JP2001059440A - Exhaust emission control device for cylinder injection type internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly regenerate an occluded type NOx catalyst without causing torque variations or unintentional discharge of NOx in an exhaust emission control device provided with an occluded type NOx catalyst. SOLUTION: When the quantity of NOx of an occluded type NOx catalyst or SOx reaches a specified quantity, and a switching command to the operation at a stoichiometric air fuel ratio or at a rich air fuel ratio is generated (moment A in (a)), the air fuel ratio is slowly changed toward a specified stoichiometric air fuel ratio or rich air fuel ratio, and the air fuel ratio is slowly changed toward a lean air fuel ratio until the switching command is stopped after the specified stoichiometric air fuel ratio or rich air fuel ratio is held for a specified time (b). Further, while the switching command is generated, the fuel quantity is additionally supplied into the cylinder by a sub-injection means in an expansion stroke of an internal combustion engine based on the air fuel ratio (b).

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 type internal combustion engine, and more particularly to a NOx or SOx purging technique for an exhaust gas purifying apparatus having a storage type NOx catalyst.

[0002]

2. Related Art When the internal combustion engine is in a predetermined operating state, the air-fuel ratio is controlled to a target value (for example, a value of 22 or more) leaner (lean) than the stoichiometric air-fuel ratio (value 14.7). An air-fuel ratio control method for improving the fuel efficiency characteristics of an engine and the like is known. In such a lean air-fuel ratio control method, there is a problem that NOx (nitrogen oxide) in exhaust gas cannot be sufficiently purified by the conventional three-way catalyst.

[0003] In order to solve this problem, NOx in exhaust gas is converted to nitrate X- in an oxygen-excess state (oxidizing atmosphere).
NO ₃ is absorbed and stored, and the stored NOx is CO 2
N ₂ (nitrogen) in excess (carbon monoxide) (reducing atmosphere)
(Simultaneously carbonate X-CO ₃ generated) characteristic of reducing the exhaust gas purifying catalyst having a using a so-called occlusion-type NOx catalyst, it is known to reduce NOx emissions to the atmosphere. In this storage type NOx catalyst, NOx is stored during the lean air-fuel ratio control as described above. However, if the lean combustion operation is continuously performed for a long time, the NOx storage amount of the catalyst is limited, so that the NOx storage amount is limited. When the storage amount reaches the saturation amount, NOx in the exhaust gas is discharged to the atmosphere without being stored in the catalyst.

Therefore, before the storage amount of the storage NOx catalyst reaches saturation, the air-fuel ratio is periodically switched to a rich air-fuel ratio operation for controlling the air-fuel ratio to a stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio (this is referred to as a rich spike). Japanese Patent Application Laid-Open No. Hei 7 (1994) discloses an exhaust gas purification apparatus configured to perform purification and reduction of NOx (NOx purge) in a reducing atmosphere (rich state) with a large amount to regenerate a storage-type NOx catalyst.
This is known from, for example, JP-A-166913.

Further, the exhaust gas contains a sulfur component (S component), and when the storage NOx catalyst stores NOx, it also stores sulfur oxides (SOx), so that the catalyst carrier is poisoned. Therefore, there is a problem that the purification efficiency of the catalyst is reduced. Therefore, it is necessary to make the air-fuel ratio rich as in the case of the NOx purge in order to release SOx from the NOx catalyst and regenerate the purification efficiency of the catalyst. As an example of this, Japanese Patent Application Laid-Open No. 6-66129 discloses a technique of estimating the amount of sulfur adsorbed, setting the catalyst temperature to a high temperature by an electric heater or the like, and changing the air-fuel ratio to a rich state over a predetermined time.

[0006]

When the air-fuel ratio is switched from a lean air-fuel ratio to a stoichiometric air-fuel ratio or a rich air-fuel ratio, if the switching is performed to increase the fuel amount at a stretch as in the latter publication, the in-cylinder pressure is reduced. And the output torque of the internal combustion engine temporarily fluctuates greatly. Therefore, in the former publication, the air-fuel ratio is tailed as slowly as possible to a desired rich air-fuel ratio by gradually increasing the fuel injection amount, thereby suppressing output torque fluctuation. Apart from this, the fuel injection amount is increased and the intake air amount is appropriately changed to gradually shift the air-fuel ratio to the rich air-fuel ratio to suppress output torque fluctuation.

