JP2003286878A - Device and method for exhaust-emission control of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for exhaust-emission control of an internal combustion engine provided with a NOx catalyst in an exhaust path in which the NOx catalyst can be regenerated favorably from SOx poisoning irrespective of the operation condition of the internal combustion engine. <P>SOLUTION: An air-fuel ratio of exhaust gas is controlled firstly to a 1st predetermined air-fuel ratio at which the volume of discharged smoke is set at an allowable upper limit. Then, the exhaust ratio is intermittently controlled to a 2nd predetermined air-fuel ratio which is overrich richer than the 1st air- fuel ratio enabling the NOx catalyst to recover from SOx poisoning, and the temperature of the NOx catalyst is controlled in the range of predetermined temperatures in which the catalyst can be recovered from SOx poisoning and the degradation of the NOx catalyst is not accelerated. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust emission control device for an internal combustion engine having a NOx catalyst, and more particularly to a technique for recovering NOx catalyst from sulfur oxide (SOx) poisoning.

[0002]

2. Description of the Related Art In a lean-burn internal combustion engine represented by a diesel engine, various measures are taken to reduce the emission of nitrogen oxides (NOx) and unburned fuel components (HC, CO).

For example, there is known an exhaust gas purification device in which an NOx catalyst is provided in an exhaust passage of an internal combustion engine in order to purify NOx in exhaust gas.

The NOx catalyst occludes NOx contained in the exhaust gas when the oxygen concentration of the inflow exhaust gas is high, that is, when the air-fuel ratio of the exhaust gas is lean, and when the oxygen concentration of the inflow exhaust gas is low, That is, when the air-fuel ratio of the exhaust gas is rich, the stored NOx is replaced with nitrogen dioxide N
Nitrogen N is obtained by reducing and releasing O ₂ and NO in the form of NO in the exhaust gas, and at the same time oxidizing the NO ₂ and NO with the unburned fuel components CO and HC contained in the exhaust gas. _It has an exhaust purification function to purify to ₂ .

By the way, the NOx catalyst has a property of occluding SOx when the exhaust gas contains sulfur oxides (SOx), like NOx. Moreover, SOx
Is more stably stored in the NOx catalyst than NOx, and thus is less likely to be reduced than NOx, and tends to be stored in the NOx catalyst. As a result, NO
The amount of SOx stored in the x catalyst increases, NOx cannot be stored correspondingly, the NOx storage capacity of the NOx catalyst decreases, and the original exhaust gas purification function is impaired (hereinafter, this phenomenon is referred to as SOx poisoning). .

Therefore, conventionally, the NOx catalyst has been replaced with SOx.
So-called SOx poisoning recovery control is performed to recover from poisoning.

In order to release and reduce the SOx stored in the NOx catalyst, it is necessary to make the temperature of the NOx catalyst higher than that at the time of NOx reduction and to make the ambient atmosphere a stoichiometric air-fuel ratio or a rich air-fuel ratio.

Therefore, when the operating state of the internal combustion engine is excessive oxygen exhaust and the exhaust gas or the NOx catalyst is at high temperature, the internal combustion engine is provided with an exhaust oxygen concentration control means for decreasing the oxygen concentration of the exhaust gas flowing into the NOx catalyst. An exhaust emission control device for an engine is known (for example, see Patent Document 1).

Further, when the amount of recirculated exhaust gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of recirculated exhaust gas supplied to the combustion chamber is further increased. In this case, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot generation temperature, and the first combustion (hereinafter referred to as low temperature combustion) in which the amount of soot generation is suppressed, Low-temperature combustion in an internal combustion engine that selectively switches between second combustion (hereinafter, referred to as normal combustion) in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated exhaust gas that produces a peak. There is known a technique for recovering from NOx poisoning of the NOx catalyst when the above is performed.

In low-temperature combustion, since the combustion temperature is low, smoke is hardly generated even if the air-fuel ratio in the combustion chamber is made richer than the stoichiometric air-fuel ratio. Therefore, NO
When the SOx stored in the x catalyst exceeds the allowable amount, low-temperature combustion is performed, and at the same time, the air-fuel ratio in the combustion chamber is set to the rich air-fuel ratio to make the air-fuel ratio of the exhaust gas the rich air-fuel ratio, By raising the temperature of the NOx catalyst, the NOx catalyst is recovered from SOx poisoning (for example, refer to Patent Document 2).

[0011]

[Patent Document 1] JP-A-6-88518

[Patent Document 2] Japanese Patent No. 3104692

[0012]

As described above, NO
In order to recover the x-catalyst from SOx poisoning, it is necessary to make the temperature of the NOx catalyst higher than that at the time of NOx reduction and set the ambient atmosphere to the theoretical air-fuel ratio or the rich air-fuel ratio.

However, if the air-fuel ratio of the ambient atmosphere is reduced, the NOx catalyst will rise in temperature. Therefore, when the oxygen concentration of the exhaust gas is reduced when the exhaust gas or NOx catalyst is at a high temperature, the temperature of the NOx catalyst becomes excessive. Becomes higher,
There is a risk of deterioration of the NOx catalyst.

Further, in an internal combustion engine which selectively switches between low temperature combustion and normal combustion, low temperature combustion becomes impossible when the amount of intake air into the combustion chamber exceeds a certain amount. It is not possible to carry out low temperature combustion,
Further, in normal combustion, if the air-fuel ratio in the combustion chamber is set to the rich air-fuel ratio or the stoichiometric air-fuel ratio, a large amount of smoke may be discharged.

Therefore, an object of the present invention is to add NO to the exhaust passage.
In an internal combustion engine provided with an x catalyst, it is possible to provide an exhaust purification device and a purification method for an internal combustion engine, which can more preferably recover a NOx catalyst from SOx poisoning regardless of the operating state of the internal combustion engine. .

[0016]

The present invention employs the following means in order to solve the above problems. That is, the present invention first controls the air-fuel ratio of the exhaust gas to a predetermined air-fuel ratio at which the amount of smoke discharged becomes the upper limit of the allowable amount, and then intermittently makes the rich air-fuel ratio or the stoichiometric air-fuel ratio. At the same time, the temperature of the NOx catalyst is raised to raise the temperature of the NOx catalyst from the SOx.
Is to be released.

Therefore, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes a NOx catalyst provided in the exhaust passage and the NOx catalyst.
NOx catalyst temperature detection means for detecting the temperature of the catalyst, exhaust air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas in the exhaust passage, temperature of the NOx catalyst detected by the NOx catalyst temperature detection means, and the exhaust gas Exhaust air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas in the exhaust passage based on the air-fuel ratio of the exhaust gas detected by the air-fuel ratio detection means,
When the air-fuel ratio of the exhaust gas detected by the exhaust air-fuel ratio detection means is less than the first predetermined air-fuel ratio, the exhaust air-fuel ratio control means changes the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio. The fuel ratio is controlled to a second predetermined air-fuel ratio, which is intermittently richer than the first predetermined air-fuel ratio and enables recovery from SOx poisoning of the NOx catalyst. The temperature of the NOx catalyst is set to the SOx of the NOx catalyst.
It is configured to be controlled within a predetermined temperature range in which recovery from poisoning is possible and deterioration of the NOx catalyst is not promoted.

In the above construction, the first predetermined air-fuel ratio is preferably an air-fuel ratio at which the amount of smoke discharged becomes the upper limit of the allowable amount, and the second predetermined air-fuel ratio is a rich air-fuel ratio or a stoichiometric air-fuel ratio. Is also good.

According to the above structure, the air-fuel ratio of the exhaust gas is set to the first predetermined air-fuel ratio, and then is set to the second predetermined air-fuel ratio intermittently, so that the smoke amount is increased regardless of the operating state of the internal combustion engine. It is possible to recover the NOx catalyst from SOx poisoning while suppressing the emission.

Further, when the air-fuel ratio of exhaust gas becomes small, N
The temperature of the Ox catalyst rises, and when the ambient atmosphere has a rich air-fuel ratio or a stoichiometric air-fuel ratio, the temperature of the stored SOx is raised to a temperature at which SOx is reduced / released (for example, 600 ° C. or higher), and the NOx catalyst is heated. However, if the temperature becomes too high (for example, 700 ° C. or higher), the deterioration of the NOx catalyst will be accelerated. Therefore, if the atmosphere around the NOx catalyst is continuously set to the rich air-fuel ratio or the stoichiometric air-fuel ratio in the state where the temperature of the exhaust gas is high, the NOx catalyst may be deteriorated.

Therefore, by intermittently setting the air-fuel ratio of the exhaust gas to the rich air-fuel ratio or the stoichiometric air-fuel ratio, NOx
It raises the temperature of the catalyst and prevents overheating. Therefore, the temperature of the NOx catalyst can be controlled to a temperature at which SOx poisoning can be recovered and deterioration is not promoted.

Further, by first setting the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio, the air-fuel ratio of the exhaust gas can be controlled to the second predetermined air-fuel ratio more accurately and more quickly. Becomes Therefore, it is possible to prevent excessive temperature rise of the NOx catalyst and discharge of unburned components due to the exhaust gas having an excessively rich air-fuel ratio, and to reduce the NOx catalyst to S
It is possible to recover more quickly from Ox poisoning.

In addition, the fact that the air-fuel ratio of the exhaust gas is intermittently controlled to the rich air-fuel ratio or the stoichiometric air-fuel ratio means that the air-fuel ratio of the exhaust gas intermittently becomes the lean air-fuel ratio. Therefore, when the NOx catalyst is a catalyst that has an oxygen retention capacity such as a particulate filter and that oxidizes and purifies fine particles (for example, soot) in exhaust gas, the exhaust gas and the lean air-fuel ratio of the stoichiometric air-fuel ratio or rich air-fuel ratio Since the particulates such as soot are purified by alternately flowing with the exhaust gas of NOx, the NOx catalyst can be recovered from SOx poisoning more effectively while suppressing the discharge of smoke.

When the amount of recirculated exhaust gas supplied to the combustion chamber of the exhaust gas purification apparatus for an internal combustion engine as described above is increased, the amount of soot generated gradually increases and reaches a peak, and the soot is supplied to the combustion chamber. When the amount of recirculated exhaust gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are lower than the temperature at which soot is generated, and the first amount of soot is suppressed, Even when applied to an internal combustion engine provided with a switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated exhaust gas at which the soot generation amount reaches a peak. good.

