JP2015028312A - 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 a carbon deposit from being generated at a dispersion plate.SOLUTION: An engine 1 includes: an SCR catalyst 41 for cleaning an exhaust gas by adding urea water; an urea water supply mechanism 200 for adding the urea water into an exhaust passage 26; the dispersion plate 60 for dispersing the urea water on an exhaust-upstream side relative to the SCR catalyst 41; and a control device 80 for controlling the urea water supply mechanism 200 to add the urea water. The control device 80 prohibits addition of the urea water when the temperature of the dispersion plate 60 is lower than a 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 selective reduction type NOx catalyst which is one of catalysts for purifying nitrogen oxide (NOx) in exhaust gas, and this selective reduction type NOx catalyst is used for NOx purification. 2. Description of the Related Art An exhaust gas purification apparatus for an internal combustion engine is known that includes a reducing agent supply mechanism that adds a reducing agent into an exhaust passage and a dispersion plate that is provided in the exhaust passage and disperses the reducing agent.

  In this exhaust purification device, urea water is injected into the exhaust passage from the reducing agent supply mechanism. The injected urea water is atomized by the dispersion plate and becomes ammonia by hydrolysis by exhaust heat. This ammonia is supplied to the catalyst as a reducing agent.

  In the exhaust emission control device described in Patent Document 1, the reducing agent attached to the dispersion plate is collected near the center of the exhaust passage in order to promote the vaporization of the reducing agent attached to the dispersion plate. The reducing agent collected in the vicinity of the center of the exhaust passage in this way is vaporized by the exhaust near the center whose temperature is higher than the vicinity of the wall surface of the exhaust passage.

JP 2009-138592 A

  Incidentally, the addition of the reducing agent into the exhaust passage is performed when the temperature of the catalyst is equal to or higher than the activation temperature. Here, for example, when the outside air temperature is low, the amount of heat released from the exhaust passage increases, so the temperature of the dispersion plate provided in the exhaust passage tends to be low. Therefore, even if the temperature of the catalyst is equal to or higher than the activation temperature, the temperature of the dispersion plate may be in a relatively low state. In this case, the reducing agent added in the exhaust passage is applied to the dispersion plate. There is a risk that it will remain attached and subsequently deposited.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress the formation of deposits on a dispersion plate.

  An exhaust gas purification apparatus for an internal combustion engine that solves the above problems includes a catalyst that purifies exhaust gas by adding a reducing agent, a reducing agent supply mechanism that adds the reducing agent into the exhaust passage, and a catalyst provided in the exhaust passage that is more A dispersion plate that disperses the reducing agent upstream and a control unit that controls addition of the reducing agent by the reducing agent supply mechanism are provided. The control unit prohibits the addition of the reducing agent when the temperature of the dispersion plate is lower than the predetermined temperature.

  According to this configuration, the addition of the reducing agent is prohibited when the temperature of the dispersion plate is lower than the predetermined temperature and the reducing agent tends to remain attached to the dispersion plate. Therefore, the adhesion of the reducing agent on the dispersion plate can be suppressed, and the generation of deposits due to the adhesion of the reducing agent can be suppressed. The predetermined temperature having the same configuration is desirably set to a temperature at which the adhesion of the reducing agent on the dispersion plate can be suppressed, for example, the boiling point of the reducing agent.

  In the exhaust purification apparatus, the control unit cancels the reduction agent addition prohibition for a predetermined period only when there is a request for addition of the reducing agent even when the temperature of the dispersion plate is lower than the predetermined temperature. Add agent. And it is preferable that a control part makes the predetermined period shorter than the addition period when the temperature of a dispersion plate is more than predetermined temperature.

  According to this configuration, even when the temperature of the dispersion plate is lower than the predetermined temperature, if there is a request for addition of the reducing agent, the reducing agent is only added for a predetermined period in order to prioritize the request. Added. Here, in the same configuration, the predetermined period that is an addition period when the reducing agent is added when the temperature of the dispersion plate is lower than the predetermined temperature is the addition when the temperature of the dispersion plate is equal to or higher than the predetermined temperature. Shortened compared to the period. By reducing the addition period of the reducing agent in this way, the amount of reducing agent adhering to the dispersion plate is reduced. Therefore, when there is a request to add a reducing agent when the temperature of the dispersion plate is low, the reducing agent can be added while suppressing the attachment of the reducing agent to the dispersion plate. Therefore, for example, even if the dispersion plate is in a low temperature state, exhaust purification by adding a reducing agent can be maintained.

In the exhaust emission control device, the control unit preferably shortens the predetermined period as the temperature of the dispersion plate is lower.
According to this configuration, as the temperature of the dispersion plate is lower and the reducing agent is more likely to adhere, the addition period of the reducing agent is shortened, so that the amount of the reducing agent attached to the dispersion plate is reduced. Therefore, the amount of the reducing agent adhering to the dispersion plate can be appropriately suppressed according to the temperature of the dispersion plate.

