JP5834978B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

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

  2. Description of the Related Art An exhaust gas purification device for an internal combustion engine that includes a NOx purification catalyst that purifies nitrogen oxide (NOx) in exhaust gas is known. In such an exhaust purification device, for example, a reducing agent such as urea water is injected from the injection valve toward the exhaust passage. When the injected reducing agent reaches the NOx purification catalyst, it is adsorbed on the NOx purification catalyst as ammonia. The NOx is reduced and purified by ammonia adsorbed on the catalyst.

  Further, in the apparatus described in Patent Document 1, when the engine load is low, the reducing agent is effectively stored by the catalyst by injecting and supplying the reducing agent in a pulsed manner.

JP 2005-201283A

  By the way, when the reducing agent addition amount set based on the engine operating state is divided and injected from the reducing agent injection valve a plurality of times, the reducing agent is pulsed as described in Patent Document 1. It is supplied by injection. When the reducing agent is injected and supplied in a pulse manner in this manner, the atomization of the reducing agent is promoted and the reducing agent is dispersed in the exhaust passage as compared with the case where the reducing agent is continuously supplied by injection. As a result, the NOx purification rate increases.

  However, when the reducing agent is injected and supplied in a pulsed manner, the number of operations of the reducing agent injection valve (the number of times the valve is opened and closed) is much greater than when the reducing agent is continuously supplied and supplied. As a result, the durability of the reducing agent injection valve tends to decrease.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust purification device for an internal combustion engine that can improve the durability of the reducing agent injection valve.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 includes a NOx purification catalyst that purifies NOx by adding a reducing agent, and a reducing agent injection valve that injects the reducing agent into the exhaust passage, and is set based on the engine operating state. In the exhaust gas purification apparatus for an internal combustion engine that divides and injects the agent addition amount from the reducing agent injection valve into a plurality of times, the reducing agent is added during the fuel cut in which the fuel injection from the engine fuel injection valve is stopped, When the reducing agent is added in a state where the exhaust temperature during the fuel cut is equal to or higher than a predetermined value, the gist is to reduce the number of injections of the reducing agent as compared with the case of adding the reducing agent during fuel injection.

  In this configuration, the reducing agent addition amount that is set based on the engine operating state is dividedly injected from the reducing agent injection valve in a plurality of times. Accordingly, as described above, the reducing agent is injected and supplied in a pulsed manner, and compared with the case where the reducing agent is continuously supplied by injection, atomization of the reducing agent is promoted and the exhaust passage is increased. The dispersibility of the reducing agent is improved. Therefore, the NOx purification rate is increased.

  On the other hand, when fuel injection from the fuel injection valve is being performed, NOx is generated in the combustion chamber. When the reducing agent is added in a state where NOx is generated in this way, a part of the reducing agent reacts with NOx in the exhaust gas before reaching the NOx purification catalyst. Therefore, the amount of reducing agent that reaches the NOx purification catalyst is reduced by the amount of reaction with NOx, and the ammonia adsorption amount of the NOx purification catalyst is reduced by the amount of reduction of the reducing agent.

  On the other hand, NOx is not generated in the combustion chamber during fuel cut in which fuel injection from the fuel injection valve is stopped. Therefore, in this configuration, the reducing agent is added even during fuel cut. Thus, the reducing agent added during the fuel cut reaches the NOx purification catalyst as it is without reacting with the NOx in the exhaust gas. Accordingly, the amount of reducing agent that reaches the NOx purification catalyst is increased as compared with the case where the same amount of reducing agent is added during fuel injection, and more ammonia can be adsorbed on the NOx purification catalyst.

  Here, since NOx is not generated during the fuel cut as described above, when the reducing agent is added during the fuel cut, the atomization of the reducing agent is much less than when the reducing agent is added during the fuel injection. The demand is not high. Moreover, since the atomization of the reducing agent is promoted to some extent by the exhaust heat if the exhaust temperature is high, the number of injections when the reducing agent is dividedly injected can be reduced. Therefore, in this configuration, when the reducing agent is added when the exhaust gas temperature during fuel cut is higher than a predetermined value, the amount of reducing agent is smaller than when the reducing agent is added during fuel injection. The number of injections is reduced. Therefore, the durability of the reducing agent injection valve can be improved while promoting atomization of the reducing agent.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, when the reducing agent is added in a state where the exhaust temperature during fuel cut is equal to or higher than the predetermined value, the reducing agent injection mode is changed. The gist is to switch from split injection to single injection.

