafter, it is possible to smoothly shift to performance control for obtaining good cooling performance.

In addition to or instead of the above configuration, the discharge displacement control of the compressor 2 may be performed as a configuration that suppresses an abnormal increase in pressure at the time of starting the compressor.

That is, the compressor 2 used in the refrigeration cycle 1 may be provided with a discharge capacity adjusting mechanism, and the adjusting mechanism may be controlled by an external control signal. The discharge capacity adjustment mechanism may be configured such that the discharge capacity is controlled by the control unit 44 by turning on / off the electromagnetic clutch 43 or the like, but the capacity is controlled using a variable capacity compressor. It is preferable to control the amount of electricity supplied to the variable adjustment unit 45 by the control unit 44 to adjust the discharge capacity.

The control unit 44 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), an input / output port (I / O), and the like. 0 N / 0 FF capacity A refrigerant pressure detection sensor 46 configured to have a drive circuit for controlling the variable capacity adjustment section 45 for detecting the refrigerant pressure on the expansion device inlet side, and the refrigerant temperature on the expansion device inlet side. A signal is input from an A / C switch 49 or the like that commands the start of a compressor installed in the refrigerant temperature detection sensor 47, air conditioning control panel 48, etc. According to this program, signals from various sensors and the air conditioning control panel are processed to control the capacity of the compressor 2 and the like. FIG. 5 is a flow chart showing a specific operation example of controlling the discharge capacity of the compressor 2.The control unit 44 will be described below by pressing the A / C switch 49. It is determined whether or not there is a drive request for the refrigeration cycle 1 (step 50). If the A / C switch 49 is not pressed (NO), this cycle is performed without operating the refrigeration cycle 1. When the control routine is completed and the AZC switch 49 is pressed (YES), it is determined whether the compressor 2 has been started or the refrigeration cycle 1 has been stabilized after the start (step 5 2). This determination is made during a period in which the refrigerant pressure detected by the refrigerant pressure detection sensor 46 is equal to or higher than a certain pressure, even if the start of the compressor 2 is within a predetermined time after the start. At the start.

When the compressor 2 is started, the process proceeds to step 54, and the discharge capacity of the compressor 2 is significantly reduced or minimized so that the increase in high pressure generated at the time of startup does not exceed a predetermined pressure. As a result, even if the compressor 2 is started under a high load, a sudden abnormal increase in the high pressure can be avoided.

When the refrigerant pressure in the cycle has stabilized, the process proceeds to step 56, where the control (capacity control) for giving priority to the optimum cooling capacity, that is, the refrigerant pressure and the refrigerant temperature satisfying the sandy region in FIG. 2 are obtained. The discharge capacity of the compressor 2 is controlled.

Further, in addition to the above-described compressor control or instead of the above-described compressor control, the opening degree control of the expansion device 5 may be performed. In performing this control, the expansion device 5 is not an expansion device shown in FIGS. 3 and 4, but an electric expansion valve known per se whose opening is adjusted by a control signal from the outside. And is controlled by the control unit 44. FIG. 5 is a flowchart showing a specific example of the operation of the inflation device 5. The control unit 44 will be described below. The same control as in Steps 50 and 52 is performed.When the compressor 2 is started, the process proceeds to Step 58, and the opening of the expansion device 5 is controlled so that the increase in high pressure generated at the time of starting does not exceed a predetermined pressure. Should be increased or maximized. As a result, even if the compressor 2 starts at a high load, the high pressure escapes to the low pressure via the expansion device 5, and a sudden increase in the high pressure can be avoided.

Then, when the refrigerant pressure in the cycle has stabilized, the process proceeds to step 60, and thereafter, the control (capacity control) for giving priority to the optimal cooling capacity, that is, the refrigerant pressure and the refrigerant temperature satisfying the sandy region in FIG. The opening degree of the expansion device 5 is controlled so as to obtain the following.

Therefore, in any of the configurations and combinations thereof, when the compressor 2 is started from the stop of the high load, the pressure increase that occurs at the time of the start is caused by the opening of the relief valve 15 or the compressor 2. It is possible to suppress the burst pressure by controlling the discharge capacity or adjusting the opening degree of the expansion device 5. In particular, according to the above-described configuration in which the relief valve 15 is provided in the expansion device 5, the bellows of the pressure reducing control valve 14 is cooled by the circulating refrigerant even when the relief valve 15 is opened, so that the high pressure is reduced. After stabilization, the system can smoothly shift to capacity control to obtain optimal cooling capacity. Industrial applicability

As described above, according to the present invention, since the pressure reducing valve and the relief valve are provided in the expansion device, and the pressure reducing valve is provided on the path for guiding the refrigerant to the relief valve, the high-pressure pressure is reduced by the compressor. Even when the pressure rises at the time of startup, the relief valve can be opened to suppress the sudden increase in pressure.Also, while the refrigerant is flowing through the relief valve, this refrigerant flows around the pressure reducing valve. This can promote cooling of the pressure-reducing control valve, avoiding the situation where the expansion device is closed after startup, and changing the pressure control by the relief valve to the performance by the pressure-reducing valve. A smooth transition to force control is possible.

