JP2015071994A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine that can suppress generation of NOx caused by an increase in a temperature of an oxidation catalyst.SOLUTION: An engine 1 includes: an urea water supply mechanism 200 for adding ammonia-derived urea water to inside of an exhaust passage 26; an SCR catalyst 41 for purifying exhaust gas by addition of the urea water; an ammonia oxidation catalyst 51 arranged downstream of the SCR catalyst 41 in the exhaust passage 26; and a control device 80 for controlling addition amount of the urea water by using the urea water supply mechanism 200. The control device 80 performs addition amount reduction control for reducing the addition amount of the urea water in the state where a temperature of the ammonia oxidation catalyst 51 is a predetermined temperature or higher, compared to the state where the temperature of the ammonia oxidation catalyst 51 is lower than the predetermined temperature.

Description

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

  For example, as described in Patent Document 1, a reducing agent supply mechanism for adding an ammonia-derived reducing agent into the exhaust passage, a reducing catalyst for purifying exhaust gas by adding the reducing agent, and a reducing catalyst in the flow direction of the exhaust gas In addition, an exhaust emission control device including an oxidation catalyst provided on the downstream side is known.

  The ammonia-derived reducing agent (for example, urea water) added in the exhaust passage becomes ammonia by hydrolysis by exhaust heat. This ammonia is adsorbed by the reduction catalyst, and NOx in the exhaust is reduced and purified by the adsorbed ammonia. In addition, ammonia that has passed through the reduction catalyst or desorbed from the reduction catalyst is oxidized by the oxidation catalyst, so that release of ammonia into the atmosphere is suppressed.

JP 2008-115775 A

  By the way, in an internal combustion engine provided with an exhaust emission control device, there is a case where a process for raising the temperature of exhaust gas is performed, and when such a temperature raising process is executed, the oxidation catalyst is heated to a high temperature. When the oxidation catalyst is heated to high temperature, there is a possibility that an oxidation reaction of ammonia occurs on the oxidation catalyst and NOx is generated.

  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 NOx due to a high temperature of an oxidation catalyst.

  An exhaust gas purification apparatus for an internal combustion engine that solves the above problems includes a reducing agent supply mechanism that adds a reducing agent derived from ammonia in an exhaust passage, a reducing catalyst that purifies exhaust gas by adding the reducing agent, and a reducing catalyst in the exhaust passage. Also, an oxidation catalyst provided on the downstream side and a control unit for controlling the amount of reducing agent added by the reducing agent supply mechanism are provided. Then, the control unit performs an addition amount reduction process for reducing the addition amount of the reducing agent when the oxidation catalyst is in a state equal to or higher than a predetermined temperature compared to when the oxidation catalyst is in a state below the predetermined temperature. .

  According to this configuration, when the oxidation catalyst is at a predetermined temperature or higher and there is a possibility that NOx may be generated on the oxidation catalyst, the amount of addition of the ammonia-derived reducing agent that is one of the causes for generating NOx Is reduced. By such a decrease in the amount of addition, the amount of ammonia adsorbed on the reduction catalyst and the amount of ammonia that passes through the reduction catalyst are reduced, so that the amount of ammonia reaching the oxidation catalyst is reduced. Therefore, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the oxidation catalyst having a high temperature. The predetermined temperature in the configuration is desirably set to a temperature at which it is possible to appropriately determine whether or not NOx is generated by the oxidation reaction of ammonia on the oxidation catalyst.

  In addition, a filter that collects particulate matter in the exhaust gas is provided on the upstream side of the reduction catalyst in the exhaust passage, and when a regeneration process for regenerating the filter by raising the temperature of the exhaust gas is being performed, Exhaust gas increases the temperature of the oxidation catalyst. Therefore, NOx resulting from the oxidation of ammonia tends to occur on the same oxidation catalyst. Therefore, it is preferable that the control unit performs the addition amount reduction process described above during the execution of the regeneration process.

According to this configuration, even when the oxidation catalyst is heated to a predetermined temperature or higher by the regeneration process of the filter, it is possible to suppress the generation of NOx due to the high temperature of the oxidation catalyst.
Further, in the exhaust purification apparatus, it is preferable that the control unit performs a reduction correction of the reducing agent addition amount as the addition amount reduction processing, and increases the reduction correction amount of the reducing agent addition amount as the exhaust temperature is higher.

  According to this configuration, as the exhaust gas temperature is higher, that is, as the oxidation reaction of ammonia on the oxidation catalyst is promoted and NOx is more likely to be generated, the amount of reducing agent added is reduced. The amount of ammonia that reaches is reduced. Therefore, even if the exhaust temperature changes, the generation of NOx can be suitably suppressed.

