JP2009092029A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology enabling exhaust emission control even right after completion of fuel cut in an exhaust emission control device for an internal combustion engine. <P>SOLUTION: An exhaust emission control device is provided with a first catalyst 3, a second catalyst 4 at a downstream of the first catalyst 3, and a bypass passage 7 bypassing the first catalyst. During fuel increase right after completion of fuel cut of the internal combustion engine, the device makes exhaust gas flow to the bypass passage and the first catalyst when gas in the first and the second catalysts is at lean air-fuel ratio, makes the exhaust gas flow to the bypass passage but not flow to the first catalyst when gas in the second catalyst is at lean air-fuel ratio and gas in the first catalyst is at rich air-fuel ratio, and makes the exhaust gas not flow to the bypass passage but flow to the first catalyst when gas in the second catalyst is at rich air-fuel ratio, to make gas in at least a part of an upstream side of at least one of the first and the second catalysts rich air-fuel ratio. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  A catalyst is provided in series in the exhaust passage, and includes a bypass passage that bypasses the upstream catalyst and a valve that adjusts the amount of exhaust gas that passes through the bypass passage and the upstream catalyst, and is bypassed during lean operation of the internal combustion engine A technique is known in which exhaust gas is supplied to a passage and exhaust gas is supplied to an upstream catalyst except during lean operation (see, for example, Patent Document 1).

According to this technique, even in the lean operation of the internal combustion engine, N
Ox purification efficiency can be ensured.

However, immediately after the end of the fuel cut, if the fuel cut time is long, both the upstream catalyst and the downstream catalyst have a lean air-fuel ratio. This makes it difficult to purify NOx. Further, the supplied fuel may be increased in order to quickly bring the catalyst to a rich air-fuel ratio immediately after the end of the fuel cut. However, if the amount of fuel is increased too much, both the upstream catalyst and the downstream catalyst have a rich air-fuel ratio. For this reason, it becomes difficult to purify HC and CO. Thus, immediately after the fuel cut, it may be difficult to purify the exhaust gas.
JP-A-5-231137 JP-A-5-312031

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technology capable of purifying exhaust gas even after the end of fuel cut in an exhaust gas purification apparatus for an internal combustion engine. To do.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention comprises:
A first catalyst provided in an exhaust passage of the internal combustion engine;
A second catalyst provided in an exhaust passage downstream of the first catalyst;
A bypass passage connecting an exhaust passage upstream of the first catalyst and an exhaust passage downstream of the first catalyst and upstream of the second catalyst;
An exhaust passage amount adjusting means for adjusting a ratio of exhaust gas passing through the first catalyst and the bypass passage;
First air-fuel ratio estimating means for estimating an air-fuel ratio in the first catalyst;
Second air-fuel ratio estimating means for estimating an air-fuel ratio in the second catalyst;
Immediately after the fuel cut of the internal combustion engine is completed, an increase means after fuel cut for increasing the amount of fuel supplied from other times; and
With
When the fuel supply is increased by the increase means after the fuel cut, when the second catalyst is at a lean air-fuel ratio and the first catalyst is at a lean air-fuel ratio, exhaust gas is allowed to flow to the bypass passage and to the first catalyst. When exhaust gas is flown and the second catalyst has a lean air-fuel ratio and the first catalyst has a rich air-fuel ratio, the exhaust gas flows into the bypass passage and does not flow into the first catalyst, and the second catalyst has a rich air-fuel ratio In such a case, the exhaust gas does not flow to the bypass passage and the exhaust gas flows to the first catalyst,
At least a part of at least one upstream side of the first catalyst or the second catalyst has a rich air-fuel ratio.

That is, even if the first catalyst and the second catalyst have a lean air-fuel ratio at the time of fuel cut, at least a part of at least one upstream side of the first catalyst or the second catalyst has a rich air-fuel ratio, so that NOx can be quickly obtained. It can be in a state that can be purified. Also, the first catalyst or the second
When the catalyst has a rich air-fuel ratio, the lean air-fuel ratio was not achieved because the fuel cut time was short, etc., so that the purification ability equivalent to that before the fuel cut can be exhibited. In such a case, it is possible to suppress excessive richness by preventing the exhaust when the fuel supply amount is increased by the increase means after the fuel cut, thereby purifying CO and HC. be able to.

  Here, the first air-fuel ratio estimating means and the second air-fuel ratio estimating means may directly measure the air-fuel ratio or may estimate it from the operating state of the internal combustion engine. Further, the air-fuel ratio in each catalyst may be estimated by measuring the air-fuel ratio of the upstream or downstream exhaust of each catalyst.

