JPH11257050A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent HC emission owing to ignition lag of an exhaust emission control device for accelerated activation of the catalyst and to avoid adverse effect caused by desorption of adsorbed HC. SOLUTION: An exhaust re-combustion device 21 is disposed upstream of a catalytic device 22 within an exhaust passage 14 of an internal combustion engine 1. An HC adsorbent 18 is disposed upstream of the exhaust re-combustion device 21 for adsorption. A secondary air pump 20 is provided with an upstream air inlet 27 and a downstream air inlet 29, controlled by opening/closing valves 28, 30, respectively. An engine control unit 26 makes the air/fuel ratio of the internal combustion engine 1 rich via a fuel injection valve 8 for re-combustion by supplying secondary air. The secondary air is supplied from the downstream of the HC adsorbent 18 until the combustion actually starts. After start of the combustion, it is switched such that the secondary air is supplied from the upstream. The flow of the secondary air will promote the HC desorption.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to an exhaust gas purifying apparatus for purifying exhaust gas immediately after starting.

[0002]

2. Description of the Related Art A catalyst device carrying a catalyst made of a noble metal (platinum, rhodium, or the like) or another metal has been widely used for purifying exhaust gas discharged from an internal combustion engine of an automobile. Such a catalyst purifies by oxidizing and reducing HC, CO, NOx, and the like, which are harmful components in the exhaust gas. By the way, in order to obtain this catalytic action, the exhaust gas temperature must be high, for example, a temperature around 300 ° C. is required. However, immediately after the start of the internal combustion engine,
Exhaust gas temperature is low and the temperature at which the catalyst is activated (300 ° C
(Before and after), there is a problem that exhaust harmful components are hardly purified, and a relatively large amount of exhaust harmful substances are released into the atmosphere.

[0003] In order to solve the above problem, an upstream side of a catalyst device provided in an exhaust system of an internal combustion engine is further provided.
It is known that an exhaust gas reburner is provided, in which the combustible exhaust gas is burned in the reburner immediately after the start, and the catalyst is quickly activated by the heat of combustion (Japanese Patent Application Laid-Open No. Hei 6-5).
08409). This exhaust purification device does not inject fuel into an exhaust reburner, but enriches the air-fuel ratio of the internal combustion engine and supplies secondary air to generate combustible exhaust gas containing combustible components and air. However, the combustible gas is burned by the ignition device, and the catalyst can be quickly activated with a very simple configuration. In addition, since HC and CO can be purified by combustion even before the catalytic activity, it can be said that this is a very effective means for purifying exhaust gas as a whole.

[0004]

However, in the above-mentioned conventional exhaust gas purifying apparatus, there is no problem if the exhaust gas is reburned immediately after the start of the engine. However, there is a delay of about several seconds to control and ignite this, and there is a disadvantage that HC which is unburned fuel is released in a relatively large amount during that period.

In particular, as a prerequisite for operating the exhaust gas reburner, for example, if the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine is set to a rich state, the unburned fuel HC also increases accordingly. The emission of HC due to the combustion delay is a major problem.

In order to prevent the discharge of HC immediately after the start, it is conceivable to dispose the HC adsorbent on the upstream side. However, the adsorbed HC is then heated to a temperature higher than that of the HC adsorbent. , And flows into the catalyst device, which would undesirably affect the air-fuel ratio control for a relatively long time.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method of starting exhaust reburning by arranging an HC adsorbent upstream of an exhaust reburner for heating a catalytic device. And discharge of HC during this time.
By introducing secondary air from the further upstream side of the C adsorbent, the desorption of HC was completed quickly.

That is, an exhaust gas purifying apparatus for an internal combustion engine according to a first aspect of the present invention includes a catalyst device provided in an exhaust passage of the internal combustion engine, and an exhaust reburner located upstream of the catalyst device and provided with ignition means. And an unburned component supply means for temporarily increasing unburned components in the exhaust gas of the internal combustion engine for reburning in the exhaust reburner, and the exhaust gas for reburning in the exhaust reburner. 2 in the exhaust gas upstream of the reburner
A secondary air supply device for supplying secondary air, wherein an H (hydrocarbon component) in the exhaust gas is adsorbed on the upstream side of the exhaust gas recombustor.
It is characterized in that a C adsorbent is provided, and a secondary air introduction part by the secondary air supply device is arranged upstream of the HC adsorbent.

