JP2013113267A - Exhaust emission purifying apparatus of internal combustion engine - Google Patents

Abstract

An exhaust emission control device for an internal combustion engine that can suppress NOx purification performance at the time of engine start and suppress deterioration of fuel consumption.
An engine 1 is provided with a NOx purification catalyst 41 that purifies NOx by supplying a reducing agent, and a urea addition valve 230 that injects urea water into an exhaust passage 26. The control device 80 injects urea water from the urea addition valve 230 after the engine is stopped.
[Selection] Figure 1

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 NOx purification catalyst that purifies nitrogen oxide (NOx) in exhaust gas, and a reducing agent supply that supplies a reducing agent used for NOx purification in the exhaust gas into the exhaust passage. An exhaust gas purification apparatus for an internal combustion engine including a mechanism is known.

  In this exhaust purification device, urea water is injected toward the exhaust passage from a reducing agent injection valve provided in the reducing agent supply mechanism during engine operation. The injected urea water is hydrolyzed by the heat of the exhaust to become ammonia. This ammonia is adsorbed on the NOx purification catalyst as a reducing agent.

  By the way, since NOx is discharged from the combustion chamber when the engine start is started, it is desirable to quickly purify NOx after the engine start. Therefore, for example, in the apparatus described in Patent Document 1, a sufficient amount of ammonia is adsorbed by the NOx purification catalyst prior to engine start. More specifically, it is determined whether or not the ammonia adsorption amount of the NOx purification catalyst when the ignition switch is turned off has reached a target value. When the ammonia adsorption amount does not reach the target value, idle operation and reducing agent supply are continued, and the engine is stopped when the ammonia adsorption amount reaches the target value.

JP 2009-197728 A

  By the way, in the above-mentioned conventional apparatus, even if the ignition switch is turned off, the engine operation is continued until the ammonia adsorption amount reaches the target value. That is, the engine stop is delayed. Therefore, although NOx purification performance at the time of starting the engine is ensured, the fuel consumption is deteriorated by the amount of fuel consumed during the engine stop delay process.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine capable of suppressing deterioration of fuel consumption while ensuring NOx purification performance at the time of engine start. is there.

In the following, means for achieving the above object and its effects are described.
The invention according to claim 1 is an exhaust gas purification apparatus for an internal combustion engine comprising a NOx purification catalyst that purifies NOx by supplying a reducing agent, and a reducing agent injection valve that injects the reducing agent into the exhaust passage. The gist is to perform the reducing agent injection from the reducing agent injection valve.

According to this configuration, the reducing agent is injected after the engine is stopped. That is, since the engine operation accompanying the reducing agent injection is not performed, deterioration of fuel consumption can be suppressed.
In addition, the temperature in the exhaust passage after the engine is stopped does not rapidly decrease, and is often in a high temperature state that allows the reducing agent to vaporize until a certain period of time has elapsed. Therefore, when the reducing agent is injected after the engine is stopped as in the same configuration, the injected reducing agent is vaporized in the exhaust passage and then stays in the exhaust passage. When the engine is started, NOx is purified by the reducing agent staying in the exhaust passage. Further, when the engine is started, the reducing agent staying in the exhaust passage reaches the NOx purification catalyst together with the exhaust gas, and the NOx is purified by the NOx purification catalyst. Therefore, even if the reducing agent is injected after the engine is stopped, the NOx purification performance at the time of starting the engine can be ensured.

  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, an injection pressure of the reducing agent when performing the reducing agent injection is set higher than an injection pressure during engine operation. The gist.

According to this configuration, since the atomization of the reducing agent is promoted by increasing the injection pressure, it is possible to suppress the droplets of the reducing agent and to vaporize more reducing agent.
The gist of a third aspect of the invention is that the reducing agent is intermittently injected in the exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect.

  When the reducing agent is intermittently injected, atomization of the reducing agent tends to be promoted compared to the case of continuous injection. Therefore, in this configuration, the reducing agent injection after the engine stop is performed by intermittent injection. Accordingly, the atomization of the reducing agent can be promoted even when the reducing agent is injected after the engine is stopped because there is no flow of exhaust gas and the reducing agent is difficult to atomize.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to third aspects, the reducing agent injection amount when the reducing agent injection is performed is determined by a temperature in the exhaust passage. The gist is that it is variably set so as to increase as the height increases.