However, when the air-fuel ratio is tailed in this way, if the tailing is gentle enough to suppress fluctuations in output torque, it takes time for the air-fuel ratio to reach a desired rich air-fuel ratio. During this tailing period, the amount of generated CO is small and the NOx purge is not performed well, that is, the start of the NOx purge is delayed, which is not preferable. In other words, the slower the tailing, the longer the time required for NOx purging as a whole, which affects the original operating state of the internal combustion engine, which is not preferable.

Further, NOx is most frequently generated when the air-fuel ratio is near the value 16. When the air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio as described above, the NOx always passes near this value 16. However, if the air-fuel ratio tailing period is long as described above, the air-fuel ratio inevitably becomes the value 1
There is also a problem that a large amount of NOx is generated during the switching of the air-fuel ratio (this is referred to as a NOx spike), and a large amount of NOx is discharged without being purified during this period.

When the stored NOx amount is large, a large amount of NOx may be released from the storage NOx catalyst when the air-fuel ratio is near the stoichiometric air-fuel ratio. However, NOx is reduced near the stoichiometric air-fuel ratio. Reducing agents (CO, HC
And the like, the tailing is gradual and the period near the stoichiometric air-fuel ratio becomes longer as described above.
There is also a problem that the amount of released Ox is necessarily increased, thereby increasing the amount of NOx discharged into the atmosphere.

The present invention has been made to solve such a problem, and an object thereof is to provide a storage type N.
It is an object of the present invention to provide an exhaust purification device for an in-cylinder injection type internal combustion engine that can quickly regenerate an occluded NOx catalyst without torque fluctuation or inadvertent emission of NOx.

[0011]

In order to achieve the above-mentioned object, the invention of claim 1 is provided in an internal combustion engine having main injection means for directly supplying fuel into a cylinder in an intake stroke or a compression stroke. When the stored NOx catalyst is regenerated, the air-fuel ratio of the internal combustion engine is gradually changed between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio by the air-fuel ratio switching means. The fuel is additionally supplied into the cylinder by the sub-injection means in the air-fuel ratio region including the air-fuel ratio in which a large amount of air is generated.

According to the present invention, the air-fuel ratio is gradually changed when the air-fuel ratio is switched for the catalyst regeneration, and the fluctuation of the engine output torque caused by the air-fuel ratio change is suppressed. On the other hand, the fuel is additionally supplied into the cylinder by the sub-injection means to enrich the air-fuel ratio, and the reduction of the storage NOx catalyst is promoted, whereby the NOx purge period required for catalyst regeneration (air-fuel ratio enrichment period) Is shortened. Moreover, the additional supply of fuel by the sub-injection means is performed in the air-fuel ratio range including the air-fuel ratio where a large amount of NOx is generated, so that the air-fuel ratio in the cylinder becomes the air-fuel ratio including the air-fuel ratio where a large amount of NOx is generated. Area within a short period of time, and therefore the NOx emissions are greatly reduced.

According to a second aspect of the present invention, the air-fuel ratio of the internal combustion engine is gradually changed between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio by the air-fuel ratio switching means during regeneration of the storage NOx catalyst provided in the internal combustion engine. The fuel is additionally supplied into the cylinder by the sub-injection means in the air-fuel ratio range including the air-fuel ratio where the reducing agent that can be used for the reduction of NOx released from the catalyst is reduced.

According to the present invention, when the air-fuel ratio is switched during the regeneration of the catalyst, the air-fuel ratio gradually changes to suppress the fluctuation of the engine output torque, and the fuel is additionally supplied into the cylinder by the auxiliary injection means to store the fuel. The reduction of the type NOx catalyst is promoted,
The NOx purge period is shortened. In addition, in the air-fuel ratio range in which the air-fuel ratio that changes under the air-fuel ratio switching control includes the air-fuel ratio in which the reducing agent supplied for NOx reduction is insufficient, the fuel is additionally supplied by the sub-injection means, and the air-fuel ratio in the cylinder is reduced. NOx passes through the air-fuel ratio range including the air-fuel ratio in which the reducing
Emissions are significantly reduced.

According to a third aspect of the present invention, while the air-fuel ratio of the internal combustion engine having the main injection means for directly supplying fuel into the cylinder is controlled to the stoichiometric air-fuel ratio or the rich air-fuel ratio by the air-fuel ratio control means, An amount of fuel corresponding to the difference between the target air-fuel ratio related to the air-fuel ratio control and a predetermined rich air-fuel ratio is additionally supplied into the cylinder by the sub-injection means during the expansion stroke of the internal combustion engine.

