Ebullient cooling device

An ebullient cooling device includes: a coolant passage configured to be formed inside an internal-combustion engine, and allow a coolant that cools the internal-combustion engine by boiling to flow therethrough; an expander configured to be driven by the coolant that has boiled in the internal-combustion engine; a condenser configured to be located at a downstream side of the expander, and cool the coolant that has passed through the expander; and a heat exchanger configured to cool a cooling object by heat exchange with the coolant, wherein a low-pressure region including the expander and the condenser and a high-pressure region other than the low-pressure region are formed in a path through which the coolant circulates, and a passage connecting to a part through which a liquid-phase coolant flows and a passage connecting to the low-pressure region are coupled to the heat exchanger.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2015/069326 filed Jul. 3, 2015, claiming priority based on Japanese Patent Application No. 2014-139950 filed Jul. 7, 2014, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an ebullient cooling device.

BACKGROUND ART

There have been known, as cooling devices of internal-combustion engines, ebullient cooling devices that cool the internal-combustion engine with the heat of vaporization by boiling of the coolant flowing through a coolant passage (e.g., a water jacket) formed inside the internal-combustion engine. For example, Patent Document 1 suggests combining such an ebullient cooling device with a Rankine cycle.

PRIOR ART DOCUMENT

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

To efficiently use an expander such as a turbine included in a Rankine cycle, the pressure at the upstream side of the expander is desired to be high, and is required to be the atmospheric pressure or greater. That is, to improve the efficiency of the Rankine cycle that uses vapor obtained by ebullient cooling of the internal-combustion engine, the pressure at the internal-combustion engine side is also increased. As a working fluid of the internal-combustion engine, i.e., a coolant, selected is, for example, water, an LLC (long life coolant), or ethyl alcohol, which has a boiling point close to that of water. When water is selected as a coolant, the boiling temperature of the coolant is 100° C. at 1 atmosphere, and 120° C. at 2 atmospheres. In the internal-combustion engine, various types of cooling with a coolant such as a lubricating oil or a transmission oil may be perforated. For example, the temperature of the lubricating oil circulating through the internal-combustion engine is generally higher than that of the coolant by about 10 to 30° C. Thus, when the lubricating oil is to be cooled by heat exchange with the coolant, the temperature of the lubricating oil never becomes equal to or less than the temperature of the coolant with high temperature, and the lubricating oil may thus deteriorate, or the sliding portion of the internal-combustion engine may seize.

Thus, the ebullient cooling device disclosed in the present specification aims to appropriately cool a cooling object to be cooled by heat exchange with a coolant that cools an internal-combustion engine.

Means for Solving the Problems

To achieve the above aim, an ebullient cooling device disclosed in the present specification includes: a coolant passage configured to be formed inside an internal-combustion engine, and to allow a coolant that cools the internal-combustion engine by boiling to flow therethrough; an expander configured to be driven by the coolant that has boiled in the internal-combustion engine; a condenser configured to be located at a downstream side of the expander, and to cool the coolant that has passed through the expander; and a heat exchanger configured to cool a cooling object by heat exchange with the coolant, wherein a low-pressure region including the expander and the condenser and a high-pressure region other than the low-pressure region are formed in a path through which the coolant circulates, and a passage connecting to a part through which a liquid-phase coolant flows and a passage connecting to the low-pressure region are coupled to the heat exchanger. Connecting the heat exchanger to the low-pressure region causes a state where ebullient cooling easily occurs in the heat exchanger. Thus, the heat exchanger is made to be in the ebullient cooling state, and the cooling object can be appropriately cooled even while a Rankine cycle is utilized.

The ebullient cooling device may further include a flow control valve configured to adjust an amount of the liquid-phase coolant that flows through the passage coupled to the heat exchanger and the part through which the liquid-phase coolant flows, the flow control valve being located in the passage. The provision of the flow control valve allows the amount of the coolant in the heat exchanger to be adjusted and facilitates ebullient cooling in the heat exchanger.

The ebullient cooling device may further include: a passage configured to diverge from the passage connecting to the low-pressure region and to be communicated with the coolant passage formed inside the internal-combustion engine; and a control valve configured to switch between a state where a passage leading to the low-pressure region is opened and a state where a passage leading to the coolant passage formed inside the internal-combustion engine is opened, the control valve being located in a point at which the passage diverges from the passage connecting to the low-pressure region. This configuration allows for switching between an ebullient cooling state in which latent heat of vaporization by boiling of the coolant is utilized and a liquid cooling state in which cooling is performed by taking heat by a liquid-phase coolant.