The unburned component supply means may be, for example,
And an air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state.

[0010] In the exhaust gas purifying apparatus configured as described above, the exhaust combustor is operated at the time of low temperature start or the like in order to activate the catalyst device early. That is, the exhaust gas containing the discharged combustible components (CO, HC, H _2, etc.) from the internal combustion engine, O ₂ is added by the secondary air, and is supplied to the exhaust re combustor after passing through the HC adsorbent You. Then, combustion is performed in the exhaust reburner by the ignition of the ignition means such as an ignition plug, and the catalyst device is heated. The HC adsorbent is made of, for example, zeolite or the like, and has a characteristic of adsorbing HC in a low temperature state lower than a predetermined temperature and desorbing the adsorbed HC at a high temperature higher than a predetermined desorption temperature. . Therefore, when the exhaust gas passes through the HC adsorbent,
Is adsorbed, HC is prevented from being discharged to the outside even if there is an ignition delay in the exhaust reburner.

The ignition in the exhaust gas reburner involves CO,
If there is H ₂ and O ₂ is sufficient, even if HC has not been removed by the adsorbent, there is no problem in the combustion of the second exhaust combustor.

As a secondary effect, by adsorbing HC in advance, the combustion temperature in the exhaust combustor can be slightly suppressed. That is, since only CO and H ₂ are burned, the combustion temperature is reduced from, for example, about 950 ° C. to about 750 ° C. In general, the catalyst accelerates its deterioration as the temperature becomes higher, but shows a characteristic of rapidly deteriorating particularly at 900 ° C. or higher. When the combustion temperature can be reduced from about 950 ° C. to about 750 ° C. as described above, catalyst deterioration can be sufficiently suppressed, and overall exhaust performance can be improved over a long period of time. In particular, since the activation temperature of the catalyst is about 300 ° C., a sufficient catalyst early activation effect can be obtained even with a combustion gas of about 750 ° C.

Then, the HC adsorbed on the HC adsorbent immediately after the start is desorbed as the temperature of the HC adsorbent rises. Here, desorption from the adsorbent depends on the adsorbent temperature,
As shown in FIG. 6, it also depends on the flow rate of the gas passing through the adsorbent per unit time. In the present invention, the secondary air is H
Since it is introduced from the upstream side of the C adsorbent and passes through the HC adsorbent, the desorption is completed in a short time.

Further, in the invention according to claim 3, the above-mentioned 2
Secondary air introduction units by the secondary air supply device are provided on both the upstream side and the downstream side of the HC adsorbent, and the air introduction from each of them is controlled according to conditions.

According to a fourth aspect of the present invention, the means for detecting the start of combustion of the exhaust gas recombustor and the secondary air from the downstream introduction section before the start of combustion are provided. And secondary air control means for introducing secondary air from the upstream introduction section after the start of combustion. As the combustion start detection means, for example, a temperature sensor is provided in the exhaust gas reburner, and the start of combustion is detected from the temperature of the exhaust gas reburner.

That is, during the period of combustion delay in the exhaust reburner, by introducing secondary air from the downstream side of the HC adsorbent, only exhaust gas flows through the HC adsorbent, HC can be efficiently adsorbed on the HC adsorbent. And after the start of combustion of the exhaust reburner,
By introducing the secondary air from the upstream side of the HC adsorbent, the desorption of HC can be promoted.

According to the present invention, between the stop of the secondary air from the downstream inlet and the start of the secondary air from the upstream inlet following the start of combustion of the exhaust gas recombustor, An appropriate overlap period is provided.

