Rankine cycle system
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.
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The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2005-69367 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 an exhaust gas of an engine so as to generate a gas-phase working medium, and a displacement type expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy.
2. Description of Background Art
Japanese Utility Model Registration Publication No. 2-38162 discloses an arrangement in which the temperature of steam generated by waste heat from a boiler using exhaust gas of an engine rotating at a constant speed as a heat source is compared with a target temperature. When a water supply signal obtained from this deviation is used in feedback control of the amount of water supplied to the waste heat once-through boiler, a feedforward signal 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 and thereby improving the precision of control.
The arrangement provided in WO03/031775 discloses steam temperature that is controlled by manipulating the amount of water supplied to an evaporator of a Rankine cycle system. The steam pressure is controlled by manipulating the rotational speed of a displacement type expander into which steam flows.
The steam temperature and the steam pressure can be controlled by a conventional technique to a degree corresponding to load variation accompanying normal acceleration/deceleration after an engine and a Rankine cycle system are warmed up. However, in the process of operations from starting the engine in a low temperature state to completing warm-up of the Rankine cycle system, there are unstable states involving the effect of phase changes of a working medium within a system in going from water to saturated steam and then to superheated steam, and control of the amount of water supplied until the temperature gradient of the interior of the evaporator becomes stable. Furthermore, when the engine is stopped by a driver's intention by means of, for example, an ignition switch ON/OFF (hereinafter, ‘when the engine is stopped’ means this state), and not by means of transitional operating conditions such as fuel cut or idle stop when driving a vehicle, high temperature, high pressure steam remains in the interior of the evaporator. If the Rankine cycle system is also stopped at the same time there is a loss from the viewpoint of the efficiency of energy recovery. Moreover, if the expander is made to freely rotate (freely run) without load by the high temperature, high pressure steam remaining in the interior of the evaporator at the same time as the engine stops, there are problems that the rotational speed of the expander increases rapidly and the high temperature, high pressure steam remaining in the interior of the evaporator causes the temperature of an engine compartment to become high.
For example, as shown in
The present invention has been accomplished under the above-mentioned circumstances, and it is an object of an embodiment thereof to effectively utilize thermal energy remaining in the interior of an evaporator when an engine stops and to allow a Rankine cycle system to make a transition to a stable stopped state.
In order to achieve the above-mentioned object, according to a first feature of the invention, there is provided a Rankine cycle system including 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 a displacement type expander for converting the thermal energy of the gas-phase working medium generated by the evaporator into mechanical energy. A temperature control means is provided 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. Pressure control means are provided 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. Thus, 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.
With the first feature, in an arrangement in which the temperature control means manipulates the amount of liquid-phase working medium supplied to the evaporator in order to make the temperature of the gas-phase working medium coincide with the target temperature, and the pressure control means manipulates the rotational speed by changing the load of the expander in order to make the pressure of the gas-phase working medium coincide with the target pressure, a control of the amount of liquid-phase working medium supplied to the evaporator and/or control of the rotational speed of the expander are continued so as to be in the set ranges even after the engine has stopped and the thermal energy of the exhaust gas has disappeared. Therefore, it is possible to effectively recover the thermal energy remaining in the interior of the evaporator while making a transition to a stable stopped state by inhibiting a rapid increase in the rotational speed of the expander after the engine stops. Moreover, it is possible to prevent, by converting the thermal energy into mechanical energy, the temperature of the interior of an engine compartment from increasing.
According to a second feature of the present invention, 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.
With the second feature, after the engine has stopped, 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 the temperature at which the expander does not generate an output. Therefore, it is possible to use the thermal energy remaining in the evaporator efficiently to the very end.
According to a third feature of the present invention, 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.
With the third feature, after the engine has stopped, the pressure control means continues to control the rotational speed of the expander until the pressure of the gas-phase working medium decreases to the pressure at which the expander does not generate an output. Therefore, it is possible to use the thermal energy remaining in the evaporator efficiently to the very end.
According to a fourth feature of the present invention, 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.
