JP5874455B2 - Heat exchanger - Google Patents

Description

  The present invention relates to a heat exchanger, and more particularly to a heat exchanger that recovers heat of exhaust gas emitted from an engine.

  There is a heat exchanger in which a water jacket is provided on the outer periphery of the exhaust manifold so that the heat of the exhaust is recovered in cooling water flowing through the water jacket (see Patent Document 1).

JP 11-317947 A

  However, in the technique of Patent Document 1, it is conceivable that the cooling water flowing through the water jacket is boiled and vaporized by the heat of exhaust gas that has become high temperature when the engine is under a heavy load. Since the engine is based on cooling with liquid cooling water, it is a problem if the cooling water evaporates.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heat exchanger that does not evaporate the cooling water of the engine even when the heat of the exhaust gas of the engine is recovered into the cooling water.

  The heat exchanger according to the present invention includes an exhaust gas passage through which exhaust gas of an engine flows, and a first medium passage through which a first medium always used in a liquid phase flows, and between the exhaust gas and the first medium. In the heat exchanger for exchanging heat in the exhaust gas passage, the exhaust gas passage and the first medium passage are adjacent to each other with the second medium passage through which the second medium flows, and heat exchange between the exhaust gas and the first medium is performed. When the second medium passage sandwiched between the exhaust gas passage and the first medium passage is filled with the liquid phase second medium, and when the heat exchange between the exhaust gas and the first medium is suppressed, the exhaust gas passage It is a heat exchanger in which the inside of the second medium passage sandwiched between the first medium passages is filled with gas.

  According to the present invention, the exhaust gas passage and the first medium passage are adjacent to each other with the second medium passage interposed therebetween, and when the heat exchange between the exhaust gas and the first medium is promoted, the exhaust gas passage and the first medium passage are disposed in the second medium passage. Since the liquid phase is filled with the second medium, heat exchange using the convection of the liquid phase second medium suppresses boiling and vaporization of the first medium more gently than when direct heat exchange is performed without using the second medium. When the heat exchange between the exhaust gas and the first refrigerant is suppressed, the second medium passage is filled with gas, so that the first medium is boiled and vaporized by a simple operation simply by replacing it with gas. Can be effectively suppressed.

It is a top view of the exhaust manifold which shows the installation place of the heat exchanger of 1st Embodiment of this invention. It is sectional drawing along the XX line of FIG. It is sectional drawing along the XX line of FIG. It is sectional drawing along the XX line of FIG. It is a model figure of the heat exchanger of 1st Embodiment. It is a general view of an engine coolant circuit. It is sectional drawing along the YY line of FIG. It is sectional drawing along the YY line of FIG. It is a flowchart for demonstrating control of the on-off valve, a pump, and a flow regulating valve after engine warm-up completion. It is a driving | operation area | region figure of an engine. It is a flowchart for demonstrating control of the on-off valve and a pump at the time of an engine stop. It is a flowchart for demonstrating control of the on-off valve and pump at the time of engine cold start.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(First embodiment)
1 is a plan view of an exhaust manifold showing the installation location of the heat exchanger 21 according to the first embodiment of the present invention, FIGS. 2A, 2B, and 2C are cross-sectional views taken along line XX of FIG. 1, FIG. 5B is a cross-sectional view taken along line YY of FIG.

  As shown in FIG. 1, in the three-cylinder engine 1, the exhaust manifold 2 is composed of three branch portions 2a and an aggregate portion 2b that collects these branch portions, and a catalyst 15 such as a three-way catalyst is provided immediately downstream thereof. It has been. The heat exchanger 21 of 1st Embodiment is provided in one branch part 2a of three branch parts. In FIG. 1, the heat exchanger 21 is provided in the left branch portion 2 a, but the heat exchanger 21 may be provided in the center, the right side, all the branch portions 2 a, or the gathering portion 2 b.

  FIG. 3 shows the heat exchanger 21 of the first embodiment as a model. That is, the whole is constituted by a triple pipe composed of three cylindrical pipes of an inner pipe 22, an intermediate pipe 23, and an outer pipe 24, and the inner pipe 22 corresponds to the branch portion 2 a and the passage 3 inside the inner pipe 22. Is an exhaust passage. Here, it is assumed that the exhaust flows in one direction (leftward in FIG. 3) through the exhaust passage 3.