The ebullient cooling device may switch the control valve to the state where the passage leading to the coolant passage formed inside the internal-combustion engine is opened during warm-up of the internal-combustion engine. The cooling object can be warmed up early by causing the cooling state to be the liquid cooling state during warm-up of the internal-combustion to use the coolant of which the temperature increases more easily than that of the cooling object during the warm-up of the internal-combustion engine.

The ebullient cooling device may switch the control valve to the state where the passage leading to the coolant passage formed inside the internal-combustion engine is opened when the internal-combustion engine is in a high-rotation state or a high-load state. Accordingly, the operation of the Rankine cycle is stopped and the liquid cooling in the internal-combustion engine and the heat exchanger is performed when the internal-combustion engine is in the high-rotation state or the high-load state. While the Rankine cycle is stopped, the pressure of the coolant decreases, and the boiling point also decreases. Thus, the temperature of the coolant also decreases, and the cooling object can be thereby appropriately cooled.

The ebullient cooling device may further include: a bypass passage configured to diverge from a path connecting the coolant passage formed inside the internal-combustion engine and the expander, and to bypass the expander and connect to the condenser; and a control valve configured to switch between a state where a passage leading to the expander is opened and a state where the bypass passage is opened, the control valve being located at a point at which the bypass passage diverges from the path connecting the coolant passage and the expander. When the ebullient cooling state is selected, the flow of vapor into the bypass passage can be avoided, and when the liquid cooling state is selected, the coolant can be cooled by sending the liquid-phase coolant to the condenser.

Effects of the Invention

The ebullient cooling device disclosed in the present specification can cool a cooling object to be cooled by heat exchange with a coolant that cools an internal-combustion engine.

MODES FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. However, in the drawings, the dimensions of each part, ratios, and the like may not completely correspond to actual ones. In addition, the specifics may be omitted in some drawings.

With reference toFIG. 1, a description will first be given of an ebullient cooling device100of an embodiment built in an internal-combustion engine10.FIG. 1is an explanatory diagram illustrating an overall configuration of the ebullient cooling device100of the embodiment. The internal-combustion engine10includes an intake system and an exhaust system, and the exhaust system includes an exhaust manifold10a. The internal-combustion engine10includes an oil pan10b. The oil pan10bis equipped with an oil temperature sensor10b1. The oil temperature sensor10b1detects the temperature of the oil stored in the oil pan10b. The ebullient cooling device100includes a coolant passage12that is formed inside the internal-combustion engine10and through which a coolant that cools the internal-combustion engine10by boiling flows. The coolant passage12is, for example, a water jacket that is formed around the cylinder of the internal-combustion engine10, but may have other configuration as long as it can cool the internal-combustion engine10by the coolant in the coolant passage12. The coolant flowing through the coolant passage12absorbs the heat of the internal-combustion engine10and boils, thereby cooling the internal-combustion engine10. The coolant flowing through the coolant passage12is not specifically limited as long as it is a liquid that absorbs the heat of the internal-combustion engine10and boils, such as water, an LLC (long life coolant), ethyl alcohol, or the like. The present embodiment uses a coolant formed of a mixture of water and ethylene glycol. The ebullient cooling device100can achieve two cooling states: an ebullient cooling state in which the internal-combustion engine10is cooled by boiling of the coolant flowing through the coolant passage12; and a liquid cooling state in which the internal-combustion engine10is cooled by removing heat by the liquid-phase coolant. When the ebullient cooling device100is in the ebullient cooling state, a Rankine cycle, in which exhaust heat is recovered by using generated vapor, is formed. When the pressure in the region through which the coolant flows decreases, the coolant easily boils, and the ebullient cooling device100easily shifts to the ebullient cooling state. On the contrary, when the pressure in the region through which the coolant flows increases, the coolant has difficulty in boiling, and the ebullient cooling device100easily shifts to the liquid cooling state.

The coolant passage12has an outlet12alocated in the cylinder head of the internal-combustion engine10, and the outlet12aconnects to a first passage13. The first passage13is equipped with a first temperature sensor13a. The first temperature sensor13ameasures the temperature of the coolant flowing through the first passage13. The other end of the first passage13is connected to a gas-liquid separator14. The coolant flowing through the first passage13is mainly a gas-phase coolant that has vapored in the coolant passage12, but may contain a liquid-phase coolant.

