JP4435028B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a so-called oxygen poisoning purge technique for releasing oxygen adsorbed on a noble metal of a catalyst.

In a lean combustion engine such as an in-cylinder injection engine, in order to improve fuel consumption characteristics and exhaust characteristics, the engine is operated at a lean air-fuel ratio that is leaner than the stoichiometric air-fuel ratio (stoichiometric) in a predetermined operating range.
In such a lean combustion engine operation at a lean air-fuel ratio, the exhaust gas contains a large amount of oxygen. The oxygen is adsorbed on the noble metal of the catalyst, and when the oxygen is excessively adsorbed on the noble metal of the catalyst, the catalyst becomes a so-called oxygen poisoning state and the exhaust purification function is deteriorated.

In such an oxygen poisoned catalyst, the exhaust gas purifying function can be recovered by performing a so-called oxygen poisoning purge in which the adsorbed oxygen is desorbed by supplying a reducing agent with a rich or stoichiometric air-fuel ratio. Yes (see Patent Document 1).
JP 2002-364411 A

In the technique disclosed in Patent Document 1, if it is determined that the exhaust purification function of the catalyst is deteriorated due to the influence of oxygen poisoning, NOx occlusion, etc., the rich air-fuel ratio operation is performed to reduce the oxygen concentration in the exhaust. The catalyst is recovered.
However, since oxygen poisoning occurs relatively frequently, there is a problem that the fuel efficiency is greatly deteriorated when the rich air-fuel ratio operation is performed every time oxygen poisoning is detected.

  The present invention has been made to solve such problems, and an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can improve exhaust gas purification performance while suppressing deterioration of fuel consumption. There is.

In order to achieve the above object, in the exhaust gas purification apparatus for an internal combustion engine according to claim 1, the internal combustion engine is provided in a fuel injection means for directly injecting fuel into a combustion chamber of the internal combustion engine, and in an exhaust passage of the internal combustion engine. NOx in the exhaust gas is stored during lean air-fuel ratio operation, and the NOx catalyst that releases and stores the stored NOx during the theoretical air-fuel ratio operation or rich air-fuel ratio operation of the internal combustion engine, and the temperature of the NOx catalyst are detected Separately from the catalyst temperature detecting means, the oxygen poisoning state detecting means for detecting that the noble metal contained in the NOx catalyst has become a predetermined oxygen poisoning state, and the NOx occluded by the NOx catalyst being released and reduced. During the lean air-fuel ratio operation of the internal combustion engine, the oxygen poisoning state detecting means detects that the noble metal contained in the NOx catalyst has become a predetermined oxygen poisoning state. , By the fuel injection means, the main injection is performed in the intake stroke or compression stroke, and the expansion stroke or carried in the exhaust stroke and to perform the fuel injection by the auxiliary injection, the catalyst temperature detecting means for the fuel injection amount of sub-injection And an oxygen poisoning purge control means for controlling the temperature of the NOx catalyst detected by the above.

In other words, in an internal combustion engine having a NOx catalyst, in addition to releasing and reducing NOx stored by the NOx catalyst, when the NOx catalyst is oxygen-poisoned, the main injection performed in the intake stroke or the compression stroke, and the expansion stroke or exhaust By performing fuel injection by sub-injection performed in the stroke, an oxygen poisoning purge is performed by supplying an optimal reducing agent to the NOx catalyst by the sub-injection and desorbing oxygen adsorbed on the noble metal of the NOx catalyst. The fuel injection amount of the sub-injection of this oxygen poisoning purge is controlled according to the temperature of the NOx catalyst.

The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the oxygen poisoning purge control means is configured such that the higher the temperature of the NOx catalyst detected by the catalyst temperature detection means, the higher the fuel by the sub-injection. It is characterized by increasing the injection amount .

According to a third aspect of the present invention, there is provided an exhaust gas purification apparatus for an internal combustion engine according to the first or second aspect, further comprising ignition means for igniting in a combustion chamber of the internal combustion engine. The timing of the sub-injection is controlled so as not to contribute to the generation of torque, and the ignition timing of the main injection by the ignition means is controlled.
That is, in the oxygen poisoning purge , the sub injection timing and the main injection ignition timing are controlled so that the fuel of the sub injection does not contribute to the generation of torque.