  Cooling water (first medium) flows through the cylindrical space formed between the intermediate pipe 23 and the outer pipe 24 as the cooling water passage 11 (first medium passage). Here, the engine cooling water circuit as a whole will be described. As shown in FIG. 4, the cooling water exiting the engine 1 includes a cooling water passage 6 passing through the radiator 4, a bypass cooling water passage 7 bypassing the radiator 4, and Divided into flows. Thereafter, the two flows are merged again by a thermostat 8 that determines the distribution of the flow rate of the cooling water flowing through both passages 6 and 7, and then returns to the engine 1 via the cooling water pump 9. The cooling water passage 11 provided in the heat exchanger 21 of the first embodiment is provided in the middle of the bypass cooling water passage 7. That is, when the engine 1 is cold started, the heat of the exhaust gas is recovered by the heat exchanger 21 into the cooling water flowing through the cooling water passage 11, so that the engine 1 can be warmed up quickly. In addition, as shown in FIG. 3, the flow of the cooling water inside the cooling water passage 11 is made to flow opposite to the flow of the exhaust (rightward in FIG. 3).

  Now, instead of providing the intermediate tube 23 as in the heat exchanger 21 of the present embodiment, exhaust gas is exhausted inside the inner tube as a double tube of the inner tube and the outer tube, and in the space between the inner tube and the outer tube. There is a conventional apparatus that allows cooling water to flow and directly exchanges heat between cooling water and exhaust. However, if direct heat exchange is performed between the cooling water and the exhaust as in the conventional device, the heat exchange is performed under conditions where the cooling water is hot enough to reduce the amount of heat exchange between the cooling water and the exhaust. It is conceivable that the cooling water evaporates in the middle of flowing through the vessel. However, the cooling water (first refrigerant) is always used only in the liquid phase. If the cooling water evaporates, the engine 1 cannot be efficiently cooled with the liquid.

  Therefore, in the present embodiment 21, the heat exchanger 21 exchanges heat between the exhaust gas of the engine 1 and the cooling water that is liquid through the second medium that is liquid, and the second medium that is liquid is replaced with gas. The heat exchanger 21 is made possible. Specifically, the intermediate pipe 23 is added as shown in FIG. 3, and a cylindrical space between the inner pipe 22 and the intermediate pipe 23 is newly formed as a refrigerant passage 25 (second medium passage). The refrigerant passage 25 is filled with a liquid refrigerant (second medium), and the liquid refrigerant becomes hot when the cooling water is hot enough to reduce the amount of heat exchange with the exhaust of the engine 1. Heat exchange with the exhaust gas to boil and evaporate into a gas. That is, an exhaust passage 3 (exhaust gas passage) through which engine exhaust (exhaust gas) flows, and a cooling water passage 11 (first medium passage) through which cooling water (first medium) always used in the liquid phase flows. In the heat exchanger 21 that performs heat exchange between the exhaust gas and the cooling water, the exhaust passage 3 and the cooling water passage 11 have a refrigerant passage 25 (second medium passage) through which a refrigerant (second medium) flows. When the heat exchange between the exhaust gas and the cooling water is promoted, the refrigerant passage 25 sandwiched between the exhaust passage 3 and the cooling water passage 11 is filled with the liquid phase refrigerant, and the exhaust gas and the cooling water are filled. When suppressing the heat exchange, the refrigerant passage 25 sandwiched between the exhaust passage 3 and the cooling water passage 11 is filled with gas.

  Here, the condition where the coolant temperature becomes so high that it is desired to reduce the amount of heat exchange with the exhaust of the engine 1, specifically, the high load of the engine 1 at which the exhaust temperature of the engine 1 becomes the highest. State. For this reason, the second medium is liquid when the engine 1 is not in a high load state, and has a property suitable for boiling and evaporating into a gas when the engine 1 is in a high load state (for example, pure water). ) Is selected as the refrigerant. However, the gas does not necessarily have to be the gas phase second refrigerant. For example, when the refrigerant passage 25 is filled with gas, the second refrigerant may be replaced with air.

  How the heat exchange is performed in the heat exchanger 21 when the heat exchanger 21 is configured in this way will be described with reference to FIGS. 5A and 5. First, when the engine 1 is not in a high load state, the refrigerant filling the refrigerant passage 25 is liquid. At this time, as shown in FIG. 5A, heat exchange is performed between the exhaust in the exhaust passage 3 and the refrigerant filled in the refrigerant passage 25, and the heat of the exhaust is transmitted to the refrigerant. Heat exchange is also performed between the refrigerant filled in the refrigerant passage 25 and the cooling water in the cooling water passage 11, and the heat transferred to the refrigerant is transferred to the cooling water in the cooling water passage 11. That is, when the engine 1 is not in a high load state, the heat of the exhaust flowing through the exhaust passage 3 is transmitted to the cooling water flowing through the cooling water passage 11 via the liquid refrigerant. In particular, when the refrigerant flows in the refrigerant passage 25, forced convection of the refrigerant occurs, and heat transfer between the exhaust gas and the cooling water is promoted.