The gas-liquid separator14includes a steam outlet14a. The steam outlet14aconnects to a fourth passage15. Vapor that has passed through the gas-liquid separator14flows into the fourth passage15. A turbine18, which is an example of an expander, is located at the other end of the fourth passage15. A superheater16is located between the gas-liquid separator14and the turbine18in the fourth passage15. The superheater16is provided with an exhaust gas that has passed through an exhaust heat steam generator20described later, thereby further applying heat to the vapor that has passed through the gas-liquid separator14. The turbine18is driven by superheated steam that flows from the superheater16thereinto. The turbine18connects to, for example, a power generator that generates power by using the driving force of the turbine18. This configuration allows for the recovery of the exhaust heat of the internal-combustion engine10. The driving force of the turbine18may be used to assist the driving force of the internal-combustion engine10. As described above, the ebullient cooling device100of the present embodiment also functions as a Rankine cycle. The superheater16and the exhaust heat steam generator20may be reversed with respect to the flow path of the exhaust gas. That is, with respect to the flow path of the exhaust gas, the superheater16may be located further upstream than the exhaust heat steam generator20to allow the exhaust gas that has passed through the superheater16to be introduced into the exhaust heat steam generator20.

A second passage131diverges from the first passage13. The other end of the second passage131connects to a thirteenth passage33described later. A third passage132diverges from the first passage13further downstream than the point at which the second passage131diverges. The other end132aof the third passage132is connected to an inlet24aof a condenser (hereinafter, described as a CDN in some cases)24described later. The third passage132functions as a bypass passage that bypasses the turbine18described later. That is, the third passage132is a bypass passage that diverges from the path13and the path15, which connect the coolant passage12formed inside the internal-combustion engine10and the turbine18, and bypasses the turbine18to connect to the condenser24. A first three-way valve13bis located at the point at which the third passage132diverges from the first passage13. The first three-way valve13bcorresponds to a control valve that switches between a state in which a passage leading to the turbine18is opened and a state in which the third passage132, which is the bypass passage, is opened. Accordingly, the first three-way valve13bcauses the coolant discharged from the outlet12aof the coolant passage12to pass through the first passage13and be introduced into the gas-liquid separator14or causes the coolant to pass through the third passage132to bypass the turbine18and be introduced into the condenser24. The first three-way valve13bis a magnetic valve, and is electrically coupled to an ECU28corresponding to a controller.

As described above, the gas-liquid separator14located between the internal-combustion engine10and the turbine18separates the coolant discharged from the internal-combustion engine10into a liquid-phase coolant and a gas-phase coolant. The gas-liquid separator14stores the resultant liquid-phase coolant in the lower side thereof. A first on-off valve15ais located between the steam outlet14aof the gas-liquid separator14and the superheater16. The first on-off valve15ais a magnetic valve, and is electrically coupled to the ECU28corresponding to the controller. When the first on-off valve15ais closed, the discharge of vapor from the gas-liquid separator14is stopped. Located at the lower end of the gas-liquid separator14are a first liquid-phase coolant outlet14band a second liquid-phase coolant outlet14c. The first liquid-phase coolant outlet14bconnects to a fifth passage19. Since the separated liquid-phase coolant is stored in the lower end of the gas-liquid separator14, the liquid-phase coolant always flows through the fifth passage19. A first water pump (WP)19ais located in the fifth passage19. The first water pump19asupplies the liquid-phase coolant to the coolant passage12formed inside the internal-combustion engine10. The second liquid-phase coolant outlet14cconnects to a sixth passage21. The liquid-phase coolant also always flows through the sixth passage21as well as the fifth passage19. The other end of the sixth passage21is connected to the exhaust heat steam generator20, and supplies the liquid-phase coolant to the exhaust heat steam generator20. The exhaust heat steam generator20will be described later.

The gas-liquid separator14includes a fluid level sensor14dthat measures the level of fluid, i.e., the level of the stored liquid-phase coolant thereinside. The fluid level sensor14dis electrically coupled to the ECU28. The gas-liquid separator14includes an outlet14ethat discharges the liquid-phase coolant. As described later, the outlet14econnects to a ninth passage26. The diameter and the installation location of the outlet14eare configured to be suitable for the level of the fluid to be controlled with the fluid level sensor14d. That is, the specifications of the outlet14eare configured so that the level of the fluid to be controlled with the fluid level sensor14d, in other words, so that the upper limit fluid level and the lower limit fluid level can be achieved. If the outlet14eis configured to be located extremely higher than a desired fluid level, the liquid-phase coolant inside the gas-liquid separator14fails to be properly discharged. As a result, the volume of the gas-liquid separator14needs to be configured to be large. On the contrary, if the outlet14eis configured to be located extremely lower than the desired fluid level, the liquid-phase coolant is discharged too much. This may cause the lack of the liquid-phase coolant to be supplied to the internal-combustion engine10, causing insufficient cooling of the internal-combustion engine10. The specifications of the outlet14eare determined taking into consideration at least the above conditions. The gas-liquid separator14is also configured to be located at a position at which the liquid-phase coolant is supplied to the first water pump19aand the exhaust heat steam generator20by gravity.

