JP2009197707A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology for promoting the atomization of fuel added into exhaust gas, in an exhaust emission control device for an internal combustion engine. <P>SOLUTION: This exhaust emission control device for the internal combustion engine includes: an exhaust emission control catalyst; a cylinder air-fuel ratio control means changing an air-fuel ratio in the cylinder of the internal combustion engine; a fuel adding device adding fuel into the exhaust passage of the internal combustion engine; and a reducing agent supplying means reducing the air-fuel ratio in the cylinder by the cylinder air-fuel ratio control means when the reducing agent is supplied to the exhaust emission control catalyst in comparison with the case that the reducing agent is not supplied thereto, and adding the fuel from the fuel adding device into exhaust gas with the air-fuel ratio reduced. <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 the air-fuel ratio is reduced in the cylinder of the internal combustion engine, combustion is performed, and fuel is added to the exhaust gas to recover the purification ability of the NOx storage reduction catalyst (for example, Patent Document 1). reference.).

However, if the atomization of the fuel added to the exhaust gas is not sufficient, the catalyst may be biased to the air-fuel ratio, and the purification capacity may not be sufficiently recovered.
JP 2005-226463 A JP 2004-360575 A Japanese Patent Laid-Open No. 2007-040241 JP 2007-064167 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of promoting atomization of fuel added to exhaust gas in an exhaust gas purification apparatus for an internal combustion engine. And

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
An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An in-cylinder air-fuel ratio control means for changing an air-fuel ratio in the cylinder of the internal combustion engine;
A fuel addition device for adding fuel into the exhaust passage of the internal combustion engine;
When the reducing agent is supplied to the exhaust purification catalyst, the air-fuel ratio in the cylinder is lowered by the in-cylinder air-fuel ratio control means than when the reducing agent is not supplied. A reducing agent supply means for adding fuel;
It is characterized by comprising.

  The cylinder air-fuel ratio is changed by the cylinder air-fuel ratio control means by changing at least one of the intake air amount and the fuel injection amount. This includes changing the intake air amount or the fuel injection amount by changing the ratio of the EGR gas. Then, fuel is added from the fuel addition device into the exhaust gas whose air-fuel ratio has been lowered by the in-cylinder air-fuel ratio control means.

  Here, if the air-fuel ratio of the exhaust gas is made rich by simply adding fuel to the exhaust gas, the lean air-fuel ratio exhaust gas comes into contact with the surface of the fuel. Therefore, since oxygen and fuel react in the catalyst, a reducing atmosphere is formed only on the downstream side of the exhaust purification catalyst. Further, if the atomization of the fuel is not sufficient, the temperature rise in the catalyst will not be uniform.

  On the other hand, when the air-fuel ratio in the cylinder is set to the rich air-fuel ratio and fuel is not added to the exhaust gas, the amount of oxygen contained in the exhaust gas is reduced, but the amount of reducing agent is also small. For this reason, there is a possibility that the temperature of the catalyst is lowered or the recovery of the purification ability is insufficient.

  On the other hand, when fuel is added to the exhaust gas whose air-fuel ratio has been lowered by the in-cylinder air-fuel ratio control means, the amount of reducing agent in the exhaust gas is lower than when the air-fuel ratio is lowered only by the cylinder air-fuel ratio control means. Can be more. Further, since it is not necessary to make an excessive rich air-fuel ratio in the cylinder, the occurrence of smoke can be suppressed.

  By the way, since the exhaust gas generated when the air-fuel ratio is lowered in the cylinder is high temperature and high pressure, the volume expands in the exhaust passage. Therefore, the turbulence is large compared to the exhaust when the air-fuel ratio is not lowered in the cylinder. In particular, the turbulence increases at the exhaust boundary before and after changing the air-fuel ratio. By adding fuel to this disturbance, atomization of the fuel can be promoted. Further, since the fuel can be dispersed in the exhaust gas, it is possible to generate a uniform air-fuel ratio exhaust gas.

That is, the amount of oxygen in the exhaust gas can be reduced by lowering the air-fuel ratio in the cylinder, and the fuel atomized by the addition of fuel to the exhaust gas can be supplied to the catalyst. Thereby, the temperature of a catalyst can be raised uniformly. For example, more sulfur components stored in the NOx storage reduction catalyst can be released. Further, since the reducing agent can be added to the entire catalyst, the purification ability can be sufficiently recovered.

