Exhaust gas purification devices and methods

Abstract

An exhaust gas purification device and an exhaust gas purification method are provided. The exhaust gas purification device includes: a redox catalyst having both oxidation and reduction effects; a selective reduction catalyst disposed downstream of the redox catalyst and adsorbing ammonia; a temperature acquisition unit that acquires the temperature of a portion related to the temperature of the selective reduction catalyst; a mixing ratio acquisition unit that acquires the exhaust gas mixing ratio, representing the relationship between ammonia and oxygen at the upstream and downstream sides of the selective reduction catalyst; and a control unit that, when the acquired temperature is above a predetermined temperature, performs a first control based on the acquired exhaust gas mixing ratio. If the mixing ratio of the exhaust gas downstream of the selective reduction catalyst is greater than the mixing ratio of the exhaust gas upstream of the selective reduction catalyst, the first control changes the mixing ratio of the exhaust gas upstream of the selective reduction catalyst from a balanced ratio to a lean ratio. If the mixing ratio of the exhaust gas downstream of the selective reduction catalyst is less than the mixing ratio of the exhaust gas upstream of the selective reduction catalyst, the second control changes the mixing ratio of the exhaust gas downstream of the selective reduction catalyst from a balanced ratio to a lean ratio.

Description

Technical Field

[0001] This invention relates to an exhaust gas purification device and an exhaust gas purification method. Background Technology

[0002] It is known that catalysts are used to precipitate nitrogen oxides (NO) such as nitric oxide (NO) and nitrogen dioxide (NO2) in the exhaust of internal combustion engines, such as engines. x Technologies for purifying harmful substances such as ammonia are being developed. Furthermore, ammonia engines, which use ammonia as fuel, are being researched as internal combustion engines. Because ammonia does not contain carbon atoms, it has the advantage of not producing carbon dioxide during combustion in an ammonia engine.

[0003] When ammonia is completely burned, it is entirely converted into nitrogen and water. However, in the actual combustion of ammonia in an ammonia engine, incomplete combustion occurs, resulting in exhaust gases containing unreacted ammonia, nitrogen oxides such as NO, etc. Therefore, it is desirable to use catalysts or the like to purify the exhaust gases containing unreacted ammonia, nitrogen oxides such as NO, etc.

[0004] For example, an exhaust purification device is proposed for purifying the exhaust gas from an internal combustion engine that obtains driving power through the combustion of ammonia, and is capable of suppressing ammonia emissions. As an exhaust purification device capable of suppressing ammonia emissions, an exhaust purification device is proposed comprising: a catalyst disposed in the main flow path for the exhaust gas from an internal combustion engine fueled by ammonia, and having a three-way catalytic converter function and an ammonia adsorption function; and a control unit that, based on information relating to at least one of ammonia removal from the catalyst and the activation temperature of the catalyst, changes the mixture ratio of the exhaust gas upstream of the catalyst from a balanced ratio to a lean ratio (for example, see Patent Document 1).

[0005] Furthermore, an exhaust purification device is proposed, comprising: a redox catalyst disposed in a main flow path for exhaust gas from an ammonia-fueled internal combustion engine, and having both oxidation and reduction functions; a selective reduction catalyst disposed in the main flow path; a temperature acquisition unit that acquires the temperature of the selective reduction catalyst; and a control unit that, when the temperature of the selective reduction catalyst acquired by the temperature acquisition unit exceeds the activation temperature of the selective reduction catalyst, changes the mixing ratio of the exhaust gas upstream of the redox catalyst and the selective reduction catalyst from a balanced ratio to a lean ratio (for example, see Patent Document 2).

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-167822

[0007] Patent Document 2: Japanese Patent Application Publication No. 2019-167823

[0008] In the exhaust purification devices of Patent Documents 1 and 2, the exhaust mixture ratio is detected at a point downstream of the internal combustion engine. Therefore, there is a concern that the functions of the redox catalyst and the selective reduction catalyst may not be fully utilized. For example, in an exhaust purification device where a redox catalyst is installed upstream and a selective reduction catalyst is installed downstream in the main flow path of the exhaust gas, even if control is applied to change the exhaust mixture ratio upstream of the catalyst from a balanced ratio to a lean ratio, if the degree of control is inappropriate, there is a possibility that the mixture concentration in the selective reduction catalyst becomes below the balanced ratio, resulting in insufficient exhaust purification. Therefore, there is room for improvement in the control of exhaust purification devices that use the exhaust mixture ratio to purify the exhaust gas of an internal combustion engine. Summary of the Invention

[0009] This disclosure relates to exhaust purification devices, exhaust purification methods, and procedures capable of suppressing the emission of unburned ammonia and nitrogen oxides from ammonia-fueled internal combustion engines.

[0010] This disclosure was made to solve at least a part of the above-mentioned problems and can be implemented in a form described in the following manner.

[0011] The first aspect of this disclosure is an exhaust gas purification device comprising: a redox catalyst disposed in a main flow path and having both oxidation and reduction functions, the main flow path being for exhaust gas from an internal combustion engine that obtains driving force through the combustion of ammonia; a selective reduction catalyst disposed downstream of the redox catalyst in the main flow path and adsorbing ammonia that has passed through the redox catalyst; a temperature acquisition unit that acquires a temperature at a location relating to the temperature of the selective reduction catalyst; a mixture ratio acquisition unit that acquires an exhaust gas mixture ratio representing the relationship between ammonia and oxygen at upstream and downstream sides of the selective reduction catalyst; and a control unit that controls the temperature acquired by the temperature acquisition unit to be above a temperature corresponding to a predetermined activation temperature of the selective reduction catalyst. In the case where the mixture ratio of the exhaust gas obtained by the mixture ratio acquisition unit is greater than the mixture ratio of the exhaust gas at the downstream side of the selective reduction catalyst, a first control is performed, which changes the mixture ratio of the exhaust gas at the upstream side of the redox catalyst to a lean mixture ratio. If the mixture ratio of the exhaust gas at the downstream side of the selective reduction catalyst is less than the mixture ratio of the exhaust gas at the upstream side of the selective reduction catalyst, a second control is performed, which changes the mixture ratio of the exhaust gas at the upstream side of the redox catalyst to a lean mixture ratio.

[0012] With regard to the second aspect of this disclosure, in the exhaust gas purification device of the first aspect, when the difference between the mixing ratio of the exhaust gas at the upstream side of the selective reduction catalyst and the mixing ratio of the exhaust gas at the downstream side of the selective reduction catalyst is within a predetermined range, the control unit performs a third control, which changes the mixing ratio of the exhaust gas at the upstream side of the selective reduction catalyst from lean to balanced.

[0013] In the third aspect of this disclosure, in the exhaust purification device of the second aspect, the control unit performs control and reports information indicating an abnormality if the difference is outside a predetermined range after a predetermined time has elapsed since the start of the first or second control.

[0014] With respect to the fourth aspect of this disclosure, in the exhaust purification device of the second aspect, the control unit performs the first control, the second control, and the third control at least once when the internal combustion engine is started.

