JP2013096258A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, in which thermal damages on a reducing agent supply mechanism can be suppressed upon recovering a reducing agent after the engine is stopped.SOLUTION: An engine 1 is provided with an exhaust emission control device including a urea water supply mechanism having a supply passage 240 to supply urea water to the exhaust gas and a pump 220 to recover the urea water from the supply passage 240. A controller 80 controls recovery of the urea water by the pump 220 when the exhaust gas temperature after the engine is stopped decreases to a predetermined temperature or lower.

Description

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

  For example, as described in Patent Document 1, a selective reduction type NOx catalyst that purifies nitrogen oxides (NOx) in exhaust gas and a reducing agent that is used for NOx purification in the selective reduction type NOx catalyst are disposed in the exhaust passage. 2. Description of the Related Art An exhaust gas purification device for an internal combustion engine that includes a reducing agent supply mechanism that supplies gas to an internal combustion engine is known.

  In this exhaust purification device, urea water is injected from the supply passage of the reducing agent supply mechanism toward the exhaust passage. The injected urea water is hydrolyzed by the heat of the exhaust to become ammonia. This ammonia is supplied as a reducing agent to the selective reduction type NOx catalyst.

  By the way, when the engine operation is stopped, the supply of the reducing agent is also stopped. However, if the reducing agent remains in the supply passage of the reducing agent supply mechanism, the supply passage is caused by an increase in volume due to the freezing of the reducing agent. May be damaged.

  Therefore, in order to suppress the remaining of the reducing agent in the supply passage, the apparatus described in Patent Document 1 collects the reducing agent from the supply passage after the engine is stopped.

JP 2010-71270 A

  By the way, immediately after the engine is stopped, the temperature of the exhaust gas is relatively high. Therefore, when the reducing agent is recovered from the supply passage after the engine is stopped as in the conventional apparatus, high temperature exhaust gas is sucked into the supply passage during the recovery, which may cause thermal damage to the reducing agent supply mechanism. There is.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can suppress thermal damage of a reducing agent supply mechanism when the reducing agent is recovered after the engine is stopped. There is.

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 supply passage for supplying a liquid reducing agent to exhaust gas and a reducing agent supply mechanism having a recovery means for recovering the reducing agent from the supply passage. The gist of the present invention is that the reducing agent is recovered by the recovery means when the exhaust temperature after the engine stops becomes a predetermined temperature or lower.

  According to the configuration, the reducing agent is recovered by the recovery means after the exhaust temperature after the engine stops decreases to a predetermined temperature or lower. Accordingly, when the reducing agent is recovered after the engine is stopped, high temperature exhaust gas can be prevented from being sucked into the reducing agent supply mechanism, and thermal damage to the reducing agent supply mechanism can be suppressed. Examples of the collecting means in the same configuration include a pump provided in the supply passage and capable of forward and reverse rotation, and a switching valve provided in the supply passage to change the flow direction 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, the supply passage is provided with an addition valve for injecting a reducing agent into the exhaust passage, and the engine is stopped. In this case, the gist is to inject a predetermined amount of the reducing agent from the addition valve.

  According to this configuration, the reduction of the exhaust temperature is promoted by the vaporization of the reducing agent injected when the engine is stopped. Accordingly, the time until the exhaust temperature after the engine stops becomes equal to or lower than the predetermined temperature is shortened, and the reducing agent can be recovered earlier. If the recovery timing of the reducing agent can be advanced in this way, for example, there are the following merits.

  That is, in order to determine whether or not the exhaust gas temperature after engine stop has become equal to or lower than a predetermined temperature, it is necessary to energize the control device that performs such determination even after engine stop. However, since the alternator does not generate power while the engine is stopped, the amount of power stored in the battery that supplies power to the control device decreases. Further, when the number of times of charging / discharging increases due to such a decrease in the amount of stored electricity, deterioration of the battery is promoted. In this regard, in this configuration, the recovery timing of the reducing agent is accelerated, that is, the execution time of the determination process for determining whether or not the exhaust gas temperature is equal to or lower than the predetermined temperature is shortened. Thus, it is possible to suitably suppress a decrease in the amount of stored electricity and deterioration of the battery.

