EP1862749A2

EP1862749A2 - Vapor Compression Refrigeration Cycle

Info

Publication number: EP1862749A2
Application number: EP07108423A
Authority: EP
Inventors: Yuuichi Matsumoto; Masato Tsuboi; Kenichi Suzuki
Original assignee: Sanden Corp
Current assignee: Sanden Corp
Priority date: 2006-05-30
Filing date: 2007-05-17
Publication date: 2007-12-05
Also published as: JP2007322009A; JP4787070B2; EP1862749A3

Abstract

A vapor compression refrigerating cycle (10) has a compressor (1), a radiator (2), an oil separator (3) for separating the refrigerant radiated by the radiator (2) into refrigerant and oil containing a small amount of refrigerant, a first pressure reducer (6), an evaporator (7), and an accumulator (8), wherein a second pressure reducer (5) for reducing a pressure of the oil containing a small amount of refrigerant separated by the oil separator (3) and an inside heat exchanger (4) for exchanging heat between the refrigerant separated by the oil separator (3) and the oil containing a small amount of refrigerant reduced in pressure by the second pressure reducer (5) are provided, and the oil containing a small amount of refrigerant is injected into a midway of the compression step of the compressor (1) after being passed through the inside heat exchanger (4). Utilizing the oil containing a small amount of refrigerant separated by the oil separator, the performance of the refrigerating cycle is improved, and it becomes possible to integrate respective equipment with each other, and while the refrigeration ability can be increased, problems on space and weight can be solved.

Description

The present invention relates to a vapor compression refrigerating cycle, and specifically, to a vapor compression refrigerating cycle suitable for a case using carbon dioxide, which is a natural-system refrigerant, particularly suitable as a refrigerating cycle used in an air conditioning system for vehicles.
Carbon dioxide refrigerant is proposed as an alternate refrigerant even in the field of air conditioning systems for vehicles, form the viewpoint of environmental problems. Carbon dioxide refrigerant is poisonless and incombustible, however, the critical temperature is low (about 31°C), and when the pressure of the high-pressure side of the refrigerating cycle becomes a supercritical condition (about 7.4 MPa or more), the cycle becomes a cycle transiting a critical condition (a supercritical refrigerating cycle). Generally, because such a cycle is low in coefficient of performance (COP) for refrigeration as compared with a cycle using Freon group refrigerants, it is required to improve the COP. Further, under the supercritical condition, lubricant oil is soluble in the refrigerant and circulates together with the refrigerant. In such a condition, if the oil flows particularly into an evaporator, the heat transfer at the evaporator is damaged by the oil flowed in, and the ability of the evaporator decreases.
Fig. 7 depicts a circuit diagram of a conventional refrigerating cycle for an air conditioning system in a case using carbon dioxide as its refrigerant, for example, disclosed in JP-A-11-193967 . Refrigerating cycle 100 has a compressor 102 for compressing refrigerant and a radiator 102 (a gas cooler) for radiating heat of the refrigerant compressed by compressor 101. The high-pressure refrigerant from radiator 102 is reduced in pressure by a first pressure reducer 104, and the refrigerant reduced in pressure is evaporated by an evaporator 105. At a downstream side, an accumulator 106 is provided for separating the refrigerant flowed out from evaporator 105 at a state of gas/liquid mixing phases into gas-phase refrigerant and liquid-phase refrigerant and storing the separated liquid refrigerant, and the separated gas-phase refrigerant is sent to a suction side of compressor 101. Since this refrigerant sent to the suction side of compressor 101 is not completely in a gas-phase condition in practice, in order to prevent the gas-phase refrigerant sucked into compressor 101 from becoming wet by providing a degree of superheating thereto, an inside heat exchanger 103 is provided for exchanging heat between the refrigerant at an exit side of radiator 102 (high-pressure side refrigerant) and the refrigerant at an exit side of accumulator 106 (low-pressure side refrigerant). Further, a structure of so-called gas injection cycle is known wherein, in order to improve the efficiency of a compressor and decrease the consumption power of the whole of a refrigerating cycle, the refrigerant at an exit side of a radiator is reduced in pressure, the pressure-reduced refrigerant is separated into gas/liquid phases, and the separated gas-phase refrigerant is introduced into a midway of a compression step of the compressor (for example, JP-A-11-63694 ).