Here, the first combustion is low temperature combustion and the second combustion is normal combustion.

That is, according to the exhaust gas purifying apparatus for an internal combustion engine of the present invention, low temperature combustion is performed during idling or low load operation of a diesel engine, for example.
Even in an internal combustion engine that normally burns during medium to high load operation, the NOx catalyst can be recovered from SOx poisoning regardless of the operating state.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, a throttle valve for controlling the amount of intake air supplied to the combustion chamber and a recirculation exhaust gas recirculated to the combustion chamber (hereinafter referred to as EGR gas And a recirculation exhaust gas control valve for controlling the amount of the exhaust gas, by controlling the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve. You may control to a predetermined air fuel ratio.

That is, the air-fuel ratio in the combustion chamber is controlled to the first air-fuel ratio by controlling at least one of the intake air amount and the EGR gas amount flowing into the combustion chamber, and thereby the exhaust gas air-fuel ratio is controlled to the first air-fuel ratio. The air-fuel ratio can be controlled.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, after the air-fuel ratio of the exhaust gas is controlled to the first predetermined air-fuel ratio, the fuel is added to at least one of the combustion chamber and the exhaust passage of the internal combustion engine. It is also possible to intermittently control the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio and control the temperature of the NOx catalyst within the predetermined temperature range by controlling the above.

That is, by intermittently adding the fuel to at least one of the combustion chamber and the exhaust passage of the internal combustion engine, the air-fuel ratio of the exhaust gas can be intermittently controlled to the second predetermined air-fuel ratio, and at the same time. The temperature of the NOx catalyst can be controlled within a predetermined temperature range.

Here, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, at least one of the combustion chamber and the exhaust passage of the internal combustion engine, which is performed to intermittently control the air-fuel ratio of the exhaust gas to the second air-fuel ratio. The fuel is added to the NOx catalyst intermittently, and when the temperature of the NOx catalyst is lower than the temperature at which the NOx catalyst can be recovered from SOx poisoning, the fuel is added to the Nx catalyst.
The fuel addition may be stopped when the temperature may accelerate the deterioration of the Ox catalyst.

When the fuel addition is stopped, the air-fuel ratio of the exhaust gas becomes large and the temperature of the NOx catalyst rapidly drops, so that the deterioration of the NOx catalyst can be suppressed and the next fuel addition can be performed. Become. Therefore, by repeating the addition of fuel and the suspension of addition as described above, NOx
It is possible to recover the catalyst from SOx poisoning and suppress deterioration of the NOx catalyst.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the fuel is added to the combustion chamber of the internal combustion engine by the sub-injection other than the main injection that is injected to obtain the engine output in the fuel chamber. Also good.

As the sub-injection other than the main injection, for example, post-injection for further injecting the fuel into the combustion chamber when the fuel burned for obtaining the engine output in the cylinder is in the expansion stroke or the exhaust stroke is exemplified. You can

Further, the exhaust gas purification apparatus for an internal combustion engine according to the present invention may further comprise an exhaust gas purification catalyst in the exhaust passage upstream of the NOx catalyst for recovering from SOx poisoning.

According to this structure, NO contained in the exhaust gas
Since x, unburned components (CO, HC) and the like are oxidized or reduced in the exhaust purification catalyst arranged on the upstream side of the NOx catalyst, N that recovers from SOx poisoning by its reaction heat.
The temperature distribution of the Ox catalyst can be made more uniform than that of the NOx catalyst alone. Therefore, it becomes easy to control the temperature of the NOx catalyst for recovering from SOx poisoning.

In the exhaust emission control device according to the present invention, N
In order to purify unburned components contained in the exhaust gas on the downstream side of the Ox catalyst, the exhaust passage on the downstream side of the NOx catalyst may be further provided with an oxidation catalyst.

Further, in this configuration, the fuel addition to the combustion chamber or the exhaust passage of the internal combustion engine may be controlled based on the temperature of the oxidation catalyst installed downstream of the NOx catalyst.

For example, when the temperature of the oxidation catalyst is low, the temperature of the oxidation catalyst is activated before the air-fuel ratio of the exhaust gas is controlled to the second predetermined air-fuel ratio which enables recovery from SOx poisoning of the NOx catalyst. Fuel is added to at least one of the combustion chamber and the exhaust passage of the internal combustion engine so as to reach the temperature.

That is, according to the above configuration, since the SOx poisoning recovery from the NOx catalyst is performed after the exhaust gas purification capacity of the oxidation catalyst installed downstream of the NOx catalyst is increased, the emission of unburned components is exhausted. Can be reduced.

Further, in the above structure, the fuel addition for raising the temperature of the oxidation catalyst is intermittently performed, and at least one of the amount of fuel to be added and the interval of addition time is controlled based on the temperature of the oxidation catalyst. May be.

For example, the lower the temperature of the oxidation catalyst, the larger the amount of fuel added, and the longer the time interval for adding fuel may be.

By such control, it is possible to quickly raise the temperature of the oxidation catalyst to the activation temperature.

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, in order to purify unburned components contained in the exhaust gas downstream of the NOx catalyst, the exhaust passage downstream of the NOx catalyst is oxidized. When a catalyst is further provided, the air-fuel ratio of the exhaust gas may be controlled so that the air-fuel ratio of the exhaust gas downstream of the oxidation catalyst becomes equal to or higher than a predetermined air-fuel ratio.

For example, when the oxidizing ability of the oxidation catalyst is lowered and the air-fuel ratio of the exhaust gas downstream of the oxidation catalyst may become richer than a predetermined air-fuel ratio, at least the combustion chamber of the internal combustion engine or the exhaust passage. The air-fuel ratio of the exhaust gas is increased by controlling the addition of fuel to one side or by stopping the addition.

By such control, it is possible to prevent the air-fuel ratio of the exhaust gas from becoming excessively rich in a state where the exhaust gas purification capacity of the oxidation catalyst installed on the downstream side of the NOx catalyst is lowered, and therefore the unburned component Can be suppressed.

Further, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention may further comprise secondary air supply means in an exhaust passage downstream of the NOx catalyst and upstream of the oxidation catalyst.

According to the above construction, for example, when the fuel is added to the combustion chamber or the exhaust passage of the internal combustion engine in a slightly larger amount so that the NOx catalyst can be easily recovered from SOx poisoning,
Along with this, it is possible to supplement the shortage of oxygen (O ₂ ) required for purifying unburned components in the exhaust gas downstream of the NOx catalyst by the oxidation catalyst by supplying air by the secondary air supply means. I can.

That is, according to the above configuration, the air-fuel ratio around the NOx catalyst can be made richer, so that NO
Since the x catalyst can be recovered from SOx poisoning in a short time, and at the same time, the air-fuel ratio around the oxidation catalyst can be made leaner or closer to the theoretical air-fuel ratio than the theoretical air-fuel ratio.
It is possible to suppress the discharge of unburned components.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the NOx catalyst for recovering from SOx poisoning or the exhaust gas purification catalyst installed upstream thereof may be a catalyst having no oxygen retaining capacity.

The reason for this is that if oxygen is present in the NOx catalyst for recovering from SOx poisoning or the exhaust purification catalyst installed upstream thereof, it will hinder the lowering of the air-fuel ratio of the atmosphere around the NOx catalyst, and SOx poisoning To alienate the recovery of.

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, in order to prevent the emission of unburned components more effectively, the oxidation catalyst installed downstream of the NOx catalyst for recovering from SOx poisoning is It may be a catalyst having a high oxygen retention capacity.

Further, in the internal combustion engine that switches the first combustion, that is, the low temperature combustion and the second combustion, that is, the normal combustion, as described above, the low temperature combustion is performed when operating in the low load region. However, the normal combustion is performed when operating in the medium and high load range.

In such an exhaust gas purifying apparatus for an internal combustion engine, during low load operation, the air-fuel ratio can be set to the rich air-fuel ratio or the stoichiometric air-fuel ratio in low temperature combustion, so that the air-fuel ratio in the combustion chamber is set to the second value. The air-fuel ratio of the exhaust gas is controlled to a second predetermined air-fuel ratio by controlling the air-fuel ratio to a predetermined air-fuel ratio,
Alternatively, under low temperature combustion, the air-fuel ratio of the exhaust gas is controlled to a first predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, and then the fuel is added to at least one of the combustion chamber and the exhaust passage to form the exhaust gas. The NOx catalyst may be recovered from SOx poisoning by performing either control of controlling the air-fuel ratio of NOx to the second predetermined air-fuel ratio.
Further, during medium to high load operation, under normal combustion, the air-fuel ratio of the exhaust gas is controlled to the first predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, and then fuel is added to at least one of the combustion chamber and the exhaust passage. By doing so, the NOx catalyst may be recovered from SOx poisoning by intermittently controlling the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio.

According to the above exhaust gas purifying apparatus for an internal combustion engine, even an internal combustion engine, such as a diesel engine, which performs low temperature combustion during low load operation and performs normal combustion during medium and high load operation, is brought into an operating state. Regardless of NOx
The catalyst can be recovered from SOx poisoning.

Further, in the exhaust gas purification method for an internal combustion engine according to the present invention, when the NOx catalyst provided in the exhaust passage is recovered from SOx poisoning, first, the air-fuel ratio of the exhaust gas is brought to the first predetermined air-fuel ratio. The NOx catalyst is controlled at the same time as the second predetermined air-fuel ratio, which is intermittently richer than the first predetermined air-fuel ratio and enables recovery from SOx poisoning of the NOx catalyst. The temperature is controlled by the SOx of the NOx catalyst.
It is characterized in that the temperature is controlled within a predetermined temperature range in which recovery from x poisoning is possible and deterioration of the NOx catalyst is not promoted.

In the above structure, the first predetermined air-fuel ratio is the air-fuel ratio at which the amount of smoke discharged becomes the upper limit of the allowable amount, and the second predetermined air-fuel ratio is the rich air-fuel ratio or the stoichiometric air-fuel ratio.

