DE102012219613B4 - Emission control system of an internal combustion engine - Google Patents

Abstract

Emission control system for an internal combustion engine (1), with a reducing agent supply mechanism (200) which has a supply channel (240) through which a liquid reducing agent is passed into an exhaust gas channel (26), a collecting means (220) for collecting the reducing agent from the supply channel (26) after the internal combustion engine has stopped and comprises a urea addition valve (230) for injecting and supplying aqueous urea into the exhaust gas duct (26), and a regulator (80) which carries out a collection process by the collecting means (220), the regulator ( 80) a period of time (KH) from the stopping of the internal combustion engine (1) to the beginning of the collection of the reducing agent on the basis of the exhaust gas temperature (TH2) measured at the time the internal combustion engine (1) was stopped, characterized in that: the controller (80 ) changes the time span (KH) so that it is as long as or longer than a time span from the stopping of the internal combustion engine (1) to absent By setting a temperature around the urea addition valve (230) to a freezing risk temperature (DA) representing a temperature at which the aqueous urea solution is likely to freeze.

Description

The invention relates to an emissions control system for an internal combustion engine.

An emission control system of an internal combustion engine having a catalyst for removing NOx that removes nitrogen oxides (NOx) contained in exhaust gas and a reducing agent supply mechanism that supplies a reducing agent used for removing NOx in the catalyst into the exhaust passage is in Japanese Patent Laid-Open No. 2010-84694 ( JP 2010-84694 A ) disclosed.

In the emission control system, an aqueous urea solution is injected into the exhaust gas channel via a supply channel of the reducing agent supply mechanism. The urea aqueous solution injected in this way is hydrolyzed by the heat of the exhaust gases to produce ammonia. The ammonia produced in this way is fed to the catalytic converter as a reducing agent to remove NOx.

The supply of the reducing agent is stopped when the engine is stopped. If reducing agent remains in the supply channel of the reducing agent supply mechanism, the supply channel may be damaged if the reducing agent freezes and expands.

In order to prevent the reducing agent from remaining in the supply channel, the in the JP 2010-84694 A described system after stopping the engine, the reducing agent collected from the supply channel.

An emissions control system according to the preamble of claim 1 of the present invention is from US Pat WO 2006/064028 A1 known.

When the reducing agent is collected after the engine is stopped, the exhaust gas remaining in the exhaust passage is also drawn into the reducing agent supply mechanism, so that the reducing agent may deteriorate in quality. Thus, the present invention provides an emission control system of an internal combustion engine that minimizes the amount of exhaust gas drawn into the reductant supply mechanism.

According to the present invention, an emission control system for an internal combustion engine comprises a reducing agent supply mechanism having a supply passage through which a liquid reducing agent is supplied into an exhaust passage, a collecting means for collecting the reducing agent from the supply passage after the internal combustion engine is stopped, and a urea addition valve for injection and supplying aqueous urea into the exhaust passage, and a regulator that performs a collecting process by the collecting means, the regulator changing a period of time from stopping the engine to starting collecting the reducing agent based on the exhaust gas temperature measured at the time of stopping the internal combustion engine . The emission control system is characterized in that the controller changes the period of time so that it is equal to or longer than a period of time from stopping the internal combustion engine to when a temperature around the urea addition valve drops to a freezer temperature representing a temperature at which it it is likely that the aqueous urea solution is freezing.

When the reducing agent is collected immediately after the engine is stopped, the reducing agent is collected every time the engine is stopped, so that the frequency or frequency with which exhaust gases are drawn into the reducing agent supply mechanism is increased. In particular, when the engine is started and stopped repeatedly in a short time, the reducing agent is drawn into the reducing agent supply mechanism at a very high frequency.

