JP2016098682A - Internal combustion engine exhaust emission control apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine exhaust emission control apparatus capable of suppressing the occurrence of ammonia slip when an oxidation catalyst degrades.SOLUTION: An exhaust emission control apparatus comprises: a first purification member 30 provided in an exhaust passage 26 and carrying an oxidation catalyst; an SCR catalyst 41 provided in the exhaust passage 26 downstream of the first purification member 30 and purifying NOx; a fuel addition valve 5 adding engine fuel to exhaust gas flowing into the first purification member 30; and an urea water supply mechanism 200 adding urea water to the exhaust gas flowing into the SCR catalyst 41. This exhaust emission control apparatus adds the engine fuel by an amount in response to a degree of degradation of the first purification member 30. Furthermore, after the degree of degradation of this first purification member 30 reaches a predetermined threshold, the exhaust emission control apparatus makes an addition amount of the urea water smaller than an addition amount when the degree of degradation of the first purification member 30 reaches the threshold.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  2. Description of the Related Art An exhaust gas purification apparatus for an internal combustion engine that includes a NOx purification catalyst for purifying nitrogen oxide (NOx) in exhaust gas in an exhaust passage is known. Such an exhaust purification device has an addition mechanism for adding a reducing agent such as urea water to the exhaust gas, and ammonia derived from the added reducing agent is adsorbed by the NOx purification catalyst. Then, NOx is reduced by ammonia adsorbed on the NOx purification catalyst.

  When the molar ratio of NO (nitrogen monoxide) and NO2 (nitrogen dioxide) in the exhaust gas is 1: 1 and the chemical reaction represented by the following formula (1) occurs as shown in Patent Document 1 and the like Compared with the reduction of NOx by other chemical reactions, the NOx purification efficiency of the NOx purification catalyst is increased.

NO + NO2 + 2NH3 → 2N2 + 3H2O (1)

Hereinafter, the ratio (molar ratio) occupied by NO2 in NOx contained in the exhaust is referred to as NO2 ratio [NO2 ratio (%) = NO2 / (NO + NO2) × 100]. Therefore, when the molar ratio of NO and NO2 in the exhaust gas is 1: 1, the NO2 ratio is 50%, and this NO2 ratio of 50% is necessary for realizing high purification efficiency in the NOx purification catalyst. It becomes the optimum value.

  Here, since most of the NOx generated in the cylinder of the internal combustion engine is NO, the NO2 ratio of the exhaust gas flowing into the NOx purification catalyst cannot be brought close to the optimum value as it is.

  Therefore, in the apparatus described in Patent Document 1, an oxidation catalyst is provided upstream of the exhaust of the NOx purification catalyst, and a part of NO contained in the exhaust is changed to NO2 by utilizing an oxidation reaction by the oxidation catalyst. The chemical reaction represented by the above formula (1) proceeds.

JP 2009-216019 A

  By the way, as the oxidation catalyst deteriorates, it becomes difficult for the oxidation reaction of NO in the oxidation catalyst to proceed, so it becomes difficult to bring the NO 2 ratio close to the optimum value. Therefore, if the temperature of the oxidation catalyst is increased by adding an amount of fuel corresponding to the degree of deterioration of the oxidation catalyst to the exhaust gas, the oxidation reaction of NO in the oxidation catalyst is promoted, so that the oxidation catalyst deteriorates. Even if it does, it becomes possible to maintain the NO2 ratio close to the optimum value.

  However, if the deterioration of the oxidation catalyst progresses to a certain extent, the oxidation reaction at the oxidation catalyst hardly occurs even if such fuel addition is performed. Therefore, it becomes difficult to maintain the NO2 ratio in an appropriate state as described above, and the NOx purification efficiency of the NOx purification catalyst is reduced. If the NOx purification efficiency decreases in this way, a part of the added reducing agent passes through the NOx purification catalyst without being used for NOx reduction, and ammonia slip may occur.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress the generation of ammonia slip when an oxidation catalyst deteriorates.

