JP2022129920A - Exhaust heat recovery mechanism - Google Patents

Abstract

To provide an exhaust heat recovery mechanism using condensation water generated when heat exchange is performed between exhaust gas and a refrigerant.SOLUTION: An exhaust heat recovery mechanism 10 has an exhaust heat recovery passage 11, an exhaust gas passage changeover device 12 and a first heat exchanger 13. The exhaust heat recovery mechanism also includes a chemical thermal storage device 14 disposed on the downstream side of the first heat exchanger 13 in regard to a flow of exhaust gas in the exhaust heat recovery passage 11 and releasing heat stored through a hydration reaction with water or storing heat through a dehydration reaction by absorbing heat. The chemical thermal storage device 14 raises a temperature of exhaust gas performing the hydration reaction with the condensation water generated by the heat exchange in the first heat exchanger 13 and passing through the chemical thermal storage device 14, and raises a temperature of a temperature rise target disposed on the downstream side of the chemical thermal storage device 14.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD The present invention relates to an exhaust heat recovery mechanism, and more particularly to an exhaust heat recovery mechanism capable of exchanging heat between exhaust gas of an internal combustion engine and refrigerant.

An exhaust heat recovery device capable of exchanging heat between exhaust gas and cooling water has been proposed (see Patent Document 1, for example). The exhaust heat recovery device described in Patent Literature 1 recovers the amount of heat from the exhaust gas to raise the temperature of the cooling water, thereby promoting the warm-up of the internal combustion engine.

JP 2017-218966 A

The inventors of the present application focused on the fact that condensed water is generated when heat is exchanged between the exhaust gas and the cooling water in the exhaust heat recovery device described in Patent Document 1.

An object of the present disclosure is to provide an exhaust heat recovery mechanism that utilizes condensed water generated when heat is exchanged between exhaust gas and refrigerant.

An exhaust heat recovery mechanism of one aspect of the present invention that achieves the above objects includes an exhaust heat recovery passage that branches from an exhaust passage through which exhaust gas discharged from a cylinder of an internal combustion engine passes and then merges with the exhaust passage; an exhaust passage switching device for switching a flow to either one of the exhaust passage and the exhaust heat recovery passage; a first heat exchanger for exchanging heat between a refrigerant and exhaust gas, the exhaust heat recovery mechanism being positioned in the exhaust heat recovery passage downstream of the first heat exchanger with respect to exhaust flow , a chemical heat storage device that radiates heat stored by hydration reaction with water or stores heat by dehydration reaction by endothermic heat absorption, and the chemical heat storage device is condensed water generated by heat exchange in the first heat exchanger and the temperature of the exhaust gas passing through the chemical heat storage device is raised by hydration reaction with do.

According to one aspect of the present invention, the exhaust gas passing through the chemical heat storage device is caused to undergo a hydration reaction in the chemical heat storage device using the condensed water generated when the heat of the exhaust gas is recovered by the first heat exchanger. can be heated. This makes it possible to raise the temperature of the object to be heated that is arranged downstream of the chemical heat storage device.

It is a block diagram which illustrates the exhaust heat recovery mechanism of 1st embodiment. FIG. 4 is a flow diagram illustrating a method of controlling the exhaust heat recovery mechanism of the first embodiment; FIG. 3 is a flow diagram illustrating a control flow that is performed when a flag is set in the control flow of FIG. 2; 3 is a flow diagram illustrating the control flow continuing from I in FIG. 2; FIG. FIG. 2 is a correlation diagram illustrating the temperature of cooling water flowing through the detour passage of FIG. 1 and the temperature of exhaust gas flowing through the exhaust heat recovery passage; FIG. 5 is a configuration diagram illustrating an exhaust heat recovery mechanism of a second embodiment;

Embodiments of the exhaust heat recovery mechanism according to the present disclosure will be described below. In FIGS. 1 and 6, dashed-dotted lines indicate signal lines, white arrows indicate the flow of exhaust gas, and solid arrows indicate the flow of cooling water, which is a refrigerant. In FIGS. 1 and 6, the structures of cooling water and exhaust flow paths are changed for the sake of clarity, and do not necessarily correspond to those actually manufactured. Only one cylinder 2 is shown in order to avoid complication of FIGS.

As exemplified in FIG. 1, the exhaust heat recovery mechanism 10 of the first embodiment uses cooling water for cooling the internal combustion engine 1 as a coolant. and a second heat exchanger 15 to be described later.