As described above, the ebullient cooling device100of the present embodiment includes the exhaust heat steam generator20. The exhaust heat steam generator20is located near an exhaust pipe17coupled to the exhaust manifold10aof the internal-combustion engine10. The exhaust heat steam generator20utilizes the exhaust heat of the internal-combustion engine10discharged through the exhaust pipe17to generate vapor. This configuration makes efficient use of the exhaust heat of the internal-combustion engine10. The exhaust heat steam generator20is not essential for cooling the internal-combustion engine10, but can improve the efficiency of the exhaust heat recovery of the device as a whole.

The exhaust heat steam generator20includes an outlet20a. The outlet20aconnects to a seventh passage22. The seventh passage22is equipped with a second temperature sensor22a. The second temperature sensor22ameasures the temperature of the coolant flowing through the seventh passage22. The other end of the seventh passage22is coupled to the gas-liquid separator14. The coolant flowing through the seventh passage22is mainly a gas-phase coolant vaporized in the exhaust heat steam generator20, but may contain a liquid-phase coolant together. As described above, the gas-liquid separator14separates not only the coolant boiled in the internal-combustion engine10, but also the coolant discharged from the exhaust heat steam generator20into a liquid-phase coolant and a gas-phase coolant.

The ebullient cooling device100includes, at the downstream side of the turbine18, the condenser24that cools the gas-phase coolant that has passed through the turbine18to produce the liquid-phase coolant. That is, the condenser24is located further downstream than the turbine18, and cools the coolant that has passed through the turbine18. The condenser24also cools the coolant that has passed through the third passage132that is the bypass passage. When the ebullient cooling device100is in the liquid cooling state, the liquid-phase coolant is cooled. The condenser24connects to the other end of an eighth passage23located at the downstream side of the turbine18. The condenser24is a heat exchanger, exchanges heat with the coolant, and returns the gas-phase coolant into the liquid-phase coolant by cooling the coolant. When the ebullient cooling device100is in the liquid cooling state, the condenser24cools the liquid-phase coolant as a radiator installed in a general vehicle does. A unidirectional valve23ais located in the eighth passage23, preventing vapor from flowing back from the condenser24to the turbine18.

The ebullient cooling device100includes a catch tank25that stores the liquid-phase coolant that has been cooled by the condenser24, i.e., the coolant that has been returned to the liquid-phase coolant from the gas-phase coolant. The catch tank25includes a coolant inlet25aat the upper side, and a coolant outlet25bat the lower side. The coolant inlet25aconnects to the ninth passage26that discharges the liquid-phase coolant in the gas-liquid separator14to the catch tank25. That is, the ninth passage26is coupled to the outlet14eof the gas-liquid separator14. A second on-off valve26ais located in the ninth passage26. The second on-off valve26ais a magnetic valve and is electrically coupled to the ECU28. The coolant outlet25bconnects to a tenth passage27that supplies the liquid-phase coolant in the catch tank25to the gas-liquid separator14. A second water pump (WP)27ais located in the tenth passage27. The second water pump27ais an electric pump, is electrically coupled to the ECU28, and is controlled by the ECU28based on the measurement value of the fluid level sensor14d. A displacement pump is employed for the second water pump27a.

The above-described ebullient cooling device100can separate the path through which the coolant circulates into a low-pressure region including the turbine18and the condenser24and a high-pressure region other than the low-pressure region. More specifically, high-pressure vapor flows through the passage from the coolant passage12to the inlet of the turbine18, i.e., the first passage13and the fourth passage15, and the pressure of the vapor gradually decreases by passing through the turbine18. Thus, the region containing the turbine18through the condenser24is included in the low-pressure region in which the pressure is low. At the downstream side of the condenser24and the catch tank25, the second water pump27apumps the coolant toward the gas-liquid separator14and further toward the internal-combustion engine10. Thus, the downstream side of the condenser24and the catch tank25is included in the high-pressure region.

