JP2008267213A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for more correctly calculating a quantity of sulfur component occluded in an NO<SB>x</SB>storage reduction type catalyst even during recovery from sulfur poisoning, in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: The exhaust emission control device is provided with: an NO<SB>x</SB>storage reduction type catalyst; a reducing agent supply means for supplying a reducing agent to upstream of the NO<SB>x</SB>storage reduction type catalyst; a sulfur poisoning recovery means for recovering the NO<SB>x</SB>storage reduction type catalyst from sulfur poisoning by supplying the reducing agent; a sulfur concentration detection means for detecting concentration of the sulfur component in the reducing agent supplied by the reducing agent supply means; and a sulfur poisoning quantity estimation means for estimating the quantity of the sulfur component occluded in the NO<SB>x</SB>storage type catalyst. The sulfur poisoning quantity estimation means estimates a reducing speed of the sulfur component occluded in the NO<SB>x</SB>storage reduction type catalyst while recovering the NO<SB>x</SB>storage reduction type catalyst from the sulfur poisoning according to the concentration of the sulfur component in the reducing agent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. This NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the NOx occluded when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

  Further, the sulfur component contained in the fuel is also stored in the NOx catalyst in the same manner as NOx. The sulfur component occluded in this way is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. This sulfur poisoning reduces the NOx purification rate of the NOx catalyst, so it is necessary to recover sulfur poisoning at an appropriate time.

This sulfur poisoning recovery is performed by setting the NOx catalyst to a high temperature and circulating exhaust gas having a stoichiometric air-fuel ratio or rich air-fuel ratio to the NOx catalyst. For example, by adding fuel to the NOx catalyst, the fuel reacts with the NOx catalyst, and the NOx catalyst becomes high temperature. In this state, sulfur poisoning can be recovered by adding fuel to make the air-fuel ratio of the exhaust gas rich.

Then, the storage amount of the sulfur component in the NOx storage reduction catalyst is calculated based on the total fuel injection amount, the sulfur concentration in the fuel and the catalyst capacity, and the integrated value of the storage amount of the sulfur component exceeds the threshold value. In this case, a technique for recovering sulfur poisoning is known (for example, see Patent Document 1).
JP 2003-65041 A JP-A-8-93456 JP 2005-90277 A

By the way, when the sulfur poisoning recovery of the NOx storage reduction catalyst is performed, if the concentration of the sulfur component in the reducing agent is changed, the recovery degree of the sulfur poisoning is changed. Therefore, the time until the sulfur poisoning recovery is completed changes. Here, if the sulfur poisoning recovery is completed before the sulfur component is sufficiently released, the recovery of the NOx purification rate may be insufficient.

The present invention has been made in view of the above-described problems. In the exhaust gas purification apparatus for an internal combustion engine, the amount of sulfur component stored in the NOx storage reduction catalyst is being recovered from sulfur poisoning. It aims at providing the technique which can be calculated | required more correctly.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
A NOx storage reduction catalyst that stores NOx in the exhaust and reduces NOx in the presence of a reducing agent;
Reducing agent supply means for supplying a reducing agent to the exhaust passage upstream of the NOx storage reduction catalyst;
Sulfur poisoning recovery means for recovering sulfur poisoning of the NOx storage reduction catalyst by supplying a reducing agent from the reducing agent supply means;
A sulfur concentration detection means for detecting the concentration of the sulfur component in the reducing agent supplied by the reducing agent supply means;
A means for estimating the amount of sulfur component stored in the NOx storage reduction catalyst, and is stored in the NOx storage reduction catalyst when the poisoning of the NOx storage reduction catalyst is restored. A sulfur poisoning amount estimation means for estimating a reduction rate of the sulfur component in accordance with the concentration of the sulfur component in the reducing agent;
It is characterized by providing.