The internal combustion engine 1 is a diesel engine that uses light oil as fuel, and is an engine that obtains power by reciprocating linear motion of a piston 3 inside a cylinder 2 . The internal combustion engine 1 is a multi-cylinder engine having not only one cylinder but also other cylinders (not shown). The fuel of the internal combustion engine 1 is not limited to light oil, and may be gasoline or liquefied gas. The number and arrangement of cylinders of the internal combustion engine 1 are not particularly limited. The internal combustion engine 1 includes an exhaust heat recovery mechanism 10 , a cooling mechanism 20 and an exhaust purification mechanism 30 .

The cooling mechanism 20 is a circulation circuit including a shared passage 21, a cooling passage 22, a bypass passage 23, and a cooling water passage switching device 24. A cooling water pump 25 and a water jacket 26 are arranged in the shared passage 21, A radiator 27 is arranged in the cooling passage 22 . The cooling mechanism 20 is configured such that after the cooling water passes through the shared passage 21, it flows through at least one of the cooling passage 22 and the bypass passage 23 by the cooling water passage switching device 24, and circulates again to the shared passage 21. .

The cooling water pump 25 is a pump that discharges cooling water and circulates the cooling water. The cooling water pump 25 is exemplified by an electric water pump or a mechanical water pump connected to the crankshaft 4 by a power transmission mechanism. The water jacket 26 is a cooling water passage provided around the cylinders 2 , and the passages are formed so as to surround the plurality of cylinders 2 .

The cooling water passage switching device 24 is arranged at a branch point of the cooling passage 22 and the bypass passage 23 . The cooling water passage switching device 24 is composed of a thermostat having a lifter (not shown) that expands and contracts as the temperature of the cooling water rises and contracts as the temperature of the cooling water drops. be done. The cooling water passage switching device 24 may be configured to adjust the flow rate of the cooling water flowing through the cooling passage 22 and the bypass passage 23 according to the temperature of the cooling water, and is composed of a three-way valve capable of controlling the degree of opening. may

The radiator 27 is arranged on the front side (left side in FIG. 1) of the vehicle on which the internal combustion engine 10 is mounted, and the cooling fan 28 is arranged on the rear side. The radiator 27 is a heat exchanger that uses the vehicle speed wind and the cooling wind from the subsequent cooling fan 28 to cool the cooling water that passes through it. The cooling passage 22 is a flow path in which a radiator 27 is provided in the middle thereof and cooling water is cooled by the radiator 27 . The detour passage 23 is a passage that bypasses the cooling passage 22 so that the cooling water is not cooled by the radiator 27 .

The exhaust purification mechanism 30 includes an oxidation catalyst device 31 , a filter device 32 , a reducing agent injection device 33 and a selective reduction catalyst device 34 arranged in the exhaust passage 5 . The oxidation catalyst device 31 is arranged upstream of the filter device 32 with respect to the flow of exhaust gas and has a catalyst for oxidizing hydrocarbons, carbon monoxide and nitrogen monoxide contained in the exhaust gas. The filter device 32 filters and collects particulate matter contained in the exhaust. The reducing agent injection device 33 is arranged upstream of the selective reduction catalyst device 34 with respect to the flow of exhaust gas, and injects urea water to supply the selective reduction catalyst device 34 with ammonia as a reducing agent. The selective reduction catalyst device 34 has a catalyst that reduces and purifies nitrogen oxides contained in the exhaust gas using ammonia as a reducing agent. The exhaust purification mechanism 30 is arranged on the upstream side of the oxidation catalyst device 31 and is arranged on the downstream side of the exhaust pipe fuel injection device that injects the fuel in advance into the exhaust, or the selective reduction catalyst device 34, A reducing agent adsorption catalyst device that adsorbs and removes the reducing agent contained in the exhaust after passing through the selective reduction catalyst device 34 may be provided.

In the present disclosure, a reduction catalyst device indicates a catalyst device that reduces and purifies nitrogen oxides contained in exhaust gas, and corresponds to the selective reduction catalyst device 34 in this embodiment. The reduction catalyst device may be an occlusion-type reduction catalyst device that stores nitrogen oxides under lean air-fuel mixture (lean) conditions and reduces nitrogen oxides under rich air-fuel mixture (rich) conditions.

The exhaust heat recovery mechanism 10 includes an exhaust heat recovery passage 11 , an exhaust passage switching device 12 , a first heat exchanger 13 , a chemical heat storage device 14 and a second heat exchanger 15 . The exhaust heat recovery mechanism 10 also includes a water temperature sensor 16 as a temperature variable acquisition device, a temperature difference sensor 17 and an exhaust flow rate sensor 18 as reaction variable acquisition devices, and a control device 40 .