[0015] The fifth aspect of this disclosure is an exhaust gas purification method that uses a redox catalyst and a selective reduction catalyst to purify the exhaust gas of an internal combustion engine that obtains driving force through the combustion of ammonia. The exhaust gas purification method includes the following steps: obtaining a temperature at a location related to the temperature of the selective reduction catalyst; obtaining an exhaust gas mixing ratio representing the relationship between ammonia and oxygen at the upstream and downstream sides of the selective reduction catalyst; and, if the obtained temperature is above a temperature corresponding to a predetermined activation temperature of the selective reduction catalyst, increasing the exhaust gas mixing ratio at the downstream side of the selective reduction catalyst based on the obtained exhaust gas mixing ratio. Given the exhaust gas mixing ratio at the upstream side of the selective reduction catalyst, a first control is performed, which changes the exhaust gas mixing ratio at the upstream side of the redox catalyst from a balanced ratio to a lean ratio. If the exhaust gas mixing ratio at the downstream side of the selective reduction catalyst is less than the exhaust gas mixing ratio at the upstream side of the selective reduction catalyst, a second control is performed, which changes the exhaust gas mixing ratio at the upstream side of the redox catalyst by changing the exhaust gas mixing ratio at the downstream side of the selective reduction catalyst from a balanced ratio to a lean ratio.

[0016] The sixth aspect of this disclosure is a program stored in a computer-readable medium and used to cause a computer to perform an exhaust gas purification process. This exhaust gas purification process uses a redox catalyst and a selective reduction catalyst to purify the exhaust gas from an internal combustion engine that obtains driving force through the combustion of ammonia. The program is used to cause the computer to perform the exhaust gas purification process, which includes: acquiring the temperature of a portion related to the temperature of the selective reduction catalyst; acquiring an exhaust gas mixture ratio representing the relationship between ammonia and oxygen at the upstream and downstream sides of the selective reduction catalyst; and, if the acquired temperature is above a temperature corresponding to a predetermined activation temperature of the selective reduction catalyst, adjusting the exhaust gas mixture ratio according to the acquired exhaust gas mixture ratio. If the mixing ratio of the exhaust gas at the downstream side of the selective reduction catalyst is greater than the mixing ratio of the exhaust gas at the upstream side of the selective reduction catalyst, a first control is performed, which changes the mixing ratio of the exhaust gas at the upstream side of the redox catalyst to a lean ratio. If the mixing ratio of the exhaust gas at the downstream side of the selective reduction catalyst is less than the mixing ratio of the exhaust gas at the upstream side of the selective reduction catalyst, a second control is performed, which changes the mixing ratio of the exhaust gas at the upstream side of the redox catalyst to a lean ratio.

[0017] According to this disclosure, it is possible to suppress the emission of unburned ammonia and nitrogen oxides in an internal combustion engine that uses ammonia as fuel. Attached Figure Description

[0018] Figure 1 This is a schematic structural diagram of an exhaust purification device according to one embodiment of the present disclosure.

[0019] Figure 2 This is a flowchart illustrating the operation of an exhaust purification device according to one embodiment of the present disclosure.

[0020] Figure 3 This is a graph showing the characteristics of a selective reduction catalyst in an exhaust gas purification device according to an embodiment of the present disclosure, which are related to the temperature of the catalyst and the mixing ratio of the exhaust gas at the upstream and downstream sides of the selective reduction catalyst.

[0021] Figure 4 This indicates the concentration of ammonia (NH3) and nitrogen oxides (NOx) in the exhaust gas at the first stage of the exhaust flow path of an internal combustion engine. x A graph showing the relationship between the concentration of α and the concentration of hydrogen (H2).

[0022] Figure 5 This indicates the concentration of ammonia (NH3) and nitrogen oxides (NOx) in the exhaust gas at the second stage of the exhaust flow path of an internal combustion engine.x A graph showing the relationship between the concentration of α and the concentration of hydrogen (H2).

[0023] Figure 6 This indicates the nitrogen oxides (NOx) in the exhaust gas at the third stage of the exhaust flow path of an internal combustion engine. x A graph showing the relationship between the concentration of α and the concentration of hydrogen (H2).

[0024] Figure 7 This is a schematic structural diagram of an exhaust gas purification device including a reporting section, according to one embodiment of the present disclosure. Detailed Implementation

[0025] The forms used to implement the present invention will now be described in detail. However, the present invention is not limited to the embodiments described below. In the embodiments described below, structural elements (including element steps, etc.) are not essential, except where specifically stated or deemed necessary in principle. The same applies to numerical values ​​and their ranges; they are not intended to limit the present invention. The numerical values ​​and ranges shown in this disclosure are examples and may be replaced with other numerical values ​​and ranges.

[0026] [Exhaust gas purification device]

[0027] The exhaust purification device according to one embodiment of the present disclosure will be described below.

[0028] Figure 1 This is a schematic structural diagram of the exhaust gas purification device disclosed herein.

[0029] Figure 1 This is a schematic diagram of an engine system 1 as one embodiment of the present disclosure. The engine system 1 is, for example, mounted on a vehicle to generate driving force for propelling the vehicle. The engine system 1 includes: a combustion device 20 that generates driving force; and an exhaust purification device 10 that removes harmful substances such as ammonia (NH3) and nitrogen oxides (NOx) from the exhaust gas from the combustion device 20. x Purification is carried out using methods such as purification.

[0030] The combustion device 20 includes a combustion state control unit 21 and an internal combustion engine 22. An example of the internal combustion engine 22 is an ammonia engine that generates power by burning ammonia. Hereinafter, ammonia will be referred to simply as "ammonia". The combustion state control unit 21 adjusts the throttle valve (not shown) to change the air flow rate supplied to the internal combustion engine 22, and adjusts the fuel supply valve (not shown) to change the fuel supply quantity to the internal combustion engine 22. Thus, the combustion state control unit 21 controls the mass ratio (mixture ratio) of air to fuel within and from the internal combustion engine 22 towards rich, balanced, and lean states. Regarding the mixture ratio, when "Φ = stoichiometric air-fuel ratio / actual air-fuel ratio of the mixture", a rich state refers to a mixture ratio where Φ > 1, a balanced state refers to a mixture ratio where Φ = 1, and a lean state refers to a mixture ratio where Φ < 1. Φ is also called the "equivalent ratio". The combustion state control unit 21 is installed, for example, via an electronic control unit (ECU).

[0031] The exhaust gas purification device 10 of this embodiment uses a redox catalyst and a selective reduction catalyst to purify harmful substances in the exhaust gas. In the following description, a three-way catalyst is cited as an example of a redox catalyst, and an SCR catalyst is cited as an example of a selective reduction catalyst that functions as an adsorption catalyst. Furthermore, as a redox catalyst, any catalyst having both oxidation and reduction effects can be used, except for a three-way catalyst. For example, a redox catalyst can be a catalyst in which ceramics, titanium dioxide, or the like are used as supports, and precious metals such as platinum, rhodium, or palladium are used as active catalyst components. For a selective reduction catalyst, any catalyst having ammonia adsorption effects can also be used, except for an SCR catalyst. For example, a selective reduction catalyst can be a catalyst in which ceramics, titanium dioxide, or the like are used as supports, and zeolite is used as an active catalyst component.

[0032] Furthermore, in the following description, the side of the exhaust purification device 10 closest to the internal combustion engine 22 will be referred to as the "upstream side," and the side furthest from the internal combustion engine 22 will be referred to as the "downstream side." Figure 1 In this case, the left side corresponds to the upstream side, and the right side corresponds to the downstream side.