  An exhaust gas purification apparatus for an internal combustion engine that solves the above problems includes an oxidation catalyst provided in an exhaust passage, an NOx purification catalyst that is provided in an exhaust passage downstream of the oxidation catalyst and purifies NOx, and exhaust gas that flows into the oxidation catalyst A fuel addition mechanism for adding engine fuel to the NOx purification catalyst, and a reducing agent addition mechanism for adding a reducing agent containing an ammonia component to the exhaust gas flowing into the NOx purification catalyst. Then, by adding an amount of engine fuel corresponding to the degree of deterioration of the oxidation catalyst, it is possible to suppress a decrease in the oxidizing action of NO accompanying the deterioration of the oxidation catalyst.

  In addition, after the deterioration degree of the oxidation catalyst reaches a predetermined threshold value, the addition amount of the reducing agent is made smaller than the addition amount of the reducing agent when the deterioration degree reaches the threshold value. Therefore, by appropriately setting such a threshold value, if the degree of deterioration of the oxidation catalyst has progressed to the extent that it is difficult to maintain the NO2 ratio at the optimum value even if fuel is added, the addition of the reducing agent is performed. The amount can be reduced. Therefore, it is possible to prevent the amount of added urea water from becoming excessive with respect to the amount of urea water used for the NOx reduction treatment in the NOx purification catalyst. Generation of ammonia slip can be suppressed.

As the threshold value, it is desirable to set a maximum value of the degree of deterioration of the oxidation catalyst that can maintain the NO2 ratio of the exhaust gas that has passed through the oxidation catalyst at a value close to 50%.
Further, the degree of deterioration of the oxidation catalyst can be determined from the total amount of heat received by the oxidation catalyst since the use of the oxidation catalyst, the total travel distance of the vehicle equipped with the oxidation catalyst, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the exhaust gas purification device of an internal combustion engine. The flowchart which shows a series of processing procedures when performing urea addition in the same embodiment. In the same embodiment, the graph which shows the relationship between an oxidation catalyst deterioration degree and fuel addition amount. In the same embodiment, the graph which shows the relationship between SCR catalyst deterioration degree and urea correction amount. The flowchart which shows a part of procedure when performing NOx reduction process in 2nd Embodiment.

Hereinafter, an embodiment of a control device for an internal combustion engine mounted on a vehicle will be described with reference to FIGS.
FIG. 1 shows an internal combustion engine 1 and a peripheral configuration of the internal combustion engine 1.

  The internal combustion engine 1 is a diesel engine and is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4a to 4d are attached to the cylinder head 2 corresponding to the cylinders # 1 to # 4. These fuel injection valves 4a-4d inject fuel into the combustion chambers of the cylinders # 1- # 4, respectively. Also, the cylinder head 2 is provided with intake ports for introducing fresh air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas to the outside of the cylinders corresponding to the respective cylinders # 1 to # 4. It has been.

  The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in the fuel tank and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.

  An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. An intake throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.

An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to the exhaust passage 26.
In the middle of the exhaust passage 26, there is provided a turbocharger 11 for supercharging intake air introduced into the cylinder using exhaust pressure. An intercooler 18 is provided in the intake passage 3 between the intake side compressor of the turbocharger 11 and the intake throttle valve 16. The intercooler 18 cools the intake air whose temperature has risen due to supercharging of the turbocharger 11.

  A first purification member 30 for purifying exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the exhaust side turbine of the turbocharger 11. Inside the first purification member 30, an oxidation catalyst 31 and a filter 32 are arranged in series with respect to the flow direction of the exhaust gas.

  The oxidation catalyst 31 carries a catalyst for oxidizing HC and NO in the exhaust. The filter 32 is a member that collects PM (particulate matter) in the exhaust gas, and is made of porous ceramic. The filter 32 carries a catalyst for promoting the oxidation of PM and NO, and the PM in the exhaust gas is collected when passing through the porous wall of the filter 32.