  The higher the temperature in the exhaust passage, the more easily the injected reducing agent is vaporized. Therefore, in the same configuration, the amount of reducing agent injected is increased as the temperature in the exhaust passage is higher, so that the NOx purification performance is more appropriately ensured.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, an injection hole of the reducing agent injection valve is opened toward the NOx purification catalyst. The gist of this is.

  When the engine is stopped, there is no exhaust flow. Therefore, when reducing agent injection is performed after the engine is stopped, it becomes difficult for the reducing agent to reach the NOx purification catalyst. In this respect, in the same configuration, since the injection hole of the reducing agent injection valve is opened toward the NOx purification catalyst, the reducing agent can be supplied to the NOx purification catalyst even if there is no exhaust flow. In addition, when combining the structure and the structure of Claim 2, since the injection pressure of a reducing agent is raised, it becomes possible to supply a reducing agent further by a NOx purification catalyst.

  According to a sixth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fifth aspects, the internal combustion engine performs automatic stop and automatic start when a predetermined condition is satisfied. The gist of the invention is that the reducing agent injection is performed when the automatic stop is performed.

  In order to improve fuel consumption and the like, an internal combustion engine that performs automatic stop and automatic start when a predetermined condition is satisfied has a greater number of engine stops than an internal combustion engine that does not perform automatic stop and automatic start. Therefore, in an internal combustion engine that performs automatic stop and automatic start, if the delay process of the engine stop is performed as in the above-described conventional device, the number of executions of the delay process increases, and the fuel consumption tends to deteriorate. In this regard, in the same configuration, the reducing agent injection is performed when the automatic stop is performed in the internal combustion engine in which the number of stoppages of the engine is likely to increase due to the automatic stop and the automatic start. Therefore, the fuel efficiency can be further improved as compared with the conventional device that performs the engine stop delay process described above.

  Further, in an internal combustion engine that performs automatic stop and automatic start, it is often restarted after a relatively short time after automatic stop. In other words, after the engine is stopped, the temperature in the exhaust passage is somewhat high. Often restarted. Therefore, when reducing agent injection is performed after the automatic stop, the injected reducing agent is often restarted after vaporizing and before droplet formation, and the injected reducing agent is effective for NOx purification. Can be used. Therefore, in the same configuration, when an automatic stop is performed in an internal combustion engine that is automatically stopped and automatically started, that is, an internal combustion engine that is often restarted while the temperature in the exhaust passage is somewhat high after the engine is stopped. In addition, the reducing agent is injected. Therefore, the injected reducing agent can be effectively used for NOx purification.

  According to a seventh aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the sixth aspect, a supply passage for supplying a reducing agent to the reducing agent injection valve, and a recovery means for recovering the reducing agent from the supply passage. And the collection means collects the reducing agent when the engine stop time exceeds a predetermined time.

  The invention according to claim 8 is the exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the supply passage for supplying the reducing agent to the reducing agent injection valve, and the recovery for recovering the reducing agent from the supply passage. And the recovery means recovers the reducing agent when the ignition switch of the internal combustion engine is turned off.

  If the reducing agent remains in the supply passage for supplying the reducing agent to the reducing agent injection valve after the engine is stopped, the supply passage or the like may be damaged due to an increase in volume due to freezing of the reducing agent. Therefore, in the same configuration as described in claims 7 and 8, in order to suppress such damage to the supply passage and the like, a recovery means for recovering the reducing agent from the supply passage is provided.

  When the reducing agent is injected after the reducing agent is recovered in this way, it is necessary to fill the reducing agent injection valve and the supply passage with the reducing agent, and until the filling of the reducing agent is completed, A sufficient amount of reducing agent cannot be supplied. Therefore, there is a possibility that the NOx purification performance is lowered until the filling of the reducing agent is completed.

  On the other hand, if the engine stop time is short, freezing of the reducing agent can be suppressed by engine heat or exhaust heat. Conversely, if the engine stop time is long, the possibility that the reducing agent will freeze increases. Therefore, when the engine stop time is short, there is no need to collect the reducing agent, and if the reducing agent is not collected, the above-described filling of the reducing agent is not necessary. There is no reduction in purification performance.

  Therefore, in the invention described in claim 7, the reducing agent is recovered when the engine stop time exceeds a predetermined time. Therefore, when the engine stop time is shorter than the predetermined time and the possibility of freezing of the reducing agent is low, the reducing agent is not recovered. Therefore, it is possible to suppress the frequency of recovery of the reducing agent, thereby suppressing a decrease in NOx purification performance during the reducing agent filling period.