  In the exhaust purification apparatus, the exhaust purification apparatus is an apparatus mounted on a vehicle, and the control unit variably sets the predetermined period based on at least one of an exhaust temperature, an outside air temperature, an exhaust flow rate, and a vehicle speed. It is preferable.

  According to this configuration, the addition period of the reducing agent at a low temperature of the dispersion plate is variably set based on at least one of the exhaust temperature, the outside air temperature, the exhaust flow rate, and the vehicle speed related to the temperature of the dispersion plate. Therefore, the reducing agent addition period can be shortened as the temperature of the dispersion plate is lower without directly detecting the temperature of the dispersion plate.

  Further, in the exhaust purification apparatus, the control unit stops prohibiting the addition of the reducing agent only for a predetermined period when there is a request for the addition of the reducing agent even when the temperature of the dispersion plate is lower than the predetermined temperature. Add the reducing agent. And it is preferable that a control part reduces the addition amount when performing the reducing agent addition from the return addition amount when the temperature of a dispersion plate is more than predetermined temperature.

  According to this configuration, even when the temperature of the dispersion plate is lower than the predetermined temperature, if there is a request for addition of the reducing agent, the reducing agent is only added for a predetermined period in order to prioritize the request. Added. Here, in the same configuration, the amount of addition when the reducing agent is added when the temperature of the dispersion plate is lower than the predetermined temperature is reduced compared to when the temperature of the dispersion plate is equal to or higher than the predetermined temperature. By reducing the amount of the reducing agent added in this way, the amount of the reducing agent adhering to the dispersion plate is reduced. Therefore, when there is a request to add a reducing agent when the temperature of the dispersion plate is low, the reducing agent can be added while suppressing the attachment of the reducing agent to the dispersion plate. Therefore, for example, even if the dispersion plate is in a low temperature state, exhaust purification by adding a reducing agent can be maintained.

In the exhaust emission control device, it is preferable that the control unit decreases the addition amount as the temperature of the dispersion plate is lower.
According to this configuration, as the temperature of the dispersion plate is lower and the reducing agent is more likely to adhere, the amount of reducing agent added is reduced, so that the amount of reducing agent attached to the dispersion plate is reduced. Therefore, the amount of the reducing agent adhering to the dispersion plate can be appropriately suppressed according to the temperature of the dispersion plate.

  In the exhaust purification apparatus, the exhaust purification apparatus is an apparatus mounted on a vehicle, and the control unit may variably set the addition amount based on at least one of an exhaust temperature, an outside air temperature, an exhaust flow rate, and a vehicle speed. preferable.

  According to this configuration, the addition amount of the reducing agent is variably set based on at least one of the exhaust temperature, the outside air temperature, the exhaust flow rate, and the vehicle speed that are related to the temperature of the dispersion plate. Therefore, the amount of the reducing agent added can be reduced as the temperature of the dispersion plate is lower without directly detecting the temperature of the dispersion plate.

  Further, in the exhaust purification apparatus, the exhaust purification apparatus is an apparatus mounted on a vehicle, and the control unit determines whether the temperature of the dispersion plate is lower than a predetermined temperature, whether or not the exhaust temperature and the outside air temperature. It is preferable to make a determination based on at least one of the exhaust flow rate and the vehicle speed.

  According to this configuration, it is determined whether or not the temperature of the dispersion plate is lower than the predetermined temperature based on parameters related to the temperature of the dispersion plate such as the exhaust temperature, the outside air temperature, the exhaust flow rate, and the vehicle speed. Therefore, it is possible to determine whether or not the temperature of the dispersion plate is lower than the predetermined temperature without directly detecting the temperature of the dispersion plate.

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 flowchart which shows a series of processing procedures when adding urea water in the same embodiment. The table | surface which shows the relationship between the vehicle speed and vehicle speed coefficient in the same embodiment. The table | surface which shows the relationship between the outside temperature in the same embodiment, and an outside temperature coefficient. The table | surface which shows the relationship between the exhaust flow volume in this embodiment, and an exhaust flow coefficient. The flowchart which shows a series of processing procedures when adding urea water in 2nd Embodiment. The flowchart which shows the procedure of the addition process in the embodiment. The table | surface which shows the relationship between the dispersion plate temperature and the time coefficient in the same embodiment. The flowchart which shows the procedure of the addition process in 3rd Embodiment. The table | surface which shows the relationship between the dispersion plate temperature in the same embodiment, and an addition amount coefficient.

(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 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 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 the PM in the exhaust gas is collected when passing through the porous wall of the filter 32.

  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 combusted 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. The carrier of the SCR catalyst 41 is made of zeolite, and a catalyst coating layer is formed on the carrier.

  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 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 urea addition valve 230 constitutes the reducing agent injection valve.

  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 occluded 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 an IG switch) 25 that is operated when the driver of the vehicle starts or stops the engine 1, and depending on 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 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, fuel injection control of the fuel injection valves 4a to 4d and the fuel addition valve 5, discharge pressure control of the supply pump 10, drive amount control of the actuator 17 for opening and closing the intake throttle valve 16, EGR valve 15 Various controls of the engine 1 such as the opening degree 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.

