JP2016102424A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress, to easily occur, a decline in a NOelimination rate when an SCR catalyst disposed in an exhaust passage of an internal combustion engine is exposed to the atmosphere with a high temperature and high fuel concentration which causes fuel poisoning.SOLUTION: An exhaust emission control system for an internal combustion engine controls an amount of an additive that is NHor a precursor of NHto be supplied to an exhaust emission control device, in accordance with the basic addition amount determined according to an NOconcentration of an exhaust gas flowing into the exhaust emission control device including an SCR catalyst. When the SCR catalyst is exposed to the atmosphere with a high temperature and high fuel concentration which causes fuel poisoning to easily occur, increase correction of the basic addition amount is performed in accordance with the fuel concentration of the exhaust gas flowing into the exhaust emission control device, and the corrected amount of the additive is supplied to the exhaust emission control device, so as to suppress a decline in an NOelimination rate caused by the fuel poisoning.SELECTED DRAWING: Figure 4

Description

The present invention relates to an exhaust gas purification system for an internal combustion engine in which an exhaust gas purification device including an SCR (Selective Catalytic Reduction) catalyst is disposed in an exhaust passage.

As an exhaust gas purification system for an internal combustion engine, an oxidation catalyst disposed in an exhaust passage, a particulate filter (SCRF) disposed in an exhaust passage downstream of the oxidation catalyst and carrying an SCR catalyst, and a fuel (hydrocarbon) to the oxidation catalyst (Fuel)) is known, and an additive supply unit that supplies ammonia (NH ₃ ) or an additive that is a precursor of NH ₃ to the SCRF SCR catalyst is known. Yes. In the exhaust gas purification system for an internal combustion engine configured as described above, particulate matter (PM) collected by the particulate filter (PM: Particulate Matter
) Is oxidized and removed, a process for raising the temperature of the particulate filter to a temperature at which PM can be oxidized (temperature increase process) is performed by supplying unburned fuel from the fuel supply unit to the oxidation catalyst ( For example, see Patent Document 1).

JP 2014-148908 A JP 2010-180814 A JP 2013-122222 A JP 2010-180792 A JP 2010-196696 A

  By the way, when the temperature raising process as described above is performed, the SCR catalyst is exposed to a high temperature atmosphere in addition to the particulate filter. Here, as an SCR catalyst mounted on a moving body such as a vehicle, a catalyst that uses zeolite ion-exchanged with an Fe complex or a Cu complex as a carrier is generally used. When such an SCR catalyst is exposed to a high-temperature atmosphere (for example, 500 ° C. or higher), the pore diameter of the support may increase. Further, when the SCR catalyst is exposed to a high-temperature atmosphere, there is a possibility that the low molecular weight of the fuel contained in the exhaust gas in the SCR catalyst is promoted.

Therefore, when the fuel concentration in the exhaust gas becomes high when the SCR catalyst is exposed to a high temperature atmosphere, the low molecular weight fuel tends to enter into the expanded pores of the carrier. When the fuel in the exhaust gas from entering the pores of the support, that the active sites of the carrier is covered by the fuel, a phenomenon reaction between adsorption and NO _X and NH ₃ in the NH ₃ is inhibited (fuel poisoning) is occurs, (relative to the amount of the NO _X flowing into the SCR catalyst, the ratio of the amount of the NO _X to be purified by the SCR catalyst) NO _X purification rate by the SCR catalyst may be reduced.

The present invention has been made in view of the above-mentioned problems, and its object is according to the basic amount determined according to the NO _X concentration of the exhaust gas flowing into an exhaust purification device that includes an SCR catalyst, the exhaust gas purifying in an internal combustion engine exhaust gas purification system for controlling the amount of a precursor which is an additive of the NH ₃ or NH ₃ is supplied to the apparatus, SCR catalyst is exposed to high ambient occurrence likely high temperature and fuel concentration of the fuel poisoning when is is to suppress decrease the deterioration of the NO _X purification rate of the SCR catalyst.

In order to solve the above-described problems, the present invention provides NH ₃ or NH ₃ supplied to the exhaust purification device according to the basic addition amount determined according to the NO _x concentration of the exhaust gas flowing into the exhaust purification device including the SCR catalyst. In an exhaust gas purification system for an internal combustion engine that controls the amount of an additive that is a precursor of SCR, when the SCR catalyst is exposed to a high temperature and high fuel concentration atmosphere where fuel poisoning is likely to occur, the fuel concentration depends on the fuel concentration. said basic amount to increase correction by supplying the additive amount of the corrected into an exhaust purification device, and so as to suppress the reduction of the NO _X purification rate of the SCR catalyst.

In particular, the present invention, supply means for supplying an exhaust gas purifying device disposed in an exhaust passage of an internal combustion engine including an SCR catalyst, an additive which is a precursor of NH ₃ or NH ₃ in the exhaust gas flowing into an exhaust purification device If, in an internal combustion engine exhaust gas purification system for and a control means for controlling the supply means based on the basic amount determined according to the NO _X concentration of the exhaust gas flowing into the exhaust purification device, detects the temperature of the SCR catalyst Detecting means for obtaining the fuel concentration of the exhaust gas flowing into the exhaust gas purification device, and the control means, when the temperature detected by the detecting means is less than a predetermined threshold, the basic addition amount When the temperature detected by the detection means is equal to or higher than the predetermined threshold, the basic addition amount is corrected to increase, and the increase rate by the correction is taken. The basic amount to be larger when higher than when low fuel concentration obtained by the means in increasing correction was an additive amount of the corrected so as to supply from the supply means. Here, the “predetermined threshold value” is a temperature at which the diameter of the pores of the carrier constituting the SCR catalyst is increased or the molecular weight of the fuel contained in the exhaust gas is easily generated, that is, the fuel in the exhaust gas is the pores of the carrier. It is the lower limit of the temperature at which it is easy to enter.

When the temperature of the SCR catalyst is lower than the predetermined threshold value, it is difficult to increase the diameter of the pores of the carrier constituting the SCR catalyst and to reduce the molecular weight of the fuel contained in the exhaust gas. Therefore, by additives of the basic amount determined according to the NO _X concentration of the exhaust gas flowing into an exhaust purification device is supplied to the exhaust purification device, it is possible to realize a suitable NO _X purification rate of the SCR catalyst .

On the other hand, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold, the pores of the carrier constituting the SCR catalyst are likely to expand, and / or the fuel contained in the exhaust gas is likely to be reduced in molecular weight. Therefore, the fuel in the exhaust gas easily enters the pores, and the fuel poisoning of the SCR catalyst easily occurs accordingly. Furthermore, when the fuel concentration of the exhaust gas flowing into the exhaust purification device is high, the amount of exhaust gas flowing into the pores is likely to increase compared to when it is low, and the HC poisoning amount of the SCR catalyst tends to increase accordingly. . In such an environment, the even basic amount of the additive is supplied to the exhaust purification device, it is difficult to realize a suitable NO _X purification rate of the SCR catalyst.

By the way, when the temperature of the SCR catalyst is high, the reaction rate of NO _X and NH ₃ is higher than when the temperature is low, and therefore NO _X that can be purified (reduced) per unit time at each active point of the SCR catalyst. The amount of increases. Therefore, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold value, the amount of additive that is corrected to increase the basic addition amount so that the increase rate when the fuel concentration is higher than when the fuel concentration is low is increased to the exhaust purification device. When supplied, it is possible to increase the amount of NO _x purified per unit time at the active point where no fuel poisoning occurs in the SCR catalyst. As a result, decrease amount of the NO _X purification rate due to the fuel poisoning occur with some active sites of the SCR catalyst, NO _X amount to be purified by the remaining active sites does not occur in the fuel poisoned supplemented by increase of the NO _X purification rate due to the increase in. Therefore, when the SCR catalyst is exposed to prone hot atmosphere of the fuel poisoning, it is possible to reduce the deterioration of the NO _X purification rate due to the fuel poisoning.

Even when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold, if the fuel concentration in the exhaust gas flowing into the SCR catalyst is sufficiently low, fuel poisoning is unlikely to occur. reduction of the NO _X purification rate due to hardly occur. Therefore, even when the temperature of the SCR catalyst detected by the detection means is equal to or higher than the predetermined threshold, when the fuel concentration acquired by the acquisition means is equal to or lower than the predetermined concentration, the control means You may make it supply the additive of a basic addition amount from a supply means. Here, the “predetermined concentration” means that NO _X suitable for the SCR catalyst can be used if the basic additive amount of the additive is supplied to the SCR catalyst even if the exhaust gas containing fuel of the predetermined concentration or less flows into the SCR catalyst. This is the upper limit of the fuel concentration that can achieve the purification rate. According to such a configuration, even when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold value, the amount of additive supplied from the supply means is not increased unnecessarily when fuel poisoning is difficult to occur. Therefore, while suppressing the consumption of the additive, it is possible to suppress the reduction of the NO _X purification rate of the SCR catalyst.

