JP6677154B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine using a selective reduction type catalyst (SCR (Selective Catalytic Reduction) catalyst), and more specifically, to estimation of deterioration of the catalyst.

The exhaust of an internal combustion engine, for example, a diesel engine mounted on a vehicle, contains nitrogen compounds (NOx) that cause air pollution. For this reason, vehicles equipped with a diesel engine are provided with an exhaust gas purification device that purifies exhaust gas. For example, such an exhaust gas purification device decomposes NOx which is a harmful substance into harmless nitrogen and water to reduce NOx in exhaust gas. Specifically, a selective reduction catalyst (hereinafter, referred to as a selective reduction catalyst) is disposed in an exhaust passage, and urea water is injected and added to the exhaust upstream of the selective reduction catalyst. Thus, NOx is reduced with ammonia (NH ₃ ) generated by hydrolysis of the urea water to be decomposed into nitrogen (N ₂ ) and water (H ₂ O).

  On the other hand, in such NOx decomposition processing, as the degradation of the selective reduction catalyst progresses, ammonia slip (a phenomenon in which ammonia passes through the selective reduction catalyst without reducing NOx) occurs. Therefore, it is necessary to estimate the deterioration (more specifically, the degree of the deterioration) of the selective reduction catalyst and reduce the amount of urea water injected into the exhaust gas.

  There are several methods for estimating the deterioration of the selective reduction catalyst. For example, as one of them, NOx sensors are arranged not only on the upstream side but also on the downstream side of the selective reduction catalyst in the exhaust passage, and the NOx content (NOx concentration) in the exhaust gas is measured by these sensors. A detection method is known (see Patent Literature 1 and Patent Literature 2). In this method, deterioration of the selective reduction catalyst is estimated based on the NOx reduction rates (purification rates) on the upstream side and the downstream side of the selective reduction catalyst.

  However, since the NOx sensor is expensive, there is also a need for a method for estimating the deterioration of the selective catalytic reduction catalyst without increasing the NOx sensor.

  As one of the methods for this, there is known a method in which temperature sensors are respectively arranged on the upstream side and the downstream side of the selective reduction catalyst in the exhaust passage, and the calorific value of the selective reduction catalyst is detected by these sensors. (See Patent Document 3). In this method, the deterioration of the selective reduction catalyst is estimated based on the calorific value of the adsorbent, utilizing the fact that the adsorbent (zeolite, for example) of the selective reduction catalyst generates heat due to the adsorption of moisture.

JP 2010-242728 A JP 2010-270614 A JP 2010-275947 A

  On the other hand, in estimating the deterioration of the selective reduction catalyst by such a temperature sensor, it is premised that the selective reduction catalyst immediately before the estimation has a water adsorption amount of a predetermined value or less. Otherwise, the deterioration of the selective reduction catalyst cannot be accurately estimated. Ideally, the amount of adsorbed water is preferably zero (a state in which water is completely lost from the selective reduction catalyst).

  Therefore, in estimating the deterioration of the selective reduction catalyst, it is required to ensure that the water adsorption amount of the selective reduction catalyst at the time of the deterioration estimation is set to a predetermined value or less.

  The present invention has been made in view of the above, and an object of the present invention is to improve the accuracy of estimating deterioration of a selective reduction catalyst in an exhaust gas purification device using the selective reduction catalyst.

  An exhaust gas purification device of the present invention includes a selective reduction catalyst disposed in an exhaust passage of an internal combustion engine, a reducing agent addition unit that adds a reducing agent to exhaust gas upstream of the selective reduction catalyst in the exhaust passage, and an internal combustion engine. A deterioration estimating unit for estimating the deterioration of the selective catalytic reduction catalyst based on the temperature rise of the selective catalytic reduction catalyst when the engine is started; and a time measurement for measuring a time from when the internal combustion engine is stopped to when it is restarted. A moisture estimating unit for estimating the amount of moisture adsorbed on the selective reduction catalyst while the internal combustion engine is stopped, based on the measurement time measured by the time measuring unit, and a moisture estimating unit. A deterioration estimation availability determination unit that determines whether deterioration of the selective reduction catalyst can be estimated when the internal combustion engine is started, based on the amount of water adsorption of the selective reduction catalyst. The deterioration estimating unit performs deterioration estimation of the selective catalytic reduction catalyst based on the determination result of the deterioration estimating possibility determining unit.

  The exhaust gas purification device further includes a moisture adjusting unit that increases the temperature of the exhaust gas flowing through the exhaust passage to reduce the amount of moisture adsorbed by the selective reduction catalyst. The deterioration estimation possibility determination unit is configured to determine whether the deterioration of the selective reduction catalyst can be estimated when the moisture adjustment unit reduces the water adsorption amount of the selective reduction catalyst within a predetermined time until the internal combustion engine is stopped. It is determined whether or not there is.

  In addition, the moisture adjustment unit operates the internal combustion engine continuously for a predetermined time or more to maintain the exhaust gas temperature at or above the predetermined temperature.

  Then, the deterioration estimation possibility determination section determines that deterioration estimation of the selective catalytic reduction catalyst is possible when the estimated moisture adsorption amount is less than the predetermined value.

  According to the exhaust emission control device of the present invention, it is possible to improve the accuracy of estimating the deterioration of the selective reduction catalyst. Specifically, by performing the deterioration estimation only when the selective reduction catalyst is in a state that can be estimated, it is possible to appropriately estimate the deterioration of the selective reduction catalyst, and as a result, Accuracy can be increased.

FIG. 1 is a block diagram illustrating a schematic configuration of an exhaust gas purification device according to an embodiment of the present invention. The figure which shows the relationship between the amount of adsorbed water of the adsorbent (zeolite) of the selective reduction type catalyst, and the calorific value in the exhaust gas purification device concerning one embodiment of the present invention. The figure which shows the relationship between the stop time of the internal combustion engine (diesel engine) in the exhaust gas purification apparatus which concerns on one Embodiment of this invention, and the water adsorption amount of a selective reduction catalyst. FIG. 4 is a diagram showing a temperature estimation model of a catalyst carrier that does not generate heat and a mode of temperature change after a cold start of an internal combustion engine (diesel engine) of a selective reduction catalyst in the exhaust purification device according to one embodiment of the present invention. FIG. 4 is a diagram showing a relationship between a water adsorption amount of the selective reduction catalyst and a calorific value of the selective reduction catalyst at the time of cold start of the internal combustion engine (diesel engine) in the exhaust purification device according to one embodiment of the present invention. FIG. 3 is a flow chart of control (deterioration estimation of a selective reduction catalyst) performed by a control device in the exhaust gas purification apparatus according to one embodiment of the present invention. FIG. 3 is a control flow chart of pre-processing performed by a control device in the exhaust gas purification device according to one embodiment of the present invention. FIG. 3 is a control flowchart of a deterioration estimation possibility determination process performed by a control device in the exhaust gas purification device according to the embodiment of the present invention. FIG. 3 is a control flow chart of a deterioration estimation process performed by a control device in the exhaust gas purification device according to the embodiment of the present invention. The figure which shows an example of the aspect which operated the internal combustion engine (diesel engine) including the moisture evaporation mode in the exhaust gas purification device which concerns on one Embodiment of this invention.