  A fuel addition valve 5 for adding engine fuel to the exhaust gas flowing into the first purification member 30 (the oxidation catalyst 31 and the filter 32) is provided in the vicinity of the collecting portion of the exhaust manifold 8. The fuel addition valve 5 is connected to the supply pump 10 through a fuel supply pipe 27. The position of the fuel addition valve 5 may be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30. The fuel addition valve 5, the fuel supply pipe 27, and the supply pump 10 constitute a fuel addition mechanism. In place of the fuel addition from the fuel addition valve 5, the engine fuel may be added to the exhaust by adjusting the fuel injection timing of each of the fuel injection valves 4a to 4d and performing the post injection. In this case, each fuel injection valve 4a-4d also functions as a fuel addition mechanism.

  When the amount of PM collected by the filter 32 exceeds a predetermined value, the regeneration process of the filter 32 is started, and fuel is injected from the fuel addition valve 5 into the exhaust manifold 8. The fuel injected from the fuel addition valve 5 is oxidized when it reaches the oxidation catalyst 31, thereby increasing the exhaust temperature. The exhaust gas whose temperature has been raised by the oxidation catalyst 31 flows into the filter 32, whereby the temperature of the filter 32 is raised, whereby the PM deposited on the filter 32 is oxidized and the filter 32 is regenerated.

  A second purification member 40 that purifies the exhaust gas is provided downstream of the first purification member 30 in the middle of the exhaust passage 26. A selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) 41 that reduces and purifies NOx in the exhaust using a reducing agent is disposed inside the second purification member 40.

  Further, a third purification member 50 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the second purification member 40. Inside the third purification member 50, an ammonia oxidation catalyst 51 for purifying ammonia in the exhaust is disposed.

  The internal combustion engine 1 is provided with a urea water supply mechanism 200 as a reducing agent supply mechanism for adding a reducing agent to the SCR catalyst 41. The urea water supply mechanism 200 includes a tank 210 that stores urea water, a urea addition valve 230 that injects urea water into the exhaust passage 26, a supply passage 240 that connects the urea addition valve 230 and the tank 210, and a supply passage 240. The pump 220 is provided in the middle.

  The urea addition valve 230 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, and the injection hole is opened toward the SCR catalyst 41. When the urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the supply passage 240.

  The pump 220 is an electric pump, and at the time of forward rotation, the urea water is fed from the tank 210 toward the urea addition valve 230. On the other hand, during reverse rotation, urea water is sent from the urea addition valve 230 toward the tank 210. In other words, during the reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the supply passage 240 and returned to the tank 210.

  A dispersion plate 60 is provided in the exhaust passage 26 between the urea addition valve 230 and the SCR catalyst 41 to promote atomization of the urea water by dispersing the urea water injected from the urea addition valve 230. It has been.

  The urea water injected from the urea addition valve 230 is hydrolyzed to ammonia by the heat of the exhaust. This ammonia is supplied to the SCR catalyst 41 as a NOx reducing agent. Ammonia supplied to the SCR catalyst 41 is adsorbed by the SCR catalyst 41 and used for NOx reduction.

  Here, when the exhaust discharged from the internal combustion engine 1 passes through the first purification member 30, a part of NO contained in the exhaust is oxidized and changed to NO2. Therefore, the NO2 ratio of the exhaust after passing through the first purification member 30 is higher than the NO2 ratio of the exhaust before passing through the first purification member 30, and the NO2 ratio of the exhaust flowing into the SCR catalyst 41 is as described above. It approaches the optimal value (50%). Due to the oxidizing action of NO by the first purification member 30, the chemical reaction represented by the above formula (1) proceeds in the SCR catalyst 41, and the NOx purification efficiency is improved in the SCR catalyst 41.

  In addition, the internal combustion engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device). By this EGR device, exhaust gas recirculation processing (hereinafter referred to as EGR processing) in which part of the exhaust gas is recirculated to the intake air is performed, so that the combustion temperature in the combustion chamber is lowered and the amount of NOx generated is reduced. The The EGR device includes an EGR passage 13 that communicates the intake passage 3 and the exhaust manifold 8, an EGR valve 15 provided in the EGR passage 13, an EGR cooler 14, and the like. The exhaust gas recirculation amount introduced from the exhaust passage 26 to the intake passage 3 is adjusted by adjusting the opening degree of the EGR valve 15. Further, the temperature of the exhaust gas flowing through the EGR passage 13 is lowered by the EGR cooler 14.