However, when an inside heat exchanger and an oil separator are provided separately in a vapor compression refrigerating cycle, the number of parts becomes large and there is a problem on space. Because the carbon dioxide refrigerant becomes a supercritical condition when the pressure of the refrigerant at a high-pressure side exceeds its critical pressure as described above, it is necessary to investigate a material and a structure capable of bearing such a pressure, and the thickness of equipment tends to become large and the weight thereof tends to become great. Because the cycle using an inside heat exchanger and an oil separator requires addition of new equipment, it is poor in property for mounting on a vehicle.
Further, in a case where the high-pressure side refrigerant and the low-pressure side refrigerant are exchanged in heat by an inside heat exchanger in order to prevent the gas-phase refrigerant sucked into a compressor from becoming wet by providing a degree of superheating to the refrigerant sent to a suction side of the compressor, it is difficult to control this degree of superheating at an optimum condition. A condition where the low-pressure side refrigerant is heated too much is not always preferable from the viewpoint of protecting the compressor and improving the efficiency.
Accordingly, it would be desirable to provide a vapor compression refrigerating cycle in which a function similar to that in a conventional gas injection cycle can be exhibited by utilizing an oil containing a small amount of refrigerant separated by an oil separator, a temperature of a high-pressure side refrigerant can be appropriately lowered through heat exchange with the oil containing a small amount of refrigerant, thereby preventing a low-pressure side refrigerant from being heated too much at the time of heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant, and protection of a compressor and improvement of an efficiency can be balanced at an optimum condition.
Further, it would be desirable to provide a vapor compression refrigerating cycle in which a radiator, an oil separator, a pressure reducer, an inside heat exchanger, etc. can be structured integrally, and while the refrigeration ability can be increased, problems on space and weight can be solved.
A vapor compression refrigerating cycle according to the present invention comprises a compressor for comprising refrigerant, a radiator for radiating heat of the refrigerant compressed by the compressor, an oil separator for separating the refrigerant radiated in heat by the radiator into refrigerant and oil containing a small amount of refrigerant, a first pressure reducer for reducing a pressure of the refrigerant separated by the oil separator, an evaporator for evaporating the refrigerant reduced in pressure by the first pressure reducer, and an accumulator for separating the refrigerant flowed out from the evaporator into gas-phase refrigerant and liquid-phase refrigerant and sending only the gas-phase refrigerant to a suction side of the compressor, and is characterized in that a second pressure reducer for reducing a pressure of the oil containing a small amount of refrigerant separated by the oil separator and at least a first inside heat exchanger for exchanging heat between the refrigerant separated by the oil separator and the oil containing a small amount of refrigerant reduced in pressure by the second pressure reducer are provided, and the oil containing a small amount of refrigerant reduced in pressure by the second pressure reducer is injected into a midway of a compression step of the compressor after being passed through the first inside heat exchanger.
Namely, the oil containing a small amount of refrigerant separated by the oil separator is utilized, after this oil is reduced in pressure by the second pressure reducer, it is exchanged in heat with the refrigerant separated by the oil separator, and thereafter, by injecting it into a midway of a compression step of the compressor, a function similar to that in a conventional gas injection cycle is exhibited, the efficiency of the compressor can be improved, and the consumption power of the cycle can be decreased. Moreover, by heat exchange between the refrigerant separated by the oil separator (that is, high-pressure side refrigerant) and the oil containing a small amount of refrigerant reduced in pressure by the second pressure reducer (middle pressure), the temperature of the high-pressure side refrigerant is appropriately lowered, and when this high-pressure side refrigerant is exchanged in heat with the low-pressure side refrigerant sucked into the compressor, the low-pressure side refrigerant is prevented from being heated too much (from becoming a too high degree of superheating) and from becoming wet, the temperature of the refrigerant to be introduced into the compressor can be controlled at an optimum temperature from the viewpoint of protecting the compressor and improving the efficiency.