  Further, in the above exhaust purification apparatus, the control unit performs a reduction correction of the reducing agent addition amount as the addition amount reduction process, and the reduction correction amount of the reducing agent addition amount increases as the amount of ammonia adsorbed on the reduction catalyst increases. It is preferable to do.

  According to this configuration, as the amount of ammonia adsorbed on the reduction catalyst increases, that is, as the amount of ammonia desorbed from the reduction catalyst increases, the amount of addition of the reducing agent is reduced, thereby reducing the oxidation catalyst. The amount of ammonia that reaches is reduced. Therefore, even if the amount of ammonia adsorbed on the reduction catalyst changes, the generation of NOx can be suitably suppressed.

  Further, in the exhaust purification apparatus, when the reducing agent supply mechanism intermittently adds the reducing agent by repeating the addition of the reducing agent and the suspension of addition at a predetermined addition cycle, the control unit performs exhaust gas reduction processing as an addition amount reduction process. The higher the temperature, the longer the addition period.

  According to this configuration, as the exhaust gas temperature is higher, that is, as the oxidation reaction of ammonia on the oxidation catalyst is promoted and NOx is more likely to be generated, the addition cycle at the intermittent addition is lengthened, thereby allowing a predetermined period of time. The number of times the reducing agent is added decreases. When the number of additions of the reducing agent is reduced in this way, the total amount of reducing agent added within a predetermined period is reduced, so that the amount of ammonia reaching the oxidation catalyst is reduced. Therefore, even if the exhaust temperature changes, the generation of NOx can be suitably suppressed.

  Further, in the above exhaust purification apparatus, when the reducing agent supply mechanism intermittently adds the reducing agent by repeating the addition of the reducing agent and the suspension of the addition at a predetermined addition cycle, the control unit performs reduction as the addition amount reduction process. It is preferable to increase the addition period as the amount of ammonia adsorbed on the catalyst is larger.

  According to this configuration, as the amount of ammonia adsorbed on the reduction catalyst is larger, that is, as the amount of ammonia desorbed from the reduction catalyst is larger, the addition period at the time of intermittent addition is lengthened, so that the predetermined period The number of times the reducing agent is added decreases. When the number of additions of the reducing agent is reduced in this way, the total amount of reducing agent added within a predetermined period is reduced, so that the amount of ammonia reaching the oxidation catalyst is reduced. Therefore, even if the amount of ammonia adsorbed on the reduction catalyst changes, the generation of NOx can be suitably suppressed.

In the exhaust purification apparatus, it is preferable that the control unit prohibits the addition of the reducing agent as the addition amount reduction process while the oxidation catalyst is in a state of the predetermined temperature or higher.
According to this configuration, the addition of the reducing agent is prohibited when the oxidation catalyst is at a predetermined temperature or higher and there is a possibility that NOx is generated on the oxidation catalyst. By prohibiting the addition of such a reducing agent, the amount of ammonia reaching the oxidation catalyst is sufficiently reduced. Accordingly, it is possible to more appropriately suppress the generation of NOx due to the oxidation of ammonia on the oxidation catalyst having a high temperature.

In the exhaust purification apparatus, it is preferable that the control unit provides a prohibition period during which the addition of the reducing agent is prohibited during the addition period of the reducing agent as the addition amount reduction process.
According to this configuration, the prohibition period for prohibiting the addition of the reducing agent is provided during the addition period of the reducing agent. Therefore, compared with the case where such a prohibition period is not provided, the total amount of reducing agent added during the addition period is reduced, and the amount of ammonia reaching the oxidation catalyst is reduced. Therefore, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the oxidation catalyst having a high temperature.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about 1st Embodiment of the exhaust gas purification device of an internal combustion engine. The time chart which shows the addition aspect of urea water in the same embodiment. The flowchart which shows the procedure about the addition amount reduction | decrease process in the embodiment. The table | surface which shows the relationship between 2nd exhaust temperature and 1st urea correction amount in the same embodiment. The table | surface which shows the relationship between ammonia adsorption amount and 2nd urea correction amount in the same embodiment. It is a time chart which shows the addition aspect of urea water in 2nd Embodiment, Comprising: (A) is a time chart which shows the addition aspect before correct | amending an addition interval. (B) is a time chart showing an addition mode after correcting an addition interval. The flowchart which shows the procedure about the addition amount reduction | decrease process in the embodiment. The table | surface which shows the relationship between 2nd exhaust temperature and 1st interval correction amount in the same embodiment. The table | surface which shows the relationship between ammonia adsorption amount and 2nd interval correction amount in the embodiment. The flowchart which shows the procedure of the addition amount reduction | decrease process in the modification of 1st Embodiment. The time chart which shows the addition aspect of the urea water in the modification of 1st Embodiment.

(First embodiment)
A first embodiment that embodies an exhaust emission control device for an internal combustion engine will be described below with reference to FIGS.

