JP2000240438A - Exhaust emission control device for cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the torque shock or deterioration of fuel consumption by injecting fuel directly into a combustion chamber during compression stroke so that the air-fuel ratio of an engine is close to a theoretical air-fuel ratio to execute a stratified combustion in the release of the occluded NOX from a NOX occlusion type catalytic device. SOLUTION: It is judged in an ECU 40 whether NOX is leaked or not from an exhaust emission purifying catalytic device 30 on the basis of the output of a NOX sensor 32. When the NOX to be occluded in an occlusion type NOX catalyst 30a is leaked, and the output from the NOX sensor 32 reaches a judgment threshold X1, resulting the judgment of YES, NOX purge is executed. Namely, the fuel regulated so that the air-fuel ratio of the engine is close to the theoretical air-fuel ratio is injected into a combustion chamber 8 through a fuel injection valve 6 in compression stroke to perform a stratified combustion. According to this, at the time of executing the stratified combustion in an extremely lean air-fuel ratio, this stratified combustion is kept to prevent a torque shock caused by the change of combustion form.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a direct injection internal combustion engine, and more particularly to a technique for releasing and reducing NOx in a NOx storage type catalytic device.

[0002]

2. Related Background Art In recent years, in order to achieve both fuel consumption and output, a direct injection internal combustion engine for directly injecting fuel into a combustion chamber has been put into practical use and mounted on vehicles. This type of internal combustion engine performs stratified combustion at an ultra-lean air-fuel ratio by injecting fuel during a compression stroke in a specific operation region. Is not sufficiently purified.

On the other hand, when the exhaust air-fuel ratio is an oxidizing atmosphere having a lean air-fuel ratio, NOx in the exhaust gas is occluded as nitrate X-NO ₃ , and when the oxygen concentration in the exhaust gas decreases, that is, when the exhaust air-fuel ratio is NOx occluded on the catalyst in a reducing atmosphere of an air-fuel ratio or a rich air-fuel ratio
Is released once as NOx, and N ₂ (nitrogen) and carbonate X-
Patent No. 25867 is an intake pipe injection type internal combustion engine employing a NOx absorbent having a characteristic of reducing to CO ₃ as a catalyst device.
No. 39, etc.

[0004] Therefore, it has been considered to apply a catalyst device comprising the NOx absorbent to a direct injection type internal combustion engine. In this case, when releasing and reducing NOx stored on the catalyst, Fuel is injected during the intake stroke so that the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, that is, the air-fuel ratio of the engine becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio. As in the case of the above, uniform combustion is performed.

[0005]

The above-mentioned NOx
In a catalyst device made of an absorbent, there is a limit to the amount of NOx that can be stored on the catalyst. Therefore, when the catalyst device is applied to an in-cylinder injection internal combustion engine, when the purification efficiency of the catalyst device deteriorates, In order to release and reduce the reduced NOx, it is necessary to frequently perform uniform combustion by injecting fuel during the intake stroke so that the air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio.

However, if switching from stratified combustion at an ultra-lean air-fuel ratio to uniform combustion at an excessive air-fuel ratio occurs contrary to the intention of the driver of the vehicle, the vehicle such as the driver or the like may change due to the difference in combustion mode. In addition, there is a risk of causing a torque shock to the occupants, and the frequent uniform combustion is repeatedly performed while the operation in the stratified combustion is continued, which makes the stratified combustion advantageous in terms of fuel efficiency. Nevertheless, fuel efficiency may deteriorate, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a NOx storage-type catalyst device which can release and release NOx without causing a torque shock or deterioration of fuel efficiency. An object of the present invention is to provide a reducible in-cylinder injection type exhaust gas purification apparatus for an internal combustion engine.

[0008]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for a direct injection type internal combustion engine, comprising a NOx storage type catalytic device. When releasing the stored NOx from the storage type catalytic device, the NOx release control means injects the fuel directly into the combustion chamber during the compression stroke so that the air-fuel ratio of the engine becomes close to the stoichiometric air-fuel ratio, and stratified combustion is performed. Will be implemented.