According to the present invention, when fuel is additionally supplied by the sub-injection means while the internal combustion engine is operating at the stoichiometric air-fuel ratio or the rich air-fuel ratio, the overall air-fuel ratio in the cylinder becomes the predetermined rich air-fuel ratio. Thus, NOx released from the catalyst can be sufficiently reduced, and thus regeneration of the catalyst is promoted. Moreover, since the additional supply of fuel is performed during the expansion stroke, this fuel supply does not contribute to an increase in engine output torque,
Therefore, catalyst regeneration is performed without causing torque fluctuation.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment 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 of a direct injection internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the exhaust purification device according to the present invention will be described based on the drawing. Will be described.

As shown in FIG.
For example, the in-cylinder injection type spark ignition system 1 is capable of performing fuel injection in an intake stroke or fuel injection in a compression stroke (main injection means) by switching a fuel injection mode (operation mode). An in-line four-cylinder gasoline engine is applied. 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). Is feasible.

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 directly injected into the combustion chamber. It is possible. An ignition coil 8 that outputs a high voltage is connected to the ignition plug 4. Further, a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe 7. 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 is determined from the fuel discharge pressure of the high-pressure fuel pump and the opening time of the fuel injection valve 6, that is, the fuel injection time Tinj.

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. 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.

The in-cylinder injection type engine 1 is already known, and a detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the intake manifold 10, and a muffler (not shown) is connected to the exhaust pipe 14 via an exhaust purification catalyst device 20. . In addition, O ₂
A sensor 18 is provided. The O ₂ sensor 18 mainly detects the air / fuel ratio A / in the combustion chamber based on the amount of O _{2 in} the exhaust gas.
F is to be detected.

The exhaust purification catalyst device 20 is provided with two catalysts, that is, a storage NOx catalyst 20a and a three-way catalyst 20b, and the three-way catalyst 20b uses the storage NOx catalyst 2a.
0a is disposed downstream. The storage NOx catalyst 20a temporarily stores NOx in an oxidizing atmosphere,
It has a function of reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere where CO is present. Specifically, the storage NOx catalyst 20a is configured as a catalyst having platinum (Pt), rhodium (Rh), or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage material. Has been adopted.

Further, an input / output device, a storage device (ROM,
RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (electronic control unit) 30 including a timer counter and the like is installed.
Thereby, comprehensive control of the exhaust gas purification apparatus according to the present invention including the engine 1 is performed. On the input side of the ECU 30,
Various sensors such as the above-described O ₂ sensor 18 are connected, and detection information from these sensors is input. In addition, a distance meter 32 for detecting the traveling distance of the vehicle is provided on the input side.
Is also connected.

On the other hand, the above-mentioned fuel injection valve 6, ignition coil 8 and the like are connected to the output side, and these fuel injection valve 6, ignition coil 8 and the like are operated based on detection information from various sensors. Optimum values such as the determined fuel injection amount and ignition timing are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6, and ignition is performed at an appropriate timing by the ignition plug 4.

Next, the operation of the exhaust gas purifying apparatus according to the present invention configured as described above will be described. Here, an example in which the engine 1 performs the fuel injection (main injection) in the compression stroke and is in the lean air-fuel ratio operation will be described. First, the general operation will be described. When the engine 1 is operated at the lean air-fuel ratio, the amount of generated NOx is increasing. However, here, as described above, the storage type N
The Ox catalyst 20a and the three-way catalyst 20b are arranged in series, and the occluded NOx catalyst 20a purifies NOx to the extent that the three-way catalyst 20b cannot purify NOx. Therefore, not only HC and CO but also NO
x is almost completely purified without leakage.

However, as for the storage type NOx catalyst 20a, when the NOx stored in the oxidizing atmosphere reaches the saturation amount, the NOx storage capacity is reduced. Therefore, the stored NOx is converted to N ₂ or the like in the reducing atmosphere as described above. It needs to be reduced and removed. Therefore, in the exhaust gas purifying apparatus having the storage type NOx catalyst 20a, for example, the target air-fuel ratio (main-injection air-fuel ratio) is reduced and the fuel injection amount (main injection amount) is increased once at a predetermined cycle. A rich air-fuel ratio operation is performed for a predetermined time (this is referred to as a rich spike), thereby forcibly generating a CO excess state, that is, a reducing atmosphere, in the occlusion type NOx catalyst 20a, and releasing the stored NOx to reduce and remove it ( (NOx purge).