There is still a slight delay before the secondary air introduced from the upstream introduction section actually reaches the exhaust reburner. In particular, since it is further upstream than the downstream introduction section, the delay is relatively large with respect to the downstream introduction section. Therefore, if the stop of the secondary air from the downstream inlet and the start of the secondary air from the upstream inlet are performed simultaneously, the supply of air to the exhaust recombustor is temporarily insufficient, and combustion is not performed. May be stable. On the other hand, according to the invention of claim 6, since the introduction of the secondary air from the upstream introduction portion is started, the secondary air introduction of the downstream introduction portion is stopped after the overlap period has elapsed. The actual air supply to the exhaust reburner is continuous.

Since the flow velocity of the exhaust gas becomes faster in the higher speed range according to the engine speed, for example, in the invention according to the seventh aspect, the overlap time as the overlap period is changed on the high speed side according to the engine speed. Set to be shorter.

[0020]

According to the present invention, in the exhaust reburner for heating the catalytic device, the HC discharged during the ignition delay period until the reburn actually occurs is trapped by the HC adsorbent, and the adsorbed HC is removed by the HC adsorbent. Since the desorption is performed early by using the flow of the secondary air, it is possible to prevent the release of HC exhausted from the internal combustion engine to the atmosphere at the time of starting and to activate the catalyst at an early stage. The effect of desorption of HC adsorbed on the HC adsorbent can be eliminated at an early stage, and normal exhaust gas purification by the catalyst can be started, and as a whole, harmful components discharged during cold start can be significantly reduced. It becomes possible.

In particular, according to the third and fourth aspects of the present invention, secondary air is introduced from the downstream side of the HC adsorbent until the start of combustion in the exhaust gas recombustor. Since it is switched to the introduction, it is possible to achieve both efficient adsorption of HC during the delay of exhaust gas reburning and early desorption after the start of reburning.

According to the invention of claim 6 or 7, when switching between introduction from the downstream side and introduction from the upstream side, shortage of air actually supplied to the exhaust reburner occurs. And stable combustion can be continued.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of the present invention. In the intake passage 7 of the internal combustion engine 1, a throttle valve 4 is interposed upstream of the collector 6, and an air flow meter 3 and an air cleaner 2 are interposed upstream thereof. The opening of the throttle valve 4 is detected by a throttle valve opening sensor 5. Also, the intake valve 9
The fuel injection valve 8 is arranged so as to inject fuel toward the fuel injection valve. In addition, 10 is a combustion chamber defined by the piston 11, 12 is a spark plug, and 13 is an exhaust valve.

The exhaust passage 14 of the internal combustion engine 1 is provided with a three-way catalyst device 23 in which a catalyst such as platinum is supported on a carrier made of ceramics or the like. A combustor 21 is provided. The exhaust gas reburner 21 has a spark plug 22 as ignition means. The ignition plug 22 is connected to an ignition device (not shown) including an ignition coil and the like, and performs a spark discharge by the ignition device. In this embodiment, the catalyst device 23 and the exhaust reburner 21 are housed in the same casing. A temperature sensor 24 for detecting the internal temperature is provided in the exhaust gas reburner 21.

An HC adsorbent 18 housed in a casing separate from the exhaust reburner 21 is interposed in the exhaust passage 14 on the upstream side of the exhaust reburner 21. The HC adsorbent 18 is obtained by coating a honeycomb structure with an adsorption component mainly composed of, for example, zeolite.
HC has a characteristic of adsorbing HC in a low temperature state of 00 to 200 ° C., and desorbing the adsorbed HC at a temperature higher than that.

A secondary air pump 20 is provided as a secondary air supply device for supplying secondary air to the exhaust passage 14. The secondary air pump 20 has a pair of discharge passages 31 and 32, and one of the passages 31
The upstream passage 8 communicates with the upstream air introduction section 27, and the other passage 32 communicates with the downstream air introduction section 29 downstream of the HC adsorbent 18. Opening / closing valves 28 and 30 for opening and closing these discharge passages 31 and 32 are interposed respectively.

Reference numeral 17 denotes a water temperature sensor for detecting the temperature of the cooling water of the internal combustion engine 1, 16 denotes an air-fuel ratio sensor disposed in the exhaust passage 14, and 33 denotes an engine speed sensor. Is detected by the air flow meter 3
And a detection signal from the throttle valve opening sensor 5 and the like are input to an engine control unit (ECU) 26.