[0033] The exhaust purification device 10 includes: a control unit 11 that controls each part of the exhaust purification device 10, an exhaust pipe 19 extending from the internal combustion engine 22, a three-way catalyst 12, an SCR catalyst 13 respectively installed on the exhaust pipe 19, a first mixture ratio acquisition unit 14, a second mixture ratio acquisition unit 15, and a temperature acquisition unit 16.

[0034] The control unit 11 receives signals representing the acquired values ​​obtained from the first mixing ratio acquisition unit 14, the second mixing ratio acquisition unit 15, and the temperature acquisition unit 16. The control unit 11 uses the received acquired values ​​to perform the control described later. Figure 2 The system switches the air-fuel mixture ratio of the internal combustion engine 22, thereby switching the air-fuel mixture ratio of the exhaust gas upstream of the three-way catalytic converter 12 and the SCR catalyst 13. The control unit 11 is installed, for example, via an ECU. The exhaust pipe 19 forms a main flow path for the exhaust gas from the internal combustion engine 22. The exhaust gas from the internal combustion engine 22 passes through the main flow path within the exhaust pipe 19, passes through the three-way catalytic converter 12 and the SCR catalyst 13, and is released to the outside air.

[0035] The three-way catalytic converter 12 is positioned on the upstream side of the main road, in other words, upstream of the SCR catalyst 13. The three-way catalytic converter 12 has the following characteristics: it can purify ammonia and NO in exhaust gas. x Hydrogen (H2) can be mixed, but their purification performance decreases when the mixing ratio deviates from the predetermined range near the mixing ratio.

[0036] Additionally, the exhaust purification device 10 may have a sensor (not shown) upstream of the three-way catalytic converter 12 to measure the oxygen (O2) concentration (i.e., mixture ratio) of the exhaust gas (exhaust gas) from the internal combustion engine 22. The control unit 11 can obtain the mixture ratio through this sensor. The sensor that obtains the mixture ratio upstream of the three-way catalytic converter 12 may, for example, obtain the measurement signals measured by the oxygen sensor or ammonia sensor installed in the exhaust pipe 19.

[0037] Furthermore, the exhaust purification device 10 can be equipped with a sensor (not shown) for measuring the temperature inside the catalyst of the three-way catalyst 12 (so-called bed temperature). This sensor can also replace the bed temperature of the three-way catalyst 12 to measure the temperature near the inlet and outlet of the three-way catalyst 12.

[0038] The SCR catalyst 13 is positioned on the downstream side of the main road, meaning it is downstream of the three-way catalyst 12. The SCR catalyst 13 can use ammonia as a reducing agent to remove NO from the exhaust gas. x Purification is performed. The temperature acquisition unit 16 is a sensor that measures the temperature related to the temperature of the SCR catalyst 13. In this embodiment, it measures the temperature inside the SCR catalyst 13 (so-called bed temperature). Alternatively, the temperature acquisition unit 16 may measure the temperature of a region surrounding the SCR catalyst 13, such as near the inlet or outlet of the SCR catalyst 13, instead of the bed temperature. The temperature acquisition unit 16 is an example of the "temperature acquisition unit" disclosed herein.

[0039] The first mixture ratio acquisition unit 14 and the second mixture ratio acquisition unit 15 acquire the oxygen (O2) concentration (i.e., mixture ratio) of the exhaust gas (exhaust gas) from the internal combustion engine 22 near the inlet and outlet of the SCR catalyst 13. Specifically, the first mixture ratio acquisition unit 14 is located near the inlet of the SCR catalyst 13 and acquires the oxygen (O2) concentration (i.e., mixture ratio) of the exhaust gas (exhaust gas) from the internal combustion engine 22 at a location downstream of the three-way catalyst 12 and upstream of the SCR catalyst 13. The first mixture ratio acquisition unit 14 can be implemented, for example, by acquiring measurement signals from an oxygen sensor and an ammonia sensor installed in the exhaust pipe 19. The second mixture ratio acquisition unit 15 is located downstream of the SCR catalyst 13 (e.g., near the outlet) and acquires the oxygen (O2) concentration (i.e., mixture ratio) of the exhaust gas (exhaust gas) from the internal combustion engine 22 at a location downstream of the SCR catalyst 13. The second mixture ratio acquisition unit 15 can also be implemented, for example, by acquiring measurement signals from an oxygen sensor and an ammonia sensor installed in the exhaust pipe 19. The first mixing ratio acquisition unit 14 and the second mixing ratio acquisition unit 15 are examples of the "mixing ratio acquisition unit" of this disclosure. Furthermore, the first mixing ratio acquisition unit 14 is an example of the "mixing ratio acquisition unit" in the case of acquiring the mixing ratio at the upstream side of the selective reduction catalyst, and the second mixing ratio acquisition unit 15 is an example of the "mixing ratio acquisition unit" in the case of acquiring the mixing ratio at the downstream side of the selective reduction catalyst.

[0040] The oxygen (O2) concentration in the exhaust gas (exhaust gas) from the internal combustion engine 22, i.e., the mixture ratio of the exhaust gas in the exhaust pipe 19, can be considered as indicating the degree of excess or deficiency of air containing oxygen (O2). In this disclosure, an air excess coefficient λ, which indicates the degree of excess or deficiency of air relative to the mixture ratio, is used as an indicator of the degree of excess or deficiency of air. In the following description, the exhaust gas mixture ratio obtained by the first mixture ratio obtaining unit 14 will be used as the air excess coefficient λ1, and the exhaust gas mixture ratio obtained by the second mixture ratio obtaining unit 15 will be used as the air excess coefficient λ2.

[0041] Figure 2 This is a flowchart illustrating an example of the control process of the control unit 11. Figure 2 The control involves monitoring the status of the exhaust purification device 10 and is related to the adsorption of ammonia in the SCR catalyst 13. This is performed by starting the internal combustion engine 22. Figure 2 The controls are shown. Additionally... Figure 2 The control shown is not limited to execution when the internal combustion engine 22 is started. For example, it can also be executed periodically. Figure 2 The control can also predetermine the starting conditions, and execute the operation when the starting conditions are suitable. Figure 2 Control. Additionally. Figure 2The control process shown is an example of a "program" of this disclosure stored in a computer-readable medium (storage unit) not shown, for causing a computer to perform exhaust purification treatment to purify the exhaust gas of an internal combustion engine 22 that obtains driving power through the combustion of ammonia.

[0042] In step S100, the control unit 11 sets the initial values ​​for starting control. In this embodiment, the count value M and the discrimination index N are set as the initial values. i The values ​​of (i = 0, 1, 2) are used. The count value M represents the number of repetitions of the main control. The discriminant index N is used. i It is an indicator representing the behavior of SCR catalyst 13.

[0043] In this embodiment, as the discrimination index N i The behavior of the SCR catalyst 13 is represented by the states of "adsorption of SCR catalyst 13", "regeneration of SCR catalyst 13", and "end of regeneration of SCR catalyst 13". The discrimination index N0 represents the state of "adsorption of SCR catalyst 13" where ammonia is adsorbed onto the SCR catalyst 13. It is set to "1" in the state of "adsorption of SCR catalyst 13" and reset to "0" in other states. The discrimination index N1 is set to "1" in the state of "regeneration of SCR catalyst 13" where the adsorbed ammonia is consumed and the adsorption capacity of SCR catalyst 13 is restored. It is reset to "0" in other states. The discrimination index N2 is set to "1" in the state of "end of regeneration of SCR catalyst 13" where the regeneration of SCR catalyst 13 has ended. It is reset to "0" in other states. In step S100, in order to obtain at least one state of "adsorption of SCR catalyst 13" and "regeneration of SCR catalyst 13", M=0, N0=1, N1=0, N2=0 are set as initial values.