  Various sensors for detecting the engine operating state are attached to the internal combustion engine 1. For example, the air flow meter 19 detects the intake air amount GA. The throttle valve opening sensor 20 detects the opening of the intake throttle valve 16. The engine rotation speed sensor 21 detects the rotation speed of the crankshaft, that is, the engine rotation speed NE. The accelerator sensor 22 detects an accelerator pedal depression amount, that is, an accelerator operation amount ACCP. The outside air temperature sensor 23 detects the outside air temperature THout around the vehicle. The outside air temperature sensor 23 is disposed at a position that is not easily affected by the heat released from the internal combustion engine 1 or the like. For example, the outside air temperature sensor 23 is provided on the vehicle front side of a radiator that is provided in front of the vehicle and cools engine coolant. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the internal combustion engine 1 is mounted. The water temperature sensor 25 detects the cooling water temperature THW of the internal combustion engine 1. The intake air temperature sensor 150 detects the intake air temperature THA in the vicinity of the air flow meter 19.

  The first exhaust temperature sensor 100 provided upstream of the oxidation catalyst 31 detects a first exhaust temperature TH1 that is the temperature of the exhaust gas flowing into the oxidation catalyst 31. The differential pressure sensor 110 detects the pressure difference ΔP between the exhaust pressure upstream and downstream of the filter 32.

  A second exhaust temperature sensor 120 and a first NOx sensor 130 are provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40 and upstream of the urea addition valve 230. The second exhaust temperature sensor 120 detects a second exhaust temperature TH2, which is the temperature of the exhaust flowing into the SCR catalyst 41. The first NOx sensor 130 detects the amount of NOx contained in the exhaust before flowing into the SCR catalyst 41, more specifically, the first NOx concentration N1, which is the NOx concentration (unit: ppm).

  The exhaust passage 26 downstream of the third purification member 50 is provided with a second NOx sensor 140 that detects a second NOx concentration N2 that is the NOx concentration of the exhaust purified by the SCR catalyst 41.

  Outputs of these various sensors and the like are input to a control device 80 constituting a control unit. The control device 80 includes a central processing control device (CPU), a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like.

  Then, by this control device 80, for example, the fuel injection amount control and injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, the discharge pressure control of the supply pump 10, and the drive amount of the actuator 17 that opens and closes the intake throttle valve 16 Various controls of the internal combustion engine 1 such as control are performed.

The exhaust gas purification control such as the regeneration process for burning the PM collected by the filter 32 is also performed by the controller 80.
The control device 80 performs urea water addition control by the urea addition valve 230 as one of exhaust purification control. In this addition control, the urea addition amount necessary for reducing the NOx generated in the combustion chamber of the internal combustion engine 1 by the SCR catalyst 41 is calculated based on the engine operating state and the like. For example, the basic urea addition amount Qurb is calculated according to the amount of NOx generated in the combustion chamber, the amount of ammonia adsorbed on the SCR catalyst 41, and the basic urea addition amount Qurb is corrected with various correction values. Thus, the urea addition amount Qur is calculated. Then, the valve opening state of the urea addition valve 230 is controlled such that an amount of urea water corresponding to the calculated urea addition amount Qur is injected from the urea addition valve 230.

Hereinafter, a series of processing procedures for urea water addition control will be described with reference to FIG. The series of processes shown in FIG. 2 is repeatedly executed by the control device 80 at predetermined intervals.
When this process is started, it is first determined whether or not an execution condition for urea water addition is satisfied (S100). In this step S100, for example, when the temperature of the SCR catalyst 41 is equal to or higher than the activation temperature at which the NOx reduction action is obtained, it is determined that the execution condition for urea water addition is satisfied. The temperature of the SCR catalyst 41 is estimated based on various parameters related to the heat balance of the SCR catalyst 41, for example, the second exhaust temperature TH2 that is the temperature of the exhaust gas flowing into the SCR catalyst 41. Incidentally, a temperature sensor may be provided in the SCR catalyst 41 to directly detect the temperature of the SCR catalyst 41.