  According to the eighth aspect of the present invention, the reducing agent is recovered when the ignition switch of the internal combustion engine is turned off. Therefore, at the time of automatic stop where the engine stop time tends to be relatively short, the reducing agent is not recovered. Therefore, even with the same configuration, the frequency of reducing agent recovery can be suppressed, and thereby a reduction in NOx purification performance during the reducing agent charging period can be suppressed.

  Examples of the recovery means include a forward / reversible pump provided in the supply passage, a switching valve provided in the supply passage and capable of changing the flow direction of the reducing agent.

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 the internal combustion engine concerning this invention. The flowchart which shows the procedure of the urea addition process at the time of a stop in the embodiment. The graph which shows the relationship between the 2nd exhaust temperature in the same embodiment, and the addition amount at the time of a stop. The flowchart which shows the part about the procedure of the urea addition process at the time of a stop in 2nd Embodiment. The flowchart which shows the procedure of the determination process of collection | recovery control in 3rd Embodiment.

(First embodiment)
A first embodiment of an internal combustion engine exhaust gas purification apparatus according to the present invention will be described below with reference to FIGS.

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 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.

  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. 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 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 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. The pump 220 constitutes the collecting means.

  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. The 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. A part of the hydrolyzed ammonia is directly used for NOx reduction before being occluded by 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 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 a pressure difference ΔP between the exhaust pressure upstream and the exhaust downstream of the filter 32.

  In the exhaust passage 26 between the first purification member 30 and the second purification member 40, a second exhaust temperature sensor 120 and a first NOx sensor 130 are provided 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.

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

  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.

  In addition to starting and stopping the engine 1 based on the operation of the ignition switch 25, the control device 80 performs automatic stop control and automatic start control of the engine 1 according to the vehicle running state as one of various controls of the engine 1. As the automatic stop condition of the engine 1, for example, “the vehicle speed falls below the reference speed while the vehicle is traveling”, “the accelerator pedal is depressed“ 0 ””, or the like is set. Further, as an automatic start condition of the engine 1, for example, “the accelerator pedal is depressed during automatic stop”, “the battery charge amount is reduced”, “the electric load is increased”, or the like is set. ing.

The exhaust gas purification control such as the regeneration process for burning the PM collected by the filter 32 is also performed by the controller 80.
The control device 80 performs urea water addition control by the urea addition valve 230 as one of exhaust purification control. In this addition control, a urea addition amount without excess or deficiency is calculated based on the engine operating state or the like in order to reduce the NOx discharged from the engine 1, and the calculated urea addition amount is injected from the urea addition valve 230. Thus, the valve opening state of the urea addition valve 230 is controlled.

  If urea water remains in the supply passage 240 of the urea water supply mechanism 200 or in the urea addition valve 230 after the urea water addition is stopped, the supply passage 240 or The urea addition valve 230 may be damaged. Therefore, in order to suppress such freezing of urea water, the control device 80 also performs recovery control for recovering urea water from the urea addition valve 230 and the supply passage 240 after the engine is stopped. In this recovery control, the urea addition valve 230 is opened and the pump 220 is reversely rotated for a predetermined time. As a result, the urea water remaining in the urea addition valve 230 and the supply passage 240 is collected in the tank 210.

  In the present embodiment, NOx purification performance at the time of starting the engine is ensured by performing addition at the time of injecting urea water after the engine is stopped. Hereinafter, with reference to FIG. 2 as well, the procedure of the stop-time urea addition process for performing the stop-time addition will be described. The stop urea addition process is executed by the controller 80.

  When this process is started, it is first determined whether or not the automatic stop of the engine 1 has started (S100). Then, when the automatic stop is not started (S100: NO), this process is ended.

  On the other hand, when the automatic stop is started (S100: YES), it is determined whether or not the second exhaust temperature TH2 detected immediately before the start of the automatic stop is equal to or higher than the threshold value α (S110). The threshold α is set to a value that can determine whether or not the temperature in the exhaust passage 26 is a temperature at which urea water vaporizes.