The exhaust heat recovery passage 11 is a passage that joins the exhaust passage 5 after branching from the exhaust passage 5 through which the exhaust gas discharged from the cylinder 2 passes. The exhaust heat recovery passage 11 is desirably configured to pass through each device of the exhaust purification mechanism 30 even when the exhaust flows through the exhaust heat recovery passage 11 . Moreover, it is desirable that the exhaust heat recovery passage 11 joins the exhaust passage 5 upstream of the selective catalytic reduction device 34 with respect to the flow of the exhaust. The exhaust heat recovery passage 11 is configured to branch from the exhaust passage 5 on the downstream side of the filter device 32 with respect to the flow of exhaust gas and join the exhaust passage 5 on the upstream side of the selective catalytic reduction device 34 .

The exhaust passage switching device 12 is disposed at a branch point of the exhaust heat recovery passage 11 and the exhaust passage 5, or at a midway position between the branch points and confluence points of the exhaust heat recovery passage 11 and the exhaust passage 5. placed in The exhaust passage switching device 12 may be any one of the exhaust heat recovery passage 11 and the exhaust passage 5 as long as it can direct the flow of the exhaust gas. , a globe valve, a gate valve, a butterfly valve, or the like, which opens or blocks the exhaust passage 5 when placed in the middle position.

The first heat exchanger 13 is arranged midway between the exhaust heat recovery passage 11 and the bypass passage 23 . The first heat exchanger 13 exchanges heat between the exhaust gas flowing through the exhaust heat recovery passage 11 and the cooling water flowing through the bypass passage 23 . The configuration of the first heat exchanger 13 is not particularly limited as long as heat can be exchanged between the exhaust gas and the cooling water.

The chemical heat storage device 14 is arranged in the exhaust heat recovery passage 11 on the downstream side of the first heat exchanger 13 with respect to the exhaust flow. The chemical heat storage device 14 has a configuration in which the chemical heat storage material undergoes a hydration reaction with water to radiate the stored heat, or heat is absorbed and the chemical heat storage material undergoes a dehydration reaction to store heat. The chemical heat storage device 14 is desirably composed of a porous material in order to secure a contact surface area with passing exhaust gas. An example of the chemical heat storage device 14 is an open type device in which a honeycomb-shaped ceramic is used as a base material and a chemical heat storage material such as magnesium hydroxide or calcium chloride is supported.

The second heat exchanger 15 is arranged in the exhaust heat recovery passage 11 on the downstream side of the chemical heat storage device 14 with respect to the flow of exhaust gas and in the bypass passage 23 on the downstream side of the first heat exchanger 13 with respect to the flow of cooling water. be. The first heat exchanger 13 exchanges heat between the exhaust gas that has passed through the chemical heat storage device 14 and the cooling water that has passed through the first heat exchanger 13 . The configuration of the second heat exchanger 15 is not particularly limited as long as heat can be exchanged between the exhaust gas and the cooling water.

The water temperature sensor 16 is arranged in the common passage 21 between the water jacket 26 and the cooling water passage switching device 24, and serves as a temperature variable for cooling after passing through the water jacket 26 and before passing through the cooling water passage switching device 24. Obtain the water temperature Tw. The water temperature sensor 16 is a sensor that functions as a temperature variable acquisition device.

The temperature difference sensor 17 is the first temperature sensor arranged in the exhaust heat recovery passage 11 between the first heat exchanger 13 and the chemical heat storage device 14, and the exhaust gas between the chemical heat storage device 14 and the second heat exchanger 15. It consists of a second temperature sensor located in the heat recovery passage 11 . The temperature difference sensor 17 obtains the temperature difference ΔT by subtracting the outlet temperature of the exhaust gas passing through the outlet of the chemical heat storage device 14 from the inlet temperature of the exhaust gas passing through the inlet of the chemical heat storage device 14 .

The exhaust flow rate sensor 18 only needs to be able to acquire the volumetric flow rate Qg per unit time of the exhaust gas passing through the chemical heat storage device 14, and is arranged upstream of the chemical heat storage device 14 with respect to the flow of the exhaust gas.

The control device 40 is hardware composed of a central processing unit (CPU) that performs various types of information processing, an internal storage device capable of reading and writing programs used for performing the various types of information processing and information processing results, and various interfaces. be. The control device 40 is electrically connected to the exhaust passage switching device 12, the fuel injection device 7, and each acquisition device.

The control device 40 has a determination section 41, a switching control section 42, and a temperature increase control section 43 as functional elements. Each functional element is stored as a program in the internal storage device and executed by the central processing unit at appropriate times. Each functional element may be composed of a programmable controller (PLC) or an electric circuit that functions independently of the program.

The determination unit 41 is a functional element that receives variables acquired by each acquisition device and outputs a determination result based on the input variables to each control unit. The determination unit 41 determines whether the temperature state of the internal combustion engine 1 is cold, determines whether the dehydration reaction has started in the chemical heat storage device 14, and determines whether the dehydration reaction has completed. . Further, the determination unit 41 determines whether or not the time required to complete the dehydration reaction is long.