According to the exhaust gas purification method for the internal combustion engine of the present invention, after the air-fuel ratio of the exhaust gas is set to the first predetermined air-fuel ratio,
By intermittently setting the second predetermined air-fuel ratio, the NOx catalyst can be recovered from SOx poisoning while suppressing the discharge of smoke regardless of the operating state of the internal combustion engine.

Further, by first setting the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio, it is possible to control the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio more accurately and more quickly. Becomes Therefore, it is possible to prevent excessive temperature rise of the NOx catalyst and discharge of unburned components due to the exhaust gas having an excessively rich air-fuel ratio, and to reduce the NOx catalyst to S
It is possible to recover more quickly from Ox poisoning.

Further, the air-fuel ratio of the exhaust gas is intermittently set to the rich air-fuel ratio or the stoichiometric air-fuel ratio to raise the temperature of the NOx catalyst and prevent excessive temperature rise. Therefore, the temperature of the NOx catalyst can be controlled to a temperature at which SOx poisoning can be recovered and deterioration is not promoted.

The fact that the air-fuel ratio of the exhaust gas is intermittently controlled to the rich air-fuel ratio or the stoichiometric air-fuel ratio means that the air-fuel ratio of the exhaust gas intermittently becomes the lean air-fuel ratio. Therefore, when the NOx catalyst is a catalyst that has an oxygen retaining capacity such as a particulate filter and that oxidizes and purifies fine particles (for example, soot) in the exhaust gas, the smoke in the exhaust can be more effectively purified. .

Further, the internal combustion engine is provided with a throttle valve for controlling the amount of intake air supplied to the combustion chamber and a recirculation exhaust gas control valve for controlling the amount of recirculation exhaust gas recirculated to the combustion chamber. When the air-fuel ratio of the exhaust gas is controlled to the first predetermined air-fuel ratio, for example, the air-fuel ratio in the combustion chamber is controlled by controlling the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve. May be controlled to the first air-fuel ratio, and thereby the air-fuel ratio of the exhaust gas may be controlled to the first air-fuel ratio.

Further, as a method for controlling the air-fuel ratio of the exhaust gas to the first air-fuel ratio and then intermittently controlling it to the second predetermined air-fuel ratio, the fuel is added to at least one of the combustion chamber and the exhaust passage. May be controlled, that is, fuel may be intermittently added to at least one of the combustion chamber and the exhaust passage.

Further, in the exhaust gas purification method for an internal combustion engine in which the NOx catalyst is provided in the exhaust passage and the low temperature combustion and the normal combustion are selectively switched, when recovering the NOx catalyst from the SOx poisoning during the normal combustion, By controlling the air-fuel ratio to make the air-fuel ratio of the exhaust gas the first predetermined air-fuel ratio, and then controlling the addition of fuel to at least one of the combustion chamber and the exhaust passage, that is, by intermittently adding fuel. The air-fuel ratio of the exhaust gas is intermittently controlled to a second predetermined air-fuel ratio which is richer than the first predetermined air-fuel ratio and enables recovery from SOx poisoning of the NOx catalyst, and at the same time NOx
The temperature of the catalyst is controlled within a predetermined temperature range in which the NOx catalyst can be recovered from SOx poisoning and the deterioration of the NOx catalyst is not promoted.
When recovering from Ox poisoning, the air-fuel ratio of the exhaust gas is controlled to the second predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, or the exhaust gas of the exhaust gas is controlled by controlling the air-fuel ratio in the combustion chamber. Whether the air-fuel ratio of the exhaust gas is controlled to the second predetermined air-fuel ratio by controlling the addition of fuel to at least one of the combustion chamber and the exhaust passage after the air-fuel ratio is set to the first predetermined air-fuel ratio At the same time that either control is performed, the temperature of the NOx catalyst may be controlled within the predetermined temperature range.

According to the above exhaust gas purification method for an internal combustion engine, for example, even in an internal combustion engine such as a diesel engine, which performs low temperature combustion during idling or low load operation and performs normal combustion during medium and high load operation, It is possible to recover the NOx catalyst from SOx poisoning regardless of the operating state.

In the exhaust gas purification method for an internal combustion engine according to the present invention, in order for the internal combustion engine to purify unburned components contained in the exhaust gas downstream of the NOx catalyst, an exhaust passage downstream of the NOx catalyst is provided. When equipped with an oxidation catalyst,
By controlling the addition of the fuel to at least one of the combustion chamber and the exhaust passage, the temperature of the oxidation catalyst is raised to the activation temperature, and then the air-fuel ratio of the exhaust gas is intermittently controlled to the second air-fuel ratio to reduce the NOx catalyst. You may make it recover from SOx poisoning.

According to such control, the SOx poisoning recovery from the NOx catalyst is performed after the exhaust gas purification capability of the oxidation catalyst installed on the downstream side of the NOx catalyst is increased. Emissions can be reduced.

In the exhaust gas purification method for an internal combustion engine according to the present invention, in order for the internal combustion engine to purify unburned components contained in the exhaust gas downstream of the NOx catalyst, an exhaust passage downstream of the NOx catalyst is provided. When equipped with an oxidation catalyst,
The air-fuel ratio of the exhaust gas may be controlled so that the air-fuel ratio of the exhaust gas downstream of the oxidation catalyst becomes equal to or higher than a predetermined air-fuel ratio.

For example, when the oxidizing ability of the oxidation catalyst is lowered and the air-fuel ratio of the exhaust gas on the downstream side of the oxidation catalyst may become richer than a predetermined air-fuel ratio, at least the combustion chamber of the internal combustion engine or the exhaust passage. The air-fuel ratio of the exhaust gas is increased by controlling the addition of fuel to one side or by stopping the addition.

By such control, it is possible to prevent the air-fuel ratio of the exhaust gas from becoming excessively rich in a state where the exhaust gas purification capability of the oxidation catalyst installed downstream of the NOx catalyst is lowered. The emission of unburned components can be reduced.

[0071]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of an exhaust gas purification apparatus and an exhaust gas purification method for an internal combustion engine according to the present invention will be described.

(First Embodiment) FIG. 1 shows a case where an exhaust purification system for an internal combustion engine according to the present embodiment is applied to an exhaust purification system for a vehicle diesel engine which is a kind of a lean burn internal combustion engine. Shows. The internal combustion engine 1 according to this embodiment includes four cylinders 2 (combustion chambers), a fuel supply system, an intake system, an exhaust system, a control system, and the like.

The fuel supply system includes a fuel injection valve 3, a common rail (accumulation chamber) 4, a fuel supply pipe 5, a fuel pump 6, and the like, and supplies fuel to each cylinder 2. The fuel injection valve 3 is an electromagnetically driven on-off valve provided for each cylinder 2, and each fuel injection valve 3 is connected to a common rail 4 that serves as a fuel distribution pipe. Further, the common rail 4 is connected to the fuel pump 6 via the fuel supply pipe 5. The pulley 6 a of the fuel pump 6 is connected via a belt 7 to the crankshaft 1 a that is the output shaft of the internal combustion engine 1. The fuel pump 6 is rotationally driven using the rotation of the crankshaft 1a as a drive source.

In the fuel supply system thus constructed, first, the fuel in the fuel tank (not shown) is pumped up by the fuel pump 6. The pumped fuel is supplied to the common rail 4 via the fuel supply pipe 5. The fuel supplied to the common rail 4 is increased to a predetermined fuel pressure in the common rail 4 and distributed to each fuel injection valve 3. When a drive voltage is applied to the fuel injection valve 3 and the fuel injection valve 3 opens, the fuel is injected into the combustion chamber of each cylinder 2 via the fuel injection valve 3.

On the other hand, the intake system includes an intake pipe 9, a throttle valve 13, an intake branch pipe 8, an air cleaner box 10, an intercooler 16 and the like, and forms an intake passage for supplying air (intake air) to each cylinder 2. is doing.

The intake pipe 9 forms a passage for guiding the intake air taken in through the air cleaner box 10 to the intake branch pipe 8. The intake branch pipe 8 forms a passage for distributing intake air that flows in through the intake pipe 9 to each cylinder 2. Further, in the vicinity of the connecting portion between the intake pipe 9 and the air cleaner box 10,
An intake air temperature sensor 44a for measuring the temperature of intake air flowing into the intake pipe 9 is provided.

Further, the intake pipe 9 extending from the air cleaner box 10 to the throttle valve 13 has a turbocharger 15 (compressor housing 1) for compressing the intake air taken in.
5a) and an intercooler 16 that cools the intake air compressed by the turbocharger 15, and an airflow meter 45 that measures the flow rate of the intake air flowing into the combustion chamber 2 through the intake pipe 9 is provided upstream of the turbocharger 15. I have it.

Immediately upstream of the intake branch pipe 8, the intake pipe 9
A throttle valve 13 for adjusting the amount of intake air flowing into each cylinder 2 through is provided, and the opening degree of the throttle valve 13 is controlled by an actuator 14 composed of a stepper motor or the like. An intake air temperature sensor 44 for measuring the temperature in the intake branch pipe 8 is provided immediately downstream of the throttle valve 13.
b, and an intake pressure sensor 46 for measuring the pipe internal pressure in the intake branch pipe 8.

In the intake system thus constructed, first,
Intake air to be supplied to each cylinder 2 flows into the air cleaner box 10 due to generation of negative pressure due to engine operation. The intake air that has flowed into the air cleaner box 10 is cleaned of dust and dirt inside the air cleaner box 10, and then the intake pipe 9
After that, it flows into the turbocharger 15. The intake air flowing into the turbocharger 15 is compressed by the compressor wheel 15
After being compressed at a, it is cooled by the intercooler 16. Then, after the flow rate is adjusted by the throttle valve 13 as necessary, it flows into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to each cylinder 2 through each branch pipe, and is burned together with the fuel injected and supplied from the fuel injection valve 3. Outputs of various sensors are input to an electronic control unit 30 described later, and are fed back to, for example, basic fuel injection control of the internal combustion engine.

The exhaust system is provided with an exhaust branch pipe 18 and an exhaust pipe 19, and forms an exhaust passage for discharging the exhaust gas discharged from each cylinder 2 to the outside of the engine body. In addition, the EGR device 2
0, a catalytic converter 50, a reducing agent addition device 60, etc., and has a function as an exhaust gas purification device for purifying nitrogen oxides (NOx), soot (smoke), etc. contained in the exhaust gas.