The ebullient cooling device100includes an oil cooler (hereinafter, referred to as an EOC in some cases)30, which is an example of a heat exchanger. The oil cooler30cools a lubricating oil, which is a cooling object, by exchanging heat with the coolant. The oil cooler30connects to an oil filter31. The oil cooler30includes a first mouth30aand a second mouth30b. Inside the oil cooler30, the coolant flows through a passage connecting the first mouth30aand the second mouth30b. The first mouth30aconnects to a twelfth passage32. The twelfth passage32diverges from the fifth passage19. More specifically, the twelfth passage32diverges from the fifth passage19between the gas-liquid separator14and the first water pump19a. The first mouth30ais required to connect to a point through which the liquid-phase coolant always flows. Additionally, taking into consideration that the ebullient cooling device100becomes in the liquid cooling state and the coolant flowing through the oil cooler30is also circulated by the first water pump19a, the twelfth passage32preferably diverges further upstream than the water pump19aof the fifth passage19. A flow control valve32ais located in the twelfth passage32. The flow control valve32aadjusts the amount of the liquid-phase coolant flowing through the twelfth passage32. That is, the flow control valve32aadjusts the amount of the liquid-phase coolant introduced into the oil cooler30through the first mouth30a. The flow control valve32ais a magnetic valve and electrically coupled to the ECU28corresponding to the controller.

The second mouth30bconnects to the thirteenth passage33. The other end of the thirteenth passage33connects to the inlet24aof the condenser24. More specifically, the other end of the thirteenth passage33joins the third passage132, thereby connecting to the inlet24aof the condenser24. Thus, the thirteenth passage33is coupled to the low-pressure region. The first mouth30aand the second mouth30bmay function as the inlet or outlet for the coolant depending on the flow direction of the coolant. For example, when the ebullient cooling device100is in the ebullient cooling state, the first mouth30aserves as an inlet and the second mouth30bserves as an outlet. On the other hand, when the ebullient cooling device100is in the liquid cooling state, the second mouth30bserves as an inlet, and the first mouth30aserves as an outlet.

The thirteenth passage33connects to the second passage131diverging from the first passage13. That is, the second passage131is a passage that diverges from the thirteenth passage33and is communicated with the coolant passage12formed inside the internal-combustion engine10. At the point at which the second passage131connects to the thirteenth passage33, in other words, the point at which the thirteenth passage33diverges from the second passage131, located is a second three-way valve33a. The second three-way valve33acorresponds to a control valve configured to switch between a state where a passage leading to the low-pressure region is opened and a state where a passage leading to the coolant passage12formed inside the internal-combustion engine10is opened. Accordingly, the second three-way valve33acouples the second mouth30bto the outlet12aof the coolant passage12or to the inlet24aof the condenser24. The second three-way valve33ais a magnetic valve and electrically coupled to the ECU28corresponding to the controller.

The oil cooler30includes an oil inlet30cand an oil outlet30d. The oil inlet30cconnects to the oil pan10b, and introduces the oil in the oil pan10binto the oil cooler30. The oil outlet30dis coupled to an oil passage that supplies the oil to parts necessary to be supplied with the oil in the internal-combustion engine10. The oil can be cooled by the above-described oil cooler30.

In the present embodiment, the oil cooler30cooling the lubricating oil is assumed to be a heat exchanger, but a cooler of which the cooling object is, for example, ATF (Automatic Transmission Fluid) or mission oil may be the heat exchanger.

The ebullient cooling device100includes the ECU28as the controller. The ECU28is coupled to various sensors, various on-off valves, and the like, and controls the operation of each part. The control of the ECU28is executed by the cooperation between hardware including a CPU (Central Processing Unit) and software stored in a ROM (Read Only Memory) or the like. The ECU28includes a timer28a. The timer28ameasures time in an example of the control described later.

The following will describe an example of the control executed in the ebullient cooling device100with reference toFIG. 2.FIG. 2is a flowchart illustrating an example of the control of the ebullient cooling device100of the embodiment. The control executed in the ebullient cooling device100is schematically described as follows. First, during the warm-up, the internal-combustion engine10switches the second three-way valve33ato the state where the passage leading to the coolant passage12formed inside the internal-combustion engine10is opened. When the internal-combustion engine10is in a high-rotation state or a high-load state, the second three-way valve33ais also switched to the state where the passage leading to the coolant passage12formed inside the internal-combustion engine10is opened. In the cases other than these cases, the second three-way valve33ais made to be in the state where the passage leading to the low-pressure region is opened. Hereinafter, an example of the control will be described in detail.