According to a fourth aspect of the present invention, there is provided an exhaust purification apparatus for an internal combustion engine according to any one of the first to third aspects, wherein the NOx catalyst occludes the NOx stored during the sub-injection period by the oxygen poisoning purge control means. The period is shorter than the period during which the theoretical air-fuel ratio operation or the rich air-fuel ratio operation is performed.
That is, the period during which the oxygen poisoning purge is performed is shorter than the period of the NOx purge in which the NOx stored by the NOx catalyst is released and reduced.

According to the exhaust gas purification apparatus for an internal combustion engine according to claims 1 and 2 of the present invention using the above means, oxygen for desorbing oxygen adsorbed on the NOx catalyst separately from NOx purge for releasing and reducing NOx occluded by the NOx catalyst. By performing the poisoning purge, the exhaust purification performance of the NOx catalyst is always kept good, and the NOx purging is completed in a short period of time because it is possible to perform almost no oxygen poisoning purge when performing the NOx purge. Can do. Therefore, the time for performing the lean operation as a whole becomes longer, and the fuel consumption reduction by the lean operation can be increased.

Further, in the oxygen poisoning purge, since the main injection maintains a lean air-fuel ratio, fuel consumption due to the oxygen poisoning purge can be suppressed.
Further, the oxygen injection purge can be efficiently performed by controlling the fuel injection amount of the sub-injection according to the activation state of the NOx catalyst.
Thereby, exhaust purification performance can be improved while suppressing deterioration of fuel consumption.
According to the exhaust gas purification apparatus for an internal combustion engine of claim 3 , since the sub-injection timing and the main injection ignition timing are controlled so that the sub-injection during the oxygen poisoning purge does not contribute to the generation of torque. Torque shock due to poisoning purge can be suppressed.

According to the exhaust purification system 請 Motomeko 4, period for oxygen poisoning purge shorter than the time period for performing the NOx purge can be reduced fuel consumption as a whole.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
As shown in FIG. 1, an engine 1 (internal combustion engine) is a so-called cylinder in which a combustion plug 2 faces an ignition plug 4 (ignition means) for igniting and an injector 6 (fuel injection means) capable of directly injecting fuel. This is an internal injection type engine.

Further, the combustion chamber 2 communicates with an intake port 8 that extends substantially in the vertical direction of the engine 1 and an exhaust port 10 that extends substantially in the width direction of the engine 1.
The intake port 8 is provided with an intake valve 12 for connecting and blocking the combustion chamber 2 and the intake port 8, and the exhaust port 10 is provided with an exhaust valve 14 for connecting and blocking the combustion chamber 2 and the exhaust port 10. It has been.

The intake port 8 is connected to an intake manifold 16, and the exhaust port 10 is connected to an exhaust manifold 18.
The intake manifold 16 is provided with a throttle valve 17, and the throttle valve 17 is provided with a throttle sensor 17a for detecting the throttle opening.
On the other hand, the exhaust manifold 18 is connected to an exhaust pipe 20, and the exhaust pipe 20 is provided with an exhaust purification device 30.

Inside the exhaust purification device 30, a NOx catalyst 32 is provided upstream of the exhaust, and a three-way catalyst 34 is provided downstream of the exhaust.
Specifically, the NOx catalyst 32 has platinum (Pt), palladium (Pd), rhodium (Rh) or the like as a noble metal, and an alkali metal such as potassium (K), barium (Ba) or sodium (Na) as an occlusion material, Alkaline earth metal is employed, and when the engine 1 is performing a lean air-fuel ratio operation (hereinafter referred to as lean operation), NOx in the exhaust of the engine 1 is occluded and stoichiometric air-fuel ratio operation (hereinafter stoichiometric operation). And a so-called NOx purge function for releasing and reducing the stored NOx during a rich air-fuel ratio operation (hereinafter referred to as a rich operation).

The three-way catalyst 34 has any one of platinum (Pt), rhodium (Rh), palladium (Pd), copper (Cu), cobalt (Co), and silver (Ag) as a noble metal on the carrier, 1 has a function of oxidizing HC and CO in the exhaust gas and reducing NOx.
Further, the noble metals of the NOx catalyst 32 and the three-way catalyst 34 also have a function of adsorbing oxygen.