Here, upon increase correction of the basic amount, fuel poisoning of SCR catalyst is likely to occur than when at high fuel concentration of the exhaust gas flowing into the exhaust purification device is low, and NO _X purification rate decrease Based on the viewpoint that it is easy to do, the basic addition amount may be increased and corrected according to the fuel concentration of the exhaust gas flowing into the exhaust purification device. Further, when the temperature of the SCR catalyst is above the predetermined threshold value, based on the viewpoint as NO _X purification rate fuel poisoned SCR catalyst progresses decreases, the fuel concentration of the exhaust gas flowing into an exhaust purification device From this, the actual fuel poisoning amount of the SCR catalyst may be estimated, and the basic addition amount may be increased and corrected according to the fuel poisoning amount. The fuel poisoning amount of the SCR catalyst correlates with the temperature of the SCR catalyst in addition to the fuel concentration of the exhaust gas flowing into the exhaust purification device. Therefore, when the temperature detected by the detection means is in a high temperature range equal to or higher than the predetermined threshold, the control means according to the present invention sets the parameter detected by the temperature detected by the detection means and the fuel concentration acquired by the acquisition means. As described above, the basic poisoning amount may be increased and corrected so that the fuel poisoning amount of the SCR catalyst is estimated and the rate of increase when the estimated fuel poisoning amount is larger than when the fuel poisoning amount is small. According to this construction, since it possible to an amount corresponding to a high temperature for the addition amount of the actual fuel poisoning amount of the SCR catalyst, to suppress more surely reduce the deterioration of the NO _X purification rate due to the fuel poisoned Can do.

Here, the exhaust emission control device according to the present invention may include a particulate filter that collects PM in the exhaust gas, and the SCR catalyst may be carried on the particulate filter. When the exhaust purification device includes a particulate filter, a configuration in which the SCR catalyst is disposed downstream of the particulate filter, or a configuration in which the SCR catalyst is supported on the particulate filter can be considered. And, according to the configuration in which the SCR catalyst is supported on the particulate filter, the path length from the internal combustion engine to the SCR catalyst is shorter than the configuration in which the SCR catalyst is arranged downstream of the particulate filter. It is easy to be exposed to high-temperature exhaust gas, and accordingly, the frequency of occurrence of fuel poisoning in the SCR catalyst tends to increase. Therefore, in the configuration in which the SCR catalyst is supported on the particulate filter, when the temperature of the SCR catalyst rises to the predetermined threshold value or more, the basic addition amount is corrected based on the fuel concentration and corrected as described above. When the supply means according to the amount of post is controlled, the effect of suppressing the reduction of the NO _X purification rate due to the fuel poisoning becomes larger.

  When the exhaust gas purification device includes a particulate filter, it is necessary to oxidize and remove PM collected by the particulate filter by raising the temperature of the particulate filter to a predetermined regeneration temperature. For this reason, the exhaust purification device may further include an oxidation catalyst disposed upstream of the particulate filter. The exhaust purification system supplies a fuel to the exhaust gas flowing into the oxidation catalyst, and oxidizes the fuel with the oxidation catalyst, thereby performing a temperature raising process for increasing the temperature of the exhaust gas flowing into the particulate filter. You may make it further provide a temperature rising control means. The “predetermined regeneration temperature” here is a temperature at which PM is oxidized (for example, 500 ° C. to 650 ° C.).

Here, when the particulate filter is heated to the predetermined regeneration temperature by executing the temperature increasing process, the SCR catalyst carried on the particulate filter is also heated to the predetermined regeneration temperature. there is a possibility. When the temperature of the SCR catalyst is raised to the predetermined regeneration temperature, the pores of the zeolite constituting the SCR catalyst may expand. Further, when the write-on process is executed, the fuel that is not sufficiently oxidized by the oxidation catalyst may be exposed to a high-temperature atmosphere, so that the fuel may be reduced in molecular weight. Therefore, when the Atsushi Nobori processing is executed, the fuel poisoning is likely to occur in the SCR catalyst, it can be said that NO _X purification rate of the SCR catalyst with the it tends to decrease. Therefore, when the temperature of the SCR catalyst rises to the predetermined regeneration temperature by executing the temperature raising process, the basic addition amount is corrected to increase based on the fuel concentration as described above, and the corrected amount if supply means is controlled in accordance with, the effect of suppressing the reduction of the NO _X purification rate of the SCR catalyst becomes larger. Therefore, in the exhaust gas purification system in which the temperature raising process as described above is executed, it is desirable that the predetermined threshold value is set to the regeneration temperature or less.

According to the present invention, the additive that is NH ₃ or the precursor of NH ₃ supplied to the exhaust purification device according to the basic addition amount determined according to the NO _x concentration of the exhaust gas flowing into the exhaust purification device including the SCR catalyst in an internal combustion engine exhaust gas purification system for controlling the amount of, when the SCR catalyst is exposed to high ambient occurrence likely high temperature and fuel concentration of the fuel poisoning, reduce the deterioration of the NO _X purification rate of the SCR catalyst Can be suppressed.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and an intake / exhaust system thereof in a first embodiment. It is a figure which shows the temperature characteristic of an SCR catalyst. In case the temperature of the SCR catalyst is above a predetermined threshold, the fuel concentration of the exhaust gas flowing into the SCRF, is a timing chart showing changes with time of the NO _X purification rate of the feed amount, and the SCR catalyst of the urea aqueous solution. It is a flowchart which shows the process routine performed when controlling an additive supply valve in a 1st Example. It is a figure which shows the correlation with the fuel concentration of the exhaust gas which flows into SCRF, and the increase amount of the fuel poisoning amount per unit time. It is a figure which shows the correlation with the temperature of an SCR catalyst, and the reduction amount of the fuel poisoning amount per unit time. In case the temperature of the SCR catalyst is above a predetermined threshold, the fuel poisoning amount of the SCR catalyst is a timing chart showing changes with time of the NO _X purification rate of the feed amount, and the SCR catalyst of the urea aqueous solution. It is a flowchart which shows the process routine performed when controlling an additive supply valve in a 2nd Example. It is a flowchart which shows the process routine for estimating the fuel poisoning amount of an SCR catalyst.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake / exhaust system. Internal combustion engine 1 shown in FIG.
Is a compression ignition internal combustion engine (diesel engine) using light oil as fuel. However, the internal combustion engine according to the present invention is not limited to a diesel engine, and may be a spark ignition internal combustion engine (gasoline engine) using gasoline as fuel.

An exhaust passage 2 is connected to the internal combustion engine 1. The exhaust passage 2 is provided with a particulate filter (hereinafter referred to as “SCRF”) 4 carrying an SCR catalyst. The SCR catalyst here includes a support composed of zeolite and an active component generated by ion exchange of a part of the support with an Fe complex, a Cu complex or the like, and exhausts with NH ₃ as a reducing agent. It is a catalyst that selectively reduces NO _X therein. The particulate filter is a wall flow type filter that collects PM in the exhaust gas.

An additive supply valve 7 for supplying the additive stored in the tank 8 into the exhaust is attached to the exhaust passage 2 upstream of the SCRF 4. As an additive stored in the tank 8, NH ₃ gas or a urea aqueous solution that is a precursor of NH ₃ can be used. In this embodiment, a urea aqueous solution is used. The urea aqueous solution supplied into the exhaust gas from the additive supply valve 7 is thermally decomposed by receiving heat from the exhaust gas or hydrolyzed in the SCR catalyst. When the urea aqueous solution is thermally decomposed or hydrolyzed, NH ₃ is generated. The NH ₃ thus generated is adsorbed on the SCR. NH ₃ adsorbed on the SCR reacts with NO _X contained in the exhaust to generate nitrogen (N ₂ ) and water (H ₂ O). That is, NH ₃ functions as a NO _X reducing agent. Here, the additive supply valve 7 corresponds to a “supply means” according to the present invention.

The exhaust passage 2 downstream of the SCRF 4 is provided with an oxidation catalyst (hereinafter referred to as “ASC”) 5 for oxidizing NH ₃ that has passed through the SCRF 4. ASC5 may be a catalyst configured by combining an oxidation catalyst and an SCR catalyst. In this case, for example, an oxidation catalyst is formed by supporting a noble metal such as platinum (Pt) on a carrier made of aluminum oxide (Al ₂ O ₃ ), zeolite or the like, and Fe or Cu is used on the carrier made of zeolite. An SCR catalyst may be formed by supporting a base metal such as a zeolite (ion exchange with a part of zeolite by Fe complex or Cu complex). When the ASC 5 is configured in this way, the fuel, CO, and NH ₃ in the exhaust gas can be oxidized, and NO _X produced by the oxidation of the NH ₃ can be reduced with excess NH _3. You can also.