FIG. 1 shows a configuration of a diesel engine (hereinafter simply referred to as an “engine”) that is an internal combustion engine to which an exhaust purification device is applied, and an exhaust purification device provided in the engine 1.
The engine 1 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 to 4d inject fuel into the combustion chambers of the cylinders # 1 to # 4. 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 that supercharges 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 that purifies the 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 oxidizes HC in the exhaust. The filter 32 is a filter that collects PM (particulate matter) in the exhaust gas and is made of porous ceramic, and further supports a catalyst for promoting the oxidation of PM. The PM in the exhaust gas is collected when passing through the porous wall of the filter 32. The filter 32 constitutes the exhaust purification member.

  Further, a fuel addition valve 5 for supplying fuel as an additive to 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 can be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30. Further, the fuel may be supplied as an additive to the oxidation catalyst 31 or the filter 32 by adjusting the fuel injection timing and performing the post injection.

  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 burned when it reaches the oxidation catalyst 31, thereby raising the temperature of the exhaust. 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 in the middle of the exhaust passage 26 and downstream of the first purification member 30. Inside the second purification member 40, a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) 41 is disposed as a reduction catalyst for reducing and purifying NOx in the exhaust using a reducing agent.

  Further, a third purification member 50 for purifying 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 engine 1 is provided with a urea water supply mechanism 200 as a reducing agent supply mechanism for adding urea water as a reducing agent derived from ammonia into the exhaust passage 26. 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 by the heat of the exhaust to become ammonia. 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.

  In addition, the engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device). This EGR device is a device that reduces the combustion temperature in the cylinder by introducing a part of the exhaust gas into the intake air, thereby reducing the amount of NOx generated. 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. By adjusting the opening degree of the EGR valve 15, the exhaust gas recirculation amount introduced into the intake passage 3 from the exhaust passage 26, that is, the so-called external EGR amount is adjusted. 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 operation state are attached to the 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. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted. The engine 1 is also provided with an ignition switch (hereinafter referred to as IG switch) 25 that is operated when a driver of the vehicle starts or stops the engine 1, and the engine 1 corresponds to the operation position of the IG switch 25. The engine is started and stopped.

  The first exhaust temperature sensor 100 provided upstream of the oxidation catalyst 31 detects the first exhaust temperature TH1 that is the exhaust temperature before 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 exhaust temperature before flowing into the SCR catalyst 41. The first NOx sensor 130 detects a first NOx concentration N1, which is the NOx concentration in the exhaust before flowing into the SCR catalyst 41.

  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 as 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, the controller 80 controls, for example, the fuel injection amount control / fuel 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 engine 1 such as control and opening control of the EGR valve 15 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 amount of urea necessary for reducing the NOx discharged from the engine 1 is calculated based on the engine operating state and the like. Further, the amount of urea necessary to maintain the ammonia amount adsorbed on the SCR catalyst 41 at a predetermined amount is calculated. The ammonia adsorption amount NHR of the SCR catalyst 41 is estimated by an appropriate method. For example, the ammonia adsorption amount NHR is estimated based on parameters that correlate with the ammonia adsorption amount, such as urea addition amount, exhaust temperature, and exhaust flow rate.

  The sum of the urea amount necessary for reducing NOx and the urea amount necessary for maintaining the ammonia adsorption amount is calculated as the urea addition amount QE, and the urea water of the urea addition amount QE is used as the urea addition valve. The driving state of the urea addition valve 230 is controlled such that the urea addition valve 230 is injected.

  As shown in FIG. 2, in this embodiment, urea water is added intermittently. That is, by repeatedly opening and closing the urea addition valve 230 at a predetermined addition cycle (hereinafter referred to as an addition interval) INT, addition and stoppage of urea water are repeated at the predetermined addition interval INT. By such intermittent addition of urea water, atomization of urea water in the exhaust passage 26 is promoted.

  By the way, ammonia desorbed from the SCR catalyst 41 and ammonia that has passed through the SCR catalyst 41 are oxidized by the ammonia oxidation catalyst 51 to be changed into nitrogen and water. This suppresses ammonia release into the atmosphere. However, when the temperature of the exhaust gas rises and the temperature of the ammonia oxidation catalyst 51 increases, in some cases, oxidation of ammonia in the ammonia oxidation catalyst 51 may generate NOx and water instead of nitrogen and water.

  For example, when the regeneration process of the filter 32 described above is performed, the temperature raising process of the exhaust gas is performed, so that the temperature of the ammonia oxidation catalyst 51 becomes very high compared to the case where the regeneration process is not performed. Therefore, ammonia regeneration NOx may be generated in the ammonia oxidation catalyst 51 during the regeneration process of the filter 32.