  According to this configuration, when the reducing agent is added while the exhaust temperature during the fuel cut is equal to or higher than a predetermined value, the number of reducing agent injections is minimized because the number of reducing agent injections is one. Therefore, it is possible to maximize the durability of the reducing agent injection valve by reducing the number of injections.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the exhaust gas purification device of the internal combustion engine concerning this invention. The flowchart which shows the procedure about the addition process of urea water in the embodiment. It is a time chart which shows the addition aspect of urea water in the embodiment, Comprising: (A) is a time chart which shows the addition aspect during fuel injection. (B) is a time chart showing an addition mode during fuel cut.

  Hereinafter, an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS. Note that “upstream” and “downstream” described in this specification are based on the flow direction of the exhaust gas in the exhaust system.

FIG. 1 is a schematic configuration diagram showing a diesel engine (hereinafter simply referred to as “engine”) to which the exhaust emission control device according to the present embodiment is applied, and a peripheral configuration thereof.
The engine 1 is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4 a to 4 d are attached to the cylinder head 2. 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 DPF catalyst 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 DPF catalyst 32 is a filter that collects PM (particulate matter) in the exhaust gas and is composed of a porous ceramic, and further supports a catalyst for promoting oxidation of PM. . The PM in the exhaust gas is collected when it passes through the porous wall of the DPF catalyst 32. The DPF catalyst 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 DPF catalyst 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.

  When the amount of PM collected by the DPF catalyst 32 exceeds a predetermined value, regeneration processing of the DPF catalyst 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 heated by the oxidation catalyst 31 flows into the DPF catalyst 32, whereby the DPF catalyst 32 is heated, whereby the PM deposited on the DPF catalyst 32 is oxidized to regenerate the DPF catalyst 32. Is planned.

  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 NOx purification catalyst that reduces and purifies 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 that supplies 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.

  When urea water injected from the urea addition valve 230 reaches the SCR catalyst 41, it is adsorbed as ammonia. Then, NOx is reduced and purified by the ammonia adsorbed on the SCR catalyst 41.

  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. This exhaust gas recirculation 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 in the intake passage 3. 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 ignition switch 25 detects a start operation and a stop operation of the engine 1 by a vehicle driver.

  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 DPF catalyst 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 from these various sensors are input to the control device 80. 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 DPF catalyst 32 is also performed by the controller 80.
The control device 80 also performs urea water addition control by the urea addition valve 230 as one of such exhaust gas purification controls. In this addition control, the urea addition amount QE necessary for reducing the NOx discharged from the engine 1 is calculated based on the engine operating state and the like, and the calculated urea addition amount QE is injected from the urea addition valve 230. Thus, the valve opening state of the urea addition valve 230 is controlled.

By the way, the ammonia adsorption amount of the SCR catalyst 41 varies depending on the temperature of the SCR catalyst 41 (approximately, the second exhaust temperature TH2) and the state of fuel injection.
First, the higher the second exhaust temperature TH2, that is, the higher the temperature of the SCR catalyst 41, the smaller the amount of ammonia adsorbed to the SCR catalyst 41. When the adsorbing limit temperature is exceeded, ammonia cannot be adsorbed.

  Further, when fuel injection from the fuel injection valves 4a to 4d is being executed, NOx is generated in the combustion chamber of each cylinder. When urea water is added in a state where NOx is generated in this way, a part of the urea water reacts with NOx in the exhaust gas before reaching the SCR catalyst 41 to purify the NOx. Therefore, the amount of urea water reaching the SCR catalyst 41 is reduced by the amount of reaction with NOx, and the amount of ammonia adsorption is reduced by the amount of reduction of the urea water.

