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Supercritical refrigeration cycle system

Supercritical refrigeration cycle system description/claims

1. Field of the Invention

This invention relates to a supercritical refrigeration cycle system of a vapor-compression-type comprising a plurality of evaporators in which the refrigeration pressure on high pressure side increases to at least the critical pressure.

2. Description of the Related Art

A conventional refrigeration cycle system of this type is known to include a compressor for compressing a refrigerant, a radiator for cooling the refrigerant discharged from the compressor, a first decompressor and a second decompressor for reducing the pressure of the refrigerant flowing out of the radiator, a first evaporator for evaporating the refrigerant flowing out of the first decompressor, a second evaporator for evaporating the refrigerant flowing out of the second decompressor, and a solenoid valve for controlling the refrigerant flow from the radiator into the second decompressor, wherein the air blown into the front part of the compartment is cooled by the first evaporator and the air blown into the rear part of the compartments is cooled by the second evaporator (Japanese Unexamined Patent Publication No. 2000-35250 (Patent Document 1)).

As a measure for suppressing the production cost, on the other hand, a system in which the number of expansion valves for decompressing the refrigerant is reduced and the decompressed refrigerant is distributed to each evaporator has been proposed (Japanese Unexamined Patent Publication No. 2005-106318 (Patent Document 2)).

In the refrigeration cycle system described in Patent Document 1, however, if the low pressure of the refrigerant is reduced during the transient period of starting or increasing the rotational speed of the compressor, and because a temperature-type expansion valve is used as a second decompressor, the drop in the low pressure immediately acts to open the second decompressor as shown in the example of the behavior of starting the system using a mechanical expansion valve (see FIGS. 11A, 11B). Further, the temperature drop at the evaporator outlet is accompanied by the delay due to heat transmission and, therefore, the valve opening degree of the second decompressor is excessively increased temporarily, with the result that the refrigerant flow rate is not properly distributed to each evaporator, thereby posing the problem that the blowout air temperature, of the evaporator short in the refrigerant flow rate, increases.

In the case where an electrical expansion valve is used as a second decompressor, on the other hand, the low pressure has no effect. Even in the case where the low pressure drops during the transient period, therefore, the valve opening degree is not excessively increased. Although the detection of a superheat amount requires the detection of the refrigerant temperature at the outlet of the evaporator, an excessively fast response destabilizes the operation of the electrical expansion valve and leads to the problem of hunting, etc. To secure stability, the response to temperature detection is required to be somewhat slow. In the case where the thermal load or the rotational speed of the compressor undergo an abrupt change, therefore, the refrigerant flows excessively, temporarily, and the resultant increased superheat amount of the first evaporator may increase the blowout air temperature.

In the refrigeration cycle system described in Patent Document 2, on the other hand, the high-pressure refrigerant, after being decompressed in the expansion valve, is required to be sent to each evaporator by piping. In the automotive air conditioning system, for example, the refrigerant is sent to the front evaporator in the dashboard for the front seats on the one hand and must send the low-pressure low-temperature refrigerant to the rear evaporator for the rear seats through a long pipe. To suppress the heat loss in the long pipe and the frosting of the pipe, the pipe is required to be covered by a heat insulating material.

This invention has been developed to solve the problems described above and the object thereof is to provide a supercritical refrigeration cycle system having a simple flow path structure in which the refrigerants flowing in a plurality of evaporators are appropriately controlled to suppress the increase in the blowout air temperature.

In order to achieve the object described above, this invention employs the technical means described below. Specifically, the supercritical refrigeration cycle system of vapor compression type according to the invention, in which the high pressure in the refrigeration cycle reaches a value not lower than the critical pressure of the refrigerant, comprises a compressor (1) for sucking in and compressing the refrigerant, a radiator (2) for radiating the heat of the high-pressure refrigerant discharged from the compressor (1), a plurality of decompressors (5, 12) into which the high-pressure refrigerant flowing out from the radiator (2) is distribute and flows, a first evaporator (6) for evaporating the refrigerant decompressed by the first decompressor (5), and a second evaporator (9) for evaporating the refrigerant decompressed by the second decompressor (12), wherein the refrigerant flowing out of one of the first evaporator (6) and the second evaporator (9) flows into the other evaporator.

According to a first aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein the high-pressure refrigerant is distributed and then decompressed, and the refrigerant flowing out of one of the first evaporator (6) and the second evaporator (9) is rendered to flow into the other evaporator, so that the refrigerant flowing through each evaporator can be properly controlled with a simple refrigerant path configuration. Especially, a stable air-conditioning air can be supplied by reducing the difference of the blowout air temperatures between the evaporators.

According to a second aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein one of the plurality of the decompressors constitutes a high-pressure control valve (5) for maintaining a high pressure maximizing the coefficient of performance of the refrigeration cycle.

In the second aspect of the invention, one of the plurality of the decompressors constitutes the high-pressure control valve (5) and the operation efficiency of the refrigeration cycle is improved.

According to a third aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein the refrigerant flowing out of the second evaporator (9) flows into the first evaporator (6), and the second decompressor constitutes a mechanical superheat control valve (12) for controlling the superheat amount of the refrigerant at the outlet of the second evaporator (9).

In the third aspect of the invention, the control circuit for controlling the superheat amount is eliminated and the cycle configuration is simplified.

According to a fourth aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein the refrigerant flowing out of the second evaporator (9) flows into the first evaporator (6), and the second decompressor constitutes a fixed diaphragm unit (14) or a differential pressure valve with the opening area thereof variable by the pressure before and after the diaphragm mechanism.

In the fourth aspect of the invention, the trouble of hunting is not caused in the high pressure control which otherwise might be caused by the superheat control of the refrigerant at the outlet of the evaporator, thereby improving the operation efficiency of the refrigeration cycle.

According to a fifth aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein the refrigerant flowing out of the second evaporator (9) flows into the first evaporator (6) and the second decompressor makes up an electrical expansion valve (19).

In the fifth aspect of the invention, the fact that the second decompressor constitutes the electrical expansion valve (19) makes it possible to switch on/off the refrigerant flowing into the second evaporator (9) with the electrical expansion valve alone without using any on/off solenoid valve.

According to a sixth aspect of the invention, there is provided a supercritical refrigeration cycle system, wherein the opening degree of the electrical expansion valve (19) is controlled based on the temperature information of the refrigerant before and after the second evaporator (9).

In the sixth aspect of the invention, the refrigerant flow can be controlled with a fast response.

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