Hereinafter, an exhaust emission control device according to an embodiment of the present invention will be described with reference to FIGS. The exhaust gas purification device of the present embodiment is a device that purifies exhaust gas of an internal combustion engine, for example, a diesel engine mounted on a vehicle. Specifically, urea water is added to the exhaust of a diesel engine, and a nitrogen compound (hereinafter referred to as NOx) in the exhaust is reduced by using ammonia (NH ₃ ) generated by hydrolysis of the urea water as a reducing agent. This is a device that decomposes and reduces nitrogen (N ₂ ) and water (H ₂ O). The vehicle on which the exhaust gas purification apparatus of the present embodiment is mounted may be a private passenger car or a commercial vehicle such as a truck or a bus, and the use and the type of the vehicle are not particularly limited.

  FIG. 1 is a block diagram illustrating a schematic configuration of an exhaust gas purification device 1 according to the present embodiment. As shown in FIG. 1, the exhaust gas purification device 1 is configured to purify exhaust gas discharged from a combustion chamber 21 of a diesel engine (hereinafter, simply referred to as an engine) 2.

  The intake valve 22 is opened and the intake air is sucked into the combustion chamber 21 of the engine 2 from the intake passage 3a. The amount of intake air to the combustion chamber 21 is adjusted by opening and closing the intake throttle valve 23. Next, when fuel (light oil) is injected from the fuel injection nozzle (fuel injector) 24 into the heated and compressed intake air, the fuel ignites, and a mixture containing air and fuel burns in the combustion chamber 21. The combustion of the air-fuel mixture causes the piston 25 to reciprocate in the combustion chamber 21 and the crankshaft 26 connected to the piston 25 rotates. The air-fuel mixture after combustion (exhaust gas) is discharged from the combustion chamber 21 through the exhaust passage 3b by opening the exhaust valve 27, and is discharged into the atmosphere after being purified by the exhaust gas purification device 1.

  The engine 2 has an exhaust circulation path 3c that diverges from the exhaust path 3b and circulates exhaust gas to the combustion chamber 21. The circulating air (EGR gas) passes through an EGR cooler (not shown) provided in the exhaust circulation path 3c, and is introduced into the most downstream of the intake passage 3a by opening and closing an EGR valve (not shown). The intake passage 3a is supplied with intake air (fresh air) upstream of the intake throttle valve 23 via an air cleaner (not shown), a turbocharger 4, an intercooler (not shown), and the like.

  The exhaust gas purification device 1 is provided in the exhaust passage 3b, and includes a first purification device 1a, a second purification device 1b, and a reducing agent adding section (reducing agent adding device) 1c. . In these purifiers 1a and 1b, the first purifier 1a is disposed on the upstream side and the second purifier 1b is disposed on the downstream side in the exhaust passage 3b. The reducing agent addition device 1c is disposed between the first purification device 1a and the second purification device 1b, and adds a reducing agent to the exhaust gas upstream of the second purification device 1b.

  The first purification device 1a includes a main body 11, an oxidation catalyst 12, and an exhaust filter (for example, a diesel particulate filter) 13. The main body 11 is a substantially cylindrical structure having an air passage 11a through which the exhaust gas flows, and is disposed in the middle of an exhaust passage 3b connected to the combustion chamber 21 and constitutes a part of the exhaust passage 3b. I have. The oxidation catalyst 12 and the exhaust filter 13 are members for purifying exhaust gas by removing particulates (hereinafter, referred to as PM) contained in exhaust gas discharged from the combustion chamber 21. The exhaust filter 13 is positioned on the upstream side of the flow and the exhaust filter 13 is positioned on the downstream side, and is disposed in the ventilation path 11a. PM is a general term for particulate matter mainly composed of a carbon component (Carbon) and a soluble organic component (Soluble Organic Fraction). The oxidation catalyst 12 oxidizes the components to be oxidized in the exhaust gas. The exhaust filter 13 captures, burns, and removes PM in the exhaust gas.

  The second purification device 1b includes a main body 14, a selective reduction catalyst 15, and first and second temperature measuring units 16 and 17. The main body portion 14 is a substantially cylindrical structure having an air passage 14a through which exhaust gas flows, and forms a part of the exhaust passage 3b together with the main body portion 11. The ventilation passage 14a is an exhaust passage 3b on the downstream side of the ventilation passage 11a of the main body 11, and allows the purified exhaust gas to flow through the oxidation catalyst 12 and the exhaust filter 13.

  The selective reduction catalyst 15 is a catalyst that selectively adsorbs polar molecules such as ammonia and reduces NOx in exhaust gas using the adsorbed ammonia or the like as a reducing agent. The exhaust gas is purified by coming into contact with the selective reduction catalyst 15. In the present embodiment, as an example, the selective reduction catalyst 15 includes an adsorbent made of zeolite. As the zeolite, for example, a zeolite containing a metal ion (such as Cu or Fe), that is, a zeolite having a Lewis acid point can be used. Such a zeolite is made into a powder or paste, and is applied to a carrier such as a net or a frame to form a selective reduction catalyst 15. Zeolite has the property of adsorbing moisture from the atmosphere (air or exhaust) to generate heat. FIG. 2 shows the relationship between the amount of water adsorbed on the zeolite and the calorific value. As shown in FIG. 2, the amount of heat generated by zeolite increases in proportion to the amount of absorbed moisture. Ammonia for reducing NOx is generated by hydrolyzing urea water added to exhaust gas from the reducing agent adding device 1c.