In this context, the higher the exhaust gas temperature measured when the engine is stopped, the lower the probability that the reducing agent will freeze after the engine has stopped. Therefore, the higher the exhaust gas temperature measured when the engine is stopped, the longer the time from stopping the engine to starting collecting the reducing agent. In particular, the time at which the reducing agent is collected after the engine has stopped can be delayed all the more, the higher the exhaust gas temperature measured when the engine is stopped. Further, if the engine is restarted before the collection timing, the reducing agent is not collected, so that the exhaust gases are prevented from being drawn into the reducing agent supply mechanism.

According to one aspect of the invention, the likelihood that the reducing agent will not be collected when the engine is restarted is increased, in other words, the frequency or frequency with which the exhaust gases are extracted is decreased. Therefore, if the engine is started and stopped repeatedly in a short period of time, the frequency or frequency with which the exhaust gases are extracted is significantly increased compared with the known system. Thus, the above-described arrangement according to the aspect of the invention makes it possible to minimize the amount of that sucked into the reducing agent supply mechanism Exhaust gases, while at the same time preventing the reducing agent from freezing.

As described above, the likelihood of freezing of the reducing agent after the engine is stopped is decreased as the exhaust gas temperature measured when the engine is stopped increases. Accordingly, in the above arrangement, in which the time from stopping the engine to starting collecting the reducing agent is lengthened as the exhaust gas temperature increases, it is possible to delay the time of collecting the reducing agent as much as possible after stopping the engine, whereby at the same time a freezing of the reducing agent is prevented. Thus, the likelihood that the reducing agent will not be collected when the engine is restarted can be maximized.

The above-mentioned given temperature can be set to a temperature at which the reducing agent is likely to freeze. The above-mentioned collecting means can be designed as a pump which is arranged in the supply channel and can be rotated forwards and backwards, or as a switching valve which is suitable for changing the flow direction of the reducing agent, or the like.

• 1 eine schematische Ansicht ist, die ein Emissionsregelungssystem eines Verbrennungsmotors gemäß der Erfindung, den Verbrennungsmotor, in dem das System verwendet wird, und dessen periphere Komponenten zeigt;
• 2 ein Flussdiagramm ist, das eine Folge von Schritten eines in einer Ausführungsform der Erfindung ausgeführten Sammlungsprozesses zeigt;
• 3 eine Kennlinie ist, die die Beziehung zwischen einer zweiten Abgastemperatur und einem kritischen Zählwert in der Ausführungsform zeigt.

The features, advantages and the technical and industrial significance of this invention are described in the following detailed description of exemplary embodiments of the invention with reference to the accompanying drawings, in which the same reference symbols denote the same elements and where:

• 1 Fig. 3 is a schematic view showing an emission control system of an internal combustion engine according to the invention, the internal combustion engine in which the system is used, and its peripheral components;
• 2 Figure 3 is a flow chart showing a sequence of steps of a collection process carried out in an embodiment of the invention;
• 3 Fig. 13 is a graph showing the relationship between a second exhaust gas temperature and a critical count value in the embodiment.

Below is an embodiment of the invention with reference to FIG 1 to 3 described.

1 Fig. 13 schematically shows a diesel engine (hereinafter simply referred to as “engine”) in which an emission control system according to this embodiment is used and its peripheral components. The motor 1 has multiple cylinders # 1 - # 4 on. Multiple injectors 4a - 4d are in a cylinder head 2 of the motor 1 built-in. The injectors 4a - 4d are suitable for fuel in the combustion chambers of the respective cylinder #1 # 4 inject. The cylinder head also includes 2 Intake openings through which fresh air is brought into the cylinders and outflow openings 6a-6d , through which exhaust gases are discharged from the cylinders, and so that these openings the respective cylinders # 1 - # 4 correspond.

The injectors 4a - 4d are with a common fuel supply line 9 connected, in which a high pressure fuel is stored. The common fuel line 9 is with a feed pump 10 connected. The feed pump 10 sucks a fuel in a fuel tank and supplies a high pressure fuel to the common rail 9 . The one on the common fuel line 9 Delivered high pressure fuel is injected through the injectors 4a - 4d injected into the appropriate cylinder if the appropriate injector 4a - 4d is open.