First, the exhaust branch pipe 18 is connected to an exhaust port 18a provided for each cylinder 2, and collects exhaust gas discharged from the exhaust port 18a to guide it to the turbine housing 15b of the turbocharger 15. Is formed. Further, the exhaust pipe 19 forms a passage from the turbine housing 15b to a silencer (not shown).

The EGR device 20 includes an EGR passage 25, an EG
An R valve 26, an oxidation catalyst 28 for the EGR device 20, an EGR cooler 27, etc. are provided.

The EGR passage 25 is a passage that connects the exhaust branch pipe 18 and the intake branch pipe 8. Further, the EGR valve 26 is
It is an electric on-off valve provided in a connection portion between the EGR passage 25 and the intake branch pipe 8 and adjusts the amount of exhaust gas flowing in the EGR passage 25. The oxidation catalyst 28 for the EGR device 20 is arranged in the EGR passage 25 that connects the exhaust branch pipe 18 and the EGR cooler 27, and purifies unburned components in the exhaust gas flowing from the exhaust branch pipe 18. EGR cooler 2
Reference numeral 7 cools the exhaust gas flowing in the EGR passage 25 by using the engine cooling water as a heat medium. In the following description, the exhaust gas flowing into the intake branch pipe 8 through the EGR passage 25 will be simply referred to as EGR gas.

According to the EGR device 20 configured as described above, a part of the exhaust gas flowing through the exhaust branch pipe 18 is EGR.
It flows into the passage 25. Further, the EGR gas (exhaust gas) flowing into the EGR passage 25 flows into the EGR cooler 27 via the oxidation catalyst 28 for the EGR device 20. EGR
The EGR gas flowing into the cooler 27 is
Is cooled when passing through the intake manifold 8 and flows into the intake branch pipe 8 at a flow rate corresponding to the opening amount of the EGR valve 26. The EGR gas flowing into the intake branch pipe 8 mixes with the intake air flowing from the upstream side of the intake branch pipe 8 to form an air-fuel mixture, and is used for combustion together with the fuel injected from the fuel injection valve 3.

In the exhaust gas which becomes EGR gas,
It contains an inert gas such as water vapor (H ₂ O) and carbon dioxide (CO ₂ ). Therefore, when the exhaust gas, which is an inert gas, flows into the combustion chamber 2, the combustion temperature is lowered due to the mixing of the exhaust gas, and the generation of NOx is suppressed. In addition, since the amount of oxygen in the combustion chamber 2 decreases as the EGR gas is introduced, the connection between nitrogen (N ₂ ) and oxygen (O ₂ ) is suppressed in this respect as well, and the emission of nitrogen oxides (NOx) is suppressed. Is suppressed.

Next, the catalytic converter 50 will be described. The catalytic converter 50 includes a casing 51 and a NOx catalyst in the casing 51, and has an exhaust gas purification action of purifying harmful substances in the exhaust gas discharged from the engine body 1.

More specifically, the turbine housing 15b
The casing 51 is arranged near the outlet of the casing 5 and
1 contains fine particles (for example, soot) and NOx in the exhaust gas.
A particulate filter (hereinafter, simply referred to as a filter) 50b for purifying the like is incorporated.

The filter 50b has an exhaust gas purifying action of oxidizing and burning fine particles (eg, soot) contained in the exhaust gas. More specifically, it has a filter 58 carrying an activated oxygen releasing agent, and has an exhaust gas purifying action of removing (purifying) the fine particles collected on the filter 58 by oxidizing them with activated oxygen.

As shown in FIG. 2, the filter 50b alone has a honeycomb shape formed of a porous material such as cordierite, and has a plurality of flow channels 55 and 56 extending in parallel with each other. There is. More specifically, the exhaust gas inflow passage 55 whose downstream end is closed by the plug 55a.
And an exhaust gas outflow passage 56 whose upstream end is closed by a plug 56a. Each exhaust gas inflow passage 55 and exhaust gas outflow passage 56 are provided with a thin partition wall 57 through which the filter 5
8 are arranged side by side in the vertical and horizontal directions.

Further, a layer of a carrier formed of alumina (Al ₂ O ₃ ) or the like is provided on the surface and inside pores of the partition wall 57, and a noble metal catalyst such as platinum (Pt) is formed on the carrier. In addition, an active oxygen-releasing agent that occludes the excess oxygen when it exists in the surroundings and conversely releases the occluded oxygen in the form of active oxygen when the oxygen concentration decreases is carried.

As the active oxygen release agent, alkali metals such as potassium (K), sodium (Na), lithium (Li), cesium (Cs) and rubidium (Rb), barium (Ba), calcium (Ca). ), At least one selected from alkaline earth metals such as strontium (Sr), rare earths such as lanthanum (La) and yttrium (Y), and transition metals such as cerium (Ce) and tin (Sn). Should be used.

Further, preferably, an alkali metal or alkaline earth metal having a higher ionization tendency than calcium (Ca), that is, potassium (K), lithium (Li), cesium (Cs), rubidium (Rb), barium (Ba). ),
It is preferable to use strontium (Sr) or the like.

In the filter 50b thus constructed, first, the exhaust gas flows in the order of the exhaust gas inflow passage 55, the partition wall 57, and the exhaust gas outflow passage 56 (arrow a in FIG. 2), and the fine particles contained in the exhaust gas are In the process of passing through the partition wall 57, it is collected on the surface and inside of the partition wall 57. The fine particles collected in the partition wall 57 are oxidized by activated oxygen by changing the oxygen concentration of the exhaust gas flowing into the partition wall 57 (filter) over a plurality of times,
Finally, it burns out without emitting a bright flame, and the filter 58
Removed from above.

Further, the filter 50b controls the NO in the exhaust gas.
It also has an exhaust gas purification effect that purifies x. More specifically, when the oxygen concentration of the exhaust gas flowing into the filter 50b is high, NOx in the exhaust gas is stored, and when the oxygen concentration in the exhaust gas is low, that is, when the air-fuel ratio of the exhaust gas flowing into the filter 50b is low. The NOx stored in the exhaust gas is reduced and released into the exhaust gas in the form of nitrogen dioxide (NO ₂ ) or nitric oxide (NO), and further NO ₂ and NO are contained in the exhaust gas. It has the ability to purify exhaust gas to purify it into nitrogen (N ₂ ) by oxidizing it with (CO, HC).

However, in a diesel engine such as the internal combustion engine 1 shown in the present embodiment, combustion is usually performed in an oxygen excess atmosphere. Therefore, the oxygen concentration of the exhaust gas discharged along with the combustion hardly decreases until the reduction / release action is promoted, and the amount of unburned components (CO, HC) contained in the exhaust gas. Is also very small.

Therefore, by adding fuel as a reducing agent to the exhaust passage on the upstream side of the catalytic converter 50, the oxygen concentration in the exhaust gas is reduced and the unburned hydrocarbons (HC) and the like are supplemented. It promotes the reduction and release of NOx stored in 50b. The addition of fuel to the exhaust passage is performed by a reducing agent addition device 60 described later.

Next, the reducing agent adding device 60 will be described. The reducing agent addition device 60 includes a reducing agent addition valve 61, a reducing agent supply passage 62, a fuel pressure control valve 64, a fuel pressure sensor 63,
An emergency shutoff valve 66 and the like are provided, and an appropriate amount of fuel as a reducing agent is added to the exhaust passage upstream of the catalytic converter 50 as needed. That is, fuel as a reducing agent is added to the exhaust gas so that the air-fuel ratio of the exhaust gas flowing into the catalytic converter 50 becomes the target air-fuel ratio.

The reducing agent addition valve 61 is an electric on-off valve which is provided in the gathering portion of the exhaust branch pipes 18 and opens when a predetermined voltage is applied. The reducing agent supply passage 62 forms a passage for guiding a part of the fuel pumped up by the fuel pump 6 to the reducing agent addition valve 61. Fuel pressure control valve 6
4 is disposed in the middle of the reducing agent supply passage 62, and maintains the fuel pressure in the reducing agent supply passage 62 at a predetermined fuel pressure. The fuel pressure sensor 63 detects the fuel pressure in the reducing agent supply passage 62. The emergency cutoff valve 66 stops the addition of fuel to the reducing agent supply passage 62 when the pressure in the reducing agent supply passage 62 becomes abnormal.

In the reducing agent adding device 60 thus configured, the fuel discharged from the fuel pump 6 is supplied to the fuel pressure control valve 6
The fuel pressure is maintained at a predetermined fuel pressure at 4, and is supplied to the reducing agent addition valve 61 through the reducing agent supply passage 62. Then, the reducing agent addition valve 61
When a predetermined voltage is applied to the reducing agent addition valve 61, the reducing agent addition valve 61 is opened, and the fuel in the reducing agent supply passage 62 is added to the exhaust branch pipe 18 through the reducing agent addition valve 61. The fuel (reducing agent) added to the exhaust branch pipe 18 is the turbine housing 15b.
After being stirred inside, it flows into the catalytic converter 50 through the exhaust pipe 19. Therefore, in the catalytic converter 50, the oxygen concentration is low and hydrocarbons (H
The exhaust gas containing C) will flow in, and the reduction / release of NOx stored in the filter 50b will be promoted.

Next, the control system will be described. The control system is a ROM connected to each other by a bidirectional bus 31.
This is a so-called electronic control unit 30 (ECU) including a (read only memory) 32, a RAM (random access memory) 33, a CPU (central control unit) 34, an input port 35, and an output port 36.

At the input port 35, in addition to the output signals of the various sensors described above, a load sensor 41 for detecting the depression amount of the accelerator pedal 40, a crank angle sensor 42 for detecting the rotational speed of the crankshaft 1a, and a vehicle speed are measured. The vehicle speed sensor 43 or the like is directly input via the corresponding A / D converter 37. On the other hand, at the output port 36, the fuel injection valve 3, the reducing agent addition valve 61, the throttle valve driving actuator 14, and the EG via the corresponding drive circuit 38.
The R valve 26, etc. are connected.