In such a vapor compression refrigerating cycle according to the present invention, a structure is preferred wherein a second inside heat exchanger is provided for exchanging heat between the refrigerant separated by the oil separator and the refrigerant sent to the suction side of the compressor. This second inside heat exchanger is one similar to a conventional inside heat exchanger (for example, inside heat exchanger 107 depicted in Fig. 7), and it provides a degree of superheating so that the refrigerant sent to the suction side of the compressor does not become wet.
Further, in the present invention, it is possible to form the first and second inside heat exchangers integrally with each other. In particular, as shown in the embodiment described later, it is possible to employ a structure wherein the radiator is structured integrally with the oil separator, the second pressure reducer, the first inside heat exchanger and the second inside heat exchanger. In such an integrated structure, substantially the number of equipments can be reduced, the refrigeration ability can be increased, and the problems on space and weight when mounted on a vehicle can be solved.
In the present invention, it is preferred that each of the first pressure reducer and the second pressure reducer is structured as a pressure reducer capable of changing its degree of opening in accordance with a pressure or a temperature, or both, of refrigerant in the vapor compression refrigerating cycle. By this structure, a further optimum control becomes possible.
Further, the vapor compression refrigerating cycle according to the present invention is suitable as a vapor compression refrigerating cycle having a supercritical region, in particular, for a cycle using carbon dioxide as its refrigerant. Furthermore, the vapor compression refrigerating cycle according to the present invention is suitable as a refrigerating cycle used for an air conditioning system for a vehicle.
Thus, in the vapor compression refrigerating cycle according to the present invention, by effectively utilizing the oil containing a small amount of refrigerant separated by the oil separator, a function similar to that in a conventional gas injection cycle can be exhibited, and protection of the compressor and improvement of the efficiency can be balanced at an optimum condition by appropriately lowering the temperature of the high-pressure side refrigerant (the refrigerant separated by the oil separator) through heat exchange with the oil containing a small amount of refrigerant, and preventing the low-pressure side refrigerant from being heated too much at the time of heat exchange between the high-pressure side refrigerant and the low-pressure side refrigerant. Namely, it becomes possible to control the low-pressure side refrigerant sucked into the compressor at an optimum degree of superheating.
Further, if the first inside heat exchanger and the second inside heat exchanger are integrated with each other, and further, if the radiator is integrated with the oil separator, the second pressure reducer, the first inside heat exchanger and the second inside heat exchanger, while the refrigeration ability can be increased, problems on space and weight can be solved. Moreover, because the number of equipment and the number of junction parts can be decreased, prevention of refrigerant leakage and improvement of property of mounting on a vehicle can be expected.
Further objects, features, and advantages of the present invention will be understood from the following detailed description of preferred embodiments of the present invention with reference to the accompanying figures.
Embodiments of the invention now are described with reference to the accompanying figures, which are given by way of example only, and are not intended to limit the present invention.

Fig. 1 is a circuit diagram of a vapor compression refrigerating cycle according to an embodiment of the present invention.
Fig. 2 is a Mollier chart of the refrigerating cycle depicted in Fig. 1.
Fig. 3 is a circuit diagram of a vapor compression refrigerating cycle, showing an example of a gas cooler module in which a radiator and an inside heat exchanger are integrated with each other.
Fig. 4 depicts an appearance of the gas cooler module depicted in Fig. 3 shown by trigonometry, Fig. 4A is an elevational view, Fig. 4B is a plan view, Fig. 4C is a side view, and Fig. 4D is a bottom view.