The engine control unit 26 controls the fuel injection amount from the fuel injection valve 8 and the ignition timing by the spark plug 12 based on the signals indicating the engine operating conditions, and also controls the secondary air pump 20 And re-combustion of exhaust gas by the ignition plug 22 and the like.

The basic operation of the exhaust gas purifying apparatus will be described. When the internal temperature of the catalytic converter 23 is determined to be lower than a predetermined temperature (for example, 300 ° C.) when the internal combustion engine 1 is started, the engine control unit 26 According to the signal, the injection amount of the fuel injection valve 8 is increased so that the air-fuel ratio becomes very rich (air-fuel ratio is 10 or less). at the same time,
The secondary air pump 20 and the spark plug 22 are operated by the control signal of the engine control unit 26, and the supply of the secondary air and the spark discharge are started. The flow rate of the secondary air by the secondary air pump 20 is set to a flow rate at which at least oxygen becomes excessive in a state of being mixed with the exhaust gas in a rich state. Since this differs depending on the displacement of the internal combustion engine 1 and the operating state, it is set in advance by experiment to obtain a sufficient flow rate. Here, the initial introduction of the secondary air is performed from the downstream air introduction section 29, and the upstream open / close valve 28 is closed.

As a result, the combustible components (H
C, CO, H ₂ ) and O ₂ from the secondary air are supplied to the downstream side in a mixed state, which is ignited by the spark of the ignition plug 22 and burns in the exhaust reburner 21. The heat of the exhaust gas re-combustion promotes the activation of the catalyst device 23. Here, since the exhaust gas passes through the HC adsorbent 18 before reaching the exhaust reburner 21, HC in the exhaust gas is adsorbed by the adsorbent 18 and removed in advance. Therefore, even during the period from the start to the time when the exhaust gas is actually reburned in the exhaust gas reburner 21, the emission of HC into the atmosphere is prevented. In the exhaust reburner 21, CO, H ₂ , and O ₂ burn, so that trapping HC does not hinder exhaust reburn. Whether or not the exhaust reburner 21 has actually started combustion is determined by a change in the temperature detected by the temperature sensor 24. When it is determined that combustion has started, the secondary air is introduced into the upstream air introduction section. On-off valve 2 as performed from 27
8, 30 are switched.

The temperature of the HC adsorbent 18 rises due to the heating effect caused by the flow of exhaust gas and the heat transmitted from the exhaust gas reburner 21, and with this temperature rise, the adsorbed H
At this stage, the secondary air is supplied from the upstream side of the HC adsorbent 18 and passes through the inside of the adsorbent 18, so that the desorption of HC is promoted, and C is released for a short time. Completes the desorption. The desorbed HC burns in the downstream exhaust reburner 21 and is purified.

By the above-described exhaust gas reburning, the catalyst device 23
If it is determined that the internal temperature has become equal to or higher than a predetermined temperature (for example, 350 ° C.), the discharge of the ignition plug 22 and the secondary air pump 20 stop, and the exhaust reburning ends. At the same time, the fuel injection amount is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio so that the three-way catalyst in the catalyst device 23 operates efficiently.

As described above, the exhaust gas purifying apparatus traps HC discharged during the ignition delay period from the start of the internal combustion engine until the exhaust gas recombustes to prevent the HC from being released to the atmosphere. Desorb HC as early as possible,
Since the influence on the air-fuel ratio control is not caused, the harmful components discharged at the time of the cold start are largely reduced as a whole.

The above operation will be described more specifically with reference to the flowchart of FIG. This routine is repeatedly executed in the engine control unit 26, for example, at regular intervals. First, in step 1 (abbreviated as S1 in the figure), the cooling water temperature Tw, the intake air amount Qa, the engine speed Ne, the throttle valve opening TVO
And the reburner temperature TE are read. Next, in step 2, it is determined whether the cooling water temperature Tw is lower than a predetermined temperature TwL. Here, if the temperature is lower than the predetermined temperature TwL, it is determined that the catalyst is inactive, and the process proceeds to step 3 and thereafter to perform exhaust reburning. Note that a catalyst temperature sensor that directly detects the temperature of the catalyst device 23 may be provided, and whether or not the catalyst device 23 is activated may be determined based on the detected temperature.