  On the other hand, when the engine 1 is in a high load state, the liquid refrigerant filling the refrigerant passage 25 evaporates. The inside of the refrigerant passage 25 is replaced with gas by this vaporization of vapor, and eventually the whole is replaced with gas. In this state, the cylindrical refrigerant passage 25 between the cooling water passage 11 and the exhaust passage 3 becomes a heat insulating layer as shown in FIG. 5B. Due to the presence of the heat insulating layer (25) surrounding the outer periphery of the inner pipe 22, the amount of heat exchange between the cooling water in the cooling water passage 11 and the exhaust gas in the exhaust passage 3 is greatly reduced. By reducing the heat exchange amount, it is possible to avoid boiling and evaporating the cooling water in the cooling water passage 11 even when the engine 1 is in a high load state.

  In order to remove the refrigerant evaporated in the refrigerant passage 25 from the refrigerant passage 25 and let it escape to the refrigerant tank 31 (second medium tank), the heat exchanger 21 of the triple pipe is inclined with respect to the horizontal direction. Thus, one end 25a (right end in FIG. 3) of the refrigerant passage 25 is lifted. For this reason, the other end 25b (left end in FIG. 3) of the refrigerant passage 25 hangs vertically downward. The reason why the one end 25a is lifted is to guide the refrigerant that has been boiled and vaporized vertically upward to the one end 25a. 2A, 2B, and 2C, the one end 25a of the refrigerant passage 25 and the bottom surface 31a of the refrigerant tank 31 are connected to the first circulation passage 32 (communication passage), and the other end 25b of the refrigerant passage 25 is provided. And a bottom surface 31a of the refrigerant tank 31 are respectively connected by a second circulation refrigerant 33 (communication passage) to form a circulation path in which refrigerant moves back and forth between the refrigerant passage 25 of the heat exchanger 21 and the refrigerant tank 31. To do. The refrigerant tank 31 may be an open tank provided with an open end with the atmosphere vertically above, or a sealed tank. Here, FIG. 2A shows how the refrigerant state changes when the engine 1 is in the initial state, FIG. 2B shows when the engine 1 is in a high load region, and FIG. Is shown.

  The first circulation passage 32 is provided with a normally closed on-off valve 34 and a pump 35. In other than a high load state, for example, in a low load state, the refrigerant passage 25 is filled with a liquid-phase refrigerant as shown in FIG. 2C. By opening the on-off valve 34 and operating the pump 35, the refrigerant is circulated through the communication passage, and the heat exchange between the exhaust gas and the cooling water is promoted by forced convection generated in the refrigerant in the refrigerant passage. The normally closed on-off valve 34 is for confining the pressure of the refrigerant gas that has boiled and vaporized inside the refrigerant passage 25 when the engine 1 is in a high load state. When the engine 1 is in a high load state, the on-off valve 34 is closed, and the refrigerant gas evaporated and boiled in the refrigerant passage 25 moves vertically upward. Since one end 25a of the refrigerant passage 25 is located at the uppermost vertical position, the refrigerant gas moves toward the one end 25a, enters the first circulation passage 32 connected to the one end 25a, and is stored in front of the on-off valve 34. When a certain amount of refrigerant gas is stored in front of the on-off valve 34, the pressure of the refrigerant gas is still inside the refrigerant passage 25, and liquid refrigerant still flows from the other end 25 b of the refrigerant passage 25 to the second circulation passage 33. Push out. As the amount of gas stored in front of the on-off valve 34 increases, the amount of liquid refrigerant pushed out from the other end 25b of the refrigerant passage 25 to the second circulation passage 33 increases. It reaches the state where the refrigerant has been expelled (see FIG. 2B).

  In this way, the state of the refrigerant passage 25 can be switched from the liquid phase to the gas phase when the engine 1 is in a high load state. When the refrigerant passage 25 is filled with gas, for example, the refrigerant may be replaced with air. However, a dedicated passage for air introduction and a pump are required, which is complicated. On the other hand, if the vaporized refrigerant as in the present embodiment is used, the structure is greatly simplified. The second circulation passage 33 is provided with a check valve 36 that prevents the liquid refrigerant expelled from the refrigerant passage 25 to the second circulation passage 33 from returning to the refrigerant passage 25.