As described above, when the fuel is injected during the compression stroke so that the air-fuel ratio of the engine becomes close to the stoichiometric air-fuel ratio and the stratified combustion is formed, the fuel concentrates around the spark plug and is near the spark plug. The air-fuel ratio locally becomes a rich air-fuel ratio, incomplete combustion occurs, and a large amount of carbon monoxide (CO) is generated. When the CO reaches the catalytic converter in the NOx occlusion-type through an exhaust passage, the NOx occlusion-type catalytic device becomes a reducing atmosphere, NOx that has been occluded as nitrate X-NO ₃ is,
Once released, they are well reduced and removed by the catalytic reaction of the catalytic device.

At this time, since the fuel is injected during the compression stroke with the air-fuel ratio of the engine being close to the stoichiometric air-fuel ratio, the stratified combustion is performed during the stratified combustion at the ultra-lean air-fuel ratio. It is possible to efficiently perform NOx emission and reduction while maintaining the torque to prevent the occurrence of torque shock due to the change of the combustion mode and suppressing the increase in the rich air-fuel ratio so as not to deteriorate the fuel efficiency.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust purification device for a direct injection internal combustion engine according to the present invention mounted on a vehicle, and based on the drawing, a direct injection internal combustion engine according to the present invention will be described below. The configuration of the exhaust gas purification device of the engine will be described.

Engine body (hereinafter simply referred to as engine) 1
Performs, for example, fuel injection in the intake stroke (intake stroke injection mode) in which uniform combustion is performed by switching the fuel injection mode (operation mode) or fuel injection in the compression stroke (compression stroke injection mode) in which stratified combustion is performed. It is a possible in-cylinder injection spark ignition in-line four-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). Operation), and especially in the compression stroke injection mode, the super lean air-fuel ratio (for example, a value of 25 to
Operation at the value 50) is possible.

As shown in FIG. 1, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby fuel is injected into the combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. Reference numeral 13 in the figure denotes a crank angle sensor for detecting a crank angle CA, and the crank angle sensor 13 is capable of detecting the engine rotation speed Ne together with the crank angle CA.

The in-cylinder injection type engine 1 is already known, and a detailed description of its configuration is omitted here. An exhaust pipe (exhaust passage) 20 is connected to the exhaust manifold 12, and a muffler (not shown) is connected to the exhaust pipe 20 via an exhaust purification catalyst device 30.

The exhaust purification catalyst device 30 is provided with two catalysts, that is, a storage NOx catalyst 30a and a three-way catalyst 30b.
0a is disposed downstream. The storage-type NOx catalyst 30a has a function of storing NOx in an oxidizing atmosphere, releasing NOx once in a reducing atmosphere mainly containing CO, and then reducing it to N ₂ (nitrogen) or the like. More specifically, the storage NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh), or the like as a noble metal, and barium (B) as a storage material.
Alkali metals and alkaline earth metals such as a) are employed.

A NOx sensor 32 for detecting the concentration of NOx contained in the exhaust gas passing through the exhaust gas purifying catalyst device 30 is provided downstream of the three-way catalyst 30b. It should be noted that the storage NOx catalyst 30a or the three-way catalyst 30
Since NOx can be purified by b, the output of the NOx sensor 32 becomes a value 0 or a value near the value 0. Therefore, here, the NOx sensor 32 is used as a means for detecting the leakage of the NOx to the downstream when NOx cannot be purified by the storage-type NOx catalyst 30a or the three-way catalyst 30b.