Here, the amount of ammonia desorbed by the SCR catalyst 41 and the amount of ammonia that passes through the SCR catalyst 41 tend to decrease by decreasing the amount of urea water added.
Therefore, in the present embodiment, the amount of ammonia reaching the ammonia oxidation catalyst 51 is reduced by performing an addition amount reduction process for reducing the addition amount of urea water, thereby generating NOx in the ammonia oxidation catalyst 51 in a high temperature state. I try to suppress it.

FIG. 3 shows the procedure of the addition amount reduction process. This process is executed by the control device 80.
When this process is started, the control device 80 first determines whether or not the regeneration process of the filter 32 is currently being performed (S100).

  When the regeneration process is not being performed (S100: NO), the control device 80 determines whether or not the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110). The second exhaust temperature TH2 is used as a substitute value for the temperature of the ammonia oxidation catalyst 51. However, the temperature of another part may be used as a substitute value. For example, when the temperature of the filter 32 is detected or estimated, the temperature of the filter 32 may be used as a substitute value for the temperature of the ammonia oxidation catalyst 51. Further, the temperature of the ammonia oxidation catalyst 51 may be directly detected by a sensor or the like. The determination temperature α is a value for determining whether or not NOx may be generated on the ammonia oxidation catalyst 51. When the second exhaust temperature TH2 is equal to or higher than the determination temperature α, the determination temperature α is It is determined that there is a possibility that NOx is generated on the ammonia oxidation catalyst 51 because the temperature is in a high temperature state equal to or higher than a predetermined temperature.

When the second exhaust temperature TH2 is less than the determination temperature α (S110: NO), the control device 80 once ends this process.
On the other hand, when the regeneration process of the filter 32 is being performed (S100: YES), or when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than a predetermined temperature. Therefore, it is determined that NOx may be generated in the ammonia oxidation catalyst 51, and the processing after step S120 is performed.

  In step S120, the control device 80 sets the first urea correction amount QEH1 based on the second exhaust temperature TH2 (S120). The first urea correction amount QEH1 is a decrease correction amount for correcting the decrease in the basic urea addition amount QEB, and a value of “0” or more is variably set based on the second exhaust temperature TH2. The basic urea addition amount QEB is a base value of the urea addition amount QE described above, and is set based on the engine operating state, the ammonia adsorption amount NHR, and the like.

As shown in FIG. 4, the first urea correction amount QEH1 is set to a larger value as the second exhaust temperature TH2 is higher.
Next, the control device 80 sets the second urea correction amount QEH2 based on the ammonia adsorption amount NHR (S130). The second urea correction amount QEH2 is also a decrease correction amount for correcting the decrease in the basic urea addition amount QEB, and a value of “0” or more is variably set based on the ammonia adsorption amount NHR.

As shown in FIG. 5, the second urea correction amount QEH2 is set to a larger value as the ammonia adsorption amount NHR is larger.
Next, the controller 80 calculates the urea addition amount QE by correcting the basic urea addition amount QEB based on the first urea correction amount QEH1 and the second urea correction amount QEH2 (S140). In step S140, as shown in the following equation (1), a value obtained by subtracting the first urea correction amount QEH1 and the second urea correction amount QEH2 from the basic urea addition amount QEB is set as the urea addition amount QE.

QE = QEB-QEH1-QEH2 (1)

As can be seen from the equation (1), the urea addition amount QE decreases as the value of the first urea correction amount QEH1 increases. Further, the urea addition amount QE decreases as the value of the second urea correction amount QEH2 increases.

When the urea addition amount QE is calculated in this way, the controller 80 once ends this process.
Next, the effect | action of the said addition amount reduction process is demonstrated.
When the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), unlike the case where the second exhaust temperature TH2 is lower than the determination temperature α (S110: NO), the processing of steps S120 to S140 is performed. The basic urea addition amount QEB is corrected to decrease, and the urea addition amount QE decreases. As described above, when it is determined that the temperature of the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than the predetermined temperature, compared to when it is determined that the temperature of the ammonia oxidation catalyst 51 is lower than the predetermined temperature. As a result, the amount of urea added decreases. The amount of ammonia adsorbed on the SCR catalyst 41 and the amount of ammonia passing through the SCR catalyst 41 are reduced by reducing the amount of ammonia-derived urea water added, which is one of the causes for generating NOx. Therefore, the amount of ammonia that reaches the ammonia oxidation catalyst 51 decreases. Therefore, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the ammonia oxidation catalyst 51 at a high temperature.

  Also, during the regeneration process of the filter 32 (S100: YES), the basic urea addition amount QEB is corrected to decrease and the urea addition amount QE decreases by performing the processing of step S120 to step S140. Accordingly, even when it can be determined that the temperature of the ammonia oxidation catalyst 51 is in a high temperature state higher than a predetermined temperature due to the regeneration process of the filter 32, the ammonia reaching the ammonia oxidation catalyst 51 is reduced by reducing the amount of urea water added. The amount of will decrease. Therefore, the generation of NOx due to the high temperature of the ammonia oxidation catalyst 51 due to the regeneration process of the filter 32 is suppressed.