Fig. 5 shows examples of structure of an inside heat exchanger in the gas cooler module depicted in Fig. 3, Figs. 5A-5D are cross-sectional views, Fig. 5E is a schematic view of an example of an end structure for inlet and outlet ports, and Fig. 5F is a vertical sectional view of the structure depicted in Fig. 5E.
Fig. 6 is a vertical sectional view of the gas cooler module depicted in Fig. 3, showing the more detailed structure thereof.
Fig. 7 is a circuit diagram of a conventional refrigerating cycle.

Hereinafter, desirable embodiments of the present invention will be explained referring to the drawings.
Fig. 1 depicts a circuit diagram of a vapor compression refrigerating cycle according to an embodiment of the present invention for use in an air conditioning system for a vehicle, using carbon dioxide which is a natural-system refrigerant. Refrigerating cycle 10 has a compressor 1 for compressing refrigerant and a radiator 2 (a gas cooler) for radiating heat of the refrigerant compressed by compressor 1. Lubricant oil is soluble in refrigerant at a supercritical condition, and circulates together with the refrigerant. In such a condition, if the oil flows particularly into an evaporator, the heat transfer is damaged by the oil, and the evaporation ability of the evaporator decreases. Accordingly, an oil separator 3 is provided for separating the oil contained in refrigerant from the refrigerant. A second pressure reducer 5 reduces the pressure of the oil which is separated by oil separator 3 and which contains a small amount of refrigerant, and a gas injection cycle is formed by flowing the pressure-reduced oil, containing a small amount of refrigerant, through an inside heat exchanger 4 and introducing it into a midway of a compression step of compressor 1. Because the refrigerant on the way of compression is cooled by the injected oil, the temperature of discharged refrigerant does not elevate so much and the efficiency of compressor 1 does not decrease so much. On the other hand, the refrigerant (high-temperature and high-pressure refrigerant) separated by oil separator 3 passes through inside heat exchanger 4, and is reduced in pressure by a first pressure reducer 6. The refrigerant reduced in pressure by first pressure reducer 6 is evaporated at an evaporator 7 by heat exchange with outside heat exchange medium (for example, air sent in an air path of an air conditioning system). An accumulator 8 is provided at a position downstream of evaporator 7 for separating the refrigerant flowed out from evaporator 7 into gas and liquid phases and storing the separated liquid-phase refrigerant therein. The separated gas-phase refrigerant (low-pressure refrigerant, in practice, it is frequently a mixing-phase refrigerant mixed with a small amount of liquid-phase refrigerant) is flowed out to inside heat exchanger 4, and after an appropriate degree of superheating is given by the heat exchange at inside heat exchanger 4, it is sent to the suction side of compressor 1. In Fig. 1, the arrows represent flows of refrigerant and oil containing a small amount of refrigerant.
In this embodiment, the above-described inside heat exchanger 4 is formed as a structure wherein a first inside heat exchanger 41 according to the present invention (a heat exchanger for exchanging heat between the refrigerant separated by oil separator 3 and the oil containing a small amount of refrigerant reduced in pressure by second pressure reducer 5) and a second inside heat exchanger 42 according to the present invention (a heat exchanger for exchanging heat between the refrigerant separated by oil separator 3 and the refrigerant sent to the suction side of compressor 1) are integrated with each other. Namely, it is provided as an integrated-type inside heat exchanger 4 for exchanging heat between the refrigerant separated by oil separator 3 and the oil containing a small amount of refrigerant after passing through second pressure reducer 5 and the refrigerant to be sucked into compressor 1. The oil containing a small amount of refrigerant after passing through second pressure reducer 5 is injected into a midway of the compression step of compressor 1 after passing through inside heat exchanger 4. Where, as the refrigerant for refrigerating cycle 10, a refrigerant, such as water or hydrocarbon, whose high-pressure side pressure becomes its critical pressure or more, may used. Further, refrigerating cycle 10 may be used for application other than an air conditioning system for a vehicle.