In step 3, the amount of fuel required for exhaust gas reburning is increased. For example, using the increasing equivalent ratio TFEGI greater than 1 as the target equivalent ratio TFBYA so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio, the fuel injection amount Tp
Is calculated. Then, the process proceeds to a step 4, wherein the secondary air amount necessary for the exhaust gas reburning is calculated by comparing the intake air amount Qa with the target equivalent ratio TF.
From BYA, it is calculated as Qa × (TFBYA-1) × C, and the amount of secondary air supplied by the secondary air pump 20 is controlled. Note that C is a constant. For reliable ignition and combustion, the lower the temperature, the higher the concentration of unburned components and oxygen is required.
As shown in FIG. 3, the value is given as a large value so that the lower the reburner temperature TE, the richer the air-fuel ratio. In addition, you may make it determine the increase equivalent ratio TFEGI according to the coolant temperature Tw instead of the reburner temperature TE.

Next, at step 5, the overlap time DTOV at the time of switching the secondary air introduction section is determined. This is because the secondary air supplied from the upstream air introduction unit 27 is
This corresponds to the time required to reach the downstream air introduction section 29, and is set to have such a characteristic that it becomes shorter in a higher speed range according to the rotation speed of the internal combustion engine, as shown in FIG.

In step 6, it is determined from the temperature TE whether or not combustion in the exhaust reburner 21 has actually started. That is, the predetermined temperature T is compared with the predetermined temperature TEL.
At the point of time equal to or higher than EL, it is determined that combustion has started. If the temperature is lower than the predetermined temperature TEL, the combustion in the exhaust gas reburner 21 has not started, so the process proceeds to step 7, in which the upstream open / close valve 28 is closed, the downstream open / close valve 30 is opened, and the downstream air Secondary air is introduced from the introduction section 29. In step 8, a counter DT for measuring the overlap time is used.
Reset. Then, at step 9, the ignition plug 2
2 is operated to perform reburning in the exhaust reburner 21.

On the other hand, if the temperature TE of the exhaust gas reburner 21 is equal to or higher than the predetermined temperature TEL in step 6, it is determined that combustion has started, and the routine proceeds to step 10, where the upstream open / close valve 2 is opened.
8, the secondary air introduction from the upstream air introduction part 27 is started. Then, in a step 11, it is determined whether or not the value of the counter DT has exceeded the above-mentioned overlap time DTOV. Until the value of the counter DT exceeds the overlap time DTOV, the introduction of the secondary air from both the downstream air introduction unit 29 and the upstream air introduction unit 27 is continued, and in step 13, the value of the counter DT is sequentially increased. Increment. If the value of the counter DT exceeds the overlap time DTOV, the process proceeds from step 11 to step 12, in which the on-off valve 30 on the downstream side is closed, and
Stop the next air introduction.

As described above, the secondary air is introduced from the upstream air introduction part 27 at the time when the exhaust reburner 21 actually starts combustion, so that the desorption of HC from the HC adsorbent 18 is promoted. . Then, the desorbed HC flows into the exhaust reburner 21 together with the secondary air, and burns there.

When the cooling water temperature rises and becomes equal to or higher than the predetermined temperature TwL in step 2, it is determined that the catalyst has been activated, and the routine proceeds to step 14, where the target equivalent ratio TFBYA is set to 1 corresponding to the stoichiometric air-fuel ratio. return. Then, in step 15, the secondary air pump 20 is stopped.
8, 30 are closed, and this routine ends.

Next, a second embodiment will be described with reference to the flowchart of FIG. This takes into consideration the case where the combustion becomes unstable at the beginning of the combustion start, and switches the air introduction section after confirming that the combustion has been stabilized. This characteristic part mainly consists of step 10
7, steps 111 and 112, and other steps 101 to 106, step 1
Steps 08 to 110 and steps 113 to 119 are substantially the same as steps 1 to 6, steps 7 to 9, and steps 10 to 16 in the flowchart of FIG.