  In step S140, the basic urea addition amount QEB is corrected to decrease. The first urea correction amount QEH1 for the reduction correction is increased as the second exhaust temperature TH2 is higher. Accordingly, the higher the exhaust temperature, that is, the more the NOx is easily generated due to the promotion of the ammonia oxidation reaction on the ammonia oxidation catalyst 51, the urea addition amount QE is reduced, thereby reaching the ammonia oxidation catalyst 51. The amount of ammonia is reduced. Therefore, even if the exhaust temperature changes, the generation of NOx can be suitably suppressed.

  Further, the second urea correction amount QEH2 for performing the reduction correction of the basic urea addition amount QEB is increased as the ammonia amount adsorbed on the SCR catalyst 41 is increased. Therefore, as the amount of ammonia adsorbed on the SCR catalyst 41 increases, that is, as the amount of ammonia desorbed from the SCR catalyst 41 also increases, the urea addition amount QE is reduced, thereby reaching the ammonia oxidation catalyst 51. The amount of ammonia is reduced. Therefore, even if the amount of ammonia adsorbed on the SCR catalyst 41 changes, the generation of NOx is suitably suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the ammonia oxidation catalyst 51 can be determined to be in a state of a predetermined temperature or higher, the amount of addition reduction that decreases the urea addition amount is compared to when the ammonia oxidation catalyst 51 can be determined to be in a state of less than the predetermined temperature. Processing is performed. Therefore, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the ammonia oxidation catalyst 51 at a high temperature.

  (2) The addition amount reduction process described above is performed even during the regeneration process of the filter 32. Therefore, even when the ammonia oxidation catalyst 51 is heated to a predetermined temperature or higher by the regeneration process of the filter 32, generation of NOx due to the temperature increase of the ammonia oxidation catalyst 51 can be suppressed.

  (3) As the addition amount reduction processing, the urea addition amount reduction correction is performed. Then, as the second exhaust temperature TH2 is higher, the first urea correction amount QEH1, which is a reduction correction amount, is increased. Therefore, even if the exhaust temperature changes, the generation of NOx can be suitably suppressed.

  (4) The second urea correction amount QEH2, which is the reduction correction amount, is increased as the ammonia adsorption amount NHR increases. Therefore, even if the amount of ammonia adsorbed on the SCR catalyst 41 changes, the generation of NOx can be suitably suppressed.

(Second Embodiment)
Next, a second embodiment that embodies an exhaust emission control device for an internal combustion engine will be described with reference to FIGS.

  In the first embodiment, when the ammonia oxidation catalyst 51 is in a high temperature state, the basic urea addition amount QEB is corrected to decrease in order to reduce the addition amount of urea water. On the other hand, in the present embodiment, the total addition amount of the reducing agent within a predetermined period is reduced by correcting and increasing the addition interval INT described above.

  FIG. 6 shows an aspect of adding urea water. 6A shows the addition mode before correcting the addition interval, and FIG. 6B shows the addition mode after correcting the addition interval. As shown in FIG. 6B, when the addition interval INT is corrected and lengthened, the number of times of urea water addition within a predetermined period decreases. For example, in the state shown in FIG. 6A, urea water is added six times within a certain predetermined period. On the other hand, in the state shown in FIG. 6B, urea water is added three times within the same predetermined period. When the number of urea water additions is reduced in this way, the total amount of urea water addition within a predetermined period is reduced. Therefore, also in this embodiment, the amount of ammonia desorbed on the SCR catalyst 41 and the amount of ammonia that passes through the SCR catalyst 41 are reduced, and the amount of ammonia that reaches the ammonia oxidation catalyst 51 is reduced. Therefore, even in this embodiment, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the ammonia oxidation catalyst 51 that has been heated to a high temperature.

In FIG. 7, the procedure of the addition amount reduction | decrease process in this embodiment is shown. In this process, steps that perform the same process as in the first embodiment are given the same step numbers.
When this process is started, the control device 80 first determines whether or not the regeneration process of the filter 32 is currently being performed (S100).

  When the regeneration process is not being performed (S100: NO), the control device 80 determines whether or not the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110). In the present embodiment as well, the second exhaust temperature TH2 is used as a substitute value for the temperature of the ammonia oxidation catalyst 51, but the temperature of another part may be used as a substitute value. For example, when the temperature of the filter 32 is detected or estimated, the temperature of the filter 32 may be used as a substitute value for the temperature of the ammonia oxidation catalyst 51. Further, the temperature of the ammonia oxidation catalyst 51 may be directly detected by a sensor or the like. The determination temperature α is a value for determining whether or not NOx may be generated on the ammonia oxidation catalyst 51. When the second exhaust temperature TH2 is equal to or higher than the determination temperature α, the determination temperature α is It is determined that there is a possibility that NOx is generated on the ammonia oxidation catalyst 51 because the temperature is in a high temperature state equal to or higher than a predetermined temperature.

