JPH11229855A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the temperature of a NOx catalyst from suddenly rising during a change to normal operation by reviving the storage NOx catalyst when the deterioration thereof is determined, and controlling excess oxygen within the exhaust flowing into the NOx catalyst for a predetermined time after operation of revival means ends. SOLUTION: A catalyst 16 interposed in the exhaust system of an engine 1 is provided with an NOx catalyst 19, which stores NOx and SOx therein in an excessive oxygen atmosphere, and acts to discharge the NOx and SOx that accumulate when the oxygen content drops, and a 3-way catalyst 20. Then, according to this NOx catalyst 19, when more than a constant amount of SO2 accumulates and it is determined that the catalyst 19 is deteriorating, fuel is introduced, the catalyst 19 is heated to a high temperature, and then the stored SO2 is discharged. When this type of S purge operation is finished and it has shifted back into normal operation, the excess oxygen within the exhaust that flows into the NOx catalyst 19 is controlled and the HC and CO which have accumulated in the catalyst 19 are combusted with a small amount of oxygen, thereby preventing the temperature of the catalyst 19 from suddenly rising.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine in which the air-fuel ratio of an air-fuel mixture is controlled to be leaner than the stoichiometric air-fuel ratio to improve the fuel consumption characteristics, and a sulfur component which is adsorbed in a catalyst and reduces purification efficiency. It is intended to improve the function of releasing methane.

[0002]

2. Description of the Related Art As NO _x catalyst for purifying NO _x in the exhaust, the NO _x in an oxygen-rich atmosphere to purify NO _x in the exhaust by occluding on the catalyst, the oxygen concentration is attached to decrease it is known that has a function of releasing NO _x. That, the NO _x catalyst, in an oxygen concentration excess atmosphere, the NO _x in the exhaust is oxidized to produce nitrate, thereby while occluding NO _x in the atmosphere in which the oxygen concentration is lowered, and occluded in the NO _x catalyst reacting the CO in the exhaust nitrates to produce a carbonate, thereby so as to release NO _x.

[0003] Incidentally, a sulfur component (S component) is contained in fuel and lubricating oil, and such a sulfur component is also contained in exhaust gas. In the NO _x catalyst, an oxygen concentration excess atmosphere, sulfur components together with storage of the NO _x is also occluded. That is, the sulfur component burns and is further oxidized on the NO _x catalyst to SO ₃ . Then, a part of the SO ₃ reacts with the NO _x storage agent on the NO _x catalyst to form a sulfate, which is stored in the NO _x catalyst.

[0004] Therefore, nitrate and sulfate adhere to the NO _x catalyst. Sulfate has higher stability as a salt than nitrate, and even in an atmosphere where the oxygen concentration is reduced, the sulfate is one of them. since part only degraded, the amount of sulfate remaining in the nO _x catalyst is increased with time. This results in NO _x
Storage capacity of the catalyst decreases with time, the performance of the the NO _x catalyst will worsen (S poisoning).

[0005] Sulfates which lower the NO _x storage capacity of the NO _x catalyst have the property of decomposing when the oxygen concentration is low and the temperature is high. Therefore, for example, as shown in JP-A-7-217474, when a certain amount or more of a sulfur component (SO _x ) adheres to the NO _x catalyst, the air-fuel ratio of the exhaust gas is changed to an atmosphere with a reduced oxygen concentration. Te (introduction of fuel) to generate a large amount of HC and CO, and so the NO _x catalyst becomes a predetermined high temperature, sO
_{Releases x} .

[0006]

SUMMARY OF THE INVENTION In a conventional internal combustion engine,
After releasing the air-fuel ratio of the exhaust gas in the oxygen concentration lowering atmosphere was occluded in the NO _x catalyst SO _x (after S purge operation) by controlling the fuel lean side from the stoichiometric air-fuel ratio of the mixture again It is driven (normal operation). Therefore, at the time of switching to normal operation from the S purge operation, exhaust rapidly becomes oxygen rich atmosphere, to burn a large amount of oxygen react with the accumulated HC and CO in the NO _x catalyst, of the NO _x catalyst The temperature rises temporarily. S purge operation, originally because the temperature of the NO _x catalyst is set to the high temperature side, when switched to the normal operation
When the temperature of the NO _x catalyst is temporarily spike, if the NO _x catalyst exceeds the upper temperature limit is considered, there is a risk that leads to thermal degradation of the NO _x catalyst.

