Refrigeration cycle device

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No. 2008-196320 filed on Jul. 30, 2008, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a refrigeration cycle device with a mixed refrigerant.

BACKGROUND OF THE INVENTION

A refrigeration cycle device is disclosed in JP-A-2007-071461, corresponding to US 2007/074538, for example. In the refrigeration-cycle device, a compressor, a condenser, an expansion valve and an evaporator are circularly-connected. The refrigeration cycle device further includes an internal heat exchanger for exchanging heat between a high-pressure refrigerant, which flows between the condenser and the expansion valve, and a low-pressure refrigerant, which flows between the evaporator and the compressor. A refrigerant circulating in the refrigeration cycle device is a single refrigerant or a mixed refrigerant. A temperature-sensitive expansion valve is widely used as the expansion valve.

JP-A-2-203175 discloses a refrigeration cycle device using a mixed refrigerant, and a temperature-sensitive expansion valve. Furthermore, JP-A-2-203175 discloses that a refrigerant that is the same with a circulating refrigerant in the refrigeration cycle device or a refrigerant having a pressure-temperature property similar to that of the circulating refrigerant is filled in a temperature-sensitive portion of the expansion valve. The refrigerant filled in the temperature-sensitive portion is referred to as a filled fluid.

Temperature-sensitive expansion valves having various configurations are generally known. For example, JP-A-2-203175 discloses a joint-type expansion valve including a joint portion for connecting to a pipe configuring the refrigeration cycle device. JP Patent No. 4039069 discloses a box-type expansion valve including a housing, in which a high-pressure passage and a low-pressure passage are formed. JP-U-7-40139 discloses a cassette-type structure, in which a temperature-sensitive portion and a valve portion are unitized. JP-A-2-203175 further discloses an internal-equalizing expansion valve that draws a pressure between the expansion valve and an evaporator. JP-U-7-40139 discloses an external-equalizing expansion valve that draws a pressure between an evaporator and a compressor.

The conventional temperature-sensitive expansion valve controls a state of the refrigerant at an outlet portion of the evaporator. For example, the temperature-sensitive expansion valve controls such that the degree of superheat of the refrigerant circulating in the refrigeration cycle device at the outlet portion of the evaporator becomes a predetermined value.

However, in the case where the mixed refrigerant is used as the refrigerant circulating in the refrigeration cycle device, a pressure difference between a saturated vapor pressure curve of the circulating refrigerant and a valve-opening property depending on a saturated vapor pressure curve of the filled fluid may show an undesirable increase or decrease in a low-temperature region or a high-temperature region. The behavior appears prominently when the filled fluid and the; circulating refrigerant are different. Thereby, a desired control property may not be obtained in the low-temperature region or the high-temperature region.

For example, in the case where the pressure difference between the saturated vapor pressure curve of the circulating refrigerant and the valve-opening property increases as the temperature decreases, the excess pressure difference is obtained, and thereby, the expansion valve opens beyond necessity. When the opening degree of the expansion valve becomes excessively large, the liquid back occurs. Thereby, the control of the degree of superheat is broken, and the refrigeration capacity may be decreased.

Because thermally load is large in the high-temperature region, it is preferable that the flow amount of the circulating refrigerant is increased. However, in the case where the pressure difference between the saturated vapor pressure curve of the circulating refrigerant and the valve-opening property decreases as the temperature increases, the pressure difference becomes too little. Thereby, the expansion valve may not obtain the necessary opening degree.

SUMMARY OF THE INVENTION

In view of the above points, it is an object of the present invention to provide an improved refrigeration cycle device with a mixed refrigerant.

It is another object of the present invention to provide a refrigeration cycle device, in which a mixed refrigerant circulates, that can stably operate in a low-temperature region or a high-temperature region.

Furthermore, it is another object of the present invention to provide a refrigeration cycle device, in which a mixed refrigerant circulates, that can stably operate in a range from a low-temperature region to a high-temperature region.

According to one aspect of the present invention, a refrigeration cycle device includes a refrigerant cycle including a compressor, a condenser, an expansion valve and an evaporator, which are coupled in this order; and a mixed refrigerant made of a plurality of component refrigerants, which is circulated in the refrigerant cycle. The expansion valve includes a valve portion configured to adjust an amount of the mixed refrigerant supplied into the evaporator based on an opening degree of the valve portion, and a power element configured to adjust the opening degree of the valve portion based on a pressure of a filled fluid that is filled inside the power element. A slope of a saturated vapor pressure curve of the filled fluid is larger than a slope of a saturated vapor pressure curve of the mixed refrigerant.