[0044] If an initial value is set in step S100, the control unit 11 will transfer the processing to step S102.

[0045] In step S102, the control unit 11 acquires the temperature of the SCR catalyst 13 from the temperature acquisition unit 16 and determines whether the acquired temperature Tc of the SCR catalyst 13 is above the set temperature Ta of the SCR catalyst 13. The start temperature of the catalyst reaction in the SCR catalyst 13 is preset to the set temperature Ta. In this embodiment, the activation temperature is used as an example of the start temperature of the catalyst reaction in the SCR catalyst 13. This "activation temperature" refers to the temperature at which NO is formed from ammonia in the SCR catalyst 13. xThe lower limit temperature for activation of the reduction reaction is predetermined and stored in a storage unit (not shown) within the control unit 11. The control unit 11 monitors the temperature of the SCR catalyst 13 and repeatedly performs negative checks until the temperature Tc of the SCR catalyst 13 reaches or exceeds the set temperature (activation temperature) Ta. If the temperature Tc of the SCR catalyst 13 reaches or exceeds the set temperature (activation temperature) Ta, the control unit 11 confirms the condition in step S102 and proceeds to step S104 for further processing.

[0046] In this disclosure, the set temperature Ta is set to a value above the activation temperature, which is an example of the reaction start temperature of the SCR catalyst 13, but the set temperature Ta is not limited to the activation temperature of the SCR catalyst 13. For example, the set temperature Ta can be any temperature at which the reaction start of the SCR catalyst 13 can be determined, or it can be any other temperature, such as the cooling water temperature of the internal combustion engine 22, the temperature of the area surrounding the SCR catalyst 13 (e.g., near the inlet and outlet of the SCR catalyst 13), or a temperature derived from a prediction formula based on a model. When other temperatures are used as the temperature of the SCR catalyst 13, the temperature of the SCR catalyst 13, such as the bed temperature, can be inferred from the obtained temperature using known estimation methods.

[0047] Furthermore, in step S102 described above, it is determined whether the temperature Tc of the SCR catalyst 13 is above the set temperature Ta (Tc≥Ta), but this could also be determined by the temperature of the catalyst included in the exhaust purification device 10. For example, the control unit 11 could also determine whether the temperature of the three-way catalyst 12 is above the predetermined reaction start temperature. This determination is effective immediately after the internal combustion engine 22 is started. That is, if the temperature of the three-way catalyst 12 is above the predetermined reaction start temperature, a positive determination can be made in step S102, and the process can proceed to step S104. In addition, in step S102, after the temperature of the three-way catalyst 12 becomes above the predetermined reaction start temperature, it can also be determined whether the temperature of the SCR catalyst 13 becomes above the set temperature Ta. Furthermore, it can also be determined whether the temperatures of the three-way catalyst 12 and the SCR catalyst 13 are above their respective activation temperatures.

[0048] In step S104, the control unit 11 determines whether the termination condition is met. In this embodiment, this is done by determining whether the count value M is insufficient for a predetermined maximum value M. max To determine if the termination condition is met. When the count value M is the maximum value M... max In the above cases (M≥M) max In step S104, the control unit 11 performs a negative determination and terminates the processing procedure. On the other hand, if the count value M is less than the predetermined maximum value M...max In the case of (M < M) max In step S104, the control unit 11 makes a positive determination and transfers the processing to step S106. Additionally, the maximum value M... max It can be determined to be any value depending on the operating conditions of the internal combustion engine 22.

[0049] For example, in deciding M max Under the condition that M=2, the control unit 11 determines that the termination condition has been met when the processing during the starting of the internal combustion engine 22 has ended. This termination condition is effective when it is necessary to remove ammonia adsorbed on the SCR catalyst 13 during the starting of the internal combustion engine 22.

[0050] In addition, the maximum value M max It can also determine the termination condition based on count values ​​greater than 3. For example, by setting the maximum value M... max The decision to set a predetermined smaller count value, such as 3 or 4, is effective when the internal combustion engine 22 is stopped immediately after starting and then restarted after a predetermined time. Specifically, this condition is effective when the internal combustion engine 22 is stopped after starting, before the temperature of the three-way catalyst 12 reaches its activation temperature, and when exhaust gases remain in the SCR catalyst 13, and the internal combustion engine 22 is restarted, in order to remove ammonia. That is, this termination condition is effective when the internal combustion engine 22 is restarted and the goal is to remove ammonia adsorbed on the SCR catalyst 13.

[0051] Furthermore, the maximum value M max The count value is not limited to the above-mentioned count value; a count value larger than the above-mentioned count value can also be used as the termination condition. This termination condition is effective when the internal combustion engine 22 is continuously under a high load condition higher than the normal load condition, and ammonia adsorbed on the SCR catalyst 13 is detected and removed. As an example of a high load condition, the acceleration state of a moving body such as a vehicle equipped with an internal combustion engine 22 can be cited. Alternatively, in order to continue processing, if the control unit 11 detects that the moving body is accelerating, a negative determination can be made in step S104 when the moving body is accelerating.

[0052] In step S106, the control unit 11 determines whether the adsorption state of the SCR catalyst 13 is positive by determining that N0 ≥ 1. If N0 ≥ 1, the process is affirmed in step S106 and proceeds to step S108. On the other hand, if N0 < 1, the process is negative in step S106, skipping step S108 and proceeding to step S110.

[0053] In step S108, the control unit 11 controls the change of the air-fuel mixture ratio of the internal combustion engine 22 from a balanced ratio to a lean ratio. Specifically, the control unit 11 sends an indication signal to the combustion state control unit 21 indicating that the air-fuel mixture ratio of the internal combustion engine 22 should be changed to a lean ratio. Upon receiving the indication signal, the combustion state control unit 21 changes the air-fuel mixture ratio of the internal combustion engine 22 from a balanced ratio to a lean ratio by changing the air and fuel supply to the internal combustion engine 22. As a result, the air-fuel mixture ratio of the exhaust gas upstream of the three-way catalyst 12 also changes from a balanced ratio to a lean ratio. Therefore, the excess air coefficient λ1 obtained by the first air-fuel mixture ratio acquisition unit 14 becomes an excess air coefficient λ1 (λ1 > 1) representing excess air, i.e., lean fuel.

[0054] However, the temperature of the three-way catalyst 12 gradually increases due to the high-temperature exhaust gas (exhaust gas) from the internal combustion engine 22. Incomplete combustion components that flow into the three-way catalyst 12 up to the temperature at which the catalytic reaction begins flow into the SCR catalyst 13. That is, unpurified ammonia that has passed through the three-way catalyst 12 flows into the downstream SCR catalyst 13. The ammonia flowing into the SCR catalyst 13 is adsorbed at the SCR catalyst 13, preventing ammonia from flowing out of the SCR catalyst 13. Therefore, the amount of ammonia flowing out of the SCR catalyst 13 varies depending on the excess air coefficient λ1 at the upstream side of the SCR catalyst 13 and the behavior of the SCR catalyst 13.