Further, a temperature sensor 36 (catalyst temperature detecting means) is provided at an exhaust inlet portion of the exhaust purification device 30.
Various devices and various sensors such as the ignition plug 4, the injector 6, the throttle valve 17, the throttle sensor 17a, and the temperature sensor 36 are ECU (electronic control unit) 40 (oxygen poisoning state detecting means, oxygen poisoning purge). Control means). The ECU 40 is based on information from various sensors such as the throttle sensor 17a and the temperature sensor 36, and various other devices such as the ignition timing by the spark plug 4, the fuel injection amount by the injector 6, the injection timing, the throttle opening of the throttle valve 17, etc. Perform operation control. In addition, a timer 40a is provided in the ECU 40, and the timer 40a measures the accumulated time of the lean operation of the engine 1.

The operation of the exhaust gas purification apparatus for an internal combustion engine according to the present invention configured as described above will be described below.
Referring to FIG. 2, a purge control routine executed by the ECU 40 in the exhaust gas purification apparatus for an internal combustion engine according to the present invention is shown in a flowchart, and will be described below based on the flowchart.

First, in step S1, it is determined whether or not the engine 1 is in a lean operation. If the determination result is false (No), the routine is exited because it is not necessary to perform the purge control. On the other hand, if the determination result is true (Yes), the process proceeds to step S2.
In step S2, the operating conditions of the engine 1 such as the accumulated time of the lean operation and the throttle opening are detected from the timer 40a and the throttle sensor 17a.

Next, in step S <b> 3, the temperature of the NOx catalyst 32 is detected from the temperature of the inlet portion of the exhaust purification device 30 detected by the temperature sensor 36.
Subsequently, in step S4, NOx purge conditions are determined.
The NOx purge condition is a condition for determining that the NOx occlusion amount of the NOx catalyst 32 is saturated. For example, here, the NOx occlusion amount is estimated based on the accumulated time of the lean operation detected in step S2, for example. Based on the temperature of the NOx catalyst 32 detected in step S3, a predetermined lean operation integration time is determined so that the NOx occlusion amount is saturated.

In step S5, it is determined whether or not the NOx purge condition determined in step S4 is satisfied, that is, whether or not the lean operation integrated time has reached a predetermined lean operation integrated time. If the determination result is false (No), that is, if the lean operation integration time has not yet reached the predetermined lean operation integration time, the process proceeds to step S6.
In step S6, oxygen poisoning purge conditions are determined.

  The oxygen poisoning purge condition is a condition in which oxygen is adsorbed on the noble metal contained in the NOx catalyst 32 and can be regarded as a predetermined oxygen poisoning state. For example, here, the intake air amount is determined from the throttle opening detected in step S2. Is calculated from the intake air amount, and a predetermined oxygen passage integrated amount is determined based on the temperature of the NOx catalyst 32 detected in step S3, so that a predetermined oxygen poisoning state is obtained. To decide.

  In step S7, it is determined whether or not the oxygen poisoning purge condition determined in step S6 is satisfied, that is, whether or not a predetermined oxygen passage integrated amount has been reached. When the determination result is false (No), that is, when the predetermined oxygen passage integrated amount has not been reached, the routine is exited. On the other hand, if the determination result is true (Yes), that is, if the predetermined oxygen poisoning state is reached and the oxygen poisoning purge needs to be performed, the process proceeds to step S8.

In step S8, the control content of the oxygen poisoning purge is determined.
Specifically, in the oxygen poisoning purge control, fuel injection is performed by main injection that injects fuel in the compression stroke while maintaining the lean air-fuel ratio in the lean operation, and sub-injection that injects fuel in the expansion stroke. Note that the deterioration of fuel consumption can be suppressed by making the air-fuel ratio of the main injection and the sub-injection as a whole lean air-fuel ratio.

  The period for performing the sub-injection and the fuel injection amount are determined based on the temperature of the NOx catalyst 32 detected in step S3. For example, when the temperature of the NOx catalyst 32 is high, the fuel injection amount by the sub-injection is determined. On the contrary, when the temperature of the NOx catalyst 32 is low, it is decreased, and when the temperature of the NOx catalyst is in an extremely low temperature, for example, when the engine 1 is idling, the secondary injection is not performed. Thus, by determining the fuel injection amount of the sub-injection according to the catalyst temperature, an efficient oxygen poisoning purge according to the active state of the NOx catalyst 32 becomes possible.