The determination unit 41 determines whether or not the temperature state of the internal combustion engine 1 is in the cold state by determining whether or not the coolant temperature Tw acquired by the water temperature sensor 16 is lower than a preset temperature threshold value Ta. The temperature threshold Ta is a temperature below the target temperature of the cooling water, and is preferably set to a temperature at which the cooling water passage switching device 24 starts to flow the cooling water to the cooling passage 22 . The temperature threshold Ta is obtained in advance by experiments, tests, or simulations. A target temperature of the cooling water may be used as the temperature threshold Ta. As a target temperature of the cooling water, around 85°C is exemplified.

When the temperature state of the internal combustion engine 1 is cold, it means that the internal combustion engine 1 is cold-started. A cold start indicates a state in which the temperature of each part of the internal combustion engine 1 is equal to or lower than the ambient temperature. The equivalent temperature includes the same temperature, and may be a temperature higher than that temperature within a range that can be regarded as the same temperature. For example, if the temperature difference is less than 10 degrees with respect to the ambient temperature, it is regarded as the same temperature.

The determination unit 41 determines whether or not the dehydration reaction has started by determining whether or not the temperature difference ΔT acquired by the temperature difference sensor 17 has become a negative value. The hydration reaction is a heat-generating reaction. When the hydration reaction occurs, the temperature of the exhaust gas after passing through the chemical heat storage device 14 becomes higher than the temperature of the exhaust gas before passing through, and the temperature difference ΔT is positive. becomes the value of The dehydration reaction is a reaction involving endothermic heat. When the dehydration reaction occurs, the temperature of the exhaust gas after passing through the chemical heat storage device 14 becomes lower than the temperature of the exhaust gas before passing through the chemical heat storage device 14, and the temperature difference ΔT is a negative value. become.

The determining unit 41 determines whether or not the dehydration reaction is completed based on the heat input threshold value Qa, which is the integrated value ΣQh of the heat input Qh per unit time to the chemical heat storage device 14 after the start of the dehydration reaction. It judges whether it is above or not. The heat input Qh is obtained from the temperature difference ΔT and the exhaust volumetric flow rate Qg obtained by the exhaust flow rate sensor, and the integrated value ΣQh is a value obtained by integrating the heat input Qh per unit time. The heat input amount threshold Qa is a threshold that can determine that the dehydration reaction of the chemical heat storage device 14 has been completed, and is obtained in advance by experiments, tests, or simulations. The amount of heat required to complete the dehydration reaction of the chemical heat storage device 14 depends on the amount of chemical heat storage material that the chemical heat storage device 14 has. The dehydration reaction may be completed when half or more of the chemical heat storage material of the chemical heat storage device 14 is dehydrated, and desirably when 80% or more is dehydrated.

The judging unit 41 judges whether or not the time required to complete the dehydration reaction is long by measuring the time tx that has elapsed since the temperature difference ΔT became negative. It is determined whether or not the time has passed more than the time threshold ta. The time threshold ta can be set as appropriate.

The switching control unit 42 receives the determination result of the determination unit 41, and controls the exhaust passage switching device 12 based on the determination result so that the exhaust passage switching device 12 changes the passage through which the exhaust flows to the exhaust heat recovery passage 11. Alternatively, it is a functional element that controls switching to either one of the exhaust passages 5 . The switching control unit 42 controls the exhaust passage switching device 12 to flow the exhaust gas to the exhaust heat recovery passage 11 when the determining unit 41 determines that the temperature state of the internal combustion engine 1 is cold. When the determination unit 41 determines that the temperature state of the internal combustion engine 1 is not cold, and the determination unit 41 determines that the dehydration reaction is completed, the switching control unit 42 switches the exhaust passage switching device 12 to Exhaust gas is controlled to flow to the exhaust passage 5 .

The temperature increase control unit 43 is a functional element that receives the determination result of the determination unit 41 and increases the temperature of the exhaust gas passing through the chemical heat storage device 14 based on the determination result. The temperature increase control unit 43 controls the fuel injection device 7 when the determination unit 41 determines that the time required for the dehydration reaction to complete is long. Means for raising the temperature of the exhaust gas passing through the chemical heat storage device 14 may be means for raising the temperature of the exhaust gas discharged from the fuel injection device 7 by increasing the amount of fuel injected from the fuel injection device 7, or A means for supplying part of the injected fuel to the oxidation catalyst device 31 in the exhaust passage 5 to raise the temperature of the exhaust gas passing through the oxidation catalyst device 31 is exemplified.