  It should be noted that at least a part of the fuel added from the fuel addition device at one time is added to the exhaust with the air-fuel ratio lowered or to the downstream end or the upstream end (the above-mentioned boundary) of the exhaust with the air-fuel ratio lowered. It should be.

  In the present invention, the reducing agent supply means adds fuel over the entire period during which the exhaust gas passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the cylinder air-fuel ratio control means. In addition, the amount of fuel added from the fuel addition device can be adjusted so that fuel is added only during this period.

  That is, atomization of the fuel can be promoted by adding the fuel only to the exhaust gas whose air-fuel ratio is lowered. Further, by adding fuel over the entire period when the exhaust gas when the air-fuel ratio in the cylinder is lowered passes through the fuel addition device, more turbulent flow effects can be obtained.

  In the present invention, the reducing agent supply means adds fuel over the entire period during which the exhaust gas passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the cylinder air-fuel ratio control means. When adding more fuel than is possible at one time, fuel addition is started before the exhaust gas whose air-fuel ratio has been lowered reaches the fuel addition device, and the air-fuel ratio is lowered. Further, the amount of fuel added from the fuel addition device can be adjusted so that the addition of fuel from the fuel addition device is completed when the last part of the exhaust gas passes through the fuel addition device.

  That is, when the period when the exhaust gas when the air-fuel ratio in the cylinder is lowered passes through the fuel addition device is short, the fuel may not be completely added to the exhaust gas whose air-fuel ratio is lowered. In such a case, the addition of fuel is started before the exhaust gas whose air-fuel ratio has been lowered arrives at the fuel addition device. By doing in this way, the temperature of the catalyst can be raised before the exhaust gas whose air-fuel ratio is lowered arrives. Thereafter, fuel is added throughout the exhaust gas whose air-fuel ratio has been lowered through the fuel addition device. The fuel atomization can be promoted as much as possible by combining the timing when the fuel addition is completed and the timing when the last part of the exhaust gas whose air-fuel ratio is lowered passes.

In the present invention, the reducing agent supply means adds fuel over the entire period during which the exhaust gas passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the cylinder air-fuel ratio control means. When adding less fuel than is possible at a time, the addition of fuel can be started when the exhaust gas with the lowered air-fuel ratio reaches the fuel addition device.

  That is, when the fuel is added over the entire exhaust gas whose air-fuel ratio has been lowered, such as when the exhaust gas when the air-fuel ratio in the cylinder is lowered passes through the fuel addition device for a long period of time, the desired reducing agent Concentration may not be achieved. In such a case, the fuel is added so that the concentration of the reducing agent necessary for restoring the exhaust purification capacity is reached, and the addition of the fuel is started at the same time as the exhaust with the lowered air-fuel ratio arrives. To do. That is, fuel is not added in the vicinity of the rearmost portion of the exhaust gas whose air-fuel ratio has been lowered. In this way, by adding the fuel in accordance with the foremost part of the exhaust gas whose air-fuel ratio has been lowered, fuel can be added to the catalyst at the same time as the exhaust gas whose air-fuel ratio has been lowered reaches the catalyst. The temperature of the catalyst can be raised early.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention can promote atomization of fuel added to the exhaust gas.

  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 intake / exhaust system thereof. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle engine.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. An air flow meter 4 that outputs a signal corresponding to the flow rate of the intake air flowing through the intake passage 2 is provided in the middle of the intake passage 2. The air flow meter 4 measures the intake air amount Ga of the internal combustion engine 1. Further, the amount of exhaust gas can be obtained based on the intake air amount Ga.

On the other hand, an oxidation catalyst 5 and an NOx storage reduction catalyst 6 (hereinafter referred to as NOx catalyst 6) are provided in the exhaust passage 3 in order from the upstream side (that is, the internal combustion engine 1 side). The oxidation catalyst 5 includes Pt, and has a function of storing oxygen (O ₂ storage capability). The O ₂ storage capacity of the oxidation catalyst 5 is to store excess oxygen present in the exhaust when the air-fuel ratio of the air-fuel mixture becomes lean, and to release the stored oxygen when the air-fuel ratio becomes rich.

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.

When NOx stored in the NOx catalyst 6 is reduced, a reducing agent is intermittently supplied to the NOx catalyst 6.