  On the other hand, NOx is not generated in the combustion chamber during the fuel cut in which the fuel injection from the fuel injection valves 4a to 4d is stopped. Therefore, when urea water is added during fuel cut, the added urea water reaches the SCR catalyst 41 as it is without reacting with NOx in the exhaust gas. Therefore, when urea water is added during fuel cut, the amount of urea water reaching the SCR catalyst 41 is larger than when urea water of the same amount is added during fuel injection. Therefore, even when the temperature of the SCR catalyst 41 is the same, when the urea water is added during the fuel cut, the ammonia adsorption amount is larger than when the same amount of urea water is added during the fuel injection. .

  Thus, if urea water is added even during fuel cut where NOx is not generated, ammonia can be efficiently adsorbed to the SCR catalyst 41. Therefore, in this embodiment, urea water is also added during fuel cut. ing.

  Further, in the present embodiment, the urea addition amount QE set based on the engine operating state is dividedly injected from the urea addition valve 230 in a plurality of times. When the urea water is injected and supplied in a pulse manner in this manner, the atomization of the urea water is promoted and the dispersibility of the urea water in the exhaust passage 26 is increased as compared to the case where the urea water is continuously supplied. As a result, the NOx purification rate increases.

  However, when the urea water is injected and supplied in a pulse manner in this way, the number of operations of the urea addition valve 230 (the number of times the valve is opened and closed) is significantly increased as compared with the case where the urea water is continuously supplied and supplied. The durability of the urea addition valve 230 tends to decrease.

  Here, as described above, NOx is not generated during the fuel cut, so when adding urea water during the fuel cut, the atomization of urea water is much less than when adding urea water during fuel injection. The demand is not high. Moreover, since the atomization of urea water is promoted to some extent by the exhaust heat if the exhaust gas temperature is high, the number of injections when the urea water is dividedly injected can be reduced.

  Therefore, in the present embodiment, when adding urea water when the exhaust temperature during fuel cut is a high temperature state equal to or higher than a predetermined value, the urea water is compared to when adding urea water during fuel injection. The number of operations of the urea addition valve 230 is reduced by reducing the number of injections (the number of divisions of the urea addition amount QE).

Hereinafter, the urea water addition process for performing such a process will be described with reference to FIG. This process is executed by the control device 80.
When this process is started, first, the addition frequency TS is set based on the engine speed NE and the fuel injection amount Q (S100). This addition frequency TS (unit: Hz) is the frequency of the voltage applied to the urea addition valve 230, and is the same as the number of times of opening (number of operations) of the urea addition valve 230 in one second. As the addition frequency TS is higher, the number of divisions of the urea addition amount QE is increased, and the number of operations of the urea addition valve 230 until the addition of the urea addition amount QE is increased.

  Further, as the engine rotational speed NE is higher, the exhaust gas flow rate per unit time is increased and the dispersibility of the urea water is improved, so that the number of injections when the urea water is dividedly injected can be reduced. Therefore, the addition frequency TS is set to a lower value as the engine speed NE is higher.

  Further, as the fuel injection amount Q injected from the fuel injection valves 4a to 4d increases, the exhaust temperature becomes higher and atomization of the urea water is promoted, thereby improving the dispersibility of the urea water. Also, the number of injections when the urea water is divided and injected can be reduced. Therefore, the addition frequency TS is set to a lower value as the fuel injection amount Q is larger. Thus, the addition frequency TS is variably set based on the engine speed NE and the fuel injection amount Q.

  Next, the first correction coefficient K1 is set based on the second exhaust temperature TH2. The first correction coefficient K1 is a correction coefficient for lowering the addition frequency TS, and its value is variably set within the range of “0 <K1 ≦ 1”. More specifically, as the second exhaust temperature TH2 is higher, the atomization of the added urea water is promoted and the dispersibility of the urea water is improved, so the number of injections when the urea water is dividedly injected is reduced. Can do. Therefore, the first correction coefficient K1 is set to a smaller value as the second exhaust temperature TH2 is higher. Thus, as the first correction coefficient K1 is set to a smaller value, the addition frequency TS is corrected to a lower value, thereby reducing the number of injections at the time of divided injection, and the operation of the urea addition valve 230. The number of times decreases.