When the second exhaust temperature TH2 is less than the determination temperature α (S110: NO), the control device 80 once ends this process.
On the other hand, when the regeneration process of the filter 32 is being performed (S100: YES), or when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than a predetermined temperature. Therefore, it is determined that there is a possibility that NOx is generated in the ammonia oxidation catalyst 51, and the processing after step S200 is performed.

  In step S120, the control device 80 sets the first interval correction amount INTH1 based on the second exhaust temperature TH2 (S200). The first interval correction amount INTH1 is a correction amount for correcting the basic addition interval INTB, and a value of “0” or more is variably set based on the second exhaust temperature TH2. The basic addition interval INTB is a base value of the above-described addition interval INT, and an appropriate value is set based on the engine operating state and the like.

As shown in FIG. 8, the first interval correction amount INTH1 is set longer as the second exhaust temperature TH2 is higher.
Next, the control device 80 sets the second interval correction amount INTH2 based on the ammonia adsorption amount NHR (S210). The second interval correction amount INTH2 is also a correction amount for correcting the basic addition interval INTB, and a value of “0” or more is variably set based on the ammonia adsorption amount NHR.

As shown in FIG. 9, the second interval correction amount INTH2 is set longer as the ammonia adsorption amount NHR is larger.
Next, the control device 80 calculates the addition interval INT by correcting the basic addition interval INTB based on the first interval correction amount INTH1 and the second interval correction amount INTH2 (S220). In step S220, as shown in the following equation (2), a value obtained by adding the first interval correction amount INTH1 and the second interval correction amount INTH2 to the basic addition interval INTB is set as the addition interval INT.

INT = INTB + INTH1 + INTH2 (2)

As can be seen from this equation (2), the addition interval INT becomes longer as the value of the first interval correction amount INTH1 is longer. Further, the addition interval INT becomes longer as the value of the second interval correction amount INTH2 is longer.

When the addition interval INT is calculated in this way, the control device 80 once ends this process.
Next, the effect | action of the said addition amount reduction process is demonstrated.

  When the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), unlike the case where the second exhaust temperature TH2 is lower than the determination temperature α (S110: NO), the processing of step S200 to step S220 is performed. The basic addition interval INTB is corrected to increase the addition interval INT. As described above, as the addition interval INT becomes longer, the total amount of urea water added within a predetermined period decreases.

  As described above, when it is determined that the temperature of the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than the predetermined temperature, compared to when it is determined that the temperature of the ammonia oxidation catalyst 51 is lower than the predetermined temperature. Thus, the total amount of urea water added within a predetermined period decreases. Thus, the amount of ammonia adsorbed on the SCR catalyst 41 and the amount of ammonia passing through the SCR catalyst 41 are reduced by reducing the amount of ammonia-derived urea water added, which is one of the causes for generating NOx. Therefore, the amount of ammonia that reaches the ammonia oxidation catalyst 51 decreases. Therefore, it is possible to suppress the generation of NOx due to the oxidation of ammonia on the ammonia oxidation catalyst 51 at a high temperature.

  Further, during the regeneration process of the filter 32 (S100: YES), the basic addition interval INTB is corrected and the addition interval INT is lengthened by performing the processing of Step S200 to Step S220. Accordingly, even when it can be determined that the temperature of the ammonia oxidation catalyst 51 is in a high temperature state higher than a predetermined temperature due to the regeneration process of the filter 32, the ammonia reaching the ammonia oxidation catalyst 51 is reduced by reducing the amount of urea water added. The amount of will decrease. Therefore, the generation of NOx due to the high temperature of the ammonia oxidation catalyst 51 due to the regeneration process of the filter 32 is suppressed.

  In step S220, the basic addition interval INTB is corrected. The first interval correction amount INTH1 for the correction is made longer as the second exhaust temperature TH2 is higher. Therefore, the higher the exhaust temperature, that is, the more the NOx is easily generated due to the promotion of the ammonia oxidation reaction on the ammonia oxidation catalyst 51, the longer the addition interval INT during intermittent addition, the longer the predetermined period. The number of additions of urea water in is reduced. When the number of times of urea water addition is reduced in this way, the total amount of urea water added within a predetermined period is reduced, so that the amount of ammonia reaching the ammonia oxidation catalyst 51 is reduced. Therefore, even if the exhaust temperature changes, the generation of NOx is preferably suppressed.