Further, 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 urea amount necessary for maintaining the ammonia adsorption amount of the SCR catalyst 41 at a predetermined amount is calculated. The ammonia adsorption amount is estimated by an appropriate method. For example, the ammonia adsorption amount is estimated based on parameters that correlate with the ammonia adsorption amount, such as urea addition amount, exhaust temperature, exhaust flow rate, and the like.

  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 addition amount QE is injected from the urea addition valve 230. Thus, the driving state of the urea addition valve 230 is controlled. In the present embodiment, when the urea water is injected into the exhaust passage 26, the urea addition valve 230 is periodically opened and closed repeatedly. Thereby, urea water is intermittently injected and supplied, and atomization in the exhaust passage 26 is promoted. Incidentally, by maintaining the urea addition valve 230 in an open state, the urea water may be continuously supplied instead of intermittently.

  Such urea water injection is performed when the temperature of the SCR catalyst 41 is equal to or higher than the activation temperature. Here, for example, when the outside air temperature is low, the amount of heat released from the exhaust passage 26 increases, so the temperature of the dispersion plate 60 provided in the exhaust passage 26 tends to be low. Therefore, even if the temperature of the SCR catalyst 41 is equal to or higher than the activation temperature, the temperature of the dispersion plate 60 may be relatively low. In this case, urea water added to the exhaust passage 26 May remain attached to the dispersion plate 60 and then deposit on the surface of the dispersion plate 60.

  In addition, when the temperature of the dispersion plate 60 is relatively low, a part of the urea water added in the exhaust passage 26 may reach the SCR catalyst 41 in a liquid state without being diffused by the dispersion plate 60. . Here, when moisture adheres to the zeolite-based SCR catalyst 41, the zeolite constituting the carrier becomes brittle and the coating layer is easily peeled off.

  Therefore, in the present embodiment, the processing shown in FIG. 2 is performed by the control device 80 to suppress the generation of deposit on the dispersion plate 60 and the peeling of the coating layer on the SCR catalyst 41.

  As shown in FIG. 2, when this process is started, the control device 80 determines whether or not there is a request for adding urea water (S100). Such a urea water addition request is made when the ammonia adsorption amount of the SCR catalyst 41 is insufficient, or when the NOx emission amount increases rapidly.

And when there is no addition request | requirement of urea water (S100: NO), the control apparatus 80 complete | finishes this process.
On the other hand, when there is a request for addition of urea water (S100: YES), the controller 80 determines the second exhaust temperature TH2, which indicates the exhaust temperature in the vicinity of the dispersion plate 60, the vehicle speed SPD, the outside air temperature THout, and the exhaust gas flow rate GEX. Based on the above, a dispersion plate temperature TB which is an estimated temperature of the dispersion plate 60 is calculated (S110). More specifically, a value obtained by correcting the second exhaust temperature TH2 with the vehicle speed SPD, the outside air temperature THout and the exhaust flow rate GEX is used as the estimated temperature of the dispersion plate 60. The dispersion plate temperature TB is based on the following equation (1). Calculated.

TB = TH2 × K1 × K2 × K3 (1)
TB: Dispersion plate temperature TH2: Second exhaust temperature K1: Vehicle speed coefficient (0 <K1 ≦ 1)
K2: outside air temperature coefficient (0 <K2 ≦ 1)
K3: Exhaust flow coefficient (0 <K3 ≦ 1)

FIG. 3 shows how the vehicle speed coefficient K1 is set. The vehicle speed coefficient K1 is variably set within a range greater than “0” and equal to or less than “1”. The value of the vehicle speed coefficient K1 is increased as the vehicle speed SPD is lower. This is because the lower the vehicle speed SPD, the lower the cooling effect of the exhaust passage 26 by the traveling wind and the higher the temperature of the dispersion plate 60.

  FIG. 4 shows how the outside air temperature coefficient K2 is set. The outside air temperature coefficient K2 is also variably set within a range larger than “0” and not larger than “1”. And the value of outside temperature coefficient K2 is made small, so that outside temperature THout is low. This is because the lower the outside air temperature THout, the lower the temperature of the exhaust passage 26 and the lower the temperature of the dispersion plate 60.

  FIG. 5 shows how the exhaust flow coefficient K3 is set. The exhaust flow coefficient K3 is also variably set within a range greater than “0” and less than “1”. And the value of the exhaust flow coefficient K3 is made smaller as the exhaust flow rate GEX is smaller. This is because the amount of heat transferred from the exhaust to the dispersion plate 60 decreases as the exhaust flow rate GEX decreases, and the temperature of the dispersion plate 60 decreases. The exhaust flow rate GEX can be estimated based on the intake air amount GA and the like. Therefore, the exhaust flow coefficient K3 may be set based on the intake air amount GA or the like. Further, the exhaust gas flow rate GEX can be estimated based on the engine speed NE and the fuel injection amount Q from each of the fuel injection valves 4a to 4d. Therefore, the exhaust flow coefficient K3 may be set based on the engine speed NE and the fuel injection amount Q.