In the ROM 32, control programs for various devices, control maps referred to when the programs are processed, and the like are recorded in association with each device. Also,
In the RAM 33, output signals of various sensors input to the input port 35, control signals output to the output port 36, and the like are recorded as an operation history of the internal combustion engine. CPU
Reference numeral 34 compares output signals of various sensors recorded on the RAM 33 with control maps developed on the ROM 32 on a desired program, and various control signals output during the processing are compared with the output port 36. The data is output to the corresponding device via, and various devices are centrally managed.

For example, the CPU 34 controls the air-fuel ratio sensor (A / F sensor) 4 provided downstream of the catalytic converter 50.
7, the air-fuel ratio of the exhaust gas flowing into the filter 50b is calculated, and the temperature of the filter 50b is calculated from the output signals of the exhaust gas temperature sensors 48a and 48b provided upstream and downstream of the filter 50b. Also, CP
U34 controls the air-fuel ratio of the exhaust gas flowing into the filter 50b by controlling the opening / closing timing or opening degree of the fuel injection valve 3, the reducing agent addition valve 61, the throttle valve 13, the EGR valve 26, and the like.

By the way, in the above filter 50b,
As described in the prior art, the sulfur oxide (SOx) contained in the exhaust gas is also stored in the same manner as NOx. The storage mechanism is considered to be the following mechanism.

First, when the air-fuel ratio of the exhaust gas flowing into the filter 50b is high, oxygen O ₂ in the exhaust gas adheres to the platinum (Pt) supported on the carrier in the form of O ₂ ⁻ or O ^{2 −.} is doing. Therefore, the sulfur oxide (S
Ox) is platinum (P) in the same manner as nitrogen oxide (NOx).
t) Oxidized to SO ₃ ⁻ or SO ₄ ⁻ .

Then, the generated SO₃ ^-And SO
_Four ^-Is further oxidized on platinum (Pt) and sulfate ion (S
O_Four ^2-), And does not bond with barium oxide (BaO)
Are stored in the filter 50b. Also, the stored sulfuric acid
Ion (SO_Four ^2-) Is barium ion over time
(Ba²⁺) And chemically stable sulfate (BaS
O _Four).

Thus, SOx is considered to be occluded. By the way, the sulfate salt (BaSO ₄ ) generated by the absorption of SOx is a substance which is likely to have coarse crystals and is chemically stable and difficult to decompose. Therefore, NOx
Even if the air-fuel ratio of the inflowing exhaust gas is reduced in the same manner as the reduction / release of SOx, SOx that has been once occluded is not easily released, but is accumulated as sulfate (BaSO ₄ ).

If the accumulated amount of sulfate (BaSO ₄ ) becomes excessive, barium oxide (B
The amount of aO) naturally decreases, and therefore, the amount of active oxygen released in the filter 50b decreases, and the filter area that can contribute to the oxidative combustion of fine particles also decreases. In addition, nitrogen oxides (NO
The storage capacity of x) will also decrease. That is, the exhaust purification rate of the exhaust purification catalyst that stores and reduces NOx is reduced.
Causes so-called "SOx poisoning".

Next, the conditions for SOx poisoning recovery of the filter 50b will be described. S stored in the filter 50b
In order to release Ox, the temperature of the filter 50b is set to NOx.
The temperature is raised to a higher temperature (for example, 600 to 700 ° C.) than during reduction, and the accumulated barium sulfate (BaSO ₄ ) is reduced to SO ₃
^- and SO ₄ ^- thermally decomposed to. At the same time, the air-fuel ratio of the exhaust gas flowing into the filter 50b is set to an air-fuel ratio richer than the stoichiometric air-fuel ratio or near the stoichiometric air-fuel ratio, and barium sulfate (Ba
SO ₄₎ pyrolysis SO ₃ produced by the ^- or SO ₄ ^- a,
Hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas
Is reacted with gaseous SO ₂ ^- it is reduced to the filter 50b
The gaseous SO ₂ ⁻ is released together with the exhaust gas flowing into the.

However, as described above, in the internal combustion engine 1 according to the present embodiment, since combustion is normally performed in an oxygen excess atmosphere, the air-fuel ratio of the exhaust gas is also very large ( For example, A / F = 25-4
0).

Therefore, when the SOx poisoning recovery of the filter 50b is performed, first, the throttle valve 13 and / or E
The air-fuel ratio in the combustion chamber is controlled by controlling the opening degree of the GR valve 26, and the air-fuel ratio of the exhaust gas flowing into the filter 50b is adjusted to a first predetermined air-fuel ratio in which the amount of smoke discharged is the upper limit of the allowable amount. (For example, A / F = 20 to 25). Then, after the air-fuel ratio of the exhaust gas is set to the first predetermined air-fuel ratio, the reducing agent addition device 60 intermittently adds the fuel to the exhaust passage upstream of the catalytic converter 50, as shown in FIG. , Filter 50b
The S / F stored in the exhaust gas intermittently changes the air-fuel ratio of the exhaust gas flowing into the
The air-fuel ratio at which Ox is reduced / released, that is, the stoichiometric air-fuel ratio or the second predetermined air-fuel ratio that is the rich air-fuel ratio is controlled to be the same, and the temperature of the filter 50b is set to the stored SOx.
Is reduced and released, and is controlled to a predetermined temperature (for example, 600 ° C. to 700 ° C.) at which deterioration of the filter 50b is not promoted.

According to the exhaust gas purifying apparatus for an internal combustion engine of the present embodiment, even when combustion is performed in an oxygen excess atmosphere, the air-fuel ratio of the exhaust gas is intermittently changed to the second predetermined air-fuel ratio. Thus, as shown in FIG. 3, the SOx stored in the filter 50b is reduced / released in the exhaust gas, so that the filter 50b is suppressed while suppressing the discharge of smoke.
Can be recovered from SOx poisoning.

Further, when the air-fuel ratio of the ambient atmosphere becomes small, the temperature of the filter 50b rises.
If the air-fuel ratio of the exhaust gas flowing into the engine is continuously set to the stoichiometric air-fuel ratio or the rich air-fuel ratio, the temperature of the filter 50b may excessively rise, which may accelerate the deterioration of the filter 50b. According to the exhaust purification system of the engine, the temperature of the filter 50b can be recovered from SOx poisoning by intermittently setting the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio, and the filter 50b can be recovered. The temperature is controlled within the temperature range that does not accelerate the deterioration. Therefore, the deterioration of the filter 50b can be suppressed.

Further, by first controlling the air-fuel ratio of the combustion chamber to bring the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio, the air-fuel ratio of the exhaust gas is in a normal state (for example,
It is possible to control the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio more accurately and faster than the case where fuel is added to the exhaust gas when A / F = 25-40). It will be possible. Therefore, it is possible to prevent excessive temperature rise of the NOx catalyst and discharge of unburned components due to the air-fuel ratio of the exhaust gas becoming excessively rich, and the filter 50
b can be recovered more quickly from SOx poisoning.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the fuel addition to the exhaust passage for intermittently controlling the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio is as follows:
When the temperature of the filter 50b is intermittently lower than the temperature at which recovery from SOx poisoning is possible (for example, 600 ° C.), fuel is added to accelerate the deterioration of the filter 50b (for example, When there is a possibility that the temperature becomes 700 ° C. or higher, the fuel addition may be stopped (for example, the addition for 9 seconds and the pause for 13 seconds are repeated).

When the fuel addition is stopped, the air-fuel ratio of the exhaust gas becomes large and the temperature of the filter 50b rapidly drops, so that the deterioration of the filter 50b can be suppressed and the next fuel addition can be performed. . Therefore, the filter 50b can be recovered from SOx poisoning and the deterioration of the filter 50b can be suppressed by repeating the addition of fuel and the suspension of addition as described above.

Further, as shown in FIG. 5, the filter 50b
Since the temperature increase rate of the filter 50b due to the fuel addition increases as the amount of exhaust gas flowing into the engine increases, the time interval of fuel addition or the amount of fuel added may be adjusted according to the operating state of the internal combustion engine 1. .

Further, according to the exhaust purification system of the internal combustion engine of the present embodiment, the fuel addition to the exhaust passage by the reducing agent addition device 60 is performed intermittently. Therefore, as shown in FIG. 3, the filter 50b is used. The air-fuel ratio of the exhaust gas flowing into the exhaust gas becomes a lean air-fuel ratio intermittently. That is, since the exhaust gas of the stoichiometric air-fuel ratio or the rich air-fuel ratio and the exhaust gas of the lean air-fuel ratio alternately flow into the filter 50b, the fine particles trapped in the filter 50b are oxidized as shown in FIG. It will be. Therefore, smoke emission can be suppressed more effectively.

In the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the auxiliary injection other than the main injection that is injected to obtain the engine output is intermittently performed from the fuel injection valve 3 in the combustion chamber. Thus, the air-fuel ratio of the exhaust gas may be intermittently controlled to the second predetermined air-fuel ratio. Further, in this case, the sub-injection other than the main injection is performed by post-injection in which fuel is further injected into the combustion chamber when the fuel for obtaining the engine output is combusted in each cylinder 2 and the piston is in the expansion stroke or the exhaust stroke. Also good.

In the exhaust gas purification apparatus for an internal combustion engine according to this embodiment, NOx installed in the catalytic converter 50.
The catalyst was a particulate filter equipped with an oxygen retaining capacity (active oxygen releasing agent), but NO with no oxygen retaining capacity was used.
It may be an x catalyst.

In this case, it becomes easy to reduce the air-fuel ratio of the atmosphere around the NOx catalyst, that is, it becomes easy to control the air-fuel ratio to the second predetermined air-fuel ratio. It becomes possible to perform recovery more efficiently.

(Second Embodiment) Next, a second embodiment of an exhaust gas purification apparatus and an exhaust gas purification method for an internal combustion engine according to the present invention will be described.

FIG. 6 shows an internal combustion engine and an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. In the internal combustion engine 1 according to the present embodiment, the exhaust purification catalyst 50a is provided upstream of the filter 50b in the catalytic converter 50 of the exhaust system.
Is equipped with. Other configurations are similar to those of the above-described first embodiment.