[0055] The control unit 11 adjusts the mixture ratio of the internal combustion engine 22 in a manner that appropriately treats ammonia in the SCR catalyst 13 based on the relationship between the excess air coefficient λ1 on the upstream side and the excess air coefficient λ2 on the downstream side of the SCR catalyst 13. Specifically, in step S110, the control unit 11 acquires the excess air coefficients λ1 and λ2 and determines the relationship between them. That is, in step S110, it determines whether the relationship is λ1 < λ2, λ1 > λ2, or λ1 = λ2.

[0056] Regarding the state of "adsorption of SCR catalyst 13" where ammonia flowing into SCR catalyst 13 is adsorbed by SCR catalyst 13, the change in the air (oxygen) to ammonia (hydrogen) ratio before and after SCR catalyst 13 results in a difference in the excess air coefficient λ before and after SCR catalyst 13. Specifically, the excess air coefficient λ before and after SCR catalyst 13 is related as λ2 > λ1.

[0057] If, in step S110, the control unit 11 determines that the excess air coefficient λ2 is greater than the excess air coefficient λ1 (λ2 > λ1), it transfers the process to step S112 as a state of "adsorption of SCR catalyst 13". In step S112, the control unit 11 controls the process to make the excess air coefficient λ1 become excess air (λ1 ≥ 1). Specifically, the control unit 11 sends an indication signal to the combustion state control unit 21 indicating that the air-fuel mixture ratio of the internal combustion engine 22 should be changed to lean. Upon receiving the indication signal, the combustion state control unit 21 changes the air and fuel supply to the internal combustion engine 22 to make the excess air coefficient λ1 become excess air (λ1 ≥ 1), thus changing the air-fuel mixture ratio of the internal combustion engine 22 from a lean mixture. Furthermore, in step S114, the determination index N0 = 1 is set, and the process transfers to step S124. The process in step S112 is an example of the "first control" process based on this disclosure.

[0058] In step S112, when the excess air coefficient λ1 is λ1=1, the incomplete combustion components are reduced to almost zero through a redox reaction formed by the catalyst. When the excess air coefficient λ1 is λ1>1, unpurified nitrogen oxides remain, but ammonia and hydrogen are oxidized. Furthermore, for the period during which the excess air coefficient λ1 is controlled, it is desirable that the period during which the excess air coefficient λ1<1 is zero or short in order to reduce the amount of ammonia flowing into the SCR catalyst 13.

[0059] Furthermore, the incomplete combustion components flowing into the SCR catalyst 13 are reduced to almost zero, and the ammonia disappears. Consequently, the difference in the excess air coefficient λ before and after the SCR catalyst 13 disappears, becoming λ2 = λ1. λ2 = λ1 indicates that the ammonia can be fully purified by the three-way catalyst 12. In addition, the ammonia adsorbed on the SCR catalyst 13 remains in an adsorbed state until it reaches the removal temperature.

[0060] Furthermore, in the above description, when the excess air coefficient λ1 is λ1 = 1, the incomplete combustion components are reduced to almost zero through a redox reaction. However, this disclosure is not limited to reducing the incomplete combustion components to almost zero through a redox reaction. For example, the difference between the excess air coefficient λ1 and the excess air coefficient λ2 can also be a predetermined range including zero. This predetermined range can be determined based on the amount and ratio of the incomplete combustion components in the exhaust gas that is determined to be purified.

[0061] On the other hand, when the excess air coefficient λ1 is greater than 1 (λ1 > 1), the exhaust gas contains more oxygen. Therefore, the oxidation of ammonia and hydrogen by the three-way catalyst 12 is maintained, but a portion of the nitrogen oxides remains unpurified, and the oxygen-containing nitrogen oxides flow into the SCR catalyst 13. In the SCR catalyst 13, the nitrogen oxides and the amino groups adsorbed on the SCR catalyst 13 undergo an SCR reaction as shown in equations (1) to (3) below, converting them into nitrogen and water. In this reaction, ammonia is added to the gas composition flowing into the SCR catalyst 13, thus the excess air coefficient λ becomes λ1 > λ2.

[0062] 4NO + 4NH3 + O2 → 4N2 + 6H2O (1)

[0063] NO + NO₂ + 2NH₃ → 2N₂ + 3H₂O (2)

[0064] 2NO2 + 2NH3 → N2 + N2O + 3H2O (3)

[0065] If, in step S110, the control unit 11 determines that the excess air coefficient λ2 is less than the excess air coefficient λ1 (λ1 > λ2), it considers the process to be in a state of "regeneration of the SCR catalyst 13" and transfers the process to step S116. In step S116, the control unit 11 controls the process to make the excess air coefficient λ2 become excess air (λ2 ≥ 1) in a way that prevents the generation of oxygen and nitrogen oxides in the SCR catalyst 13. Specifically, the control unit 11 sends an instruction signal to the combustion state control unit 21 to change the air excess ratio of the internal combustion engine 22 from a lean ratio to an excess air ratio (λ2 ≥ 1). Furthermore, in step S118, the discrimination index N1 is set to 1, and the process is transferred to step S124. The process in step S116 is an example of the "second control" process of this disclosure.

[0066] Furthermore, if the adsorbed ammonia is consumed in the SCR catalyst 13, the adsorption capacity of the SCR catalyst 13 will be restored to the capacity before adsorption at the SCR catalyst 13. Therefore, the state in the above treatment represents the state of "regeneration of SCR catalyst 13".

[0067] Furthermore, regarding the adsorption catalyst used as a selective reduction catalyst, it is desirable that λ2 > 1 in the aforementioned SCR catalyst 13, but it is desirable that λ2 = 1 when using noble metal supported zeolite as the adsorption catalyst.

[0068] As described above, the catalytic reaction of the three-way catalyst 12 reduces the outflow of ammonia from the three-way catalyst 12, and the ammonia flowing into the SCR catalyst 13 through regeneration reduces and eventually disappears. Consequently, the difference in the excess air coefficient λ between the upstream and downstream sides of the SCR catalyst 13 decreases and eventually disappears (λ2 = λ1). That is, in the state where the ammonia in the SCR catalyst 13 has been fully purified and is gone, the composition of the exhaust gas flowing into and out of the SCR catalyst 13 is the same, λ1 = λ2. Therefore, it can be determined that the state where the excess air coefficient λ becomes λ1 = λ2 is the state where the regeneration of the SCR catalyst 13 is complete.

[0069] Furthermore, the above explanation describes the case where the difference between the excess air coefficients λ on the upstream and downstream sides disappears (λ2 = λ1) due to the reduction of ammonia flowing into the SCR catalyst 13, but it is not limited to the case where the excess air coefficients λ1 on the upstream side and λ2 on the downstream side are the same. For example, it is also possible that, within a predetermined range, the excess air coefficients λ1 on the upstream side and λ2 on the downstream side are the same (λ2 = λ1).

[0070] If, in step S110, the control unit 11 determines that the excess air coefficient λ1 and the excess air coefficient λ2 are the same (λ1 = λ2), it proceeds to step S120. In step S120, the control unit 11 controls the excess air coefficient λ1 to become a predetermined value (λ1 = 1) corresponding to the state where the regeneration of the SCR catalyst 13 is completed, indicating an excess or deficiency of air. Specifically, the control unit 11 sends an instruction signal to the combustion state control unit 21 to change the mixture ratio of the internal combustion engine 22 so that the excess air coefficient λ1 becomes the predetermined value (λ1 = 1). Furthermore, in step S122, if the states of "adsorption of SCR catalyst 13" and "regeneration of SCR catalyst 13" have been completed (N0·N1 > 0), it is considered that the state of "regeneration of SCR catalyst 13 is completed," and the determination index N2 is set to 1, thus proceeding to step S124. Otherwise, the process remains unchanged (the determination index N2 is maintained) and proceeds to step S124. The processing in step S120 is an example of the processing based on the “third control” of this disclosure.