Further, the injection timing is set so that the secondary injection does not contribute to the generation of torque, and the fuel injection amount of the secondary injection and the ignition timing of the main injection are set.
In the next step S9, the oxygen poisoning purge control with the content determined in step S8 is executed, and the routine is exited.
By executing the oxygen poisoning purge control, the secondary injection is performed after the combustion by the main injection, and the NOx catalyst 32 and the three-way catalyst 34 are sufficiently supplied with reducing agents such as HC and CO by the secondary injection. Supplied. In the NOx catalyst 32 and the three-way catalyst 34 supplied with the reducing agent, the oxygen adsorbed on the noble metal is desorbed and the exhaust purification performance of the catalyst is restored. When the oxygen poisoning purge control is completed, the oxygen passing integrated amount is reset.

If the determination result of whether or not the NOx purge condition in step S5 is satisfied is true (Yes), the process proceeds to step S10.
In step S10, the content of NOx purge control for releasing and reducing NOx stored by the NOx catalyst 32 is determined.
Specifically, in the NOx purge control, fuel injection is performed by main injection that injects fuel during the intake stroke and sub-injection that injects fuel during the expansion stroke. However, the main injection and the sub-injection are operated so as to achieve a rich air-fuel ratio as a whole.

The period for performing the NOx purge and the fuel injection amounts of the main injection and the sub-injection are determined by the catalyst temperature detected in step S3. Since NOx is less likely to be reduced than oxygen, the period during which the NOx purge is performed is at least longer than the period during which the oxygen poisoning purge is performed.
In step S11, the NOx purge control having the content determined in step S10 is executed, and the routine is exited.

  By executing the NOx purge control, a reducing agent such as HC or CO is sufficiently supplied to the NOx catalyst 32 by the combustion by the rich air-fuel ratio main injection and the sub-injection. In the NOx catalyst 32 supplied with the reducing agent, the stored NOx is released and reduced, and the NOx storage function is restored. When the NOx purge control ends, the lean operation integration time and the oxygen passage integration amount by the timer 40a are reset.

Here, referring to FIG. 3, a time chart when the purge control in the present embodiment is performed is shown, and FIG. 4 is a time chart when the conventional general purge control is performed. Has been.
First, as shown in FIG. 4, in the conventional purge control, only the NOx purge is performed without performing the special oxygen poisoning purge. In such a control, the oxygen poisoning purge is performed simultaneously with the NOx purge. The period for performing the NOx purge is relatively long.

On the other hand, as shown in FIG. 3, when the purge control is performed in this embodiment, the NOx purge is performed, and several oxygen poisoning purges are performed during the next NOx purge.
In this way, by performing the oxygen poisoning purge between the NOx purges, the exhaust purification performance of the NOx catalyst 32 and the three-way catalyst 34 is always kept good. In addition, the NOx purge can be completed in a short time since almost no oxygen poisoning purge is required. Therefore, it is possible to lengthen the time for performing the lean operation as a whole, and to increase the fuel consumption reduction effect by the lean operation.

Further, in the oxygen poisoning purge in this embodiment, since the main injection maintains a lean air-fuel ratio, it is possible to suppress fuel consumption, and the sub-injection does not contribute to the generation of torque, so the oxygen poisoning purge is performed. Torque shock can also be prevented.
Thus, the exhaust gas purification apparatus for an internal combustion engine according to the present invention can improve the exhaust gas purification performance while suppressing deterioration of fuel consumption.

Although the description of the embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention is finished above, the embodiment is not limited to the above embodiment.
In the above embodiment, the NOx catalyst 32 is provided on the exhaust upstream side inside the exhaust purification device 30 and the three-way catalyst 34 is provided on the exhaust downstream side, but the configuration of the exhaust purification device 30 is not limited to this. Alternatively, a three-way catalyst may be provided on the exhaust upstream side, a NOx catalyst may be provided on the exhaust downstream side, and a three-way catalyst may be provided on the exhaust downstream side.

In the above embodiment, in the oxygen poisoning purge control, the overall air-fuel ratio of the main injection and the sub-injection is set to the lean air-fuel ratio, but it may be stoichiometric operation or rich operation. .
In the above embodiment, in the NOx purge control, the air-fuel ratio as a whole of the main injection and the sub-injection is set to the rich air-fuel ratio, but it may be stoichiometric operation. Furthermore, it is not necessary to perform sub injection.