Fig. 2 exemplifies an operation condition of refrigerating cycle 10 depicted in Fig. 1 by using a Mollier chart. Curved line 21 represents a saturated vapor curved line of carbon dioxide refrigerant. Curved line 22 represents an isothermal line passing through the critical temperature. Curved line 23 represents a constant-pressure line passing through the critical pressure. By injecting the oil containing a small amount of refrigerant after passing through second pressure reducer 5 into a midway of the compression step of compressor after passing through inside heat exchanger 4, a gas injection cycle like one compressing refrigerant at two steps is formed.
Fig. 3 depicts a circuit diagram in a case where the respective components in Fig. 1 are integrated with each other. A difference form the structure depicted in Fig. 1 is in that radiator 2 (a gas cooler), oil separator 3, second pressure reducer 5 and inside heat exchanger 4 (having a structure integrated with first inside heat exchanger 41 and second inside heat exchanger 42) are all integrated to be formed as a gas cooler module 31. By integrating the respective components, the property for mounting on a vehicle is improved, and a fear of refrigerant leakage is removed by decreasing the number of junction parts. A demister 32 (a fine net woven with fibrous metal wires) is provided in one tank of radiator 2 as a member for forming oil separator 3 to separate oil. The oil containing a small amount of refrigerant, which is separated by demister 32 and stored at the bottom part of demister 32, is reduced in pressure by second pressure reducer 5 provided at a lower position of demister 32, and thereafter, flowed through the part of first inside heat exchanger 41 of inside heat exchanger 4 disposed at a lower position of radiator 2. On the other hand, the refrigerant passes through radiator 2 at a cross-flow condition, and it is flowed through inside heat exchanger 4 disposed at a lower position of radiator 2. At that time, the refrigerant and the oil containing a small amount of refrigerant which is reduced in pressure by second pressure reducer 5 are flowed through the part of first inside heat exchanger 41 of inside heat exchanger 4 at a counter-flow condition. Further, the gas-phase refrigerant flowed out from accumulator 8 is flowed through the part of second inside heat exchanger 42 of inside heat exchanger 4. The gas-phase refrigerant flowed out from accumulator 8 (low-pressure refrigerant) is exchanged in heat with the refrigerant at the exit side of radiator 2 (that is, high-pressure refrigerant after being separated by oil separator 3) in the part of second inside heat exchanger 42 of inside heat exchanger 4 at a counter-flow condition. Namely, the oil containing a small amount of refrigerant which is reduced in pressure by second pressure reducer 5, and the refrigerant at the exit side of accumulator 8, are in a parallel-flow condition. The efficiency of the heat exchange can be improved by setting the high-pressure refrigerant and the low-pressure refrigerant at a counter-flow condition.
For first pressure reducer 6 and second pressure reducer 5, it is preferred to use a pressure-reducing mechanism capable of changing its opening degree in accordance with pressure or temperature or both.
Further, by integrating all of radiator 2 (a gas cooler), oil separator 3, second pressure reducer 5 and inside heat exchanger 4 to form gas cooler module 31, heat transfer from the refrigerant at the entrance side of radiator 2 is achieved over the entire of gas cooler module 31, therefrom the heat is transferred to the middle-pressure side and the low-pressure side in inside heat exchanger 4, and the degrees of superheating of the middle-pressure side refrigerant and the low-pressure side refrigerant are increased. In this case, in order to prevent the efficiency of compressor 1 from decreasing by the increase of the degree of superheating, it is preferred to suppress the heat transfer from the part of radiator 2 to the part of inside heat exchanger 4 in gas cooler module 31 by employing a structure such as one providing a gap between the part of radiator 2 and the part of inside heat exchanger 4. Alternatively, a structure may be employed wherein the part of radiator 2 and the part of inside heat exchanger 4 are separated by a heat insulation material and the like.