  An oxidation catalyst 3 having an oxidation function is provided in the exhaust passage 2 upstream of the SCRF 4 and the additive supply valve 7. A fuel supply valve 6 for supplying the fuel of the internal combustion engine 1 to the oxidation catalyst 3 through the exhaust gas flowing into the oxidation catalyst 3 is disposed in the exhaust passage 2 upstream of the oxidation catalyst. The fuel supplied to the exhaust from the fuel supply valve 6 is oxidized by the oxidation catalyst 3, and the temperature of the exhaust flowing into the SCRF 4 located downstream can be raised.

In the exhaust passage 2 between the oxidation catalyst 3 and the SCRF 4, a first NO _X sensor 10 that detects the NO _X concentration of the exhaust flowing into the SCRF 4 and a temperature of the exhaust flowing out from the oxidation catalyst 3 are detected. One temperature sensor 13 is provided. Note that the NO _x concentration of the exhaust gas flowing into the SCRF 4 may be estimated from the operating state of the internal combustion engine 1 or the like. In the exhaust passage 2 between the SCRF 4 and the ASC 5, a second temperature sensor 14 for detecting the temperature of the exhaust gas flowing out from the SCRF 4 is provided. The exhaust passage 2 downstream of the ASC 5 is provided with a second NO _X sensor 11 that detects the NO _X concentration of the exhaust gas flowing out from the ASC 5. Further, a differential pressure sensor 12 for detecting a differential pressure between the exhaust pressure upstream of the SCRF 4 and the exhaust pressure downstream is provided in the exhaust passage 2 in parallel with the SCRF 4. The combination of the oxidation catalyst 3, SCRF4, and ASC5 is an embodiment of the exhaust gas purification apparatus according to the present invention.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. The ECU 20 includes a crank position sensor 21, an accelerator position sensor 22, an air flow meter in addition to the first NO _X sensor 10, the second NO _X sensor 11, the first temperature sensor 13, the second temperature sensor 14, and the differential pressure sensor 12 described above. 26 and the like, and output signals from various sensors are input to the ECU 20. Here, the crank position sensor 21 is a sensor that detects the rotational position of the output shaft (crankshaft) of the internal combustion engine 1. The accelerator position sensor 22 is a sensor that detects an operation amount (accelerator opening) of an accelerator pedal. The air flow meter 26 is a sensor that is attached to the intake passage 25 of the internal combustion engine 1 and detects the amount of air taken into the internal combustion engine 1 (intake air amount).

The ECU 20 controls the operating state of the internal combustion engine 1 and the exhaust purification system based on the detection values of the various sensors. For example, ECU 20 determines a target amount of the urea aqueous solution supplied from the additive supply valve 7 based on the concentration of NO _X exhaust gas flowing into SCRF4 (basic amount), additive supply valve in accordance with the basic amount 7 To control. In determining the basic addition amount, the ECU 20 first estimates the NH ₃ adsorption amount of the SCR catalyst. The amount of NH ₃ adsorbed is determined based on the amount of NH ₃ consumed in the SCR catalyst (NO ₃ ) from the amount of NH ₃ (NH ₃ produced by thermal decomposition or hydrolysis of urea aqueous solution) supplied to the SCR catalyst of SCRF4. It is estimated by integrating the value obtained by subtracting the amount of NH ₃ consumed for the reduction of _X ) and the amount of NH ₃ slip (the amount of NH ₃ passing through the SCR catalyst).

Wherein the amount of NH ₃ to be consumed in the SCR catalyst is calculated and the amount of the NO _X flowing into the SCR catalyst (NO _X inflow) and NO _X purification rate of the SCR catalyst as a parameter. At that time, the NO _X inflow amount is calculated by adding the exhaust value (intake air amount per unit time and fuel injection amount per unit time) to the detection value of the first NO _X sensor 10 (NO _X concentration of exhaust gas flowing into the SCRF 4). It is obtained by multiplying the total amount). Note that the NO _X concentration of the exhaust gas flowing into the SCRF 4 correlates with the operating state of the internal combustion engine 1, and therefore may be estimated based on the operating state of the internal combustion engine 1. On the other hand, NO _X purification rate is NO _X purification rate when the SCR catalyst is assumed to be normal (fuel state poisoning and degradation has not occurred), of the exhaust gas flowing into the SCR catalyst flow rate and SCR catalyst As a parameter. At this time, NO _X purification rate of normal SCR catalyst becomes lower as the exhaust flow rate increases, and because it has a higher becomes properties as the temperature of the SCR catalyst is increased, NO _X purification of the SCR catalyst based on such properties The rate can be determined.

NH ₃ slip amount used in the estimation of the adsorbed NH ₃ amount is calculated and the previous estimate of the adsorbed NH ₃ amount, and the temperature of the SCR catalyst, and the flow rate of the exhaust gas, as a parameter. Here, if the flow rate of the exhaust gas is constant, the NH ₃ concentration in the exhaust gas flowing out from the SCR catalyst increases as the NH ₃ adsorption amount increases and the temperature of the SCR catalyst increases. Further, if the NH ₃ concentration in the exhaust gas flowing out from the SCR catalyst is constant, the NH ₃ slip amount per unit time increases as the exhaust gas flow rate increases. Based on these correlations, the NH ₃ concentration of the exhaust gas flowing out from the SCR catalyst is obtained by using the NH ₃ adsorption amount of the SCR catalyst and the temperature of the SCR catalyst as parameters, and then the NH ₃ concentration is multiplied by the flow rate of the exhaust gas. , NH ₃ slip amount can be obtained.

When adsorbed NH ₃ amount of the SCR catalyst by the method described above can be estimated, ECU 20 may subtract the estimated value of the adsorbed NH ₃ amount from the difference (target adsorbed NH ₃ amount between the adsorbed NH ₃ amount and the target adsorbed NH ₃ amount The amount of urea aqueous solution corresponding to the difference is determined as the basic addition amount. The target adsorbed NH ₃ amount referred to here, a certain amount (e.g., NH ₃ adsorption amount when the NH ₃ adsorption rate and NH ₃ desorption rate of the SCR catalyst in equilibrium) may be used. Further, the target NH ₃ adsorption amount may be changed according to the NO _X inflow amount so that the NO _X purification rate of the SCR catalyst becomes constant.

  Further, the ECU 20 oxidizes and removes the PM trapped in the particulate filter when the amount of PM trapped in the particulate filter of the SCRF 4 (PM trap amount) exceeds a predetermined amount. To perform the process (temperature increase process). Specifically, the ECU 20 calculates the PM collection amount of the particulate filter using the exhaust flow rate calculated from the detection value of the air flow meter 26, the fuel injection amount, and the like, the detection value of the differential pressure sensor 12, and the like as parameters. Such calculation processing of the amount of collected PM is repeatedly executed at a predetermined cycle during the operation period of the internal combustion engine 1. Then, the ECU 20 performs the temperature raising process when the calculated value of the PM collection amount becomes a predetermined amount or more. The temperature raising process here refers to supplying fuel into the exhaust from the fuel supply valve 6 or post-injecting it from a fuel injection valve (not shown) of the internal combustion engine 1 to supply the fuel to the exhaust of the internal combustion engine 1. This is a process of raising the temperature of the SCRF 4 to a predetermined regeneration temperature (a temperature at which PM can be oxidized, for example, 500 ° C. to 650 ° C.) using reaction heat generated when the fuel is oxidized by the oxidation catalyst 3. . When such a temperature raising process is performed, PM collected by the particulate filter of SCRF4 is oxidized and removed. The post-injection here is fuel injection performed at a time when the injected fuel hardly contributes to the output of the internal combustion engine 1, for example, at the latter stage of the expansion stroke or the first half of the exhaust stroke. When the ECU 20 executes such a temperature increase process, the “temperature increase control means” according to the present invention is realized.

By the way, when the temperature raising process as described above is executed, there is a high possibility that the SCR catalyst carried on the particulate filter of the SCRF 4 is also raised to the regeneration temperature like the particulate filter. Here, when the temperature of the SCR catalyst rises to the regeneration temperature of 500 ° C. or more, the pores of the zeolite constituting the SCR catalyst may expand. In addition, when the above-described temperature raising process is executed, a part of the fuel supplied to the oxidation catalyst 3 that is not sufficiently oxidized by the oxidation catalyst 3 is exposed to a high-temperature atmosphere to reduce the molecular weight. There is a possibility. Therefore, when the above-described temperature raising process is executed, the low molecular weight fuel easily enters the pores whose diameter has been expanded in the zeolite. When the fuel enters the pores of the zeolite, that the active ingredient, such as Fe and Cu which are carried on the zeolite are covered by the fuel, the fuel react with the adsorption and NH ₃ and NO _X in the NH ₃ is inhibited Poisoning is likely to occur.