  Next, when the operating condition of the engine 1 changes and the engine 1 is not in a high load state, it is necessary to return the state of the refrigerant passage 25 from the gas phase to the liquid phase again. In this case, the on-off valve 34 is opened and the pump 35 is operated to supply the liquid phase refrigerant in the refrigerant tank 31 to the refrigerant passage 25. As another method, potential energy utilizing the height of the refrigerant tank 31 can be used. That is, the liquid level 31b inside the refrigerant tank 31 is pushed up by the liquid refrigerant expelled to the second circulation passage 33 when the engine 1 is in a high load state. When the liquid refrigerant is expelled from all of the refrigerant passage 25, the height H2 of the liquid surface 31b inside the refrigerant tank 31 is vertical to the one end 25a of the refrigerant passage 25 as shown in FIG. 2B. It is made higher by a predetermined value ΔH (positive value) than the direction height H1. This is to store potential energy in the liquid refrigerant vertically above the height H1.

  On the other hand, the open / close valve 34 is opened when the engine 1 is not in a high load state. It is assumed that the pump 35 is open without blocking the first circulation passage 32 when not in operation. Then, the liquid refrigerant in the refrigerant tank 31 vertically above the height H <b> 1 flows into the first circulation passage 32. The refrigerant that has flowed into the first circulation passage 32 further flows into the refrigerant passage 25 from one end 25a of the refrigerant passage 25, and the refrigerant passage 25 is completely filled with the liquid refrigerant. At this time, the height H3 of the liquid surface 31b inside the refrigerant tank 31 is made higher than the position of the first circulation passage 32 as shown in FIG. 2C so that the first circulation passage 32 is completely liquid-tight. . In this way, all of the refrigerant passage 25 and the first and second circulation passages 32 and 33 can be returned from the gas phase to the liquid phase.

  The time required for switching the state of the refrigerant passage 25 from the liquid phase to the gas phase or vice versa depends on the request. Accordingly, the heat exchanger 21, the first and second circulations are configured so that the state of the refrigerant passage 25 can be switched from the liquid phase to the gas phase or vice versa in a time determined by the request. The specifications of the passages 32 and 33, the refrigerant tank 31, and the on-off valve 34, the type of refrigerant, and the total amount are determined. In FIG. 2, although the pump 35 is provided so that the refrigerant can be introduced into the refrigerant passage using the pump, the refrigerant tank 31 is provided above and the refrigerant is introduced into the refrigerant passage using gravity. Although the example which can also be shown was shown, you may make it the structure which employ | adopted only one of the methods.

  If the refrigerant passage 25 is filled with the liquid phase refrigerant when the operation of the engine 1 is stopped, the heat of the exhaust gas is taken away by the cooling water when the engine 1 is started next time, and the exhaust gas temperature decreases. There is a possibility that the activity of the catalyst provided in the exhaust passage is delayed. If the liquid-phase refrigerant is extracted from the refrigerant passage 25 before the stop, the non-return for preventing the liquid refrigerant expelled from the refrigerant passage 25 to the second circulation passage 33 from returning to the refrigerant passage 25 as described above. Because of the valve 36, the liquid refrigerant inside the refrigerant tank 31 does not flow into the refrigerant passage 25 via the second circulation passage 33.

  If the heat exchanger 21 is in the initial state shown in FIG. 2A when the engine 1 is cold started, the heat of the exhaust gas is taken away by the cooling water in the cooling water passage 11 by using the refrigerant passage 25 as a heat insulating layer. Disappears. As a result, it is possible to supply all the heat of the exhaust to the catalyst 15, and the warm-up completion of the catalyst 15 can be accelerated. If the warm-up completion of the catalyst 15 can be accelerated, the air-fuel ratio feedback control using the three-way catalyst can be started earlier.

  Since the warm-up of the catalyst 15 is completed when a predetermined time has elapsed from the cold start timing of the engine 1, it is determined that the warm-up of the catalyst 15 is completed at that timing, and then the engine 1 is warmed up. Therefore, the on-off valve 34 is fully opened. Then, in FIG. 2A, the liquid refrigerant in the refrigerant tank 31 that is vertically above the height H <b> 1 flows into the first circulation passage 32. The refrigerant that has flowed into the first circulation passage 32 further flows into the refrigerant passage 25 from one end 25a of the refrigerant passage 25, and the refrigerant passage 25 is completely filled with the liquid refrigerant. Then, as shown in FIG. 2C, the height H <b> 3 of the liquid level 31 b inside the refrigerant tank 31 is higher than the position of the first circulation passage 32. In this way, by returning all of the refrigerant passage 25 and the first and second circulation passages 32 and 33 from the gas phase to the liquid phase, the forced convection of the refrigerant is utilized after the warm-up of the catalyst 15 is completed. The temperature of the cooling water in the cooling water passage 11 can be increased, and the engine 1 can be warmed up. As described above, the pump 35 may be operated in order to fill the refrigerant passage 25 with the liquid second refrigerant.