The control flow illustrated in FIG. 2 is repeatedly performed at predetermined intervals during operation of the internal combustion engine 1, and the control flow illustrated in FIGS. 3 and 4 is performed when a flag is set in the control flow of FIG. This is done until the flag is dropped. The predetermined cycle is defined as a cycle in which each acquisition device acquires an acquired value. The passage of one cycle in the flow chart is indicated by "return". A flag in the flow chart is a variable that holds the result of determination, and "1" indicates the state in which the flag is set, and "0" indicates the state in which the flag is turned off.

As illustrated in FIG. 2, when the water temperature sensor 16 acquires the coolant temperature Tw (S110), the determination unit 41 determines whether the acquired temperature Tw is lower than the temperature threshold Ta (S120). When determining that the temperature Tw is lower than the temperature threshold Ta (S120: YES), the determination unit 41 raises a flag (S130). When it is determined that the temperature Tw is equal to or higher than the temperature threshold Ta (S120: NO), the determination unit 41 determines whether or not the flag is turned down (S140).

Next, when the flag is set, the switching control unit 42 switches the passage through which the exhaust gas flows to the exhaust heat recovery passage 11 by the exhaust passage switching device 12 (S150). On the other hand, when the flag is lowered, the switching control unit 42 switches the passage through which the exhaust gas flows to the exhaust passage 5 by the exhaust passage switching device 12 (S160). The above control flow is repeated.

As illustrated in FIGS. 3 and 4, when the flag is set in the control flow of FIG. 2 and the temperature difference sensor 17 acquires the temperature difference ΔT (S210), the determination unit 41 determines whether the acquired temperature difference ΔT has become negative. It is determined whether or not (S220).

If it is determined that the temperature difference ΔT is not negative (S220: NO), the control flow returns to START. When it is determined that the temperature difference ΔT has become negative (S220: YES), and the exhaust gas flow rate sensor 18 acquires the volumetric flow rate Qg of the exhaust gas (S230), the determination unit 41 determines the unit time based on the temperature difference ΔT and the volumetric flow rate Qg. A heat input Qh per unit is estimated (S240). Next, the determination unit 41 calculates an integrated value ΣQh obtained by integrating the heat input amount Qh for each unit time (S250). Next, the determination unit 41 determines whether or not the integrated value ΣQh is greater than or equal to the heat input amount threshold Qa (S260). When it is determined that the integrated value ΣQh is equal to or greater than the heat input amount threshold Qa (S260: YES), the determination unit 41 clears the flag (S270), and this control flow ends.

When it is determined that the integrated value ΣQh is less than the heat input amount threshold Qa (S260: NO), the determination unit 41 determines whether or not the time tx that has elapsed since the temperature difference ΔT became negative has passed the time threshold ta or more ( S280). When it is determined that the time tx has exceeded the time threshold ta (S280: YES), the temperature increase control unit 43 increases the temperature of the exhaust gas by the fuel injection device 7 (S290), and the control flow returns to the start. If it is determined that the time tx has not passed the time threshold ta (S280: NO), the control flow returns to START.

When the internal combustion engine 1 is cold-started, the cooling water passage switching device 24 flows the cooling water only to the bypass passage 23 , and the exhaust passage switching device 12 flows the exhaust gas to the exhaust heat recovery passage 11 . Next, the first heat exchanger 13 heat-exchanges the cooling water and the exhaust, increases the temperature of the cooling water, and decreases the temperature of the exhaust. As the temperature of the exhaust gas drops, the water vapor contained in the exhaust gas becomes condensed water. Next, when the generated condensed water is carried by the exhaust gas to the chemical heat storage device 14 and collides with the chemical heat storage material of the chemical heat storage device 14, the chemical heat storage device 14 undergoes a hydration reaction with the collided condensed water, generating heat. do. The chemical heat storage device 14 raises the temperature of the exhaust gas passing through the chemical heat storage device 14 by heat generation of the chemical heat storage material. Next, the second heat exchanger 15 exchanges heat between the cooling water heated by the first heat exchanger 13 and the exhaust gas heated through the chemical heat storage device 14 to further increase the temperature of the cooling water, Lower the temperature of the exhaust.

As illustrated in FIG. 5, the exhaust heat recovery mechanism 10 raises the temperature of the exhaust gas whose temperature has decreased in the first heat exchanger 13 due to the hydration reaction of the chemical heat storage device 14. The temperature of the cooling water is raised in two steps by the two heat exchangers with the second heat exchanger 15 .

When the temperature of the cooling water rises, the cooling water passage switching device 24 causes the cooling water to flow through both the cooling passage 22 and the bypass passage 23 to reduce the flow rate of the cooling water flowing through the bypass passage 23 . On the other hand, when the hydration reaction is completed, the chemical heat storage material in the chemical heat storage device 14 undergoes a dehydration reaction and absorbs the heat of the exhaust gas. The chemical heat storage device 14 lowers the temperature of the exhaust gas passing through the chemical heat storage device 14 by absorbing the heat of the chemical heat storage material. The exhaust passage switching device 12 allows the exhaust gas to flow to the exhaust heat recovery passage 11 until the dehydration reaction is completed, and allows the exhaust gas to flow to the exhaust passage 5 when the dehydration reaction is completed.