First, when the ignition of the internal-combustion engine10is turned ON, and the internal-combustion engine10is started, a sequence of the control starts. At step S1, it is determined whether the rotation speed NE of the internal-combustion engine is greater than a high rotation determination threshold value NE1and the temperature Tw of the coolant is greater than a warm-up determination temperature Tw1. At step S1, it is determined which control is to be mainly executed: the control for cold start executed from step S2; or the control, executed from step S11, for restart of the internal-combustion engine. Here, it is assumed that the internal-combustion engine10is restarted when the internal-combustion engine in operation once stops and starts again. More specifically, it is assumed that the internal-combustion engine is restarted when the internal-combustion engine10completes the warm-up and stops, and thereafter starts again before cooled. Additionally, even when the internal-combustion engine10does not once stop, if the predetermined conditions to be determined at step S1is met, the processes from step S11are executed. The ebullient cooling device100of the present embodiment switches between the ebullient cooling state and the liquid cooling state, and the high-rotation determination threshold value NE1is a threshold value for the liquid cooling state to be selected. Additionally, the warm-up determination temperature Tw1is a threshold value for determining whether the warm-up of the internal-combustion engine10has been completed. The temperature Tw of the coolant is obtained by the first temperature sensor13a.

When the determination at step S1is NO, that is, when at least one of the rotation speed NE of the internal-combustion engine10or the temperature Tw of the coolant fails to meet the predetermined condition, the process moves to step S2. At step S2, it is determined whether the temperature Tw of the coolant is equal to or less than the warm-up determination temperature Tw1. When the determination at step S2is NO, that is, when it is determined that the warm-up of the internal-combustion engine10has been completed, the process moves to step S3. When the determination at step S2is NO, it is determined that the warm-up of the internal-combustion engine10has been completed, and the ebullient cooling device100is made to be in the ebullient cooling state. When the ebullient cooling device100is in the ebullient cooling state, the internal-combustion engine10and the oil cooler30are cooled by ebullient cooling. At step S3, as illustrated inFIG. 3, the first on-off valve15ais opened. At this time, as indicated by black fill inFIG. 3, the first three-way valve13bcloses the third passage132, which is the bypass passage, and opens the first passage13leading to the gas-liquid separator14. This control allows vapor gradually generated in the internal-combustion engine10to be sent to the gas-liquid separator14. When the first on-off valve15ais opened while the warm-up of the internal-combustion engine10is completed, the gas-phase coolant stored in the gas-liquid separator14and separated from the liquid-phase coolant is sent to the superheater16. When the first on-off valve15ais opened, the pressure at the upstream side of the gas-liquid separator14decreases, causing the state where more vapor is easily generated. Thus, continuously generated vapor is sent to the superheater16. At step S4subsequent to step S3, as illustrated inFIG. 3, the flow control valve32ais fully closed. This control stops the flow of the liquid-phase coolant into the oil cooler (EOC)30. Then, while the flow control valve32ais closed, the state of the second three-way valve33ais made to be a state where the oil cooler30is communicated with the condenser24. That is, the oil cooler30is made to be coupled to the low-pressure region. This control decreases the pressure inside the oil cooler30, causing low pressure boiling to occur inside the oil cooler30and ebullient cooling to be performed. At this time, since the flow control valve32ais fully closed, and the amount of the coolant inside the oil cooler30easily decreases, the temperature of the oil cooler30is effectively decreased by ebullient cooling. At this time, as indicated by black fill inFIG. 3, the second three-way valve33acloses the second passage131. Accordingly, vapor generated in the internal-combustion engine10is sent to the gas-liquid separator14through the first passage13without joining the thirteenth passage33. The processes of steps S3and S4may be simultaneously executed, or switched in order. After steps S3and S4, the process moves to step S6.

On the other hand, when the determination at step S2is YES, that is, when it is determined that the warm-up of the internal-combustion engine10has not been completed, the process moves to step S5. When the determination at step S2is YES, it is determined that the warm-up of the internal-combustion engine10has not been completed, and the ebullient cooling device100is made to be in the liquid cooling state. Here, although it is referred to as the liquid cooling state for the convenience sake, it mainly aims to circulate the liquid-phase coolant in the internal-combustion engine10while the internal-combustion engine10is warmed up. As described above, while the internal-combustion engine10is warmed up, the liquid-phase coolant is made to pass through the oil cooler30as well as the coolant passage12formed inside the internal-combustion engine10to cool the lubricating oil by sensible heat. The liquid cooling state during the warm-up of the internal-combustion engine10allows for the heat exchange between the coolant of which the temperature increases more easily than that of the lubricating oil, which is a cooling object, and the lubricating oil. This helps the increase in temperature of the lubricating oil and early completion of the warm-up. At step S5, the flow control valve32ais fully opened as illustrated inFIG. 4. This control allows the liquid-phase coolant to keep flowing into the oil cooler (EOC)30. Then, while the flow control valve32ais opened, the state of the second three-way valve33ais made to be the state where the oil cooler30and the water jacket (WJ), i.e., the coolant passage12are communicated with each other. As described above, while the internal-combustion engine10is warmed up, the second three-way valve33acorresponding to the control valve is switched to the state where the passage leading to the coolant passage12formed inside the internal-combustion engine10is opened. This control allows a circulation path of the liquid-phase coolant including the oil cooler30and the coolant passage12to be formed. That is, as illustrated inFIG. 4, the liquid-phase coolant flows through the circulation path including the oil cooler and the coolant passage12in a counterclockwise direction inFIG. 4. The liquid-phase coolant is circulated by the first water pump19a. At this time, as indicated by black fill inFIG. 4, the first three-way valve13bcloses the first passage13, and opens the third passage132that bypasses the gas-liquid separator14and the turbine18. This control causes the liquid-phase coolant to flow into the condenser24. At this time, the condenser24functions as a radiator, and cools the liquid-phase coolant. After the process at step S5is ended, the processes from step S2are repeated again.