  Next, the second correction coefficient K2 is set based on the intake air amount GA. The second correction coefficient K2 is also a correction coefficient for lowering the addition frequency TS, and its value is variably set within the range of “0 <K2 ≦ 1”. More specifically, as the intake air amount GA increases, the exhaust flow rate in the exhaust passage increases and the dispersibility of the urea water improves, so that the number of injections when the urea water is dividedly injected can be reduced. Therefore, the second correction coefficient K2 is set to a smaller value as the intake air amount GA is larger. Thus, as the second correction coefficient K2 is set to a smaller value, the addition frequency TS is corrected to be a lower value, thereby reducing the number of injections during divided injection, and the operation of the urea addition valve 230. The number of times decreases.

Next, it is determined whether or not the following condition (1) and condition (2) are both satisfied (S130).
Condition (1): The accelerator is off. When this condition (1) is satisfied, it is determined that the fuel is being cut.

  Condition (2): The second exhaust temperature TH2 is higher than the threshold value γ. When this condition (2) is satisfied, the atomization of the urea water is promoted to some extent by the exhaust heat, and the number of injections when the urea water is dividedly injected may be reduced compared to the time of fuel injection. It is judged that it is possible.

  When a negative determination is made in step S130, that is, when NOx is generated due to the accelerator pedal being depressed and fuel injection being performed, or when the second exhaust temperature TH2 is lower than the threshold γ and due to exhaust heat When the atomization of the urea water is delayed, the processes after step S140 are performed to divide and inject the urea water.

In step S140, the corrected addition frequency TSH is calculated from the following equation (1) based on the addition frequency TS, the first correction coefficient K1, and the second correction coefficient K2.

TSH = TS × K1 × K2 (1)
TSH: Added frequency after correction TSH
TS: Addition frequency K1: First correction coefficient K2: Second correction coefficient

Next, the equivalence ratio TT is set based on the second exhaust temperature TH2 and the intake air amount GA (S150). This equivalent ratio TT is the amount of urea water added per unit time that is sufficient for reducing NOx, and more specifically, the amount added per unit time required per unit concentration of NOx. (For example, in this embodiment, the addition amount per hour (g) necessary for completely reducing 1 ppm of NOx). Then, as the intake air amount GA increases (that is, the exhaust flow rate increases) or the second exhaust temperature TH2 increases, the required addition amount per unit concentration of NOx tends to increase. The equivalence ratio TT is variably set so that the value of the equivalence ratio TT increases as TH2 increases or the intake air amount GA increases.

Next, by multiplying the equivalent ratio TT by the first NOx concentration N1, the urea addition amount QE (g / h) corresponding to the current NOx discharge amount is calculated (S160).
Next, the addition interval INT is calculated based on the corrected addition frequency TSH (S170). The addition interval INT is an injection interval time at the time of divided injection of urea water, and is calculated from the following equation (2).

Addition interval INT (seconds) = 1 / added frequency after correction TSH (2)

Next, based on the corrected addition frequency TSH and the urea addition amount QE, the valve opening time KT per one time at the time of divided injection of urea water is calculated (S180). In step S180, the unit urea addition amount QET, which is the urea addition amount per injection, is calculated based on the following equation (3).

QET = (QE / 3600) × (1 / TSH) (3)
QET: Unit urea addition amount (g)
QE: Amount of urea added (g / h)
TSH: Correction frequency after correction (Hz)

The value of (urea addition amount QE / 3600) in equation (3) indicates the urea addition amount that needs to be added in one second. Then, the unit urea addition amount QET is calculated by multiplying the value of this (urea addition amount QE / 3600) by (1 / corrected addition frequency TSH). The valve opening time KT of the urea addition valve 230 is set so that the unit urea addition amount QET can be added.

  Next, urea addition is executed in step S190, and this process is terminated. When urea addition is executed in step S190, as shown in FIG. 3A, the urea addition valve 230 is opened only during the valve opening time KT within the addition interval INT, and such intermittent injection is performed in the addition interval. By performing for each INT, divided injection of urea water is performed.