As described above, the exhaust heat recovery mechanism 10 causes the exhaust passage switching device 12 to flow the exhaust gas to the exhaust heat recovery passage 11 when the temperature state of the internal combustion engine 1 is cold. As a result, the condensed water generated when the heat of the exhaust gas is recovered by the first heat exchanger 13 is used to cause a hydration reaction in the chemical heat storage device 14 to raise the temperature of the exhaust gas. By exchanging heat between the cooling water and the heated exhaust gas again in the second heat exchanger 15, the temperature of the cooling water can be further increased. As a result, it is possible to shorten the time required for warming up the internal combustion engine 1 when the internal combustion engine 1 is cold-started.

It is preferable that the exhaust heat recovery mechanism 10 continues to flow the exhaust gas to the exhaust heat recovery passage 11 until the dehydration reaction of the chemical heat storage device 14 is completed. As a result, the state in which the chemical heat storage device 14 stores heat can be maintained until the temperature state of the internal combustion engine 1 becomes cold next time. As a result, the temperature state of the internal combustion engine 1 next becomes cold, and when the exhaust gas flows into the exhaust heat recovery passage 11, a hydration reaction occurs and the temperature of the exhaust gas passing through the chemical heat storage device 14 rises. can be done.

The exhaust heat recovery mechanism 10 can determine the completion of the dehydration reaction of the chemical heat storage device 14 based only on the change in the temperature difference ΔT before and after the chemical heat storage device 14. It is desirable to make a determination based on the integrated value ΣQh of the heat input. As the flow rate of the cooling water flowing through the detour passage 23 decreases over time, the temperature change due to heat exchange in the first heat exchanger 13 becomes poor, making it difficult to determine the completion of the dehydration reaction based only on the temperature difference ΔT. Become. Therefore, by making a judgment based on the integrated value ΣQh of the amount of heat input to the chemical heat storage device 14, it is possible to judge the completion of the dehydration reaction with high accuracy.

The exhaust heat recovery mechanism 10 raises the temperature of the exhaust gas when a long time has elapsed since the start of the dehydration reaction, so that the time required for the completion of the dehydration reaction can be shortened. This is advantageous for avoiding the effects on devices arranged downstream of the exhaust heat recovery mechanism 10 .

It is desirable that the exhaust heat recovery mechanism 10 has a configuration in which the hydration reaction of the chemical heat storage device 14 is not completed while the temperature state of the internal combustion engine 1 is cold. Specifically, it is desirable that the amount of chemical heat storage material in the chemical heat storage device 14 is set to an amount that does not complete the hydration reaction until the temperature state of the internal combustion engine 1 exits from the cold state. This amount can be determined in advance by tests, experiments, or simulations. In the present disclosure, "while the temperature state of the internal combustion engine 1 is in the cold state" means that the cooling water flows only through the bypass passage 23 by the cooling water passage switching device 24 of the cooling mechanism 20 .

As illustrated in FIG. 6, the exhaust heat recovery mechanism 10 of the second embodiment differs from the first embodiment in the object to be heated. In the exhaust heat recovery mechanism 10 of the second embodiment, the target for temperature rise is the selective catalytic reduction device 34, the second heat exchanger 15 is not provided, and the exhaust heat recovery passage 11 on the downstream side of the chemical heat storage device 14 is selected. It is configured to merge with the exhaust passage 5 before the target reduction catalyst device 34 . The exhaust heat recovery mechanism 10 also includes an exhaust temperature sensor 19 as a temperature variable acquisition device.

The exhaust temperature sensor 19 is a sensor that is arranged upstream and/or downstream of the selective catalytic reduction device 34 and acquires the temperature Tg of the passing exhaust gas. A device that indirectly acquires the exhaust temperature from the fuel injection amount instead of the exhaust temperature sensor 19 and a sensor that directly acquires the temperature of the selective catalytic reduction device 34 are also exemplified.

A determination unit 41 determines whether the temperature state of the internal combustion engine 1 is in a cold state, determines whether the coolant temperature Tw obtained by the water temperature sensor 16 is lower than the temperature threshold value Ta, and determines whether the temperature of the cooling water Tw obtained by the exhaust temperature sensor 19 is lower than the temperature threshold Ta. is lower than a preset temperature threshold value Tb. The temperature threshold Tb is the temperature at which the catalyst of the selective catalytic reduction device 34 is activated, and is obtained in advance by experiments, tests, or simulations. The temperature at which the catalyst is activated is the temperature at which the urea water is injected from the reducing agent injection device 33. The injected urea water hydrolyzes into ammonia, and the selective reduction catalyst device 34 to which the ammonia is supplied produces nitrogen. This is the temperature at which oxide purification begins. Temperatures in the range of 200° C. to 300° C. are exemplified as the temperature at which the catalyst is activated. In other words, the state in which the catalyst activation temperature is not reached is the state in which the purification rate of the selective catalytic reduction device 34 decreases.