  Further, the second interval correction amount INTH2 for correcting the basic addition interval INTB is made longer as the ammonia amount adsorbed on the SCR catalyst 41 is larger. Therefore, as the amount of ammonia adsorbed on the SCR catalyst 41 increases, that is, as the amount of ammonia desorbed from the SCR catalyst 41 also increases, the addition interval INT during intermittent addition is lengthened, so that The number of additions of urea water in is reduced. When the number of times of urea water addition is reduced in this way, the total amount of urea water added within a predetermined period is reduced, so that the amount of ammonia reaching the ammonia oxidation catalyst 51 is reduced. Therefore, even if the amount of ammonia adsorbed on the SCR catalyst 41 changes, the generation of NOx is suitably suppressed.

As described above, according to the present embodiment, in addition to the effects (1) and (2), the following effects can be further obtained.
(5) The addition interval INT is corrected as the addition amount reduction process. Then, as the second exhaust temperature TH2 is higher, the first interval correction amount INTH1 is lengthened to increase the addition interval INT. Therefore, even if the exhaust temperature changes, the generation of NOx can be suitably suppressed.

  (6) As the ammonia adsorption amount NHR increases, the addition interval INT is lengthened by increasing the second interval correction amount INTH2. Therefore, even if the amount of ammonia adsorbed on the SCR catalyst 41 changes, the generation of NOx can be suitably suppressed.

In addition, each said embodiment can also be changed and implemented as follows.
In the first embodiment, the setting of the first urea correction amount QEH1 may be omitted, or the setting of the second urea correction amount QEH2 may be omitted.

  In the first embodiment, when the filter 32 is being regenerated (S100: YES), or when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), the processing after step S120 is performed. I made it. In addition, the determination process in step S100 may be omitted, and the process after step S120 may be performed when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES). Further, the determination process in step S110 may be omitted, and when the regeneration process of the filter 32 is not in progress (S100: NO), the addition amount reduction process may be temporarily ended.

In the second embodiment, the setting of the first interval correction amount INTH1 may be omitted, or the setting of the second interval correction amount INTH2 may be omitted.
In the second embodiment, when the regeneration process of the filter 32 is being performed (S100: YES), or when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), the processes after step S200 are performed. I made it. In addition, the determination process in step S100 may be omitted, and the process after step S200 may be performed when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES). Further, the determination process in step S110 may be omitted, and when the regeneration process of the filter 32 is not in progress (S100: NO), the addition amount reduction process may be temporarily ended.

  In the first embodiment, the urea water is intermittently added. However, the urea water may be continuously added instead of intermittently by maintaining the urea addition valve 230 in an open state. .

  In the first embodiment, addition amount reduction correction is performed as addition amount reduction processing. In addition, addition of urea water may be prohibited while the temperature of the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than the predetermined temperature described above.

  FIG. 10 shows an example of the procedure of the additive amount reduction process in this modification. In this process shown in FIG. 10, the same step numbers are assigned to steps for performing the same process as in the first embodiment.

When this process is started, the control device 80 first determines whether or not the regeneration process of the filter 32 is currently being performed (S100).
When the regeneration process is not being performed (S100: NO), the control device 80 determines whether or not the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110). Also in this modified example, the second exhaust temperature TH2 is used as a substitute value for the temperature of the ammonia oxidation catalyst 51, but the temperature of another part may be used as a substitute value. For example, when the temperature of the filter 32 is detected or estimated, the temperature of the filter 32 may be used as a substitute value for the temperature of the ammonia oxidation catalyst 51. Further, the temperature of the ammonia oxidation catalyst 51 may be directly detected by a sensor or the like. The determination temperature α is a value for determining whether or not NOx may be generated on the ammonia oxidation catalyst 51. When the second exhaust temperature TH2 is equal to or higher than the determination temperature α, the determination temperature α is It is determined that there is a possibility that NOx is generated on the ammonia oxidation catalyst 51 because the temperature is in a high temperature state equal to or higher than a predetermined temperature.

When the second exhaust temperature TH2 is lower than the determination temperature α (S110: NO), the control device 80 permits urea addition (S310) and once ends this process.
On the other hand, when the regeneration process of the filter 32 is being performed (S100: YES), or when the second exhaust temperature TH2 is equal to or higher than the determination temperature α (S110: YES), the ammonia oxidation catalyst 51 is in a high temperature state equal to or higher than a predetermined temperature. Therefore, it is determined that NOx may be generated in the ammonia oxidation catalyst 51. And the control apparatus 80 prohibits urea addition (S300), and once complete | finishes this process.