  The engine controller 41 performs opening / closing driving of the opening / closing valve 34 and operation / non-operation of the pump 35. That is, the engine controller 41 determines whether or not the engine 1 is in a high load state based on the load of the engine 1 while the engine 1 is in operation. 34 is opened and the pump 35 is operated to keep the heat exchanger 21 in the state shown in FIG. 2C. When it is determined that the engine 1 is in a high load state, the on-off valve 34 is fully opened, the pump 35 is stopped, and the heat exchanger 21 is brought into the state shown in FIG. 2B. Thereafter, when the engine 1 is no longer in a high load state, the on-off valve 34 is opened and the pump 35 is operated to return the heat exchanger 21 to the state shown in FIG. 2C. Further, immediately before the engine 1 is stopped, the on-off valve 34 is fully closed, the pump 35 is stopped, and the heat exchanger 21 is set to the initial state shown in FIG. 2A. If the vaporization of the refrigerant is insufficient and the liquid-phase refrigerant remains in the refrigerant passage 25, the refrigerant tank 31 may be recovered by operating the pump 35 (reversely rotating normally). After the initial state, the on-off valve 34 is fully closed. When the engine 1 is started next time, the on-off valve 34 is kept in a fully closed state, the operation of the pump 35 is stopped, and the completion of warming up of the catalyst 15 is awaited. After the completion of warming up of the catalyst 15, in order to promote warming up of the engine 1, the on-off valve 34 is fully opened, and the heat exchanger 21 is shifted to the state shown in FIG. 2C.

  This control performed by the engine controller 41 will be described with reference to the flowcharts of FIGS.

  First, the flow of FIG. 6 is for controlling the on-off valve 34, the pump 35, and the flow rate adjusting valve 42 after the warm-up of the engine 1 is completed, and is executed at regular intervals (for example, every 10 ms).

  In step 1, it is determined whether or not the engine 1 is in a high load state. For example, a high load region may be determined on a map of an operation region diagram as shown in FIG. 7 using the load and rotation speed of the engine 1 as parameters. If the operating range determined from the load and rotation speed of the engine 1 belongs to this high load range, the engine 1 is in a high load state, and if it belongs to the low to medium load range, the engine 1 has a high load. What is necessary is just to make it judge that it is not a state. When the engine 1 is not in a high load state, the routine proceeds to step 2 and the flow rate adjustment valve 42 (see FIG. 4) is fully opened.

  In steps 3 and 4, the on-off valve 34 is fully opened and the pump 35 is operated. As a result, the heat exchanger 21 is brought into the state shown in FIG. 2C.

  On the other hand, when the load is high in step 1, the process proceeds to step 5 where the opening degree of the flow rate adjustment valve 42 is decreased. The flow rate adjusting valve 42 is a valve that can adjust the flow rate of the cooling water flowing through the cooling water passage 11 inside the heat exchanger 21, and from the engine outlet to the cooling water passage 11 inside the heat exchanger 21 as shown in FIG. 4. The bypass cooling water passage 7 is interposed. The reason why the opening degree of the flow rate adjustment valve 42 is reduced when the engine 1 is in a high load state (that is, the flow rate of the cooling water flowing through the cooling water passage 11 is reduced) is less than when the engine 1 is not in a high load state. This is to speed up the transition from the state shown in FIG. 2 to the state shown in FIG. 2B. That is, when the flow rate of the cooling water flowing through the cooling water passage 11 is decreased, the heat of the exhaust gas transmitted from the refrigerant in the refrigerant passage 25 to the cooling water in the cooling water passage 11 is reduced, and the reduced amount of heat is the liquid refrigerant. Is held on. Since the heat retained in the liquid refrigerant is used to increase the temperature of the liquid refrigerant, the vaporization of the liquid refrigerant is accelerated. As soon as the boiling of the refrigerant evaporates, the liquid refrigerant can be removed from the refrigerant passage 25, and the state shown in FIG.

  In steps 6 and 7, the on-off valve 34 is fully closed, and the operation of the pump 35 is stopped. Thereby, the heat exchanger 21 is brought into the state shown in FIG. 2B.

  Next, the flow of FIG. 8 is for controlling the on-off valve 34 and the pump 35 when the engine is stopped, and is executed at regular intervals (for example, every 10 ms).

  In step 21, it is checked whether or not the ignition switch 44 (see FIG. 2A) is OFF this time. When the ignition switch 44 is not OFF, it is determined that the engine is not stopped, and the current process is terminated.