[0007] The present invention has been made in view of the above situation, when switching to normal operation after releasing the SO _x that is occluded in the NO _x catalyst and the air-fuel ratio of the exhaust gas in the oxygen concentration lowering atmosphere,
Aims to temperature of the NO _x catalyst to provide an internal combustion engine is not to jump.

[0008]

In the present invention for achieving the above object means to provide a process, if the occlusion-type the NO _x catalyst of is determined to be deteriorated by the deterioration determining means, and the oxygen concentration decreases atmosphere exhaust atmosphere by the reproducing means to release the sulfur component in the NO _x catalyst by, inhibiting the excess oxygen in the exhaust gas flowing into between the NO _x catalyst of the predetermined time after the end of the operation of the reproducing means by excess oxygen inhibition means, the operation end of the regeneration means During the subsequent predetermined time, that is, when the air-fuel ratio of the exhaust gas is
when switching to normal operation after releasing the SO _x that was occluded in the _x catalyst, the exhaust does not become oxygen-rich atmosphere, accumulated HC and CO are burned in a small amount of oxygen into the NO _x catalyst, the NO _x catalyst Temperature does not rise rapidly.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. This embodiment is a multi-cylinder in-cylinder injection in which fuel is directly injected into a combustion chamber as an internal combustion engine in which the air-fuel ratio of an air-fuel mixture is controlled to be leaner than the stoichiometric air-fuel ratio to improve fuel economy characteristics. The internal combustion engine is described as an example. FIG. 1 shows a schematic configuration of an internal combustion engine according to an embodiment of the present invention, and FIG. 2 shows a fuel injection control map.

As the multi-cylinder in-cylinder injection internal combustion engine, for example, an in-cylinder injection in-line four-cylinder gasoline engine (in-cylinder injection engine) 1 that directly injects fuel into a combustion chamber is applied. In the direct injection engine 1, a combustion chamber, an intake device, an exhaust gas recirculation device (EGR device), and the like are designed exclusively for direct injection.

The cylinder head 2 of the direct injection engine 1 is provided with an ignition plug 3 for each cylinder and an electromagnetic fuel injection valve 4 for each cylinder.
An injection port of the fuel injection valve 4 is opened in the combustion chamber 5, and fuel injected from the fuel injection valve 4 is directly injected into the combustion chamber 5. Cylinder 6 of in-cylinder injection engine 1
A piston 7 is slidably supported in the up-down direction, and a hemispherically concave cavity 8 is formed on the top surface of the piston 7. The cavity 8 generates a reverse tumble flow in the intake flow, which is opposite to a normal tumble flow.

An intake port 9 and an exhaust port 10 facing the combustion chamber 5 are formed in the cylinder head 2.
Is opened and closed by the drive of the intake valve 11, and the exhaust port 10
Is opened and closed by driving the exhaust valve 12. Exhaust port 1
0 is a large-diameter exhaust gas recirculation port (EGR port) 1
3 branches.

An intake pipe 14 is connected to the intake port 9,
A surge tank, an air cleaner, a throttle body, and the like (not shown) are connected to the intake pipe 14. On the other hand, an exhaust pipe 15 is connected to the exhaust port 10, and the exhaust pipe 15 is provided with a catalyst 16 and a muffler (not shown). The EGR port 13 is connected to the intake pipe 14 via a large-diameter EGR pipe 17, and the EGR pipe 17 is provided with a stepper motor type EGR valve 18.

[0014] The catalyst 16 is in an oxygen-rich atmosphere to purify NO _x in the exhaust by occluding NO _x on the catalyst,
And the NO _x catalyst 19 having an oxygen concentration having a function of releasing NO _x adhering to decrease, CO in the atmosphere of the stoichiometric air-fuel ratio, HC and
And a three-way catalyst 20 to the NO _x had can purify ternary functions. Temperature of the catalyst 16 detected by the temperature sensor 21, the concentration of the NO _x in the exhaust of the downstream side of the NO _x catalyst 19 is NO
It is detected by the _x sensor 22. The configuration of the catalyst 16, as long as having at least one the NO _x catalyst 19, disposed and function and the like are not limited to the above embodiment.

