JP2013113195A - 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, capable of suppressing suction of exhaust gas into a reducing agent supply mechanism as much as possible.SOLUTION: An engine 1 includes a urea water supply mechanism 200 having: a supply passage 240 for supplying urea water into an exhaust passage 26; and a pump 220 for recovering the urea water from the supply passage 240 after stopping the engine. A control device 80 changes the recovering time in such a manner that the higher the exhaust gas temperature in the stop of the engine is, the longer the time between the stop of the engine and the start of recovery of reducing agent becomes.

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 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 NOx purification 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 such freezing 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 2010-84694 A

By the way, when the reducing agent is recovered after the engine is stopped, the exhaust gas remaining in the exhaust passage is also sucked into the reducing agent supply mechanism, which may reduce the quality of the reducing agent.
The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust gas purification apparatus for an internal combustion engine that can suppress the intake of exhaust gas into the reducing agent supply mechanism as much as possible.

In the following, means for achieving the above object and its effects are described.
According to the first aspect of the present invention, there is provided an exhaust gas for an internal combustion engine having a reducing agent supply mechanism having a supply passage for supplying a liquid reducing agent to exhaust gas and a recovery means for collecting the reducing agent from the supply passage after the engine is stopped. The gist of the purifying apparatus is that the time from when the engine is stopped to when the recovery of the reducing agent is started is changed based on the exhaust temperature when the engine is stopped.

  When the reducing agent is recovered immediately after the engine is stopped, the reducing agent is recovered every time the engine is stopped, so that the frequency of suction of exhaust gas into the reducing agent supply mechanism is increased. In particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust becomes very high.

  Here, the possibility of freezing of the reducing agent after the engine is stopped decreases as the exhaust temperature when the engine is stopped is higher. Therefore, the higher the exhaust temperature when the engine is stopped, the longer the time from when the engine is stopped until the recovery of the reducing agent is started. That is, the higher the exhaust temperature when the engine is stopped, the later the recovery timing of the reducing agent after the engine is stopped. When the engine is restarted earlier than the recovery timing, the reducing agent is not recovered, so that exhaust is not sucked into the reducing agent supply mechanism.

  Therefore, in this configuration, the recovery timing of the reducing agent after the engine is stopped is changed based on the exhaust temperature when the engine is stopped, thereby increasing the chance that the reducing agent is not recovered by restarting the engine. In other words, the exhaust suction frequency is made low. Therefore, in particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust gas is very low compared to the conventional device.

Therefore, according to this configuration, it is possible to suppress the intake of exhaust gas into the reducing agent supply mechanism as much as possible while suppressing freezing 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 time from when the engine is stopped until the recovery of the reducing agent is started becomes longer as the exhaust gas temperature is higher. The gist is to be done.

  As described above, the possibility of freezing of the reducing agent after the engine is stopped becomes lower as the exhaust temperature when the engine is stopped is higher. Therefore, as the exhaust gas temperature is higher, the time from when the engine is stopped until recovery of the reducing agent is started is lengthened as the exhaust temperature is higher. The recovery timing of the reducing agent can be delayed as much as possible, thereby increasing the chance that the recovery of the reducing agent is not executed by restarting the engine.

  According to a third aspect of the present invention, there is provided an exhaust gas for an internal combustion engine having a reducing agent supply mechanism having a supply passage for supplying a liquid reducing agent to exhaust gas and a recovery means for collecting the reducing agent from the supply passage after the engine is stopped The purport of the purifying apparatus is that the recovery of the reducing agent is started when the temperature in the exhaust passage after the engine stops becomes equal to or lower than a predetermined temperature.

  As described above, when the reducing agent is recovered immediately after the engine is stopped, the reducing agent is recovered every time the engine is stopped, so that the frequency of suction of exhaust into the reducing agent supply mechanism is increased. In particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust becomes very high.

  Here, the possibility of freezing of the reducing agent after the engine is stopped becomes lower as the temperature in the exhaust passage after the engine is stopped is higher. Therefore, conversely, there is no need to start the recovery of the reducing agent until the temperature in the exhaust passage after the engine stops is lowered to some extent, and the recovery timing of the reducing agent after the engine stops is It can be slowed down to a certain degree. When the engine is restarted earlier than the recovery timing, the reducing agent is not recovered, so that exhaust is not sucked into the reducing agent supply mechanism.