And when the execution conditions of urea water addition are not satisfied (S100: NO), this process is once complete | finished.
On the other hand, when the execution condition for urea water addition is satisfied (S100: YES), the fuel addition amount Qad is calculated based on the oxidation catalyst deterioration degree MHD (S110).

  The oxidation catalyst deterioration degree MHD is a value indicating the degree of thermal deterioration of the oxidation catalyst when the first purification member 30 composed of the oxidation catalyst 31 and the filter 32 is regarded as one oxidation catalyst. The degree of deterioration can be estimated in an appropriate manner. For example, the degree of thermal degradation of the first purification member 30 has a correlation with the total amount of heat received since the use of the first purification member 30 is started, and therefore flows into the temperature of the first purification member 30 and the first purification member 30. The larger the value obtained by time-integrating the multiplication value with the exhaust gas flow rate, the larger the value. Therefore, in the present embodiment, the temperature of the first purification member 30 is estimated based on the first exhaust temperature TH1 that is the temperature of the exhaust gas flowing into the first purification member 30 in a process different from the present process. Yes. Then, for each predetermined period, a process of calculating a multiplication value of the estimated temperature of the first purification member 30 and the flow rate of the exhaust gas flowing into the first purification member 30 and integrating the multiplication value is executed, and thus calculated. The time integrated value of the multiplied value is set as the current oxidation catalyst deterioration degree MHD.

Further, the fuel addition amount Qad is an amount of fuel added from the fuel addition valve 5 and is a fuel addition amount for compensating for a decrease in NO oxidation action accompanying thermal deterioration of the first purification member 30.
As shown in FIG. 3, the fuel addition amount Qad increases as the oxidation catalyst deterioration degree MHD increases until the oxidation catalyst deterioration degree MHD reaches the threshold value α. Then, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, the fuel addition amount Qad is reduced as the oxidation catalyst deterioration degree MHD increases. The threshold α is set to the maximum value of the oxidation catalyst deterioration degree MHD that can maintain the NO 2 ratio of the exhaust gas that has passed through the first purification member 30 in the vicinity of 50% by using fuel addition together.

  Next, it is determined whether the oxidation catalyst deterioration degree MHD is equal to or greater than the threshold value α (S120). When the oxidation catalyst deterioration degree MHD is less than the threshold value α (S120: NO), the urea correction amount Qurc is calculated based on the SCR catalyst deterioration degree SHD (S130).

  The SCR catalyst degradation degree SHD is a value indicating the thermal degradation degree of the SCR catalyst 41, and the thermal degradation degree of such a catalyst can be estimated in an appropriate manner. For example, since the degree of thermal degradation of the SCR catalyst 41 has a correlation with the total amount of heat received after the use of the SCR catalyst 41 is started, the product of the temperature of the SCR catalyst 41 and the flow rate of the exhaust gas flowing into the SCR catalyst 41 The larger the value obtained by integrating the time, the larger the value. Therefore, in the present embodiment, in a process different from this process, a multiplication value of the estimated temperature of the SCR catalyst 41 and the flow rate of the exhaust gas flowing into the SCR catalyst 41 is calculated every predetermined cycle, and the multiplication value is integrated. The time integrated value of the multiplication value thus calculated is set as the current SCR catalyst deterioration degree SHD.

  The urea correction amount Qurc is a value for correcting the basic urea addition amount Qurb, which is the basic value of the urea addition amount Qur, and is a correction amount for compensating for a decrease in the NOx purification rate due to thermal degradation of the SCR catalyst 41. is there.

  As shown in FIG. 4, the urea correction amount Qurc is set to “0” until the SCR catalyst deterioration degree SHD reaches the threshold value β. After the SCR catalyst deterioration degree SHD reaches the threshold value β, the urea correction amount Qurc increases as the SCR catalyst deterioration degree SHD increases. The threshold value β is set to the maximum value of the SCR catalyst deterioration degree SHD that can maintain the NOx purification rate at the start of use of the SCR catalyst 41. Incidentally, the urea correction amount Qurc may be continuously increased according to the magnitude of the SCR catalyst deterioration degree SHD without providing a region where the urea correction amount Qurc is set to “0”. Further, the NOx purification rate is a value represented by “{(first NOx concentration N1−second NOx concentration N2) / first NOx concentration N1} × 100 (%)”.