Here, when the fuel poisoning of SCR catalysts occurs, NO _X purification rate of the SCR catalyst may be reduced. In particular, when the temperature of the SCR catalyst by raising the temperature process described above is performed is heated to the regeneration temperature of more than 500 ° C., the fuel poisoning is likely to occur, the SCR catalyst accordingly NO _X The purification rate tends to decrease. Here, the correlation between temperature and NO _X purification rate of the SCR catalyst in FIG. Incidentally, FIG. 2 shows the correlation between the temperature and the NO _X purification rate of normal SCR catalyst does not occur in the fuel poisoning. As shown in FIG. 2, the SCR catalyst achieves a sufficiently high NO _x purification rate (for example, 80% or more) when the temperature of the SCR catalyst is in an appropriate temperature range of about 200 ° C. to 350 ° C. , the temperature of the SCR catalyst is more than about 350 ° C. the SCR catalyst temperature becomes higher as the NO _X purification rate has a characteristic to be low. Therefore, when the temperature of the SCR catalyst is increased to the regeneration temperature of more than 500 ° C., the fuel poisoning of SCR catalysts occurs, effects the generation of fuel poisoning on the NO _X purification rate becomes large, it there is a possibility that the decline in association with NO _X purification rate is increased. Thus, by raising the temperature process described above is executed, when together with the particulate filter temperature of the SCR catalyst is increased to the regeneration temperature, the fuel poisoning is likely to occur, and the NO _X purification rate tends to decrease environmental SCR It can be said that the catalyst is placed. In the case where the fuel poisoning or deterioration occurs in the SCR catalyst, although a proper temperature range above or slightly shifted to the high temperature side, or the absolute value of the NO _X purification rate may become small, 500 ° C. it is similar to the normal effects of the generation of fuel poisoning on the NO _X purification rate is large in the above high temperature range.

Therefore, in this embodiment, when the temperature of the SCR catalyst by the execution of the Atsushi Nobori process described above has risen above a predetermined threshold, i.e., the fuel poisoning is likely to occur, reduced NO _X purification rate accordingly When the SCR catalyst is placed in an easily accessible environment, the basic addition amount (SCR
And increase correction of the amount) determined according to the NO _X concentration of the exhaust gas flowing into F4, the amount of the corrected (hereinafter, controls the additive supply valve 7 according referred to as "high temperature additive amount") I did it. The predetermined threshold here is a lower limit value of the temperature at which the pores of the zeolite, which is the carrier of the SCR catalyst, may expand and the temperature at which the fuel in the exhaust gas may become low in molecular weight. The following temperature (for example, 500 ° C.).

The above high temperature addition amount can be obtained by multiplying the basic addition amount by a correction coefficient corresponding to the fuel concentration of the exhaust gas flowing into the SCRF 4. Here, the fuel concentration of the exhaust gas flowing into the SCRF 4 is the fuel concentration of the exhaust gas that reaches the SCRF 4 from the internal combustion engine 1 via the oxidation catalyst 3 when the temperature raising process is being executed. Therefore, when acquiring the fuel concentration flowing into the SCRF 4, the fuel concentration of the exhaust gas discharged from the internal combustion engine 1, the amount of fuel supplied into the exhaust gas by the execution of the temperature raising process, and the fuel consumption amount in the oxidation catalyst 3 (Oxidation reaction amount) is considered, and specifically, the fuel concentration of the exhaust gas flowing into the SCRF 4 is calculated by the following procedure (step 1-4).
(Step 1)
In step 1, the fuel concentration of the exhaust discharged from the internal combustion engine 1 is calculated. Specifically, a map in which the correlation between the engine load, the engine speed, and the fuel concentration of the exhaust gas discharged from the internal combustion engine 1 is stored in advance in the ROM of the ECU 20, and the engine load and the engine speed are arguments. By accessing the map, the fuel concentration of the exhaust discharged from the internal combustion engine 1 may be calculated.
(Step 2)
In step 2, the fuel flowing into the oxidation catalyst 3 per unit time in consideration of the amount of fuel supplied to the exhaust by the fuel supply valve 6 or the amount of fuel supplied to the exhaust by post injection by the fuel injection valve. A quantity is calculated. Specifically, the value obtained by multiplying the fuel concentration calculated in step 1 above and the flow rate of exhaust gas (the total amount of the intake air amount detected by the air flow meter 26 and the fuel injection amount) is multiplied by the fuel supplied by the fuel supply valve 6. The amount of fuel flowing into the oxidation catalyst 3 per unit time may be calculated by adding the supply amount or the fuel supply amount by post injection from the fuel injection valve.

(Step 3)
In step 3, the temperature of the oxidation catalyst 3 is calculated based on the detection value of the first temperature sensor 13. Then, the oxidation capacity of the oxidation catalyst 3 at this time (the oxidation capacity of the fuel per unit time) is calculated based on the temperature of the oxidation catalyst 3 and the exhaust gas flow rate. Specifically, the oxidation capability tends to increase as the temperature of the oxidation catalyst 3 increases, and the oxidation capability tends to decrease as the flow rate of exhaust gas flowing into the oxidation catalyst 3 increases. Therefore, a map reflecting these trends is stored in the ROM of the ECU 20 in advance, and the map is accessed using the temperature of the oxidation catalyst 3 and the exhaust gas flow rate as arguments, so that the oxidation capability of the oxidation catalyst 3 (for example, oxidation) What is necessary is just to calculate the oxidation rate which is the ratio of the fuel concentration flowing out from the oxidation catalyst 3 to the fuel concentration flowing into the catalyst 3.
(Step 4)
In step 4, based on the result of step 1-3, the fuel concentration of the exhaust gas flowing into SCRF 4 is calculated according to the following equation (1).
(Fuel concentration of exhaust gas flowing into SCRF 4) = (fuel concentration calculated from the amount of fuel flowing into oxidation catalyst 3) × (1- (oxidation rate as oxidation ability of oxidation catalyst 3)) (1)

  Note that the oxidation rate of the fuel in the oxidation catalyst 3 may depend on the molecular weight of the fuel. That is, low molecular weight fuel is relatively less oxidized, while high molecular weight fuel is more likely to be oxidized. Therefore, when the fuel supply is performed by the post injection in which the fuel having a relatively low molecular weight is supplied, the oxidation catalyst is compared with the case where the fuel is supplied by the fuel supply valve 6 to which the fuel having a relatively high molecular weight is supplied. The oxidation rate of the oxidation ability may be set low.

When the fuel concentration of the exhaust gas flowing into the SCRF 4 is obtained by the above procedure, the correction coefficient is determined using the fuel concentration as a parameter. At that time, the fuel poisoning is likely to occur in the SCR catalyst as a higher fuel concentration flowing into SCRF4, and NO _X purification rate of the SCR catalyst is considered to be likely to decrease. Further, when the temperature of the SCR catalyst is a high temperature range of not lower than the predetermined threshold value, as described with reference to FIG. 2 described above, as the temperature of the SCR catalyst is increased NO _X purification rate tends to be low. Therefore, as the temperature of the SCR catalyst is increased, the influence of the generation of fuel poisoning on the NO _X purification rate can be said to be greater. Therefore, it is desirable that the correction coefficient is determined in consideration of the temperature of the SCR catalyst in addition to the fuel concentration flowing into the SCRF 4. Therefore, in this embodiment, the basic addition amount is calculated using the first correction coefficient k1 determined according to the fuel concentration of the exhaust gas flowing into the SCRF 4 and the second correction coefficient k2 determined according to the temperature of the SCR catalyst. The amount of increase was corrected. At this time, the first correction coefficient k1 may be set to a value larger than 1 and larger as the fuel concentration of the exhaust gas flowing into the SCR catalyst becomes higher. The second correction coefficient k2 may be a value larger than 1 and set to a larger value as the temperature of the SCR catalyst becomes higher. And ECU20 should just obtain | require the addition amount for high temperature by carrying out the increase correction | amendment of the basic addition amount according to the following formula | equation of (2).
(Addition amount for high temperature) = (Basic addition amount) * (First correction coefficient) * (Second correction coefficient) (2)

High temperature additive amount calculated according to the formula (2) is an amount greater than the base amount determined according to the NO _X concentration of the exhaust gas flowing into the SCRF4, the fuel concentration of the exhaust gas flowing into the SCRF4 The higher the temperature and the higher the temperature of the SCR catalyst, the larger the amount. The increase rate (ratio of the high temperature addition amount to the basic addition amount) by such correction increases as the fuel concentration of the exhaust gas flowing into the SCRF 4 increases and the temperature of the SCR catalyst increases.