[0071] In addition, step S120 above includes: a process in which the excess air coefficient λ1 and the excess air coefficient λ2 are the same as the result of the adsorption of ammonia by the SCR catalyst 13; and a process in which the excess air coefficient λ1 and the excess air coefficient λ2 are the same as the result of the regeneration of the SCR catalyst 13.

[0072] In step S124, the control unit 11 determines whether the control based on the states of "adsorption of SCR catalyst 13", "regeneration of SCR catalyst 13" and "end of regeneration of SCR catalyst 13" has ended by determining whether N0·N1·N2>0. That is, it determines whether a series of controls based on adsorption, regeneration and end of regeneration for SCR catalyst 13 has ended when the internal combustion engine 22 is started.

[0073] On the one hand, if the series of controls based on adsorption, regeneration, and completion of regeneration for the SCR catalyst 13 is incomplete (N0·N1·N2=0), the control unit 11 makes a negative determination in step S124 and returns to the processing in step S102. On the other hand, if a positive determination is made in step S124 (N0·N1·N2>0), the discrimination index N is reset in step S126. i (N0=0, N1=0, N2=0), in the next step S128, after incrementing the count value M (M=M+1), return to step S102 for processing.

[0074] Furthermore, the above-described control is preferably performed after the temperature of the three-way catalyst 12 has risen above the reaction start temperature, and after the temperature of the SCR catalyst 13 has reached the reaction start temperature. However, it can also be applied before the temperature of the three-way catalyst 12 reaches the activation temperature, when the temperature of the SCR catalyst 13 reaches the activation temperature. In this case, both the ammonia flowing into the SCR catalyst 13 and the adsorbed ammonia are oxidized, and the SCR catalyst 13 is regenerated. At this time, the excess air coefficient λ changes from a state of λ2 > λ1 to a state of λ1 > λ2.

[0075] The exhaust purification device 10 described above functions effectively during the start-up of the internal combustion engine 22, for example, during the warm-up process after start-up. Furthermore, the exhaust purification device of this disclosure is not limited to the start-up of the internal combustion engine 22; it also functions effectively during the operation of the internal combustion engine 22. For example, in cases of rapid changes in the load of the internal combustion engine 22, where the control of the fuel-air mixture ratio fails to keep pace with the rapidly changing load, and unpurified ammonia flows out from the three-way catalyst 12, the aforementioned control can determine the adsorption of ammonia onto the SCR catalyst 13 and regenerate it.

[0076] Furthermore, it is effective to detect abnormalities generated by the exhaust purification device 10, and it is also effective to report the abnormalities to the user. As mentioned above, the excess air coefficient λ1 and excess air coefficient λ2 are consistent (λ1 = λ2), thereby allowing the determination of the start period of ammonia purification based on the three-way catalyst 12. However, if a continuous difference occurs (λ1 < λ2 or λ1 > λ2), an abnormality may occur in the catalyst system. This abnormality in the catalyst system can be detected if the duration for detecting abnormalities in the catalyst system is predetermined and exceeds that duration. Moreover, it is sufficient to report any detected abnormality. That is, the control unit 11 performs control, and if, after a predetermined time has elapsed since the start of the first or second control, the difference between the excess air coefficient λ1 and the excess air coefficient λ2 is outside a predetermined range, it reports information indicating an abnormality.

[0077] For example, such as Figure 7 As shown, as long as the reporting unit 30 has a warning information reporting unit, the control unit 11 can control the reporting unit 30. The warning information, for example, uses information indicating an abnormality in the catalyst system. This abnormality information indicates that a continuous difference in the excess air coefficient (λ1 < λ2 or λ1 > λ2) may be occurring, suggesting a possible malfunction in the catalyst system. In the above control, for example, in the determination step S110, the following control can be added: determining whether the time during which the excess air coefficient difference (λ1 < λ2 or λ1 > λ2) occurs exceeds a certain duration; if the duration exceeds this duration, a warning information is reported as an abnormality in the catalyst system. This report can be used for the diagnosis of the exhaust gas purification device 10. The duration is measured after control begins for the time during which a difference in the excess air coefficient occurs. Furthermore, the duration is not limited to being measured after control begins; measurement can also begin at the moment a difference in the excess air coefficient occurs.

[0078] Figures 3-6 This diagram shows the changes in the state of various parts related to the SCR catalyst 13 after the internal combustion engine 22 is started.

[0079] Figure 3 This is a graph showing the temperature of the SCR catalyst 13 and the excess air coefficients at the upstream and downstream sides of the SCR catalyst 13 after the internal combustion engine 22 is started, as a function of time. Figure 3 In the figure, the excess air coefficient is shown as the change over time near the inlet and outlet of the SCR catalyst 13 in the exhaust gas from the internal combustion engine 22. Figure 3 In the figure, the temperature of the SCR catalyst 13 changes over time as a solid line. Furthermore, the position B (on the upstream side of the SCR catalyst 13) is shown as a dashed line representing the change in the excess air coefficient over time. Figure 1The change of the excess air coefficient λ1 at point C as a function of time is shown by the double-dotted line at point C, which is the downstream side. Figure 1 The change of the excess air coefficient λ2 at point () over time.

[0080] Figures 4-6 This is a graph showing the change over time in the concentration of exhaust gas from the internal combustion engine 22 at different locations on the exhaust pipe 19. In detail, Figure 4 The concentrations of ammonia (NH3) and NO are shown in the figure, representing the gas concentrations of the exhaust gas flowing into the SCR catalyst 13. x Concentration (NO) x The changes in hydrogen concentration (H2) over time. Figure 4 This indicates position A on the upstream side of the three-way catalyst 12 near the outlet of the internal combustion engine 22. Figure 1 A graph showing the change in gas concentration of exhaust gas at point ) over time. Figure 5 This indicates the position B on the upstream side of the SCR catalyst 13, near the inlet of the SCR catalyst 13. Figure 1 A graph showing the change of gas concentration at a given location over time. Figure 6 This indicates the position C on the downstream side of the SCR catalyst 13 near the outlet of the SCR catalyst 13. Figure 1 A graph showing the change of gas concentration at a given location over time. Figures 4-6 In the diagram, the solid line represents the change of ammonia concentration (NH3) over time, and the dashed line represents NO. x Concentration (NO) x The change of hydrogen concentration (H2) over time is represented by a double-dotted line. Additionally, Figure 6 In the diagram, the dashed line represents NO at position B. x Concentration (NO) x The change of ) over time.

[0081] Next, use Figures 3-6 , for through Figure 2 The changes in the state of each controlled component over time are explained.

[0082] First, the exhaust gas from the internal combustion engine 22 contains not only water vapor and nitrogen, but also unburned ammonia, hydrogen, nitrogen oxides, and other incompletely combusted components. Ammonia, even at low concentrations, has an irritating odor, and at high concentrations, it poses a significant risk of harm to human health. Therefore, it is necessary to suppress its outflow. The exhaust purification device 10 of this disclosure regulates the airflow and fuel supply to the internal combustion engine 22 to reduce the emission of at least ammonia from the exhaust gas.