An intake manifold 7th is connected to the suction openings. The intake manifold 7th is with an intake port 3 connected. In the intake duct 3 is an intake throttle 16 arranged to adjust the amount of intake air.

An exhaust manifold 8th is with the outflow openings 6a -6d connected. The exhaust manifold 8th is with an exhaust duct 26th connected. A turbocharger 11 for charging the intake air to be drawn into the cylinders, which uses the exhaust pressure, is in the exhaust passage 26th arranged. A charge air cooler 18th is between a suction-side compressor of the turbocharger 11 and the intake throttle 16 in the intake duct 3 arranged. The intercooler 18th is used to cool the intake air, the temperature of which is increased by charging the turbocharger 11 has increased.

A first exhaust aftertreatment device 30th that purifies exhaust gases is in the exhaust duct 26th , viewed in the flow direction of the exhaust gases, downstream of an exhaust-gas-side turbine of the turbocharger 11 arranged. In the first exhaust aftertreatment device 30th are an oxidation catalyst 31 and a filter 32 , viewed in the flow direction of the exhaust gases, arranged one behind the other.

The oxidation catalyst 31 carries a catalyst that oxidizes HC contained in the exhaust gas. The filter 32 that is an element that PM (Fine dust) in the exhaust gas is made of a porous, ceramic material. The filter 32 carries a catalyst to accelerate an oxidation of the PM , where the PM will be trapped in the exhaust gas if it passes through the porous walls of the filter 32 flows.

A fuel addition valve 5 , which is used to fuel as an additive to the oxidation catalyst 31 and the filter 32 is to be conducted in the vicinity of a gas collecting section of the exhaust manifold 8th arranged. The fuel addition valve 5 is via a fuel supply pipe 27 with the feed pump 10 connected. The position where the fuel addition valve 5 can be changed as necessary, provided the fuel addition valve is installed 5 is upstream of the first exhaust aftertreatment device 30th in the exhaust system.

When the amount of through the filter 32 intercepted PM exceeds a predetermined value, a process for regenerating the filter is started 32 started, and the fuel is fed through the fuel addition valve 5 into the exhaust manifold 8th injected. The one via the fuel addition valve 5 injected fuel is burned when it hits the oxidation catalyst 31 reached in order to increase the exhaust gas temperature. When the exhaust gases, their temperature through the oxidation catalyst 31 has been increased in the filter 32 flow, the temperature of the filter becomes 32 increased, and those on the filter 32 secluded PM are oxidized, causing the filter 32 is regenerated.

There is also a second exhaust gas aftertreatment device 40 that purifies exhaust gases in the exhaust duct 26th viewed in the flow direction of the exhaust gases, downstream of the first exhaust gas aftertreatment device 30th arranged. A selective NOx reducing catalytic converter (hereinafter referred to as "SCR catalytic converter") 41 for reducing and eliminating NOx in the exhaust gases with the aid of a reducing agent is in the second exhaust gas aftertreatment device 40 arranged.

There is also a third exhaust gas aftertreatment device 50 that purifies exhaust gases in the exhaust duct 26th , viewed in the flow direction of the exhaust gases, downstream of the second exhaust gas aftertreatment device 40 , arranged. An ammonium oxidation catalyst 51 to remove ammonium in the exhaust gases is in the third exhaust gas aftertreatment device 50 arranged.

The motor 1 includes a mechanism 200 for supplying an aqueous urea solution as a reducing agent supply mechanism to supply a reducing agent to the SCR catalyst 41 to direct. The mechanism 200 for supplying an aqueous urea solution essentially comprises a tank 210 , in which aqueous urea (ie, an aqueous urea solution) is stored, a urea addition valve 230 for the injection and supply of aqueous urea into the exhaust gas duct 26th , a feed channel 240 that controls the urea addition valve 230 with the tank 210 connects, and a pump 220 that are in the supply channel 240 is arranged.