In the above configuration, the opening degree, which corresponds to a load, of the expansion valve can be obtained. When the slope of the saturated vapor pressure curve of the filled fluid is larger than the slope of the saturated vapor pressure curve (SV0) of the mixed refrigerant, the opening degree of the expansion valve can be prevented from exceeding in a low-temperature region. When the slope of the saturated vapor pressure curve of the filled fluid is larger than the slope of the saturated vapor pressure curve (SV0) of the mixed refrigerant, the opening degree of the expansion valve can be prevented from becoming too little in a high-temperature region.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a refrigeration cycle device according to an embodiment of the present invention;

FIG. 2 is a temperature-pressure graph showing a saturated vapor pressure curve of a refrigerant according to the embodiment of the present invention;

FIG. 3 is a temperature-pressure graph showing a vapor pressure of a filled fluid in a power element of an expansion valve; and

FIG. 4 is a temperature-pressure graph showing a characteristic of a valve-open pressure in the expansion valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment

Hereinafter, an embodiment that is applied to a refrigeration cycle device 10 of a refrigerator will be described. As shown in FIG. 1, the refrigeration cycle device 10 includes a compressor 20, a condenser 30, an expansion valve 40 and an evaporator 50. These components are connected by plural pipes in this order to form a closed circuit. In the refrigeration cycle device 10, an internal heat exchanger 60 for exchanging heat between a high-pressure refrigerant, which flows between the condenser 30 and the expansion valve 40, and a low-pressure refrigerant, which flows between the evaporator 50 and the compressor 20.

The refrigeration cycle device 10 is used for the refrigerator. A refrigerant is compressed by the compressor 20 to become the high temperature and high pressure refrigerant. The compressor 20 is driven by an internal combustion engine or an electric motor. A fixed-capacity type compressor or a variable-capacity type compressor may be used as the compressor 20. The condenser 30 is a high-pressure side heat exchanger. The condenser 30 is coupled to a discharge portion of the compressor 20. The refrigerant is condensed by exchanging heat with ambient air to become liquid. The expansion valve 40 is a decompressor. The expansion valve 40 decompresses the liquid refrigerant flowing out of the condenser 30 in iso-enthalpy and expands the refrigerant. The expansion valve 40 controls the throttle opening degree such that a state of the refrigerant at an outlet portion of the evaporator 50 becomes a predetermined state. The expansion valve 40 is a temperature-sensitive expansion valve that detects the state of the refrigerant based on a temperature. The evaporator 50 is a low-pressure side heat exchanger, and is referred to as a cooler or a heat absorber. The evaporator 50 cools air in a freezer as an object to be cooled by evaporating the refrigerant in the evaporator 50.

The expansion valve 40 will be described with reference to FIG. 1. An external-equalizing expansion valve is used as the expansion valve 40. The expansion valve 40 includes a valve portion 41 that adjusts the amount of the refrigerant supplied into the evaporator 50, and a power element 42 that adjusts the opening degree of the valve portion 41. The valve portion 41 is configured by a valve seat, a valve disc and a valve-closing spring. The power element 42 as a temperature-sensitive portion is a fluid pressure type device that can function as a detection portion for detecting the state of the refrigerant at the outlet portion of the evaporator 50, a control portion for controlling an operation degree of the valve portion 41 such that the state of the refrigerant corresponds to a target state, and a drive portion for adjusting the opening degree of the valve portion 41 depending on the operation degree.

The power element 42 includes a diaphragm 43 as a pressure-sensitive member. The diaphragm 43 is divided into a first chamber 44 and a second chamber 45. A valve shaft 46 for driving the valve disc is connected to the diaphragm 43. The diaphragm 43 is displaced by a differential pressure between the first chamber 44 and the second chamber 45, and adjusts the opening degree of the valve portion 41. The first chamber 44 is communicated with a temperature-sensitive tube 48 through a pipe 47, and forms an enclosed space. A fluid is filled in the first chamber 44. The filled fluid in the first chamber 44 is a two-phase refrigerant and auxiliary gas for adjusting condition of the refrigerant. The temperature-sensitive tube 48 is provided in contact with a pipe in the vicinity of the outlet portion of the evaporator 50. Thereby, the temperature of the refrigerant at the outlet portion of the evaporator 50 is conducted to the filled fluid in the first chamber 44. The filled fluid detects the temperature of the refrigerant at the outlet portion of the evaporator 50. The filled fluid changes a pressure of the first chamber 44 depending on the temperature of the refrigerant at the outlet portion of the evaporator 50. The second chamber 45 is communicated with a passage in the vicinity of the outlet portion of the evaporator 50 through a pipe 49. Thereby, an evaporating pressure of the refrigerant in the evaporator 50 is introduced into the second chamber 45. In the expansion valve 40, the diaphragm 43 is displaced by a differential pressure between the evaporating pressure in the evaporator 50 and the pressure depending on the temperature of the refrigerant at the outlet portion of the evaporator 50.