Further, an input / output device, a storage device (ROM,
RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (electronic control unit) 40 including a timer counter and the like is installed.
Thus, comprehensive control of the direct injection internal combustion engine according to the present invention including the engine 1 is performed. Various sensors such as the above-described throttle sensor 11a, crank angle sensor 13, and NOx sensor 32 are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4 and the fuel injection valve 6 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are connected to various sensors. The optimum values such as the fuel injection amount, the fuel injection timing, and the ignition timing calculated based on the detection information are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

In practice, the ECU 40 determines the target average effective pressure Pe corresponding to the engine load based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Normally, a fuel injection mode, that is, an operation mode is set from a fuel injection mode setting map (not shown) according to the target average effective pressure Pe and the engine rotation speed information Ne. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both small, the operation mode is the compression stroke injection mode (compression lean mode), and fuel is injected in the compression stroke, while the target average effective pressure Pe is large. Or the engine speed Ne increases, the operation mode is set to the intake stroke injection mode,
Fuel is injected during the intake stroke. The intake stroke injection mode includes an intake lean mode having a lean air-fuel ratio (for example, a value of 18 to 22), and a stoichiometric feedback mode (S-F / B mode) in which actual A / F is feedback-controlled to be stoichiometric. And an open loop mode (O / L mode) in which a rich air-fuel ratio is set.

Then, a target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate fuel injection amount is determined based on the target A / F. Further, in the present invention, when releasing and reducing the NOx stored in the storage-type NOx catalyst 30a, that is, when performing the NOx purge, the air-fuel ratio in the compression stroke is set to a value close to the stoichiometric pressure including the stoichiometric pressure in the compression stroke. Compression stroke stoichiometric operation (compression stoichiometric operation) controlled to an air-fuel ratio (for example, value 14 to value 15)
Can be implemented.

Hereinafter, the operation of the exhaust gas purifying apparatus for a direct injection type internal combustion engine according to the present invention, ie, the NOx release according to the present invention when releasing and reducing NOx from the storage NOx catalyst 30a will be described. The reduction control, that is, the NOx purge control (NOx release control means) will be described. Referring to FIG. 2, a control routine of the NOx purge control is shown in a flow chart.
A time chart showing an example of the control result of the Ox purge control is shown. Hereinafter, description will be given along the flowchart of FIG. 2 with reference to the time chart of FIG. In addition,
Here, a case where the engine 1 is not in a cold state but in a sufficiently warmed-up state will be described as an example.

In step S10, based on the output information from the NOx sensor 32, the NO.
It is determined whether or not x is leaked. That is, the storage type N
NOx to be stored in the Ox catalyst 30a overflows and NO
The output from the x sensor 32 reaches the determination threshold X1, and the storage type N
It is detected whether or not the NOx storage amount of the Ox catalyst 30a has reached an allowable storage amount (limit). If the determination result is false (No), it can be determined that the storage type NOx catalyst 30a is functioning properly. In this case, the process proceeds to step S11, and the normal control is performed based on the fuel injection mode setting map. I do.

On the other hand, the operation in the compression lean mode is performed for a long time, and the result of the determination in step S10 is true (Ye
s), that is, when it is determined that the output from the NOx sensor 32 has reached the determination threshold value X1 and the NOx storage amount of the storage NOx catalyst 30a has reached the allowable storage amount (see FIG. 3B),
Next, the process proceeds to step S12 to start the NOx purge.

In step S12, a timer TM is set, and the measurement of the elapsed time is started simultaneously with the start of the NOx purge. Normally, when stratified combustion is performed by injecting fuel in the compression stroke, the fuel is locally concentrated near the spark plug 4 and combusted due to the characteristics of stratified combustion. Therefore, usually, fuel is injected near the spark plug 4 so that the air-fuel ratio becomes close to stoichiometric. In order to obtain stable combustion, the overall air-fuel ratio is set to a lean air-fuel ratio (for example, a value of 25 or more). Is done. That is, in the compression stroke injection mode, the compression lean mode is usually set.

In other words, when the above-described compression stoichiometric operation is performed to perform the NOx purge, the air-fuel ratio as a whole is set to a value near stoichiometric (for example, a value of 14 to 15), while the combustion is stratified. Because of the combustion, a rich air-fuel ratio state where the fuel concentration is extremely high locally in the vicinity of the ignition plug 4, and the combustion state tends to deteriorate. Therefore, in step S14, first, it is determined whether or not the compression stoichiometric operation may be performed in the NOx purge, that is, whether or not there is no problem even if the combustion state tends to be slightly deteriorated. Specifically, since the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V are highly correlated, the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V are each lower than the corresponding predetermined value. It is determined whether or not there is.