When the second exhaust temperature TH2 is less than the threshold value α (S110: NO), this process is terminated.
On the other hand, when the second exhaust temperature TH2 is equal to or higher than the threshold value α (S110: YES), the stop addition amount TS is set based on the second exhaust temperature TH2. The stop addition amount TS is the amount of urea water per unit time injected from the urea addition valve 230 after the engine is stopped. And, as the temperature in the exhaust passage 26 is higher, the injected urea water is more easily vaporized. Therefore, as shown in FIG. 3, the stop addition amount TS increases as the second exhaust temperature TH2 is higher. In this way, the stop addition amount TS is variably set.

Next, the set stop-time addition amount TS is injected from the urea addition valve 230, whereby stop-time addition while the engine is stopped is executed (S130).
Next, it is determined whether or not the total addition amount TSA is equal to or greater than the stop determination value S (S140). The total addition amount TSA is the total amount of urea water injected from the urea addition valve 230 in the stop addition, and the addition amount per unit time is integrated over time during the stop addition execution period. Is calculated by Further, the stop determination value S indicates whether or not the total addition amount TSA is increased to a certain extent that ammonia slip (ammonia generated from the urea water passes through the ammonia oxidation catalyst 51 and is released to the atmosphere) may occur. It is a value that can be determined, and an appropriate value is set through a prior experiment or the like.

  When the total addition amount TSA is equal to or greater than the stop determination value S (S140: YES), ammonia slip may occur if the stop addition is continued any more, so the stop addition is terminated (S160), This process is terminated.

  On the other hand, when the total addition amount TSA is less than the stop determination value S (S140: NO), it is determined whether or not at least one of the following condition (A) and condition (B) is satisfied (S150).

(A) The second exhaust temperature TH2 is lower than the low temperature determination value A, which is the temperature at which the purification function of the SCR catalyst 41 is lowered.
(B) Engine start has started.

When neither the condition (A) nor the condition (B) is satisfied (S150: NO), the process returns to step S130 and the addition at the stop is continued.
On the other hand, when at least one of the condition (A) and the condition (B) is satisfied (S150: NO), the addition at the time of stop is ended (S160), and this process is ended.

Next, the operation of this embodiment will be described.
First, urea water is injected after the engine is stopped. Therefore, unlike the conventional apparatus, the engine operation accompanying the injection of the reducing agent is not performed, so that deterioration of fuel consumption can be suppressed.

  In addition, the temperature in the exhaust passage 26 does not drop rapidly after the engine is stopped, and the temperature is often high enough to vaporize urea water until a certain period of time elapses. Therefore, the urea water injected after the engine stops is vaporized inside the exhaust passage 26 and then becomes ammonia and stays in the exhaust passage 26. When the engine is started, the NOx is purified by the ammonia retained in the exhaust passage 26. Further, when the engine is started, ammonia staying in the exhaust passage 26 reaches the SCR catalyst 41 together with the exhaust gas, and the SCR catalyst 41 purifies NOx. In this way, by injecting urea water after the engine is stopped, the amount of ammonia can be appropriately ensured prior to engine start, thereby ensuring NOx purification performance at the time of engine start.

  Further, the higher the temperature in the exhaust passage 26, the more easily the injected urea water is vaporized. Therefore, in the present embodiment, during stop addition performed after the engine is stopped, the urea water injection amount (stop addition amount TS) increases as the temperature in the exhaust passage 26 (second exhaust temperature TH2) increases. I have to. Therefore, more urea water is vaporized according to the temperature in the exhaust passage 26, and the NOx purification performance is more appropriately ensured.

  Further, when the engine is stopped, the flow of exhaust gas disappears. Therefore, when the urea water is injected after the engine is stopped, the urea water is difficult to reach the SCR catalyst 41 and the dispersion plate 60. In this respect, in this embodiment, since the injection hole of the urea addition valve 230 is opened toward the SCR catalyst 41, urea water is supplied to the SCR catalyst 41 even when there is no exhaust flow. Therefore, ammonia can be adsorbed to the SCR catalyst 41 even when the engine is stopped, and NOx can be purified using the adsorbed ammonia when the engine is started. When the elapsed time since the engine stop is short, the urea water injected from the urea addition valve 230 comes into contact with the high-temperature dispersion plate 60 and the SCR catalyst 41. Therefore, the amount of heat of the dispersion plate 60 and the SCR catalyst 41 is reduced. Urea water can be vaporized by using it.