  Therefore, in this configuration, the recovery of the reducing agent is started when the temperature in the exhaust passage after the engine stops becomes equal to or lower than the predetermined temperature, whereby the recovery of the reducing agent is performed by restarting the engine. Increasing the chance of disappearing, in other words, reducing the frequency of inhaling exhaust gas. Therefore, in particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust gas is very low compared to the conventional device.

Therefore, even with this configuration, it is possible to suppress the intake of exhaust gas into the reducing agent supply mechanism as much as possible while suppressing freezing of the reducing agent.
According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the third aspect, a temperature sensor for detecting the temperature in the exhaust passage is provided, and the engine is stopped at a predetermined energization cycle after the engine is stopped. The gist of the invention is to energize the temperature sensor to detect the temperature in the exhaust passage, and to stop energizing the temperature sensor until the next energization cycle after detecting the temperature.

  When the temperature in the exhaust passage after the engine is stopped is detected by the temperature sensor, it is necessary to energize the temperature sensor even after the engine is stopped, which increases power consumption while the engine is stopped. In this respect, in this configuration, the temperature sensor is energized at a predetermined energization cycle to detect the temperature, and after the temperature detection is completed, the energization to the temperature sensor is stopped until the next energization cycle. . That is, the temperature sensor is energized intermittently. Therefore, compared with the case where the temperature sensor is continuously energized, it is possible to suppress the power consumption when the engine is stopped.

  The predetermined temperature is preferably set to a temperature at which the reducing agent may freeze. Examples of the recovery means include a forward / reverse pump provided in the supply passage, and 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 collection process in the embodiment. The graph which shows the relationship between the 2nd exhaust temperature in the same embodiment, and a counter determination value. The flowchart which shows the procedure of the collection process in 2nd Embodiment. The flowchart which shows the procedure of the collection process in 3rd Embodiment. The timing chart which shows the electricity supply state of the temperature sensor in the 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. 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) 80a, a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, and a timer counter 80b. The microcomputer is mainly configured with an input interface and an output interface. Note that power is supplied from the battery to each of the CPU 80a, the timer counter 80b, and the various sensors described above.

  Then, the controller 80 controls, for example, the fuel injection amount control / fuel injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, the discharge pressure control of the supply pump 10, and the drive amount of the actuator 17 that opens and closes the intake throttle valve 16. Various controls of the engine 1 such as control and opening control of the EGR valve 15 are performed. The exhaust gas purification control such as the regeneration process for burning the PM collected by the filter 32 is also performed by the controller 80.

  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, urea water addition is also stopped. However, if urea water remains in the supply passage 240 of the urea water supply mechanism or the urea addition valve 230, There is a possibility that the supply passage 240 and the urea addition valve 230 may be damaged due to an increase in volume due to freezing of the urea water. Therefore, in order to suppress such freezing of urea water, the control device 80 performs recovery control for recovering urea water from the urea addition valve 230 and the supply passage 240 after the engine is stopped.

  However, when such urea water is recovered after the engine is stopped, the exhaust gas remaining in the exhaust passage 26 is also sucked into the urea water supply mechanism 200, and the quality of the urea water may be deteriorated. In particular, if urea water is collected immediately after the engine is stopped, urea water is collected every time the engine is stopped when the engine is started and stopped repeatedly in a short time. The frequency of sucking exhaust into the mechanism 200 is very high.

  Therefore, in the present embodiment, the collection process shown in FIG. 2 is executed in order to suppress such exhaust suction, and more specifically, to suppress the exhaust suction frequency. This collection process is executed by the control device 80.

When this process is started, it is first determined whether or not it is immediately after the engine is stopped (S100). If not immediately after the engine is stopped (S100: NO), this process is terminated.
On the other hand, when it is immediately after the engine is stopped (S100: YES), the counter determination value KH is set based on the second exhaust temperature TH2 when the engine is stopped (S110). The counter determination value KH is a value corresponding to the time required for the temperature around the urea addition valve 230 to decrease to the freezing danger temperature DA after the engine is stopped. The freezing temperature DA is a temperature at which urea water may freeze. As shown in FIG. 3, the counter determination value KH is set to a larger value as the second exhaust temperature TH2 when the engine is stopped is higher.