The greatest feature of the present invention is that the sulfur component occlusion is recovered at the time of sulfur poisoning recovery, based on the fact that the ease of desorption of the sulfur component from the NOx storage reduction catalyst varies depending on the concentration of the sulfur component in the reducing agent. The amount is to estimate.

The NOx storage reduction catalyst stores NOx, and the stored NOx is reduced by supplying a reducing agent from the reducing agent supply means. Further, by supplying a reducing agent to the NOx storage reduction catalyst, the sulfur poisoning of the NOx storage reduction catalyst is also recovered.

  The sulfur concentration detecting means may obtain the concentration of the sulfur component in the reducing agent by a sensor or the like, or may be obtained based on a value input by a driver or the like. Furthermore, when the concentration of the sulfur component in the reducing agent is known in advance, the value may be used.

The sulfur poisoning amount estimation means estimates the amount of sulfur component by adding the amount of sulfur component stored in the NOx storage reduction catalyst and subtracting the amount of released sulfur component. The value to be subtracted at this time varies depending on the concentration of the sulfur component in the reducing agent. Therefore, the sulfur poisoning recovery rate calculation means calculates the decrease rate of the sulfur component stored in the NOx storage reduction catalyst according to the concentration of the sulfur component in the reducing agent. And the occlusion amount of a sulfur component can be obtained by calculating | requiring the decreasing amount of a sulfur component from the decreasing rate of the sulfur component obtained in this way. The reduction rate of the sulfur component may be the amount of the sulfur component that decreases per unit time.

The sulfur poisoning amount estimation means may estimate the reduction amount of the sulfur component instead of the reduction rate of the sulfur component. The sulfur poisoning amount estimation means may estimate the amount of the sulfur component remaining in the NOx storage reduction catalyst after the sulfur component is reduced. Furthermore, the sulfur poisoning amount estimation means may estimate the release amount of the sulfur component instead of the decrease rate of the sulfur component.

In the present invention, the sulfur poisoning amount estimation means increases the decrease rate of the sulfur component stored in the NOx storage reduction catalyst as the concentration of the sulfur component detected by the sulfur concentration detection means increases. Can be late.

Here, when sulfur poisoning is recovered, it is estimated that SO ₃ is released from the NOx storage reduction catalyst when the reducing agent acts on, for example, Pt in a high-temperature atmosphere, and this SO ₃ is reduced to SO ₂ by the reducing agent. Is done. When the concentration of the sulfur component in the reducing agent increases, the concentration of the sulfur component locally increases around Pt, and it is estimated that SO ₃ release is inhibited. Therefore, it is considered that as the concentration of the sulfur component in the reducing agent is higher, the decreasing rate of the sulfur component stored in the NOx storage reduction catalyst becomes slower. By estimating the amount of the sulfur component stored in the NOx storage reduction catalyst based on this relationship, it is possible to estimate the reduction rate of the sulfur component more accurately.

In the present invention, the sulfur poisoning amount estimation means detects the amount of the sulfur component stored in the NOx storage reduction catalyst when the sulfur poisoning recovery is completed by the sulfur concentration detection means. It can be estimated that the higher the concentration of the sulfur component, the greater.

In other words, when the concentration of the sulfur component in the reducing agent increases, the amount of sulfur component released from the NOx storage reduction catalyst decreases, so that the sulfur component stored in the NOx catalyst even after the recovery from sulfur poisoning is completed. The amount of increases. Based on this relationship, based on the concentration of the sulfur component in the reducing agent, the amount of the sulfur component stored in the NOx storage reduction catalyst at the end of the sulfur poisoning recovery can be estimated.

In the present invention, the sulfur poisoning recovery means recovers sulfur poisoning until the amount of the sulfur component stored in the NOx storage reduction catalyst becomes a threshold value or less,
A threshold value determining means for increasing the threshold value as the concentration of the sulfur component detected by the sulfur concentration detecting means is higher can be further provided.