  When it is determined in step S120 that the oxidation catalyst deterioration degree MHD is equal to or greater than the threshold value α (S120: YES), the urea correction amount Qurc is reduced (S140). In this step S140, a value obtained by subtracting the preset subtraction amount D from the urea correction amount Qurc set at the previous execution of the main processing is set as the urea correction amount Qurc at the current main processing execution. The subtraction amount D is an amount that can suppress the occurrence of ammonia slip while suppressing a rapid change in the urea addition amount, and an appropriate value is obtained through a preliminary experiment or the like.

  Here, when an affirmative determination is made in step S120 for the first time, that is, immediately after the oxidation catalyst deterioration degree MHD becomes equal to or greater than the threshold value α, the “urea correction amount Qurc set at the time of the previous main processing execution” The urea correction amount Qurc that has already been set at the time when the degree MHD becomes equal to or greater than the threshold value α and has the following value. That is, it is the urea correction amount Qurc set by the negative determination in step S120 when this process was executed last time, and is the last urea correction amount Qurc set based on the SCR catalyst deterioration degree SHD. When the oxidation catalyst deterioration degree MHD becomes equal to or higher than the threshold value α, step S140 is executed every time this process is executed. Therefore, the urea correction amount set after the oxidation catalyst deterioration degree MHD becomes equal to or higher than the threshold value α. Qurc is decreased by the subtraction amount D with reference to the last urea correction amount Qurc set based on the SCR catalyst deterioration degree SHD. Note that the urea correction amount Qurc is decreased in step S140 until the urea correction amount Qurc becomes “0” or until the NOx purification rate of the SCR catalyst 41 falls below a predetermined threshold value.

  If the urea correction amount Qurc in the current execution cycle is set in step S130 or step S140, then the urea addition amount Qur is calculated based on the basic urea addition amount Qurb and the urea correction amount Qurc (S150). . In this step S150, the sum of the basic urea addition amount Qurb and the urea correction amount Qurc is set as the urea addition amount Qur.

  Next, execution of urea water addition by the urea addition amount Qur calculated in step S150 (S160) and fuel addition by the fuel addition amount Qad calculated in step S110 are executed (S170), and this processing is temporarily performed. Is terminated.

Next, the operation of the present embodiment will be described with reference to FIG.
Since the oxidation reaction of NO by the first purification member 30 becomes difficult to proceed as the oxidation catalyst deterioration degree MHD increases, as it is, as shown by a two-dot chain line L1 in FIG. The ratio becomes lower than the optimum value (for example, “50%”, etc.) as the oxidation catalyst deterioration degree MHD increases.

  In this regard, in the present embodiment, the fuel addition amount Qad is increased as the oxidation catalyst deterioration degree MHD increases until the oxidation catalyst deterioration degree MHD reaches the threshold value α. In this way, when an amount of engine fuel corresponding to the oxidation catalyst deterioration degree MHD is added to the exhaust gas, the engine fuel is oxidized in the exhaust gas or in the first purification member 30, so that the temperature of the first purification member 30 is increased. As the temperature of the first purification member 30 increases, the NO oxidation reaction in the first purification member 30 is promoted. Therefore, even if the deterioration of the first purification member 30 progresses, the NO2 ratio is maintained in a state close to the optimum value as indicated by the solid line in FIG. 5 until the oxidation catalyst deterioration degree MHD reaches the threshold value α.

  Further, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, the deterioration of the first purification member 30 has progressed too much, so that it becomes difficult to optimize the NO 2 ratio by adding fuel. Therefore, in the present embodiment, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, the fuel addition amount Qad is decreased as the oxidation catalyst deterioration degree MHD increases. Therefore, it is possible to suppress consumption of unnecessary engine fuel that does not contribute to the optimization of the NO 2 ratio.