  The first and second temperature measuring units 16 and 17 are sensors for measuring the temperature of the exhaust gas. In these temperature measuring units 16 and 17, the first temperature measuring unit 16 is disposed upstream of the selective reduction catalyst 15 and the second temperature measuring unit 17 is disposed downstream of the selective reduction catalyst 15 in the exhaust passage 3b. In the present embodiment, the first temperature measurement unit 16 measures the exhaust gas temperature near the entrance of the ventilation path 14a, and the second temperature measurement unit 17 measures the exhaust temperature near the exit of the ventilation path 14a. Therefore, the exhaust gas temperature measured by the second temperature measurement unit 17 substantially corresponds to the temperature of the selective reduction catalyst 15 (more specifically, the temperature of the selective reduction catalyst 15 obtained by reducing NOx). Therefore, the temperature of the selective reduction catalyst 15 can be indirectly measured without separately providing a temperature sensor for directly measuring the temperature of the selective reduction catalyst 15 itself. In the following description, the first temperature measuring unit 16 is referred to as an inlet temperature measuring unit 16, and the second temperature measuring unit 17 is referred to as an outlet temperature measuring unit 17.

  The reducing agent addition device 1c is a device that adds a reducing agent (in this embodiment, urea water that is hydrolyzed to ammonia) to the exhaust gas in contact with the selective reduction catalyst 15. The reducing agent addition device 1c includes a urea water injection nozzle (urea water injector) 18 and a urea water tank 19. The urea water injector 18 injects (sprays) urea water into mist during exhaust. The urea water injector 18 is arranged with the injection port facing inside the exhaust passage 3b connecting the first purification device 1a and the second purification device 1b. Specifically, in the exhaust passage 3b, a urea water injector 18 is disposed upstream of the selective reduction catalyst 15 and further upstream of the inlet temperature measurement unit 16.

  The urea water is stored in a urea water tank 19 and is supplied from the urea water tank 19 to the urea water injector 18 through a supply path. In addition, the position of the injection port of the urea water injector 18, in other words, the injection position of the urea water into the exhaust gas is set to be equal to or longer than a distance required until the injected urea water is hydrolyzed to generate ammonia. Is preferred. Thus, the urea water injected from the urea water injector 18 is hydrolyzed before reaching the selective reduction catalyst 15 to generate ammonia.

  Further, in the present embodiment, the exhaust gas purification device 1 is further configured to include a NOx concentration measurement unit 1d. The NOx concentration measuring unit 1d is a sensor that measures the concentration of NOx in the exhaust gas in the exhaust passage 3b. The NOx concentration measuring unit 1d is disposed upstream of the injection port of the aqueous urea injector 18 in the exhaust passage 3b. In the present embodiment, the NOx concentration measuring unit 1d measures the NOx concentration from the outlet of the air passage 11a to the injection port of the urea water injector 18. The injection amount of urea water injected into the exhaust gas from the urea water injector 18 is adjusted based on the NOx concentration of the exhaust gas measured by the NOx concentration measurement unit 1d. For example, when the NOx concentration measured by the NOx concentration measuring unit 1d increases, the injection amount of urea water from the urea water injector 18 into the exhaust gas is increased so that the generated ammonia (reducing agent) increases. On the other hand, when the NOx concentration measured by the NOx concentration measurement unit 1d decreases, the injection amount of the urea water is reduced so that the generated ammonia decreases.

  The operation of the exhaust gas purification device 1 is controlled by the control device 10. The control device 10 is configured as a microcomputer including a CPU, a memory, an input / output circuit, a timer, and the like. The control device 10 reads various data by an input / output circuit, and performs arithmetic processing by a CPU using a program read from a memory. Then, based on the processing result, the control device 10 controls the first purification device 1a, the second purification device 1b (the inlet temperature measuring unit 16 and the outlet temperature measuring unit 17), the reducing agent adding device 1c (the urea water injector 18). ) And the operation of the NOx concentration measuring unit 1d are controlled respectively. In this case, the control device 10 can be configured to be included in, for example, an engine control unit (ECU). Alternatively, the control device 10 may be configured as a part of the exhaust gas purification device 1 separately from the ECU.

  In the present embodiment, the control device 10 estimates the deterioration of the selective reduction catalyst 15. As an example, when the engine 2 is started (restarted), the control device 10 controls the selective reduction catalyst 15 based on the temperature rise of the selective reduction catalyst 15 (more specifically, the adsorbent). Estimate deterioration. Before estimating the deterioration of the selective reduction catalyst 15, the control device 10 controls the selective reduction catalyst 15 (more specifically, its adsorbent) until the engine 2 is stopped and restarted. Is determined based on the relationship between the amount of water adsorbed and the calorific value of the selective reduction catalyst 15 when the engine 2 is started (restarted).

  In order to execute these specific controls, the control device 10 includes a moisture adjusting unit 10a, a time measuring unit 10b, a moisture estimating unit 10c, a deterioration estimation availability determining unit 10d, and a deterioration estimating unit 10e. It is configured. The moisture adjusting unit 10a, the time measuring unit 10b, the moisture estimating unit 10c, the deterioration estimation availability determining unit 10d, and the deterioration estimating unit 10e are stored in a memory, for example, as programs. Note that the configuration may be such that these programs are stored in a cloud, and the control device 10 appropriately communicates with the cloud to use a desired program. In this case, the control device 10 has a configuration including a communication module with the cloud. Further, the moisture adjusting unit 10a, the time measuring unit 10b, the moisture estimating unit 10c, the deterioration estimation availability determining unit 10d, and the deterioration estimating unit 10e may be configured as independent microcomputers, for example.

  The moisture adjuster 10a controls the engine 2 to reduce the amount of moisture adsorbed by the selective reduction catalyst 15. At that time, the moisture adjusting unit 10a controls the operation of the engine 2 based on the exhaust gas temperature measured by the outlet temperature measuring unit 17. Since the exhaust gas temperature measured by the outlet temperature measuring unit 17 substantially corresponds to the temperature of the selective catalytic reduction catalyst 15, the moisture adjusting unit 10a determines the moisture adsorption of the selective catalytic reduction catalyst 15 based on the temperature of the selective catalytic reduction catalyst 15. The amount is reduced to a predetermined amount (hereinafter, referred to as a reference adsorption amount) or less. The reference adsorption amount is set as a minimum water adsorption amount in which the selective reduction catalyst 15 can still sufficiently adsorb moisture without the water adsorption amount of the selective reduction catalyst 15 reaching the saturated water adsorption amount. . The saturated water adsorption amount is the maximum water amount that the selective reduction catalyst 15 can adsorb. When the saturated water adsorption amount is reached, the selective reduction catalyst 15 can no longer adsorb water. In the present embodiment, as an example, the reference adsorption amount is set to substantially zero (a state in which moisture is almost completely evaporated from the selective reduction catalyst 15). When the reference adsorption amount is set to zero, the selective reduction catalyst 15 has a margin for water adsorption corresponding to the saturated water adsorption amount.

