Patent ID: 8042347

Claim:
A compressor inlet pressure estimation apparatus for a refrigeration cycle system, the refrigeration cycle system comprising: a compressor for sucking, compressing and discharging a refrigerant; a cooler for cooling the refrigerant discharged from the compressor; a decompressor for reducing the pressure of the refrigerant cooled by the cooler; an evaporator for evaporating the refrigerant, which is reduced in pressure by the decompressor, by absorbing heat from air, the compressor inlet pressure estimation apparatus comprising: a temperature sensor for detecting the surface temperature of the evaporator; a first refrigerant temperature estimation means for estimating the refrigerant temperature in the evaporator based on a function set in accordance with the temperature detected by the temperature sensor; and a pressure estimation means for estimating the refrigerant inlet pressure of the compressor based on the refrigerant temperature estimated by the first refrigerant temperature estimation means; wherein the function is a first-order lead function for estimating the refrigerant temperature in the evaporator based on a change rate of the surface temperature of the evaporator, the compressor inlet pressure estimation apparatus further comprising: a second refrigerant temperature estimation means for estimating the refrigerant temperature in the evaporator by a means different from the first refrigerant temperature estimation means; and a setting means for setting the apparatus in such a manner that a value estimated by the second refrigerant temperature estimation means is used as an estimated temperature during a predetermined time period after starting the compressor and a value estimated by the first refrigerant temperature estimation means is used as an estimated temperature after the lapse of the predetermined time period, wherein the second refrigerant temperature estimation means estimates the refrigerant temperature in the evaporator after a certain time following the start of the compressor, using a first-order lag function for indicating a relationship between the time and the estimated refrigerant temperature in the evaporator, and wherein the first-order lag function connects, with a downwardly convex curve in the X-Y coordinate system with Y axis representing the estimated refrigerant temperature in the evaporator and X axis the time, the surface temperature of the evaporator detected by the temperature sensor at the time of starting the compressor and an estimated target temperature providing the estimated refrigerant temperature after a predetermined time following the start of the compressor.