  Further, the exhaust gas flow is adjusted to at least one of the first catalyst and the bypass passage by the exhaust gas passage amount adjusting means. When the exhaust gas flows through the first catalyst and the bypass passage, the ratio of the exhaust gas flowing through each of the first catalyst and the bypass passage may be constant or variable.

  The increase means after the fuel cut increases the fuel more than the fuel supply amount determined at another time (hereinafter also referred to as “normal time”). For example, in normal times, the fuel supply amount is determined based on the load of the internal combustion engine, and the post-fuel cut increasing means increases the fuel supply amount determined based on the load of the internal combustion engine.

Here, if the second catalyst has a rich air-fuel ratio immediately after the fuel cut is completed, NOx can be purified without flowing the rich air-fuel ratio to the second catalyst. That is, it is not necessary to flow the exhaust gas when the fuel supply amount is increased by the increasing means after the fuel cut to the second catalyst. Therefore, no exhaust gas is allowed to flow into the bypass passage.

Further, at this time, by flowing the exhaust gas to the first NOx catalyst, at least a part of the first catalyst has a rich air-fuel ratio, so the NOx purification rate of the exhaust gas purification device as a whole can be increased.

On the other hand, when the second catalyst has a lean air-fuel ratio immediately after the fuel cut is finished, it is difficult to purify NOx in the second catalyst unless a part of the second catalyst is quickly made to have a rich air-fuel ratio. . On the other hand, if the exhaust gas is flowed to the bypass passage, the exhaust gas when the fuel supply amount is increased can be directly flowed to the second catalyst. Therefore, at least a part of the second catalyst can have a rich air-fuel ratio. .

When the second catalyst has a lean air-fuel ratio and the first catalyst also has a lean air-fuel ratio, it becomes difficult to purify NOx as the whole exhaust gas purification device. In this case, exhaust gas is allowed to flow to the bypass passage, and exhaust gas is also allowed to flow to the first catalyst. That is, by flowing the exhaust gas when the fuel supply amount is increased also to the first catalyst, at least a part of the first catalyst can be made to have a rich air-fuel ratio. Therefore, NOx purification is also performed in the first catalyst. Is possible. On the other hand, when the second catalyst has a lean air-fuel ratio and the first catalyst has a rich air-fuel ratio, it is not necessary to flow exhaust when the fuel supply amount is increased. On the other hand, if the exhaust gas is prevented from flowing to the first catalyst and the exhaust gas is allowed to flow to the bypass passage, a part of the second catalyst can be quickly made to have a rich air-fuel ratio. As a result, the NOx purification rate can be quickly increased as the whole exhaust gas purification apparatus.

As described above, depending on the state of the first catalyst and the second catalyst, the exhaust air is allowed to flow through the first catalyst and the bypass passage, or at least a part of at least one of the catalysts is set to the rich air-fuel ratio. be able to. Thereby, the NOx purification rate as the whole exhaust gas purification device can be increased.

In the present invention, the amount of fuel increase by the means for increasing after the fuel cut is
When the second catalyst is a lean air-fuel ratio and the first catalyst is a lean air-fuel ratio,
When the second catalyst has a rich air-fuel ratio and the first catalyst has a lean air-fuel ratio,
When the second catalyst is a lean air-fuel ratio and the first catalyst is a rich air-fuel ratio, or when the second catalyst is a rich air-fuel ratio and the first catalyst is a rich air-fuel ratio,
Can be reduced in order.

  When the second catalyst has a lean air-fuel ratio and the first catalyst has a lean air-fuel ratio, exhaust gas is allowed to flow to the first catalyst and the bypass passage, and a part of each of the first catalyst and the second catalyst is set to a rich air-fuel ratio. Therefore, since a lot of fuel is required, the amount of increase in fuel is increased.

  When the second catalyst has a rich air-fuel ratio and the first catalyst has a lean air-fuel ratio, no exhaust gas flows through the bypass passage. Since at least a part of the first catalyst only needs to have a rich air-fuel ratio, the amount of fuel increase may be smaller than when at least a part of both catalysts have a rich air-fuel ratio.