The urea addition valve 230 is between the first exhaust aftertreatment device 30th and the second exhaust aftertreatment device 40 in the exhaust duct 26th arranged, and an injection hole of the urea addition valve 230 is on the SCR catalytic converter 41 directed. When the urea addition valve 230 is opened, is via the supply channel 240 aqueous urea solution and injected into the exhaust duct 26th directed.

The pump 220 is an electric pump and, when it rotates forward, delivers aqueous urea solution from the tank 210 to the urea addition valve 230 . When the pump 220 on the other hand, if it rotates backwards, it conveys the aqueous urea solution via the urea addition valve 230 to the tank 210 . In particular, when the pump turns 220 rotates backwards, aqueous urea solution via the urea addition valve 230 and the supply channel 240 collected and to the tank 210 returned. The pump 220 serves as the above-mentioned collecting means.

Next is an atomizer plate 60 for fine distribution of via the urea addition valve 230 injected aqueous urea to aid atomization or atomization of the aqueous urea between the urea addition valve 230 and the SRC catalyst 41 in the exhaust duct 26th arranged.

The one via the urea addition valve 230 injected aqueous urea solution is hydrolyzed by the heat of the exhaust gases to produce ammonium. The ammonium is then used as a NOx reducing agent in the SCR catalyst 41 directed. About the SCR catalytic converter 41 ammonium is passed on to the SCR catalyst 41 adsorbed and used to reduce NOx. Some of the ammonium produced by hydrolysis is used directly to reduce NOx before it reaches the SCR catalytic converter 41 is adsorbed.

The motor 1 further comprises an exhaust gas recirculation system (hereinafter referred to as “EGR system”). The EGR system is capable of introducing a portion of the exhaust gases into the intake air, thereby reducing the oxygen concentration in the intake air drawn into the cylinders, thereby lowering the combustion temperature and reducing the amount of NOx generated. The exhaust gas recirculation system essentially consists of an EGR duct 13 , the intake duct 3 with the exhaust manifold 8th connects, an EGR valve 15th that is in the EGR channel 13 is arranged, an EGR cooler 14th and so on. By adjusting the opening of the EGR valve 15th becomes the amount of from the exhaust duct 26th in the intake duct 3 introduced, recirculated exhaust gas, the EGR amount, regulated. Furthermore, the temperature of the in the EGR passage 13 exhaust gas flowing through the EGR cooler 14th decreased.

The motor 1 includes various sensors for detecting engine operating conditions. For example, an air flow meter detects 19th the amount GA of intake air in the intake duct 3 . A throttle opening sensor 20th detects the opening of the intake throttle valve 16 . An engine speed sensor 21st detects the speed of the crankshaft or the engine speed NE . A gas lift sensor 22nd detects the amount of depression of the accelerator pedal or the accelerator operating amount ACCP . An outside air sensor 23 detects an outside air temperature THout . A vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle in which the engine 1 is built in. An ignition switch 25th detects the actions of the vehicle driver to the engine 1 to start or the engine 1 to stop.

A first exhaust gas temperature sensor also detects 100 , which, viewed in the direction of flow of the exhaust gases, is upstream of the oxidation catalytic converter 31 is arranged, a first exhaust gas temperature TH1 as a temperature of the exhaust gases before they enter the oxidation catalyst 31 pour in. A differential pressure sensor 110 detects a pressure difference ΔP between one upstream of the filter 32 measured exhaust pressure and one downstream of the filter 32 measured exhaust pressure.

A second exhaust temperature sensor 120 and a first NOx sensor 130 are in the exhaust duct 26th between the first exhaust aftertreatment device 30th and the second exhaust aftertreatment device 40 , viewed in the flow direction of the exhaust gases, upstream of the urea addition valve 230 arranged. The second exhaust temperature sensor 120 detects a second exhaust gas temperature TH2 as a temperature of the exhaust gases before they enter the SCR catalyst 41 pour in. The first NOx sensor 130 detects the first NOx concentration N1 as the concentration of NOx in the exhaust gases before they enter the SCR catalyst 41 pour in.