  When the dispersion plate temperature TB is calculated in this way, the control device 80 determines whether or not the dispersion plate temperature TB is equal to or higher than a determination value A that is a predetermined temperature (S120). The determination value A is set to a temperature at which adhesion of urea water on the dispersion plate 60 can be suppressed, for example, the boiling point of urea water is set as an example, but a temperature near the boiling point may be set.

  When the dispersion plate temperature TB is equal to or higher than the determination value A (S120: YES), the control device 80 permits urea addition (S130) and injects urea water. And the control apparatus 80 complete | finishes this process.

  On the other hand, when the dispersion plate temperature TB is lower than the determination value A (S120: NO), the control device 80 prohibits urea addition even if there is a request for addition of urea water (S140). And the control apparatus 80 complete | finishes this process.

Next, the operation of this embodiment will be described.
When the estimated dispersion plate temperature TB is lower than the determination value A (S120: NO), and it can be determined that the actual temperature of the dispersion plate 60 is lower than the determination value A, the dispersion plate 60 Since urea water is likely to remain attached to the water, addition of urea is prohibited (S140). Therefore, adhesion of urea water on the dispersion plate 60 can be suppressed, and generation of deposits due to such adhesion of urea water can be suppressed.

  Further, when the dispersion plate temperature TB is lower than the determination value A (S120: NO), and there is a possibility that a part of the urea water added into the exhaust passage 26 may reach the SCR catalyst 41 in a liquid state, urea addition Is prohibited (S140). Therefore, peeling of the coating layer due to moisture adhering to the zeolite-based SCR catalyst 41 is also suppressed.

  Further, based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust flow rate GEX, and the vehicle speed SPD, which are related to the temperature of the dispersion plate 60, the dispersion plate temperature TB that is the estimated temperature of the dispersion plate 60 is calculated (S110). Then, it is determined whether or not the dispersion plate temperature TB is lower than the determination value A (S120). In this way, whether or not the temperature of the dispersion plate 60 is lower than the determination value A is determined using values estimated based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Like to do. Therefore, it is possible to determine whether or not the temperature of the dispersion plate 60 is lower than the predetermined temperature without directly detecting the temperature of the dispersion plate 60.

As described above, according to the present embodiment, the following effects can be obtained.
(1) When the temperature of the dispersion plate 60 is lower than the judgment value A, addition of urea water into the exhaust passage 26 is prohibited. Therefore, in the dispersion plate 60, the generation of deposit due to the adhesion of urea water can be suppressed. Also, peeling of the coating layer due to moisture adhering to the zeolite-based SCR catalyst 41 can be suppressed.

(2) Whether the temperature of the dispersion plate 60 is lower than the determination value A is determined using values estimated based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. doing. Therefore, it is possible to determine whether or not the temperature of the dispersion plate 60 is lower than the predetermined temperature without directly detecting the temperature of the dispersion plate 60.
(Second Embodiment)
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described with reference to FIGS.

  In the first embodiment, even when there is a request for adding urea water, when the temperature of the dispersion plate 60 is lower than the determination value A, addition of urea water is prohibited. However, if the addition of urea water is completely prohibited in spite of a request for addition of urea water, the purification rate of NOx will decrease.

  Therefore, in this embodiment, even when the temperature of the dispersion plate 60 is lower than the determination value A, when there is a request for addition of urea water, the prohibition of addition of urea water is stopped for a predetermined period of time, and urea water is stopped. Is added. The predetermined period is shorter than the addition period when the temperature of the dispersion plate 60 is equal to or higher than the determination value A.

  This embodiment is implemented by changing a part of the series of processes shown in FIG. More specifically, as shown in FIG. 6, when a negative determination is made in step S120 shown in FIG. 2, the process of step S200 is newly executed. And after performing the process of step S200, the process of step S140 is performed and the urea addition is prohibited, and these points differ from 1st Embodiment. Therefore, in the following, the present embodiment will be described focusing on the differences from the first embodiment.

FIG. 6 shows a series of processing procedures performed by the control device 80.
Also in this embodiment, when there is a request for adding urea water (S100: YES), the control device 80 is based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD that are related to the temperature of the dispersion plate 60. The dispersion plate temperature TB is calculated (S110).

  When the dispersion plate temperature TB is lower than the determination value A (S120: NO), the control device 80 executes a process different from the first embodiment, that is, an addition process for adding urea water only for a predetermined period ( S200).

In FIG. 7, the detailed process sequence of the addition process performed by step S200 is shown.
When this addition process is started, the control device 80 sets the low temperature addition time TL based on the dispersion plate temperature TB (S300). The low temperature addition time TL is a value corresponding to the predetermined period in which the prohibition of urea water addition is stopped and urea water is added, and is calculated based on the following equation (2).