It is desirable that the reducing agent is injected from the addition valve when the exhaust temperature when the engine is stopped is higher than a predetermined temperature.
Further, the injection amount of the reducing agent from the addition valve is increased as the exhaust temperature when the engine is stopped is increased, as in the invention according to claim 4, whereby the injection amount of the reducing agent for cooling is increased. Can be suitably set.

  The determination as to whether or not the exhaust temperature after the engine has stopped is equal to or lower than a predetermined temperature can be made by comparing the actual exhaust temperature or the estimated exhaust temperature with the predetermined temperature. In addition, the exhaust temperature after the engine stops correlates with the elapsed time from the engine stop. Therefore, it is also possible to estimate a reduction time until the exhaust temperature after the engine stops becomes equal to or lower than a predetermined temperature, and to collect the reducing agent when this reduction time has elapsed.

  Therefore, as in the fifth aspect of the present invention, when the injection of the reducing agent is completed, the reduction time from the completion of the injection of the reducing agent from the addition valve until the exhaust temperature becomes equal to or lower than the predetermined temperature. The recovery agent recovery timing is also set appropriately by adopting a configuration in which the recovery agent recovery is performed when the reduction time has elapsed after the completion of the injection of the reducing agent. be able to.

  When the reducing agent is not injected when the engine is stopped, as in the sixth aspect of the present invention, a decrease from when the engine stops until the exhaust temperature falls below the predetermined temperature. By adopting a configuration in which the time is estimated based on the exhaust temperature when the engine is stopped and the reduction time is elapsed after the engine is stopped, the reducing agent recovery timing is appropriately set. Can be set.

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 collection process performed in the same embodiment. The flowchart which shows the procedure of the collection process performed in 2nd Embodiment. The graph which shows the relationship between the 2nd exhaust gas temperature and delay time in the same embodiment. The flowchart which shows the procedure of the collection process performed in 3rd Embodiment. The graph which shows the relationship between the 2nd exhaust temperature in the same embodiment, and the addition amount for cooling.

(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. 1 and 2.

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. A selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) 41 that reduces and purifies NOx in the exhaust using a reducing agent is disposed inside the second purification member 40.

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

  The 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 its injection hole is directed to the SCR catalyst 41. When the urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the supply passage 240.

  The pump 220 is an electric pump, and at the time of forward rotation, the urea water is fed from the tank 210 toward the urea addition valve 230. On the other hand, during reverse rotation, urea water is sent from the urea addition valve 230 toward the tank 210. In other words, during the reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the supply passage 240 and returned to the tank 210. 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, by this control device 80, for example, fuel injection amount control / fuel injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, discharge pressure control of the supply pump 10, and driving of the actuator 17 for opening and closing the intake throttle valve 16 Various controls of the engine 1 such as quantity control and opening control of the EGR valve 15 are performed. The exhaust gas purification control such as the regeneration process for burning the PM collected by the filter 32 is also performed by the controller 80.

  Further, the control device 80 performs urea water addition control by the urea addition valve 230 as one of exhaust purification control. In this addition control, 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. The urea water addition for NOx reduction is continuously performed during engine operation, and is stopped when the engine operation is stopped.

  By the way, when the engine operation is stopped as described above, the addition of urea water is also stopped. However, if urea water remains in the supply passage 240 of the urea water supply mechanism, the volume of the urea water due to freezing is reduced. The supply passage 240 may be damaged by the increase. Therefore, in order to suppress such residual urea water in the supply passage 240, the control device 80 performs recovery control for recovering urea water from the supply passage 240 after the engine is stopped.

  Here, immediately after the engine is stopped, the temperature of the exhaust gas is relatively high. Therefore, if urea water is recovered from the supply passage 240 immediately after the engine is stopped, high-temperature exhaust gas is sucked into the supply passage 240, and the urea water supply mechanism such as the supply passage 240 and the urea addition valve 230 may be thermally damaged. There is. Therefore, in the present embodiment, the recovery process shown in FIG. 2 is executed in order to suppress such thermal damage. This collection process is executed by the control device 80.

  When this processing is started, first, whether the vehicle speed SPD is “0” and the ignition switch is turned off, that is, the vehicle equipped with the engine 1 is stopped, and the engine 1 is stopped. It is determined whether or not it is immediately after (S100). Then, when the vehicle speed SPD is not “0” or the ignition switch is not turned off (S100: NO), this process ends.