On the other hand, the NOx catalyst 6 also stores sulfur oxide (SOx) generated by combustion of sulfur contained in the fuel by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst 6. And as much as SOx is occluded, NOx
As a result, the amount of NOx stored in the NOx catalyst 6 decreases. This is called sulfur poisoning (SOx poisoning), and it is necessary to perform a poisoning recovery process for recovering from sulfur poisoning at an appropriate time.
This poisoning recovery process is performed by intermittently supplying a reducing agent while keeping the NOx catalyst 6 at a high temperature (for example, about 600 to 650 ° C.).

Further, the reducing agent can be supplied to the oxidation catalyst 5 when the temperature of the NOx catalyst 6 is raised. That is, the reaction of the reducing agent at the oxidation catalyst 5 raises the temperature of the exhaust gas, so that the temperature of the downstream NOx catalyst 6 can be raised. Thereby, the temperature of the NOx catalyst 6 can be raised to a temperature required for NOx reduction and sulfur poisoning recovery. In this embodiment, the oxidation catalyst 5 or the NOx catalyst 6 corresponds to the exhaust purification catalyst in the present invention.

  A fuel injection valve 11 that injects fuel into a cylinder or an intake passage 2 of the internal combustion engine 1 is attached to the internal combustion engine 1. By adjusting the fuel injection amount from the fuel injection valve 11, the internal combustion engine 1 can be operated at a rich air-fuel ratio, a stoichiometric air-fuel ratio, or a lean air-fuel ratio. Thereby, the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 5 can be changed.

A first air-fuel ratio sensor 7 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage 3 is attached to the exhaust passage 3 upstream of the oxidation catalyst 5. On the other hand, a second air-fuel ratio sensor 8 for detecting the air-fuel ratio of the exhaust gas flowing through the exhaust passage 3 is attached to the exhaust passage 3 downstream of the oxidation catalyst 5 and upstream of the NOx catalyst 6. The air-fuel ratio obtained from the first air-fuel ratio sensor 7 is hereinafter referred to as upstream air-fuel ratio. The air-fuel ratio obtained from the second air-fuel ratio sensor 8 is hereinafter referred to as a downstream air-fuel ratio.

  In this embodiment, a fuel addition valve 9 for injecting fuel (light oil) as a reducing agent into the exhaust passage 3 upstream of the oxidation catalyst 5 is provided. Here, the fuel addition valve 9 is opened by a signal from the ECU 10 described later to inject fuel. The fuel injected from the fuel addition valve 9 into the exhaust passage 3 makes the air-fuel ratio of the exhaust flowing from the upstream of the exhaust passage 3 rich. In this embodiment, the fuel addition valve 9 corresponds to the fuel addition device in the present invention.

  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.

  Various sensors and the like are connected to the ECU 10 via electric wiring, and output signals from the sensors and the like are input. On the other hand, a fuel addition valve 9 and a fuel injection valve 11 are connected to the ECU 10 via electric wiring, and the fuel injection amount from the fuel addition valve 9 and the fuel injection valve 11 is controlled by the ECU 10.

  In this embodiment, when the storage capacity of the NOx catalyst 6 is recovered (that is, when NOx is reduced and sulfur poisoning is recovered), the air-fuel ratio of the internal combustion engine 1 is intermittently reduced to about 15 to 18, for example. Hereinafter, the gas discharged from the internal combustion engine 1 when operating at such an air-fuel ratio is referred to as “air-fuel ratio lowering exhaust”. The air-fuel ratio lowering exhaust gas has the same air-fuel ratio as that in the cylinder. The air-fuel ratio can be lowered by decreasing the intake air amount, increasing the fuel injection amount from the fuel injection valve 11, increasing the EGR gas, or the like. The air-fuel ratio in the cylinder can be obtained as a ratio between the intake air amount obtained by the air flow meter 4 and the fuel injection amount from the fuel injection valve 11. In this embodiment, the ECU 10 that controls the air-fuel ratio in the cylinder by controlling the fuel injection amount from the fuel injection valve 11 corresponds to the in-cylinder air-fuel ratio control means in the present invention.

Then, the fuel is injected from the fuel addition valve 9 toward the air-fuel ratio lowering exhaust gas. That is, the fuel addition from the fuel addition valve 9 is performed when the air-fuel ratio lowering exhaust gas passes through the location where the fuel addition valve 9 is attached.