Low time addition time TL = addition time T × time coefficient K4 (2)

The addition time T is a urea addition time when the temperature of the dispersion plate 60 is equal to or higher than the determination value A, and is a basic addition time when normal urea addition is performed.

The time coefficient K4 is a coefficient for correcting the addition time T according to the dispersion plate temperature TB.
FIG. 8 shows how the time coefficient K4 is set. The time coefficient K4 is variably set within a range greater than “0” and equal to or less than “1”. And the value of the time coefficient K4 is made smaller as the dispersion plate temperature TB is lower. This is to reduce the amount of urea water adhering to the dispersion plate 60 by shortening the urea water addition time as the dispersion plate temperature TB is lower.

  The low temperature addition time TL may be obtained directly from a one-dimensional map of the dispersion plate temperature TB, in addition to the calculation by the above formula (2). For example, the low temperature addition time TL is directly set based on the dispersion plate temperature TB such that the lower the dispersion plate temperature TB is, the shorter the low temperature addition time TL is. The maximum value of the low temperature addition time TL that is variably set is set to be equal to or less than the addition time T. Even in this way, a time similar to the low temperature addition time TL obtained from the above equation (2) can be set.

  When the low temperature addition time TL is set in this manner, the control device 80 executes urea addition (S310). Incidentally, the addition amount of urea water set at the time of urea addition is the urea addition amount QE described above.

  Next, the control device 80 determines whether or not the low temperature addition time TL has elapsed since the start of urea addition in step S310 (S320). Then, when the low temperature addition time TL has not elapsed (S320: NO), the urea addition is continued by repeating the processing of step S310 and step S320 until the low temperature addition time TL has elapsed.

  On the other hand, when the low temperature addition time TL has elapsed since the start of urea addition in step S310 (S320: YES), the control device 80 ends this process and performs the process of step S140 shown in FIG. I do. When the process of step S140 is performed, urea addition is prohibited. Therefore, the urea addition started in step S310 in FIG. 7 is executed until the low temperature addition time TL has elapsed, and is terminated by prohibiting urea addition in step S140 in FIG.

Next, a specific action obtained by this embodiment will be described.
When there is a request for addition of urea water (S100 in FIG. 6: YES), the addition request has priority even if the temperature of the dispersion plate 60 is lower than the determination value A (S120: NO in FIG. 6). In order to do this, the addition of urea is stopped after the prohibition of addition of urea water is stopped for a predetermined period. More specifically, even when the temperature of the dispersion plate 60 is lower than the determination value A, urea water is added until the low temperature addition time TL has elapsed (S200 in FIG. 6 and S300 in FIG. 7). ~ S320).

  Here, the low temperature addition time TL when the urea water is added when the temperature of the dispersion plate 60 is lower than the determination value A is calculated based on the above formula (2), so that the low temperature addition time TL is The addition time T is shortened when the temperature of the dispersion plate 60 is equal to or higher than the determination value A. By reducing the urea water addition time in this manner, the amount of urea water adhering to the dispersion plate 60 is reduced. Therefore, when there is a request for addition of urea water while the temperature of the dispersion plate 60 is low, it is possible to add urea water while suppressing adhesion of urea water to the dispersion plate 60. Therefore, for example, even when the dispersion plate 60 is in a low temperature state, the ammonia adsorption amount of the SCR catalyst 41 can be increased, and NOx purification by adding urea water can be maintained.

  Also, as shown in FIG. 8, the time coefficient K4 is decreased as the dispersion plate temperature TB is lower, so that the lower temperature addition time TL is shortened as the temperature of the dispersion plate 60 is lower. Accordingly, the lower the temperature of the dispersion plate 60 and the easier the urea water adheres, the shorter the low temperature addition time TL, and the less the amount of urea water attached to the dispersion plate 60. Therefore, the amount of urea water adhering to the dispersion plate 60 can be appropriately suppressed according to the temperature of the dispersion plate 60.

  The time coefficient K4 is variably set based on the dispersion plate temperature TB. Here, the dispersion plate temperature TB is estimated based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Therefore, if at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD changes, the dispersion plate temperature TB also changes, and the time coefficient K4 also changes. Therefore, in this embodiment, the low temperature addition time TL is variably set based on at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD, which are related to the temperature of the dispersion plate 60. Therefore, the low temperature addition time TL can be shortened as the temperature of the dispersion plate 60 is lower without directly detecting the temperature of the dispersion plate 60.

As described above, according to the present embodiment, in addition to the effects (1) and (2), the following effects can be further obtained.
(3) Even when the temperature of the dispersion plate 60 is lower than the judgment value A, when there is a request for addition of urea water, the addition of urea water is stopped only during the low temperature addition time TL. Like to do. The low temperature addition time TL is shorter than the addition time T when the temperature of the dispersion plate 60 is equal to or higher than the determination value A. Therefore, when there is a request for addition of urea water while the temperature of the dispersion plate 60 is low, it is possible to add urea water while suppressing adhesion of urea water to the dispersion plate 60. Therefore, for example, even if the dispersion plate 60 is in a low temperature state, exhaust purification by adding urea water can be maintained.