  Further, in the engine 1 in which automatic stop and automatic start are performed, the number of engine stops tends to increase as compared with an engine that does not perform automatic stop and automatic start. Therefore, if the engine 1 is subjected to the engine stop delay process as in the conventional device described above, the number of executions of the delay process increases, and the fuel consumption tends to deteriorate. In this regard, in the present embodiment, when automatic stop is performed in the engine 1 in which the number of stoppages of the engine is likely to increase due to automatic stop and automatic start (positive determination in step S100 in FIG. 2), The urea water is injected (execution at the time of stoppage in step S130 in FIG. 2). Therefore, the fuel efficiency is further improved as compared with the conventional device that performs the engine stop delay process described above.

  Further, the engine 1 that is automatically stopped and automatically started is often restarted after a relatively short period of time after the automatic stop. In other words, after the engine is stopped, the temperature in the exhaust passage 26 is to some extent. Often restarted while expensive. Therefore, when addition at stop is performed after automatic stop, the injected urea water is often restarted after vaporizing and before droplet formation, and the injected urea water is effective for NOx purification. Can be used. Therefore, in the present embodiment, automatic stop is performed in the engine 1 that is automatically stopped and automatically started, that is, the engine 1 that is often restarted while the temperature in the exhaust passage 26 is high to some extent after the engine is stopped. The urea water is injected (added when stopped). Therefore, the injected urea water is effectively used for NOx purification.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea water injection from the urea addition valve 230 is performed after the engine is stopped. Therefore, since the engine operation accompanying the reducing agent injection is not performed, deterioration of fuel consumption can be suppressed.

  (2) The temperature in the exhaust passage 26 after the engine is stopped does not drop sharply, and is often in a high temperature state at which urea water can be vaporized until a certain period of time elapses. Therefore, the NOx purification performance at the time of starting the engine can be ensured even if urea water is injected after the engine is stopped.

  (3) The injection amount (addition amount TS at the time of stoppage) when performing urea water injection after the engine is stopped is variably set so as to increase as the temperature in the exhaust passage 26 increases. Therefore, the NOx purification performance is more appropriately ensured.

  (4) The injection hole of the urea addition valve 230 is opened toward the SCR catalyst 41. Therefore, urea water can be supplied to the SCR catalyst 41 even after the engine is stopped and there is no exhaust flow.

(5) The engine 1 is an engine that is automatically stopped and automatically started when a predetermined condition is established, and urea water is injected when the automatic stop is performed. Therefore, the fuel efficiency can be further improved as compared with the conventional device that performs the engine stop delay process described above. Further, the injected reducing agent can be effectively used for NOx purification.
(Second Embodiment)
Next, a second embodiment in which the exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied will be described with reference to FIG.

  When urea water is injected after the engine is stopped, if the injected urea water is not sufficiently atomized, the urea water is formed into droplets and vaporization is hindered. If the vaporization of urea water is inhibited in this way, the NOx purification performance may be reduced.

Further, since there is no exhaust flow after the engine is stopped, the urea water injected from the urea addition valve 230 is less likely to reach the SCR catalyst 41 compared to when the engine is operating.
Therefore, in this embodiment, when the urea water is injected after the engine is stopped, the injection pressure of the urea water is set higher than the injection pressure during the engine operation, and the urea water is intermittently injected. Only a part of the stop urea addition treatment shown in FIG. Hereinafter, the stop urea addition process of this embodiment will be described focusing on the differences from the stop urea addition process described in the first embodiment.

  In the stop urea addition process of the present embodiment, as shown in FIG. 4, when the process of step S120 of FIG. 2, that is, the setting of the stop addition amount TS based on the second exhaust temperature TH2, is completed, Stop injection pressure SP is set (S200). A pressure higher than the injection pressure of urea water during engine operation is set as the stop-time injection pressure SP. The injection pressure is increased by increasing the discharge pressure of the pump 220.

  Next, addition of urea water at the time of stop is performed at the stop-time injection pressure SP (S210), and the processing after step S140 in FIG. 2 is performed. In the stop addition in step S210, urea water is intermittently injected, that is, the urea addition valve 230 is repeatedly opened and closed in a short cycle.

Next, operations unique to the present embodiment will be described.
The urea water injection pressure at the time of stop addition is made higher than the urea water injection pressure during engine operation. As the injection pressure is increased, atomization of the urea water is promoted, so that formation of droplets of the urea water is suppressed, and more urea water is vaporized. Further, since the spraying distance of the urea water is increased by increasing the injection pressure, the urea water is likely to reach the SCR catalyst 41, and the urea water is further supplied to the SCR catalyst 41.