A circulating refrigerant is a mixed refrigerant that is made by mixing plural component refrigerants. Saturated vapor pressure curves of the respective plural component refrigerants are different each other. The circulating refrigerant may include three or more component refrigerants. The mixed refrigerant includes a first component refrigerant, a second component refrigerant and a third component refrigerant. The boiling points of the component refrigerants decrease in the following order; the first component refrigerant, the second component refrigerant, and the third component refrigerant. The filled fluid in the power element 42 is only one component refrigerant. Thereby, the refrigerant can be easily filled in the power element 42.

FIG. 2 to FIG. 4 are temperature-pressure graphs, in which the horizontal axis indicates a temperature T (° C.) and the vertical axis indicates a pressure P (MPa). FIG. 2 shows a saturated vapor pressure curve SV0 of the mixed refrigerant, and saturated vapor pressure curves SV1, SV2, SV3 of the respective component refrigerants. As shown in FIG. 2, a saturated vapor pressure of the first component refrigerant is the highest, and a saturated vapor pressure of the third component refrigerant is the lowest. The saturated vapor pressure curve SV0 of the mixed refrigerant is located between the saturated vapor pressure curves of the two component refrigerants, which have the relatively low saturated vapor pressures. Specifically, the saturated vapor pressure curve SV0 of the mixed refrigerant is located between the saturated vapor pressure curve SV2 of the second component refrigerant and the saturated vapor pressure curve SV3 of the third component refrigerant.

A slope of the saturated vapor pressure curve SV1 of the first component refrigerant is the largest, and a slope of the saturated vapor pressure curve SV3 of the third component refrigerant is the smallest. The slope of the saturated vapor pressure curve SV1 of the first component refrigerant, which corresponds to the filled fluid, is larger than a slope of the saturated vapor pressure curve SV0 of the mixed refrigerant in a range from a low-temperature region to a high-temperature region. A slope of the saturated vapor pressure curve SV2 of the second component refrigerant is larger than the slope of the saturated vapor pressure curve SV0 of the mixed refrigerant in the range from the low-temperature region to the high-temperature region. The slope of the saturated vapor pressure curve SV3 of the third component refrigerant is smaller than the slope of the saturated vapor pressure curve SV0 of the mixed refrigerant in the range from the low-temperature region to the high-temperature region.

A saturated vapor pressure difference SD between the saturated vapor pressure curve SV1 of the first component refrigerant and the saturated vapor pressure curve SV0 of the mixed refrigerant gradually increases as an evaporation temperature increases. Thereby, a saturated vapor pressure difference SD2 in a high-load temperature is larger than a saturated vapor pressure difference SD1 in a low-load temperature. In the present embodiment, the high-load temperature is −10° C. and the low-load temperature is −40° C.

As a comparative example, a saturated vapor pressure curve SVC of a comparative refrigerant is shown in FIG. 2. The comparative refrigerant differs from the component refrigerants of the mixed refrigerant. When the comparative refrigerant is used for the filled fluid, the slope of the saturated vapor pressure curve SVC is smaller than the slope of the saturated vapor pressure curve SV0 of the mixed refrigerant.

FIG. 3 illustrates a characteristic curve showing a vapor pressure of the fluid after auxiliary gas such as helium is added to the respective component refrigerants. The characteristic curve in FIG. 3 is adjusted by the auxiliary gas such that the circulating refrigerant is controlled to be a predetermined state at a temperature of −30° C., which is a standard temperature for the refrigerator. A characteristic curve SV1+ shows the characteristic after the first component refrigerant is adjusted. A characteristic curve SV2+ shows the characteristic after the second component refrigerant is adjusted. A characteristic curve SV3+ shows the characteristic after the third component refrigerant is adjusted. A characteristic curve SVC+ shows the characteristic after the comparative refrigerant is adjusted. The slope of the saturated vapor pressure curve of the respective component refrigerants can be kept even when the adjustment by the auxiliary gas is performed.

FIG. 4 illustrates a characteristic curve showing a valve-open pressure based on bias force such as the valve-closing spring of the expansion valve 40. A characteristic curve SV1D shows the valve-open characteristic of the filled fluid including the first component refrigerant. A characteristic curve SVCD shows the valve-open characteristic of the filled fluid including the comparative refrigerant.