Actually, the predetermined period is measured by a timer counter in the ECU 30, and the ECU 30 controls the valve opening time of the fuel injection valve 6, ie, the fuel injection time Tinj, to increase by a predetermined amount at each predetermined period. . As a result, the storage NOx catalyst 20a is regenerated and NOx is constantly maintained in a state capable of purifying NOx, and NOx purification is stably and continuously performed.

The predetermined period is set in advance based on the time when it is estimated that the NOx occluded in the occlusion type NOx catalyst 20a has reached the saturation amount during normal operation. It can also be estimated based on the traveling distance of the vehicle detected by the total 32. That is, the rich air-fuel ratio operation may be performed after traveling a predetermined distance.

In the present invention, the target air-fuel ratio is tailed from the lean air-fuel ratio to the rich air-fuel ratio and from the rich air-fuel ratio to the lean air-fuel ratio for the purpose of suppressing the fluctuation of the output torque during the NOx purging. Further, the fuel is injected (sub-injection) into the combustion chamber during the expansion stroke of the engine 1 in accordance with the tailing of the target air-fuel ratio (sub-injection means). Hereinafter, the air-fuel ratio switching control (rich spike control) according to the present invention will be described with reference to the time chart of FIG.
Here, the case where the target air-fuel ratio switches from the lean air-fuel ratio to the rich air-fuel ratio will be mainly described.

When the above-mentioned predetermined period is timed, FIG.
As shown in (2), at time A, an air-fuel ratio switching command is issued inside the ECU 30 (air-fuel ratio switching means), and the air-fuel ratio mode (A / F mode) is switched from the lean air-fuel ratio mode to the rich air-fuel ratio mode. As a result, the target air-fuel ratio (target A / F) switches from the lean air-fuel ratio to a predetermined rich air-fuel ratio (for example, A / F = 12). At this time, as shown in FIG. Then, the target air-fuel ratio is tailed as described above and gradually becomes a rich air-fuel ratio (air-fuel ratio switching means or air-fuel ratio control means). The degree (tilt) of the tailing, that is, the tailing coefficient is set in advance to such an extent that the output torque does not fluctuate.

Further, in accordance with the tailing, as shown in (c), when the engine 1 is in the expansion stroke, the fuel is injected from the fuel injection valve 6 in a sub-injection manner. In this sub-injection, as shown in (d), the overall air-fuel ratio (all A / F) becomes a predetermined rich air-fuel ratio (for example, A / F = 12) according to the degree of tailing of the target air-fuel ratio. Fuel is injected as follows. That is, in the sub-injection, the amount of fuel corresponding to the difference between the target air-fuel ratio changed by tailing and a predetermined rich air-fuel ratio (for example, A / F = 12) is equal to E.
The CU 30 calculates the amount of fuel, and the amount of fuel corresponding to the difference is injected from the fuel injection valve 6 so as to supplement the target air-fuel ratio that changes due to tailing. Note that the total A / F is constantly detected by the O ₂ sensor 18, and the timing of this sub-injection is arbitrary during the expansion stroke.

As described above, at the time of switching the air-fuel ratio, all the A / Fs finally become the predetermined rich air-fuel ratio (for example, A
/ F = 12), the sub-injection is not performed because a part of the sub-injected fuel burns due to the presence of residual O _{2 in} the combustion chamber, but is in an excessive fuel state. As in the case where the injection amount of the normal main injection is increased, H
Large amounts of C and CO are emitted.

That is, by performing the sub-injection, the CO required for NOx reduction starts to be supplied to the storage NOx catalyst 20a immediately after the point A at which the air-fuel ratio switching command is issued, and the NOx purge is delayed. It will be started immediately without any. If the NOx purge is started without delay as described above, the execution period of the NOx purge can be shortened as a result, whereby the influence of the NOx purge on the normal operation state of the internal combustion engine can be suppressed as small as possible.

When the sub-injection is performed in the expansion stroke as described above, the sub-injection additionally supplies fuel after the piston starts descending, and as shown in FIG. Is performed without substantially contributing to the in-cylinder pressure Pe, that is, the output torque of the engine 1. Therefore, the output torque of the engine 1 does not fluctuate carelessly due to the sub-injection.

When the sub-injection is performed in this manner, all the A / Fs instantaneously change to a predetermined rich air-fuel ratio (for example, A / F = 1).
2), the air-fuel ratio is the air-fuel ratio at which NOx is generated most (A / F = around 16) and the air-fuel ratio that releases the stored NOx but cannot reduce it sufficiently (A / F = 14.5)
(NO), and therefore, as shown in (f), the NOx amount does not fluctuate when the air-fuel ratio is switched, that is, NOx spike does not occur, and NOx is inadvertently discharged into the atmosphere. Nor. However, while the NOx purge is being performed, the NOx exhausted from the engine 1 cannot be processed by the storage NOx catalyst 20a, but during this time the air-fuel ratio is surely rich as described above. Since it is assumed that the air-fuel ratio is set, the three-way catalyst 2
By 0b, the purification process is favorably performed.