  On the other hand, when an affirmative determination is made in step S130, that is, when the fuel is being cut and the second exhaust temperature TH2 is higher than the threshold γ, the urea addition amount QE is set based on the second exhaust temperature TH2 (S200). ). In step S200, a urea addition amount QE (g) suitable for optimizing the ammonia adsorption amount of the SCR catalyst 41 during the fuel cut is set. That is, as described above, the ammonia adsorption amount of the SCR catalyst 41 decreases as the exhaust gas temperature increases. Therefore, in step S200, the urea addition amount QE decreases so that the urea addition amount QE decreases as the second exhaust gas temperature TH2 increases. The addition amount QE is variably set. Thereby, generation | occurrence | production of the ammonia slip by the excessive urea addition amount QE is suppressed.

  Next, the valve opening time KT of the urea addition valve 230 is set based on the urea addition amount QE set in step S200 (S210). In this step S210, the valve opening time KT of the urea addition valve 230 is set so that the urea addition amount QE can be added by one valve opening operation.

  Then, urea addition is executed (S190), and this process is terminated. When an affirmative determination is made in step S130 and urea addition is executed in step S190, as shown in FIG. 3B, one valve opening operation is required during the valve opening time KT. A urea addition amount QE is added. That is, the urea water injection mode is not divided injection but single injection (continuous injection).

Next, the operation of this embodiment will be described.
In the present embodiment, urea water is dividedly injected in order to improve the dispersibility of urea water. Further, in order to efficiently adsorb ammonia to the SCR catalyst 41, urea water is added even during fuel cut in which NOx is not generated. Here, when an affirmative determination is made in step S130 shown in FIG. 2, that is, when the fuel is being cut and the second exhaust temperature TH2 is in a high temperature state equal to or higher than the threshold value γ, urea water is injected during fuel injection. As compared with the case of injecting water, the number of times of urea water injection is reduced. More specifically, when adding urea water during a fuel cut, split injection of urea water is stopped and switched to single injection. In this way, when urea water is added while the second exhaust temperature TH2 during fuel cut is equal to or higher than the threshold γ, the number of injections of urea water is set to one, so that the same division during fuel cut as during fuel injection is performed. Compared with the case of performing injection, the number of times of urea water injection is minimized, and the number of operations of the urea addition valve 230 is suppressed to the maximum. Therefore, the durability of the urea addition valve 230 can be maximized by reducing the number of injections.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea addition amount QE is set based on the engine operating state, and the set urea addition amount QE is dividedly injected from the urea addition valve 230 in a plurality of times. As a result, the dispersibility of urea water in the exhaust passage 26 is improved, and the NOx purification rate is increased.

(2) Since urea water is added even during fuel cut, more ammonia can be adsorbed to the SCR catalyst 41.
(3) When urea water is added in a state where the second exhaust temperature TH2 during fuel cut is equal to or higher than the threshold γ, the number of injections of urea water is made smaller than when urea water is added during fuel injection. ing. Therefore, the durability of the urea addition valve 230 can be improved while promoting the atomization of urea water by the exhaust heat.

  (4) When adding urea water in a state where the second exhaust temperature TH2 during fuel cut is equal to or higher than the threshold γ, the urea water injection mode is switched from split injection to single injection. Therefore, the durability of the urea addition valve 230 can be maximized by reducing the number of injections.

  (5) The addition frequency TS related to the dispersibility of the urea water and the number of operations of the urea addition valve 230 is variably set based on the engine speed NE and the fuel injection amount Q related to the dispersibility of the urea water. ing. Accordingly, when the urea water is dividedly injected, the number of operations of the urea addition valve 230 can be reduced as much as possible while ensuring the dispersibility of the urea water.

  (6) Further, the addition frequency TS related to the dispersibility of the urea water and the number of operations of the urea addition valve 230 is further corrected based on the second exhaust temperature TH2 and the intake air amount GA related to the dispersibility of the urea water. Like to do. Therefore, when the urea water is dividedly injected, the number of operations of the urea addition valve 230 can be further reduced as much as possible while further ensuring the dispersibility of the urea water.