Here, when an aqueous urea solution having a higher temperature addition amount than the basic addition amount is supplied into the exhaust gas from the additive supply valve 7, it is generated from an increased amount of urea solution (difference between the high temperature addition amount and the basic addition amount). There is a concern that the NH ₃ that passes through the SCR catalyst. However, when the temperature of the SCR catalyst is in a high temperature range equal to or higher than the predetermined threshold value, the reaction rate between NO _X and NH _{3 at} the active point of the SCR catalyst increases. Therefore, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold, the amount of NO _X that can be purified (reduced) per unit time at the active point where fuel poisoning has not occurred increases. Therefore, NH ₃ produced from the increased amount of urea aqueous solution contributes to the reaction with NO _{X at the} active point where no fuel poisoning occurs. As a result, decrease amount of the NO _X purification rate due to a part of the active sites of the SCR catalyst is poisoned by fuel, by the fuel to increase the amount of NO _X to be purified in active sites that are not poisoned It is compensated by increase of the NO _X purification rate due to. Therefore, even if an additive having a high temperature addition amount higher than the basic addition amount is supplied into the exhaust gas from the additive supply valve 7, NO _X resulting from fuel poisoning is suppressed while suppressing an increase in NH ₃ that passes through the SCR catalyst. A decrease in the purification rate can be suppressed to a small extent.

3, in the case the temperature of the SCR catalyst is above the predetermined threshold value, when the temperature of the exhaust gas of the NO _X concentration and the SCR catalyst flowing into SCRF4 is constant, the fuel concentration of the exhaust gas flowing into the SCRF4, urea supply amount of the aqueous solution, and is a diagram showing changes with time of the NO _X purification rate of the SCR catalyst. As shown in FIG. 3, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold, the high temperature addition amount (solid line in FIG. 3 (b)) is the basic addition amount (dashed line in FIG. 3 (b)). ) many made for than, NO _X purification rate of the SCR catalyst when the amount of the additive for high temperature is supplied from the additive supply valve 7 into the exhaust solid line (in FIG. 3 (c)), the basic amount additive is higher than the NO _X purification rate of the SCR catalyst when it is fed into the exhaust gas (two-dot chain line in FIG. 3 (c)) from the additive supply valve 7. When the fuel concentration of the exhaust gas flowing into the SCRF 4 increases (t2 in FIG. 3), the first correction coefficient k1 is increased accordingly, whereby the high temperature additive amount is increased. As a result, the NO _X purification rate of the SCR catalyst when the basic addition amount is supplied, but decreases after the fuel concentration of the exhaust gas flowing into SCRF4 increased, the SCR catalyst when the amount of addition for the high temperature is supplied NO _X purification rate also will not decrease after the fuel concentration of the exhaust gas flowing into SCRF4 increased. Therefore, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold value, the SCR catalyst is likely to be poisoned by supplying the additive for the high temperature into the exhaust gas from the additive supply valve 7. it is possible to suppress the NO _X purification rate of the SCR catalyst in.

  The correction coefficient multiplied by the basic addition amount when determining the high temperature addition amount does not necessarily have to be divided into the first correction coefficient and the second correction coefficient as described above, and the fuel of the exhaust gas flowing into the SCRF 4 One correction coefficient may be determined using the concentration and the temperature of the SCR catalyst as parameters. In that case, a map storing the correlation between the fuel concentration of the exhaust gas flowing into the SCRF 4, the temperature of the SCR catalyst and the correction coefficient is stored in advance in the ROM of the ECU 20, and the fuel concentration of the exhaust gas flowing into the SCRF 4 and the SCR catalyst are stored. The correction coefficient may be calculated by accessing the map with the temperature of

  Hereinafter, the control procedure of the additive supply valve 7 in the present embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a processing routine executed by the ECU 20 when the additive supply valve 7 is controlled. This processing routine is stored in advance in the ROM of the ECU 20 and is periodically executed by the ECU 20.

In the processing routine of FIG. 4, the ECU 20 first determines whether or not a temperature raising process for oxidizing and removing PM collected in the particulate filter of the SCRF 4 in the process of S101 is being executed. Here, since the case where the temperature increasing process is not running, fuel poisoning, and the SCR catalyst in the NO _X purification rate difficult environment decrease occurred due to the fuel poisoning is believed to be laid, be to supply the urea aqueous solution of the basic amount of additive supply valve 7, it is considered possible to realize a suitable NO _X purification rate in the SCR catalyst. Therefore, if a negative determination is made in the processing of S101, ECU 20 proceeds to the processing of S108, the urea aqueous solution of the basic additive amount determined is supplied into the exhaust gas on the basis of the NO _X concentration of the exhaust gas flowing into the SCRF4 Thus, the additive supply valve 7 is controlled. On the other hand, if an affirmative determination is made in the process of S101, the ECU 20 proceeds to the process of S102.

  In the process of S102, the ECU 20 detects the temperature Tc of the SCR catalyst of SCRF4. The temperature Tc of the SCR catalyst may be directly detected by a dedicated temperature sensor, but may be estimated from the detection value of the second temperature sensor 14, or the detection value of the first temperature sensor 13 and the second temperature sensor 14. It may be estimated from the difference from the detected value. During the temperature increase process, the temperature of the SCR catalyst can be temporarily increased by directly transferring the oxidation heat of PM trapped in the particulate filter of SCRF4 to the SCR catalyst. Therefore, the temperature Tc of the SCR catalyst may be estimated in consideration of such a phenomenon. By executing the processing of S102 in this way, the “detection means” according to the present invention is realized.

In the process of S103, the ECU 20 determines whether or not the SCR catalyst temperature (SCR catalyst temperature) Tc acquired in the process of S102 is equal to or higher than a predetermined threshold Tcthre. As described above, the predetermined threshold value Tcthre is the lower limit value of the temperature at which the pores of the zeolite, which is the carrier of the SCR catalyst, may expand, and the fuel in the exhaust gas may become low molecular. is there. That is, the predetermined threshold Tcthre, by low molecular weight fuel from entering the pores larger diameter of the zeolite, poisoning occurs fuel SCR catalyst, reduce the NO _X purification rate of the SCR catalyst with it This is the temperature that can be considered. Here, when the temperature Tc of the SCR catalyst is lower than the predetermined threshold value Tcthre, the pores of the zeolite are difficult to expand, and the fuel in the exhaust gas is difficult to decrease in molecular weight. Therefore, the fuel poisoning of SCR catalysts, and reduced of the NO _X purification rate due to the fuel poisoning is less likely to occur. Therefore, if a negative determination is made in step S103, the ECU 20 proceeds to step S108, and controls the additive supply valve 7 in accordance with the basic addition amount. On the other hand, when the temperature Tc of the SCR catalyst is equal to or higher than the predetermined threshold value Tcthre, the pores of the zeolite are likely to expand, and the fuel in the exhaust gas tends to be low molecular. Therefore, the fuel poisoning of SCR catalysts, and reduced of the NO _X purification rate due to the fuel poisoning can be said to likely occur. Therefore, if a positive determination is made in the processing of the S103, ECU 20, by sequentially executing the processing of S104-S107, suppressing deterioration of the NO _X purification rate of the SCR catalyst.

  First, in the process of S104, the ECU 20 acquires the fuel concentration Dhc of the exhaust gas flowing into the SCRF 4. As described above, the fuel concentration Dhc of the exhaust gas flowing into the SCRF 4 is the fuel concentration of the exhaust gas flowing into the SCRF 4 when the temperature raising process is being performed, and the fuel concentration of the exhaust gas discharged from the internal combustion engine 1. The calculation is performed based on the equation (1) in consideration of the amount of fuel supplied into the exhaust gas by the execution of the temperature raising process and the amount of fuel consumed in the oxidation catalyst 3 (oxidation reaction amount). As described above, the “acquiring unit” according to the present invention is realized by executing the processing of S104.

  In the process of S105, the ECU 20 determines the first correction coefficient k1 based on the fuel concentration Dhc acquired in the process of S104, and the second based on the temperature Tc of the SCR catalyst acquired in the process of S102. A correction coefficient k2 is determined. In this case, the first correction coefficient k1 is a value greater than 1 and increases as the fuel concentration Dhc increases. Further, the second correction coefficient k2 is a value larger than 1 and is made larger as the temperature Tc of the SCR catalyst becomes higher.

In the process of S106, the ECU 20 calculates the high temperature addition amount according to the equation (2). That, ECU 20 multiplies the basic addition amount is determined based on the concentration of NO _X exhaust gas flowing into SCRF4, a first correction coefficient k1 obtained by the processing of the S104 by multiplying the second correction factor k2 The amount added for high temperature is calculated.