According to the present embodiment, the catalytic converter 5
NOx or unburned components (C
O, HC) is oxidized or reduced by the exhaust purification catalyst 50a, and the reaction heat at that time causes the filter 5 to
The temperature distribution of 0b is more uniform than that when the filter 50b is arranged alone. Therefore, the filter 50b
It becomes possible to easily control the temperature.

The temperature distribution of the filter 50b when the filter 50b is arranged alone in the catalytic converter 50 is shown in FIG. 7, and the temperature of the filter 50b when the exhaust purification catalyst 50a is arranged in series upstream of the filter 50b. The distribution is shown in FIG.

Further, the exhaust purification catalyst 5 according to the present embodiment
0a may be a catalyst having no oxygen retaining ability.

In this case, it becomes easy to reduce the air-fuel ratio of the atmosphere around the filter 50b, that is, it becomes easy to control the air-fuel ratio to the second predetermined air-fuel ratio.
It is possible to more efficiently recover from SOx poisoning of 0b.

As the exhaust gas purification catalyst 50a installed on the upstream side of the filter 50b, there are used an oxidation catalyst and a storage reduction type NOx.
A catalyst can be illustrated.

(Third Embodiment) Next, the third embodiment of the exhaust gas purification apparatus and the exhaust gas purification method for an internal combustion engine according to the present invention will be described.

FIG. 9 shows an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to this embodiment. In the internal combustion engine 1 according to the present embodiment, the oxidation catalytic converter 59 is provided in the exhaust pipe 19 downstream of the catalytic converter 50 in the exhaust system.
An oxidation catalyst 59a is installed inside the oxidation catalyst converter 59. Further, an exhaust gas temperature sensor 67 and an air-fuel ratio sensor 68 are installed in the exhaust pipe 19 downstream of the oxidation catalytic converter 59. Other configurations are similar to those of the second embodiment described above.

The output signals of the exhaust gas temperature sensor 67 and the air-fuel ratio sensor 68 are also sent to the ECU 3 via the input port 35 in the same manner as the output signals of the various sensors in the first embodiment.
Read to zero. Further, the CPU 34 uses the output signals of the exhaust gas temperature sensors 48b and 67 to cause the oxidation catalyst 5
The temperature of 9a is calculated. In addition, the oxidation catalytic converter 5
The air-fuel ratio of the exhaust gas downstream of 9 is detected by the air-fuel ratio sensor 68.

In the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, since the oxidation catalytic converter 59 is installed on the downstream side of the catalytic converter 50, it is built in the oxidation catalytic converter 59 during operation of the internal combustion engine 1. The temperature of the oxidation catalyst 59a is lower than the temperature of the filter 50b (for example, the temperature of the filter 50b is about 300 ° C.).
At that time, the temperature of the oxidation catalyst 59b is about 250 ° C.).

Therefore, when recovering the SOx poisoning of the filter 50b, intermittent fuel addition to the exhaust passage is gradually carried out so that the temperature of the oxidation catalyst 59 becomes the activation temperature, and the temperature of the oxidation catalyst 59 becomes the activation temperature. After that, the fuel addition by the reducing agent addition device 60 is controlled so that the air-fuel ratio of the exhaust gas becomes intermittently the second air-fuel ratio.

According to the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, SOx poisoning recovery of the filter 50b is performed after the exhaust gas purification capacity of the oxidation catalyst 59a is increased. Since the unburned components that are generated are purified by the oxidation catalyst 59a, the emission of unburned components can be reduced.

Further, when the fuel is added to raise the temperature of the oxidation catalyst 59a to the activation temperature, the lower the temperature of the oxidation catalyst 59a is, the larger the amount of the fuel to be added and the time when the fuel is added are increased. The interval may be lengthened.

By such control, the temperature of the oxidation catalyst 59a can be quickly raised to the activation temperature.

Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the air-fuel ratio of the exhaust gas downstream of the oxidation catalytic converter 59 becomes richer than the predetermined air-fuel ratio due to the deterioration of the oxidizing ability of the oxidation catalyst 59a. When there is a possibility of this, the amount of fuel added to the exhaust passage may be reduced, or the fuel addition may be stopped.

By such control, it is possible to prevent the air-fuel ratio of the exhaust gas from becoming excessively rich in a state where the exhaust gas purification capability of the oxidation catalyst built in the oxidation catalytic converter 59 is lowered, and therefore the unburned component Can be suppressed.

Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, by using the oxidation catalyst 59a as a catalyst having a high oxygen retention capacity, that is, a high oxidation capacity, the unburned components are more effectively discharged. It becomes possible to suppress.

In addition, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the fuel addition for raising the temperature of the oxidation catalyst 59a is performed in the combustion chamber by a sub injection other than the main injection that is injected to obtain the engine output. Alternatively, the fuel may be injected intermittently from the fuel injection valve 3.

(Fourth Embodiment) Next, a fourth embodiment of the exhaust gas purification apparatus and the exhaust gas purification method for an internal combustion engine according to the present invention will be described.

FIG. 10 shows an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to this embodiment. The internal combustion engine 1 according to the present embodiment is provided with a secondary air supply device 69 in the exhaust pipe 19 on the downstream side of the catalytic converter 50 and on the upstream side of the oxidation catalytic converter 59 in the exhaust system. Other configurations are the same as those in the third embodiment described above.

The secondary air supply device 69 has a secondary air pump 70 and a secondary air flow rate control valve 71, and the exhaust pipe 1
Air is supplied to the oxidation catalytic converter 59 via 9.
Further, the air supply by the secondary air supply device 69 is performed by the CPU 3
Controlled by 4.

According to the exhaust gas purification apparatus for an internal combustion engine in accordance with the present embodiment, for example, engine fuel is added to the exhaust passage by the reducing agent addition device 60 in a large amount in order to accelerate SOx poisoning recovery of the filter 50b. If the catalytic converter 5
Oxygen (O ₂ ) required for purifying unburned components in the exhaust gas downstream of 0 on the oxidation catalyst contained in the oxidation catalytic converter 59 is insufficient, but the shortage of O ₂ is It can be supplemented by supplying air by the air supply device 69.

That is, since the air-fuel ratio of the exhaust gas flowing into the filter 50b can be made richer,
The filter 50b can be efficiently recovered from SOx poisoning, and the air supply device 69 supplies air to adjust the air-fuel ratio of the exhaust gas flowing into the oxidation catalyst 59a to the lean air-fuel ratio or near the stoichiometric air-fuel ratio. Therefore, it is possible to suppress the emission of unburned components.

(Fifth Embodiment) Next, a fifth embodiment of the exhaust gas purification apparatus and the exhaust gas purification method for an internal combustion engine according to the present invention will be described.

In this embodiment, the internal combustion engine 1 is
When the amount of EGR gas supplied to the combustion chamber is increased with the fuel injection timing fixed, the amount of soot generated gradually increases and reaches a peak, further increasing the amount of EGR gas supplied to the combustion chamber. When this is done, the temperature of the fuel and the gas around it during combustion in the combustion chamber becomes lower than the soot generation temperature, and the first combustion in which the soot generation amount is suppressed and the soot generation amount peaks The internal combustion engine selectively switches between the second combustion in which the EGR gas amount supplied to the combustion chamber is smaller than the gas amount, that is, the low temperature combustion and the normal combustion are selectively switched. Other configurations of the internal combustion engine 1 according to the present embodiment are the same as those of the internal combustion engine 1 according to the first embodiment described above.

FIG. 11 is a graph obtained in accordance with actual experimental results, showing the correlation between the EGR rate of the air-fuel mixture in the combustion chamber and the amount of smoke produced by the combustion of the air-fuel mixture. ing.

As can be seen from FIG. 11, the amount of smoke generated reaches a peak between the EGR rate of about 40% and 50%, and almost no smoke is generated in the region where the EGR rate is 55% or more. . Therefore, the EGR rate 55
%, Preferably, the EGR rate is 65% or more, the engine operation can be performed in a state where the smoke emission amount is substantially zero. The EGR rate at which the amount of smoke generated is substantially zero can be reduced by cooling the EGR gas with the EGR cooler 27 or the like.

However, in the operation at the EGR rate of 65% or more, there occurs a problem that the engine output cannot be sufficiently obtained due to the shortage of the air amount and the decrease of the combustion pressure. On the other hand, in the region where the EGR rate is less than 40% where sufficient engine output is obtained,
Although a slight amount of smoke is observed, the amount of smoke is sufficiently smaller than that in an operating region where the EGR rate is 40% to 50%.

Therefore, in the internal combustion engine 1 according to the present embodiment, the engine operation is performed while maintaining the EGR rate at 65% or more during the low load operation that does not require the engine output so much.
During high load operation, which requires a sufficient engine output,
By operating the engine while suppressing the EGR rate to less than 40%, a comfortable operating condition is secured while suppressing the generation of smoke.

That is, the internal combustion engine 1 according to the present embodiment
Then, the EGR rate at which the amount of smoke generated peaks is 40
By switching the combustion state in steps so as to avoid the operation at 50% to 50%, both soot emission suppression and operability are ensured.

In the present embodiment, the first combustion,
That is, the low temperature combustion is a combustion state realized with the above-mentioned high EGR rate, while the second combustion, that is, the normal combustion, is low E
It is a combustion state realized with a GR rate.

Further, the numerical values exemplified above, that is, EGR
The specific numerical value of the rate is merely an example, and the numerical value slightly changes depending on the combustion characteristics specific to the applied internal combustion engine and the cooling temperature of the EGR gas. However, the smoke emission characteristic, that is, the presence of a peak is common to all internal combustion engines.

Next, the control for recovering the filter 50b from SOx poisoning in the internal combustion engine exhaust gas purification apparatus according to the present embodiment will be described.

Since the combustion temperature is low in the low temperature combustion as described above, the air-fuel ratio of the combustion chamber can be made the rich air-fuel ratio or the stoichiometric air-fuel ratio without generating smoke.

Therefore, when the internal combustion engine 1 is under low load operation, that is, during low temperature combustion, the opening degree of the throttle valve 13 or / and the EGR valve 26 is controlled to increase the air-fuel ratio in the combustion chamber. The air-fuel ratio of the exhaust gas which is controlled and flows into the filter 50b is controlled by the stored SO
x is an air-fuel ratio at which it is reduced / released, that is, a second air-fuel ratio that is a stoichiometric air-fuel ratio or a rich air-fuel ratio, and the temperature of the filter 50b is reduced and released by the stored SOx, and the filter 50b. It is also possible to recover the filter 50b from SOx poisoning by setting it to a predetermined temperature at which the deterioration of No. 2 is not promoted.