  When the ignition switch 44 is OFF at this time in step 21, the routine proceeds to step 22 where the on-off valve 34 is fully closed.

  In step 23, it is checked whether or not the ignition switch 44 was previously turned off. When the ignition switch 44 was not OFF last time, that is, when the ignition switch 44 was switched from ON to OFF, it is determined that the engine was stopped, and the process proceeds to Steps 24 and 25. In steps 24 and 25, a timer is started (timer value t1 = 0), and the pump 35 is operated. The timer is for measuring the elapsed time from when the ignition switch 44 is switched from ON to OFF.

  If the ignition switch 44 was previously turned off in step 23, that is, if the ignition switch 44 is subsequently turned off, the process proceeds to step 26 and thereafter. In step 26, the timer value t1 is compared with a predetermined time Δ1. The predetermined time Δ1 determines the time required for the transition from the state shown in FIG. 2C to the state shown in FIG. 2A, and is set in advance. Before the timer value t1 passes the predetermined time Δ1, it is determined that the transition to the state shown in FIG. 2A has not been completed, and the routine proceeds to step 25 where the engine operation is continued. In step 22, the on-off valve 34 is fully closed, and the operation of the engine is continued in step 25, whereby the liquid refrigerant is expelled from the refrigerant passage 25.

  When the timer value t1 reaches the predetermined time Δ1 in step 26, it is determined that all of the liquid refrigerant is expelled from the refrigerant passage 25 and the transition to the state shown in FIG. 2A is completed, and the process proceeds from step 26 to step 27. Stop engine operation.

  As described above, in this embodiment, since the engine stop control is performed for a short time after the ignition switch 44 is switched from ON to OFF, the engine is operated during this time. Therefore, what is performed in the flow of FIG. 8 is an operation when the engine is stopped.

  In this embodiment, the engine operation is continued for a while after the ignition switch is turned off, but the engine operation is stopped simultaneously with turning off the ignition switch and the on-off valve 34 is closed, and the remaining heat is used when the engine is stopped. The inside of the refrigerant passage 25 may be replaced with a gas-phase refrigerant. Further, based on information from the navigation system and the like, it is predicted that the engine will be stopped before arrival at the destination, and the inside of the refrigerant passage 25 is replaced with a gas phase refrigerant in advance, and the engine is turned on simultaneously with the ignition switch being turned off. The operation may be stopped.

  Next, the flow of FIG. 9 is for controlling the on-off valve 34 and the pump 35 when the engine 1 is cold-started, and is executed at regular intervals (for example, every 10 ms).

  In step 31, it is checked whether or not the cold start is being performed. This can be done as follows. That is, the start-up water temperature detected by the water temperature sensor 43 (see FIG. 2A) is compared with a predetermined value, and when the start-up water temperature is equal to or lower than the predetermined value, the cold start is performed and the start-up water temperature exceeds the predetermined value. It is determined that it is not a cold start when Here, as the predetermined value, an upper limit value of a temperature range in which the catalyst 15 is desired to be warmed up may be determined. If it is not a cold start, the current process is terminated.

  When it is a cold start, the routine proceeds to step 32 where it is checked whether or not the catalyst provided in the exhaust passage has been warmed up. For example, it may be determined that the catalyst has been warmed up when the predetermined time Δ3 has elapsed since the ignition switch 44 was switched from OFF to ON. Before the catalyst warm-up is completed, the process proceeds to steps 33 and 34, where the on-off valve 34 is fully closed and the pump 35 is deactivated. That is, by maintaining the state of FIG. 2A, heat is not taken away from the exhaust by the heat exchanger 21, and warming up of the catalyst is promoted.

  On the other hand, when it is determined in step 32 that the catalyst has been warmed up, the routine proceeds to steps 35 and 36, where the on-off valve 34 is fully opened and the pump 35 is operated. As a result, the heat exchanger 21 is shifted to the state shown in FIG. 2C.

  Here, the operation of the present embodiment will be described.

  According to the present embodiment, the exhaust passage 3 (exhaust gas passage) through which the engine exhaust (exhaust gas) flows and the cooling water passage 11 (first medium) through which the cooling water (first medium) always used in the liquid phase flows. In the heat exchanger 21 that performs heat exchange between the exhaust gas and the cooling water, the exhaust passage 3 and the cooling water passage 11 are provided with a refrigerant passage 25 (through which the refrigerant (second medium) flows. When the heat exchange between the exhaust and the cooling water is promoted, the refrigerant passage 25 sandwiched between the exhaust passage 3 and the cooling water passage 11 is filled with the liquid phase refrigerant. When suppressing the heat exchange between the exhaust gas and the cooling water, the refrigerant passage 25 sandwiched between the exhaust passage 3 and the cooling water passage 11 is filled with gas. The refrigerant passage 25 is adjacent to the refrigerant passage 25 to promote heat exchange. 5 is filled with a liquid-phase refrigerant, so heat exchange using convection of the liquid-phase refrigerant allows heat exchange to be performed while suppressing boiling and evaporating of the cooling water compared to direct heat exchange without using the refrigerant. When the heat exchange is suppressed, the refrigerant passage 25 is filled with the gas, so that the boiling and evaporating of the cooling water can be effectively suppressed by a simple operation of replacing the gas with the gas.