  (4) As the temperature of the dispersion plate 60 is lower, the low temperature addition time TL is shortened. Therefore, the amount of urea water adhering to the dispersion plate 60 can be appropriately suppressed according to the temperature of the dispersion plate 60.

(5) The low temperature addition time TL is variably set based on at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Accordingly, the temperature addition time TL can be shortened as the temperature of the dispersion plate 60 is lower without directly detecting the temperature of the dispersion plate 60.
(Third embodiment)
Next, a third embodiment of the exhaust gas purification apparatus for an internal combustion engine will be described with reference to FIGS.

In the addition process in the second embodiment shown in FIG. 7, the urea water addition time is shortened in order to reduce the amount of urea water adhering to the dispersion plate 60 in the low temperature state.
On the other hand, in the present embodiment, the amount of urea water adhering to the dispersion plate 60 in the low temperature state is reduced by reducing the amount of urea water itself. That is, in the present embodiment, the content of the addition process in step S200 shown in FIG. 6 is different from the process content in the second embodiment shown in FIG. Therefore, in the following, the addition process in the present embodiment will be described.

In FIG. 9, the procedure of the addition process in this embodiment is shown. The addition process in the present embodiment is also executed as the process of step S200 shown in FIG.
When this addition process is started, the controller 80 sets the low temperature addition amount QEL of urea water based on the dispersion plate temperature TB (S400). This low temperature addition amount QEL is calculated based on the following equation (3).

Low temperature addition amount QEL = urea addition amount QE × addition amount coefficient K5 (3)

As described above, the urea addition amount QE is the sum of the urea amount necessary for reducing NOx and the urea amount necessary for maintaining the ammonia adsorption amount, and is calculated based on the engine operating state and the like. The

The addition amount coefficient K5 is a coefficient for correcting the urea addition amount QE according to the dispersion plate temperature TB.
FIG. 10 shows how the addition amount coefficient K5 is set. The addition amount coefficient K5 is variably set within a range greater than “0” and equal to or less than “1”. The value of the addition amount coefficient K5 is reduced as the dispersion plate temperature TB is lower. This is because the amount of urea water adhering to the dispersion plate 60 is reduced by decreasing the amount of urea water added as the dispersion plate temperature TB is lower.

  The low temperature addition amount QEL may be directly obtained from a one-dimensional map of the dispersion plate temperature TB or the like in addition to the calculation by the above formula (3). For example, the low temperature addition amount QEL is directly set based on the dispersion plate temperature TB so that the lower the dispersion plate temperature TB, the lower the low temperature addition amount QEL. The maximum value of the low temperature addition amount QEL that is variably set is set to be equal to or less than the urea addition amount QE that is set based on the engine operating state or the like. Even in this way, it is possible to set an addition amount similar to the low temperature addition amount QEL obtained from the above formula (3).

  When the low temperature addition amount QEL is thus set, the control device 80 performs urea addition by performing drive control of the urea addition valve 230 in accordance with the low temperature addition amount QEL (S410).

  Next, the control device 80 determines whether or not the currently calculated dispersion plate temperature TB is less than the determination value B (S420). The determination value B is a temperature slightly lower than the determination value A for determining whether or not the temperature of the dispersion plate 60 is in a low temperature state (for example, a temperature about 5 ° C. lower than the determination value A). Is set.

  When the dispersion plate temperature TB is equal to or higher than the determination value B (S420: NO), the control device 80 repeats each process of Step S400 to Step S420 until the dispersion plate temperature TB becomes less than the determination value B. Continue urea addition.

  On the other hand, when the dispersion plate temperature TB is lower than the determination value B (S420: YES), the temperature of the dispersion plate 60 is excessively low. If urea addition is continued further, the amount of urea water adhering to the dispersion plate 60 May exceed the allowable amount. Therefore, when an affirmative determination is made in step S420, control device 80 ends this process and performs the process of step S140 shown in FIG. When the process of step S140 is performed, urea addition is prohibited. Therefore, the urea addition started in step S410 in FIG. 9 is executed during a predetermined period until the dispersion plate temperature TB becomes lower than the determination value B, and is terminated by prohibiting urea addition in step S140 in FIG. .

  Instead of adding urea until the dispersion plate temperature TB becomes lower than the determination value B, the urea addition valve 230 is driven and controlled according to the low temperature addition amount QEL only during a predetermined period. May be executed.

Next, a specific action obtained by this embodiment will be described.
When there is a request for addition of urea water (S100 in FIG. 6: YES), the addition request has priority even if the temperature of the dispersion plate 60 is lower than the determination value A (S120: NO in FIG. 6). Therefore, the urea water addition is stopped only during a predetermined period and the urea water addition prohibition is stopped. More specifically, during the period in which the dispersion plate temperature TB is lower than the determination value A and is in the range of the determination value B or higher, the prohibition of urea water addition is stopped and urea water is added ( S200 in FIG. 6 and S400 to S420 in FIG. 9).