  On the other hand, when the vehicle speed SPD is “0” and the ignition switch is turned off (S100: YES), the exhaust temperature upstream of the SCR catalyst 41, that is, the exhaust temperature around the urea addition valve 230 is close. It is determined whether or not the second exhaust temperature TH2 is lower than the permitted temperature A (S110). This permitted temperature A is the maximum value of the exhaust temperature that can suppress the above-described thermal damage, and is obtained in advance by a test or the like. Then, the determination process in step S110 is repeated until the second exhaust temperature TH2 becomes lower than the permitted temperature A.

  If it is determined in step S110 that the second exhaust temperature TH2 has become lower than the permitted temperature A due to a decrease in the exhaust temperature after the engine is stopped (S110: YES), the urea water recovery control described above is executed. Then (S120), this process ends. 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.

Next, the operation of this embodiment will be described.
In the urea water recovery process in the present embodiment, the urea water is not recovered immediately after the engine is stopped, but the urea water is recovered after the second exhaust temperature TH2 after the engine stops becomes lower than the permitted temperature A. Like to do. Therefore, when recovering urea water after the engine is stopped, high temperature exhaust gas can be prevented from being sucked into the urea water supply mechanism, and thermal damage to the urea water supply mechanism can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea water is recovered after the second exhaust temperature TH2 after the engine stops becomes lower than the permitted temperature A. Therefore, thermal damage to the urea water supply mechanism can be suppressed.
(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 FIGS.

  In the first embodiment, the recovery control is performed when the second exhaust temperature TH2 detected by the second exhaust temperature sensor 120 is lower than the permitted temperature A. In other words, the determination as to whether or not the exhaust temperature after the engine has stopped is equal to or lower than a predetermined temperature is made based on the actual exhaust temperature.

  In addition, the exhaust temperature after the engine stops correlates with the elapsed time from the engine stop. Therefore, even if the reduction time until the exhaust temperature after the engine stops becomes equal to or lower than the predetermined temperature is estimated, and the urea water recovery control is executed when this reduction time has elapsed, the urea water recovery timing is set appropriately. Thus, the occurrence of the thermal damage can be suppressed.

  In addition, the urea addition valve is provided at a position away from the exhaust temperature sensor, and if there is a difference between the detected value of the exhaust temperature sensor and the exhaust temperature around the urea addition valve, it is based on the actual exhaust temperature. There is a possibility that it is difficult to accurately determine the execution of the collection control. In this regard, when the above-described reduction time is estimated, if the difference between the detected value of the second exhaust temperature sensor 120 and the exhaust temperature around the urea addition valve 230 is taken into consideration, the execution determination of the recovery control is performed more accurately. The urea water recovery timing can be set appropriately.

  Therefore, in the present embodiment, a delay time DLY corresponding to the above-described decrease time is set, and recovery control is executed when the stop time ST indicating the elapsed time after the engine stop becomes equal to or greater than the delay time DLY. This point is different from the first embodiment. Therefore, hereinafter, the collection process in the present embodiment will be described focusing on the differences from the first embodiment.

The collection process of this embodiment shown in FIG. 3 is executed by the control device 80.
When this processing is started, first, whether the vehicle speed SPD is “0” and the ignition switch is turned off, that is, the vehicle equipped with the engine 1 is stopped, and the engine 1 is stopped. It is determined whether or not it is immediately after (S200). Then, when the vehicle speed SPD is not “0” or the ignition switch is not turned off (S200: NO), this process is terminated.

  On the other hand, when the vehicle speed SPD is “0” and the ignition switch is turned off (S200: YES), the delay time DLY is set based on the second exhaust temperature TH2 and the outside temperature THout when the engine is stopped. (S210). This delay time DLY is a time corresponding to the above-described decrease time, and is a time required for the exhaust temperature around the urea addition valve 230 to decrease to the allowable temperature A after the engine stops. As shown in FIG. 4, the delay time DLY is set to be longer as the second exhaust temperature TH2 when the engine is stopped is higher. Further, as indicated by the solid line L1 and the two-dot chain line L2, the delay time DLY is set to a longer time as the outside air temperature THout at the time of engine stop is higher even at the same second exhaust temperature TH2.