When the internal combustion engine 1 is operating at low load, that is, when performing low temperature combustion, first,
The air-fuel ratio in the combustion chamber is controlled by controlling the opening of the throttle valve 13 or / and the EGR valve 26, and the amount of smoke discharged from the air-fuel ratio of the exhaust gas flowing into the filter 50b becomes the upper limit of the allowable amount. The air-fuel ratio is 1.
Then, after the air-fuel ratio of the exhaust gas is set to the first predetermined air-fuel ratio, the reducing agent addition device 60 adds fuel to the exhaust passage on the upstream side of the catalytic converter 50 so that the air-fuel ratio of the exhaust gas flowing into the filter 50b. Is controlled to a second predetermined air-fuel ratio, and the temperature of the filter 50b is controlled to a predetermined temperature, whereby the filter 50b is adjusted to S
It may be possible to recover from Ox poisoning.

When the internal combustion engine 1 is operating under high load, that is, when it is performing normal combustion, first of all, as in the above-described first embodiment, the throttle valve 13
Alternatively, the air-fuel ratio in the combustion chamber is controlled by controlling the opening degree of the EGR valve 26, and the air-fuel ratio of the exhaust gas flowing into the filter 50b is set to the first air-fuel ratio. And
After the air-fuel ratio of the exhaust gas is set to the first predetermined air-fuel ratio, the reducing agent addition device 60 intermittently adds the fuel to the exhaust passage on the upstream side of the catalytic converter 50 so that the exhaust gas flowing into the filter 50b becomes empty. Second fuel ratio intermittently
The air-fuel ratio of the filter 50
The filter 50 is controlled by controlling the temperature of b to a predetermined temperature.
b may be recovered from SOx poisoning.

According to the exhaust gas purifying apparatus for an internal combustion engine of the present embodiment, even in an internal combustion engine that switches between low temperature combustion and normal combustion depending on the operating state, the filter 50b can be recovered from SOx poisoning regardless of the operating state. Can be done.

FIG. 12 shows the operating range of the internal combustion engine in which the filter 50b of the internal combustion engine exhaust gas purification apparatus according to the present embodiment can be recovered from SOx poisoning.

As shown in FIG. 12, the higher the heat-resistant temperature of the filter 50b, the wider the operating range for recovering from SOx poisoning.

Further, as in the first to fourth embodiments described above, the reducing agent addition device 6 is also used in this embodiment.
The addition of fuel to the exhaust passage by 0 may be a secondary injection of fuel into the combustion chamber.

[0164]

According to the exhaust gas purification apparatus and exhaust gas purification method for an internal combustion engine of the present invention, the NOx catalyst is poisoned with SOx while suppressing the exhaust of smoke and the deterioration of the NOx catalyst regardless of the operating state of the internal combustion engine. Can be recovered from.

Further, when the NOx catalyst is a catalyst having an oxygen retaining capacity such as a particulate filter and capable of oxidizing and purifying fine particles in the exhaust gas, the exhaust gas of the stoichiometric air-fuel ratio or the rich air-fuel ratio and the exhaust of the lean air-fuel ratio are exhausted. Since the particulates in the exhaust gas are purified by alternately flowing with the gas, the NOx catalyst can be recovered from SOx poisoning while suppressing the emission of smoke more effectively.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the internal structure of a particulate filter.

FIG. 3 is a graph showing the relationship between the air-fuel ratio of exhaust gas, the temperature of the particulate filter, and the amount of SOx released into the exhaust gas when fuel is intermittently added to the exhaust passage.

FIG. 4 is a diagram showing a particulate filter differential pressure when fuel is intermittently added.

FIG. 5 is a graph showing the exhaust gas flow rate and the temperature rise of the particulate filter due to the addition of fuel.

FIG. 6 is a schematic configuration diagram of an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to a second embodiment.

FIG. 7 is a graph showing the temperature distribution of the particulate filter when an exhaust purification catalyst is arranged on the upstream side of the particulate filter.

FIG. 8 is a graph showing the temperature distribution of the particulate filter when the particulate filter is arranged alone.

FIG. 9 is a schematic configuration diagram of an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to a third embodiment.

FIG. 10 is a schematic configuration diagram of an internal combustion engine and an exhaust gas purification device for an internal combustion engine according to a fourth embodiment.

FIG. 11 is a graph showing the correlation between the amount of smoke generated and the EGR rate.

FIG. 12 is a graph showing an operating region of an internal combustion engine capable of performing SOx poisoning recovery.

[Explanation of symbols]

1 Internal combustion engine 1a crankshaft 2 cylinders (combustion chamber) 3 Fuel injection valve 4 common rail 5 Fuel supply pipe 6 Fuel pump 6a pulley 8 intake branch pipe 9 Intake pipe 10 air cleaner box 12 Intake air temperature sensor 13 Throttle valve 14 Actuator 15 Turbocharger 15a Compressor housing 15b turbine housing 16 Intercooler 18 Exhaust branch pipe 18a exhaust port 19 Exhaust pipe 20 EGR device 25 EGR passage 26 EGR valve 27 EGR cooler 28 Oxidation catalyst for EGR device 30 electronic control unit 31 bidirectional bus 35 input ports 36 output ports 37 A / D converter 38 Drive circuit 40 accelerator pedal 41 Load sensor 42 crank angle sensor 43 Vehicle speed sensor 44a Intake air temperature sensor 44b Intake air temperature sensor 45 Air flow meter 46 Intake pressure sensor 47 Air-fuel ratio sensor 48a Exhaust gas temperature sensor 48b Exhaust gas temperature sensor 50 catalytic converter 50a exhaust purification catalyst 50b particulate filter 51 casing 55 Exhaust gas inflow passage 55a stopper 56 Exhaust gas outflow passage 56a stopper 57 partitions 58 Filter 59 Oxidation catalytic converter 59a Oxidation catalyst 60 Reductant addition device 61 Reductant addition valve 62 Reductant supply path 63 Fuel pressure sensor 64 Fuel pressure control valve 66 Emergency shutoff valve 67 Exhaust gas temperature sensor 68 Air-fuel ratio sensor 69 Secondary air supply device 70 Secondary air pump 71 Secondary air flow rate adjustment valve

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/02 F01N 3/02 321D 3G301 321H 3/08 3/08 A G 3/10 3/10 A 3 / 18 3/18 E 3/20 3/20 E 3/22 301 3/22 301M 3/24 3/24 R S 3/28 301 3/28 301C 301D F02D 21/08 301 F02D 21/08 301A 301F 301H 41/38 41/38 B CD 41/40 41/40 F 43/00 301 43/00 301K 301N 301T F02M 25/07 570 F02M 25/07 570J (72) Inventor Hisashi Oki 1 Toyota Town, Toyota City, Aichi Prefecture Address Toyota Motor Co., Ltd. (72) Inventor Masaaki Kobayashi Toyota Town, Aichi Prefecture Toyota Town No. 1 Toyota Motor Co., Ltd. (72) Inventor Daisuke Shibata Toyota City, Aichi Prefecture Toyota Town Address Toyota Motor Co., Ltd. F term (reference) 3G062 AA01 BA04 BA05 BA06 BA07 CA06 DA02 ED08 ED09 FA05 GA01 GA02 GA08 GA09 GA12 GA17 GA25 3G084 AA01 BA04 BA09 BA13 BA15 BA20 BA24 BA25 CA03 DA10 DA19 EA07 EA11 EB06 FA02 EB02 FA02 FA02 FB02 FA02 FA02 FA02 FA02 FA02 FA07 FA11 FA20 FA26 FA27 FA38 3G090 AA03 BA01 DA09 DA10 DA12 DA18 DA19 DA20 EA02 EA05 EA06 EA07 3G091 AA02 AA10 AA11 AA18 AA28 AB02 AB06 AB13 BA00 BA04 BA11 BA14 BA15 BA19 BA33 CA13 CA18 CA22 CB02 CB03 CB07 CB08 DA01 DA02 DB10 EA00 EA01 EA03 EA05 EA06 EA07 EA15 EA17 EA31 EA34 EA39 FB02 FB03 FB10 FB11 FB12 FC02 FC07 FC08 GA06 GA18 GA20 GB01X GB02W GB03W GB04W GB05W GB06W GB10X GB16X HA09 HA14 HA15 HA16 HA36 HA37 HA36 HA36 HA37 HA42 HB05 HB06 3G092 A16A18A18 A18 DE11S DF09 EA05 EA11 EC03 EC08 FA17 FA18 FA20 GA05 HA01Z HA04Z HA05Z HA11Z HB03Z HD01Z HD02Z HD05Z HE03Z HF21Z 3G301 HA02 HA04 HA11 HA13 JA24 JA25 JA29 JA33 KA08 LA08 MA02 MA13 MA22 NC02 MA23 MA23 MA23 MA23 01Z PA07Z PA10Z PA17Z PB08Z PD02Z PD11Z PD12Z PD15A PE03Z PF01Z

Claims (21)