  When the counter determination value KH is set in this way, it is determined whether or not the post-stop counter KS indicating the elapsed time after the engine stop is equal to or greater than the counter determination value KH (S120). Then, the determination process in step S120 is repeated until the post-stop counter KS becomes equal to or greater than the counter determination value KH.

  If it is determined in step S120 that the post-stop counter KS has become equal to or greater than the counter determination value KH (S120: YES), the urea water recovery control is executed (S130). . 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.

Then, when the execution of the collection control is completed, energization to the CPU 80a, the second exhaust temperature sensor 120, etc. is stopped (S140), and this process is terminated.
Next, the operation of this embodiment will be described.

  The possibility of freezing urea water after the engine is stopped decreases as the exhaust temperature when the engine is stopped is higher. Therefore, the higher the exhaust temperature when the engine is stopped, the longer the time from the stop of the engine until the start of the recovery of urea water. That is, the higher the exhaust gas temperature when the engine is stopped, the more the urea water is not frozen even if the recovery timing of the urea water after the engine is stopped is delayed. Then, when the engine is restarted earlier than the recovery timing, urea water is not recovered, so that exhaust gas is not sucked into the urea water supply mechanism 200.

  Therefore, in this embodiment, the recovery timing of urea water after the engine is stopped is changed based on the exhaust temperature when the engine is stopped. More specifically, the counter determination value KH is set based on the second exhaust temperature TH2 when the engine is stopped, and the collection control is started when the counter KS after the stop becomes equal to or greater than the counter determination value KH. This increases the chance that urea water is not recovered by restarting the engine, in other words, the frequency of intake of exhaust gas is reduced. Therefore, in particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust gas is very low compared to the conventional device.

  Since the collection control is started when the counter KS after the stop becomes equal to or greater than the counter determination value KH, a certain amount of time has elapsed since the engine stop when the counter determination value KH is set to a certain large value. After that, the collection control is started. When recovery control is started after a certain amount of time has passed in this way, there is a high possibility that the exhaust gas in the exhaust passage 26 is diluted with air at the start of the recovery control. For this reason, the amount of exhaust gas sucked into the urea water supply mechanism 200 at the time of executing the recovery control is also reduced.

  Further, the higher the second exhaust temperature TH2 when the engine is stopped, the greater the counter determination value KH. Therefore, the time from when the engine is stopped to when the urea water recovery is started becomes longer as the second exhaust temperature TH2 is higher. As a result, the urea water recovery timing after the engine is stopped can be delayed as much as possible while suppressing the freezing of the urea water, so that the opportunity for non-execution of urea water recovery by restarting the engine increases.

As described above, according to the present embodiment, the following effects can be obtained.
(1) A counter determination value KH is set based on the second exhaust temperature TH2 when the engine is stopped, and recovery control is executed when the counter KS after the stop becomes equal to or greater than the counter determination value KH. That is, the time from when the engine is stopped to when the urea water recovery is started is changed based on the second exhaust temperature YH2 when the engine is stopped. For this reason, the opportunity for the urea water to be not recovered by restarting the engine is increased, in other words, the frequency of intake of exhaust gas is reduced. Therefore, the suction of the exhaust gas into the urea water supply mechanism 200 can be suppressed as much as possible while suppressing the freezing of the urea water.

(2) The counter determination value KH increases as the second exhaust temperature TH2 when the engine is stopped is higher. That is, the time from when the engine is stopped to when the recovery of urea water is started is made longer as the second exhaust temperature TH2 is higher. Therefore, the urea water recovery timing after the engine stop can be delayed as much as possible while suppressing the freezing of the urea water, thereby increasing the chance that the urea water recovery is not executed by restarting the engine. .
(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.

  As described above, when the urea water is recovered immediately after the engine is stopped, the urea water is recovered every time the engine is stopped. Therefore, the frequency of sucking the exhaust gas into the urea water supply mechanism 200 is increased. In particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust becomes very high.