After the process at step S4is ended, the process moves to step S6. At step S6, it is determined whether the temperature To of the lubricating oil is equal to or less than an upper limit temperature Tohigh. The temperature To of the lubricating oil is obtained by the oil temperature sensor10b1. The upper limit temperature Tohigh is stored in the memory in the ECU28. The upper limit temperature Tohigh is defined as an oil temperature that ensures the performance of the lubricating oil. When the determination at step S6is YES, the process moves to step S7. On the other hand, when the determination at step S6is NO, the process moves to step S10. That is, when the temperature To of the lubricating oil is greater than the upper limit temperature Tohigh, the process moves to step S10. At step S10, the flow control valve32ais fully opened. This control introduces the liquid-phase coolant into the oil cooler30, facilitating the cooling of the lubricating oil. After the flow control valve32ais fully opened at step S10, the flow control valve32ais kept fully opened till the determination at step S6becomes YES.

At step S7, it is determined whether the temperature To of the lubricating oil is equal to or greater than the temperature Tw of the coolant, and equal to or less than a temperature slightly higher than the temperature Tw, i.e., Tw+α. This condition is set to prevent the lubricating oil from removing heat from the coolant more than necessary. More specifically, when the temperature To of the lubricating oil is less than the temperature Tw of the coolant, the heat of the coolant is removed by the lubricating oil in the oil cooler30. The heat removed in the oil cooler30is discarded in the condenser24. That is, the heat of the coolant is discarded in the condenser24. As a result, the amount of vapor generated by evaporation of the coolant decreases, and the turbine output thereby decreases. Accordingly, the determination at step S7is performed to prevent the heat quantity of the coolant from being removed by the lubricating oil.

When the determination at step S7is NO, the process moves to step S8. On the other hand, when the determination at step S7is YES, it is determined that the temperature of the lubricating oil has not reached a proper temperature yet, and the processes from step S6are repeated.

At step S8, the open degree of the flow control valve32ais adjusted based on the difference between the temperature Tw+α of the coolant and the temperature To of the lubricating oil. More specifically, the open degree of the flow control valve32ais adjusted by referring to a map illustrated inFIG. 5. As the difference between Tw+α and To increases, the open degree of the flow control valve32aincreases. Since the process at step S8is performed when the determination at step S7is NO, the difference between Tw+α and To is always equal to or greater than zero. The execution of the feedback control referring to this map regulates the temperature To of the lubricating oil within a proper range. The determination at step S7also becomes NO when T0is less than Tw, and step S8is executed. When T0is less than Tw, in the map illustrated inFIG. 5, the value of the horizontal axis represents − (minus), but as the value of the horizontal axis decreases, the flow control valve open degree decreases. As the flow control valve open degree decreases, the heat exchange between the coolant and the lubricating oil is reduced, and the situation in which the heat of the coolant is removed by the lubricating oil is improved.

After the open degree of the flow control valve32ais adjusted at step S8, the process moves to step S9. At step S9, it is determined whether the internal-combustion engine10has stopped. This process is a condition for ending the sequence of control. When the determination at step S9is NO, the processes from step S1are repeated, while when the determination at step S9is YES, the sequence of processes is ended (END).

On the other hand, when the determination at step S1is YES, the process moves to step S11. That is, when both the rotation speed NE of the internal-combustion engine10and the temperature Tw of the coolant meet the predetermined conditions, the process moves to step S11. At step S11, it is determined whether the state where the rotation speed NE of the internal-combustion engine is greater than the high-rotation determination threshold value NE1and the temperature Tw of the coolant is greater than the warm-up determination temperature Tw1continues for t1seconds. Here, the timer28ameasures t1seconds. The timer28astarts measuring the time when the rotation speed NE exceeds the high-rotation determination threshold value NE1and the temperature Tw exceeds the warm-up determination temperature Tw1. The length of time t1can be appropriately determined. The reason why the passage of t1seconds is required is for stable control. The determination at step S11determines the switching condition between the ebullient cooling and the liquid cooling. Thus, if the cooling state is changed even when the rotation speed NE of the internal-combustion engine slightly exceeds the high-rotation determination threshold value NE1, the switching frequency of the control increases, and stable control is not achieved.