In addition, a pressure reducing control valve and a relief valve are provided in the expansion device, and a pressure reducing control valve is provided in the relief valve. When the pressure exceeds a predetermined pressure, the relief valve is displaced integrally with the control valve. According to the configuration in which the valve is opened, if the pressure rises at the time of starting the compressor, the pressure in the high pressure line is released to the low pressure line at once, thereby suppressing an abnormal rise in the high pressure. Moreover, according to this configuration, since the pressure-reducing control valve is provided in the relief valve, the pressure of the high-pressure line can be cooled even while the pressure of the high-pressure line is flowing to the low-pressure line via the relief valve. As a result, it is possible to avoid a situation in which the expansion device is closed after starting, and to smoothly shift from pressure control by the relief valve to capacity control by the pressure-reducing control valve.

As a means to avoid abnormal rise in high pressure at the start of the refrigeration cycle, the refrigerant discharge amount of the compressor can be changed, and the high pressure is controlled to a predetermined pressure or less by giving priority to the discharge amount control at the start of the compressor. It is also effective to use an electric expansion device and control the high pressure to a predetermined pressure or less at the start of the compressor by giving priority to the pressure reduction amount control.

Claims

The scope of the claims

1. A compressor that raises the pressure of the refrigerant to the supercritical region, a radiator that cools the refrigerant that has reached the supercritical region, an expansion device that depressurizes the refrigerant after being cooled by the radiator, and a decompression device that depressurizes the refrigerant. A refrigerating cycle, comprising: an evaporator for evaporating the separated refrigerant; and an internal heat exchanger for exchanging heat between the refrigerant flowing out of the evaporator and the refrigerant in the supercritical region.

A pressure-reducing control valve for controlling an opening degree of the expansion device according to a refrigerant temperature and a refrigerant pressure on an inflow side; and an inflow side and an outflow of the expansion device when the refrigerant pressure on the inflow side becomes a predetermined pressure or more. A refrigeration cycle, comprising: a relief valve communicating with a side of the expansion device; and a pressure reduction control valve provided on a path through which the refrigerant flowing into the expansion device reaches the relief valve.

2. A compressor that increases the pressure of the refrigerant to the supercritical region, a radiator that cools the refrigerant that has reached the supercritical region, an expansion device that reduces the pressure of the refrigerant after being cooled by the radiator, A refrigerating cycle, comprising: an evaporator for evaporating the separated refrigerant; and an internal heat exchanger for exchanging heat between the refrigerant flowing out of the evaporator and the refrigerant in the supercritical region.

The expansion device, a pressure-reducing control valve that adjusts an opening degree by a refrigerant temperature and a refrigerant pressure on an inflow side, and an inflow side and an outflow side of the expansion device when the refrigerant pressure on the inflow side becomes a predetermined pressure or more. A relief valve that communicates with the pressure control valve, the pressure reducing control valve is provided in the relief valve, and when the refrigerant pressure on the inflow side becomes equal to or higher than the predetermined pressure, the relief valve is displaced integrally with the control valve. A refrigeration cycle characterized in that the valve is opened.

3. A compressor that raises the pressure of the refrigerant to the supercritical region, a radiator that cools the refrigerant that has reached the supercritical region, and an expander that depressurizes the refrigerant after being cooled by the radiator A refrigerating cycle comprising: a tensioning device; an evaporator for evaporating the refrigerant decompressed by the decompression means; and an internal heat exchanger for exchanging heat between the refrigerant flowing out of the evaporator and the refrigerant in the supercritical region. At

It is possible to change the refrigerant discharge amount of the compressor,

A refrigeration cycle characterized in that when the compressor is started, the refrigerant discharge amount is controlled so that the refrigerant pressure in a high-pressure line from the compressor to the expansion device is equal to or lower than a predetermined pressure.

4. A compressor that pressurizes the refrigerant to the supercritical region, a radiator that cools the refrigerant that has reached the supercritical region, an expansion device that depressurizes the refrigerant after being cooled by the radiator, A refrigerating cycle, comprising: an evaporator for evaporating the separated refrigerant; and an internal heat exchanger for exchanging heat between the refrigerant flowing out of the evaporator and the refrigerant in the supercritical region.

The expansion device is an electric type in which the opening can be arbitrarily controlled by an external control signal.

When the compressor is started, the amount of pressure reduction by the expansion device is controlled so that the refrigerant pressure in the high-pressure line from the compressor to the expansion device is equal to or lower than a predetermined pressure. .