Here, the amount of sulfur component stored in the NOx storage reduction catalyst is reduced to 0 by recovering sulfur poisoning.
It is difficult to reduce to Therefore, when the storage amount of the sulfur component is reduced to a threshold value or less, the recovery from sulfur poisoning is terminated by assuming that the release of the sulfur component is completed. However, if the concentration of the sulfur component in the reducing agent is high, the rate of reduction of the sulfur component stored in the NOx storage reduction catalyst becomes slow, so it takes time until the sulfur component decreases below the threshold value. It is also possible that the amount of the sulfur component stored in the NOx storage reduction catalyst does not decrease below the threshold value.

  On the other hand, as the concentration of the sulfur component in the reducing agent is higher, the sulfur poisoning recovery is suppressed for a long time by increasing the threshold value.

Here, it can be considered that by increasing the threshold value, the NOx purification rate after completion of the sulfur poisoning recovery is lowered. However, when the fuel of the internal combustion engine is used as the reducing agent, the sulfur concentration in the fuel increases, so that a large amount of sulfur components are discharged from the internal combustion engine, so that the progress of sulfur poisoning is rapid. In other words, even if the sulfur poisoning recovery is carried out for a long time and the amount of occlusion of the sulfur component is further reduced, the sulfur poisoning progresses quickly. Reach quickly. Therefore, even if the threshold value is increased, the influence on the NOx purification rate is small.

Further, when the threshold value is increased, the amount of sulfur component stored in the NOx storage reduction catalyst is increased when the recovery from sulfur poisoning is completed. However, by increasing the frequency of the sulfur poisoning recovery, NOx purification can be achieved. Reduction in rate can be suppressed.

By the way, as the amount of the sulfur component stored in the NOx storage reduction catalyst at the time of sulfur poisoning recovery decreases, the decrease rate of the sulfur component decreases. Therefore, when the amount of the sulfur component is close to the threshold value, a large amount of reducing agent is required to release the same amount of the sulfur component as compared to immediately after the start of the recovery from sulfur poisoning. However, as described above, the NOx purification rate is not so high. On the other hand, as the concentration of the sulfur component in the reducing agent is higher, the consumption of the reducing agent can be reduced by increasing the threshold value.

  In the present invention, the threshold value determining means can provide an upper limit value of the threshold value so that the NOx purification rate in the NOx storage reduction catalyst becomes a predetermined value or more.

Here, the NOx purification rate decreases as the threshold value is increased. That is, if the threshold value is too large, the NOx purification rate may be lower than, for example, an allowable value. On the other hand, the threshold value is determined so that the NOx purification rate becomes, for example, an allowable value or more. That is, the upper limit value of the threshold value can be a value that allows the NOx purification rate to fall within an allowable range.

In the present invention, the sulfur poisoning recovery means, when the amount of the sulfur component stored in the NOx storage reduction catalyst does not fall below the threshold during the sulfur poisoning recovery, You can take action to speed up.

The treatment for increasing the reduction rate of the sulfur component refers to a treatment for releasing more sulfur component during recovery from sulfur poisoning. For example, the temperature of the NOx storage reduction catalyst is increased or the concentration of the reducing agent is increased. Or higher. And it can suppress that a NOx purification rate becomes lower than an allowable value by performing the treatment which makes the decrease rate of a sulfur component faster.

According to the present invention, the amount of the sulfur component stored in the NOx storage reduction catalyst can be determined more accurately even during recovery from sulfur poisoning.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied and an exhaust system thereof. The internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. A throttle 4 is provided in the middle of the intake passage 2. The throttle 4 is opened and closed by an electric actuator. An air flow meter 5 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake passage 2 is provided in the intake passage 2 upstream of the throttle 4. The air flow meter 5 measures the amount of fresh intake air in the internal combustion engine 1.

  On the other hand, an NOx storage reduction catalyst 6 (hereinafter referred to as NOx catalyst 6) is provided in the middle of the exhaust passage 3. The NOx catalyst 6 has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have.