The vehicle has an electronic control unit (ECU) 23
The ECU 23 is provided with an input / output device, a storage device for storing a control program, a control map, and the like, a central processing unit, and a timer and counters. EC
Comprehensive control of the direct injection engine 1 is performed by U23. The detection information of the various sensors is input to the ECU 23. The ECU 23 determines the ignition timing, the amount of the EGR gas introduced, etc., including the fuel injection mode and the fuel injection amount, based on the detection information of the various sensors. 4, the spark plug 3, the EGR valve 18 and the like are drive-controlled.

In the above-described in-cylinder injection engine 1, the intake air flowing into the combustion chamber 5 from the intake port 9 forms a reverse tumble flow, and is disposed at the center of the top of the combustion chamber 5 using the reverse tumble flow. A small amount of fuel is collected only in the vicinity of the spark plug 3 and an extremely lean air-fuel ratio state is formed in a portion separated from the spark plug 3. By setting the stoichiometric air-fuel ratio or the rich air-fuel ratio only in the vicinity of the spark plug 3, fuel consumption is suppressed while achieving stable stratified combustion (stratified super-lean combustion). The optimal fuel injection timing in this case is the latter half of the compression stroke in which the air flow is weak.

In order to obtain a high output from the engine, the fuel from the injector 8 is homogenized throughout the combustion chamber 1 and the interior of the combustion chamber 1 is brought to a stoichiometric air-fuel ratio or a lean air-fuel ratio air-fuel mixture. Perform mixed combustion. Of course, a higher output can be obtained with the stoichiometric air-fuel ratio than with the lean air-fuel ratio. In this case, too, the fuel is injected at a timing such that the fuel is sufficiently atomized and vaporized, and the high output is efficiently obtained. I'm trying to get In this case, the optimal fuel injection timing is set so that the fuel injection is terminated during the intake stroke so that the atomization and vaporization of the fuel can be promoted using the intake flow.

The ECU 23 determines the fuel injection mode by searching the current fuel injection area from the fuel injection map of FIG. 2 based on the operating load Pe and the engine speed Ne according to the opening of the throttle valve. . Thereby, the fuel injection amount according to the target air-fuel ratio in each fuel injection mode is determined, and the drive of the fuel injection valve 4 and the drive control of the ignition plug 3 are controlled according to the fuel injection amount. At the same time, EG
Open / close control of the R valve 18 is also performed.

The NO _x catalyst 19 of the catalyst 16 is capable of absorbing NO _x on the catalyst in an oxygen-excess atmosphere so that
It has a function of purifying NO _x. That, NO _x catalyst 1
9, the oxygen concentration excess atmosphere such as during stratified super lean burn operation in the compressed lean mode and the intake lean mode, the NO _x in the exhaust gas is oxidized nitrates are produced, thereby NO _x is occluded, the exhaust Purification is performed.

Meanwhile, NO _x catalyst 19 of the catalyst 16, the oxygen concentration has a function of releasing NO _x adhering to decrease. In other words, the oxygen concentration in the atmosphere decreases, carbonate is generated by reaction with CO in the exhaust and nitrate occluded in the NO _x catalyst 19, thereby NO _x is released. Therefore, NO
_When the storage of NO _{x in} the _x catalyst 19 proceeds and the NO _x sensor 22 detects that the concentration of NO _{x in} the exhaust gas has increased, the oxygen concentration is reduced by performing additional fuel injection or the like.
To release the NO _x from the NO _x catalyst 19, so as to maintain the function of the NO _x catalyst 19.

[0021] Incidentally, the sulfur components contained in fuel and lubrication in oil (SO _x) is also present in the exhaust, in the NO _x catalyst 19,
In an oxygen-rich atmosphere, SO _x is also stored together with NO _x . That is, the sulfur component is burned, further the NO _x catalyst 19
Is oxidized above becomes SO _3. And part of this SO ₃
Reacts with occluding agent for the NO _x catalyst 19 on an additional NO _x occluding the the NO _x catalyst 19 becomes sulfate.