  Here, the possibility of freezing of urea water after the engine is stopped decreases as the temperature in the exhaust passage 26 after the engine stops increases. Therefore, conversely, it is not necessary to start the recovery of the urea water until the temperature in the exhaust passage 26 after the engine stops is lowered to some extent, and the recovery timing of the urea water after the engine stops is the timing in the exhaust passage 26. It can be slowed until the temperature is lowered to some extent. Then, when the engine is restarted earlier than the recovery timing, urea water is not recovered, so that exhaust gas is not sucked into the urea water supply mechanism 200.

  Therefore, in the present embodiment, instead of setting the counter determination value KH, the recovery of urea water is started when the temperature in the exhaust passage 26 after the engine stops becomes equal to or lower than a predetermined temperature. The conditions for starting the execution of the collection control are different from those in the first embodiment.

Hereinafter, with reference to FIG. 4, the collection process in the present embodiment will be described. The collection process shown in FIG. 4 is repeatedly executed by the control device 80 at predetermined intervals.
When this process is started, it is first determined whether or not the engine is stopped (S200). When the engine is not stopped (S200: NO), this process is temporarily terminated.

  On the other hand, when the engine is stopped (S200: YES), it is determined whether the current temperature in the exhaust passage 26, that is, the currently detected second exhaust temperature TH2 is equal to or lower than the determination temperature FT (S210). . As the determination temperature FT, the above-described freezing danger temperature DA is set. When the second exhaust temperature TH2 is higher than the determination temperature FT (S210: NO), this process is temporarily terminated.

  On the other hand, when the second exhaust temperature TH2 is equal to or lower than the determination temperature FT (S210: YES), the urea water recovery control similar to step S130 is executed (S220). Then, when the execution of the collection control is completed, the energization to the CPU 80a, the second exhaust temperature sensor 120, etc. is stopped (S230), and this process is temporarily terminated.

Next, the operation of this embodiment will be described.
When the temperature in the exhaust passage 26 after the engine is stopped (second exhaust temperature TH2) becomes equal to or lower than the determination temperature FT, the recovery of urea water is started, so the recovery control is started immediately after the engine is stopped. As compared with, the recovery timing of urea water after engine stop is delayed. This increases the chance that urea water is not recovered by restarting the engine, in other words, the frequency of intake of exhaust gas is reduced. Therefore, in particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust gas is very low compared to the conventional device.

  Note that since the recovery control is started when the second exhaust temperature TH2 becomes equal to or lower than the determination temperature FT, if the second exhaust temperature TH2 when the engine is stopped is high to some extent, it takes a long time from the engine stop. After the elapse of time, the collection control is started. When recovery control is started after a certain amount of time has passed in this way, there is a high possibility that the exhaust gas in the exhaust passage 26 is diluted with air at the start of the recovery control. For this reason, the amount of exhaust gas sucked into the urea water supply mechanism 200 at the time of executing the recovery control is also reduced.

As described above, according to the present embodiment, the following effects can be obtained.
(1) The urea water recovery control is executed when the temperature in the exhaust passage 26 (second exhaust temperature TH2) after the engine stops becomes equal to or lower than the determination temperature FT. For this reason, the opportunity for the urea water to be not recovered by restarting the engine is increased, in other words, the frequency of intake of exhaust gas is reduced. Therefore, the suction of the exhaust gas into the urea water supply mechanism 200 can be suppressed as much as possible while suppressing the freezing of the urea water.
(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 the recovery process of the second embodiment, after the engine is stopped, the second exhaust temperature TH2 detected by the second exhaust temperature sensor 120 is compared with the determination temperature FT. As described above, in order to detect the second exhaust temperature TH2 even after the engine is stopped, it is necessary to energize the second exhaust temperature sensor 120 even after the engine is stopped, which increases power consumption while the engine is stopped.

  Therefore, in the present embodiment, the second exhaust temperature sensor 120 is energized at a predetermined energization cycle to detect the second exhaust temperature TH2, and after the temperature detection is finished, the second exhaust temperature TH2 is detected until the next energization cycle. The power supply to the temperature sensor 120 is stopped. That is, by intermittently energizing the second exhaust temperature sensor 120, power consumption during engine stoppage is suppressed as compared to the case where the second exhaust temperature sensor 120 is continuously energized.