When the second catalyst has a lean air-fuel ratio and the first catalyst has a rich air-fuel ratio, exhaust gas flows through the bypass passage, and no exhaust gas flows through the first catalyst. In such a case, NOx can be purified by the first catalyst, but NOx may flow out from the first catalyst, so at least a part of the second catalyst has a rich air-fuel ratio. As described above, since it is sufficient that at least a part of the second catalyst has a rich air-fuel ratio, the amount of increase in fuel may be small.

Further, when the second catalyst has a rich air-fuel ratio and the first catalyst has a rich air-fuel ratio, it is possible to purify NOx, but the fuel is increased due to the inflow of air to the catalyst when the fuel is cut. The amount of increase may be small.

  In this way, by determining the degree of increase in the fuel supply amount according to the state of each catalyst, it is possible to quickly pass both catalysts to the rich air-fuel ratio while passing both catalysts to HC and CO, and further to NOx. Can be suppressed.

  According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine, exhaust gas can be purified even immediately after the end of fuel cut.

  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 illustrating a schematic configuration of an exhaust emission control apparatus according to the present embodiment.

An exhaust passage 2 is connected to the internal combustion engine 1 according to this embodiment. The exhaust passage 2 is provided with a first catalyst 3 and a second catalyst 4 in order from the upstream side. The first catalyst 3 and the second catalyst 4 are catalysts capable of reducing at least NOx, and for example, a three-way catalyst can be employed.

  A bypass passage that connects the exhaust passage 2 upstream of the first catalyst 3 and the exhaust passage 2 downstream of the first catalyst 3 and upstream of the second catalyst 4 to bypass the first catalyst 3. 5 is provided. A first shutoff valve 6 is provided in the exhaust passage 2 upstream of the first catalyst 3 and downstream of the connection location of the bypass passage 5. A second cutoff valve 7 is provided in the middle of the bypass passage 5. The first shut-off valve 6 and the second shut-off valve 7 circulate exhaust gas by opening each passage, and close the valve to stop the exhaust gas flow. In the present embodiment, the first shut-off valve 6 and the second shut-off valve 7 correspond to the exhaust passage amount adjusting means in the present invention.

  An upstream air-fuel ratio sensor 8 for measuring the air-fuel ratio of exhaust gas is attached to the exhaust passage 2 upstream of the first catalyst 3 and further upstream of the location where the bypass passage 5 is connected. Furthermore, a first air-fuel ratio sensor 9 for measuring the air-fuel ratio of the exhaust is attached to the exhaust passage 2 downstream of the first catalyst 3 and upstream of the location where the bypass passage 5 is connected. A second air-fuel ratio sensor 10 that measures the air-fuel ratio of the exhaust is attached to the exhaust passage 2 downstream of the second catalyst 4. The air / fuel ratio in the first catalyst 3 is measured by the first air / fuel ratio sensor 9. Further, the air / fuel ratio in the second catalyst 4 is measured by the second air / fuel ratio sensor 10. That is, in the present embodiment, the first air-fuel ratio sensor 9 corresponds to the first air-fuel ratio estimation means in the present invention. In the present embodiment, the second air-fuel ratio sensor 10 corresponds to the second air-fuel ratio estimation means in the present invention.

Instead of obtaining the air-fuel ratio in the second catalyst 4 by the second air-fuel ratio sensor 10, the air-fuel ratio obtained by the upstream air-fuel ratio sensor 8 and the first air-fuel ratio sensor 9 and the exhaust gas flowing into the second catalyst 4. The air-fuel ratio in the second catalyst 4 can also be estimated based on the air-fuel ratio and the intake air amount. In this case, the air-fuel ratio in the second catalyst 4 is affected by the degree of deterioration of the second catalyst 4. Here, the degree of deterioration of the first catalyst 3 can be estimated based on the amount of O ₂ storage, and the degree of deterioration of the second catalyst 4 can be estimated based on this. The estimated value of the air-fuel ratio in the second catalyst 4 may be corrected according to the degree of deterioration of the second catalyst 4. The degree of deterioration of the first catalyst 3 can be obtained during air-fuel ratio feedback control.

  The internal combustion engine 1 is also provided with a fuel injection valve 11 for supplying fuel into the cylinder of the internal combustion engine 1.

  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 controls the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver.

  The sensor is connected to the ECU 20 via electrical wiring, and output signals of these various sensors are input to the ECU 20. Further, the ECU 20 is connected to the first cutoff valve 6, the second cutoff valve 7, and the fuel injection valve 11 through electric wiring, and these devices are controlled by the ECU 20.