  In this modification, addition of urea water is prohibited while the temperature of the ammonia oxidation catalyst 51 is in a high temperature state that is equal to or higher than a predetermined temperature and there is a possibility that NOx is generated on the ammonia oxidation catalyst 51. By prohibiting the addition of urea, the amount of ammonia reaching the ammonia oxidation catalyst 51 is sufficiently reduced. Accordingly, it is possible to more appropriately suppress the generation of NOx resulting from the oxidation of ammonia on the ammonia oxidation catalyst 51 at a high temperature.

  In the first embodiment, addition amount reduction correction is performed as addition amount reduction processing. In addition, as the addition amount reduction process, a prohibition period for prohibiting the addition of urea water during the urea water addition period may be provided.

  FIG. 11 shows how urea water is added in this modification. As shown in FIG. 11, there is a request for adding urea water, and when the urea water is being added based on this request, when the filter 32 is being regenerated, or when the second exhaust temperature TH2 is the determination temperature. When it is α or more, a prohibition period PP for prohibiting the addition of urea water is set. And even during the period of adding urea water based on the addition request of urea water, addition of urea water is prohibited during this prohibition period PP. A plurality of such prohibition periods PP may be set. Further, the prohibition period PP may be lengthened as the exhaust gas temperature is higher, or the prohibition period PP may be lengthened as the ammonia adsorption amount NHR is larger.

  According to such a modified example, compared with the case where the prohibition period PP is not provided, the total amount of urea water added during the addition period is decreased, and the amount of ammonia reaching the ammonia oxidation catalyst 51 is decreased. become. Therefore, even in this modification, the generation of NOx due to the oxidation of ammonia on the ammonia oxidation catalyst 51 at a high temperature can be suppressed.

  Although urea water is used as the reducing agent, other ammonia-derived reducing agents may be used.

  DESCRIPTION OF SYMBOLS 1 ... 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 Degree sensor, 21 ... Engine rotation speed sensor, 22 ... Accelerator sensor, 23 ... Outside air temperature sensor, 24 ... Vehicle speed sensor, 25 ... Ignition switch, 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 ... first Purifying member 51 ... Ammonia oxidation catalyst 60 ... Dispersion plate 80 ... Control device 100 ... First exhaust temperature sensor 110 ... Differential pressure sensor 120 ... Second exhaust temperature sensor 130 ... First NOx sensor 140 ... First 2NOx sensor, 200 ... urea water supply mechanism, 210 ... tank, 220 ... pump, 230 ... urea addition valve, 240 ... supply passage.

Claims (8)

A reducing agent supply mechanism for adding a reducing agent derived from ammonia into the exhaust passage;
A reduction catalyst for purifying exhaust gas by adding the reducing agent;
An oxidation catalyst provided downstream of the reduction catalyst in the exhaust passage;
A control unit that controls the amount of the reducing agent added by the reducing agent supply mechanism;
The control unit performs an addition amount reduction process for reducing the addition amount of the reducing agent when the oxidation catalyst is in a state of a predetermined temperature or higher compared to when the oxidation catalyst is in a state of less than the predetermined temperature. An exhaust gas purification apparatus for an internal combustion engine characterized by the above. In the exhaust passage, on the upstream side of the reduction catalyst, a filter for collecting particulate matter in the exhaust is provided,
The exhaust emission control device for an internal combustion engine according to claim 1, wherein the control unit performs the addition amount reduction process during the execution of a regeneration process for regenerating the filter by raising the temperature of exhaust gas. The exhaust gas purification for an internal combustion engine according to claim 1, wherein the control unit performs a reduction correction of the addition amount as the addition amount reduction process, and increases the reduction correction amount of the addition amount as the exhaust temperature is higher. apparatus. The said control part performs the reduction | decrease correction of the said addition amount as the said addition amount reduction | decrease process, and increases the reduction correction amount of the said addition amount, so that there is much ammonia amount adsorb | sucked to the said reduction catalyst. An exhaust emission control device for an internal combustion engine according to any one of the preceding claims. The reducing agent supply mechanism intermittently adds the reducing agent by repeating the addition and suspension of addition of the reducing agent at a predetermined addition cycle,
3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control unit increases the addition period as the exhaust gas temperature increases as the addition amount reduction process. The reducing agent supply mechanism intermittently adds the reducing agent by repeating the addition and suspension of addition of the reducing agent at a predetermined addition cycle,
The exhaust of the internal combustion engine according to any one of claims 1, 2, and 5, wherein the control unit increases the addition period as the amount of ammonia adsorbed on the reduction catalyst increases as the addition amount reduction process. Purification equipment. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control unit prohibits the addition of the reducing agent as the addition amount reduction process while the oxidation catalyst is in the state of the predetermined temperature or higher. . The exhaust emission control device for an internal combustion engine according to claim 1 or 2, wherein the control unit provides a prohibition period for prohibiting the addition of the reducing agent during the addition period of the reducing agent as the addition amount reduction process.