  When the delay time DLY is set in this way, it is determined whether or not the stop time ST indicating the elapsed time after the engine stop is equal to or longer than the delay time DLY (S220). This stop time ST is a time when measurement is started when the engine stops. Then, the determination process in step S220 is repeatedly performed until the stop time ST becomes equal to or longer than the delay time DLY.

  If it is determined in step S220 that the stop time ST has become equal to or greater than the delay time DLY (S220: YES), the urea water recovery control described above is executed (S230). This process is terminated. The collection control here is the same as the collection control described in the first embodiment.

Next, the operation of this embodiment will be described.
In the urea water recovery process in this embodiment, the delay time DLY is set to estimate the time from when the engine stops until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A. I am doing so. The urea water is collected when the stop time ST after the engine stops becomes equal to or longer than the delay time DLY. Therefore, when recovering urea water after the engine is stopped, high temperature exhaust gas can be prevented from being sucked into the urea water supply mechanism, and thermal damage to the urea water supply mechanism can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The time from when the engine stops until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A is set as the delay time DLY, and the stop time ST after the engine stops is delayed. The urea water is collected when the time DLY is exceeded. Therefore, the recovery timing of urea water can be set appropriately, and thermal damage to the urea water supply mechanism can be suppressed.

(2) Further, the time from when the engine is stopped until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A is estimated as the delay time DLY. Therefore, the urea addition valve 230 is provided at a position away from the second exhaust temperature sensor 120, and the second exhaust temperature TH2 that is a detection value of the second exhaust temperature sensor 120, the exhaust temperature around the urea addition valve 230, and Even when there is a difference, the recovery timing of urea water can be set appropriately.
(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 FIGS.

  In order to determine whether or not the exhaust temperature after the engine has stopped is equal to or lower than a predetermined temperature, it is necessary to energize the control device 80 that performs such determination even after the engine has stopped. However, since the alternator does not generate power while the engine is stopped, the amount of power stored in the battery that supplies power to the control device 80 decreases. Further, when the number of times of charging / discharging of the battery increases due to such a decrease in the amount of stored electricity, deterioration of the battery is promoted. Therefore, if the recovery time of the urea water is advanced, that is, if the execution time of the determination process for determining whether or not the exhaust gas temperature is equal to or lower than the predetermined temperature can be shortened, the energization time to the control device 80 is also shortened, A decrease in the amount and deterioration of the battery can be suitably suppressed. Therefore, in this embodiment, the urea temperature for cooling is added after the engine is stopped to quickly reduce the exhaust temperature, thereby shortening the execution time of the exhaust temperature determination process, thereby energizing the control device 80. I try to shorten the time.

  The collection process in the present embodiment can be realized by partially changing the collection process in the second embodiment. Therefore, hereinafter, the collection processing in the present embodiment will be described focusing on the differences from the second embodiment.

The collection process of the present embodiment shown in FIG.
When this processing is started, first, whether the vehicle speed SPD is “0” and the ignition switch is turned off, that is, the vehicle equipped with the engine 1 is stopped, and the engine 1 is stopped. It is determined whether or not it is immediately after (S300). Then, when the vehicle speed SPD is not “0” or the ignition switch is not turned off (S300: NO), this process ends.

  On the other hand, when the vehicle speed SPD is “0” and the ignition switch is turned off (S300: YES), it is determined whether the second exhaust temperature TH2 is equal to or higher than the permitted temperature A (S310). When the second exhaust temperature TH2 is lower than the permitted temperature A (S310: NO), the recovery control is immediately executed (S360) because there is no fear of thermal damage as described above. The collection control in step S360 is the same as the collection control described in the first embodiment.

  On the other hand, when the second exhaust temperature TH2 is equal to or higher than the permitted temperature A (S310: YES), the cooling addition amount is based on the second exhaust temperature TH2 when the engine is stopped in order to add the urea solution for cooling. CT is set (S320). As shown in FIG. 6, the cooling addition amount CT is increased as the second exhaust temperature TH2 when the engine is stopped is higher.