  Here, the low temperature addition amount QEL when the urea water is added when the temperature of the dispersion plate 60 is lower than the determination value A is calculated based on the above formula (3), so that the low temperature addition amount is calculated. The QEL is reduced as compared with the urea addition amount QE at the normal time when the temperature of the dispersion plate 60 is equal to or higher than the determination value A. By reducing the amount of urea water added in this way, the amount of urea water adhering to the dispersion plate 60 is reduced. Therefore, when there is a request for addition of urea water while the temperature of the dispersion plate 60 is low, it is possible to add urea water while suppressing adhesion of urea water to the dispersion plate 60. Therefore, for example, even when the dispersion plate 60 is in a low temperature state, the ammonia adsorption amount of the SCR catalyst 41 can be increased, and NOx purification by adding urea water can be maintained.

  Further, as shown in FIG. 10, the addition amount coefficient K5 is decreased as the dispersion plate temperature TB is lower, so that the lower temperature addition amount QEL is decreased as the temperature of the dispersion plate 60 is decreased. Accordingly, the lower the temperature of the dispersion plate 60 and the easier the urea water adheres, the lower the amount of addition QEL at low temperature, the less the amount of urea water attached to the dispersion plate 60. Therefore, the amount of urea water adhering to the dispersion plate 60 can be appropriately suppressed according to the temperature of the dispersion plate 60.

  Further, the addition amount coefficient K5 is variably set based on the dispersion plate temperature TB. Here, the dispersion plate temperature TB is estimated based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Therefore, if at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD changes, the dispersion plate temperature TB also changes, and the addition amount coefficient K5 also changes. Therefore, in the present embodiment, the low temperature addition amount QEL is variably set based on at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD, which are related to the temperature of the dispersion plate 60. Therefore, the lower temperature addition amount QEL can be reduced as the temperature of the dispersion plate 60 is lower without directly detecting the temperature of the dispersion plate 60.

As described above, according to the present embodiment, in addition to the effects (1) and (2), the following effects can be further obtained.
(6) Even when the temperature of the dispersion plate 60 is lower than the determination value A, when there is a request for addition of urea water, the urea water is within the period until the temperature of the dispersion plate 60 becomes less than the determination value B. The prohibition of addition is stopped and urea is added. The low temperature addition amount QEL is reduced from the urea addition amount QE when the temperature of the dispersion plate 60 is equal to or higher than the determination value A. Therefore, when there is a request for addition of urea water while the temperature of the dispersion plate 60 is low, it is possible to add urea water while suppressing adhesion of urea water to the dispersion plate 60. Therefore, for example, even if the dispersion plate 60 is in a low temperature state, exhaust purification by adding urea water can be maintained.

  (7) The lower temperature addition amount QEL is reduced as the temperature of the dispersion plate 60 is lower. Therefore, the amount of urea water adhering to the dispersion plate 60 can be appropriately suppressed according to the temperature of the dispersion plate 60.

  (8) The low temperature addition amount QEL is variably set based on at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Therefore, the lower temperature addition amount QEL can be reduced as the temperature of the dispersion plate 60 is lower without directly detecting the temperature of the dispersion plate 60.

In addition, each said embodiment can also be changed and implemented as follows.
-The temperature of the dispersion plate 60 was estimated. In addition, instead of such an estimated value, the temperature of the dispersion plate 60 may be directly detected by a temperature sensor or the like.

  The temperature of the dispersion plate 60 is estimated based on the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. In addition, the temperature of the dispersion plate 60 may be estimated based on at least one of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. Preferably, at least the second exhaust temperature TH2 and the outside air temperature THout are included as parameters for estimating the temperature of the dispersion plate 60.

  The temperature of the dispersion plate is estimated in order to determine that the temperature of the dispersion plate 60 is low enough to cause the urea water to adhere to the dispersion plate 60. In addition, the parameters of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD are values related to the temperature of the dispersion plate 60. Therefore, it may be directly determined whether or not the temperature of the dispersion plate 60 is low based on at least one of these parameters. For example, when the outside air temperature THout is lower than a predetermined determination temperature, it is determined that the temperature of the dispersion plate 60 is low enough to cause the urea water to adhere to the dispersion plate 60. May be.

  In the second embodiment, the low temperature addition time TL is variably set based on the dispersion plate temperature TB, but the low temperature addition time TL may be set to a fixed value. However, even in this case, the low temperature addition time TL is set shorter than the addition time T when normal urea addition is performed. Even in such a modification, the effect (3) can be obtained.