A second NOx sensor 140 that detects the second NOx concentration N2 as the concentration of NOx in the exhaust gases generated by the SCR catalyst 41 have been cleaned is, viewed in the flow direction of the exhaust gases, downstream of the third exhaust gas aftertreatment device 50 in the exhaust duct 26th arranged.

A controller or regulator 80 receives output signals from the various sensors mentioned above. The regulator 80 consists essentially of a microcomputer that is a central processing unit (CPU) 80a , a read-only memory (ROM) in which various programs, cards, etc. are stored in advance, a random access memory (RAM) in which calculation results of the CPU, etc. are temporarily stored, a timer 80b , an input interface, an output interface and so on. In operation, electrical power is supplied from a battery to the CPU 80a , the timer 80b and supplied to the various sensors mentioned above.

The regulator 80 performs various engine controls 1 such as controlling the fuel injection quantities and fuel injection timing of the injectors 4a - 4d and the fuel addition valve 5 , a regulation of the delivery or discharge pressure of the delivery pump 10 , a regulation of the actuation amount of an actuator 17th holding the intake throttle 16 opens and closes, and a regulation of the opening of the EGR valve 15th by. The regulator 80 also performs various exhaust emission controls such as the aforementioned recirculation process of the burning of the in the filter 32 intercepted PM by.

The controller regulates as one of the exhaust emission regulations 80 the injection of aqueous urea solution through the urea addition valve 230 . In the injection control, the amount of urea to be injected, which must be neither too large nor too small, is used by the engine 1 to reduce emitted NOx is calculated based on the engine operating conditions, etc., and the opening state of the urea addition valve 230 is controlled so that the calculated amount of urea solution via the urea addition valve 230 is injected. The injection of urea aqueous solution for reducing NOx is continuously performed while the engine is running and is stopped when the running engine is stopped.

As described above, when the engine is stopped, the urea aqueous solution injection is stopped. However, if the urea aqueous solution is in the supply channel 240 the mechanism for supplying an aqueous urea solution remains or in the urea addition valve 230 remains when the engine is stopped, the supply duct 240 or the urea addition valve 230 due to an increase in their volume caused by freezing of the remaining aqueous urea solution. Thus the controller leads 80 In order to prevent the urea aqueous solution from freezing, a collection control for controlling the urea aqueous solution from the urea addition valve 230 and the Supply duct 240 after the engine has stopped.

However, when urea aqueous solution is collected after the engine is turned off, exhaust gases that are in the exhaust pipe are also released 26th remain in the mechanism 200 sucked to the supply of an aqueous urea solution, whereby the quality of aqueous urea can deteriorate. In particular, when aqueous urea is collected immediately after the engine is turned off and the engine is started and stopped repeatedly in a short time, exhaust gases are introduced into the mechanism at a very high frequency 200 to supply an aqueous urea solution, as aqueous urea is always collected when the engine is not in operation.

Thus, in this embodiment, a collection process as shown in 2 is shown, designed so that suction of exhaust gases is prevented, in particular the frequency of the suction of exhaust gases is reduced. The collection process is controlled by the regulator 80 executed.

Once the process is in 2 is started, it is determined at the beginning whether it is (i.e. the current time) immediately after the motor has stopped ( S100 ). If it is not immediately after the engine stops ( S100 : No), the process of 2 . On the other hand, if it is immediately after the engine has stopped ( S100 : YES), becomes a counter judgment value KH based on the second exhaust temperature TH2 which is measured when the engine is stopped. The counter judgment value KH corresponds to the period of time that is required until the temperature around the urea addition valve 230 to a freezer temperature THERE is decreased after the engine stops. The freezer temperature THERE is a temperature at which the urea aqueous solution is likely to freeze. Like it in 3 is shown, becomes the counter judgment value KH set to a higher value, the higher the second exhaust gas temperature TH2 that is measured when the engine is stopped.