The NO _x catalyst 19 has a function of releasing the attached SO _x when the oxygen concentration decreases. That is, in the atmosphere in which the oxygen concentration is lowered, NO _x partially CO and carbonates react in the exhaust gas of the occluded sulfate in the catalyst 19 is produced SO ₃ is released, SO ₃ released in Is reduced by HC and CO in the exhaust gas.

[0023] However, sulfates have high stability as salts than nitrates, since the oxygen concentration is not decomposed only a part thereof even if the atmosphere is reduced, time is the amount of sulfate remaining in the NO _x catalyst 19 Increase with. This results in NO _x
Storage capacity of the catalyst 19 decreases with time, NO _x catalyst 1
The performance as No. 9 will be deteriorated (S poisoning).

[0024] Therefore, when the NO _x catalyst 19 adheres more than a certain amount of sulfur components (SO _x) is the the NO _x catalyst 19 is determined to be deteriorated, the introduction of fuel as a reproduction unit, empty exhaust Change the fuel ratio to an atmosphere with a low oxygen concentration and use a large amount of HC
And CO is generated, the the NO _x catalyst 19 to a high temperature is reacted with the remaining oxygen on the NO _x catalyst 19, so as to release the occluded SO _x (S purge operation).

That is, apart from the driving of the fuel injection valve 4 in the main fuel injection for normal combustion in the combustion chamber 5 (fuel injection in the compression stroke and the intake stroke), it is difficult to influence the output of the engine ( In the expansion stroke), the fuel injection valve 4 is driven to inject additional fuel, and the additional fuel is burned.
The NO _x catalyst 19 supplying a large amount of HC and CO to, the the NO _x catalyst 19 together to reduce the SO ₃ to a high temperature, to release the occluded SO _x.

Since the above-mentioned internal combustion engine is the direct injection engine 1 which injects fuel directly into the combustion chamber 5, additional fuel is injected during the expansion stroke. when performing the insertion of the fuel as the reproduction means when the engine to be introduced, by controlling the air-fuel ratio of the mixture to the rich side to supply larger amount fuel than normal operation in the NO _x catalyst 19 a large amount of HC and CO Supply.

[0027] As determined deterioration determining unit deterioration of the NO _x catalyst 19, and are inserted into the NO _x catalyst 19, based on the total fuel injection quantity obtained from the integrated value of the driving time of the fuel injection valve 4 for all operating modes It estimates the amount of SO _x . Note that the deterioration determination means may be configured to estimate the amount of SO _x stored in the NO _x catalyst 19 based on the traveling distance of the vehicle. Further, the SO _x stored in the NO _x catalyst 19 may be configured. For example, a sensor or the like that can directly detect the amount of methane may be used.

[0028] In-cylinder injection engine 1 described above, when moving to a normal operation in S purge operation is completed, to suppress the excess oxygen in the exhaust gas flowing into the NO _x catalyst 19 by the excess oxygen inhibition means, NO HC and CO accumulated in the _x catalyst 19 are burned with a small amount of oxygen so that the temperature of the NO _x catalyst 19 does not rise rapidly. Hereinafter, the operation state of the surplus oxygen suppression means will be described with reference to FIGS.

[0029] FIG. 3 is shows a graph showing changes with time of the temperature of the air-fuel ratio and NO _x catalyst in excess oxygen inhibition in the flow chart, Figure 4 represents the situation of excess oxygen inhibition immediately after completion of the S purge operation .

[0030] In the S purge operation, HC is present in the NO _x catalyst 19, the the NO _x catalyst 19 even after the completion of the injection of additional fuel
HC and CO are accumulated. Therefore, when directly proceeds to the normal operation mode after completion of the S purge operation, exhaust rapidly become oxygen-rich atmosphere, a large amount of oxygen react with the accumulated HC and CO in the NO _x catalyst 19 combustion and the temperature of the NO _x catalyst 19 will temporarily spike.

In step S1, it is determined whether or not a predetermined time has elapsed since the end of the S purge operation, that is, whether or not immediately after the end of the S purge operation. If it is immediately after, in step S2, it is determined whether or not excess oxygen increases when the normal operation mode is set. The determination of whether there is a large amount of excess oxygen depends on, for example, the air-fuel ratio.
Judgment is made based on whether AF is equal to or greater than a predetermined value a. If it is determined in step S2 that there is a large amount of excess oxygen (AF ≧ a),
Move to 3.