  The moisture adjusting unit 10a raises the temperature of the selective reduction catalyst 15 in order to reduce the amount of water adsorbed by the selective reduction catalyst 15 to a reference adsorption amount or less. Therefore, the moisture adjusting unit 10a operates the engine 2 under a predetermined condition (hereinafter, referred to as a moisture evaporation mode) to evaporate the moisture adsorbed on the selective reduction catalyst 15.

  In the moisture evaporation mode, the moisture adjustment unit 10a operates the engine 2 continuously for a predetermined time or more to maintain the exhaust gas temperature at or above a predetermined temperature. In the present embodiment, as an example, the engine 2 is operated for 10 minutes or more with the exhaust temperature kept at 150 ° C. or more. By operating the engine 2 in such a moisture evaporation mode, exhaust gas of 150 ° C. or more passes through the selective reduction catalyst 15. Thus, the water is evaporated from the selective reduction catalyst 15, and the amount of water adsorbed by the selective reduction catalyst 15 can be reduced to substantially zero. For example, after the engine 2 is started, the engine 2 is operated in the water evaporation mode before the engine 2 is stopped, so that the water adsorbed on the selective reduction catalyst 15 can be almost completely removed while the vehicle is running (including idling). Can be evaporated. In particular, it is preferable to evaporate the water adsorbed on the selective reduction catalyst 15 within a predetermined time until the engine 2 is stopped.

  In the moisture evaporation mode, the moisture adjusting unit 10a confirms that the exhaust gas temperature is maintained at 150 ° C. or higher by the exhaust gas temperature measured by the inlet temperature measuring unit 16. The predetermined temperature of the exhaust gas temperature in the moisture evaporation mode (for example, 150 ° C.) corresponds to a high temperature threshold used by the deterioration estimation possibility determination unit 10d, which will be described later, to determine whether the selective reduction catalyst 15 can be estimated for deterioration.

  In order to maintain the exhaust temperature at or above a predetermined temperature (for example, 150 ° C.), for example, post-injection of fuel or intake throttle may be performed. In this case, the moisture adjusting unit 10a controls the operation of the fuel injector 24, the intake throttle valve 23, and the like to appropriately adjust the amount of fuel sent to the ventilation path 14a, the amount of intake air to the combustion chamber 21, and the like. Further, for example, the moisture adjustment unit 10a controls the operation of the EGR valve and the like, and adjusts the oxygen concentration by appropriately introducing EGR gas. The moisture adjustment unit 10a may have a unique timer function for measuring the operating time of the engine 2, or such a timer function may be provided for the time measurement unit 10b. With such a timer function, the moisture adjusting unit 10a operates the engine 2 for a predetermined time (for example, 10 minutes) or more.

  The time measuring unit 10b measures the time from when the engine 2 is stopped to when it is restarted. That is, the time measured by the time measuring unit 10b corresponds to a time during which the stopped state of the engine 2 has been continued most recently (hereinafter, referred to as a stopped time of the engine 2). For example, the time measuring unit 10b calculates the elapsed time (soak time) from the latest stop time of the engine 2 to the subsequent restart time of the engine 2. Note that the stop time of the engine 2 includes a time during which idling is stopped.

  The moisture estimating unit 10c estimates the amount of moisture adsorbed on the selective reduction catalyst 15 while the engine 2 is stopped, based on the measurement time measured by the time measuring unit 10b. As described above, the selective reduction catalyst 15 using zeolite as an adsorbent has a property of adsorbing moisture in the atmosphere (atmosphere or exhaust gas) in addition to promoting the reduction reaction between ammonia and NOx. That is, the moisture adsorption amount estimated by the moisture estimating unit 10c indicates the moisture adsorbed by the selective reduction catalyst 15 from the atmosphere while the stopped state of the engine 2 was last (that is, the stopped time of the engine 2). (Hereinafter referred to as the amount of natural moisture adsorbed by the selective reduction catalyst 15).

  FIG. 3 shows the relationship between the stop time of the engine 2 and the amount of natural moisture adsorbed by the selective reduction catalyst 15. As shown in FIG. 3, in the selective reduction catalyst 15, the shorter the stop time of the engine 2, the smaller the natural moisture adsorption amount. Then, as the stop time of the engine 2 becomes longer, the natural moisture adsorption amount rapidly increases, and thereafter, the natural moisture adsorption amount gradually approaches the saturated moisture adsorption amount. The moisture estimating unit 10c refers to the table shown in FIG. 3 and estimates the natural moisture adsorption amount of the selective reduction catalyst 15 corresponding to the stop time of the engine 2 measured by the time measuring unit 10b. The table shown in FIG. 3 is stored in the memory of the control device 10, and is appropriately referred to by the moisture estimating unit 10c.

  In the present embodiment, when estimating the natural moisture adsorption amount of the selective reduction catalyst 15, only the stop time of the engine 2 is used as an element. However, in addition to this, for example, humidity, air pressure, or the like may be added as an element. . Thus, it is possible to take into account the difference in the amount of natural moisture adsorbed by the selective reduction catalyst 15 due to, for example, the weather or a stop location, and it is possible to further improve the estimation accuracy of the amount of natural water adsorbed.

  The deterioration estimation availability determination unit 10d determines whether to estimate the deterioration of the selective reduction catalyst 15 based on the natural water adsorption amount of the selective reduction catalyst 15 estimated by the moisture estimation unit 10c, in other words, the selective reduction. It is determined whether or not the deterioration of the type catalyst 15 is in a state where it can be estimated. The deterioration estimation possible / impossible determination unit 10d performs the estimation possible / impossible determination of the deterioration of the selective reduction catalyst 15 when the engine 2 is started.

  In determining whether or not the deterioration of the selective reduction catalyst 15 can be estimated, the deterioration estimation possibility determination unit 10d compares the natural moisture adsorption amount of the selective reduction catalyst 15 with a predetermined value (hereinafter, referred to as an adsorption amount threshold). The adsorption amount threshold value is determined for the selective reduction catalyst 15 that is in a state capable of adsorbing a water amount that can generate a minimum amount of heat that can be used to estimate the deterioration of the selective reduction catalyst 15 by the subsequent deterioration estimating unit 10e. It is set as the value of the amount of natural moisture adsorption. That is, the adsorption amount threshold value is an index indicating whether the residual capacity of the selective reduction catalyst 15 for water adsorption is sufficient.