  On the other hand, when the basic urea addition amount Qurb is not corrected by the urea correction amount Qurc, as indicated by a two-dot chain line L2 in FIG. 5, after the SCR catalyst deterioration degree SHD reaches the threshold value β, the SCR catalyst deterioration degree As the SHD increases, the NOx purification rate decreases.

  In this regard, in this embodiment, after the SCR catalyst deterioration degree SHD reaches the threshold value β, the urea correction amount Qurc is increased as the SCR catalyst deterioration degree SHD increases. Therefore, after the SCR catalyst deterioration degree SHD reaches the threshold value β, the urea addition amount Qur is increased in accordance with the progress of deterioration of the SCR catalyst 41.

  Incidentally, the SCR catalyst 41 does not deteriorate uniformly in the exhaust flow direction, but basically gradually deteriorates from the exhaust upstream side portion (front end) toward the exhaust downstream side portion (rear end). Will progress. Therefore, the part where ammonia is adsorbed in the SCR catalyst 41 gradually shifts to the part on the exhaust downstream side as the SCR catalyst deterioration degree SHD increases.

  Further, as described above, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, even if the fuel is added, the NO purification reaction does not easily occur in the first purification member 30, so the NO2 ratio is as described above. It is difficult to maintain the appropriate state, and the NOx purification rate of the SCR catalyst 41 is reduced. If the increase in the urea addition amount Qur is continued in a state where the NOx purification rate is reduced in this way, the amount of urea water added is excessive with respect to the amount of urea water used for the reduction treatment. become. Therefore, a part of the added urea water passes through the SCR catalyst 41 without being used for NOx reduction, and ammonia slip may occur.

  In this regard, in the present embodiment, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, the urea correction amount Qurc starts to be reduced (the process of step S140 shown in FIG. 2). Therefore, the urea addition amount Qur after the oxidation catalyst deterioration degree MHD reaches the threshold value α is smaller than the urea addition amount Qur when the oxidation catalyst deterioration degree MHD reaches the threshold value α, and an excessive amount of urea Since the addition of water is suppressed, the occurrence of ammonia slip is suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea addition amount Qur after the oxidation catalyst deterioration degree MHD reaches the threshold value α is made smaller than the urea addition amount Qur when the oxidation catalyst deterioration degree MHD reaches the threshold value α. Therefore, even if the oxidation catalyst 31 and the filter 32 deteriorate, the occurrence of ammonia slip can be suppressed.

  (2) Since the fuel is added in an amount corresponding to the oxidation catalyst deterioration degree MHD, even if the oxidation catalyst 31 and the filter 32 are thermally deteriorated, the SCR is not changed until the oxidation catalyst deterioration degree MHD reaches the threshold value α. The NO2 ratio of the exhaust gas flowing into the catalyst 41 can be maintained at a value near the optimum value.

(3) Since urea water is added in an amount corresponding to the degree of SCR catalyst deterioration SHD, a decrease in the NOx purification rate accompanying thermal deterioration of the SCR catalyst 41 can be suppressed.
In addition, the said embodiment can also be changed and implemented as follows.

  The oxidation catalyst deterioration degree MHD was a value indicating the degree of thermal deterioration of the oxidation catalyst when the first purification member 30 composed of the oxidation catalyst 31 and the filter 32 is regarded as one oxidation catalyst. In addition, the degree of thermal degradation of the oxidation catalyst 31 and the filter 32 may be calculated individually, and the fuel addition amount may be set based on the degree of thermal degradation. For example, it is assumed that the deterioration degree of the oxidation catalyst 31 is MHD1, and the fuel addition amount corresponding to the deterioration degree MHD1 is Qad1. Further, it is assumed that the degree of deterioration of the filter 32 is MHD2, and the fuel addition amount corresponding to the degree of deterioration MHD2 is Qad2. In this case, the sum of Qad1 and Qad2 may be used as the fuel addition amount Qad, and an amount of engine fuel corresponding to the fuel addition amount Qad may be added from the fuel addition valve 5.

  -After the oxidation catalyst deterioration degree MHD reaches the threshold value α, the fuel addition amount Qad decreases as the oxidation catalyst deterioration degree MHD increases. In addition, the fuel addition amount Qad may be set to “0” after the oxidation catalyst deterioration degree MHD reaches the threshold value α.