Here, in this embodiment, a fuel cut is performed to stop the supply of fuel to the internal combustion engine 1 when the vehicle is decelerated. For example, the fuel cut is performed when the vehicle speed decreases and the driver does not step on the accelerator. When the vehicle changes from deceleration to acceleration, the supply of fuel to the internal combustion engine 1 is resumed, but the fuel supply amount is increased for a predetermined period after the restart. That is, since air flows into the exhaust passage when the fuel cut is performed, there is a possibility that the atmosphere in the first catalyst 3 and the second catalyst 4 becomes a lean air-fuel ratio. If it does so, purification of NOx will become difficult. On the other hand, if the fuel supply amount is increased immediately after the end of the fuel cut, the air-fuel ratio in the first catalyst 3 and the second catalyst 4 can be quickly lowered by the exhaust with the lower air-fuel ratio. Note that after the increase in the fuel supply amount is completed, the fuel supply amount is set so that the air-fuel ratio measured by the upstream air-fuel ratio sensor 8 is slightly richer than the stoichiometric air-fuel ratio (hereinafter referred to as weakly rich). Is feedback controlled. In the present embodiment, the ECU 20 that increases the fuel supply amount after the end of the fuel cut corresponds to the post-fuel cut increasing means in the present invention.

  Note that if the period for increasing the fuel supply amount is long or the amount is too large, the air-fuel ratio in the first catalyst 3 or the second catalyst 4 may be too low. In order to suppress this, the following control is performed in this embodiment.

  FIG. 2 is a flowchart showing a flow of air-fuel ratio control according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, it is determined whether or not the fuel is being cut. That is, it is determined whether or not fuel is being supplied to the internal combustion engine 1. The fuel supply amount is not increased except immediately after the end of the fuel cut, and the normal fuel amount is supplied. If a positive determination is made in step S101, the process proceeds to step S102, whereas if a negative determination is made, the process proceeds to step S116.

  In step S102, it is determined whether or not the fuel cut is completed. That is, it is determined whether or not the fuel increase after the fuel cut is completed. If an affirmative determination is made in step S102, the process proceeds to step S103, whereas if a negative determination is made, the process proceeds to step S116.

In step S103, it is determined whether the inside of the second catalyst 4 has a lean air-fuel ratio. That is, it is determined whether the air-fuel ratio obtained by the second air-fuel ratio sensor 10 is lean. This determines whether or not it is necessary to promptly supply exhaust gas having a rich air-fuel ratio to the second catalyst 4 because the entire inside of the second catalyst 4 has a lean air-fuel ratio. In other words, if the inside of the second catalyst 4 has a lean air-fuel ratio due to the fuel cut, the NOx that has passed through the first catalyst 3 cannot be purified, so that the inside of the second catalyst 4 has a rich air-fuel ratio. In this case, the upstream side in the second catalyst 4 is a rich air-fuel ratio, and the downstream side is a lean air-fuel ratio. That is, at least a part of the second catalyst 4 has a rich air-fuel ratio. By doing so, the second catalyst 4 can purify NOx, HC, and CO. If an affirmative determination is made in step S103, the process proceeds to step S104. On the other hand, if a negative determination is made, the process proceeds to step S110.

  In step S104, the second cutoff valve 7 is opened. By doing so, since the exhaust gas flows into the bypass passage 5, the exhaust gas having a rich air-fuel ratio due to the increase in fuel can be supplied to the second catalyst 4.

In step S105, it is determined whether or not the inside of the first catalyst 3 has a lean air-fuel ratio. That is, it is determined whether the air-fuel ratio obtained by the first air-fuel ratio sensor 9 is lean. This is because it is determined whether or not it is necessary to quickly supply exhaust gas having a rich air-fuel ratio to the first catalyst 4 because the entire inside of the first catalyst 3 has a lean air-fuel ratio. That is, if the first catalyst 3 has a lean air-fuel ratio due to the fuel cut, the first catalyst 3 cannot purify NOx, so the first catalyst 3 has a rich air-fuel ratio. In this case, the upstream side of the first catalyst 3 is a rich air-fuel ratio, and the downstream side is a lean air-fuel ratio. That is, at least a part of the first catalyst 3 has a rich air-fuel ratio. In this way, in the first catalyst 3, NOx, HC,
CO purification becomes possible. If an affirmative determination is made in step S105, the process proceeds to step S106, whereas if a negative determination is made, the process proceeds to step S108.

In step S106, the first cutoff valve 6 is opened. That is, rich air-fuel ratio exhaust gas is supplied to the first catalyst 3. As a result, at least a part of the first catalyst 3 can have a rich air-fuel ratio.