Hereinafter, with reference to FIG. 5 and FIG. 6, the collection processing in the present embodiment will be described. The collection process shown in FIG. 5 is repeatedly executed by the control device 80 at predetermined intervals.
When this process is started, it is first determined whether or not the engine is stopped (S300). When the engine is not stopped (S300: NO), this process is temporarily terminated.

  On the other hand, when the engine is stopped (S300: YES), it is determined whether the post-stop counter KS is equal to or greater than the reliability limit value L (S310). The post-stop counter KS is the same as the post-stop counter KS described in the first embodiment, and is a value indicating the elapsed time after the engine stops. Here, the post-stop counter KS is measured by the timer counter 80b, but the post-stop counter KS has a maximum value corresponding to the number of bits prepared. Therefore, if the elapsed time after the engine stop becomes very long, the value of the counter KS after the stop reaches the maximum value, and thereafter, the value of the counter KS after the stop becomes the maximum value, or the counter after the stop The value of KS is reset. Therefore, after the value of the counter KS after stop reaches the maximum value, the measurement of the elapsed time after the engine stops becomes inaccurate, and the reliability of the counter KS after stop decreases. Therefore, in step S310, it is determined whether or not the current value of the counter KS after stopping is a highly reliable value before reaching the maximum value. More specifically, a value slightly smaller than the maximum value of the post-stop counter KS is set as the reliability limit value L, and it is determined whether or not the post-stop counter KS is equal to or greater than the reliability limit value L. .

  When the post-stop counter KS is equal to or greater than the reliability limit value L (S310: YES), the urea water recovery control similar to step S220 is executed (S380). When the execution of the collection control is completed, the power supply to the CPU 80a is stopped (S390), and this process is temporarily terminated.

  On the other hand, when the after-stop counter KS is less than the reliability limit value L (S310: NO), it is determined that the reliability of the after-stop counter KS is high, and in the next step S320, the above-described energization cycle is determined. .

  In step S320, it is determined whether or not the current post-stop counter KS is a value obtained by adding a predetermined value A to the previous counter value KP. The predetermined value A is a value corresponding to the energization cycle, and is set to a value that can suppress the energization to the second exhaust temperature sensor 120 as much as possible while appropriately securing the measurement cycle of the second exhaust temperature TH2. ing. The previous counter value KP is a value with an initial value “0”, and is updated when the next step S330 is performed. The previous counter value KP is the value of the counter KS after stop when the second exhaust temperature sensor 120 is energized last time. Therefore, when an affirmative determination is made in step S320, that is, when the current post-stop counter KS is a value obtained by adding the predetermined value A to the previous counter value KP, the second exhaust temperature sensor 120 is energized last time. Thus, the time corresponding to the predetermined value A has elapsed.

When the current post-stop counter KS is not a value obtained by adding the predetermined value A to the previous counter value KP (S320: NO), this process is temporarily terminated.
On the other hand, when the current post-stop counter KS is a value obtained by adding the predetermined value A to the previous counter value KP (S320: YES), the current post-stop counter KS value is stored in the control device 80 as the previous counter value KP. As a result, the previous counter value KP is updated.

  Next, energization of the second exhaust temperature sensor 120 is started (S340), and when the second exhaust temperature TH2 is read (S350), the energization of the second exhaust temperature sensor 120 is stopped (S360). ).

  Then, it is determined whether or not the second exhaust temperature TH2 read in step S350, that is, the current temperature in the exhaust passage 26 is equal to or lower than the determination temperature FT (S370). This determination temperature FT is the same as the determination temperature FT described in the second embodiment. When the second exhaust temperature TH2 is higher than the determination temperature FT (S370: NO), this process is temporarily terminated.

  On the other hand, when the second exhaust temperature TH2 is equal to or lower than the determination temperature FT (S370: YES), urea water recovery control is executed (S380). When the execution of the collection control is completed, the power supply to the CPU 80a is stopped (S390), and this process is temporarily terminated.