Once the meter judgment value KH is set in the above-described manner, it is determined whether an engine stop count value KS , which is a measure of an elapsed time since the engine was stopped (ie, a time elapsed since the engine was stopped) equal to or greater than the counter judgment value KH is ( S120 ). The determination operation of step S120 is repeated until the engine stop count KS equal to or greater than the counter judgment value KH becomes.

If in step S120 it is determined that the engine stop count KS equal to or greater than the counter judgment value due to an elapsed time since the engine was stopped KH becomes ( S120 : YES), a regulation for the collection of the aqueous urea solution is carried out ( S130 ). The urea addition valve is used in the collection control 230 open, and the pump 220 is rotated in reverse for a predetermined period of time. As a result, the in the urea addition valve 230 and the supply channel 240 remaining aqueous urea solution in the tank 210 collected.

When the execution of the collection control is completed, the power is supplied to the CPU 80a , the second exhaust gas temperature sensor 120 , etc. interrupted ( S140 ), and the process of 2 ends. The following describes the operation of this embodiment.

The likelihood that the urea aqueous solution will freeze after the engine has stopped becomes smaller as the exhaust gas temperature, which is measured when the engine is stopped, increases. Therefore, the period from when the engine is stopped to when the urea aqueous solution collection is started can be extended or lengthened as the exhaust temperature increases, which is measured at the time the engine is stopped. In particular, as the exhaust gas temperature, measured at the time of stopping the engine, increases, the urea aqueous solution becomes less and less likely or unlikely to freeze even if the time at which the urea aqueous solution is collected after the engine is stopped is delayed. If the engine is restarted before the collection time, no aqueous urea solution is collected, with the result that no exhaust gas enters the mechanism 200 is sucked in to supply an aqueous urea solution.

Thus, in this embodiment, the timing of collecting the urea aqueous solution after the engine is stopped is changed based on the exhaust gas temperature measured when the engine is stopped. In particular, the counter judgment value becomes KH based on the second exhaust gas temperature measured when the engine is stopped TH2 is set and the collection control is started when the engine stop count KS equal to or greater than the counter judgment value KH becomes. This increases the likelihood that the urea aqueous solution will not be collected when the engine is restarted, or in other words, decreases the frequency with which exhaust gas is sucked in. This is the frequency with which the exhaust gas is extracted, especially when the engine is started and stopped repeatedly in a short time becomes significantly smaller compared to the known system.

The collection control is started when the engine stop count KS equal to or greater than the counter judgment value KH becomes. Therefore, the collection control becomes when an appropriately large value as the counter judgment value KH is started after a reasonably long period of time has passed since the engine was stopped. If the collection control is started after a lapse of a reasonably long period of time, the exhaust gases are likely to be in the exhaust duct 26th is diluted or made thinner with air when the collection control is started. Therefore, the amount of the while performing the collection regulation in the mechanism 200 to supply an aqueous urea solution reduced exhaust gas sucked.

The counter judgment value KH is set to a higher value, the higher the second exhaust gas temperature measured when the engine is stopped TH2 is. Therefore, the time from stopping the engine to starting the collection of the urea aqueous solution becomes higher as the second exhaust gas temperature becomes higher TH2 longer. It is thus possible to delay the time of collecting the urea aqueous solution as much as possible after the engine is stopped while preventing the urea aqueous solution from freezing. Therefore, the possibility that the urea aqueous solution collection will not be performed when the engine is restarted is increased.

As explained above, this embodiment provides the following effects. (1) The counter judgment value KH is based on the second exhaust gas temperature measured when the engine is stopped TH2 is set, and the collective control is performed when the engine stop count KS equal to or greater than the counter judgment value KH becomes. Specifically, the time from when the engine is stopped to when the urea aqueous solution starts to be collected is determined based on the second exhaust gas temperature measured when the engine is stopped TH2 changed. Therefore, the likelihood that the urea aqueous solution will not be collected when the engine is restarted is increased, or in other words, the frequency at which the exhaust gases are sucked becomes lower. As a result, it is possible to prevent exhaust gas from entering the mechanism as much as possible 200 to supply an aqueous urea solution is sucked, while at the same time freezing of the aqueous urea solution is prevented.