[0032] as in step S3 by burning HC and CO accumulated by suppressing the excess oxygen in the small amount of oxygen temperature of the NO _x catalyst 19 is not temporarily spike, Ya accumulated HC
Switch to normal lean operation mode with CO burned.

The surplus oxygen suppression in step S3 will be described with reference to FIG. When the S purge operation is completed (P), FIG.
As shown in (a), the driving of the fuel injection valve 4 is controlled to make the air-fuel ratio AF stoichiometric or rich (excess oxygen suppression means) without shifting to the normal operation mode. During a predetermined time period up to the set time Q, the air-fuel ratio AF is kept stoichiometric or rich so that the exhaust does not become an atmosphere with an excessive oxygen concentration, and the accumulated HC and CO are burned with a small amount of oxygen. After the air-fuel ratio AF is kept stoichiometric or rich until the set time Q, the air-fuel ratio AF is controlled to the state of the compression lean mode (solid line in the figure) or the intake lean mode (dashed line in the figure).

The temperature of the NO _x catalyst 19 in surplus oxygen suppression is as follows:
As shown by the solid line in FIG. 4 (b), the accumulated HC and CO slightly increase after the end of the S purge operation (P), and decrease after that in the vicinity of the set time Q by the amount burned by a small amount of oxygen. Is constant. When the air-fuel ratio is shifted to the operation mode in which the excess oxygen is large immediately after the end of the S purge operation without performing the excess oxygen suppression (indicated by the middle dotted line in FIG. 4A), the exhaust gas suddenly becomes an oxygen-rich atmosphere. For this reason, as shown by the dotted line in FIG. 4B, the temperature of the NO _x catalyst 19 temporarily rises suddenly, and the temperature of the NO _x catalyst 19 exceeds the allowable temperature TS.

[0035] Therefore, by executing the excess oxygen inhibition, prevents the temperature of the NO _x catalyst 19 is temporarily spike, the temperature of the NO _x catalyst 19 is no longer exceed the heat resistant temperature TS. Therefore, it is possible to suppress the thermal deterioration of the NO _x catalyst 19.

The time from the end (P) of the S purge operation to the set time Q may be a fixed time, or may be variable according to the detection result by directly detecting HC using an HC sensor.
The state of occlusion of HC and CO into the NO _x catalyst 19 from the operating state is obtained in advance as data, and the time can be set by estimating the amount of HC based on the data. Further, the time can be set based on the detection of the temperature sensor 21.

Another embodiment of suppressing excess oxygen is shown in FIG.
A description will be given below. In the present embodiment, the surplus oxygen suppressing means
Then, the EGR valve 18 is opened and the exhaust gas is re-introduced into the intake pipe 14.
(EGR input), and exhaust gas is suppressed by suppressing fresh air.
This is to prevent an atmosphere with an excessive element concentration. Figure
5 shows the air-fuel ratio, EGR injection and NO at the time of excess oxygen suppression. _x
3 is a graph showing the change over time in the temperature of the catalyst.

Normally, during operation in the compression lean mode, E
When the engine is operated in the intake lean mode, the EG
R is not supplied.

When the normal operation after the completion of the S purge operation is the compression lean mode, when the S purge operation is completed (P), as shown by the solid line in FIG. The mode is set slightly lower than the mode, and as shown by the solid line in FIG. 5B, the EGR is applied more than in the normal compression lean mode. That is, in the normal compression lean mode, the EGR valve 18 is supplied to a moderate level by the duty control of the EGR valve 18, but in the case of suppressing excess oxygen, the EGR is supplied more than the medium level.

During a predetermined time period up to the set time Q, EGR is supplied more than in the normal compression lean mode, so that the exhaust gas is prevented from becoming an oxygen-rich atmosphere, and is stored.
HC and CO are burned with a small amount of oxygen. EG until set time Q
After R is input more than in the normal compression lean mode, the injection of EGR is made medium and the air-fuel ratio AF is controlled to the state of the compression lean mode (shown by the solid line in FIG. 5A).

When the normal operation after the end of the S purge operation is the intake lean mode, when the S purge operation is completed (P), as shown by a dotted line in FIG. The mode is set slightly lower than the mode, and the EGR is supplied slightly less as shown by the dotted line in FIG. 5 (b). That is, in the normal intake lean mode, E
GR is not supplied, but in the case of surplus oxygen suppression, EGR
Is thrown in a little.