  Therefore, the deterioration estimating unit 10e can estimate the deterioration of the selective reduction catalyst 15 based on the amount of heat generated by the remaining power (the amount of water that can be adsorbed before reaching the saturated water adsorption amount). The adsorption amount threshold value can be calculated as a value obtained by subtracting the natural water adsorption amount that generates the minimum heat generation amount at which the deterioration of the selective reduction catalyst 15 can be estimated from the saturated water adsorption amount. The adsorption amount threshold value is ideally zero (the selective reduction catalyst 15 has a residual water adsorption capacity corresponding to the saturated water adsorption amount). In addition, the natural moisture adsorption amount of the selective reduction catalyst 15 is estimated by the moisture estimation unit 10c.

  In determining whether or not the estimation is possible, the deterioration estimation possibility determination unit 10d determines the exhaust temperature of the engine 2, specifically, the exhaust temperature measured by the outlet temperature measurement unit 17, as two predetermined values (hereinafter, a high temperature threshold and a low temperature). Threshold value). Since the exhaust gas temperature measured by the outlet temperature measurement unit 17 substantially corresponds to the temperature of the selective reduction catalyst 15, the deterioration estimation possibility determination unit 10d compares the temperature of the selective reduction catalyst 15 with a high temperature threshold and a low temperature threshold, respectively. . The high temperature threshold is set to a predetermined temperature (for example, 150 ° C.) at which the water adsorbed on the selective reduction catalyst 15 is almost completely evaporated, and the amount of water adsorbed can be made almost zero. On the other hand, the low temperature threshold is set to the outside air temperature (generally, about −10 ° C. to about 40 ° C.) as the temperature of the selective reduction catalyst 15 assumed at the time of the cold start of the engine 2.

  The deterioration estimation availability determination unit 10d determines whether the deterioration of the selective reduction catalyst 15 is in a state where the deterioration of the selective reduction catalyst 15 can be estimated when the moisture adjustment unit 10a reduces the natural moisture adsorption amount of the selective reduction catalyst 15 to the adsorption amount threshold value or less. Determine whether or not. In other words, if the temperature of the selective reduction catalyst 15 (the exhaust gas temperature measured by the outlet temperature measuring unit 17) becomes equal to or higher than the high temperature threshold and then becomes equal to or lower than the low temperature threshold, the deterioration estimating unit 10e It is determined that it is possible to estimate the deterioration of the selective reduction catalyst 15 due to the above. In this case, the moisture adjusting unit 10a operates the engine 2 in the moisture evaporation mode within a predetermined time from when the engine 2 is started to when the engine 2 is stopped. (For example, it may be reduced to approximately zero or less). That is, after the engine 2 is operated in the moisture evaporation mode, if the natural moisture adsorption amount of the selective reduction catalyst 15 is maintained at or below the adsorption amount threshold, the deterioration estimation possibility determination unit 10 d It is determined whether or not deterioration is in a state in which estimation is possible.

  The deterioration estimating unit 10e executes the deterioration estimation of the selective reduction catalyst 15 based on the determination result of the deterioration estimation possibility of the selective reduction catalyst 15 by the deterioration estimation possibility determining unit 10d. That is, when it is determined that the deterioration of the selective reduction catalyst 15 can be estimated, the deterioration estimating unit 10e estimates the deterioration of the selective reduction catalyst 15, and the selective reduction catalyst 15 performs the reduction reaction of NOx in the exhaust gas. It is determined whether or not it has contributed effectively.

  The deterioration estimating unit 10e calculates the temperature rise of the selective reduction catalyst 15 at the time of cold start of the engine 2, that is, the calorific value (the calorific value from the time when the engine 2 is started to the time of estimation; Based on this, the deterioration of the selective reduction catalyst 15 is estimated. In estimating the deterioration, the deterioration estimating unit 10e estimates the starting calorific value of the selective catalytic reduction catalyst 15 corresponding to the temperature of the selective catalytic reduction catalyst 15 (the exhaust gas temperature measured by the outlet temperature measuring unit 17). The start-up heat generation can be estimated by any method. In the present embodiment, as an example, the starting calorific value of the selective reduction catalyst 15 is estimated using a temperature estimation model of the catalyst carrier that does not generate heat as shown in FIG. FIG. 4 shows a temperature estimation model of the catalyst carrier that does not generate heat and an aspect of the temperature change of the selective reduction catalyst 15 after the cold start of the engine 2.

  The deterioration estimating unit 10e compares the temperature of the temperature estimation model of the catalyst carrier that does not generate heat with the temperature of the selective reduction catalyst 15 (the exhaust gas temperature measured by the outlet temperature measuring unit 17), and based on the temperature difference, the calorific value at startup. Is estimated. At this time, the deterioration estimating unit 10e refers to the table shown in FIG. 4, and calculates the amount of heat generated at the start based on the difference area between the temperature trace of the temperature estimation model of the catalyst carrier that does not generate heat and the temperature trace of the selective reduction catalyst 15. calculate. The table shown in FIG. 4 is stored in the memory of the control device 10, and is appropriately referred to by the deterioration estimating unit 10e.

  In the table shown in FIG. 4, the thick line (L1) is a carrier temperature estimation model that does not generate heat, the thin line (L2) is when the selective reduction catalyst 15 is new, and the broken line (L3) is when the selective reduction catalyst 15 starts to deteriorate. The dashed line (L4) shows an example of the temperature trajectory in a state in which the selective reduction catalyst 15 has deteriorated. As shown in FIG. 4, when the selective reduction catalyst 15 is new, the selective reduction catalyst 15 activates the reduction reaction of NOx in the exhaust when the engine 2 is cold started, and immediately rises in temperature. On the other hand, when the selective catalytic reduction catalyst 15 is deteriorated, the selective catalytic reduction catalyst 15 does not contribute much to the reduction reaction of NOx in the exhaust gas, and the temperature hardly rises when the engine 2 is cold started.

  Note that the temperature of the exhaust gas before passing through the selective reduction catalyst 15 (the exhaust gas temperature measured by the inlet temperature measuring unit 16) and the heat balance of the carrier of the selective reduction catalyst 15 follow Expression (1) below.

_{(Ρ c A c C pc)} × (dT c / dt) = -h (T c -T g) ... (1)
In the formula (1), ρ _c : carrier density of the selective reduction catalyst 15, A _c : heat transfer area of the selective reduction catalyst 15, C _pc : specific heat of the carrier of the selective reduction catalyst 15, T _c : selective reduction catalyst 15 is a carrier temperature, T _{g is} an exhaust gas temperature on the inlet side of the selective reduction catalyst 15, and h is a heat transfer coefficient. Among them, ρ _c , A _c , C _pc , and h are all constants. The carrier temperature (T _c ) of the selective reduction catalyst 15 is a variable measured by the outlet temperature measuring unit 17 as the exhaust gas temperature near the outlet of the ventilation path 14a. The exhaust gas temperature (T _g ) on the inlet side of the selective reduction catalyst 15 is a variable measured by the inlet temperature measuring unit 16 as the exhaust gas temperature near the inlet of the ventilation path 14a.