  According to the present embodiment, as the refrigerant (second medium), when the engine 1 is in a high load state (the amount of heat exchange with the exhaust of the engine 1 is desired to be reduced, the coolant (first medium) has a higher temperature). The medium that boiles and vaporizes when the engine 1 is in a high-pressure state, so that the amount of heat exchange between the cooling water and the exhaust when the engine 1 is in a high load state is greater than when the refrigerant is liquid. It becomes possible to reduce, and it can avoid that cooling water evaporates inside the cooler 21.

  According to the present embodiment, the refrigerant passes through the refrigerant tank 31 that stores the refrigerant, the pump 35 that circulates the refrigerant between the refrigerant tank 31 and the refrigerant passage 25, the refrigerant passage 25, the refrigerant tank 31, and the pump 35. Circulation passages 32 and 33 (communication passages) communicating so as to circulate are provided, and when the heat exchange of the exhaust gas and the cooling water is promoted, the refrigerant is circulated by the pump 35 (see steps 1 and 4 in FIG. 6). When the heat exchange is suppressed, the pump 35 is stopped (see steps 1 and 7 to 11 in FIG. 6). Therefore, when the heat exchange is promoted, the circulation of the pump 35 forces the refrigerant in the refrigerant passage 25 to be forced. When heat exchange using convection is promoted and heat exchange is suppressed, the refrigerant remaining in the refrigerant passage 25 by stopping the pump 35 evaporates and evaporates by continuing to receive the heat of the exhaust, 3 and a cooling water passage 11 sandwiched by the refrigerant passage 25 can be filled with a readily gas.

  According to the present embodiment, the refrigerant tank 31 that stores the refrigerant, the circulation passages 32 and 33 (communication passage) that communicate with the refrigerant passage 25 and the refrigerant tank 31 so that the refrigerant circulates, and the circulation passages 32 and 33 are provided. The refrigerant passage 25 is provided with one end 25 a connected to the circulation passages 32, 33 and the other end 25 b positioned vertically below the one end 25 a, and the refrigerant tank 31 is connected to the refrigerant passage 25. When the refrigerant existing in liquid is guided and stored, and the liquid level 31b of the internal refrigerant when the refrigerant is guided and stored is higher than the vertical height of the one end 25a, and the heat exchange of the exhaust gas and the cooling water is suppressed. Since the on-off valve 34 is closed (see steps 1 and 6 in FIG. 6) and the heat exchange between the exhaust gas and the cooling water is promoted, the on-off valve 34 is opened (see steps 1 and 3 in FIG. 6). Use vaporization evaporation Since the refrigerant recovered in the refrigerant tank 31 can be reintroduced into the refrigerant passage 25 using gravity, the refrigerant passage 25 is filled with the liquid phase refrigerant without using the refrigerant pump, or It can be replaced with gas.

  According to this embodiment, the on-off valve 34 that can open and close the first circulation passage 32 is provided, and the on-off valve 34 is fully closed when the engine 1 is in a high load state (steps 1 and 6 in FIG. 6). Reference), the liquid level 31b of the refrigerant (second medium) inside the refrigerant tank 31 (second medium tank) is made higher than the vertical height of one end 25a of the refrigerant path 25 (second medium path), and the engine 1 Since the on-off valve 34 is fully opened (see steps 1 and 3 in FIG. 6) when it is no longer in the high load state, liquid can be supplied to the refrigerant passage 25 and the first and second circulation passages 32 and 33 with a simple configuration. The state in which the refrigerant is filled (see FIG. 2C) and the state in which the liquid refrigerant is removed from the refrigerant passage 25 (see FIG. 2B) can be switched.

  According to the present embodiment, since the cooling water passage 11 (first medium passage) covers the outer periphery of the refrigerant passage 25 (second medium passage), the cooling water is discharged from the exhaust when the engine 1 is in a high load state. Heat conduction to the can be suppressed.