In the above embodiment, in the oxygen poisoning purge control, the main injection is set to be performed in the compression stroke, but this may be performed in the intake stroke, and the sub-injection is set to be performed in the expansion stroke. However, this may be done in the exhaust stroke.
In the above embodiment, in the NOx purge control, the main injection is set to be performed in the intake stroke, but this may be performed in the compression stroke, and the sub-injection is set to be performed in the expansion stroke. However, this may be done in the exhaust stroke. Furthermore, it is not necessary to perform sub injection.

Further, a stoichiometric operation may be added to the latter half of the NOx purge control.
In the above embodiment, the catalyst temperature sensor 38 is provided at the exhaust inlet portion of the exhaust purification device 30. However, the present invention is not limited to this position, and any position can be used as long as the temperature of the NOx catalyst 32 can be detected. .
In the above embodiment, the oxygen poisoning purge condition is determined by the integrated amount of oxygen passage calculated from the amount of intake air. However, the present invention is not limited to this. For example, an oxygen passage is provided by providing an O ₂ sensor in the exhaust passage. You may judge from quantity.

  In the above-described embodiment, the NOx purge condition is determined by the accumulated lean operation time. However, the present invention is not limited to this. For example, a NOx sensor for detecting the NOx storage amount is provided to obtain the NOx storage amount. It doesn't matter.

1 is a schematic configuration diagram of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. 3 is a flowchart showing a purge control routine executed by an ECU in the exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a time chart when purge control in this embodiment is performed. It is a time chart when the conventional general purge control is performed.

Explanation of symbols

1 engine (internal combustion engine)
4 Spark plug (ignition means)
6 Injector (fuel injection means)
DESCRIPTION OF SYMBOLS 10 Exhaust port 17 Throttle valve 17a Throttle sensor 18 Exhaust manifold 20 Exhaust pipe 30 Exhaust purification device 32 NOx catalyst 34 Three-way catalyst 36 Temperature sensor (catalyst temperature detection means)
40 ECU (oxygen poisoning state detection means, oxygen poisoning purge control means)
40a timer

Claims (4)

Fuel injection means for directly injecting fuel into the combustion chamber of the internal combustion engine;
Provided in the exhaust passage of the internal combustion engine, and stores NOx in the exhaust during the lean air-fuel ratio operation of the internal combustion engine, and releases and reduces the stored NOx during the theoretical air-fuel ratio operation or the rich air-fuel ratio operation of the internal combustion engine NOx catalyst to
Catalyst temperature detecting means for detecting the temperature of the NOx catalyst;
Oxygen poisoning state detection means for detecting that the noble metal contained in the NOx catalyst is in a predetermined oxygen poisoning state;
In addition to releasing and reducing the NOx stored by the NOx catalyst, the noble metal contained in the NOx catalyst becomes a predetermined oxygen poisoning state by the oxygen poisoning state detecting means during the lean air-fuel ratio operation of the internal combustion engine. If it is detected with the by fuel injection means, the main injection is performed in the intake stroke or compression stroke, and the performing the fuel injection by the secondary injection performed the expansion stroke or exhaust stroke, the fuel injection sub injection An exhaust gas purifying apparatus for an internal combustion engine, comprising: an oxygen poisoning purge control means for controlling the amount in accordance with the temperature of the NOx catalyst detected by the catalyst temperature detection means .   2. The internal combustion engine according to claim 1, wherein the oxygen poisoning purge control means increases the fuel injection amount by the sub-injection as the temperature of the NOx catalyst detected by the catalyst temperature detection means is higher. Exhaust purification equipment. Furthermore, it comprises ignition means for igniting in the combustion chamber of the internal combustion engine,
The oxygen poisoning purge control means controls the timing of the sub-injection and controls the ignition timing of the main injection by the ignition means so that the fuel of the sub-injection does not contribute to the generation of torque. Item 3. An exhaust emission control device for an internal combustion engine according to Item 1 or 2 .   The period for performing the sub-injection by the oxygen poisoning purge control means is shorter than the period for performing the theoretical air-fuel ratio operation or the rich air-fuel ratio operation for releasing and reducing NOx stored by the NOx catalyst. Item 6. An exhaust purification device for an internal combustion engine according to any one of Items 1 to 3.

Images