1. Field of the Invention
The present invention relates to an ejector cycle including an ejector, and a control method for controlling the ejector cycle.
2. Description of Related Art
In an ejector cycle described in JP-A-6-11197, refrigerant is decompressed and expanded in a nozzle of an ejector so that gas refrigerant evaporated in an evaporator is sucked, and pressure of refrigerant to be sucked into a compressor is increased by converting expansion energy to pressure energy. In the ejector cycle, refrigerant discharged from the compressor is circulated to a condenser (radiator) so as to radiate heat absorbed in the evaporator. The refrigerant cooled in the condenser is decompressed and expanded in a nozzle in iso-enthalpy, and refrigerant evaporated in the evaporator is drawn into the ejector by pumping operation due to entrainment of high-speed refrigerant jetted from the nozzle. That is, by the pumping operation generated in the ejector, low-pressure side refrigerant circulates a gas-liquid separator→the evaporator→the ejector→the gas-liquid separator, in this order. Accordingly, in the ejector cycle, a force for circulating the low-pressure side refrigerant is small, as compared with a general vapor-compression refrigerant cycle where the low-pressure side refrigerant is directly drawn by the compressor.
Further, in an ejector cycle where an evaporation temperature becomes extremely low, viscosity degree of oil (lubrication oil) mixed in refrigerant becomes larger, and the lubrication oil may stay in the evaporator. In this case, a sufficient amount of the lubrication oil cannot be returned to the compressor, and burning of the compressor may be caused. Hear, the lubrication oil is used for lubricating a sliding portion in the compressor, and is drawn into the compressor together with the refrigerant.