Next, the operation of this embodiment will be described with reference to FIG.
First, in this embodiment as well, as in the second embodiment, the recovery of urea water is started when the temperature in the exhaust passage 26 (second exhaust temperature TH2) after the engine stops becomes equal to or lower than the determination temperature FT. Therefore, the same operation as in the second embodiment can be obtained. That is, the recovery timing of urea water after the engine is stopped is delayed as compared with the case where the recovery control is started immediately after the engine is stopped. This increases the chance that urea water is not recovered by restarting the engine, in other words, the frequency of intake of exhaust gas is reduced. Therefore, in particular, when the engine is started and stopped repeatedly in a short time, the frequency of intake of exhaust gas is very low compared to the conventional device.

  Further, when the second exhaust temperature TH2 when the engine is stopped is high to some extent, the recovery control is started after a certain long time has passed since the engine stopped. When recovery control is started after a certain amount of time has passed in this way, there is a high possibility that the exhaust gas in the exhaust passage 26 is diluted with air at the start of the recovery control. For this reason, the amount of exhaust gas sucked into the urea water supply mechanism 200 at the time of executing the recovery control is also reduced.

  Further, as shown in FIG. 6, every time the post-stop counter KS becomes a value obtained by adding a predetermined value A to the previous counter value KP (time t2, time t3, time t4) while the engine is stopped, the next processing is performed. Done. That is, energization to the second exhaust temperature sensor 120 is started, and when the second exhaust temperature TH2 is read, the energization to the second exhaust temperature sensor 120 is stopped. That is, the energization of the second exhaust temperature sensor 120 is intermittently performed. Therefore, as indicated by a two-dot chain line L1 in FIG. 6, the power consumption during the engine stop is suppressed as compared with the case where the second exhaust temperature sensor 120 is continuously energized while the engine is stopped.

As described above, according to the present embodiment, the following effect (2) can be obtained in addition to the effect (1) described in the second embodiment.
(2) After the engine is stopped, the second exhaust temperature sensor 120 is energized at a predetermined energization cycle to detect the temperature in the exhaust passage 26. After the temperature is detected, the second exhaust gas is detected until the next energization cycle. The power supply to the temperature sensor 120 is stopped. Therefore, it becomes possible to suppress power consumption while the engine is stopped.

In addition, each said embodiment can also be changed and implemented as follows.
In the first embodiment, the second exhaust temperature TH2 is detected by the sensor, but may be estimated based on the engine operating state. Also in the second embodiment, the second exhaust temperature TH2 is detected by the sensor, but the second exhaust temperature TH2 is estimated based on the engine operating state until the engine is stopped and the elapsed time after the engine is stopped. You may do it.

  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 ... first Purifying member 51 ... Ammonia oxidation catalyst 60 ... Dispersion plate 80 ... Control device 80a ... Central processing control device (CPU) 80b ... Timer counter 100 ... First exhaust temperature sensor 110 ... Differential pressure sensor 120 ... Second exhaust temperature sensor, 130 ... first NOx sensor, 140 ... second NOx sensor, 200 ... urea water supply mechanism, 210 ... tank, 220 ... pump, 230 ... urea addition valve, 240 ... supply passage.

Claims (4)

An exhaust emission control device for an internal combustion engine comprising a supply passage for supplying a liquid reducing agent into an exhaust passage and a reducing agent supply mechanism having a recovery means for recovering the reducing agent from the supply passage after the engine is stopped.
An exhaust gas purification apparatus for an internal combustion engine, characterized in that the time from when the engine is stopped until recovery of the reducing agent is started is changed based on the exhaust temperature when the engine is stopped. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the time from when the engine is stopped until recovery of the reducing agent is started is increased as the exhaust temperature is higher. An exhaust purification device for an internal combustion engine comprising a supply passage for supplying a liquid reducing agent to exhaust and a reducing agent supply mechanism having a recovery means for recovering the reducing agent from the supply passage after the engine is stopped,
An exhaust gas purification apparatus for an internal combustion engine, characterized in that the recovery of the reducing agent is started when the temperature in the exhaust passage after the engine stops becomes equal to or lower than a predetermined temperature. A temperature sensor for detecting the temperature in the exhaust passage;
After the engine is stopped, the temperature sensor is energized at a predetermined energization cycle to detect the temperature in the exhaust passage, and after detecting the same temperature, the energization to the temperature sensor is stopped until the next energization cycle. The exhaust emission control device for an internal combustion engine according to claim 3.