Further, in this embodiment, a fuel addition valve 7 for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage 3 upstream from the NOx catalyst 6 is provided. Here, the fuel addition valve 7 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the fuel addition valve 7 into the exhaust passage 3 enriches the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 3 and reduces the NOx stored in the NOx catalyst 6. . During this NOx reduction, so-called rich spike control is performed in which the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 6 is made rich in a spike-like (short-time) manner with a relatively short cycle. In this embodiment, the fuel addition valve 7 corresponds to the reducing agent supply means in the present invention.

  Further, the NOx catalyst 6 also stores sulfur components contained in the fuel in the same manner as NOx. The sulfur component occluded in this way is less likely to be released than NOx and is accumulated in the NOx catalyst 6. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst 6 decreases due to this sulfur poisoning, it is necessary to perform sulfur poisoning recovery to recover from sulfur poisoning at an appropriate time. This sulfur poisoning recovery is performed by raising the temperature of the NOx catalyst 6 and flowing exhaust gas having a stoichiometric air-fuel ratio or rich air-fuel ratio to the NOx catalyst 6. Also at this time, the rich spike control is performed. In this embodiment, the ECU 10 that recovers sulfur poisoning corresponds to the sulfur poisoning recovery means of the present invention.

  The internal combustion engine 1 is provided with an EGR device 8 that recirculates part of the exhaust gas flowing through the exhaust passage 3 to the intake passage 2. The EGR device 8 includes an EGR passage 81 and an EGR valve 82.

The EGR passage 81 connects the exhaust passage 3 upstream of the NOx catalyst 6 and the intake passage 2 downstream of the throttle 4. Exhaust gas is recirculated through the EGR passage 81. The EGR valve 82 adjusts the amount of EGR gas flowing through the EGR passage 81 by adjusting the passage sectional area of the EGR passage 81.

  Further, a sulfur concentration detection device 72 that detects the concentration of sulfur component in the fuel added from the fuel addition valve 7 (the concentration of sulfur component is hereinafter referred to as “sulfur concentration”) is provided in the fuel passage 71 through which the fuel flows. It is provided. The sulfur concentration detection device 72 measures the sulfur concentration with a sensor, for example. Further, instead of directly detecting the sulfur concentration in the fuel, for example, the sulfur concentration in the fuel to be supplied may be obtained in advance, and the sulfur concentration may be calculated based on this value. In this embodiment, the sulfur concentration detection device 72 corresponds to the sulfur concentration detection means in the present invention.

Further, an exhaust temperature sensor 9 for detecting the temperature of the exhaust gas flowing through the exhaust passage 3 is attached to the exhaust passage 3 downstream of the NOx catalyst 6. Based on the output signal of the exhaust temperature sensor 9, the temperature of the NOx catalyst 6 is detected.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  The ECU 10 is connected to the air flow meter 5 and the exhaust gas temperature sensor 9, and further to the sulfur concentration detection device 72 through an electrical wiring, and an output signal of the exhaust gas temperature sensor 9 is input thereto. On the other hand, the throttle 10, the fuel addition valve 7, and the EGR valve 82 are connected to the ECU 10 through electrical wiring, and these are controlled by the ECU 10.

In this embodiment, the sulfur poisoning recovery is performed when the amount of the sulfur component occluded in the NOx catalyst 6 (hereinafter also referred to as sulfur poisoning amount) exceeds a specified amount. NOx
Hereinafter, the amount of the sulfur component stored in the catalyst 6 is also referred to as “sulfur poisoning amount”. The amount of sulfur component is also simply referred to as “sulfur amount”. Here, in order to obtain the sulfur poisoning amount, first, the sulfur amount discharged from the internal combustion engine 1 is calculated based on the sulfur concentration in the fuel obtained from the sulfur concentration detecting device 72 and the fuel consumption amount. Then, the amount of sulfur stored in the NOx catalyst 6 can be determined by obtaining the ratio of this sulfur stored in the NOx catalyst 6 in advance through experiments or the like.
By integrating this value, the sulfur poisoning amount can be obtained.