In the process of S107, the ECU 20 controls the additive supply valve 7 in accordance with the high temperature additive amount calculated in the process of S106. In that case, the amount of the aqueous urea solution supplied from the additive supply valve 7 into the exhaust gas is an amount greater than the base amount determined according to the NO _X concentration of the exhaust gas flowing into SCRF4, flows into SCRF4 It increases as the fuel concentration in the exhaust gas increases and the temperature of the SCR catalyst increases. That is, the amount of the urea aqueous solution supplied into the exhaust gas from the additive supply valve 7 is the amount of the fuel in the exhaust gas that easily enters the pores of the zeolite that is the carrier of the SCR catalyst, and enters the pores. The more it becomes, the more it becomes. It should be noted that the “control means” according to the present invention is realized by executing the processing of S104 to S108.

When the amount of the urea aqueous solution supplied from the additive supply valve 7 is controlled according to the processing routine described above, the molecular weight is reduced in the expanded pores of the zeolite constituting the SCR catalyst during the temperature increasing process. by fuel enters, even fuel poisoning occurs with some active sites of the SCR catalyst, it is possible to increase the amount of the nO _X to be reduced by other active sites fuel not poisoning occurs . As a result, the decrease in the NO _X purification rate due to the poisoning of some active sites of the SCR catalyst by the fuel increases the amount of NO _X purified at the active sites not poisoned by the fuel. due will be compensated by increase of the NO _X purification rate, it is possible to reduce the deterioration of the NO _X purification rate of the SCR catalyst.

<Modification of Example 1>
If the exhaust gas containing fuel flows into SCRF 4 when the temperature Tc of SCRF 4 is in a high temperature range equal to or higher than the predetermined threshold value Tcthre by executing the temperature raising process, as described above, the SCR catalyst zeolite fineness is reduced. Fuel poisoning is likely to occur when low molecular weight fuel enters the pores, but if the fuel concentration Dhc of the exhaust gas flowing into SCRF 4 is sufficiently low, the realization of a suitable NO _x purification rate is not substantially hindered. . This can be exemplified by the fuel concentration Dhc of the exhaust to which the SCR catalyst is exposed as a factor for generating or promoting fuel poisoning in the SCR catalyst. If the fuel concentration Dhc is sufficiently low, it becomes a factor of fuel poisoning. It is considered that the adsorption of fuel to the SCR catalyst is difficult to stabilize.

Considering the correlation between the fuel concentration and the fuel poisoning as described above, the fuel concentration of the exhaust gas flowing into the SCRF 4 is sufficiently low when the temperature Tc of the SCR catalyst is in the high temperature range equal to or higher than the predetermined threshold value Tcthr. If, it is possible that the temperature of the SCR catalyst is as if the is less than a predetermined threshold value Tcthre, obtain a sufficiently high NO _X purification rate by supplying the aqueous urea solution of the basic amount to SCRF4. Therefore, when the temperature Tc of the SCR catalyst is equal to or higher than the predetermined threshold value Tcthre, when the fuel concentration Dhc of the exhaust gas flowing into the SCRF 4 is lower than the predetermined concentration, the supply amount of the urea aqueous solution is controlled according to the basic addition amount. Also good. Predetermined concentration referred to here, the exhaust containing the following fuel the predetermined concentration even flows into SCRF4, which is the upper limit value of the fuel concentration can be achieved a suitable NO _X purification rate by the SCR catalyst. When the amount of the urea aqueous solution supplied from the additive supply valve 7 is controlled in this way, when the temperature Tc of the SCR catalyst is equal to or higher than the predetermined threshold value Tcthr, the consumption of the urea aqueous solution is suppressed to a small level. it can be suppressed to reduce the deterioration of the NO _X purification rate of the catalyst.

Note that fuel poisoning of the SCR catalyst is likely to occur when the temperature Tc of the SCR catalyst is higher than when the temperature is low. Considering the correlation between the temperature Tc of the SCR catalyst and the likelihood of fuel poisoning, the predetermined concentration may be set to a smaller value when the temperature Tc of the SCR catalyst is higher than when the temperature is low. As long this manner the predetermined concentration determined, by supplying the aqueous urea solution of the basic amount to SCR catalyst, when it can SCR catalyst to exhibit a sufficiently high NO _X purification rate, the supply amount of the urea aqueous solution It is possible to more reliably suppress an unnecessary increase.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted. In the first embodiment described above, when the temperature Tc of the SCR catalyst is equal to or higher than the predetermined threshold value Tcthre, the higher the fuel concentration of the exhaust gas flowing into the SCRF 4 and the higher the temperature Tc of the SCR catalyst, the higher the SCR catalyst. fuel poisoning is likely to occur in, and based on the perspective of NO _X purification rate tends to decrease, have dealt with the cases of determining the high temperature amount. In contrast, in the present embodiment will describe an example based on the viewpoint of NO _X purification rate of the SCR catalyst greater the fuel poisoning amount of SCRF4 decreases, to determine the high temperature amount. Specifically, in this embodiment, the actual fuel poisoning amount of the SCR catalyst is estimated, and a correction coefficient (hereinafter referred to as “third correction coefficient”) corresponding to the fuel poisoning amount is set as the basic addition amount. By multiplying, the addition amount for high temperature is determined.

The fuel poisoning amount of the SCR catalyst is estimated by integrating the balance of the increase in the fuel poisoning amount per unit time and the decrease in the fuel poisoning amount per unit time. The increase in the fuel poisoning amount per unit time correlates with the fuel concentration of the exhaust gas flowing into the SCRF 4 and the temperature of the oxidation catalyst 3. For example, as shown in FIG. 5, as the fuel concentration of the exhaust gas flowing into the SCRF 4 increases, the amount of increase in the fuel poisoning amount per unit time tends to increase. This is considered that as the fuel concentration of the exhaust gas flowing into the SCRF 4 increases, the adsorption of the fuel to the SCR catalyst, which causes fuel poisoning, becomes easier to stabilize and the active points covered with the fuel increase. Further, the amount of increase in the fuel poisoning amount per unit time tends to increase as the temperature of the oxidation catalyst 3 increases. This is because, as the temperature of the oxidation catalyst 3 increases, the oxidation of the fuel contained in the exhaust is promoted, while the low molecular weight of the fuel that is not sufficiently oxidized by the oxidation catalyst 3 is promoted. It is considered that the molecular weight of the inflowing fuel tends to be small and the amount of the fuel flowing into the pores of the zeolite tends to increase accordingly. Therefore, a map storing each of the above correlations is stored in advance in the ROM of the ECU 20, and the two maps are accessed by accessing the maps corresponding to the fuel concentration of the exhaust gas flowing into the SCRF 4 and the temperature of the oxidation catalyst 3, respectively. The increase amount corresponding to the parameter may be calculated. Then, by substituting these increases into the following equation (3), the increase in the fuel poisoning amount per unit time can be calculated.
(Increase in fuel poisoning amount per unit time) = (Increase amount due to fuel concentration) + (Increase amount due to temperature of oxidation catalyst 3) (3)

Next, the decrease in the fuel poisoning amount per unit time correlates with the temperature of the SCR catalyst, the oxygen concentration of the exhaust gas flowing into the SCRF 4, and the fuel poisoning amount of the SCR catalyst. For example, as shown in FIG. 6, as the temperature of the SCR catalyst increases, the amount of decrease in the fuel poisoning amount per unit time tends to increase. This is considered that the higher the temperature of the SCR catalyst, the more the oxidation and desorption of the fuel adsorbed on the SCR catalyst is promoted. Further, the amount of decrease in the fuel poisoning amount per unit time tends to increase as the oxygen concentration of the exhaust gas flowing into the SCRF 4 increases. This is because the higher the concentration of oxygen in the exhaust gas flowing into SCRF4, the more the fuel adsorbed on the SCR catalyst comes into contact with the oxygen in the exhaust gas, and accordingly the oxidation of the fuel adsorbed on the SCR catalyst is reduced. It is considered to be promoted. Further, the amount of decrease in the fuel poisoning amount per unit time tends to increase as the fuel poisoning amount of the SCR catalyst increases. This is presumably because the amount of the fuel adsorbed on the SCR catalyst that comes into contact with oxygen in the exhaust gas increases as the fuel poisoning amount of the SCR catalyst increases. Therefore, a map storing each of the above correlations is stored in the ROM of the ECU 20 in advance, and a map corresponding to each of the temperature of the SCR catalyst, the oxygen concentration of the exhaust gas flowing into the SCRF 4 and the fuel poisoning amount of the SCR catalyst is accessed. By doing so, the reduction amount corresponding to these three parameters may be calculated. Then, by substituting those reduction amounts into the following equation (4), the reduction amount of the fuel poisoning amount per unit time can be calculated.
(Decrease in fuel poisoning per unit time) = (Decrease due to SCR catalyst temperature) + (Decrease due to oxygen concentration) + (Decrease due to fuel poisoning) 4)
Note that the oxygen concentration of the exhaust gas flowing into the SCRF 4 may be detected by attaching an oxygen concentration sensor (O ₂ sensor) to the exhaust passage 2 between the oxidation catalyst 3 and the SCRF 4. It may be estimated from the temperature of the oxidation catalyst 3 or the like.