In addition, the said embodiment can also be changed and implemented as follows.
-Although the number of times of urea water injection during fuel cut is set to 1, it may be set to 2 times or more. In short, the number of injections of urea water during fuel cut may be made smaller than the number of injections during fuel injection. For example, when an affirmative determination is made in step S130 shown in FIG. 2, the third correction coefficient K3 for lowering the addition frequency TS is set. The value of the third correction coefficient K3 is appropriately set within the range of “0 <K3 <1”. Then, the third correction coefficient K3 is multiplied by the post-correction addition frequency TSH so that the addition frequency during fuel cut is lower than during fuel injection. Then, based on the value obtained by multiplying the corrected addition frequency TSH by the third correction coefficient K3, the urea addition amount QE set in step S200, etc., the addition interval INT and the valve opening time KT per injection are set. Thus, split injection may be performed during fuel cut. Even in this case, since the number of times of urea water injection during fuel cut is smaller than the number of times of urea water injection during fuel injection, the durability of the urea addition valve 230 is improved.

The correction of the addition frequency TS by the first correction coefficient K1 and the correction of the addition frequency TS by the second correction coefficient K2 may be omitted.
The addition frequency TS is set based on two parameters such as the engine speed NE and the fuel injection amount Q, but either one of the parameters may be omitted.

-Addition frequency TS is good also as a predetermined fixed value.
Although urea water is used as the reducing agent, other reducing agents may be used.

In addition, the technical idea that can be grasped from the above embodiment will be described below together with the effects thereof.
(A) The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the number of injections during the divided injection is reduced as the engine rotational speed is higher.

  According to this apparatus, the number of injections at the time of divided injection related to the dispersibility of urea water and the number of operations of the reducing agent injection valve is changed based on the engine rotational speed related to the dispersibility of urea water. Therefore, when the urea water is divided and injected, the number of operations of the reducing agent injection valve can be reduced as much as possible while ensuring the dispersibility of the urea water.

  (B) The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the number of injections during the divided injection is reduced as the fuel injection amount is larger.

  According to this apparatus, the number of injections at the time of divided injection related to the dispersibility of urea water and the number of operations of the reducing agent injection valve is changed based on the fuel injection amount related to the dispersibility of urea water. Therefore, when the urea water is divided and injected, the number of operations of the reducing agent injection valve can be reduced as much as possible while ensuring the dispersibility of the urea water.

  (C) The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the number of injections during the divided injection is reduced as the exhaust temperature in the exhaust passage is higher. Purification equipment.

  According to this apparatus, the number of injections at the time of divided injection related to the dispersibility of urea water and the number of operations of the reducing agent injection valve is changed based on the exhaust temperature related to the dispersibility of urea water. Therefore, when the urea water is divided and injected, the number of operations of the reducing agent injection valve can be reduced as much as possible while ensuring the dispersibility of the urea water.

  (D) The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the number of injections during the divided injection is reduced as the exhaust flow rate in the exhaust passage increases. Purification equipment.

  According to this apparatus, the number of injections at the time of divided injection related to the dispersibility of urea water and the number of operations of the reducing agent injection valve is changed based on the exhaust flow rate related to the dispersibility of urea water. Therefore, when the urea water is divided and injected, the number of operations of the reducing agent injection valve can be reduced as much as possible while ensuring the dispersibility of the urea water.

  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 ... NOx purification catalyst (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 (2)

The reducing agent injection valve includes a NOx purification catalyst that purifies NOx by adding a reducing agent, and a reducing agent injection valve that injects the reducing agent into the exhaust passage, and sets the reducing agent addition amount that is set based on an engine operating state. In the exhaust gas purification apparatus for an internal combustion engine that performs divided injection divided into a plurality of times,
When a reducing agent is added during a fuel cut in which fuel injection from the engine fuel injection valve is stopped, and when the exhaust temperature during the fuel cut is higher than a predetermined value, the reducing agent is added during the fuel injection. An exhaust emission control device for an internal combustion engine, characterized in that the number of times of injection of the reducing agent is reduced as compared with the case of adding. The exhaust emission control device for an internal combustion engine according to claim 1, wherein when the reducing agent is added while the exhaust temperature during fuel cut is equal to or higher than the predetermined value, the reducing agent injection mode is switched from split injection to single injection.