In the present embodiment, the cold state of the internal combustion engine 1 is a state in which the internal combustion engine 10 is cold-started, or a state in which the catalyst of the selective catalytic reduction device 34 has not yet reached a temperature that activates.

Desirably, the amount of chemical heat storage material in the chemical heat storage device 14 is larger than that in the first embodiment, and the amount is such that the hydration reaction does not complete until the catalyst of the selective catalytic reduction device 34 is activated.

As described above, the exhaust heat recovery mechanism 10 uses the condensed water generated when the heat of the exhaust gas is recovered by the first heat exchanger 13 to cause a hydration reaction in the chemical heat storage device 14 to recover the exhaust gas. It is possible to raise the temperature of the selective catalytic reduction device 34 to be heated. As a result, it is advantageous to activate the catalyst at an early stage, and the purification rate of exhaust gas can be improved.

The coolant of the exhaust heat recovery mechanism 10 of the above-described embodiment is not limited to cooling water circulating in the cooling mechanism 20, and may be composed of lubricating oil for lubricating or cooling each part of the internal combustion engine 1.

The temperature variable acquiring device of the exhaust heat recovery mechanism 10 may be any device that acquires a temperature variable that can determine whether the temperature state of the internal combustion engine 1 is cold. An oil temperature sensor that acquires the temperature of the lubricating oil of the internal combustion engine 1 is also exemplified as the temperature variable acquisition device. A sensor for acquiring the opening degree of the cooling water passage switching device 24 of the cooling mechanism 20 is also exemplified as the temperature variable acquiring device.

The reaction variable acquisition device of the exhaust heat recovery mechanism 10 may be any device that acquires a reaction variable that can determine the reaction state in the chemical heat storage device 14 . The reaction variable acquisition device may be composed only of the temperature difference sensor 17 . In addition, as a reaction variable acquisition device, an intake air amount sensor is used instead of the exhaust flow rate sensor 18, and the volumetric flow rate of the intake air acquired by the intake air amount sensor arranged in the intake passage 6, A device for estimating the exhaust volumetric flow rate Qg from the fuel injection amount is also exemplified.

The exhaust heat recovery mechanism 10 may raise the temperature of both the second heat exchanger 15 and the selective catalytic reduction device 34 . Specifically, the exhaust heat recovery mechanism 10 branches from the exhaust heat recovery passage 11 between the chemical heat storage device 14 and the second heat exchanger 15 in contrast to the configuration of the first embodiment, and selects a selective reduction catalyst device. It may be configured to include a passage that merges with the exhaust passage 5 before 34 and a passage switching device arranged at a branch of the passage and the exhaust heat recovery passage 11 . This makes it possible to raise the temperature of the selective catalytic reduction device 34 after raising the temperature of the cooling water.

The temperature raising device of the exhaust heat recovery mechanism 10 is not limited to the fuel injection device 7 as long as it can raise the temperature of the exhaust gas passing through the chemical heat storage device 14 . An example of the temperature raising device is an exhaust pipe fuel injection device when the exhaust purification mechanism 30 has an exhaust pipe fuel injection device. An electric heater installed in the exhaust heat recovery passage 11 on the upstream side of the chemical heat storage device 14 is also exemplified as the temperature raising device.

The cooling water passage switching device 24 may be arranged at either the branch point or the confluence point of the cooling passage 22 and the detour passage 23 . The outlet control type cooling mechanism 20 in which the cooling water passage switching device 24 is arranged at the branch point of the cooling passage 22 and the detour passage 23 can improve the air bleeding property and suppress the occurrence of cavitation, thereby improving the durability. It is particularly suitable for large vehicles such as trucks. The inlet control type cooling mechanism 20 in which the cooling water passage switching device 24 is arranged at the confluence point of the cooling passage 22 and the detour passage 23 is advantageous in adjusting the temperature of the cooling water compared to the outlet control type cooling mechanism 20. become.

