Rankine cycle system

Abstract

A Rankine cycle system includes an evaporator for heating water with thermal energy of exhaust gas of an engine for generating steam with a displacement type expander for converting thermal energy into mechanical energy. A temperature controller manipulates the amount of water supplied to the evaporator so that the temperature of the steam supplied from the evaporator to the expander coincides with a target temperature. A pressure controller manipulates the rotational speed of the expander by changing a load of the expander so that the pressure of the steam supplied from the evaporator to the expander coincides with a target pressure. The temperature controller and/or the pressure controller continue to control the amount of water supplied to the evaporator and/or the rotational speed of the expander in set ranges at least in a state in which the engine has stopped and the thermal energy of the exhaust gas has disappeared.

1 . 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 the 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 the temperature control means and/or the pressure control means continues to control the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander in set ranges at least in a state in which the engine has stopped and the thermal energy of the exhaust gas has disappeared.    
   
   
       2 . The Rankine cycle system according to  claim 1 , wherein the temperature control means continues to supply the liquid-phase working medium to the evaporator until the temperature of the gas-phase working medium decreases to at least a temperature at which the expander does not generate an output.  
   
   
       3 . The Rankine cycle system according to  claim 1 , wherein the pressure control means continues to control the rotational speed of the expander until the pressure of the gas-phase working medium decreases to at least a pressure at which the expander does not generate an output.  
   
   
       4 . The Rankine cycle system according to  claim 3 , wherein when the rotational speed of the expander decreases to a set rotational speed, the pressure control means maintains the set rotational speed; and when the expander attains a state in which no output is generated, the pressure control means stops controlling the rotational speed of the expander and allows the expander to rotate freely in a non-load state.  
   
   
       5 . The Rankine cycle system according to  claim 1 , and further including feedforward water supply amount calculating means for calculating a feedforward water supply amount for the evaporator based on the engine rotational speed fuel injection quantity and the exhaust gas temperature of the engine.  
   
   
       6 . The Rankine cycle system according to  claim 1 , and further including feedback water supply amount calculating means for calculating a feedback water supply amount based on a deviation of the steam temperature at the exit of the evaporator from a target steam temperature at the entrance of the expander by a predetermined gain.  
   
   
       7 . The Rankine cycle system according to  claim 1 , and further including a water supply amount control changeover means for controlling the water supply amount for the evaporator according to the internal density of the evaporator when the ignition switch is turned OFF.  
   
   
       8 . The Rankine cycle system according to  claim 1 , and further including a rotational speed calculating means for calculating a target rotational speed for a water supply pump based on a target water supply amount outputted by the water supply amount control changeover means and a steam pressure at the exit of the evaporator.  
   
   
       9 . The Rankine cycle system according to  claim 8 , wherein the rotational speed of the motor is controlled for driving the water supply pump wherein the rotational speed coincides with the target rotational speed.  
   
   
       10 . The Rankine cycle system according to  claim 1 , and further including a feedback term calculation means for calculating a target torque of a motor/generator based on a deviation of a rotational speed of the motor/generator from a target rotational speed outputted by a rotational speed control changeover means and a rotational speed of the expander is feedback-controlled by the target rotational speed by generating the target torque in the motor/generator.  
   
   
       11 . A Rankine cycle system comprising: 
 an evaporator for heating a liquid-phase working medium with thermal energy of exhaust gas of an engine for generating 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;    a temperature controller for manipulating the amount of liquid-phase working medium supplied to the evaporator wherein the temperature of the gas-phase working medium supplied from the evaporator to the expander coincides with a target temperature; and    a pressure controller for manipulating the rotational speed of the expander by changing a load of the expander wherein the pressure of the gas-phase working medium supplied from the evaporator to the expander coincides with a target pressure,    wherein the temperature controller and/or the pressure controller continue to control the amount of liquid-phase working medium supplied to the evaporator and/or the rotational speed of the expander in set ranges at least in a state in which the engine has stopped and the thermal energy of the exhaust gas has disappeared.    
   
   
       12 . The Rankine cycle system according to  claim 11 , wherein the temperature controller continues to supply the liquid-phase working medium to the evaporator until the temperature of the gas-phase working medium decreases to at least a temperature at which the expander does not generate an output.  
   
   
       13 . The Rankine cycle system according to  claim 11 , wherein the pressure controller continues to control the rotational speed of the expander until the pressure of the gas-phase working medium decreases to at least a pressure at which the expander does not generate an output.  
   
   
       14 . The Rankine cycle system according to  claim 13 , wherein when the rotational speed of the expander decreases to a set rotational speed, the pressure controller maintains the set rotational speed; and when the expander attains a state in which no output is generated, the pressure controller stops controlling the rotational speed of the expander and allows the expander to rotate freely in a non-load state.  
   
   
       15 . The Rankine cycle system according to  claim 11 , and further including a feedforward water supply amount calculator for calculating a feedforward water supply amount for the evaporator based on the engine rotational speed fuel injection quantity and the exhaust gas temperature of the engine.  
   
   
       16 . The Rankine cycle system according to  claim 11 , and further including a feedback water supply amount calculator for calculating a feedback water supply amount based on a deviation of the steam temperature at the exit of the evaporator from a target steam temperature at the entrance of the expander by a predetermined gain.  
   
   
       17 . The Rankine cycle system according to  claim 11 , and further including a water supply amount control changeover for controlling the water supply amount for the evaporator according to the internal density of the evaporator when the ignition switch is turned OFF.  
   
   
       18 . The Rankine cycle system according to  claim 11 , and further including a rotational speed calculator for calculating a target rotational speed for a water supply pump based on a target water supply amount outputted by the water supply amount control changeover and a steam pressure at the exit of the evaporator.  
   
   
       19 . The Rankine cycle system according to  claim 18 , wherein the rotational speed of the motor is controlled for driving the water supply pump wherein the rotational speed coincides with the target rotational speed.  
   
   
       20 . The Rankine cycle system according to  claim 11 , and further including a feedback term calculator for calculating a target torque of a engine based on a deviation of a rotational speed of the engine from a target rotational speed outputted by a rotational speed control changeover and a rotational speed of the expander is feedback-controlled by the target rotational speed by generating the target torque in the engine.