When the increase in the fuel poisoning amount per unit time and the decrease in the fuel poisoning amount per unit time are calculated by the method described above, the difference between them (from the increase in fuel poisoning amount per unit time to the unit The amount of fuel poisoning of the SCR catalyst is calculated by adding the amount obtained by subtracting the decrease in the amount of fuel poisoning per hour) to the previous calculated value of the fuel poisoning amount. The process for estimating the fuel poisoning amount of the SCR catalyst in this manner is repeatedly executed at a predetermined cycle during the operation period of the internal combustion engine 1. When the temperature of the SCR catalyst rises to a high temperature range equal to or higher than the predetermined threshold due to the execution of the temperature raising process, the third correction coefficient is calculated based on the fuel poisoning amount of the SCR catalyst at that time. decide. Incidentally, when the temperature of the SCR catalyst is above the predetermined threshold value, as the fuel poisoning amount of the SCR catalyst increases, since the NO _X purification rate of the SCR catalyst is easily lowered, is greater than 1 said third correction coefficient The value may be set to a larger value as the fuel poisoning amount of the SCR catalyst increases. Then, the high-temperature additive amount is calculated by substituting the third correction coefficient and the basic additive amount at that time into the following equation (5).
(Addition amount for high temperature) = (Basic addition amount) * (Third correction factor) (5)

High temperature additive amount calculated according to the formula (5) is an amount greater than the base amount determined according to the NO _X concentration of the exhaust gas flowing into the SCRF4, many HC poisoning amount of the SCR catalyst The amount will increase. The increase rate (ratio of the high temperature addition amount to the basic addition amount) due to such correction increases as the HC poisoning amount of the SCR catalyst increases.

7, when the temperature of the SCR catalyst is above the predetermined threshold value, when the temperature of the NO _X concentration and the SCR catalyst of the exhaust gas flowing into the SCRF4 is constant, the SCR catalyst HC poisoning amount, the urea aqueous solution amount of supply, and is a diagram showing changes with time of the NO _X purification rate of the SCR catalyst. As shown in FIG. 7, when the temperature of the SCR catalyst is equal to or higher than the predetermined threshold value, the basic addition amount (the one-dot chain line in FIG. 7B) is not increased even if the HC poisoning amount increases. Therefore, NO _X purification rate of the SCR catalyst when the aqueous urea solution of the basic amount is supplied from the additive supply valve 7 into the exhaust (two-dot chain line in FIG. 7 (c)), an increase of the HC poisoning amount Decreases with it. On the other hand, the high temperature addition amount (solid line in FIG. 7B) increases as the HC poisoning amount increases. In other words, the amount of high-temperature addition increases as the number of active sites where fuel poisoning actually occurs in the SCR catalyst increases. Therefore, the more active points where fuel poisoning actually occurs in the SCR catalyst, the greater the amount of reaction between NH ₃ and NO _X at the remaining active points where fuel poisoning has not occurred. As a result, the, HC poisoning amount NO _X purification rate of the SCR catalyst (solid line in to FIG. 7 (c)) in the case where the addition amount of the additive for high temperature is supplied from the additive supply valve 7 into the exhaust increases Even if it does not decrease.

  Hereinafter, the control procedure of the additive supply valve 7 in the present embodiment will be described with reference to FIG. FIG. 8 is a flowchart showing a processing routine executed by the ECU 20 when the additive supply valve 7 is controlled. This processing routine is stored in advance in the ROM of the ECU 20 and is periodically executed by the ECU 20. In the processing routine of FIG. 8, the same processes as those of the above-described processing routine of FIG. In the processing routine of FIG. 8, the processing of S201-S203 is executed instead of the processing of S104-S106 in the processing routine of FIG. Accordingly, when an affirmative determination is made in the process of S103, the ECU 20 executes the process of S201.

  In the process of S201, the ECU 20 acquires the fuel poisoning amount of the SCR catalyst. The fuel poisoning amount of the SCR catalyst is obtained according to the processing routine of FIG. The processing routine of FIG. 9 is a processing routine that is repeatedly executed at a predetermined cycle during the operation period of the internal combustion engine 1. In the processing routine of FIG. 9, the ECU 20 reads various data in the processing of S301. The various data here are data necessary for determining the fuel poisoning amount of the SCR catalyst. As described above, the fuel concentration Dhc of the exhaust gas flowing into the SCRF 4, the temperature of the oxidation catalyst 3, the temperature of the SCR catalyst, These are the oxygen concentration of the exhaust gas flowing into the SCRF 4 and the fuel poisoning amount Hold determined at the previous execution of this processing routine.

  In the process of S302, the ECU 20 calculates an increase ΔCha of the fuel poisoning amount per unit time. Specifically, the ECU 20 described above correlates the fuel concentration of the exhaust gas flowing into the SCRF 4 and the increase amount of the fuel poisoning amount per unit time, and the temperature of the oxidation catalyst 3 and the fuel poisoning amount per unit time. Based on the correlation with the increase amount, the fuel poison amount increase amount corresponding to each of the fuel concentration Dhc of the exhaust gas flowing into the SCRF 4 and the temperature of the oxidation catalyst 3 is calculated. Then, the ECU 20 calculates the sum of the increase amounts as the increase ΔCha.

  In the process of S303, the ECU 20 calculates a reduction amount ΔChd of the fuel poisoning amount per unit time. Specifically, the ECU 20 described above relates to the correlation between the temperature of the SCR catalyst and the reduction amount of the fuel poisoning amount per unit time, the oxygen concentration of the exhaust gas flowing into the SCRF 4 and the reduction of the fuel poisoning amount per unit time. The temperature of the SCR catalyst, the oxygen concentration of the exhaust gas flowing into the SCR catalyst, and the fuel based on the correlation with the amount and the correlation between the fuel poisoning amount of the SCR catalyst and the decrease amount of the fuel poisoning amount per unit time A reduction amount of the fuel poisoning amount corresponding to each of the previous values Cold of the poisoning amount is calculated. Then, the ECU 20 calculates the sum of the reduction amounts as the reduction amount ΔChd.

  In the process of S304, the ECU 20 adds the difference (ΔCha−ΔChd) between the increase ΔChha calculated in the process of S302 and the decrease ΔChd calculated in the process of S303 to the previous value Chold of the fuel poisoning amount. Thus, the fuel poisoning amount of the SCR catalyst at the present time is calculated.

  Here, returning to the processing routine of FIG. 8, the ECU 20 executes the process of S202 after executing the process of S201. In the process of S202, the ECU 20 determines the third correction coefficient k3 from the fuel poisoning amount acquired in the process of S201. As described above, the third correction coefficient k3 is a value larger than 1, and is set to a larger value as the fuel poisoning amount of the SCR catalyst increases.

In the process of S203, the ECU 20 multiplies the basic amount determined according to the NO _X concentration of the exhaust gas flowing into the SCRF4, by multiplying the third correction coefficient k3 determined in the processing of the S202, the addition amount for high temperature Is calculated. After executing the process of S203, the ECU 20 proceeds to the process of S107, and controls the additive supply valve 7 according to the high temperature additive amount calculated in the process of S202. In that case, since the amount of the urea aqueous solution supplied into the exhaust gas from the additive supply valve 7 is an amount corresponding to the actual fuel poisoning amount of the SCR catalyst, the NO of the SCR catalyst due to the occurrence of fuel poisoning. It becomes possible to more reliably suppress the decrease in the _X purification rate.

<Modification of Example 2>
In the case less to the extent that the fuel poisoning amount of the SCR catalyst does not affect the NO _X purification rate, the amount of the urea aqueous solution supplied from the additive supply valve 7 may be controlled in accordance with the basic amount. In that case, it is possible that the temperature of the SCR catalyst while suppressing decrease the consumption of the urea aqueous solution when the a predetermined threshold Tcthre above, to suppress the reduction of the NO _X purification rate of the SCR catalyst.