When the determination at step S11is NO, the process moves to step S2, and the processes after step S2are executed. The processes from step S2are already described, and thus the description thereof is omitted. On the other hand, when the determination at step S11is YES, the process moves to step S12. The process of step S12is the same as the process of step S5. That is, at step S12, the cooling state is switched to the liquid cooling state. As described above, when the internal-combustion engine10is in the high-rotation state, the second three-way valve33acorresponding to the control valve is switched to the state where the passage leading to the coolant passage12formed inside the internal-combustion engine10is opened. In the present embodiment, although the cooling state is switched to the liquid cooling when the internal-combustion engine10is in the high-rotation state where the internal-combustion engine10maintains its rotation speed at the high-rotation determination threshold value NE1or greater, the cooling state may be switched to the liquid cooling when the internal-combustion engine10is in the high-load state. In this case, a map illustrated inFIG. 6is referred to, and the cooling state is switched to the liquid cooling when the loading state of the internal-combustion engine10exceeds a threshold value for shift to liquid cooling and enters a high-load region, and this state is kept for a predetermined period of time. This control stops the operation of the Rankine cycle, and performs the liquid cooling in the internal-combustion engine10and the oil cooler (EOC)30that is a heat exchanger. While the Rankine cycle is stopped, the pressure of the coolant decreases, and the boiling point also decreases. Thus, the temperature of the coolant also decreases, and the lubricating oil, which is a cooling object, can be appropriately cooled.

After the process of step S12is ended, the process moves to step S13. At step S13, it is determined whether a state where the rotation speed NE of the internal-combustion engine10is equal to or less than a low-rotation determination threshold value NE2continues for t2seconds. Here, NE1is greater than NE2. The timer28ameasures t2seconds. The timer28astarts measuring the time when the rotation speed NE falls below the low-rotation determination threshold value NE2. The length of time t2can be appropriately determined. The reason why the passage of t2seconds is required is for stable control as the passage of t1seconds is required when the determination for the high-rotation determination threshold value NE1is made. To switch the cooling state depending on the loading state of the internal-combustion engine10, the map illustrated inFIG. 6is referred to, and the cooling state is switched to the ebullient cooling when the loading state of the internal-combustion engine10exceeds a threshold value for shift to ebullient cooling and enters a low-load region from the high-load region and this state continues for a predetermined period of time.

When the determination at step S13is NO, the processes from step S12are repeated. When the determination at step S13is YES, the process moves to step S14. At step S14, the cooling state is returned to the ebullient cooling state. The specific process at step S14is the same as the process at step S4, and thus the detailed description thereof is omitted.

After the process at step S14, the processes from step S6are executed. The processes after step S6are already described, and thus the detailed description thereof is omitted.

As described above, the ebullient cooling device100of the present embodiment can appropriately cool the lubricating oil that is a cooling object to be cooled by heat exchange with the coolant that cools the internal-combustion engine10. Since the ebullient cooling device100of the present embodiment can cool the lubricating oil by ebullient cooling, it is possible to control the temperature of the lubricating oil to be less than the temperature of the coolant circulating in the internal-combustion engine10if necessary. When the lubricating oil is cooled by heat exchange with the coolant, the temperature of the lubricating oil cannot be decreased to less than the temperature of the coolant. Thus, making the temperature of the lubricating oil less than that of the coolant by using ebullient cooling is the advantage of the ebullient cooling device100of the present embodiment.

The configuration in which the second three-way valve33ais eliminated and the oil cooler30is always coupled to the condenser24may be taken. In this case, the flow control valve32ais fully closed even while the internal-combustion engine10is warmed up. Such a configuration discards the effect of increasing the temperature of the lubricating oil by the coolant during warm-up, but the configuration of the ebullient cooling device100can be simplified.

While the exemplary embodiments of the present invention have been illustrated in detail, the present invention is not limited to the above-mentioned embodiments, and other embodiments, variations and variations may be made without departing from the scope of the present invention.

DESCRIPTION OF LETTERS OR NUMERALS

14dfluid level sensor

20exhaust heat steam generator

27asecond water pump

32aflow control valve