When the cooling addition amount CT is thus set, the set cooling addition amount CT is injected from the urea addition valve 230 (S330).
Next, the delay time DLY is set based on the second exhaust temperature TH2 and the outside air temperature THout when the urea water addition in step S330 is completed (S340). Here, the delay time DLY is set as a decrease time required until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A after the addition of the cooling urea water is completed. The delay time DLY here is also set longer as the second exhaust gas temperature TH2 is higher when the urea water addition in step S330 is completed, as shown in FIG. Further, as shown by the solid line L1 and the two-dot chain line L2, the delay time DLY becomes longer as the outside air temperature THout when the urea water addition in step S330 is completed is higher even at the same second exhaust temperature TH2. Set to

  When the delay time DLY is set in this way, it is determined whether or not the elapsed time PT after the addition of the cooling urea water is equal to or longer than the delay time DLY (S350). The elapsed time PT is a time when measurement is started when the urea water addition in step S330 is completed. The determination process in step S350 is repeated until the elapsed time PT becomes equal to or greater than the delay time DLY.

  If it is determined in step S350 that the elapsed time PT has become equal to or greater than the delay time DLY (S350: YES) due to the passage of time since the addition of the urea aqueous solution for cooling, the above-described recovery of the urea water is performed. Control is executed (S360), and this process is terminated.

Next, the operation of this embodiment will be described.
In the urea water recovery process in this embodiment, the urea water is temporarily injected immediately after the engine is stopped by performing the processes of step S320 and step S330. And the fall of the exhaust temperature around the urea addition valve 230 is accelerated | stimulated because this injected urea water vaporizes. Therefore, the time until the exhaust temperature after the engine stops becomes equal to or lower than the allowable temperature A is shorter, and in this embodiment, the delay time DLY set in step S340 is compared with the case where urea water is not added. Shorter. Therefore, it becomes possible to collect urine water at an earlier stage, that is, the collection timing of urea water can be advanced.

  Further, since the delay time DLY is set to a shorter time, the time required until an affirmative determination is made in step S350 is shortened, and thereby the energization time to the control device 80 is shortened. Therefore, a decrease in the amount of electricity stored in the battery and deterioration of the battery can be suitably suppressed.

  Further, the delay time DLY is estimated as the time from the completion of the addition of the cooling urea water to the time when the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A. Then, the urea water is collected when the elapsed time PT after the addition of the cooling urea water becomes equal to or longer than the delay time DLY. Therefore, when recovering urea water after the engine is stopped, high temperature exhaust gas can be prevented from being sucked into the urea water supply mechanism, and thermal damage to the urea water supply mechanism can be suppressed.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea water for cooling is added after the engine is stopped, and the time from when the urea water addition is completed until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A is set as the delay time DLY. Like to do. Then, the urea water is collected when the elapsed time PT after the addition of the urea water becomes equal to or longer than the delay time DLY. Therefore, the recovery timing of urea water can be set appropriately, and thermal damage to the urea water supply mechanism can be suppressed.

  (2) Also, the time from when the urea water addition is completed until the exhaust temperature around the urea addition valve 230 decreases to the permitted temperature A is estimated as the delay time DLY. Therefore, the urea addition valve 230 is provided at a position away from the second exhaust temperature sensor 120, and the second exhaust temperature TH2 that is a detection value of the second exhaust temperature sensor 120, the exhaust temperature around the urea addition valve 230, and Even when there is a difference, the recovery timing of urea water can be set appropriately.

  (3) When the engine is stopped, a predetermined amount of urea water is injected from the urea addition valve 230. Therefore, the time until the exhaust temperature after the engine stops becomes equal to or lower than the permitted temperature A is shortened, and the urea water can be recovered earlier.

(4) Further, when the collection process is executed, the energization time to the control device 80 is also shortened, so that it is possible to suitably suppress the decrease in the amount of charge of the battery and the deterioration of the battery.
(5) The injection amount of urea water (cooling addition amount CT) from the urea addition valve 230 is increased as the second exhaust temperature TH2 when the engine is stopped is increased. The injection amount of urea water can be set suitably.