A slope of the characteristic curve SVCD is smaller than a slope of the characteristic curve SV1D. Thus, the characteristic curve SVCD is located at a higher pressure side than the characteristic curve SV1D in the low-temperature region that is lower than the standard temperature. In the low-temperature region, the characteristic curve SVCD is away from the saturated vapor pressure curve SV0 of the mixed refrigerant in the pressure axis direction. That is, a pressure difference between the characteristic curve SVCD and the saturated vapor pressure curve SV0 increases as a temperature increases in the low-temperature region. The characteristic curve SVCD has a pressure difference PD1, which is larger than a pressure difference PD0 at the standard temperature, in the low-temperature region. Thereby, the excessive pressure difference is generated in the low-temperature region, and the opening degree becomes excessively large. The characteristic curve SVCD is located at a lower pressure side than the characteristic curve SV1D in the high-temperature region that is higher than the standard temperature. The characteristic curve SVCD has a pressure difference PD2, which is smaller than the pressure difference PD0 at the standard temperature, in the high-temperature region. Thereby, when the characteristic curve SVCD is used, the opening degree becomes insufficient in the high-temperature region.

In contrast, in the characteristic curve SV1D, the pressure difference gradually increases from the low-temperature region to the high-temperature region. The characteristic curve SV1D has a pressure difference PD3, which is smaller than the pressure difference PD0 at the standard temperature, in the low-temperature region. The characteristic curve SV1D has a pressure difference PD4, which is larger than the pressure difference PD0 at the standard temperature, in the high-temperature region. Thereby, the opening degree of the expansion valve 40 gradually increases from the low-temperature region to the high-temperature region.

In the present embodiment, R404A is used as the mixed refrigerant. The mixed refrigerant R404A includes R125 as the first component refrigerant, R143a as the second component refrigerant and R134a as the third component refrigerant. The filled fluid is R125 that is the first component refrigerant. As the comparative refrigerant, R22 is used.

When the refrigeration cycle device 10 is driven, the expansion valve 40 adjusts the opening degree of the valve portion 41 such that the state of the refrigerant at the outlet portion of the evaporator 50 corresponds to the target state. The refrigeration cycle device 10 as the refrigerator can drive in the range from the low-temperature region to the high-temperature region of the evaporation temperature. In the vicinity of −40° C. of the low-load temperature corresponding to a low-load state as the refrigerator is regarded as a very low-temperature in the evaporation temperature of the refrigerator. In the vicinity of the low-load temperature, a flow amount of the refrigerant decreases and the opening degree of the expansion valve 40 also decreases. In contrast, in the vicinity of −10° C. of the high-load temperature corresponding to a high-load state as the refrigerator, a large quantity of the refrigerant corresponding to the high-load is allowed to flow.

The slope of the saturated vapor pressure curve of the component refrigerant selected as the filled fluid is larger than the slope of the saturated vapor pressure curve of the mixed refrigerant as the circulating refrigerant when the evaporation temperature is in the low-temperature region, particularly, in the very low-temperature region. Thereby, the opening degree of the expansion valve 40 can be prevented from exceeding the opening degree based on the load in the low-temperature region, particularly, in the very low-temperature region. The large slope in the low-temperature region affects the pressure change and the opening degree change sufficiently with respect to the temperature change. Therefore, the stable control can be kept in the range of the small opening degree in the vicinity of the low-load temperature, and the control of the degree of superheat can be stably controlled even in the low-temperature region, specifically, in the very low-temperature region.

It is preferable that the saturated vapor pressure curve of the component refrigerant selected as the filled fluid is similar to the saturated vapor pressure curve SV0 of the mixed refrigerant when the evaporation temperature is in the high-temperature region. Thereby, the relatively-large opening degree corresponding to the high-load can be obtained and the opening degree of the expansion valve can be prevented from exceeding the opening degree based on the load in the high-temperature region including the high-load temperature. Therefore, the liquid back can be avoided and the stable driving can be operated in the high-temperature region.

Other Embodiments

The present invention is not limited to the above embodiment, and can be modified variously as follows. In the above embodiment, the refrigeration cycle device using R404A as the circulating refrigerant is described. However, a refrigeration cycle device using various mixed refrigerants as the circulating refrigerant may be used. Moreover, a refrigeration cycle device using plural refrigerants as the filled fluid may be used. One component refrigerant or plural component refrigerants other than the component refrigerant having the smallest slope of the saturated vapor pressure curve may be used as the filled fluid. For example, the second component refrigerant R143a may be used as the filled fluid. The present invention can be applied to a joint-type expansion valve or a box-type expansion valve. The present invention can be applied to an internal-equalizing expansion valve or an external-equalizing expansion valve. The present invention can be applied to an expansion valve having a cassette-type structure. Furthermore, the present invention can be applied to a refrigeration cycle device having an ejector.

While the invention has been described with reference to preferred embodiments thereof, it is to be understood that the invention is not limited to the preferred embodiments and constructions. The invention is intended to cover various modification and equivalent arrangements. In addition, while the various combinations and configurations, which are preferred, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.

Refrigeration cycle device

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