  If the estimated heating value at start-up is equal to or less than a predetermined value (hereinafter, referred to as a deterioration index value), the deterioration estimating unit 10e estimates that the selective reduction catalyst 15 has deteriorated.

  FIG. 5 shows the relationship between the amount of natural moisture adsorbed by the selective reduction catalyst 15 and the amount of heat generated when the selective reduction catalyst 15 starts. The solid line shown in FIG. 5 shows the relationship between the amount of natural moisture adsorbed when the selective reduction catalyst 15 is new and the calorific value at startup, and the broken line shows the relationship between the two when the selective reduction catalyst 15 is deteriorated. As shown in FIG. 5, in the selective reduction catalyst 15, the value of the amount of natural moisture adsorbed is inversely proportional to the value of the calorific value at startup. Compared with a new product, the deteriorated selective reduction catalyst 15 has a small starting heat value corresponding to the natural moisture adsorption amount regardless of the natural moisture adsorption amount. That is, the new selective reduction catalyst 15 activates the reduction reaction of NOx while actively adsorbing moisture in the exhaust gas, so that the calorific value increases. On the other hand, the deteriorated selective reduction catalyst 15 does not contribute much to the activation of the NOx reduction reaction, and does not adsorb much moisture in the exhaust gas, so that the calorific value becomes small.

  Therefore, the deterioration index value of the selective reduction catalyst 15 is set to a predetermined value (a value on the broken line shown in FIG. 5) smaller than the heat generation amount at the time of starting a new product. The deterioration estimating unit 10 e refers to the table shown in FIG. 5 and estimates the starting heat generation amount corresponding to the natural moisture adsorption amount of the selective reduction catalyst 15. Accordingly, the deterioration estimating unit 10e determines whether the estimated heating value at the start is equal to or less than the deterioration index value at the corresponding natural moisture adsorption amount. In addition, the natural moisture adsorption amount of the selective reduction catalyst 15 is estimated by the moisture estimation unit 10c. The table shown in FIG. 5 is stored in the memory of the control device 10, and is appropriately referred to by the deterioration estimating unit 10e.

  6 to 9 show a flow of control (deterioration estimation of the selective reduction catalyst 15) performed by the control device 10 of the exhaust gas purification device 1 in the present embodiment. Hereinafter, control by the control device 10 and its operation will be described in accordance with the flows shown in FIGS. 6 to 9.

  As shown in FIG. 6, when estimating the deterioration of the selective reduction catalyst 15, the control device 10 performs deterioration estimation availability determination processing (S 601) and deterioration estimation processing (S 603). That is, the deterioration estimation possibility determination processing is performed prior to the deterioration estimation processing, and the deterioration estimation processing is performed only when the deterioration estimation possibility determination processing determines that the deterioration estimation is possible (S602). For example, when it is determined in the deterioration estimation availability determination processing that deterioration estimation is possible, the control device 10 sets a flag (hereinafter, referred to as a deterioration estimation availability determination flag) to ON. Then, only when the deterioration estimation possibility determination flag is ON, control device 10 performs the deterioration estimation process.

  The deterioration estimation availability determination process is a process for determining whether or not the deterioration of the selective reduction catalyst 15 is in a state where it can be estimated. In the deterioration estimation availability determination processing, first, as shown in FIG. 7, preprocessing for reducing the amount of water adsorbed by the selective reduction catalyst 15 is performed. The pre-processing is performed by the moisture adjusting unit 10a. In the pre-treatment, the water adjusting unit 10a reduces the amount of water adsorbed by the selective reduction catalyst 15. For this reason, the moisture adjusting unit 10a operates the engine 2 in the moisture evaporation mode, and determines whether the operation of the engine 2 in the moisture evaporation mode has been normally performed (S701). The determination result is notified to the deterioration estimation availability determination unit 10d.

  When the operation of the engine 2 in the water evaporation mode is normally performed, the deterioration estimation possibility determination unit 10d sets the deterioration estimation possibility determination flag to ON (S702). In this case, the water adsorption amount of the selective reduction catalyst 15 is reduced to a reference adsorption amount (for example, substantially zero) or less. That is, in the selective reduction catalyst 15, the adsorbed water is almost completely evaporated, and the amount of adsorbed water is almost zero.

  On the other hand, when the operation of the engine 2 in the water evaporation mode is not performed normally, the deterioration estimation possibility determination unit 10d sets the deterioration estimation possibility determination flag to OFF (S703). When the operation of the engine 2 in the moisture evaporation mode is not performed normally, for example, the exhaust temperature is maintained at a predetermined temperature (for example, 150 ° C.) or more, and for a predetermined time (for example, 10 minutes) or more. This corresponds to the case where the engine 2 cannot be operated.

  Note that such preprocessing is performed at least before or after the engine 2 is started as a condition (premise) for performing the deterioration estimation possibility determination processing. For example, the engine 2 may be operated in the moisture evaporation mode before the engine 2 is stopped during the previous traveling of the vehicle (when the engine 2 is operating) (that is, as a post-process when the engine was last operating). However, the stop of the engine 2 is performed by the driver's intention except for a very short stop due to the idling stop which is automatically performed. Therefore, for example, the engine 2 may be operated in the moisture evaporation mode at an arbitrary timing while the vehicle is running. Thereafter, if the engine 2 is stopped in a state where the exhaust gas temperature measured by the outlet temperature measuring unit 17 is kept slightly lower than a predetermined temperature (for example, 150 ° C.), the water adsorption amount of the selective reduction catalyst 15 Can be estimated to be reduced to the reference adsorption amount or less.

  FIG. 10 shows an example of a time chart of such an operation mode of the engine 2. As shown in FIG. 10, after the engine 2 is started, both the vehicle speed and the exhaust temperature increase. On the other hand, after the engine 2 is started, the amount of water adsorbed by the selective reduction catalyst 15 decreases. Then, during traveling of the vehicle, the engine 2 is operated in the water evaporation mode at an arbitrary timing. In the moisture evaporation mode, both the vehicle speed and the exhaust temperature are kept substantially constant. When the engine 2 is operated in the moisture evaporation mode, the moisture adsorption amount of the selective reduction catalyst 15 is reduced to a reference adsorption amount (for example, substantially zero) or less. Thereafter, the vehicle speed becomes zero, the exhaust gas temperature decreases accordingly, and the engine 2 is stopped.