[0083] If the internal combustion engine 22 starts, the high-temperature exhaust gas from the internal combustion engine 22 causes the temperature of the three-way catalyst 12 to gradually rise. In the three-way catalyst 12, the incompletely combusted components flow into the SCR catalyst 13 through the three-way catalyst 12 up to the temperature at which the catalytic reaction begins. The exhaust gas flowing in causes the temperature of the SCR catalyst 13 to gradually rise.

[0084] like Figure 4 As shown, if the internal combustion engine 22 starts, the ammonia concentration (NH3) near the outlet (position A) of the internal combustion engine 22 will surge due to the large amount of unburned ammonia in the engine. Subsequently, combustion at the internal combustion engine 22 stabilizes, and the ammonia concentration (NH3) gradually decreases.

[0085] like Figure 5 and Figure 6 As shown, ammonia passing through the three-way catalyst 12 is adsorbed onto the SCR catalyst 13, thereby changing the gas composition balance. The excess air coefficient λ2 on the downstream side of the SCR catalyst 13 is larger than the excess air coefficient λ1 on the upstream side of the SCR catalyst 13 (λ1 < λ2). Furthermore, as the temperature of the three-way catalyst 12 rises, the ammonia is oxidized, and the ammonia flowing into the SCR catalyst 13 disappears. Therefore, the excess air coefficients λ1 and λ2 on the upstream and downstream sides of the SCR catalyst 13 approach a state of near-absence of air (λ = 1). At this time, the mixing ratio is controlled to a specific ratio, therefore, as... Figure 5 and Figure 6 As shown, until the SCR catalyst 13 reaches the set temperature (activation temperature) Ta, the concentrations of ammonia (NH3) and NO in the exhaust gas (discharge gas) are... x Concentration (NO) x The concentration of hydrogen (H2) becomes approximately zero (λ2 = λ1). Thus, λ2 = λ1 indicates that ammonia has been purified by the three-way catalyst 12. Furthermore, incompletely combusted components from the three-way catalyst 12, which do not react sufficiently, flow into the SCR catalyst 13, but ammonia is adsorbed onto the SCR catalyst 13. Therefore, harmful substances such as ammonia in the exhaust gas can be purified.

[0086] On the other hand, when the temperature of SCR catalyst 13 reaches the set temperature (activation temperature) Ta (time t1), such as Figure 3 As shown, the excess air coefficient λ1 on the upstream side of the SCR catalyst 13 is controlled to be lean. Therefore, nitrogen oxides (NOx)... xThe ammonia flows into the SCR catalyst 13, and thus, through the SCR reaction in the SCR catalyst 13, the ammonia adsorbed on the SCR catalyst 13 is converted into nitrogen and water as described above. During the SCR reaction, the ammonia adds to the composition of the exhaust gas flowing into the SCR catalyst 13, and the excess air coefficients λ1 and λ2 change, resulting in a difference between the excess air coefficients λ1 and λ2. That is, the SCR reaction in the SCR catalyst 13 proceeds, thereby... Figure 3 As shown, the excess air coefficients on the upstream and downstream sides of the SCR catalyst 13 are reversed, and the excess air coefficient λ2 on the downstream side is less than the excess air coefficient λ1 on the upstream side of the SCR catalyst 13 (λ1>λ2).

[0087] When the excess air coefficient λ in the SCR catalyst 13 is λ1 > λ2, the excess air coefficient λ2 is made to be excess air (λ2 ≥ 1) in a way that does not produce a deficiency of oxygen and nitrogen oxides in the SCR catalyst 13. Moreover, in the SCR catalyst 13, the adsorbed ammonia is consumed, and the SCR catalyst 13 is regenerated until the adsorption capacity of the SCR catalyst 13 is restored to the state of the SCR catalyst 13 before adsorption.

[0088] That is, if the excess air coefficient λ2 changes to excess air (the mixing ratio changes from a balanced ratio to a lean ratio) (λ2≥1) downstream of the SCR catalyst 13, then the NO based on the three-way catalyst 12 will be... x The restoration was not fully completed, such as... Figure 5 As shown, NO in the exhaust gas flowing into the three-way catalytic converter 12 x The NO flows out from the three-way catalyst 12 and into the SCR catalyst 13. At this time, the temperature of the SCR catalyst 13 is above the set temperature (activation temperature) Ta. Therefore, NO is released into the SCR catalyst 13. x The reduction reaction is activated. Therefore, in SCR catalyst 13, the accumulated ammonia is used as a reducing agent to reduce NO in the exhaust gas. x The reduction effect. Through the reduction effect of this SCR catalyst 13, such as... Figure 6 As shown, NO in SCR catalyst 13 x reduce.

[0089] Thus, if the SCR catalyst 13 reaches a set temperature (activation temperature) Ta or higher, the air excess coefficient λ2 is adjusted to achieve an air excess, thereby changing the exhaust gas mixing ratio upstream of the three-way catalyst 12 and the SCR catalyst 13 from a balanced ratio to a lean ratio. This creates a regenerated state for the SCR catalyst 13, allowing the ammonia adsorbed by the SCR catalyst 13 to react with the NO in the exhaust gas. x The reduction reaction can suppress the discharge of ammonia and remove ammonia adsorbed on SCR catalyst 13.

[0090] As described above, the ammonia flowing into the SCR catalyst 13 is reduced through the catalytic reaction of the three-way catalyst 12 and the adsorption and regeneration of the SCR catalyst 13. This reduces the difference in the excess air coefficient λ between the upstream and downstream sides of the SCR catalyst 13, eventually eliminating it (λ2 = λ1). At the end of the regeneration of the SCR catalyst 13 (time t2), which is in the state of λ1 = λ2, combustion in the internal combustion engine 22 is stable. Figure 3 Therefore, the ammonia concentration from the internal combustion engine 22 remains essentially constant. Furthermore, the oxidation reaction of ammonia in the three-way catalyst 12 reacts with NO... x The reduction reaction proceeds, and ammonia and NO in the exhaust gas flowing into the three-way catalyst 12... x The ammonia is purified separately in the three-way catalyst 12 and is not discharged. As a result, ammonia does not flow into the SCR catalyst 13, and therefore, the excess air coefficient in the SCR catalyst 13 does not change on the upstream and downstream sides of the SCR catalyst 13 (λ1 = λ2). Moreover, the excess air coefficient λ1 on the upstream side of the SCR catalyst 13 is changed in a way that makes the excess air coefficient λ1 a predetermined value (λ1 = 1) indicating the absence of excess or deficiency of air (from lean to balanced).

[0091] Thus, after the excess air coefficient λ1 on the upstream side of the SCR catalyst 13 is changed to a predetermined value (λ1 = 1) indicating a state where there is no excess or deficiency of air, the ammonia in the exhaust gas can be oxidized by the three-way catalyst 12, and the NO in the exhaust gas can be oxidized by the three-way catalyst 12. x The reduction reaction can inhibit the excretion of ammonia. Figure 6 ).

[0092] Furthermore, even if the internal combustion engine 22 stops, and the three-way catalyst 12 and SCR catalyst 13 return to a temperature that is insufficient for activation, such as room temperature, after the internal combustion engine 22 restarts, the ammonia accumulated in the SCR catalyst 13 is also removed. Therefore, the above-mentioned treatment can be repeated.