  -After the oxidation catalyst deterioration degree MHD reaches the threshold value α, the urea correction amount Qurc is gradually decreased. In addition, after the oxidation catalyst deterioration degree MHD reaches the threshold value α, the urea correction amount Qurc may be set to “0”.

  The subtraction amount D described above may be variably set so as to increase as the oxidation catalyst deterioration degree MHD increases. In this case, as the oxidation catalyst deterioration degree MHD increases, the degree of decrease in the current value with respect to the optimum value of the NO 2 ratio increases, but the urea addition amount subtraction amount D according to the degree of decrease in the NO 2 ratio. Therefore, the occurrence of ammonia slip can be more suitably suppressed.

  Although the urea correction amount Qurc is calculated according to the SCR catalyst deterioration degree SHD, the correction of the urea addition amount according to the deterioration degree of the SCR catalyst 41 can be omitted. Even in this case, at least the urea addition amount Qur after the oxidation catalyst deterioration degree MHD reaches the threshold value α is made smaller than the urea addition amount Qur when the oxidation catalyst deterioration degree MHD reaches the threshold value α, Even if the oxidation catalyst 31 and the filter 32 deteriorate, the occurrence of ammonia slip can be suppressed.

  The degree of thermal deterioration of the oxidation catalyst 31, the filter 32, and the SCR catalyst 41 tends to increase as the total travel distance of the vehicle on which the internal combustion engine 1 is mounted increases. Therefore, the oxidation catalyst deterioration degree MHD and the SCR catalyst deterioration degree based on the total travel distance so that the oxidation catalyst deterioration degree MHD and the SCR catalyst deterioration degree SHD increase as the total travel distance of the vehicle equipped with the internal combustion engine 1 increases. SHD may be obtained.

-The arrangement | positioning number of the oxidation catalyst 31, the filter 32, the SCR catalyst 41, and the ammonia oxidation catalyst 51 can be changed suitably.
Although urea water is used, other reducing agents may be used as long as the reducing agent contains an ammonia component.

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Fuel addition valve, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail DESCRIPTION OF SYMBOLS 10 ... Supply pump, 11 ... Turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... Intake throttle valve, 17 ... Actuator, 18 ... Intercooler, 19 ... Air flow meter, 20 ... Throttle valve Opening sensor, 21 ... Engine rotation speed sensor, 22 ... Accelerator sensor, 23 ... Outside air temperature sensor, 24 ... Vehicle speed sensor, 25 ... Water temperature sensor, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... First purification member, 31 ... oxidation catalyst, 32 ... filter, 40 ... second purification member, 41 ... selective reduction type NOx catalyst (SCR catalyst), 50 ... third purification member, DESCRIPTION OF SYMBOLS 1 ... Ammonia oxidation catalyst, 60 ... Dispersion plate, 80 ... Control apparatus, 100 ... 1st exhaust temperature sensor, 110 ... Differential pressure sensor, 120 ... 2nd exhaust temperature sensor, 130 ... 1st NOx sensor, 140 ... 2nd NOx sensor, 150 ... Intake air temperature sensor, 200 ... Urea water supply mechanism, 210 ... Tank, 220 ... Pump, 230 ... Urea addition valve, 240 ... Supply passage.

Claims (1)

An oxidation catalyst provided in the exhaust passage, a NOx purification catalyst provided in an exhaust passage downstream of the oxidation catalyst to purify NOx, a fuel addition mechanism for adding engine fuel to the exhaust flowing into the oxidation catalyst, An exhaust gas purification apparatus for an internal combustion engine, comprising: a reducing agent addition mechanism for adding a reducing agent containing an ammonia component to exhaust gas flowing into the NOx purification catalyst,
While adding the amount of the engine fuel according to the degree of deterioration of the oxidation catalyst,
After the degree of deterioration reaches a predetermined threshold, the amount of the reducing agent added is made smaller than the amount of reducing agent added when the degree of deterioration reaches the threshold. Exhaust purification equipment.