If the result of the determination in step S14 is false (No), and if any one of the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V is greater than the corresponding predetermined value, the combustion is started. It is determined that the state in which the state tends to deteriorate is not preferable, and the process proceeds to step S16. That is, the engine speed Ne, the target average effective pressure Pe, and the vehicle speed V
Is larger than the corresponding predetermined value, it can be determined that the driver is requesting a high output from the engine 1, for example, and the driver wants to actively drive the engine 1. When the compression stoichiometric operation is performed, the combustion state deteriorates, and consequently the torque may be insufficient. Further, since the fuel injection amount is set according to the target average effective pressure Pe, smoke is likely to occur. Therefore, the compression stoichiometric operation is not performed.

Therefore, in this case, the compression stoichiometric operation is not performed, and the NOx purge is performed by the rich air-fuel ratio operation in the conventional manner in step S16. That is, NOx is released and reduced by injecting fuel so that the air-fuel ratio becomes a rich air-fuel ratio or stoichiometry during the intake stroke. The engine speed Ne,
When either the target average effective pressure Pe or the vehicle speed V is larger than the corresponding predetermined value, the operation mode is usually set to O /
It is considered that the L mode or the SF / B mode is used.
In the mode and the SF / B mode, since the NOx purge can be performed as it is, it is not necessary to change the operation state to the rich air-fuel ratio operation again.

On the other hand, if the result of the determination in step S14 is true (Y
es), the engine speed Ne, the target average effective pressure Pe,
If it is determined that all of the vehicle speeds V are equal to or less than the corresponding predetermined values, it can be determined that there is not much problem even if the combustion state tends to deteriorate, and then step S18
To perform the compression stoichiometric operation according to the present invention (see FIG. 3A).

In the compression stoichiometric operation, as described above, the fuel injection is performed during the compression stroke by controlling the air-fuel ratio to the air-fuel ratio near stoichio including stoichio (for example, value 14 to value 15). In this way, a rich air-fuel ratio state where the fuel concentration is extremely high locally in the vicinity of the ignition plug 4, causing insufficient combustion of the fuel due to lack of oxygen, and relatively large amount of carbon monoxide (CO) is generated Will do.

That is, referring to FIG. 4, the air-fuel ratio A / F
The CO concentration in the case where the compression stroke injection is performed while changing the pressure is shown by a solid line, and the CO concentration in the case where the intake stroke injection is performed while the air-fuel ratio A / F is changed is shown by a single-dot chain line. As shown in the figure, when the intake stroke injection is performed with the air-fuel ratio near stoichiometric (dashed line), the CO concentration is substantially 0 (vol%) in order to obtain good combustion, When the compression stroke injection is performed with the air-fuel ratio near stoichiometry (solid line), sufficient CO is present and the CO concentration is high (for example, 1.5 vol% CO concentration).

That is, since the concentration of CO acting as a reducing agent for the storage NOx catalyst 30a is higher in the compression stroke injection than in the intake stroke injection, it is better to perform the compression stroke injection (compression stoichiometric operation). It can be said that the NOx purge can be performed more efficiently than in the case of the intake stroke injection. According to the figure, the amount of CO increases as the air-fuel ratio shifts to the rich air-fuel ratio side. In general, however, as the amount of CO increases, the amount of smoke also increases. Therefore, here, the limit value of the air-fuel ratio on the rich air-fuel ratio side of the air-fuel ratio in the vicinity of stoichio is, for example, about 14 so that the amount of generated smoke is suppressed within the allowable range.

Normally, when the operation mode is the compression lean mode, an EGR valve (not shown) is opened to perform exhaust gas recirculation (EGR) for the purpose of reducing NOx. In the stoichiometric operation, the EGR valve is set to the closed state to suppress the fluctuation of the air-fuel ratio and the like.
R is not performed. Thus, occlusion-type NOx catalyst 30a is sufficiently reducing atmosphere, NOx that has been occluded in the occlusion-type NOx catalyst 30a is satisfactorily discharged, and be reduced to N ₂ and the like. At this time, the storage NOx
A part of the NOx released from the catalyst 30a may flow downstream without being reduced in the occlusion type NOx catalyst 30a. Even in such a case, the outflowing NOx remains in a reducing atmosphere. Therefore, there is no problem because the three-way catalyst 30b favorably reduces and removes the catalyst.