[0093] As described above, in the exhaust purification device 10 of the above embodiment, when purifying the exhaust gas from the internal combustion engine 22, the adsorption and regeneration status of the SCR catalyst 13 can be determined based on the relationship between the excess air coefficients on the upstream and downstream sides of the SCR catalyst 13. Therefore, by controlling the mixture ratio according to the determined status, the purification of the exhaust gas from the internal combustion engine 22 can be performed efficiently and reliably. Furthermore, the regeneration completion status of the SCR catalyst 13 is determined based on the relationship between the excess air coefficients on the upstream and downstream sides of the SCR catalyst 13, thereby enabling efficient and reliable exhaust gas purification based on the determination of the adsorption and regeneration status of the SCR catalyst 13.

[0094] Furthermore, in the exhaust gas purification device 10 of the above embodiment, the three-way catalyst 12 is disposed upstream of the main flow path. Therefore, the temperature of the three-way catalyst 12 is easily raised, and the time until the three-way catalyst 12 reaches the set temperature (activation temperature) Ta can be shortened. In addition, the saturated adsorption capacity of ammonia in the SCR catalyst 13 has the characteristic that it decreases as the catalyst temperature increases. According to the exhaust gas purification device 10 of this embodiment, the SCR catalyst 13 is disposed downstream of the main flow path. Therefore, the temperature of the SCR catalyst 13 is less likely to rise, and the decrease in the saturated adsorption capacity of ammonia in the SCR catalyst 13 can be suppressed.

[0095] <Modifications of this embodiment>

[0096] This invention is not limited to the embodiments described above, and can be implemented in various ways without departing from its spirit, for example, it can also be modified as follows.

[0097] [Variation Example 1]

[0098] In the above embodiment, an example of the structure of the engine system is shown. However, the structure of the engine system can be varied in various ways. For example, the engine system may also include other devices not shown (e.g., devices for monitoring the state of a three-way catalyst, an SCR catalyst, etc.).

[0099] [Variation Example 2]

[0100] You can also configure NO as an example in the exhaust purification device. xVarious catalysts with different functions, such as NOx Storage and Reduction catalysts (NSR catalysts), Diesel Oxidation Catalysts (DOC catalysts), and Diesel Particulate Filters (DPFs), are available. The configuration of these catalysts can be arbitrarily determined.

[0101] [Variation Example 3]

[0102] In the above embodiment, an example of control based on the control unit is shown. However, control based on the control unit can be modified in various ways. For example, the order of some steps in steps S100 to S128 may be omitted, or additional steps may be added.

[0103] The present disclosure has been described above based on embodiments and variations. However, the embodiments of the present disclosure are for ease of understanding and are not intended to limit the present disclosure. The present disclosure can be modified and improved without departing from its spirit and the scope of the claims, and the present disclosure includes its equivalents. Furthermore, if a technical feature is not described as an essential structure in this specification, it can be appropriately deleted.

[0104] Explanation of reference numerals in the attached figures

[0105] 1... Engine system; 10... Exhaust purification device; 11... Control unit; 12... Three-way catalytic converter; 13... SCR catalyst; 14... First air-fuel mixture acquisition unit; 15... Second air-fuel mixture acquisition unit; 16... Temperature acquisition unit; 19... Exhaust pipe; 20... Combustion device; 21... Combustion state control unit; 22... Internal combustion engine; λ, λ1, λ2... Excess air coefficient; A... Position; B... Position; C... Position; M... Count value; M max ...maximum value; Ni(N0, N1, N2)...discrimination index; Ta...set temperature.

Claims

1. An exhaust gas purification apparatus characterized by comprising: have: A redox catalyst is disposed in the main flow path and has both oxidation and reduction functions, the main flow path being supplied with exhaust gas from an internal combustion engine that obtains driving force through the combustion of ammonia; A reduction catalyst is selected and disposed downstream of the redox catalyst in the main flow path, and adsorbs the ammonia that has passed through the redox catalyst. A temperature acquisition unit acquires the temperature of a portion related to the temperature of the selected reduction catalyst. The mixing ratio acquisition unit acquires the mixing ratio of the exhaust gas, which represents the relationship between ammonia and oxygen at the upstream and downstream sides of the selective reduction catalyst; as well as The control unit, when the temperature obtained by the temperature acquisition unit is above a predetermined temperature corresponding to the activation temperature of the selective reduction catalyst, performs a first control based on the exhaust gas mixing ratio obtained by the mixing ratio acquisition unit. If the exhaust gas mixing ratio downstream of the selective reduction catalyst is greater than the exhaust gas mixing ratio upstream of the selective reduction catalyst, the first control changes the exhaust gas mixing ratio upstream of the redox catalyst from a balanced ratio to a lean ratio. Conversely, if the exhaust gas mixing ratio downstream of the selective reduction catalyst is less than the exhaust gas mixing ratio upstream of the selective reduction catalyst, the second control changes the exhaust gas mixing ratio upstream of the redox catalyst in such a way that the exhaust gas mixing ratio downstream of the selective reduction catalyst becomes lean. When the mass ratio of air to ammonia in the exhaust gas is used as the mixing ratio of the exhaust gas, the mixing state refers to a mixing ratio of Φ = 1 when the mixing ratio is set as "Φ = theoretical air-fuel ratio / actual air-fuel ratio of the mixture".

2. The exhaust gas purification device according to claim 1, characterized in that, When the difference between the exhaust gas mixing ratio upstream of the selective reduction catalyst and the exhaust gas mixing ratio downstream of the selective reduction catalyst is within a predetermined range, the control unit performs a third control, which changes the exhaust gas mixing ratio upstream of the selective reduction catalyst from lean to balanced.

3. The exhaust gas purification device according to claim 2, characterized in that, The control unit performs control, and if the difference is outside a predetermined range after a predetermined time has elapsed since the start of the first control or the second control, it reports information indicating an anomaly.

4. The exhaust gas purification device according to claim 2, characterized in that, The control unit performs the first control, the second control, and the third control at least once when the internal combustion engine is started.

5. An exhaust gas purification method, using a redox catalyst and a selective reduction catalyst to purify the exhaust gas of an internal combustion engine that obtains driving force through the combustion of ammonia. The exhaust gas purification method is characterized by including the following steps: Obtain the temperature of the portion related to the temperature of the selected reduction catalyst; Obtain the exhaust gas mixing ratio, representing the relationship between ammonia and oxygen at the upstream and downstream sides of the selective reduction catalyst; and If the obtained temperature is above a predetermined temperature corresponding to the activation temperature of the selective reduction catalyst, and based on the obtained exhaust gas mixing ratio, if the exhaust gas mixing ratio downstream of the selective reduction catalyst is greater than the exhaust gas mixing ratio upstream of the selective reduction catalyst, a first control is performed, which changes the exhaust gas mixing ratio upstream of the redox catalyst from a balanced ratio to a lean ratio. If the exhaust gas mixing ratio downstream of the selective reduction catalyst is less than the exhaust gas mixing ratio upstream of the selective reduction catalyst, a second control is performed, which changes the exhaust gas mixing ratio upstream of the redox catalyst in such a way that the exhaust gas mixing ratio downstream of the selective reduction catalyst is changed from a balanced ratio to a lean ratio. When the mass ratio of air to ammonia in the exhaust gas is used as the mixing ratio of the exhaust gas, the mixing state refers to a mixing ratio of Φ = 1 when the mixing ratio is set as "Φ = theoretical air-fuel ratio / actual air-fuel ratio of the mixture".

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