Patent ID: 7000394

Claim:
A Rankine cycle system that includes an evaporator ( 3 ) for heating a liquid and generating a vapor, an expander ( 4 ) for expanding the vapor supplied from the evaporator ( 3 ) and outputting a shaft torque, and a condenser ( 5 ) for cooling the vapor discharged from the expander ( 4 ) and turning the vapor back into the liquid, wherein with regard to a given relationship between pressure (Pevp) and temperature (Tevp) of the vapor that is taken into the expander ( 4 ), an expansion ratio (ε 1 , ε 2 ) of the vapor that is taken into and discharged from the expander ( 4 ) is set at a predetermined expansion ratio (ε) according to the given relationship so that pressure (Pexp 2 ) and temperature (Texp 2 ) of the vapor that is discharged from the expander ( 4 ) coincide with target values, wherein the expander ( 4 ) includes an expansion chamber ( 39 ) that has the vapor at a discharge position thereof in a superheated vapor region, and the expansion chamber ( 39 ) is formed from a cylinder chamber.