The prescribed amount that is the threshold for the sulfur poisoning amount when performing sulfur poisoning recovery is set in advance in consideration of the NOx purification rate.

Further, the sulfur poisoning amount is calculated even during the sulfur poisoning recovery. That is, the sulfur poisoning amount is reduced by the amount of sulfur released by the sulfur poisoning recovery. Conventionally, the release rate of sulfur component is NOx catalyst 6
This is calculated based on the sulfur poisoning amount of NO, the temperature of the NOx catalyst 6 or the exhaust, the flow rate of the exhaust, the time when the air-fuel ratio is rich, the degree of rich when the air-fuel ratio is rich, and the like. In this embodiment, the release rate of the sulfur component is further determined based on the concentration of sulfur in the fuel added from the fuel addition valve 7. The “sulfur component release rate” may be replaced with “a reduction rate of the sulfur poisoning amount”.

FIG. 2 is a graph showing the relationship between the sulfur poisoning amount, the release rate of the sulfur component, and the sulfur concentration in the fuel. The solid line has a higher sulfur concentration in the fuel than the broken line. The release rate of the sulfur component refers to the amount of sulfur released per unit time. The greater the sulfur poisoning amount, the faster the release rate of the sulfur component. The higher the sulfur concentration in the fuel, the slower the release rate of the sulfur component.

  FIG. 3 is a diagram showing the relationship between the elapsed time from the start of recovery from sulfur poisoning, the amount of sulfur poisoning, and the sulfur concentration in the fuel. The solid line has a higher sulfur concentration in the fuel than the broken line. That is, the amount of decrease in the sulfur poisoning amount after the start of recovery from sulfur poisoning becomes smaller as the sulfur concentration in the fuel is higher. Therefore, the lower the sulfur concentration in the fuel, the faster the sulfur poisoning recovery is completed.

  If the relationship of FIG. 3 is obtained by experiment or the like for each sulfur concentration in the fuel, based on the sulfur concentration obtained by the sulfur concentration detector 72 and the elapsed time since the start of sulfur poisoning recovery, The amount of sulfur poisoning at the present time can be obtained. In FIG. 3, only two types of solid lines and broken lines are shown, but this number can be increased. Further, two values may be obtained by experiments or the like, and values at other sulfur concentrations may be estimated from these values. In this embodiment, the ECU 10 for determining the sulfur poisoning amount corresponds to the sulfur poisoning amount estimating means in the present invention.

Further, in this embodiment, the sulfur poisoning amount of the NOx catalyst 6 when the sulfur poisoning recovery is completed is obtained according to the sulfur concentration in the fuel added from the fuel addition valve 7. That is, as can be seen with reference to FIG. 3, the higher the sulfur concentration in the fuel, the more difficult it is to reduce the sulfur poisoning amount. Since it is difficult to release all the sulfur components stored in the NOx catalyst 6, the sulfur poisoning recovery is completed with some sulfur components remaining in the NOx catalyst 6.

Therefore, in the present embodiment, it is estimated that the higher the sulfur concentration in the fuel added from the fuel addition valve 7, the more sulfur component remains in the NOx catalyst 6 at the end of the sulfur poisoning recovery. The relationship between the sulfur concentration and the amount of remaining sulfur component can be obtained in advance by experiments or the like.

  As described above, according to the present embodiment, the reduction rate of the sulfur poisoning amount during the recovery of sulfur poisoning is obtained based on the sulfur concentration in the fuel. Therefore, during the sulfur poisoning recovery and at the end of the sulfur poisoning recovery, The amount of sulfur poisoning can be estimated more accurately.

Further, since the amount of the sulfur component remaining in the NOx catalyst 6 at the end of the recovery from the sulfur poisoning is obtained based on the sulfur concentration in the fuel, the subsequent calculation accuracy of the sulfur poisoning amount can be further increased.