That is, in the exhaust gas purifying apparatus for a direct injection type internal combustion engine according to the present invention, when the NOx purge of the storage type NOx catalyst 20a is performed, the NOx purge is executed without changing the output of the engine 1 without changing the air-fuel ratio. Immediately after the issuance of the vehicle, the NOx emission can always be satisfactorily suppressed even when purging the NOx, while preventing the occupants of the vehicle from feeling uncomfortable such as torque shock. Becomes

When a predetermined period elapses after the target air-fuel ratio has become a predetermined rich air-fuel ratio (for example, A / F = 12) and the NOx purge has been performed, the target air-fuel ratio is changed to an air-fuel ratio switching command. Until the engine is stopped, tailing is performed from a predetermined rich air-fuel ratio toward a lean air-fuel ratio. In this case, the sub-injection is performed in the same manner as described above.

By the way, recently, a catalyst which easily converts HC into CO has been developed. As shown in FIG. 3, by providing such a catalyst 20c upstream of the occlusion type NOx catalyst 20a, a better effect can be obtained. can get. Examples of the catalyst that easily converts HC into CO include, for example, JP-A-6-22114.
No. 0 discloses this. Hereinafter, the HC
The operation and effect when the catalyst 20c that easily converts CO into CO will be described.

When the sub-injection is performed in the latter half of the expansion stroke when performing the sub-injection in the expansion stroke, most of the injected fuel is unburned fuel without being burned because the exhaust stroke is close. That is, it is discharged as HC. At this time, if the catalyst 20c is a catalyst that easily converts HC into CO, most of the HC discharged from the engine 1 without being burned is converted into CO. Then, the CO thus converted is favorably used for NOx purging in the storage NOx catalyst 20a.

That is, if a catalyst that easily generates CO is used and the sub-injection is performed in the latter half of the expansion stroke,
The NOx purge can be performed with more CO present than when the air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio only with the main injection or when the sub-injection is performed as in the above-described embodiment. NOx occluded in the tank can be reduced and removed almost completely at an early stage. Therefore, NOx
The purge time can be reduced as much as possible, and the influence of the NOx purge on the original operating state of the engine 1 can be further reduced.

In the above embodiment, the air-fuel ratio at the time of NOx purge is set to a predetermined rich air-fuel ratio (for example, A / F = 1).
Although 2) has been described, the predetermined rich air-fuel ratio may be changed as necessary. In the above embodiment,
Although the sub-injection amount is a fuel amount corresponding to a difference between a target air-fuel ratio that changes by tailing and a predetermined rich air-fuel ratio, the fuel amount is defined as an engine speed, an in-cylinder pressure Pe, A / N, an engine cooling water temperature, and an intake air amount. The correction may be made according to the air temperature, the catalyst temperature, the exhaust gas temperature, or the like. Thereby, the NOx purge can be performed even more favorably.

In the above-described embodiment, the NOx purge is performed during the lean air-fuel ratio operation and the sub-injection is performed. However, the NOx purge may be performed during the stoichiometric air-fuel ratio operation or the rich air-fuel ratio operation. The sub-injection may be performed in conjunction with this. Further, in the above embodiment, only the purging of the NOx stored in the storage NOx catalyst 20a has been described.
It can also be applied at the time of purging SOx stored in the x catalyst 20a. In other words, the SOx purge estimates the amount of SOx stored in the storage type NOx catalyst 20a, and when the SOx amount exceeds a predetermined amount, raises the catalyst temperature with an electric heater or the like to increase the air-fuel ratio from the lean air-fuel ratio. Although the air-fuel ratio is switched to the rich air-fuel ratio, the same sub-injection as described above may be performed when the air-fuel ratio is switched.

Thus, even when purging SOx, fluctuations in the output torque of the engine 1 can be suppressed.
It is possible to prevent x-spikes and prevent inadvertent emission of NOx. In the above embodiment, the main injection and the sub-injection are performed by one injection valve. However, the main injection and the sub-injection injection valves are provided, and the main injection and the sub-injection are respectively performed. The injection valve may be used.

[0044]

As described above in detail, according to the exhaust gas purifying apparatus for a direct injection type internal combustion engine of the first and second aspects of the present invention, the air-fuel ratio is gradually changed when the air-fuel ratio is switched in the regeneration of the catalyst. In addition, since the fuel is additionally supplied by the sub-injection means, the regeneration of the catalyst can be performed in a short period of time without fluctuation of the engine output torque. In addition, since the additional fuel is supplied in an air-fuel ratio range including an air-fuel ratio in which a large amount of NOx is generated or an air-fuel ratio in which a reducing agent capable of reducing NOx is reduced, the amount of NOx emission can be reduced.

According to the third aspect of the invention, during the control to the stoichiometric air-fuel ratio or the rich air-fuel ratio, the amount of fuel corresponding to the difference between the target air-fuel ratio related to the air-fuel ratio control and the predetermined rich air-fuel ratio is reduced. Since it is additionally supplied in the expansion stroke by the injection means,
The air-fuel ratio can be enriched without increasing the engine output torque to promote the release of NOx from the catalyst and the reduction of NOx, and therefore the catalyst can be regenerated without torque fluctuation.

[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 graph showing that the rich spike control according to the present invention is performed to perform NOx.
Target A / F and sub-injection amount when purging is performed and total A
6 is a time chart showing a relationship with / F and effects.

FIG. 3 is a schematic configuration diagram showing an exhaust gas purification device in a case where a catalyst that easily converts HC into CO is provided upstream of a storage NOx catalyst.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine body (in-cylinder injection type internal combustion engine) 6 Fuel injection valve 14 Exhaust pipe (exhaust passage) 18 O ₂ sensor 20a Storage type NOx catalyst 20b Three-way catalyst 20c Catalyst 30 Electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/08 F01N 3/24 R 3/20 3/28 301C 3/24 F02D 41/02 301A 3/28 301 B01D 53/36 ZAB F02D 41/02 301 101B

Claims (3)

[Claims] 1. An exhaust passage disposed in an exhaust passage of an internal combustion engine, the NO in the exhaust when the internal combustion engine is in a lean air-fuel ratio operating state.
a storage type NOx catalyst that stores x and reduces the stored NOx when in a stoichiometric air-fuel ratio operation or a rich air-fuel ratio operation state; and in any one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operation state. Main injection means for directly supplying fuel into the cylinder; and, during regeneration of the storage NOx catalyst, gradually changing the air-fuel ratio of the internal combustion engine between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio. Air-fuel ratio switching means for controlling the air-fuel ratio, and sub-injection means for additionally supplying fuel into the cylinder in an air-fuel ratio range including an air-fuel ratio where a large amount of NOx is generated during the air-fuel ratio control by the air-fuel ratio switching means. An exhaust purification device for a direct injection internal combustion engine, comprising: 2. An exhaust gas passage disposed in an exhaust passage of an internal combustion engine, the NOx being exhausted when the internal combustion engine is in a lean air-fuel ratio operating state.
a storage type NOx catalyst that stores x and reduces the stored NOx when in a stoichiometric air-fuel ratio operation or a rich air-fuel ratio operation state; and in any one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operation state. Main injection means for directly supplying fuel into the cylinder; and, during regeneration of the storage NOx catalyst, gradually changing the air-fuel ratio of the internal combustion engine between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio. Air-fuel ratio switching means for controlling the air-fuel ratio; and controlling the air-fuel ratio by the air-fuel ratio switching means, wherein the stored NOx is released from the storage-type NOx catalyst, but the reducing agent is small and cannot be sufficiently reduced. And an auxiliary injection means for additionally supplying fuel into the cylinder in an air-fuel ratio range including: 3. An exhaust passage disposed in an exhaust passage of the internal combustion engine, the NO in the exhaust when the internal combustion engine is in a lean air-fuel ratio operating state.
a storage type NOx catalyst that stores x and reduces the stored NOx when in a stoichiometric air-fuel ratio operation or a rich air-fuel ratio operation state; and in any one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operation state. Main injection means for supplying fuel directly into the cylinder, air-fuel ratio control means for controlling the air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio or the rich air-fuel ratio based on the engine operating state, and the air-fuel ratio control means During the control of the air-fuel ratio, an auxiliary fuel is additionally supplied into the cylinder during the expansion stroke of the internal combustion engine with an amount of fuel corresponding to the difference between the target air-fuel ratio controlled by the air-fuel ratio control means and a predetermined rich air-fuel ratio. An exhaust purification device for a direct injection internal combustion engine, comprising: an injection unit.