  In step S107, the degree of increase in the fuel supply amount of the internal combustion engine 1 is maximized. That is, since both the first catalyst 3 and the second catalyst 4 have a lean air-fuel ratio, the degree of increase in the fuel supply amount is made relatively large in order to quickly bring both catalysts to the rich air-fuel ratio.

  In step S108, the first cutoff valve 6 is closed. Since the first catalyst 3 has a rich air-fuel ratio, it is not necessary to flow exhaust gas having a rich air-fuel ratio to the first catalyst 3. Therefore, the exhaust gas is prevented from passing through the first catalyst 3.

  In step S109, the degree of increase in the fuel supply amount of the internal combustion engine 1 is made relatively small. That is, since it is only necessary to supply the rich air-fuel ratio exhaust gas to the second catalyst 4, the degree of increase in the fuel supply amount is made relatively small.

  In step S110, the second shut-off valve 7 is closed. That is, since the inside of the second catalyst 4 has a rich air-fuel ratio, it is not necessary to supply exhaust gas having a rich air-fuel ratio directly to the second catalyst 4 via the bypass passage 5. Therefore, exhaust gas is prevented from flowing into the bypass passage 5.

  In step S111, it is determined whether or not the inside of the first catalyst 3 has a lean air-fuel ratio. In this step, the same determination as in step S105 is performed. If an affirmative determination is made in step S111, the process proceeds to step S112. On the other hand, if a negative determination is made, the process proceeds to step S114.

  In step S112, the first cutoff valve 6 is opened. That is, rich air-fuel ratio exhaust gas is supplied to the first catalyst 3. Thereby, the upstream side in the 1st catalyst 3 can be made into a rich air fuel ratio.

  In step S113, the degree of increase in the fuel supply amount of the internal combustion engine 1 is set to a medium level. That is, since it is only necessary to supply the rich air-fuel ratio exhaust gas to the first catalyst 4, the degree of increase in the fuel supply amount is made smaller than that in step S 107 and larger than that in step S 109.

  In step S114, the first cutoff valve 6 is opened. Here, since the first catalyst 3 and the second catalyst 4 have a rich air-fuel ratio, the exhaust gas flows to the first catalyst 3 and the second catalyst 4 as usual.

  In step S115, the degree of increase in the fuel supply amount of the internal combustion engine 1 is made relatively small. Although the first catalyst 3 and the second catalyst 4 have a rich air-fuel ratio, the fuel supply amount is slightly increased in order to maintain the rich air-fuel ratio. The degree of increase in the fuel supply amount is set to the same level as in step S109.

  In step S116, the first cutoff valve 6 is opened. That is, the exhaust gas is allowed to flow to the first catalyst 3 during normal fuel supply not immediately after the end of the fuel cut or during the fuel cut. Here, at the time of normal fuel supply, the exhaust gas with a weak rich air-fuel ratio flows into the first catalyst 3. Even in this case, oxygen remains in the exhaust gas, so that oxygen is supplied to the first catalyst 3. Therefore, oxidation of HC and CO is possible.

In step S117, it is determined whether or not the inside of the second catalyst 4 has a lean air-fuel ratio. That is, it is determined whether or not the inside of the second catalyst 4 has a lean air-fuel ratio. Here, when the inside of the second catalyst 4 has a rich air-fuel ratio, it may be difficult to purify HC and CO. In this case, the second shutoff valve 7 is opened to take in oxygen in the exhaust. If an affirmative determination is made in step S117, the process proceeds to step S118, whereas if a negative determination is made, the process proceeds to step S119.

  In step S118, the second shut-off valve 7 is closed.

  In step S119, the second cutoff valve 7 is opened.

In this way, immediately after the end of the fuel cut, at least a part of at least one of the first catalyst 3 and the second catalyst 4 can be set to a rich air-fuel ratio, and the others can be set to a lean air-fuel ratio. This makes it possible to quickly purify NOx, HC, CO, etc. immediately after the end of the fuel cut.

  In the first embodiment, immediately after the end of the fuel cut, the upstream side in each of the first catalyst 3 and the second catalyst 4 is set to a rich air-fuel ratio, and the downstream side is set to a lean air-fuel ratio. During the cut, the first catalyst 3 is set to a rich air-fuel ratio, and the second catalyst 4 is set to a lean air-fuel ratio. In the present embodiment, it is not necessary to provide the first cutoff valve 6.

