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In an ejector cycle system, a variable throttle is disposed at an upstream side of an ejector. When high-pressure side refrigerant pressure in the ejector cycle system is approximately equal to or higher than critical pressure of the refrigerant, the variable throttle is fully opened. When the high-

In an ejector cycle system, a variable throttle is disposed at an upstream side of an ejector. When high-pressure side refrigerant pressure in the ejector cycle system is approximately equal to or higher than critical pressure of the refrigerant, the variable throttle is fully opened. When the high-pressure side refrigerant pressure is approximately lower than the critical pressure of the refrigerant, a throttle open degree of the variable throttle is reduced from the fully open degree so that high-pressure side refrigerant is decompressed in two steps of the variable throttle and the ejector. Accordingly, in both cases of a high heat load and a low heat load of the ejector cycle system, COP of the ejector cycle system can be improved.

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1. An ejector cycle system comprising: a compressor for sucking and compressing refrigerant; a radiator which cools the refrigerant discharged from the compressor; an evaporator for evaporating refrigerant; an ejector including a nozzle for converting a pressure energy of high-pressure re

1. An ejector cycle system comprising: a compressor for sucking and compressing refrigerant; a radiator which cools the refrigerant discharged from the compressor; an evaporator for evaporating refrigerant; an ejector including a nozzle for converting a pressure energy of high-pressure refrigerant from the radiator to a speed energy so that the high-pressure refrigerant is decompressed and expanded and gas refrigerant evaporated in the evaporator is sucked, and a pressure-increasing portion in which the speed energy is converted to the pressure energy so that the pressure of refrigerant is increased while refrigerant discharged from the nozzle and the gas refrigerant from the evaporator are mixed; a decompression unit disposed at an upstream side of the nozzle in a refrigerant flow direction, for decompressing the refrigerant from the radiator; and a gas-liquid separator for separating the refrigerant flowing from the ejector into gas refrigerant and liquid refrigerant, wherein: when pressure of the refrigerant before flowing into the decompression unit is equal to or higher than a predetermined pressure, a throttle open degree of the decompression unit becomes larger than that when the pressure of the refrigerant before flowing into the decompression unit is lower than the predetermined pressure.2. The ejector cycle system according to claim 1, wherein the predetermined pressure is critical pressure of the refrigerant.3. The ejector cycle system according to claim 2, wherein: when the pressure of the refrigerant before flowing into the decompression unit is equal to or higher than the critical pressure of the refrigerant, the decompression unit is fully opened. 4. The ejector cycle system according to claim 3, wherein: when the pressure of the refrigerant before flowing into the decompression unit is lower than the critical pressure of the refrigerant, the opening degree of the decompression unit is reduced as the pressure of the refrigerant before flowing into the decompression unit becomes lower. 5. The ejector cycle system according to claim 1, wherein: the valve open degree is set larger as the pressure of the refrigerant before flowing into the decompression unit becomes higher. 6. The ejector cycle system according to claim 1, wherein: the gas-liquid separator has a gas refrigerant outlet coupled to a refrigerant suction side of the compressor, and a liquid refrigerant outlet coupled to the side of the evaporator. 7. The ejector cycle system according to claim 6, further comprising a variable throttle unit disposed between the evaporator and the gas-liquid separator, for controlling at least a flow amount of refrigerant flowing into the evaporator. 8. The ejector cycle system according to claim 7, wherein: the variable throttle unit is an expansion valve in which a valve open degree is controlled so that a refrigerant heating degree at an outlet side of the evaporator becomes a predetermined degree. 9. The ejector cycle system according to claim 7, wherein: the variable throttle unit is a pressure difference valve in which a valve open degree is controlled such that a pressure different between a refrigerant inlet side and a refrigerant outlet side of the pressure difference valve becomes a predetermined difference.