  In addition, after the engine 2 is stopped during the previous traveling of the vehicle, when the engine 2 is restarted during the current traveling, it is also possible to perform a pre-process (operate the engine 2 in the moisture evaporation mode). .

  That is, within a predetermined time from when the engine 2 is started to when it is stopped, the engine 2 is operated in the water evaporation mode by the water adjusting unit 10a, and the water adsorption amount of the selective reduction catalyst 15 is reduced to the reference adsorption amount or less. It should be done.

  After the pre-processing is performed, as shown in FIG. 8, the control device 10 performs deterioration estimation availability determination processing. Specifically, the deterioration estimation availability determination unit 10d determines whether the deterioration of the selective reduction catalyst 15 is in a state where it can be estimated. As an example, the deterioration estimation availability determination unit 10d determines whether the deterioration estimation availability determination flag is ON (S801). When the deterioration estimation possibility determination flag is not ON (is OFF), the deterioration estimation possibility determination unit 10d determines that the deterioration of the selective reduction catalyst 15 is not in a state in which the deterioration can be estimated, and performs the following deterioration estimation possibility determination processing; Do not perform deterioration estimation processing.

  On the other hand, when the deterioration estimation possibility determination flag is ON, the deterioration estimation possibility determination unit 10d determines that the deterioration of the selective catalytic reduction catalyst 15 is in a state where the deterioration can be estimated, and continuously performs the deterioration estimation possibility determination process thereafter. . In this case, the deterioration estimation possibility determination unit 10d compares the temperature of the selective reduction catalyst 15 with a predetermined value (low temperature threshold; for example, outside temperature) (S802). The temperature of the selective reduction catalyst 15 is measured by the outlet temperature measuring unit 17 as the exhaust gas temperature of the engine 2. The outlet temperature measurement unit 17 notifies the measured exhaust temperature to the deterioration estimation possibility determination unit 10d.

  When the temperature of the selective reduction catalyst 15 exceeds a predetermined value (low temperature threshold), the deterioration estimation possibility determination unit 10d determines that the degradation of the selective reduction catalyst 15 is not in a state in which the deterioration can be estimated, The judgment processing and the deterioration estimation processing are not performed. In this case, the deterioration estimation possibility determination unit 10d sets the deterioration estimation possibility determination flag to OFF (S803).

  On the other hand, when the temperature of the selective reduction catalyst 15 is equal to or lower than a predetermined value (low temperature threshold), the deterioration estimation possibility determination unit 10d causes the moisture estimation unit 10c to estimate the moisture adsorption amount of the selective reduction catalyst 15 (S804). ). The moisture estimating unit 10c estimates the amount of moisture (natural moisture adsorption) absorbed by the selective reduction catalyst 15 from the atmosphere (atmosphere or exhaust gas) when the engine 2 is stopped. The stop time of the engine 2 is calculated by the time measuring unit 10b as an elapsed time (soak time) from the latest stop time of the engine 2 to a restart time of the engine 2 thereafter. The time measurement unit 10b notifies the moisture estimation unit 10c of the calculated stop time of the engine 2. The moisture estimating unit 10c estimates the natural moisture adsorption amount of the selective reduction catalyst 15 corresponding to the stop time of the engine 2 with reference to the table shown in FIG.

  When the natural water adsorption amount of the selective reduction catalyst 15 is estimated, the deterioration estimation possibility determination unit 10d compares the estimated natural water adsorption amount with a predetermined value (adsorption amount threshold) (S804). Accordingly, the deterioration estimation possibility determination section 10d determines whether or not the deterioration estimation section 10e is capable of adsorbing the water amount that can generate the minimum heat generation amount that can estimate the deterioration of the selective reduction catalyst 15. Is determined. That is, the deterioration estimation availability determination unit 10d determines whether the selective reduction catalyst 15 has sufficient water adsorption capacity.

  When the natural moisture adsorption amount of the selective reduction catalyst 15 is equal to or more than a predetermined value (adsorption amount threshold value), the deterioration estimation possibility determination unit 10d determines that the deterioration of the selective reduction catalyst 15 is not in a state in which the deterioration can be estimated, and The deterioration estimation availability determination processing and the deterioration estimation processing are not performed. In this case, the deterioration estimation possibility determination unit 10d sets the deterioration estimation possibility determination flag to OFF (S803).

  On the other hand, when the natural moisture adsorption amount of the selective reduction catalyst 15 is less than a predetermined value (adsorption amount threshold), the deterioration estimation possibility determination unit 10d determines that the deterioration of the selective reduction catalyst 15 can be estimated. , And causes the deterioration estimating unit 10e to perform the deterioration estimating process. In this case, the deterioration estimation possibility determination flag is maintained as being set to ON.

  When it is determined that the selective reduction catalyst 15 is in a state where deterioration can be estimated, the control device 10 performs a deterioration estimation process as shown in FIG. Specifically, the deterioration estimating unit 10e determines whether the selective reduction catalyst 15 has deteriorated. Note that whether or not the selective reduction catalyst 15 is in a state in which deterioration can be estimated is determined by, for example, whether or not a deterioration estimation possibility determination flag is ON (S602 in FIG. 6).

  The deterioration estimating unit 10e estimates a deterioration index value corresponding to the natural moisture adsorption amount of the selective reduction catalyst 15 (S901). The deterioration index value is the amount of heat generated at the time of startup of the selective reduction catalyst 15 with respect to the amount of natural moisture absorbed when the selective reduction catalyst 15 is deteriorated. The starting heat value is a heat value of the selective reduction catalyst 15 at the time of the cold start of the engine 2. The natural water adsorption amount of the selective reduction catalyst 15 is estimated by the water estimating unit 10c. The moisture estimating unit 10c notifies the deterioration estimating unit 10e of the estimated natural moisture adsorption amount. The deterioration estimating unit 10e estimates a deterioration index value corresponding to the natural moisture adsorption amount of the selective reduction catalyst 15 with reference to the table shown in FIG.

  Further, the deterioration estimating unit 10e estimates the heat value of the selective catalytic reduction catalyst 15 corresponding to the temperature of the selective catalytic reduction catalyst 15 (S902). The temperature of the selective reduction catalyst 15 is measured by the outlet temperature measuring unit 17 as the exhaust gas temperature of the engine 2. The outlet temperature measuring unit 17 notifies the measured exhaust temperature to the deterioration estimating unit 10e. The deterioration estimating unit 10 e refers to the table shown in FIG. 4 and estimates the heat value of the selective catalytic reduction catalyst 15 corresponding to the temperature of the selective catalytic reduction catalyst 15.