  In addition, the present inventor has confirmed that when the urea water is intermittently injected, the atomization of the urea water tends to be promoted as compared with the case of continuous injection. Therefore, the urea water is injected after the engine is stopped by intermittent injection. Therefore, atomization of urea water is promoted even when urea water is injected after the engine is stopped because there is no flow of exhaust gas and urea water is difficult to atomize.

As described above, according to the present embodiment, in addition to the effects (1) to (5), the following effects can be further obtained.
(6) When the urea water is injected after the engine is stopped, the injection pressure of the urea water is set higher than the injection pressure during engine operation. Therefore, more urea water can be vaporized.

  (7) The injection hole of the urea addition valve 230 is opened toward the SCR catalyst 41. When the urea water is injected after the engine is stopped, the injection pressure of the urea water is set higher than the injection pressure during engine operation. Therefore, in the urea water injection after the engine is stopped, the spray distance of the urea water becomes long, and the urea water can be further supplied by the SCR catalyst 41.

(8) When the urea water is injected after the engine is stopped, the urea water is intermittently injected. Therefore, atomization of urea water can be promoted also by this.
(Third embodiment)
Next, a third embodiment in which the exhaust gas purification apparatus for an internal combustion engine according to the present invention is embodied will be described with reference to FIG.

In the exhaust purification system of the first embodiment, the urea water recovery control described above is performed in order to suppress freezing of the urea water in the urea addition valve 230 and the supply passage 240.
When the urea water is recovered in this way, exhaust gas and air are sucked into the urea addition valve 230 and the supply passage 240. Therefore, when injecting urea water after performing recovery control, it is necessary to fill the urea addition valve 230 and the supply passage 240 with urea water, and filling of the urea water into the urea addition valve 230 and the supply passage 240 is completed. Until then, a sufficient amount of urea water cannot be supplied into the exhaust passage 26. Therefore, there is a possibility that the NOx purification performance is lowered until the filling of the urea water is completed.

  Therefore, in the present embodiment, as shown in FIG. 5, a determination process for determining whether or not the urea water recovery control can be performed is performed to suppress a decrease in NOx purification performance during the urea water filling period. . This process is executed by the control device 80. Incidentally, in the present embodiment, the determination process is applied to the exhaust purification device of the first embodiment, but can also be applied to the exhaust purification device of the second embodiment.

When this process is started, it is first determined whether or not at least one of the following condition (C) and condition (D) is satisfied (S300).
(C) The automatic stop time AST, which is an elapsed time since the start of the automatic stop, is equal to or greater than the determination time TA.

(D) The ignition switch 25 is turned off.
The automatic stop time AST is measured by the control device 80 until the automatic start is performed after the automatic stop of the engine 1 is started. In addition, the determination time TA is set to a time until the temperature becomes low enough to freeze the urea water after the engine is stopped, and more preferably the engine water temperature, the exhaust temperature, or the outside air temperature when the engine is stopped. A more optimal time is set by variably setting according to the above.

Then, when at least one of the condition (C) and the condition (D) is satisfied (S300: YES), urea water recovery control is executed (S310), and this process ends.
On the other hand, when neither the condition (C) nor the condition (D) is satisfied (S300: NO), the urea water recovery control is prohibited (S320), and this process is terminated.

Next, operations unique to the present embodiment will be described.
If the engine stop time is short, freezing of urea water can be suppressed by engine heat or exhaust heat. Conversely, if the engine stop time is long, the possibility of the urea water freezing increases. Therefore, it is not necessary to recover urea water when the engine stop time is short, and if the urea water is not recovered, the above-described filling of urea water is not necessary. There is no reduction in purification performance.

  Therefore, when the automatic engine stop time AST is equal to or longer than the predetermined determination time TA, the urea water is collected. Accordingly, when the automatic stop time AST is shorter than the determination time TA and the possibility of freezing urea water is low, urea water is not collected. Therefore, the recovery frequency of urea water can be suppressed, thereby suppressing a decrease in NOx purification performance during the urea water filling period.

  The urea water is also collected when the ignition switch 25 is turned off. Accordingly, urea water is not collected during the automatic stop of the engine 1 whose engine stop time tends to be relatively short. Therefore, by setting the above condition (D), the urea water recovery frequency can be suppressed, thereby suppressing the NOx purification performance from being lowered during the urea water filling period.