[Claims] 1. A NOx catalyst provided in an exhaust passage, a NOx catalyst temperature detecting means for detecting a temperature of the NOx catalyst, an exhaust air-fuel ratio detecting means for detecting an air-fuel ratio of exhaust gas in the exhaust passage, The NO detected by the NOx catalyst temperature detecting means
x exhaust gas air-fuel ratio control means for controlling the air-fuel ratio of the exhaust gas in the exhaust passage based on the temperature of the catalyst and the air-fuel ratio of the exhaust gas detected by the exhaust air-fuel ratio detection means, If the detected air-fuel ratio of the exhaust gas is less than the first predetermined air-fuel ratio, the exhaust air-fuel ratio control means controls the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio, then, The temperature of the NOx catalyst is controlled at the same time as the second predetermined air-fuel ratio which is intermittently richer than the first predetermined air-fuel ratio and enables the NOx catalyst to be recovered from SOx poisoning. The exhaust emission control device for an internal combustion engine, which is capable of recovering from SOx poisoning and is controlled within a predetermined temperature range that does not promote deterioration of the NOx catalyst. 2. In the internal combustion engine, when the amount of recirculated exhaust gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the recirculated exhaust gas supplied to the combustion chamber. When the amount is further increased, the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are lower than the soot generation temperature, and the soot generation amount is suppressed. 2. The internal combustion engine according to claim 1, further comprising switching means for selectively switching between the second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the peak amount of recirculated exhaust gas. Exhaust purification device. 3. A throttle valve for controlling the amount of intake air supplied to the combustion chamber of the internal combustion engine, and a recirculation exhaust gas control valve for controlling the amount of recirculation exhaust gas recirculated to the combustion chamber. The exhaust air-fuel ratio control means controls the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio by controlling the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized in that. 4. The exhaust air-fuel ratio control means controls addition of fuel to at least one of a combustion chamber and an exhaust passage of the internal combustion engine after controlling an air-fuel ratio of exhaust gas to the first predetermined air-fuel ratio. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the air-fuel ratio of the exhaust gas is intermittently controlled to the second predetermined air-fuel ratio by doing so. 5. The addition of fuel to at least one of a combustion chamber and an exhaust passage of the internal combustion engine controlled by the exhaust air-fuel ratio control means is performed when the temperature of the NOx catalyst detected by the NOx catalyst temperature detection means is increased. 5. The process is performed when the temperature is lower than a temperature at which the NOx catalyst can be recovered from SOx poisoning, and is stopped at a temperature that may accelerate deterioration of the NOx catalyst. Exhaust gas purification device for internal combustion engine. 6. The addition of fuel to the combustion chamber of the internal combustion engine controlled by the exhaust air-fuel ratio control means is performed by a sub-injection other than the main injection that is injected to obtain the engine output in the combustion chamber. The exhaust emission control device for an internal combustion engine according to claim 4 or 5, 7. The addition of fuel to the combustion chamber of the internal combustion engine controlled by the exhaust air-fuel ratio control means is such that the fuel burned to obtain an engine output in a cylinder of the internal combustion engine is an expansion stroke or an exhaust gas. The exhaust gas purification device for an internal combustion engine according to any one of claims 4 to 6, which is performed by post injection in which fuel is further sub-injected into the combustion chamber during the stroke. 8. The exhaust gas purification device for an internal combustion engine according to claim 1, further comprising an exhaust gas purification catalyst in an exhaust passage upstream of the NOx catalyst. 9. An oxidation catalyst installed in an exhaust passage downstream of the NOx catalyst, and an oxidation catalyst temperature detection means for detecting the temperature of the oxidation catalyst, the oxidation catalyst temperature detection means detecting the temperature. When the temperature of the oxidation catalyst is lower than a predetermined temperature, the exhaust air-fuel ratio control means controls the addition of fuel to at least one of the combustion chamber and the exhaust passage of the internal combustion engine to intermittently change the exhaust gas air-fuel ratio. The combustion chamber or exhaust gas of the internal combustion engine is controlled so that the temperature of the oxidation catalyst becomes equal to or higher than the predetermined temperature before being controlled to the second predetermined air-fuel ratio that enables recovery of the NOx catalyst from SOx poisoning. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 8, wherein the addition of fuel to at least one of the passages is controlled. 10. The exhaust air-fuel ratio control means controls at least one of the amount of fuel added to at least one of a combustion chamber and an exhaust passage of the internal combustion engine or an interval of addition time based on the temperature of the oxidation catalyst. The exhaust gas purification device for an internal combustion engine according to claim 9, wherein 11. The apparatus further comprises an oxidation catalyst installed in an exhaust passage downstream of the NOx catalyst, and the exhaust air-fuel ratio control means controls the air-fuel ratio of the exhaust gas downstream of the oxidation catalyst to be higher than a predetermined air-fuel ratio. The air-fuel ratio of the exhaust gas is controlled so that the exhaust gas becomes thin.
11. The exhaust gas purification device for an internal combustion engine according to any one of 1 to 10. 12. A downstream side of the NOx catalyst, and
The exhaust gas purification device for an internal combustion engine according to claim 11, further comprising secondary air supply means in an exhaust passage upstream of the oxidation catalyst. 13. The exhaust purification system for an internal combustion engine according to claim 8, wherein the NOx catalyst or the exhaust purification catalyst is a catalyst having no oxygen holding capacity. 14. The exhaust gas purification device for an internal combustion engine according to claim 9, wherein the oxidation catalyst is a catalyst having a high oxygen retaining capacity. 15. In the internal combustion engine, the first combustion is performed when operating in a low load region, and the second combustion is performed when operating in a medium to high load region, In the low load region, the air-fuel ratio of the exhaust gas is controlled to the second predetermined air-fuel ratio by performing the first combustion and controlling the air-fuel ratio in the combustion chamber, or the first combustion is performed. And the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, and then adding fuel to at least one of the combustion chamber and the exhaust passage By performing either control of controlling the fuel ratio to the second predetermined air-fuel ratio, the NOx catalyst is recovered from SOx poisoning, and the second combustion is performed in the medium-high load region. In both cases, the air-fuel ratio of the exhaust gas is adjusted to the first predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, and then the fuel is added to at least one of the combustion chamber and the exhaust passage to increase the air-fuel ratio of the exhaust gas. The exhaust emission control device for an internal combustion engine according to claim 2, wherein recovery from SOx poisoning of the NOx catalyst is performed by intermittently controlling to the second predetermined air-fuel ratio. 16. When recovering a NOx catalyst provided in an exhaust passage from SOx poisoning, first, the air-fuel ratio of the exhaust gas is controlled to a first predetermined air-fuel ratio, and thereafter, the first air-fuel ratio is intermittently controlled. At the same time as controlling the second predetermined air-fuel ratio which is richer than the predetermined air-fuel ratio and enables recovery from SOx poisoning of the NOx catalyst, the temperature of the NOx catalyst is changed to the NO
An exhaust gas purification method for an internal combustion engine, characterized in that the x-catalyst can be recovered from SOx poisoning and is controlled to a predetermined temperature range that does not promote deterioration of the NOx catalyst. 17. The internal combustion engine comprises: a throttle valve for controlling the amount of intake air supplied to the combustion chamber; and a recirculation exhaust gas control valve for controlling the amount of recirculation exhaust gas recirculated to the combustion chamber. The air-fuel ratio of exhaust gas is controlled to the first predetermined air-fuel ratio by controlling the opening degree of at least one of the throttle valve and the recirculation exhaust gas control valve. An exhaust gas purification method for an internal combustion engine as described. 18. The air-fuel ratio of exhaust gas is controlled by controlling the addition of fuel to at least one of a combustion chamber and an exhaust passage of the internal combustion engine after controlling the air-fuel ratio of exhaust gas to the first predetermined air-fuel ratio. And controlling the temperature of the NOx catalyst within the predetermined temperature range at the same time as controlling the temperature of the NOx catalyst to the second predetermined air-fuel ratio intermittently.
7. An exhaust gas purification method for an internal combustion engine according to 7. 19. A NOx catalyst is provided in the exhaust passage, and when the amount of recirculated exhaust gas supplied to the combustion chamber is increased, the amount of soot generated gradually increases and reaches a peak, and the amount of soot generated is re-supplied to the combustion chamber. When the amount of circulating exhaust gas is further increased, the temperature of the fuel during combustion in the combustion chamber and the gas temperature around it are lower than the soot generation temperature, and the soot generation amount is suppressed.
In the exhaust gas purification method for an internal combustion engine, in which the combustion of the exhaust gas and the second combustion in which the amount of recirculated exhaust gas supplied to the combustion chamber is smaller than the amount of recirculated exhaust gas at which the amount of soot is peaked are selectively switched. When the NOx catalyst is recovered from SOx poisoning while the internal combustion engine is performing the second combustion, the air-fuel ratio of the exhaust gas is controlled to a first predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber. After that, by controlling the addition of fuel to at least one of the combustion chamber and the exhaust passage, the air-fuel ratio of the exhaust gas is intermittently richer than the first predetermined air-fuel ratio, and the SOx cover of the NOx catalyst is reduced. At the same time as controlling to a second predetermined air-fuel ratio that enables recovery from poison, the NO
The temperature of the x catalyst is controlled within a predetermined temperature range in which the NOx catalyst can be recovered from SOx poisoning and the deterioration of the NOx catalyst is not promoted, while the internal combustion engine performs the first combustion. When recovering the NOx catalyst from SOx poisoning while operating, the air-fuel ratio of the exhaust gas is controlled to the second predetermined air-fuel ratio by controlling the air-fuel ratio in the combustion chamber, or the air-fuel ratio in the combustion chamber is controlled. By controlling the air-fuel ratio of the exhaust gas to the first predetermined air-fuel ratio, and then controlling the addition of fuel to at least one of the combustion chamber or the exhaust passage to change the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio. At least one of controlling the air-fuel ratio to a predetermined value is performed, and at the same time, the NO
x An exhaust gas purification method for an internal combustion engine, characterized in that the temperature of the catalyst is controlled within the predetermined temperature range. 20. The internal combustion engine comprises an oxidation catalyst installed in an exhaust passage downstream of the NOx catalyst, and when the temperature of the oxidation catalyst is lower than a predetermined temperature, a combustion chamber of the internal combustion engine or Before controlling the air-fuel ratio of the exhaust gas to the second predetermined air-fuel ratio that enables intermittent recovery from the SOx poisoning of the NOx catalyst by controlling the addition of fuel to at least one of the exhaust passages. 20. The exhaust gas of an internal combustion engine according to claim 18, wherein the addition of fuel to at least one of the combustion chamber and the exhaust passage of the internal combustion engine is controlled so that the temperature of the oxidation catalyst becomes equal to or higher than the predetermined temperature. Purification method. 21. The internal combustion engine comprises an oxidation catalyst installed in an exhaust passage downstream of the NOx catalyst, and an air-fuel ratio of exhaust gas downstream of the oxidation catalyst becomes thinner than a predetermined air-fuel ratio. 21. The exhaust gas purification method for an internal combustion engine according to claim 16, wherein the air-fuel ratio of the exhaust gas is controlled as described above.