Figs. 4A-4D depict the appearance of gas cooler module 31 depicted in Fig. 3 shown by trigonometry. Fig. 4A is its elevational view, and is the same as that depicted in Fig. 3, and Fig. 4B (its plan view), Fig. 4C (its side view) and Fig. 4D (its bottom view) are added. In the elevational view, an assembly structure may be employed wherein air sent from a front side of a vehicle does not pass through the part of inside heat exchanger 4 provided at the lower position of gas cooler module 31. Namely, a design may be employed wherein, while the area of the part of radiator 2 is set as large as possible, inside heat exchanger 4 is incorporated thereinto.
Figs. 5A-5D show cross-sectional views of examples of inside heat exchanger 4 of gas cooler module 31, and Figs. 5E and 5F show a structure of an example of an end portion for inlet and outlet ports thereof. In a cross-sectional structure 51 depicted in Fig. 5A, an inside heat exchanger having a triple-tube structure is formed. In a cross-sectional structure 52 depicted in Fig. 5B, the inside of a tube is separated uniformly into three chambers, and each of high-pressure refrigerant, middle-pressure refrigerant and low-pressure refrigerant is flowed through each chamber. In a cross-sectional structure 53 depicted in Fig. 5C, the inside of a tube is separated non-uniformly into three chambers, and each of high-pressure refrigerant, middle-pressure refrigerant and low-pressure refrigerant is flowed through each chamber. In a cross-sectional structure 54 depicted in Fig. 5D, a flat tube stacked structure is employed, and each of high-pressure refrigerant, middle-pressure refrigerant and low-pressure refrigerant is flowed through the passageway formed in each flat tube. In the structure of the end portion for inlet and outlet ports shown in Figs. 5E and 5F, inlet and outlet ports of refrigerant are formed as a case using the inside heat exchanger having the cross-sectional structure 51 of a triple-tube structure. Port 55 shows a high-pressure side refrigerant port, port 56 shows a low-pressure side refrigerant port, and port 57 shows a middle-pressure side refrigerant port, respectively. Although it is similar to that in a conventional structure to exchange in heat between the high-pressure side refrigerant and the low-pressure side refrigerant, by flowing the middle-pressure side refrigerant at a position of outermost surface, as compared with a double-tube type conventional inside heat exchanger, it is prevented to heat the low-pressure side refrigerant too much at the exit side, and the degree of superheating of the refrigerant sucked into compressor 1 can be decreased.
Fig. 6 is a vertical sectional view of the above-described gas cooler module 31, showing the more detailed structure thereof. The refrigerant sent from compressor 1 passes through tubes 61 of the part of radiator 2, and radiated in heat through fins 62. The refrigerant flows into a second tank 64 from a first tank 63 through tubes 6I, the oil contained in the refrigerant is trapped by demister 32 provided in second tank 64, and only the refrigerant flows into first tank 63 again through tubes 61. The refrigerant flowed into first tank 63 flows from the part of radiator 2 to the part of inside heat exchanger 4 through the passageway in first tank 63. On the other hand, the oil trapped by demister 32 provided in second tank 64 is reduced in pressure by second pressure reducer 5, and flows into inside heat exchanger 4 through the passageway in second tank 64. At the same time, the refrigerant flowed out from accumulator 8 is sent to the suction side of compressor 1 through inside heat exchanger 4. At that time, at inside heat exchanger 4 (for example, flat tube structure), the oil containing a small amount of refrigerant after passing through second pressure reducer 5 (middle-pressure side refrigerant) and the low-pressure side refrigerant at the exit side of accumulator 8 are exchanged in heat with each other.
Where, the flow of the refrigerant in the radiator (gas cooler) may be any of a cross flow and a counter flow.
