Rankine cycle system

Abstract

A Rankine cycle system includes: an evaporator for heating water with thermal energy of exhaust gas of an engine so as to generate steam; an expander for converting the thermal energy of the steam generated by the evaporator into mechanical energy; and a distribution device for manipulating the amount of water supplied to the evaporator in order to make the temperature of the steam supplied from the evaporator to the expander coincide with a target temperature. The distribution device controls a distribution ratio between the amount of water supplied to the entrance of the evaporator and the amount of water supplied to a portion partway along the evaporator, thereby suppressing an overshoot in the temperature of the gas-phase working medium due to a sudden increase in the thermal energy of the exhaust gas.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2005-69366 filed on Mar. 11, 2005 the entire contents of which are hereby incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a Rankine cycle system that includes 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, an expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy, and temperature control means for manipulating the amount of liquid-phase working medium supplied to the evaporator in order to make the temperature of the gas-phase working medium supplied from the evaporator to the expander coincide with a target temperature. [0004] 2. Description of Background Art [0005] Japanese Utility Model Registra...

AI Technical Summary

Benefits of technology

[0008] The present invention has been accomplished under the above-mentioned circumstances, and it is an object thereof to carry out control with good responsiveness so that the temperature of steam generated in an evaporator does not overshoot a target temperature even when the operating conditions of the engine change and the energy of the exhaust gas increases rapidly.

[0010] With the first feature, the temperature control means for manipulating the amount of liquid-phase working medium supplied to the evaporator controls the distribution ratio of the amount of liquid-phase working medium supplied to the entrance of the evaporator and the amount of liquid-phase working medium supplied to the portion partway along the evaporator in order to make the temperature of the gas-phase working medium supplied from the evaporator to the expander of the Rankine cycle system coincide with the target temperature. Therefore, it is possible to suppress an overshoot in the temperature of the gas-phase working medium due to a sudden increase in the thermal energy of the exhaust gas by supplying the liquid- phase working medium to a portion partway along the evaporator.

[0012] With the second feature, when the temperature of the gas-phase working medium cannot be controlled at the target temperature by supplying the liquid-phase working medium only from the entrance of the evaporator due to a sudden change in the thermal energy of the exhaust gas, part of the liquid-phase working medium that has been supplied to the entrance of the evaporator until then is supplied to the portion partway along the evaporator. Therefore, it is possible to decrease the temperature of the gas-phase working medium and reliably prevent the occurrence of overshooting.

[0014] With the third feature, when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature, part of the liquid-phase working medium that has been supplied to the entrance of the evaporator until then is supplied to the portion partway along the evaporator. Therefore, it is possible to decrease the temperature of the gas-phase working medium and reliably prevent the occurrence of overshooting.

[0016] According to a fifth feature of the present invention, at least when the air / fuel ratio is stoichiometric, the temperature control means increases the distribution ratio of the liquid-phase working medium to a portion partway along the evaporator as compared with the case of another air / fuel ratio.

[0017] With the fourth and fifth features, when the air / fuel ratio is stoichiometric the temperature of exhaust gas rises and the thermal energy increases as compared with when it is rich or lean, but in this case the liquid-phase working medium is supplied to the portion partway along the evaporator at the predetermined distribution ratio according to the air / fuel ratio, that is, the distribution ratio of the liquid-phase working medium supplied to the portion partway along the evaporator is increased at least when the air / fuel ratio is stoichiometric as compared with when it is another air / fuel ratio. Therefore, it is possible to suppress an excessive increase in the temperature of the gas-phase working medium supplied from the evaporator to the expander, and it is also possible to suppress an excessive decrease in the temperature of the gas-phase working medium supplied from the evaporator to the expander when the air / fuel ratio is rich or lean, thereby making the temperature of the gas-phase working medium coincide with the target temperature with good precision.

Problems solved by technology

Thus, the steam temperature might overshoot the target temperature to deteriorate the operating efficiency of the expander.

However, if cylinder shut-off is carried out, since the engine output itself changes, there is a problem that this Rankine cycle system mounted in an automobile gives an uncomfortable feeling to the driver.

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