  In the present embodiment, the threshold of the sulfur poisoning amount used for determining the end of sulfur poisoning recovery is changed based on the sulfur concentration in the fuel. Since other devices are the same as those in the first embodiment, the description thereof is omitted. Note that the “threshold for sulfur poisoning used to determine the end of recovery from sulfur poisoning” is hereinafter referred to as “end threshold”.

  FIG. 4 is a diagram showing the relationship between the elapsed time since the start of recovery from sulfur poisoning, the amount of sulfur poisoning, and the sulfur concentration in the fuel. The solid line has a higher sulfur concentration in the fuel than the broken line.

The time taken for the sulfur poisoning amount to reach the value indicated by A is indicated by X when the sulfur concentration in the fuel is low, and indicated by Y when the sulfur concentration in the fuel is high. That is, when the sulfur concentration is high, sulfur poisoning recovery is performed longer than the time when the sulfur concentration is low by the time of the difference between Y and X. The fuel consumption deteriorates by this difference, and the thermal deterioration of the NOx catalyst 6 proceeds.

Here, if the sulfur concentration in the fuel increases, the release rate of the sulfur component decreases, so if the end threshold is too small, it takes time to complete the sulfur poisoning recovery or the sulfur poisoning recovery is completed. There is not.

  On the other hand, as can be seen with reference to FIG. 4, when a certain amount of time has elapsed since the start of the recovery from sulfur poisoning, the amount of decrease in the sulfur poisoning amount decreases. The NOx purification rate is not so high.

  Therefore, in this embodiment, the higher the concentration of sulfur in the fuel added from the fuel addition valve 7, the larger the end threshold value. That is, in FIG. 4, when the sulfur concentration in the fuel is high, the end threshold value is set to a value indicated by B, so that the sulfur poisoning recovery is ended when the sulfur poisoning amount reaches the value indicated by B. Thereby, sulfur poisoning is completed at the time indicated by Z. That is, it is suppressed that sulfur poisoning recovery is performed for a long time. In this embodiment, the ECU 10 that increases the end threshold value as the sulfur concentration in the fuel is higher corresponds to the threshold value determining means in the present invention.

By the way, by increasing the end threshold value, the NOx purification rate immediately after the end of the recovery from sulfur poisoning becomes lower. However, even if the sulfur poisoning recovery is performed for a long period of time, when the sulfur concentration in the fuel is high, a large amount of sulfur components are discharged from the internal combustion engine 1, so that sulfur poisoning proceeds immediately. Therefore, even if the end threshold value is increased, the influence due to the decrease in the NOx purification rate is reduced.

Here, if the end threshold value is too large, the NOx purification rate may fall outside the allowable range, so an upper limit is set for the end threshold value. This upper limit is set so that the NOx purification rate falls within the allowable range.

As described above, according to the present embodiment, the time during which sulfur poisoning recovery is performed can be shortened, so that deterioration of fuel consumption can be suppressed or the progress of thermal deterioration of the NOx catalyst 6 can be suppressed. Can do.

  In addition, by setting an upper limit for the threshold of the sulfur poisoning amount used for determining the end of sulfur poisoning recovery, it is possible to suppress the NOx purification rate from falling below the allowable range.

  In this embodiment, when the sulfur poisoning recovery described in the second embodiment is performed, when the sulfur poisoning amount does not decrease to the threshold value, a treatment for further promoting the sulfur poisoning recovery is performed. Since other devices are the same as those in the first embodiment, the description thereof is omitted.

  Here, if the sulfur concentration in the fuel added from the fuel addition valve 7 becomes too high, the sulfur poisoning amount cannot be reduced to the end threshold value.

