Rankine cycle system

A Rankine cycle system comprising:

• an evaporator for heating a liquid-phase working medium with thermal energy of exhaust gas of an engine so as to generate a gas-phase working medium;
• a displacement type expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy;
• temperature control means for manipulating an amount of liquid-phase working medium supplied to the evaporator so that the temperature of the gas-phase working medium supplied from the evaporator to the expander coincides with a target temperature;
• and
• pressure control means for manipulating the rotational speed of the expander by changing a load of the expander so that the pressure of the gas-phase working medium supplied from the evaporator to the expander coincides with a target pressure;
• wherein, simultaneously with operating conditions of the engine shifting to a fuel supply suspension state or a low load state, the temperature control means suspends supply of the liquid-phase working medium to the evaporator, and the pressure control means decreases the rotational speed of the expander as quickly as possible within a range in which the pressure of the gas-phase working medium does not exceed the target pressure.