(2) The counter judgment value KH is set to a higher value, the higher the second exhaust gas temperature measured when the engine is stopped TH2 is. In particular, the period of time from the stopping of the engine to the start of collecting the urea aqueous solution becomes as the second exhaust gas temperature increases TH2 elongated or enlarged. Accordingly, it is possible to delay the timing of collecting the urea aqueous solution after stopping the engine as much as possible while preventing the urea aqueous solution from freezing, thus increasing the likelihood that the urea aqueous solution will not be collected when the engine is restarted.

The embodiment described can be modified as follows. While in this embodiment the second exhaust gas temperature TH2 is detected by the sensor, the temperature can TH2 can also be estimated based on engine operating conditions.

While the aqueous urea solution from the supply channel 240 is collected by turning the pump 220 rotates backwards, it is also possible to collect the aqueous urea solution in other ways. For example, a switching valve for changing the flow direction of the aqueous urea solution or the like in the supply channel 240 be arranged.

Although a urea aqueous solution is used as a reducing agent, another liquid reducing agent can also be used.

List of reference symbols

1

engine

# 1- # 4

cylinder

2

Cylinder head

3

Intake duct

4a - 4d

Injectors

5

Fuel addition valve

6a-6d

Outflow openings

7th

Intake manifold

8th

Exhaust manifold

9

common fuel supply line

10

Feed pump

11

turbocharger

13

EGR channel

14th

EGR cooler

15th

EGR valve

16

Intake throttle

17th

Actuator

18th

Intercooler

19th

Air flow meter

20th

Throttle opening sensor

21st

Engine speed sensor

22nd

Gas lift sensor

23

Outside air sensor

24

Vehicle speed sensor

25th

Ignition switch

26th

Exhaust duct

27

Fuel supply pipe

30th

first exhaust aftertreatment device

31

Oxidation catalyst

32

filter

40

second exhaust aftertreatment device

41

SCR catalytic converter

50

third exhaust aftertreatment device

51

Ammonium oxidation catalyst

60

Atomizer plate

80

Regulator

80a

Central processing unit

100

first exhaust gas temperature sensor

110

Differential pressure sensor

120

second exhaust gas temperature sensor

130

NOx sensor

140

second NOx sensor

200

Reducing agent supply mechanism

210

tank

220

pump

230

Urea addition valve

240

Supply duct

ACCP

Accelerator operation amount

THERE

Freezer temperature

ΔP

Pressure difference

KH

Counter rating value

KS

Engine stop count

NE

Engine speed

N1

first NOx concentration

PM

Fine dust

SPD

Vehicle speed

THout

Outside air temperature

TH1

first exhaust gas temperature

TH2

second exhaust gas temperature

Claims (1)

Emission control system for an internal combustion engine (1), with a reducing agent supply mechanism (200) which has a supply channel (240) through which a liquid reducing agent is passed into an exhaust gas channel (26), a collecting means (220) for collecting the reducing agent from the supply channel (26) after the internal combustion engine has stopped and comprises a urea addition valve (230) for injecting and supplying aqueous urea into the exhaust gas duct (26), and a regulator (80) which carries out a collection process by the collecting means (220), the regulator ( 80) a period of time (KH) from the stopping of the internal combustion engine (1) to the beginning of the collection of the reducing agent on the basis of the exhaust gas temperature (TH2) measured at the time the internal combustion engine (1) was stopped, characterized in that: the controller (80 ) changes the time span (KH) so that it is as long as or longer than a time span from the stopping of the internal combustion engine (1) to the Absi A temperature around the urea addition valve (230) is a freezing danger temperature (DA), which represents a temperature at which the aqueous urea solution is likely to freeze.

Images