As described above, according to the present embodiment, in addition to the effects (1) to (5), the following effects can be further obtained.
(9) The urea water is collected when the automatic stop time AST of the engine 1 is equal to or greater than the determination time TA. Therefore, the recovery frequency of urea water can be suppressed, and this makes it possible to suppress a decrease in NOx purification performance during the urea water filling period.

  (10) The urea water is also collected when the ignition switch 25 of the engine 1 is turned off. Therefore, in this case as well, the recovery frequency of the urea water can be suppressed, and thereby the decrease in the NOx purification performance during the urea water filling period can be suppressed.

In addition, each said embodiment can also be changed and implemented as follows.
In the first embodiment, in step S110 of FIG. 2, it is determined whether or not the temperature in the exhaust passage 26 is a temperature at which urea water is vaporized. However, immediately after the engine is stopped, there is a high possibility that the temperature in the exhaust passage 26 is adjacent to the temperature at which the urea water vaporizes. Therefore, the process of step S110 can be omitted more simply.

  -In 2nd Embodiment, when performing addition at the time of a stop, the high injection pressure and intermittent injection were performed. In addition, the injection pressure may be increased and urea water may be continuously injected instead of intermittent injection. Alternatively, the intermittent injection of urea water may be performed without increasing the injection pressure.

In the third embodiment, only the condition (C) may be determined or only the condition (D) may be determined in step S300 illustrated in FIG.
The injection hole of the urea addition valve 230 was opened toward the SCR catalyst 41. In addition, the present invention can be applied even if the injection hole is not opened toward the SCR catalyst 41, for example, the injection hole is directed toward the inner wall of the exhaust passage. Even in this case, effects other than the above (4) and (7) can be obtained.

Although the second exhaust temperature TH2 is detected by the sensor, it may be estimated based on the engine operating state.
When recovering urea water from the supply passage 240, the pump 220 is rotated in the reverse direction. However, recovery may be performed in other modes. For example, a switching valve or the like that changes the flow direction of urea water in the supply passage 240 may be provided in the supply passage 240.

Although urea water is used as the reducing agent, other liquid reducing agents may be used.
The engine 1 in each embodiment is an internal combustion engine in which automatic stop and automatic start are performed. However, the present invention can also be applied to an exhaust gas purification apparatus for an internal combustion engine in which such automatic stop and automatic start are not performed. it can.

  When the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine in which automatic stop and automatic start are not performed, the engine stop is performed instead of determining whether or not the automatic stop is started in step S100 of FIG. It is determined whether or not For example, it may be determined whether or not the ignition switch 25 is turned off. Further, in step S300 of FIG. 5, the condition (C) that “the automatic stop time AST is equal to or greater than the determination time TA” is omitted. Even in such a modification, effects other than the above (5) and (9) can be obtained.

  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 (8)

In an exhaust gas purification apparatus for an internal combustion engine, comprising an NOx purification catalyst that purifies NOx by supplying a reducing agent, and a reducing agent injection valve that injects the reducing agent into an exhaust passage.
An exhaust emission control device for an internal combustion engine, wherein the reducing agent is injected from the reducing agent injection valve after the engine is stopped. The exhaust purification device for an internal combustion engine according to claim 1, wherein an injection pressure of the reducing agent when performing the reducing agent injection is higher than an injection pressure during engine operation. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the reducing agent is intermittently injected. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, wherein the reducing agent injection amount when performing the reducing agent injection is variably set so as to increase as the temperature in the exhaust passage increases. . The exhaust purification device of the internal combustion engine according to any one of claims 1 to 4, wherein an injection hole of the reducing agent injection valve is opened toward the NOx purification catalyst. The internal combustion engine is an engine that is automatically stopped and automatically started when a predetermined condition is satisfied, and performs the reducing agent injection when the automatic stop is performed. An exhaust gas purification apparatus for an internal combustion engine as described. A supply passage for supplying a reducing agent to the reducing agent injection valve, and a recovery means for recovering the reducing agent from the supply passage,
The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the recovery means recovers the reducing agent when the engine stop time exceeds a predetermined time. A supply passage for supplying a reducing agent to the reducing agent injection valve, and a recovery means for recovering the reducing agent from the supply passage,
The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the recovery means recovers the reducing agent when an ignition switch of the internal combustion engine is turned off.