That is, during the fuel cut, the first catalyst 3 is set to a rich air-fuel ratio, and the second catalyst 4 is set to a lean air-fuel ratio, so that the first catalyst 3 can be used to convert NOx to the second catalyst even immediately after the end of the fuel cut. In step 4, HC and CO can be purified.

  FIG. 3 is a flowchart showing a flow of air-fuel ratio control according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S201, it is determined whether or not the fuel is being cut. The same determination as in step S101 is performed. If an affirmative determination is made in step S201, the process proceeds to step S202. On the other hand, if a negative determination is made, the process proceeds to step S204.

  In step S202, it is determined whether or not the inside of the second catalyst 4 has a lean air-fuel ratio. If an affirmative determination is made in step S202, the process proceeds to step S203, and if a negative determination is made, the process proceeds to step S204.

  In step S203, the second cutoff valve 7 is closed. That is, since the second catalyst 4 is already at a lean air-fuel ratio, it is not necessary to supply exhaust gas during fuel cut directly to the second catalyst 4. Then, by closing the second shutoff valve 7, all of the exhaust during the fuel cut passes through the first catalyst 3.

  In step S204, the second cutoff valve 7 is opened. That is, since the second catalyst 4 has a rich air-fuel ratio, the exhaust gas containing a large amount of air during fuel cut is directly introduced into the second catalyst 4. Thereby, the inside of the 2nd catalyst 4 can be rapidly made into a lean air fuel ratio.

In this way, the inside of the first catalyst 3 can be set to a rich air-fuel ratio and the inside of the second catalyst 4 can be set to a lean air-fuel ratio during the fuel cut, so that when the fuel supply is resumed, the NOx in the first catalyst 3 is reduced. HC and CO can be purified by the second catalyst 4. In this way, a high purification capacity can be maintained as a whole exhaust gas purification device.

It is a figure which shows schematic structure of the exhaust gas purification apparatus which concerns on an Example. 3 is a flowchart showing a flow of air-fuel ratio control according to the first embodiment. 6 is a flowchart showing a flow of air-fuel ratio control according to a second embodiment.

Explanation of symbols

1 Internal combustion engine 2 Exhaust passage 3 First catalyst 4 Second catalyst 5 Bypass passage 6 First shut-off valve 7 Second shut-off valve 8 Upstream air-fuel ratio sensor 9 First air-fuel ratio sensor 10 Second air-fuel ratio sensor 11 Fuel injection valve 20 ECU

Claims (2)

A first catalyst provided in an exhaust passage of the internal combustion engine;
A second catalyst provided in an exhaust passage downstream of the first catalyst;
A bypass passage connecting an exhaust passage upstream of the first catalyst and an exhaust passage downstream of the first catalyst and upstream of the second catalyst;
An exhaust passage amount adjusting means for adjusting a ratio of exhaust gas passing through the first catalyst and the bypass passage;
First air-fuel ratio estimating means for estimating an air-fuel ratio in the first catalyst;
Second air-fuel ratio estimating means for estimating an air-fuel ratio in the second catalyst;
Immediately after the fuel cut of the internal combustion engine is completed, an increase means after fuel cut for increasing the amount of fuel supplied from other times; and
With
When the supply fuel is increased by the increasing means after the fuel cut, when the second catalyst is at a lean air-fuel ratio and the first catalyst is at a lean air-fuel ratio, exhaust gas is allowed to flow through the bypass passage and to the first catalyst. When exhaust gas is flown and the second catalyst has a lean air-fuel ratio and the first catalyst has a rich air-fuel ratio, the exhaust gas flows into the bypass passage and does not flow into the first catalyst, and the second catalyst has a rich air-fuel ratio In such a case, the exhaust gas does not flow to the bypass passage and the exhaust gas flows to the first catalyst,
An exhaust gas purification apparatus for an internal combustion engine, wherein a part of at least the upstream side of at least one of the first catalyst or the second catalyst has a rich air-fuel ratio. The amount of increase in fuel by the increase means after the fuel cut,
When the second catalyst is a lean air-fuel ratio and the first catalyst is a lean air-fuel ratio,
When the second catalyst has a rich air-fuel ratio and the first catalyst has a lean air-fuel ratio,
When the second catalyst is a lean air-fuel ratio and the first catalyst is a rich air-fuel ratio, or when the second catalyst is a rich air-fuel ratio and the first catalyst is a rich air-fuel ratio,
2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is reduced in the order of.

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