Thus, in the vapor compression refrigerating cycle according to the present invention, by using the refrigerant and the oil separated by oil separator 3 and exchanging heat between the refrigerant at the exit side of radiator 2 and the oil containing a small amount of refrigerant reduced in pressure by the integrated inside heat exchanger 4, the temperature of the high-pressure side refrigerant is lowered. Further, by flowing the low-pressure side refrigerant through inside heat exchanger 4, the low-pressure side refrigerant is heated, and the refrigerant sucked into compressor 1 is prevented from becoming wet. In this case, although the high-pressure side refrigerant is used to heat the low-pressure side refrigerant, because heat exchange with the middle-pressure side refrigerant is performed, as compared with a conventional case where heat exchange is performed only between the high-pressure side refrigerant and the low-pressure side refrigerant, increase of the temperature of the low-pressure side refrigerant can be appropriately suppressed, and the low-pressure side refrigerant sucked into compressor 1 can be controlled at an optimum degree of superheating in consideration of the efficiency together with protection of compressor 1.
On the other hand, by injecting the oil containing a small amount of refrigerant into a midway of the compression step of compressor 1 after flowing the oil through inside heat exchanger 4, the efficiency of the compression step can be improved.
Further, by integrating all of radiator 2, oil separator 3, second pressure reducer 5 and inside heat exchanger 4 with each other, while the refrigeration ability can be increased, the problems on space and weight can be solved, and further, it is possible to decrease the number of equipment and junction parts, and therefore, prevention of refrigerant leakage and improvement of property of mounting on a vehicle can be expected.
The vapor compression refrigerating cycle according to the present invention can be applied to any vapor compression refrigerating cycle capable of operating in a supercritical region of refrigerant, and in particular, it is suitable for a refrigerating cycle using carbon dioxide which is a natural-system refrigerant, and especially, suitable as a refrigerating cycle used for an air conditioning system for vehicles.

Claims

A vapor compression refrigerating cycle comprising a compressor for comprising refrigerant, a radiator for radiating heat of the refrigerant compressed by said compressor, an oil separator for separating the refrigerant radiated in heat by said radiator into refrigerant and oil containing a small amount of refrigerant, a first pressure reducer for reducing a pressure of the refrigerant separated by said oil separator, an evaporator for evaporating the refrigerant reduced in pressure by said first pressure reducer, and an accumulator for separating the refrigerant flowed out from said evaporator into gas-phase refrigerant and liquid-phase refrigerant and sending only the gas-phase refrigerant to a suction side of said compressor, characterized in that a second pressure reducer for reducing a pressure of said oil containing a small amount of refrigerant separated by said oil separator and at least a first inside heat exchanger for exchanging heat between said refrigerant separated by said oil separator and said oil containing a small amount of refrigerant reduced in pressure by said second pressure reducer are provided, and said oil containing a small amount of refrigerant reduced in pressure by said second pressure reducer is injected into a midway of a compression step of said compressor after being passed through said first inside heat exchanger.
The vapor compression refrigerating cycle according to claim 1, wherein a second inside heat exchanger is provided for exchanging heat between said refrigerant separated by said oil separator and said refrigerant sent to said suction side of said compressor.
The vapor compression refrigerating cycle according to claim 2, wherein said first and second inside heat exchangers are structured integrally with each other.
The vapor compression refrigerating cycle according to claim 2 or 3, wherein said radiator is structured integrally with said oil separator, said second pressure reducer, said first inside heat exchanger and said second inside heat exchanger.
The vapor compression refrigerating cycle according to any preceding claim, wherein each of said first pressure reducer and said second pressure reducer is structured as a pressure reducer capable of changing its degree of opening in accordance with a pressure or a temperature, or both, of refrigerant in said vapor compression refrigerating cycle.
The vapor compression refrigerating cycle according to any preceding claim, wherein carbon dioxide is used as refrigerant for said vapor compression refrigerating cycle.
The vapor compression refrigerating cycle according to any preceding claim, wherein said vapor compression refrigerating cycle is used for an air conditioning system for a vehicle.