In such a case, for example, during recovery from sulfur poisoning, the target temperature of the NOx catalyst 6 is increased, or the air-fuel ratio is decreased by increasing the amount of fuel added per unit time. By doing in this way, since the reduction rate of sulfur poisoning amount can be made faster, sulfur poisoning amount reaches a threshold more rapidly. Therefore, the required NOx purification rate can be ensured.

  FIG. 5 is a time chart showing the transition of the sulfur poisoning amount. A solid line indicates a case where the treatment according to the present embodiment is performed, and a broken line indicates a case where the treatment according to the present embodiment is not performed. The sulfur concentration in the fuel added at this time is relatively high.

  Then, in the time indicated by S, it is determined that the sulfur poisoning amount does not become the end threshold value or less, and a process for further promoting the sulfur poisoning recovery is started.

  As described above, according to this embodiment, even when the sulfur concentration in the fuel is very high, the NOx purification rate after completion of the sulfur poisoning recovery can be kept within the allowable range.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its exhaust system. It is the figure which showed the relationship between the sulfur poisoning amount, the discharge | release rate of a sulfur component, and the sulfur concentration in a fuel. It is the figure which showed the relationship between the elapsed time after starting sulfur poisoning recovery | restoration, the amount of sulfur poisoning, and the sulfur concentration in a fuel. It is the figure which showed the relationship between the elapsed time after starting sulfur poisoning recovery | restoration, the amount of sulfur poisoning, and the sulfur concentration in a fuel. It is a time chart which showed transition of sulfur poisoning amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Intake passage 3 Exhaust passage 4 Throttle 5 Air flow meter 6 Occlusion reduction type NOx catalyst 7 Fuel addition valve 8 EGR device 9 Exhaust temperature sensor 10 ECU
71 Fuel passage 72 Sulfur concentration detection device 81 EGR passage 82 EGR valve

Claims (6)

A NOx storage reduction catalyst that stores NOx in the exhaust and reduces NOx in the presence of a reducing agent;
Reducing agent supply means for supplying a reducing agent to the exhaust passage upstream of the NOx storage reduction catalyst;
Sulfur poisoning recovery means for recovering sulfur poisoning of the NOx storage reduction catalyst by supplying a reducing agent from the reducing agent supply means;
A sulfur concentration detection means for detecting the concentration of the sulfur component in the reducing agent supplied by the reducing agent supply means;
A means for estimating the amount of sulfur component stored in the NOx storage reduction catalyst, and is stored in the NOx storage reduction catalyst when the poisoning of the NOx storage reduction catalyst is restored. A sulfur poisoning amount estimation means for estimating a reduction rate of the sulfur component in accordance with the concentration of the sulfur component in the reducing agent;
An exhaust emission control device for an internal combustion engine, comprising: The sulfur poisoning amount estimation means slows down the reduction rate of the sulfur component stored in the NOx storage reduction catalyst as the concentration of the sulfur component detected by the sulfur concentration detection means is higher. The exhaust emission control device for an internal combustion engine according to claim 1. The sulfur poisoning amount estimation means determines the amount of sulfur component stored in the NOx storage reduction catalyst when the recovery of sulfur poisoning is completed, and the concentration of the sulfur component detected by the sulfur concentration detection means. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the higher the value, the higher the number. The sulfur poisoning recovery means recovers sulfur poisoning until the amount of the sulfur component stored in the NOx storage reduction catalyst falls below a threshold value,
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising a threshold value determination unit that increases the threshold value as the concentration of the sulfur component detected by the sulfur concentration detection unit is higher.   The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the threshold value determining means provides an upper limit value of the threshold value so that the NOx purification rate in the NOx storage reduction catalyst is equal to or greater than a predetermined value. The sulfur poisoning recovery means performs a process of increasing the reduction rate of the sulfur component when the amount of the sulfur component stored in the NOx storage reduction catalyst does not fall below the threshold during the sulfur poisoning recovery. 6. An exhaust emission control device for an internal combustion engine according to claim 4, wherein the exhaust gas purification device is an internal combustion engine.

Images