Until the set time Q, a small amount of EGR is supplied to prevent the exhaust gas from becoming an atmosphere with an excessive oxygen concentration, and the accumulated HC and CO are burned with a small amount of oxygen. After a small amount of EGR is supplied until the set time Q, the supply of EGR is stopped and the air-fuel ratio AF is set to the intake lean mode (FIG. 5).
(a) (indicated by the middle dotted line).

The temperature of the NO _x catalyst 19 of surplus oxygen inhibition by EGR is turned on, as in the case of excess oxygen inhibition by the additional fuel injection, as shown by the solid line in FIG. 5 (c), stored
HC and CO slightly increase after the end of the S purge operation (P) by the amount of combustion of a small amount of oxygen, and thereafter decrease and become constant near the set time Q. Therefore, as shown by a dotted line in FIG. 5 (c), the temperature of the NO _x catalyst 19 is temporarily spike, NO _x
The temperature of the catalyst 19 does not exceed the heat-resistant temperature TS.

[0044] Therefore, by executing the excess oxygen inhibited by introduction of EGR, prevents the temperature of the NO _x catalyst 19 is temporarily spike, the temperature of the NO _x catalyst 19 is no longer exceed the heat resistant temperature TS. Therefore, it is possible to suppress the thermal deterioration of the NO _x catalyst 19.

It should be noted that the surplus oxygen suppression can be started or ended gradually. Also, excess oxygen inhibition as described above, if the internal combustion engine equipped with a the NO _x catalyst 19 of the occlusion-type, can be applied to an internal combustion engine of a diesel engine or the like with various aspects.

[0046]

According to the internal combustion engine of the present invention, the deterioration determination means is used.
NO storage type NO_xIf it is determined that the catalyst is deteriorated,
Make the exhaust atmosphere a low oxygen concentration atmosphere
And NO _xReleases sulfur components in the catalyst to reduce excess oxygen
Means for a predetermined time after the end of the operation of the reproducing means._xTouch
To reduce excess oxygen in the exhaust gas flowing into the medium.
For a predetermined time after the end of the operation of the regeneration means,
The air-fuel ratio of_xOccluded in the catalyst
SO_xWhen switching to normal operation after releasing
NO atmosphere without excessive element concentration_xHC accumulated in the catalyst
CO is burned with a small amount of oxygen and NO_xCatalyst temperature rises rapidly
Never. As a result, NO_xThe temperature of the catalyst
No more, no_xControl thermal degradation of catalyst
It becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine according to an embodiment of the present invention.

FIG. 2 is a fuel injection control map.

FIG. 3 is a flowchart showing a state of surplus oxygen suppression immediately after the end of the S purge operation.

FIG. 4 is a graph showing the change over time in the air-fuel ratio and the temperature of the NO _x catalyst when suppressing excess oxygen.

FIG. 5 shows the air-fuel ratio, EGR injection, and NO during surplus oxygen suppression.
_x Graph showing the change over time in the temperature of the catalyst.

[Explanation of symbols]

1 cylinder injection engine 16 catalyst 19 NO _x catalyst 20 three-way catalyst 21 the temperature sensor 22 NO _x sensor 23 Electronic control unit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/28 301 F01N 3/28 301C F02D 41/04 305 F02D 41/04 305A 41/14 310 41/14 310D

Claims (1)

[Claims] 1. A and the NO _x catalyst to release the occluded NO _x in an oxygen concentration reduction atmosphere while absorbing the NO _x in the exhaust in an oxygen-rich atmosphere is provided in an exhaust passage of the engine, the sulfur component in the exhaust gas the NO _x by adsorbing to the the NO _x catalyst
The NO _x by the degradation determiner means a deterioration of the catalyst, the exhaust atmosphere when the the NO _x catalyst is determined to be deteriorated by the deterioration determining means and the oxygen concentration decreases Atmosphere
Features and reproducing means for releasing the sulfur component in the catalyst, that a suppressing excess oxygen suppressing means the excess oxygen in the exhaust gas flowing into operation after the end of the predetermined time the the NO _x catalyst of the reproducing device Internal combustion engine.