In addition, each said embodiment can also be changed and implemented as follows.
In the first embodiment, the second exhaust temperature TH2 that is the detection value of the second exhaust temperature sensor 120 is compared with the permitted temperature A. In addition, as described in the second embodiment, when the second exhaust temperature TH2 and the exhaust temperature around the urea addition valve 230 are different, the vicinity of the urea addition valve 230 is based on the second exhaust temperature TH2. The exhaust temperature may be estimated and the estimated exhaust temperature may be compared with the permitted temperature A. The exhaust temperature around the urea addition valve 230 can be estimated based on the second exhaust temperature TH2 and the outside air temperature THout when the engine is stopped. The exhaust temperature around the urea addition valve 230 can also be estimated based on the second exhaust temperature TH2 and the outside air temperature THout immediately after the engine is stopped and the elapsed time after the engine is stopped.

  Even in the first embodiment, when an affirmative determination is made in step S100 of FIG. 2, the processing of steps S320 and S330 shown in FIG. 5 may be performed. In other words, urea water addition after the engine stop may be executed to promote a decrease in exhaust temperature.

  In the third embodiment, the target temperature A to be compared with the second exhaust temperature TH2 in step S310 in FIG. In addition, a temperature higher than the permitted temperature A may be set.

  In the third embodiment, it is determined in step S310 in FIG. 5 whether or not the second exhaust temperature TH2 is equal to or higher than a predetermined allowable temperature A. In addition, the process of step S310 may be omitted, and urea water for cooling may be always added immediately after the engine is stopped regardless of the second exhaust temperature TH2.

In the third embodiment, the cooling addition amount CT is variably set based on the second exhaust temperature TH2, but the cooling addition amount CT may be set to a predetermined constant amount more simply.
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.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Fuel addition valve, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, DESCRIPTION OF SYMBOLS 10 ... Supply pump, 11 ... Turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... Intake throttle valve, 17 ... Actuator, 18 ... Intercooler, 19 ... Air flow meter, 20 ... Throttle valve opening Degree sensor, 21 ... Engine rotation speed sensor, 22 ... Accelerator sensor, 23 ... Outside air temperature sensor, 24 ... Vehicle speed sensor, 25 ... Ignition switch, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... First purification member, 31 ... oxidation catalyst, 32 ... filter, 40 ... second purification member, 41 ... selective reduction type NOx catalyst (SCR catalyst, 50 ... third 51 ... ammonia oxidation catalyst, 60 ... dispersion plate, 80 ... control device, 100 ... first exhaust temperature sensor, 110 ... differential pressure sensor, 120 ... second exhaust temperature sensor, 130 ... first NOx sensor, 140 ... first 2NOx sensor, 200 ... urea water supply mechanism, 210 ... tank, 220 ... pump, 230 ... urea addition valve, 240 ... supply passage.

Claims (6)

An exhaust gas purification apparatus for an internal combustion engine comprising a supply passage for supplying a liquid reducing agent to exhaust gas and a reducing agent supply mechanism having a recovery means for recovering the reducing agent from the supply passage,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the reducing agent is recovered by the recovery means when the exhaust temperature after the engine stops becomes a predetermined temperature or lower. The addition valve for injecting a reducing agent into the exhaust passage is provided in the supply passage, and a predetermined amount of the reducing agent is injected from the addition valve when the engine is stopped. An exhaust purification device for an internal combustion engine. The exhaust emission control device for an internal combustion engine according to claim 2, wherein the injection of the reducing agent from the addition valve is performed when an exhaust temperature when the engine is stopped is higher than a predetermined temperature. The exhaust emission control device for an internal combustion engine according to claim 2 or 3, wherein the injection amount of the reducing agent from the addition valve is increased as the exhaust temperature when the engine is stopped is higher. A reduction time until the exhaust temperature becomes equal to or lower than the predetermined temperature after the injection of the reducing agent from the addition valve is estimated based on the exhaust temperature when the injection of the reducing agent is completed. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 4, wherein the reducing agent is recovered when the reduction time has elapsed after completion of injection. A reduction time until the exhaust temperature becomes equal to or lower than the predetermined temperature after the engine is stopped is estimated based on the exhaust temperature when the engine is stopped, and the reducing agent is recovered when the reduction time elapses after the engine is stopped. The exhaust emission control device for an internal combustion engine according to claim 1.

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