  According to the present embodiment, since the check valve 36 that prevents the liquid-phase refrigerant from flowing into the refrigerant passage 25 is provided, the liquid in the refrigerant passage 25 can be removed when the engine 1 is in a high load state. The refrigerant can be quickly removed from the refrigerant passage 25.

  According to the present embodiment, the engine 1 is an engine including the catalyst 15 in the exhaust passage (2), and fills the refrigerant passage 25 with gas when the engine 1 is stopped (see steps 21 to 27 in FIG. 8). The heat of the exhaust is not lost to the cooling water at the next cold start of 1, and the warm-up completion of the catalyst 15 can be accelerated by that amount.

  According to this embodiment, the flow rate adjusting valve 42 that can adjust the flow rate of the cooling water (first medium) flowing through the cooling water passage 11 (first medium passage) is provided, and heat exchange between the exhaust gas and the first medium is suppressed. When the engine 1 is in a high load state, the flow rate adjustment valve 42 is used to set the flow rate of the cooling water (first medium) flowing through the cooling water passage 11 (first medium passage) to the exhaust gas and the first. Since the heat exchange of the medium is promoted (not in the high load state of the engine 1) (see steps 1, 2, and 5 in FIG. 6), the exhaust gas transmitted to the cooling water when the engine 1 is in the high load state is reduced. Since the heat is reduced and the heat of the reduced exhaust gas is retained in the liquid refrigerant, the vaporization of the liquid refrigerant is accelerated. As soon as the boiling of the liquid refrigerant evaporates, the liquid refrigerant can be quickly removed from the refrigerant passage 25.

  In the embodiment, the refrigerant passage 25 and the refrigerant tank 31 are connected by the two circulation passages 32 and 33 to form the refrigerant circulation passage. However, the embodiment is not necessarily limited thereto. For example, it may be a case where only one circulation passage 32 is provided.

11 Cooling water passage (first medium passage)
15 Catalyst 21 Heat exchanger 25 Refrigerant passage (second medium passage)
25a one end 25b other end 31 refrigerant tank (second medium tank)
32 1st circulation path 33 2nd circulation path 34 On-off valve 35 Pump 36 Check valve 41 Engine controller 42 Flow control valve 43 Water temperature sensor

Claims (7)

An exhaust gas passage through which the exhaust gas of the engine flows and a first medium passage through which the first medium always used in the liquid phase is passed, and heat exchanging heat between the exhaust gas and the first medium In the exchanger
The exhaust gas passage and the first medium passage are adjacent to each other with a second medium passage through which the second medium flows, and the exhaust gas passage is used to promote heat exchange between the exhaust gas and the first medium. When the second medium passage sandwiched between the first medium passage and the first medium passage is filled with a liquid second medium and heat exchange between the exhaust gas and the first medium is suppressed, the second medium passage is sandwiched between the exhaust gas passage and the first medium passage. A heat exchanger characterized in that the second medium passage is filled with gas. A tank for storing the second medium, a pump for circulating the second medium between the tank and the second medium passage, and a second medium for communicating with the second medium passage, the tank, and the pump so as to circulate. And a communication passage
The second medium is circulated by the pump when the heat exchange between the exhaust gas and the first medium is promoted, and the pump is stopped when the heat exchange between the exhaust gas and the first medium is suppressed. Item 2. The heat exchanger according to Item 1. A tank for storing the second medium, a communication path for communicating the second medium passage and the tank so that the second medium circulates, and an on-off valve for opening and closing the communication path,
The second medium path includes one end connected to the communication path, and the other end positioned vertically below the one end,
The tank guides and stores the second medium existing as a liquid in the second medium passage, and the liquid level of the second medium inside when the second medium is guided and stored is higher than the vertical height of the one end. Get higher,
The on-off valve is closed when heat exchange between the exhaust gas and the first medium is suppressed, and the on-off valve is opened when heat exchange between the exhaust gas and the first medium is promoted. The described heat exchanger.   The heat exchanger according to any one of claims 1 to 3, wherein the first medium passage covers an outer periphery of the second medium passage.   The heat exchanger according to any one of claims 1 to 4, further comprising a check valve that prevents the liquid-phase refrigerant from flowing into the second refrigerant passage. The engine is an engine having a catalyst in an exhaust passage,
The heat exchanger according to claim 5, wherein the second medium passage is filled with gas when the engine is stopped. A flow rate adjusting valve capable of adjusting a flow rate of the first medium flowing through the first medium passage;
When the heat exchange between the exhaust gas and the first medium is suppressed, the flow rate of the first medium flowing through the first medium passage is reduced by using the flow rate adjusting valve than when the heat exchange between the exhaust gas and the first medium is promoted. The heat exchanger according to any one of claims 1 to 6, characterized in that:

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