When the compression stoichiometric operation is performed as NOx purge during the operation in the compression lean mode, the fuel is injected in the compression stroke in both the compression lean mode and the compression stoichiometric operation. Does not switch from stratified combustion to uniform combustion as in the prior art, and the combustion mode is maintained as stratified combustion. Therefore, if the compression stoichiometric operation is performed as the NOx purge, it is possible to preferably prevent the occupant of the vehicle such as the driver from feeling the torque shock.

Further, in the compression stoichiometric operation, since the air-fuel ratio as a whole is close to stoichiometric, the fuel injection amount can be smaller than in the case of performing the rich air-fuel ratio operation. That is, when performing the rich air-fuel ratio operation as in the related art, as shown by the dashed line in FIG. 4, if the rich degree of the rich air-fuel ratio is made relatively large and the air-fuel ratio is not made a small value to a certain extent, sufficient CO can be obtained. I can't get it,
By performing the compression stoichiometric operation of the present invention, it is possible to sufficiently obtain CO by setting the overall air-fuel ratio near stoichiometric,
The NOx purge can be performed extremely efficiently without deterioration of fuel efficiency.

Further, in the NOx purge, there is a relationship that when the amount of CO is large, the NOx purge progresses rapidly and is completed in a short period of time. For example, the NOx purge cannot be completed in a short period of time unless the value is extremely small, for example, about 12, but when the compression stoichiometric operation is performed, as shown by a solid line in FIG. The same CO concentration as in the case where the rich air-fuel ratio operation is performed at the air-fuel ratio of about the above value 12 (for example, the CO concentration 1.
5 vol%), and the NOx purge can be completed in a short period of time.

That is, when the NOx purge is required, if the compression stoichiometric operation according to the present invention is performed, the NOx purge can be efficiently performed in a short period of time without generating torque shock and reducing fuel consumption. You can do it. Then, in step S20 in FIG. 2, it is determined whether or not the timer TM has counted a predetermined timer time T1. The predetermined timer time T1 is a time set in advance by an experiment or the like, and more specifically, when the compression stoichiometric operation is performed, the storage NOx catalyst 30a
The time until Ox is almost completely released and reduced is set. As described above, under the compression stoichiometric operation, the NOx purge can be completed in a short period of time, so the predetermined timer time T1 is set to a relatively short time.

The determination result of step S20 is false (No)
If it is determined that the predetermined timer time T1 has not yet elapsed and the NOx purge has not been substantially completed, the compression stoichiometric operation is continued in step S18 via step S14. On the other hand, if the determination result of step S20 is true (Yes) and it is determined that the predetermined timer time T1 has elapsed, the routine exits from the routine and ends the NOx purge control (see FIG. 3A).

In the above embodiment, the fact that the NOx storage amount of the storage NOx catalyst 30a has reached the allowable storage amount is determined by N
The NOx purging is performed by detecting the output from the Ox sensor 32. The NOx storage amount is determined based on, for example, the engine speed Ne and the target average effective pressure Pe, or the NOx based on the operating time at the lean air-fuel ratio. It may be estimated from the integrated amount.

In the above-described embodiment, whether or not NOx is almost completely released and reduced is determined by measuring the time of the timer TM. For example, the NOx release amount is determined based on the CO concentration shown in FIG. The fact that NOx has been almost completely released and reduced is determined based on the NOx integration amount.
It is also possible to estimate based on the difference value obtained by subtracting the Ox release amount.

In the above embodiment, in the compression stoichiometric operation, the air-fuel ratio is controlled to an air-fuel ratio (for example, a value 14 to a value 15) near stoichio including stoichiometric fuel injection. In consideration of the characteristics of the catalyst 30b, it is preferable to perform the fuel injection by controlling the air-fuel ratio to a slightly richer air-fuel ratio from stoichiometry (for example, a value of 14 to 14.7).