  Here, when the storage capacity of the NOx catalyst 6 is recovered, the temperature of the exhaust gas is higher because the air-fuel ratio is lower than when the storage capacity of the NOx catalyst 6 is not recovered. That is, the air-fuel ratio lowering exhaust gas is hot and flows through the exhaust passage 3 while expanding in volume. Therefore, strong turbulence (turbulent flow) occurs at the boundary between the air-fuel ratio lowering exhaust gas and other exhaust gas (that is, exhaust gas when operating at a higher air-fuel ratio).

When fuel is injected from the fuel addition valve 9 toward the air-fuel ratio lowering exhaust gas, atomization and evaporation of the fuel are promoted due to turbulence and high temperature. Further, since the fuel is dispersed in the exhaust, the fuel can be uniformly distributed in the radial direction of the exhaust passage 3. Thereby, fuel can be uniformly supplied to the NOx catalyst 6.

Further, since almost no oxygen remains in the air-fuel ratio lowering exhaust gas, the fuel can be reacted from the upstream end portion of the NOx catalyst 6, so that the temperature can be raised from the upstream end portion. Thus, since the temperature can be raised uniformly, the purification ability of the NOx catalyst 6 can be recovered in a wider range. In this embodiment, the ECU 10 that reduces the air-fuel ratio in the cylinder and adds fuel from the fuel addition valve 9 toward the air-fuel ratio lowering exhaust gas when the purification ability of the NOx catalyst 6 is recovered is the reduction in the present invention. It corresponds to the agent supply means.

2 shows the air-fuel ratio in the cylinder (in-cylinder air-fuel ratio), the air-fuel ratio of the gas discharged from the internal combustion engine 1 (exhaust gas air-fuel ratio), and the air-fuel ratio in the vicinity of the fuel addition valve 9 in this embodiment. (Air-fuel ratio near fuel addition valve), exhaust temperature near fuel addition valve 9 (temperature near fuel addition valve), temperature of NOx catalyst 6 (NOx catalyst temperature), and air-fuel ratio in NOx catalyst 6 (NOx catalyst) It is a time chart showing the transition of the air-fuel ratio).

  In the time indicated by A, the air-fuel ratio in the cylinder is lowered. Thereby, the air-fuel ratio lowering exhaust gas is generated. At this time, a plurality of cycles are operated with the air-fuel ratio in the cylinder lowered. The gas discharged at this time flows through the exhaust passage 3 as one large lump having a low air-fuel ratio. Note that the exhaust discharged in a state where the air-fuel ratio is not lowered is hereinafter referred to as “normal exhaust”. The air-fuel ratio lowering exhaust gas flows downstream so as to be sandwiched between normal exhaust gases.

  Then, fuel is injected from the fuel addition valve 9 when the air-fuel ratio lowering exhaust gas passes through the fuel addition valve 9. That is, fuel is injected during the period from B to C. At this time, the temperature near the fuel addition valve is increased by the air-fuel ratio lowering exhaust. Here, the time required for the air-fuel ratio lowered exhaust to reach the fuel addition valve 9 after being discharged from the internal combustion engine 1 is, for example, the length of the exhaust passage 3 from the internal combustion engine 1 to the fuel addition valve 9. It can be determined by dividing by the flow rate. The length of the exhaust passage 3 can be obtained in advance by experiments or the like. The exhaust flow rate can be calculated based on the intake air amount obtained by the air flow meter 4, the fuel injection amount from the fuel injection valve 11, and the cross-sectional area of the exhaust passage 3. This amount is also taken into account when supplying EGR gas. Since the exhaust flow rate has a correlation with, for example, the load of the internal combustion engine, the relationship between the load of the internal combustion engine and the flow rate of the exhaust may be obtained in advance through experiments or the like and mapped.