In this embodiment, when the temperature of the exhaust reburner 21 is ignited and the temperature TE becomes equal to or higher than the predetermined temperature TEL, the process proceeds from step 106 to step 111, and the value of the high temperature duration timer TTEH is incremented. When the temperature TE of the exhaust gas reburner 21 becomes lower than the predetermined temperature TEL, the value of the timer TTEH is set at step 107.
Is reset to 0. Then, in step 112,
It is determined whether the value of the timer TTEH has exceeded the predetermined value TTEHL. Until the value exceeds the predetermined value TTEHL, the process returns to step 108 without proceeding to step 113.

That is, unless the high temperature state of the exhaust reburner temperature TE continues for a predetermined time (TTEHL), the switching from the downstream air introduction section 29 to the upstream air introduction section 27 is not performed. Therefore, further instability of combustion due to frequent switching of the secondary air introduction position in a state where combustion in the exhaust reburner 21 is unstable is avoided.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a mechanical configuration of an exhaust gas purification device according to the present invention.

FIG. 2 is a flowchart showing the contents of control according to the present invention.

FIG. 3 shows an exhaust gas reburner temperature TE and a target fuel ratio TFEGI.
FIG. 3 is a characteristic diagram showing a relationship with the graph.

FIG. 4 is a characteristic diagram showing a relationship between an engine speed Ne and an overlap time DTOV.

FIG. 5 is a flowchart showing another embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between a required time for HC desorption and a flow rate of a passing gas per unit time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 8 ... Fuel injection valve 14 ... Exhaust passage 18 ... HC adsorbent 20 ... Secondary air pump 21 ... Exhaust recombustor 22 ... Spark plug 23 ... Catalyst device 26 ... Engine control unit 27 ... Upstream air introduction part 29… Downstream air inlet

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI F01N 3/24 F01N 3/24 EZ AB ZABL F02D 41/04 ZAB F02D 41/04 ZAB 305 305A (72) Inventor Hirofumi Tsuchida Kanagawa Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama-shi

Claims (7)

[Claims] 1. A catalyst device provided in an exhaust passage of an internal combustion engine, an exhaust reburner located upstream of the catalyst device and provided with ignition means, and a reburner for reburning in the exhaust reburner. Unburned component supply means for temporarily increasing the unburned components in the exhaust gas of the internal combustion engine, and secondary combustion in the exhaust gas upstream of the exhaust reburner for reburning in the exhaust reburner. An exhaust gas purification device for an internal combustion engine, comprising: a secondary air supply device for supplying air; an HC adsorbent for adsorbing HC (hydrocarbon component) in exhaust gas is provided upstream of the exhaust reburner. And the secondary air introduction unit by the secondary air supply unit is H
An exhaust gas purification device for an internal combustion engine, which is disposed upstream of a C adsorbent. 2. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein said unburned component supply means comprises air-fuel ratio control means for temporarily setting the air-fuel ratio of the internal combustion engine to a rich state. 3. A secondary air introduction unit provided by the secondary air supply device is provided on both the upstream side and the downstream side of the HC adsorbent, and air introduction from each of them is controlled according to conditions. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein: 4. A means for detecting the start of combustion of the exhaust gas recombustor, wherein secondary air is introduced from a downstream introduction section before the start of combustion, and secondary air is introduced from an upstream introduction section after the start of combustion. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3, further comprising: a secondary air control unit that introduces air. 5. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein a temperature sensor is provided in said exhaust gas reburner, and the start of combustion is detected from the temperature of the exhaust gas reburner. 6. A method according to claim 6, wherein the secondary air is stopped from the downstream introduction portion and the secondary air from the upstream introduction portion is caused by the start of combustion in the exhaust gas reburner.
6. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein an appropriate overlap period is provided between the start of introduction of the next air and the start of the introduction of the next air. 7. The exhaust gas purifying apparatus for an internal combustion engine according to claim 6, wherein the overlap time as the overlap period is set to be shorter on the high-speed side according to the engine speed.