With the fourth feature, when the rotational speed of the expander decreases to the set rotational speed, the pressure control means maintains this 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 it to rotate freely in a non-load state. Therefore, it is possible to recover energy by allowing the expander to rotate at a stable rotational speed while inhibiting a rapid increase in the rotational speed of the expander due to the thermal energy remaining in the evaporator, and to allow the Rankine cycle system to make a smooth transition to a stable stopped state while inhibiting a rapid increase in the rotational speed of the expander due to the thermal energy remaining in the evaporator.
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.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
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:
As shown in
The target steam temperature is determined as follows: as shown in
The internal density of the evaporator 11 is obtained as follows: as shown in
ρ=∫{Qin (t)−Qout (t)}dt/V.
The target pressure is set by applying the energy (flow rate) and temperature of steam supplied from the evaporator 11 to the expander 12 to the map of
The rotational speed control changeover means 29 controls the entrance steam pressure of the expander 12 by changing, based on an ON/OFF signal of the ignition switch, a positive torque (a torque in a direction that assists rotation of the expander 12) or a negative torque (a torque in a direction that inhibits rotation of the expander 12) generated by the motor/generator 17.
The PI feedback term calculation means 30 calculates a target torque for the motor/generator 17 from a deviation of the rotational speed of the motor/generator 17 (that is, the rotational speed of the expander 12) from a target rotational speed outputted by the rotational speed control changeover means 29. The rotational speed of the expander 12 is feedback-controlled at the target rotational speed by generating the above target torque in the motor/generator 17.
Functions of the temperature control means 21 and the pressure control means 26 when the ignition switch is turned ON are now explained.
As shown in
As shown in
As shown in
When any one of the above-mentioned three types of control when starting the engine E is completed, normal water supply control for the evaporator 11 is started based on a value obtained by adding the feedforward water supply amount and the feedback water supply amount, and normal rotational speed control is started based on a value obtained by adding the feedforward rotational speed and the feedback rotational speed.
Functions of the temperature control means 21 and the pressure control means 26 when the ignition switch of the engine E is turned OFF are now explained by reference to
In the case where there is a lot of thermal energy remaining in the interior of the evaporator 11 when the ignition switch of the engine E is turned OFF, if the Rankine cycle system R is stopped immediately, the thermal energy is wasted. Therefore, when the ignition switch is turned OFF, water supply to the evaporator 11 is not stopped immediately and additional water supply is carried out, thus continuing the generation of steam (ref. region n). The amount of water supplied in this process is decreased in response to a decrease in the internal energy of the evaporator 11. When the steam temperature attains a temperature at which the expander 12 does not generate an output (for example, the saturated steam temperature), the water supply is suspended.
As a result, the steam pressure is maintained at the target pressure for a predetermined period of time after the ignition switch is turned OFF, the expander 12 is rotated efficiently, and energy can be recovered. When the steam pressure decreases, the expander 12 is rotated at the lowest rotational speed allowing stable rotation, thus further recovering energy (ref. region o). When the regenerative torque of the motor/generator 17 becomes 0, rotation of the expander 12 is stopped, and recovery of energy is completed (ref. region p).
In this way, by continuously supplying water and operating the expander 12 for the predetermined period of time after the ignition switch is turned OFF, not only can the thermal energy remaining in the evaporator 11 be recovered without waste, but also the Rankine cycle system R can be shifted to a stable stopped state while preventing over-rotation of the expander 12 by slowly decreasing the steam pressure. In addition, it is possible to prevent the temperature of the interior of the engine compartment from increasing due to thermal energy remaining in the evaporator 11.
Although one embodiment of the present invention has been described 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.
For example, in the embodiment the amount of water supplied to the evaporator 11 is controlled based on the rotational speed of the water supply pump 14, but it may be controlled by the degree of opening of the open/close valve 15 shown in
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
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;
- 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.
Type: Application
Filed: Mar 13, 2006
Publication Date: Nov 16, 2006
Applicant: HONDA MOTOR CO., LTD. (Tokyo)
Inventors: Akihisa Sato (Wako-shi), Koji Fukutomi (Wako-shi), Kensaku Yamamoto (Wako-shi)
Application Number: 11/373,134
International Classification: F01K 13/00 (20060101);