The total amount of fuel added from the fuel addition valve 9 (hereinafter referred to as the total addition amount W) when a single air-fuel ratio lowering exhaust gas passes through the fuel addition valve 9 is the specified rich air-fuel ratio. The amount required to be reduced to the air-fuel ratio. The prescribed rich air-fuel ratio is an air-fuel ratio capable of reducing NOx and releasing sulfur components. Note that when the temperature of the NOx catalyst 6 is being increased, the amount is required to increase the temperature of the NOx catalyst 6 to a specified temperature. This amount corresponds to the energy of the portion indicated by hatching in FIG. This can be, for example, a temperature drop from the previous fuel addition. The specified temperature is, for example, a temperature required for recovery of sulfur poisoning of the NOx catalyst 6. For example, the total addition amount W can be obtained by the following equation.
W = ΔT × Ga
Here, ΔT is the temperature rise, and Ga is the intake air amount. In other words, it is necessary to add more fuel as the intake air amount Ga increases.

And the total addition amount W is injected in the period from B to C. That is, the fuel injection amount per unit time is determined so that the total amount of fuel injection from the fuel addition valve 9 in the period from B to C is equal to the total addition amount W. Then, the fuel injection amount Q per unit time can be calculated by the following equation.
Q = W / T
Here, T is the time from B to C. This time T is obtained in advance by experiments or the like in association with the operating state of the internal combustion engine 1. The amount of fuel added per unit time can be changed, for example, by changing the fuel pressure. In addition, when a rich air-fuel ratio is formed once by a plurality of times of fuel addition, the interval between fuel additions and the respective times of the fuel addition are adjusted. For example, an equal amount of fuel is added at equal intervals during the period from B to C. The total amount of fuel injection from the fuel addition valve 9 when one rich air-fuel ratio is formed is made equal to the total addition amount W.

The fuel added in this way is promoted to atomize, and thereafter the air-fuel ratio in the NOx catalyst is lowered.

  By the way, when the internal combustion engine 1 is operated at a high load, the time for reducing the air-fuel ratio in the cylinder is shortened, so the period from B to C is shortened. Therefore, the fuel from the fuel addition valve 9 may not be completely injected during the period from B to C.

  In such a case, the fuel addition is started before the air-fuel ratio lowering exhaust gas reaches the fuel addition valve 9. Then, the fuel addition start timing is determined so that the fuel addition is completed when the last part of the air-fuel ratio lowering exhaust gas passes through the fuel addition valve 9. Here, FIG. 3 is a diagram showing the fuel addition period when the amount of the air-fuel ratio lowering exhaust gas is small.

The reason why the fuel addition is started before the air-fuel ratio lowering exhaust gas reaches the fuel addition valve 9 is that the temperature of the NOx catalyst 6 can be raised in advance. That is, when the subsequent air-fuel ratio lowering exhaust gas flows into the NOx catalyst 6, the temperature rises to some extent,
When the air-fuel ratio lowering exhaust gas flows, the reactivity of the fuel can be increased.

  The reason why the fuel addition is completed when the last part of the air-fuel ratio lowering exhaust gas passes through the fuel addition valve 9 is that the fuel can be added over the entire air-fuel ratio lowering exhaust gas. This is because atomization and the like can be promoted to the maximum.

  On the other hand, if the time for lowering the air-fuel ratio in the cylinder becomes longer, it becomes difficult to add the fuel from the fuel addition valve 9 over the entire period from B to C. In such a case, it becomes a problem at which timing the addition of fuel is started from the fuel addition valve 9.

On the other hand, in this embodiment, when the foremost part of the air-fuel ratio lowering exhaust reaches the fuel addition valve 9, the addition of fuel from the fuel addition valve 9 is started. FIG. 4 is a diagram showing a fuel addition period when the amount of the air-fuel ratio lowering exhaust gas is large. By doing so, the temperature of the NOx catalyst 6 is quickly raised after the air-fuel ratio lowering exhaust gas reaches the NOx catalyst 6. For this reason, the reactivity is increased even in the air-fuel ratio reduced exhaust in the portion where no fuel is added from the fuel addition valve 9, so that the recovery of the purification ability of the NOx catalyst 6 can be promoted.

FIG. 5 is a flowchart showing a flow during NOx reduction according to the present embodiment. This routine is executed while NOx is being reduced. It is also possible to perform the recovery when the NOx catalyst 6 is recovered from sulfur poisoning.

  In step S101, the time for the air-fuel ratio lowered exhaust to reach the fuel addition valve 9 is calculated. That is, the time indicated by B in FIG. 2 is calculated. This is obtained based on the exhaust flow velocity and the length of the exhaust passage 3 to the fuel addition valve 9 as described above.