  The deterioration estimating unit 10e compares the calorific value of the selective reduction catalyst 15 with a predetermined value (deterioration index value) (S903). Thereby, the deterioration estimating unit 10e determines whether the selective reduction catalyst 15 has deteriorated.

  If the calorific value of the selective reduction catalyst 15 exceeds a predetermined value (deterioration index value), the deterioration estimating unit 10e determines that the selective reduction catalyst 15 has not deteriorated, and ends the deterioration estimation process. In this case, it is not necessary to alert the driver to special attention, but for example, an indicator lamp indicating that the selective reduction catalyst 15 is normal (not deteriorated) may be turned on.

  On the other hand, when the calorific value of the selective reduction catalyst 15 is equal to or less than a predetermined value (deterioration index value), the deterioration estimating unit 10e estimates that the selective reduction catalyst 15 has deteriorated (S904). In this case, the deterioration estimating unit 10e determines that the selective reduction catalyst 15 does not effectively contribute to the reduction reaction of NOx in the exhaust gas.

  Therefore, the deterioration estimating unit 10e gives a warning or the like that the selective reduction catalyst 15 has deteriorated, and urges the driver to call attention. For example, warnings such as lighting (flashing) of a warning light, display of a warning message, and sounding of a warning sound are issued. This makes it possible to quickly take measures such as replacing the selective reduction catalyst 15.

  When the selective reduction catalyst 15 has deteriorated, it does not contribute much to the activation of the reduction reaction of NOx in the exhaust gas. Therefore, if urea water is injected into the exhaust gas in a state where the selective reduction catalyst 15 is deteriorated as in the case of a new product, ammonia not contributing to the NOx reduction reaction may leak from the exhaust passage 3b. . Therefore, when the selective reduction catalyst 15 is deteriorated, for example, the leakage of ammonia can be prevented by controlling the urea water injector 18 and appropriately suppressing the injection amount of urea water into the exhaust gas. .

  As described above, according to the exhaust emission control device 1 of the present embodiment, the deterioration estimation availability determination is performed before performing the deterioration estimation processing of the selective reduction catalyst 15. Therefore, after estimating whether or not the selective reduction catalyst 15 is in a state in which deterioration can be estimated, only when it is estimated that the deterioration can be estimated, is the selective reduction catalyst 15 deteriorated? No. can be estimated. In the present embodiment, it is estimated whether or not the selective reduction catalyst 15 has deteriorated based on the amount of natural moisture adsorbed by the selective reduction catalyst 15 adsorbed during the stop time of the engine 2. Specifically, the deterioration can be estimated based on the calorific value of the selective reduction catalyst 15 that has adsorbed moisture from the state where the natural moisture adsorption amount is almost zero. The amount of heat generated by moisture adsorption from the state where the natural moisture adsorption amount is almost zero corresponds to the activation capability of the selective reduction catalyst 15 at that time for the NOx reduction reaction. Therefore, the deterioration of the selective reduction catalyst 15 can be properly estimated, and the accuracy of the estimation can be increased.

  Further, in the present embodiment, a NOx concentration measurement unit such as a NOx sensor is not required to estimate the deterioration of the selective reduction catalyst 15. Therefore, it is not necessary to add an NOx sensor or the like downstream of the selective reduction catalyst 15 in the exhaust passage 3b. Therefore, it is possible to easily estimate the deterioration of the selective reduction catalyst 15 at low cost. The NOx concentration measurement unit 1d is used for adjusting the injection amount of urea water injected into the exhaust gas from the urea water injector 18 and is not for estimating the deterioration of the selective reduction catalyst 15. .

  As described above, the embodiments of the present invention have been described. However, the above-described embodiments have been presented as examples, and are not intended to limit the scope of the invention. Such a novel embodiment can be implemented in other various forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and their equivalents.

  DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification device, 1a ... First purification device, 1b ... Second purification device, 1c ... Reducing agent addition device, 1d ... NOx concentration measurement part, 2 ... Internal combustion engine (engine), 3b ... Exhaust passage, 10 ... control device, 10a ... moisture adjusting unit, 10b ... time measuring unit, 10c ... moisture estimating unit, 10d ... deterioration estimation availability determination unit, 10e ... deterioration estimating unit, 14 ... body unit, 14a ... air passage, 15 ... selective reduction Type catalyst, 16: first temperature sensor (inlet temperature measuring unit), 17: second temperature sensor (outlet temperature measuring unit), 18: urea water injection nozzle (urea water injector), 19: urea water tank.

Claims (4)

A selective reduction catalyst arranged in an exhaust passage of an internal combustion engine,
A reducing agent addition unit that adds a reducing agent to exhaust gas on the upstream side of the selective reduction catalyst in the exhaust passage;
When the internal combustion engine is started, a deterioration estimating unit that estimates deterioration of the selective reduction catalyst based on a temperature increase of the selective reduction catalyst,
After the internal combustion engine has been stopped, a time measurement unit that measures the time until the restart,
Based on the measurement time measured by the time measurement unit, a moisture estimating unit that estimates the amount of moisture adsorbed on the selective reduction catalyst while the internal combustion engine is stopped,
Deterioration estimation based on the moisture adsorption amount of the selective reduction catalyst estimated by the moisture estimator to determine whether deterioration of the selective reduction catalyst is in a state where estimation of the selective reduction catalyst can be estimated at the start of the internal combustion engine. A determination unit;
The deterioration estimating unit,
An exhaust emission control device, wherein deterioration estimation of the selective reduction catalyst is performed based on a result of the determination by the deterioration estimation possibility determination section. A moisture adjusting unit configured to increase the temperature of the exhaust gas flowing through the exhaust passage so as to reduce the amount of moisture adsorbed by the selective reduction catalyst,
The deterioration estimation availability determination unit is configured to reduce the deterioration of the selective reduction catalyst when the moisture adjustment unit reduces the amount of water adsorbed on the selective reduction catalyst within a predetermined time until the internal combustion engine is stopped. The exhaust gas purifying apparatus according to claim 1, wherein it is determined whether the state is an estimable state. The exhaust purification device according to claim 2, wherein the moisture adjustment unit operates the internal combustion engine continuously for a predetermined time or more to maintain the exhaust gas temperature at or above a predetermined temperature. The said deterioration estimation possibility determination part determines that the deterioration estimation of the said selective reduction type catalyst is possible, when the estimated water adsorption amount is less than a predetermined value. The Claims 1 to 3 characterized by the above-mentioned. 2. The exhaust gas purifying apparatus according to claim 1.

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