  In the second embodiment, the parameter for variably setting the low temperature addition time TL is the dispersion plate temperature TB. In addition, the parameters of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD used for calculating the dispersion plate temperature TB are values related to the temperature of the dispersion plate 60 as described above. Therefore, the time coefficient K4 may be directly variably set based on at least one of these parameters. For example, the time coefficient K4 may be variably set based on the outside air temperature THout so that the time coefficient K4 decreases as the outside air temperature THout decreases. Even in such a modification, the same effect as the variable setting of the time coefficient K4 by the dispersion plate temperature TB can be obtained.

  Further, the low temperature addition time TL may be directly variably set based on at least one of the parameters of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. For example, the low temperature addition time TL may be variably set based on the outside air temperature THout so that the low temperature addition time TL becomes shorter as the outside air temperature THout is lower. Even in such a modification, the same effect as the variable setting of the time coefficient K4 by the dispersion plate temperature TB can be obtained.

  In the third embodiment, the low temperature addition amount QEL is variably set based on the dispersion plate temperature TB, but the low temperature addition amount QEL may be a fixed value. However, even in this case, the low temperature addition amount QEL is smaller than the urea addition amount QE when normal urea addition is performed. Even in such a modification, the effect (6) can be obtained.

  In the third embodiment, the parameter for variably setting the low temperature addition time TL is the dispersion plate temperature TB. In addition, the parameters of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD are values related to the temperature of the dispersion plate 60 as described above. Therefore, the addition amount coefficient K5 may be directly variably set based on at least one of these parameters. For example, the addition amount coefficient K5 may be variably set based on the outside air temperature THout so that the addition amount coefficient K5 decreases as the outside air temperature THout decreases. Even in such a modification, it is possible to obtain the same effect as the variable setting of the addition amount coefficient K5 by the dispersion plate temperature TB.

  Further, the low temperature addition amount QEL may be directly variably set based on at least one of the parameters of the second exhaust temperature TH2, the outside air temperature THout, the exhaust gas flow rate GEX, and the vehicle speed SPD. For example, the low temperature addition amount QEL may be variably set based on the outside air temperature THout such that the lower the outside air temperature THout, the lower the low temperature addition amount QEL. Even in such a modification, it is possible to obtain the same effect as the variable setting of the addition amount coefficient K5 by the dispersion plate temperature TB.

  The SCR catalyst 41 is supported on a zeolite carrier, but may be supported on another carrier. Even in this case, according to each of the above-described embodiments, at least the dispersion plate 60 can suppress the generation of deposit due to the adhesion of urea water.

  Although urea water is used as the reducing agent, other liquid 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 (IG 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) Medium), 50 ... third purification 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 ... 1st NOx sensor, 140 ... 2nd NOx sensor, 200 ... Urea water supply mechanism, 210 ... Tank, 220 ... Pump, 230 ... Urea addition valve, 240 ... Supply passage.

Claims (8)

A catalyst for purifying exhaust gas by adding a reducing agent;
A reducing agent supply mechanism for adding the reducing agent into the exhaust passage;
A dispersion plate that is provided in the exhaust passage and disperses the reducing agent upstream of the catalyst;
A control unit that controls addition of a reducing agent by the reducing agent supply mechanism;
The control unit prohibits addition of a reducing agent when the temperature of the dispersion plate is lower than a predetermined temperature. Even when the temperature of the dispersion plate is lower than the predetermined temperature, the control unit stops the addition of the reducing agent only for a predetermined period and adds the reducing agent when there is a request for addition of the reducing agent. The exhaust purification device for an internal combustion engine according to claim 1, wherein the predetermined period is shorter than an addition period when the temperature of the dispersion plate is equal to or higher than the predetermined temperature. The exhaust purification device for an internal combustion engine according to claim 2, wherein the control unit shortens the predetermined period as the temperature of the dispersion plate is lower. The exhaust purification device is a device mounted on a vehicle,
The exhaust purification device for an internal combustion engine according to claim 3, wherein the control unit variably sets the predetermined period based on at least one of an exhaust temperature, an outside air temperature, an exhaust flow rate, and a vehicle speed. Even when the temperature of the dispersion plate is lower than the predetermined temperature, the control unit stops the addition of the reducing agent only for a predetermined period and adds the reducing agent when there is a request for addition of the reducing agent. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of addition when the reducing agent is added is reduced from the amount of addition when the temperature of the dispersion plate is equal to or higher than the predetermined temperature. The exhaust purification device for an internal combustion engine according to claim 5, wherein the control unit decreases the addition amount as the temperature of the dispersion plate is lower. The exhaust purification device is a device mounted on a vehicle,
The exhaust purification device for an internal combustion engine according to claim 6, wherein the control unit variably sets the addition amount based on at least one of an exhaust temperature, an outside air temperature, an exhaust flow rate, and a vehicle speed. The exhaust purification device is a device mounted on a vehicle,
The control unit determines whether or not the temperature of the dispersion plate is lower than the predetermined temperature based on at least one of an exhaust temperature, an outside air temperature, an exhaust flow rate, and a vehicle speed. An exhaust emission control device for an internal combustion engine according to any one of the preceding claims.