Rankine cycle system
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.
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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 INVENTION1. Field of the Invention
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.
2. Description of Background Art
Japanese Utility Model Registration Publication No. 2-38162 discloses an arrangement in which the temperature of steam generated by a waste heat once-through boiler using, as a heat source, exhaust gas of an engine rotating at a constant speed is compared with a target temperature. When a water supply signal obtained from this deviation is used in a feedback control of the amount of water supplied to the waste heat once-through boiler, a feedforward signal, that is obtained by correcting with steam pressure a degree of throttle opening signal of the engine, is added to the above-mentioned feedback signal, thus compensating for variation in the load of the engine to improve the precision of control.
In the above-mentioned conventional arrangement, since the steam temperature is controlled only by manipulating the amount of water supplied to the evaporator, in the case where the load of the engine changes suddenly and the thermal energy of the exhaust gas increases rapidly, there is a possibility that a response lag might occur in the steam temperature due to the length of a water supply pipe or the heat capacity of the evaporator. Thus, the steam temperature might overshoot the target temperature to deteriorate the operating efficiency of the expander.
As another method for preventing the steam temperature from overshooting the target temperature when the load of the engine changes suddenly, cylinder shut-off in the engine could be considered. 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.
SUMMARY OF THE INVENTIONThe 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.
In order to achieve the above object, according to a first feature of the present invention, there is provided 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 with an expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy. Temperature control means are provided 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, wherein the temperature control means controls a distribution ratio between the amount of liquid-phase working medium supplied to the entrance of the evaporator and the amount of liquid-phase working medium supplied to a portion partway along the evaporator.
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.
According to a second feature of the present invention, the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the thermal energy of the exhaust gas changes suddenly accompanying a change in load of the engine and 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.
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.
According to a third feature of the present invention, the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature.
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.
According to a fourth feature of the present invention, the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
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.
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.
The above-mentioned object, other objects, characteristics, and advantages of the present invention will become apparent from a preferred embodiment that will be described in detail below by reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGSThe present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein:
The intermediate position water supply may be independent from the main water supply, and may optionally involve supplying water via another route and pump, etc.
The target steam temperature is determined as follows. That is, as shown in
Returning to
The above-mentioned operation is now explained in further detail by reference to the flowchart of
In step S1, the main water supply amount, the intermediate position water supply amount, and the total water supply amount are all set at 0. In the subsequent step S2, the engine rotational speed, intake negative pressure, fuel injection quantity, and exhaust gas temperature are detected, in step S3 an air/fuel ratio A/F is calculated from the engine rotational speed, the intake negative pressure, and the fuel injection quantity, and in step S4 the exhaust gas energy is estimated. Subsequently, in step S5, the total water supply amount (a feedforward value) is looked up in the map of
In the subsequent step S6, the steam temperature at the exit of the evaporator 11 is measured; if in step S7 the exit steam temperature is higher than the target steam temperature, then in step S8 a distribution ratio (intermediate position water supply amount/total water supply amount) of the intermediate position water supply amount is looked up in the map of
In the case where the air/fuel ratio A/F is rich, since the temperature of the exhaust gas decreases as compared with the case where it is stoichiometric (theoretical air/fuel ratio), and the temperature of steam at the exit of the evaporator 11 also decreases, the proportion of the intermediate position water supply amount (intermediate position water supply amount distribution ratio) for decreasing the exit steam temperature is set low. Also in the case where it is lean, in the same manner as in the case where it is rich, the exhaust gas temperature decreases as compared with the case where it is stoichiometric. Therefore, the proportion of the intermediate position water supply amount is set low as in the case of rich. Thus, in the case where it is stoichiometric, the proportion of the intermediate position water supply amount is set high. In step S9 an intermediate position water supply amount (feedforward value) is calculated by multiplying the total water supply amount by the intermediate position water supply amount distribution ratio.
The reason why the intermediate position water supply amount distribution ratio is set based on the air/fuel ratio is explained below. As shown in
Returning to the flowchart of
As shown in
Although one embodiment of the present invention is explained above, the present invention can be modified in a variety of ways as long as the modifications do not depart from the spirit and scope of the present invention.
Claims
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;
- 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,
- wherein the temperature control means controls a distribution ratio between the amount of liquid-phase working medium supplied to the entrance of the evaporator and the amount of liquid-phase working medium supplied to a portion partway along the evaporator.
2. The Rankine cycle system according to claim 1, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the thermal energy of the exhaust gas changes suddenly accompanying a change in load of the engine and 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.
3. The Rankine cycle system according to claim 1, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature.
4. The Rankine cycle system according to claim 2, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature.
5. The Rankine cycle system according to claim 1, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
6. The Rankine cycle system according to claim 2, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
7. The Rankine cycle system according to claim 3, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
8. The Rankine cycle system according to claim 4, wherein the temperature control means supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
9. The Rankine cycle system according to claim 5, wherein 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.
10. The Rankine cycle system according to claim 6, wherein at least when the air/fuel ratio is stoichiometric, the temperature control Scans 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.
11. The Rankine cycle system according to claim 7, wherein 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.
12. The Rankine cycle system according to claim 8, wherein 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.
13. 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;
- an expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy; and
- a temperature controller 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,
- wherein the temperature controller controls a distribution ratio between the amount of liquid-phase working medium supplied to the entrance of the evaporator and the amount of liquid-phase working medium supplied to a portion partway along the evaporator, and further including a feedforward liquid-phase working medium calculator for calculating a feedforward of the liquid-phase working medium based on operating conditions and a feedback liquid-phase working medium calculator for calculating a feedback of the liquid-phase working medium based on the target temperature.
14. The Rankine cycle system according to claim 13, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the thermal energy of the exhaust gas changes suddenly accompanying a change in load of the engine and 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.
15. The Rankine cycle system according to claim 13, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature.
16. The Rankine cycle system according to claim 14, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio when the temperature of the gas-phase working medium supplied from the evaporator to the expander is higher than the target temperature.
17. The Rankine cycle system according to claim 13, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
18. The Rankine cycle system according to claim 14, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
19. The Rankine cycle system according to claim 15, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
20. The Rankine cycle system according to claim 16, wherein the temperature controller supplies the liquid-phase working medium to a portion partway along the evaporator at a predetermined distribution ratio according to an air/fuel ratio.
21. The Rankine cycle system according to claim 17, wherein at least when the air/fuel ratio is stoichiometric, the temperature controller 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.
22. The Rankine cycle system according to claim 18, wherein at least when the air/fuel ratio is stoichiometric, the temperature controller 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.
Type: Application
Filed: Mar 13, 2006
Publication Date: Sep 14, 2006
Applicant: HONDA MOTOR CO., LTD. (Tokyo)
Inventors: Masashi Kato (Wako-shi), Akihisa Sato (Wako-shi), Mitsuo Kadota (Wako-shi), Kensaku Yamamoto (Wako-shi)
Application Number: 11/373,126
International Classification: F01K 13/00 (20060101);