1 Internal combustion engine 2 Cylinder 5 Exhaust passage 10 Exhaust heat recovery mechanism 11 Exhaust heat recovery passage 12 Exhaust passage switching device 13 First heat exchanger 14 Chemical heat storage device 15 Second heat exchanger 16 Water temperature sensor 17 Temperature difference sensor 18 Exhaust flow rate Sensor 19 Exhaust temperature sensor 40 Control device

Claims (8)

an exhaust heat recovery passage branching from an exhaust passage through which exhaust gas discharged from a cylinder of an internal combustion engine passes and then joining the exhaust passage; an exhaust passage switching device for switching; and a first heat exchanger arranged in the exhaust heat recovery passage for exchanging heat between a refrigerant composed of either cooling water or lubricating oil of the internal combustion engine and exhaust gas. In the exhaust heat recovery mechanism equipped with
A chemical element disposed in the exhaust heat recovery passage on the downstream side of the first heat exchanger with respect to the flow of the exhaust gas and dissipating heat stored by hydration reaction with water or storing heat by dehydration reaction by heat absorption. A heat storage device is provided, and this chemical heat storage device undergoes a hydration reaction with condensed water generated by heat exchange in the first heat exchanger to raise the temperature of the exhaust gas passing through the chemical heat storage device, and the chemical heat storage device increases the temperature of the exhaust gas passing through the chemical heat storage device. An exhaust heat recovery mechanism characterized in that it is configured to raise the temperature of an object to be heated that is arranged downstream of the device. disposed in the exhaust heat recovery passage on the downstream side of the chemical heat storage device with respect to the flow of the exhaust gas to exchange heat between the refrigerant after passing through the first heat exchanger and the exhaust gas after passing through the chemical heat storage device 2. The exhaust heat recovery mechanism according to claim 1, further comprising a second heat exchanger that serves as the object to be heated. The internal combustion engine is configured to include a reduction catalyst device for reducing and purifying exhaust gas in the exhaust passage,
2. The exhaust heat recovery system according to claim 1, wherein said exhaust heat recovery passage joins said exhaust passage on the upstream side of said reduction catalyst device with respect to the flow of exhaust gas, and said reduction catalyst device is said object to be heated. mechanism. a temperature variable acquisition device that acquires a temperature variable that can determine whether the temperature state of the internal combustion engine is cold, and a control device that controls the exhaust passage switching device,
When the control device determines that the temperature state of the internal combustion engine is cold based on the temperature variable obtained by the temperature variable obtaining device, the exhaust passage switching device causes the exhaust gas to flow to the exhaust heat recovery passage. 4. The exhaust heat according to any one of claims 1 to 3, wherein when it is determined that the temperature state of the internal combustion engine is not cold, the exhaust passage switching device controls the flow of the exhaust gas to the exhaust passage. recovery mechanism. comprising a reaction variable acquisition device for acquiring a reaction variable capable of determining a reaction state in the chemical heat storage device;
The control device determines that the dehydration reaction in the chemical heat storage device is completed based on the reaction variable acquired by the reaction variable acquisition device when exhaust gas is caused to flow into the exhaust heat recovery passage by the exhaust passage switching device. The exhaust passage switching device causes the exhaust gas to flow to the exhaust heat recovery passage until the determination is made, and the exhaust passage switching device causes the exhaust gas to flow to the exhaust passage when it is determined that the dehydration reaction is completed. The exhaust heat recovery mechanism according to claim 4. The reaction variable is composed of the difference obtained by subtracting the outlet temperature of the exhaust gas passing through the outlet of the chemical heat storage device from the inlet temperature of the exhaust gas passing through the inlet of the chemical heat storage device, and the flow rate of the exhaust gas passing through the chemical heat storage device. ,
The control device estimates the amount of heat input to the chemical heat storage device based on the difference and the flow rate, and determines that the dehydration reaction is completed when the estimated amount of heat input reaches or exceeds a preset heat input amount threshold. 6. The exhaust heat recovery mechanism according to claim 5, which is configured to determine. A temperature raising device for raising the temperature of the exhaust gas is provided on the upstream side of the chemical heat storage device with respect to the flow of the exhaust gas,
The control device measures the time elapsed after a difference obtained by subtracting the outlet temperature of the exhaust gas passing through the outlet of the chemical heat storage device from the inlet temperature of the exhaust gas passing through the inlet of the chemical heat storage device becomes negative, and measures the time. 7. The configuration according to any one of claims 4 to 6, wherein control is performed to raise the temperature of the exhaust gas passing through the chemical heat storage device by the temperature raising device when the time has passed a preset time threshold or more. The exhaust heat recovery mechanism according to the paragraph. The coolant is cooling water, and the cooling water is at least one of a cooling water pump, a water jacket, a cooling water passage switching device, a cooling passage in which a radiator is interposed, and a bypass passage that bypasses the cooling passage. It is a configuration that circulates through the passages in order,
The exhaust heat recovery mechanism according to any one of claims 1 to 7, wherein the first heat exchanger is arranged in the middle of the bypass passage.

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