Further, when fuel poisoning of the SCR catalyst has occurred, in addition to the case where the temperature of the SCR catalyst is equal to or higher than the predetermined threshold value Tcthr, even when the temperature is lower than the appropriate temperature range shown in FIG. NO _X purification rate is likely to decrease in the SCR catalyst. Therefore, in the case where fuel poisoning of the SCR catalyst has occurred, when the temperature Tc of the SCR catalyst is equal to or higher than the predetermined threshold, the temperature Tc of the SCR catalyst is lower than the appropriate temperature range. An amount of urea aqueous solution larger than the basic addition amount may be supplied from the additive supply valve 7. Here, when the temperature Tc of the SCR catalyst is lower than the appropriate temperature range, the reaction rate between NO _X and NH ₃ is relatively small, and therefore the NO _X purification rate is increased by increasing the supply amount of the urea aqueous solution. However, there is a possibility that the amount of NH ₃ flowing out from the SCRF 4 without reacting with the SCR catalyst (NH ₃ slip amount) increases. However, as shown in FIG. 1 described above, by arranging ASC 5 downstream of SCRF 4, NH ₃ flowing out from SCRF 4 can be purified (oxidized) by ASC 5. Therefore, when the urea aqueous solution in an amount larger than the basic addition amount is supplied from the additive supply valve 7 when the temperature Tc of the SCR catalyst is lower than the appropriate temperature range, the increase in the NH ₃ slip amount is suppressed while suppressing the increase in the NH ₃ slip amount. it is possible to suppress the reduction of the NO _X purification rate due to the occurrence of poisoning. However, when the temperature of the SCR catalyst is low, there is a possibility that the ASC 5 arranged downstream thereof is not activated. Therefore, in such a case, it is desirable not to increase the amount of the urea aqueous solution.

Further, when the fuel poisoning amount of the SCR catalyst is excessively large, even if increasing the amount of aqueous urea solution that is supplied from the additive supply valve 7, not be sufficiently suppress the reduction of the NO _X purification rate. Therefore, when the fuel poisoning amount of the SCR catalyst exceeds a predetermined allowable limit value, the control of the additive supply valve 7 based on the high temperature additive amount is stopped (the control of the additive supply valve 7 based on the basic additive amount). ), And a process for eliminating fuel poisoning of the SCR catalyst may be executed. Incidentally, the allowable limit value referred to herein is, when the fuel poisoning amount of the SCR catalyst is above the allowable limit value is considered to NO _X purification rate will not increase even if increasing the supply amount of the urea aqueous solution value, or the It is the value obtained by subtracting the margin from the value.

  Here, as described above, the fuel poisoning amount of the SCR catalyst decreases as the temperature of the SCR catalyst increases and the oxygen concentration of the exhaust gas flowing into the SCRF 4 increases. Therefore, in the process of eliminating fuel poisoning of the SCR catalyst (hereinafter referred to as “fuel poisoning elimination process”), the temperature of the SCR catalyst is desorbed from the SCR catalyst or adsorbed to the SCR catalyst. This is done by increasing the oxygen concentration of the exhaust gas flowing into the SCRF 4 when the fuel is in a temperature range where it can be oxidized. As a method of increasing the oxygen concentration of the exhaust gas flowing into the SCRF 4, a method of increasing the opening of a throttle valve (not shown) or reducing the amount of EGR gas recirculated from the exhaust passage 2 to the intake passage 25 by an EGR device (not shown). Can be used. Then, when the fuel poisoning elimination processing is executed by such a method, when the fuel poisoning amount of the SCR catalyst decreases below the allowable limit value, the additive supply valve based on the high temperature addition amount 7 may be resumed. The fuel poisoning amount of the SCR catalyst at the time of executing the poisoning solution processing can be obtained by the method described in the second embodiment.

<Other examples>
The method for controlling the additive supply valve 7 described in the first or second embodiment can be applied to an exhaust purification system in which the particulate filter and the SCR catalyst are separately provided in the exhaust passage 2. . That is, in an exhaust gas purification system in which a particulate filter is disposed in the exhaust passage downstream of the oxidation catalyst and an SCR catalyst is disposed in the exhaust passage downstream of the oxidation catalyst, the PM trapped in the particulate filter is oxidized and removed. When the temperature raising processing is executed, that the temperature of the SCR catalyst rises to above the predetermined threshold, the fuel poisoning is likely to occur, and the NO _X purification rate tends to decrease environment SCR catalyst is placed in the there is a possibility. Therefore, when the temperature of the SCR catalyst rises above the predetermined threshold value due to the execution of the temperature raising process, the additive supply valve 7 is controlled according to the high temperature addition amount described in the first or second embodiment. if it is, it is possible to suppress the reduction of the NO _X purification rate of the SCR catalyst.

Further, in the control method of the additive supply valve 7 described in the first or second embodiment, the SCR catalyst is arranged in the exhaust passage downstream of the storage reduction type catalyst (NSR (NO _X Storage Reduction) catalyst). It can also be applied to an exhaust purification system. In such an exhaust purification system, sulfur oxide (SO _X ) contained in the exhaust is stored in the NSR catalyst. When the amount of SO _X stored in the NSR catalyst increases, the NO _X storage capacity of the NSR catalyst decreases, and it becomes difficult to exhibit the NO _X purification function that the NSR catalyst should originally perform. Therefore, in order to release SO _X accumulated in the NSR catalyst, sulfur poisoning recovery control is performed in which the temperature of the NSR catalyst is raised and the NSR catalyst is placed in a rich atmosphere. When such sulfur poisoning recovery control is executed, the temperature of the SCR catalyst disposed downstream of the NSR catalyst rises to the predetermined threshold or higher, so that fuel poisoning is likely to occur and NO _X purification is performed. The SCR catalyst may be placed in an environment where the rate is likely to decrease. Therefore, when the temperature of the SCR catalyst becomes equal to or higher than the predetermined threshold due to the execution of the sulfur poisoning recovery control, the additive supply valve 7 is controlled according to the high temperature addition amount described in the first or second embodiment. if it is controlled, it is possible to suppress the reduction of the NO _X purification rate of the SCR catalyst.

  Note that the control method of the additive supply valve 7 described in the first or second embodiment is not limited to the above-described temperature increase processing or sulfur poisoning recovery control, but the SCR catalyst control method. It may be executed when the temperature is in a high temperature range equal to or higher than the predetermined threshold. For example, when the internal combustion engine 1 is operated at a high load and the exhaust gas temperature rises, and accordingly the temperature of the SCR catalyst rises to the predetermined threshold value or more, it will be described in the first or second embodiment. The additive supply valve 7 may be controlled according to the high temperature addition amount.

Reference Signs List 1 internal combustion engine 2 exhaust passage 3 oxidation catalyst 6 fuel supply valve 7 additive supply valve 8 tank 10 first NO _X sensor 11 second NO _X sensor 12 differential pressure sensor 13 first temperature sensor 14 second temperature sensor 20 ECU
21 Crank position sensor 22 Accelerator position sensor 25 Intake passage 26 Air flow meter

Claims (5)

An exhaust purification device that is disposed in an exhaust passage of the internal combustion engine and includes an SCR catalyst;
Supply means for supplying ammonia or an additive which is a precursor of ammonia to the exhaust gas flowing into the exhaust purification device;
And control means for controlling the supply means based on the basic amount determined according to the NO _X concentration of the exhaust gas flowing into the exhaust gas purifier,
In an exhaust gas purification system for an internal combustion engine equipped with
Detection means for detecting the temperature of the SCR catalyst;
Obtaining means for obtaining the fuel concentration of the exhaust flowing into the exhaust purification device;
Further comprising
The control means includes
If the temperature detected by the detection means is less than the predetermined threshold, the basic addition amount of the additive is supplied from the supply means,
When the temperature detected by the detection means is equal to or higher than the predetermined threshold value, the basic addition amount is corrected to increase, and when the increase rate by the correction is low in the fuel concentration acquired by the acquisition means An exhaust purification system for an internal combustion engine, wherein the basic additive amount is increased and corrected so as to increase when higher, and the corrected amount of additive is supplied from the supply means.   In the case where the temperature detected by the detection means is equal to or higher than the predetermined threshold, and the fuel concentration acquired by the acquisition means is less than or equal to a predetermined concentration, the control means adds the basic addition amount of the additive. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas purification system is supplied from the supply means.   When the temperature detected by the detection means is equal to or higher than the predetermined threshold, the control means uses the temperature detected by the detection means and the fuel concentration acquired by the acquisition means as parameters. Estimating the fuel poisoning amount, and correcting the basic additive amount to increase so that the increase rate when the estimated fuel poisoning amount is larger than when the fuel poisoning amount is small is increased. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas purification system is supplied from a supply means. The exhaust gas purification device includes a particulate filter that collects particulate matter in the exhaust gas,
The exhaust purification system for an internal combustion engine according to any one of claims 1 to 3, wherein the SCR catalyst is carried by the particulate filter. The exhaust purification device includes an oxidation catalyst disposed upstream of the particulate filter,
In order to raise the temperature of the particulate filter to a predetermined regeneration temperature, fuel is supplied to the exhaust gas flowing into the exhaust gas purification device, and the fuel is oxidized by the oxidation catalyst to flow into the particulate filter. It further comprises a temperature raising control means for performing a temperature raising process for raising the temperature of the exhaust,
The exhaust gas purification system for an internal combustion engine according to claim 4, wherein the predetermined threshold value is equal to or lower than the predetermined regeneration temperature.

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