  In step S102, the period required for the air-fuel ratio lowering exhaust gas to pass through the fuel addition valve 9 is calculated. That is, the period from B to C in FIG. 2 is calculated. As described above, this is obtained by the map associated with the operating state of the internal combustion engine 1 (for example, the load or the fuel injection amount from the fuel injection valve 11).

In step S103, the total addition amount W is calculated. The total addition amount W is calculated as an amount necessary for setting the air-fuel ratio of the exhaust to a specified air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio and keeping the temperature of the NOx catalyst 6 constant. This total addition amount W may have a certain range.

  In step S104, it is determined whether or not the fuel addition from the fuel addition valve 9 can be added only during the period from B to C and can be performed over the entire period. The relationship between the total addition amount W and the period from B to C may be determined in advance. If an affirmative determination is made in step S104, the process proceeds to step S105, whereas if a negative determination is made, the process proceeds to step S106.

  In step S105, fuel addition is performed over the entire period from B to C.

  In step S106, it is determined whether or not the total addition amount W is larger than the amount that can be supplied over the entire period from B to C. If an affirmative determination is made in step S106, the process proceeds to step S107. If a negative determination is made, step S108 proceeds.

  In step S107, fuel addition is started before the time indicated by B.

  In step S108, fuel addition is started from the time indicated by B.

As described above, according to the present embodiment, atomization of the fuel added from the fuel addition valve 9 is promoted by disturbance of the high-temperature and high-pressure exhaust. As a result, the fuel can be uniformly supplied to the oxidation catalyst 5 and the NOx catalyst 6. This makes it possible to reduce NOx or release sulfur components in a wide 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 intake / exhaust system. In the embodiment, the air-fuel ratio in the cylinder, the air-fuel ratio of the gas discharged from the internal combustion engine, the air-fuel ratio near the fuel addition valve, the temperature of the exhaust near the fuel addition valve, the temperature of the NOx catalyst, and the inside of the NOx catalyst It is the time chart which showed transition of the air fuel ratio of. It is a figure which shows a fuel addition period when the amount of air-fuel ratio fall exhaust is small. It is a figure which shows the fuel addition period when there is much quantity of air-fuel ratio fall exhaust. It is the flowchart which showed the flow at the time of the NOx reduction | restoration which concerns on an Example.

Explanation of symbols

1 internal combustion engine 2 intake passage 3 exhaust passage 4 air flow meter 5 oxidation catalyst 6 NOx storage reduction catalyst 7 first air-fuel ratio sensor 8 second air-fuel ratio sensor 9 fuel addition valve 10 ECU
11 Fuel injection valve

Claims (4)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An in-cylinder air-fuel ratio control means for changing an air-fuel ratio in the cylinder of the internal combustion engine;
A fuel addition device for adding fuel into the exhaust passage of the internal combustion engine;
When the reducing agent is supplied to the exhaust purification catalyst, the air-fuel ratio in the cylinder is lowered by the in-cylinder air-fuel ratio control means than when the reducing agent is not supplied. A reducing agent supply means for adding fuel;
An exhaust emission control device for an internal combustion engine, comprising:   The reducing agent supply means adds fuel over the entire period in which exhaust passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the in-cylinder air-fuel ratio control means, and this period 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the fuel addition amount per one time from the fuel addition apparatus is adjusted so that the fuel is added only when the fuel is added.   The reducing agent supply means is more than an amount capable of adding fuel over the entire period when the exhaust gas passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the in-cylinder air-fuel ratio control means. When a large amount of fuel is added at one time, the addition of fuel is started before the exhaust gas whose air-fuel ratio has been reduced reaches the fuel addition device, and the last part of the exhaust gas whose air-fuel ratio has been reduced. 2. The fuel addition amount per one time from the fuel addition device is adjusted so that the addition of fuel from the fuel addition device is completed when the fuel passes through the fuel addition device. An exhaust gas purification apparatus for an internal combustion engine as described.   The reducing agent supply means is more than an amount capable of adding fuel over the entire period when the exhaust gas passes through the fuel addition device when the air-fuel ratio in the cylinder is lowered by the in-cylinder air-fuel ratio control means. 2. The internal combustion engine according to claim 1, wherein when a small amount of fuel is added at one time, the addition of fuel is started when the exhaust gas whose air-fuel ratio has decreased reaches the fuel addition device. Exhaust purification device.

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