That is, the three-way catalyst 30b has a high NOx purification efficiency in a reducing atmosphere where the exhaust air-fuel ratio becomes a rich air-fuel ratio, but hardly purifies NOx in an oxidizing atmosphere where the exhaust air-fuel ratio becomes a lean air-fuel ratio. However, if the air-fuel ratio is set to a slightly richer air-fuel ratio than the stoichiometric ratio, as described above, the storage NOx catalyst 30a
Even if part of the NOx released from the NOx flows downstream, the NOx can be reliably reduced and removed by the three-way catalyst 30b without leakage.

In the present embodiment, the three-way catalyst 30b is provided downstream of the storage NOx catalyst 30a.
If the storage type NOx catalyst 30a has a sufficient three-way catalyst function, the exhaust purification catalyst device 30 may be configured only with the storage type NOx catalyst 30a without providing the three-way catalyst 30b downstream.

[0045]

As described above in detail, according to the exhaust gas purifying apparatus for a direct injection internal combustion engine of the first aspect of the present invention,
When releasing the stored NOx from the NOx storage-type catalytic device, the fuel is injected during the compression stroke so that the air-fuel ratio of the engine becomes close to the stoichiometric air-fuel ratio, and the stratified combustion is performed.
When stratified charge combustion is performed at an ultra-lean air-fuel ratio, the stratified charge combustion is maintained so that a torque shock due to a change in the combustion mode is not generated, and the rich air-fuel ratio is suppressed so that fuel efficiency is not deteriorated. In this way, NOx can be efficiently released and reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an exhaust gas purification device for a direct injection internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a control routine of NOx purge control according to the present invention.

FIG. 3 is a time chart showing an example of a control result by the NOx purge control according to the present invention of FIG. 2;

FIG. 4 shows a case where the compression stroke injection is performed while changing the air-fuel ratio A / F (solid line) and a case where the intake stroke injection is performed (dashed line).
FIG. 4 is a diagram showing a comparison of CO concentrations in the above.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (in-cylinder injection type internal combustion engine) 4 Spark plug 6 Fuel injection valve 11a Throttle sensor 12 Exhaust manifold 13 Crank angle sensor 30 Exhaust purification catalyst device 30a Storage type NOx catalyst 30b Three-way catalyst 32 NOx sensor 40 Electronic control unit (ECU) )

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/20 F02D 41/02 325A 3/28 301 41/04 305A F02D 41/02 325 B01D 53/36 ZAB 41/04 305 101B (72) Inventor Yuki Tamura 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Osamu Nakayama 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors F-term within the company (reference) 3G091 AA02 AA12 AA17 AA24 AA28 AB03 AB06 CB02 CB03 CB05 CB08 DB06 DB10 EA01 EA07 EA30 EA31 EA33 FB10 FB11 FB12 FC02 GB02W GB03W GB05W GB06W HA08 HA37 HA38 HA04 HA03 HA03 HA03 HA03 HA03 HA03 HA03 HA03 HA03 HA03 LB04 MA01 MA11 MA18 NA06 NA08 NC01 NC02 NE01 NE06 NE13 NE14 NE15 PA11B PA11Z PE01B PE01Z 4D048 AA06 AA13 AA18 AB02 AB05 BA14X B A15X BA30X BA33X BA41X CC32 CC38 CC46 DA01 DA02 DA08 EA04

Claims (1)

[Claims] 1. A catalyst device provided in an exhaust passage for storing NOx in exhaust gas when the exhaust air-fuel ratio is a lean air-fuel ratio, and releasing and reducing the stored NOx when the exhaust air-fuel ratio is a stoichiometric air-fuel ratio or a rich air-fuel ratio. When releasing the stored NOx from the catalyst device, NOx release control means for performing stratified combustion by directly injecting fuel into the combustion chamber during the compression stroke so that the air-fuel ratio of the engine becomes close to the stoichiometric air-fuel ratio, An exhaust purification device for a direct injection internal combustion engine, comprising: