JP3582582B2 - Exhaust purification system for in-cylinder injection internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for a direct injection type internal combustion engine, and more particularly to a NOx or SOx purging technique for an exhaust gas purification device provided with a storage type NOx catalyst.
[0002]
[Related background art]
When the internal combustion engine is in a predetermined operating state, the air-fuel ratio is controlled to a target value leaner (lean side) than the stoichiometric air-fuel ratio (value 14.7) (for example, a value 22 or more), and the fuel efficiency characteristics and the like of the engine are controlled. 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]
To solve this problem, in an oxygen excess state (oxidation atmosphere) by attaching NOx in the exhaust gas as nitrate X-NO ₃ occludes, the stored NOx with CO (carbon monoxide) over state (reduction atmosphere) It is possible to reduce the amount of NOx emitted into the atmosphere by using an exhaust purification catalyst having a characteristic of reducing to N ₂ (nitrogen) (carbonate X-CO ₃ is generated at the same time), that is, a so-called occlusion type NOx catalyst. Are known. 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. When the occlusion amount reaches the saturation amount, NOx in the exhaust gas is discharged to the atmosphere without being occluded by the catalyst.
[0004]
Therefore, before the storage amount of the storage-type 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). 2. Description of the Related Art An exhaust gas purifying apparatus configured to purify and reduce NOx (NOx purge) in an atmosphere (rich state) to regenerate an occluded NOx catalyst is known from Japanese Patent Application Laid-Open No. Hei 7-166913.
[0005]
In addition, the exhaust gas contains a sulfur component (S component), and when the storage NOx catalyst stores NOx, it also stores sulfur oxides (SOx). There is a problem that the purification efficiency of the fuel 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 period of time.
[0006]
[Problems to be solved by the invention]
By the way, when switching the air-fuel ratio from the lean air-fuel ratio to the stoichiometric air-fuel ratio or the rich air-fuel ratio, if the switching is performed and the fuel amount is increased at a stretch as in the latter publication, the in-cylinder pressure rises rapidly and the internal combustion engine There is a problem that the output torque temporarily largely fluctuates. 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 fluctuations in output torque.
[0007]
However, when the air-fuel ratio is tailed in this manner, 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. In this case, the amount of generated CO is small and the NOx purge is not performed favorably, 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.
[0008]
Further, NOx is most frequently generated when the air-fuel ratio is near the value 16, and 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 through the vicinity of the value 16. If the tailing period of the air-fuel ratio is long as described above, the period in which the air-fuel ratio is near the value 16 is inevitably increased, and a large amount of NOx is generated during the switching of the air-fuel ratio (this is called a NOx spike). There is also a problem that many NOx are emitted without being purified.
[0009]
Also, if the stored NOx amount is large, a large amount of NOx may be released from the storage type NOx catalyst when the air-fuel ratio is near the stoichiometric air-fuel ratio, but a reducing agent for reducing NOx near the stoichiometric air-fuel ratio may be used. (CO, HC, etc.) is small, and therefore, when the period in which the tailing is gentle and the vicinity of the stoichiometric air-fuel ratio is long as described above is long, the emission amount of the NOx is inevitably increased, whereby the NOx is discharged into the atmosphere. There is also a problem that the amount of NOx increases.
[0010]
The present invention has been made in order to solve such problems, and an object of the present invention is to provide an exhaust gas purification apparatus equipped with a storage NOx catalyst, in which the storage NOx catalyst is subjected to torque fluctuations or accidental NOx reduction. It is an object of the present invention to provide an exhaust gas purification device for an in-cylinder injection internal combustion engine that can be quickly regenerated without emission.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 regenerates a storage-type NOx catalyst provided in an internal combustion engine having a main injection means for directly supplying fuel into a cylinder in an intake stroke or a compression stroke. At this time, 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, and the air-fuel ratio including a large amount of NOx generated during the air-fuel ratio control is included. In the air-fuel ratio range, fuel is additionally supplied into the cylinder by the sub-injection means.
[0012]
According to the present invention, the air-fuel ratio gradually changes at the time of air-fuel ratio switching related to catalyst regeneration, and the fluctuation of the engine output torque due to the air-fuel ratio change is suppressed. On the other hand, fuel is additionally supplied into the cylinder by the sub-injection means to enrich the air-fuel ratio and promote the reduction of the storage type NOx catalyst, 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, and 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.
[0013]
According to a second aspect of the present invention, the air-fuel ratio of the internal combustion engine is gradually changed between a lean air-fuel ratio and a stoichiometric air-fuel ratio or a stoichiometric air-fuel ratio by the air-fuel ratio switching means during regeneration of the storage NOx catalyst provided in the internal combustion engine. On the other hand, in the air-fuel ratio range including the air-fuel ratio in which the reducing agent that can be used to reduce NOx released from the catalyst is reduced, the fuel is additionally supplied into the cylinder by the sub-injection means.
[0014]
According to the present invention, when the air-fuel ratio is switched in the catalyst regeneration, the air-fuel ratio gradually changes to suppress the fluctuation of the engine output torque, and fuel is additionally supplied into the cylinder by the sub-injection means, and the storage NOx catalyst Is promoted, and 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 used for NOx reduction is insufficient, fuel is additionally supplied by the sub-injection means, and the air-fuel ratio in the cylinder is reduced. The reducing agent passes through the air-fuel ratio range including the air-fuel ratio in which the amount of the reducing agent is insufficient, so that the NOx emission is significantly reduced.
[0015]
According to a third aspect of the present invention, the air-fuel ratio control is performed while the air-fuel ratio of the internal combustion engine having the main injection means for directly supplying the 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. The amount of fuel corresponding to the difference between the target air-fuel ratio and the predetermined rich air-fuel ratio is additionally supplied into the cylinder by the auxiliary injection means during the expansion stroke of the internal combustion engine.
[0016]
According to the present invention, when fuel is additionally supplied by the sub-injection means while the internal combustion engine is operated 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, NOx released from the catalyst can be sufficiently reduced, and thus regeneration of the catalyst is promoted. In addition, 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, and therefore, the catalyst regeneration is performed without causing torque fluctuation.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described 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 the configuration of the exhaust purification device according to the present invention will be described based on the drawing. Will be described.
[0018]
As shown in FIG. 1, as an engine body (hereinafter simply referred to as an engine) 1, for example, by switching a fuel injection mode (operation mode), fuel injection in an intake stroke or fuel injection in a compression stroke (main injection means) is performed. ) Is applicable to an in-cylinder injection spark ignition type 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). Is feasible.
[0019]
As shown in FIG. 1, an electromagnetic fuel injection valve 6 is attached to a cylinder head 2 of an engine 1 together with a spark plug 4 for each cylinder, whereby fuel can be directly injected into a combustion chamber. ing.
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 valve opening time of the fuel injection valve 6, that is, the fuel injection time Tinj.
[0020]
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.
[0021]
The in-cylinder injection type engine 1 is already known, and the details of its configuration will not be described 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. . The exhaust pipe 14 is provided with an O ₂ sensor 18. The O ₂ sensor 18 mainly detects the air-fuel ratio A / F in the combustion chamber based on the amount of O ₂ in the exhaust gas.
[0022]
The exhaust purification catalyst device 20 includes two catalysts, a storage NOx catalyst 20a and a three-way catalyst 20b. The three-way catalyst 20b is disposed downstream of the storage NOx catalyst 20a. ing.
The storage NOx catalyst 20a has a function of temporarily storing NOx in an oxidizing atmosphere and reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere in which CO is present. More 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.
[0023]
Further, an ECU (electronic control unit) 30 including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, and the like), a central processing unit (CPU), a timer counter, and the like is installed. Comprehensive control of the exhaust gas purifying apparatus according to the present invention, including the method 1, is performed. The input side of the ECU 30, various sensors such as O ₂ sensor 18 described above are connected, the detection information from these sensors is input. Further, a distance meter 32 for detecting a traveling distance of the vehicle is connected to the input side.
[0024]
On the other hand, the output side is connected to the above-described fuel injection valve 6, the ignition coil 8, and the like. The fuel injection valve 6, the ignition coil 8, and the like are connected to a fuel calculated based on detection information from various sensors. The optimum values such as the injection amount and the ignition timing are output. As a result, an appropriate amount of fuel is injected from the fuel injection valve 6, and ignition is performed by the ignition plug 4 at an appropriate timing.
[0025]
Next, the operation of the exhaust gas purification apparatus according to the present invention configured as described above will be described. Here, a case will be described as an example where the engine 1 performs fuel injection (main injection) in the compression stroke and operates at a lean air-fuel ratio.
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 NOx catalyst 20a and the three-way catalyst 20b are arranged in series, and the storage-type NOx catalyst 20a purifies NOx because the three-way catalyst 20b cannot purify NOx. become. Therefore, not only HC and CO but also NOx is almost completely purified without leakage as exhaust gas purification characteristics.
[0026]
However, for the occlusion-type NOx catalyst 20a, since the NOx occluding an oxidizing atmosphere decreases the NOx occlusion capacity reaches the saturation amount, I'll removed by reduction to N ₂ and the like in a reducing atmosphere as a NOx obtained by suction storehouse above There is a need.
Therefore, in the exhaust gas purification 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 temporarily increased at a predetermined cycle. A rich air-fuel ratio operation is performed for a predetermined period of time (this is referred to as a rich spike), thereby forcibly generating a CO excess state, that is, a reducing atmosphere, in the storage NOx catalyst 20a, and releasing the stored NOx to reduce and remove it ( (NOx purge).
[0027]
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, that is, 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 kept in a state where NOx can be purified at all times, and NOx purification is stably and continuously performed.
[0028]
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 detected travel distance of the vehicle. In other words, the rich air-fuel ratio operation may be performed after traveling a predetermined distance.
[0029]
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 output torque fluctuation during the NOx purging. Further, 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.
[0030]
When the predetermined period is counted, as shown in FIG. 2A, an air-fuel ratio switching command is issued inside the ECU 30 at the time A (air-fuel ratio switching means), and the air-fuel ratio mode (A / F mode) becomes lean. The mode is switched from the 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.
[0031]
Further, in accordance with the tailing, the fuel is injected from the fuel injection valve 6 when the engine 1 is in the expansion stroke, as shown in FIG.
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, an 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 calculated in the ECU 30, and the amount corresponding to this difference is calculated. Is injected from the fuel injection valve 6 to make up for the target air-fuel ratio that changes due to tailing. Note that the entire A / F is constantly detected by the O ₂ sensor 18, also the timing of the sub injection is arbitrary as long as during the expansion stroke.
[0032]
As described above, when the sub-injection is performed such that the total A / F finally becomes a predetermined rich air-fuel ratio (for example, A / F = 12) in the expansion stroke at the time of switching the air-fuel ratio, a part of the sub-injected fuel is Burns due to the presence of residual O _{2 in} the combustion chamber, but because of the fuel excess, a large amount of HC and CO is emitted as in the case where the injection amount of the normal main injection without performing the sub-injection is increased.
[0033]
In other words, 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 promptly performed without delay. Will be started.
If the NOx purge is started without delay, 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.
[0034]
By the way, when the sub-injection is performed in the expansion stroke as described above, the sub-injection additionally supplies the fuel after the piston starts descending. Therefore, as shown in FIG. Pe, that is, with little contribution to the output torque of the engine 1. Therefore, the output torque of the engine 1 is not inadvertently changed by the sub-injection.
[0035]
Further, when the sub-injection is performed in this manner, all the A / F instantaneously becomes a predetermined rich air-fuel ratio (for example, A / F = 12), and thus the air-fuel ratio (A / F) at which the NOx is generated most is the air-fuel ratio. = 16) and the air-fuel ratio that releases the stored NOx but cannot be reduced sufficiently (A / F = 14.5) does not stay. Therefore, as shown in (f), when the air-fuel ratio is switched, There is no fluctuation in the NOx amount, that is, no NOx spike, and no inadvertent emission of NOx into the atmosphere. 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 the air-fuel ratio is set, NOx is favorably purified by the three-way catalyst 20b.
[0036]
That is, in the exhaust gas purifying apparatus for a direct injection internal combustion engine according to the present invention, when performing NOx purging of the storage type NOx catalyst 20a, an air-fuel ratio switching command is issued for the NOx purging without fluctuation of the output of the engine 1. Immediately after the start, it is possible to carry out satisfactorily immediately, so that the occupants of the vehicle do not feel uncomfortable, such as torque shock, and it is possible to always properly suppress NOx emission even during NOx purging.
[0037]
Note that 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 air-fuel ratio switching command for the target air-fuel ratio is stopped. Up to this point, 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.
[0038]
By the way, recently, a catalyst that easily converts HC into CO has been developed. As shown in FIG. 3, by providing such a catalyst 20c upstream of the occluded NOx catalyst 20a, a better effect can be obtained. As a catalyst which easily converts HC into CO, there is, for example, a catalyst disclosed in JP-A-6-221140.
Hereinafter, the operation and effect when the catalyst 20c that easily converts the HC into CO will be described.
[0039]
If the sub-injection is performed in the latter half of the expansion stroke when performing the sub-injection in the expansion stroke, almost all of the injected fuel will not be burned and the unburned fuel, that is, HC Will be discharged as it is.
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.
[0040]
In other words, when the catalyst that easily generates CO is used and the sub-injection is performed in the latter half of the expansion stroke, the air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio only by the main injection, or as in the above-described embodiment. The NOx purge can be performed with more CO present than in the case of performing the sub-injection, and the NOx stored in the storage type NOx catalyst 20a can be reduced and removed almost completely at an early stage. Therefore, the time of the NOx purge can be shortened as much as possible, and the influence of the NOx purge on the original operating state of the engine 1 can be further reduced.
[0041]
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 = 12). However, the predetermined rich air-fuel ratio may be changed as needed. .
Further, in the above embodiment, the sub-injection amount is the fuel amount corresponding to the difference between the target air-fuel ratio changing by tailing and the predetermined rich air-fuel ratio. However, the fuel amount is used as the engine speed, the in-cylinder pressure Pe, A / The correction may be made according to N, engine cooling water temperature, intake air temperature, catalyst temperature, exhaust gas temperature, and the like. As a result, the NOx purge can be performed more favorably.
[0042]
In the above 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. At the same time, the sub-injection may be performed.
In the above embodiment, only the purging of the NOx stored in the storage NOx catalyst 20a has been described. However, the present invention can be applied to the purge of the SOx stored in the storage NOx catalyst 20a. That is, in purging SOx, the amount of SOx stored in the storage NOx catalyst 20a is estimated, and when the amount of SOx exceeds a predetermined amount, the catalyst temperature is increased by an electric heater or the like to increase the air-fuel ratio from the lean air-fuel ratio. Although the switching to the rich air-fuel ratio is performed, the same sub-injection as described above may be performed at the time of switching the air-fuel ratio.
[0043]
Thus, even when purging SOx, fluctuations in the output torque of the engine 1 can be suppressed, so-called NOx spikes can be prevented, and unintentional emission of NOx can be prevented.
Further, in the above embodiment, the main injection and the sub-injection are performed by one injection valve, but the main injection and the sub-injection injection valves are provided respectively, and the main injection and the sub-injection are respectively performed. The injection valve may be used.
[0044]
【The invention's effect】
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 for the catalyst regeneration, and the sub-injection means is used. As a result, the catalyst can be regenerated in a short period of time without causing fluctuations in 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.
[0045]
In 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 supplied by the sub-injection means. Since the fuel is additionally supplied in the expansion stroke, 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 thus the catalyst can be regenerated without torque fluctuation. .
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an exhaust purification device for a direct injection internal combustion engine according to the present invention.
FIG. 2 is a time chart showing the relationship between the target A / F and the sub-injection amount and the total A / F when the rich spike control according to the present invention is performed and the NOx purge is performed, and the effect thereof.
FIG. 3 is a schematic configuration diagram illustrating an exhaust gas purification device in the case where a catalyst that easily converts HC into CO is provided upstream of a storage NOx catalyst.
[Explanation of symbols]
1. Engine body (in-cylinder injection 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)

Claims (3)

It is disposed in an exhaust passage of the internal combustion engine, and stores NOx in exhaust gas when the internal combustion engine is in a lean air-fuel ratio operation state, and reduces the stored NOx when the internal combustion engine is in a stoichiometric air-fuel ratio operation state or a rich air-fuel ratio operation state. A storage-type NOx catalyst,
Main injection means for supplying fuel directly into the cylinder in one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operating state;
Air-fuel ratio switching means for controlling the air-fuel ratio of the internal combustion engine to gradually change between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio during regeneration of the storage NOx catalyst;
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 control of the air-fuel ratio by the air-fuel ratio switching means;
An exhaust purification device for a direct injection internal combustion engine, comprising: It is disposed in an exhaust passage of the internal combustion engine, and stores NOx in exhaust gas when the internal combustion engine is in a lean air-fuel ratio operation state, and reduces the stored NOx when the internal combustion engine is in a stoichiometric air-fuel ratio operation state or a rich air-fuel ratio operation state. A storage-type NOx catalyst,
Main injection means for supplying fuel directly into the cylinder in one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operating state;
Air-fuel ratio switching means for controlling the air-fuel ratio of the internal combustion engine to gradually change between the lean air-fuel ratio and the stoichiometric air-fuel ratio or the rich air-fuel ratio during regeneration of the storage NOx catalyst;
During the control of the air-fuel ratio by the air-fuel ratio switching means, the stored NOx is released from the storage-type NOx catalyst, but the fuel is supplied to the cylinder in an air-fuel ratio region including an air-fuel ratio including an air-fuel ratio that is small in reducing agent and cannot be sufficiently reduced. Auxiliary injection means for additionally supplying
An exhaust purification device for a direct injection internal combustion engine, comprising: It is disposed in an exhaust passage of the internal combustion engine, and stores NOx in exhaust gas when the internal combustion engine is in a lean air-fuel ratio operation state, and reduces the stored NOx when the internal combustion engine is in a stoichiometric air-fuel ratio operation state or a rich air-fuel ratio operation state. A storage-type NOx catalyst,
Main injection means for supplying fuel directly into the cylinder in one of an intake stroke and a compression stroke of the internal combustion engine based on an engine operating state;
Air-fuel ratio control means for controlling an air-fuel ratio of the internal combustion engine to the stoichiometric air-fuel ratio or the rich air-fuel ratio based on an engine operating state;
During the control of the air-fuel ratio by the air-fuel ratio control means, 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 is supplied to the cylinder during the expansion stroke of the internal combustion engine. Sub-injection means for additionally supplying into the
An exhaust purification device for a direct injection internal combustion engine, comprising:

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