JPH10299459A - Exhaust gas purifying device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely diagnose deterioration of a catalyst due to smoke and to restore catalyst performance by increasing a catalyst inlet temperature when smoke deterioration occurs, in an engine to effect stratification combustion. SOLUTION: A decision value to indicate the degree of deterioration due to smoke of a catalyst according to an engine load, an engine rotation speed, or a catalyst inlet temperature is set, and the decision value is integrated in order, (S3). A fluctuation frequency of oxygen concentrations in upper stream and downstream of the catalyst is compared to diagnose the deterioration of the catalyst (S1). When deterioration of the catalyst is diagnosed through the diagnosis, by comparing an integrated value Re of a decision value and a given value with each other, the deterioration of the catalyst is diagnosed to be caused by accumulation of smoke or not (S4). When smoke deterioration is diagnosed, stratification combustion and uniform lean combustion are prohibited and a catalyst inlet temperature is increased and catalyst performance is restored (S6) through separation and burning of smoke accumulated on the catalyst.

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 an internal combustion engine, and more particularly, to a technique for diagnosing deterioration of an exhaust gas purifying catalyst due to smoke and recovering the conversion performance of the catalyst when smoke deterioration occurs. About.

[0002]

2. Description of the Related Art In recent years, a direct injection type internal combustion engine (in-cylinder injection type internal combustion engine) for directly injecting fuel into a cylinder has been developed. In the direct injection type internal combustion engine, stratified combustion is performed in a low-load, low-speed region to enable combustion at an ultra-lean air-fuel ratio (for example, an air-fuel ratio of about 25 to 50). Smoke is likely to be produced due to the formation of a rich mixture around the spark plug.Fuel is also likely to adhere to the piston and the combustion chamber wall surface because the fuel is directly injected into the cylinder, and the deposited fuel will diffuse and burn. As a result, the wick remains and is discharged as smoke, so that there is a tendency that the amount of smoke discharged is larger than in homogeneous combustion.

[0003] The smoke discharged during the stratified combustion accumulates on the exhaust gas purifying catalyst. However, when the exhaust gas temperature increases due to the high-load, high-speed side and homogeneous combustion, the exhaust gas accumulates on the catalyst. The smoke is detached and burned. However, if stratified combustion at a low load and a low engine speed is continued for a long time, the amount of smoke deposited increases, and the conversion of the catalyst is reduced due to the poisoning of the smoke, and the exhaust emission is deteriorated. I will. Therefore, conventionally, when stratified combustion continues for a predetermined time or longer, the smoke (carbon) generated during the stratified combustion is burned off by inhibiting the stratified combustion and forcibly executing the homogeneous combustion ( JP-A-63-138120).

[0004]

However, the deposition of smoke on the catalyst during the stratified combustion does not proceed at a constant rate, but the deposition tends to proceed as the exhaust gas temperature (catalyst inlet temperature) is lower. Therefore, if the stratified combustion continues for a predetermined time or more, smoke that deteriorates the conversion performance does not always accumulate on the catalyst, and as described above, when the stratified combustion is continued for a predetermined time or more, the combustion is forcibly switched to the homogeneous combustion. In this case, although the amount of smoke deposited is small and sufficient conversion performance can be exhibited, forcible switching to homogeneous combustion is performed, which may lead to deterioration of fuel consumption and deterioration of exhaust emission.

[0005] Further, if the time allowed for the continuation of stratified combustion is lengthened in order to avoid unnecessary switching to homogeneous combustion, smoke is accumulated to reduce the conversion performance of the catalyst. Could be left unchecked and degrade exhaust emissions. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an exhaust gas purifying apparatus capable of diagnosing a state of deterioration of a catalyst due to smoke and recovering the conversion performance of the catalyst when deterioration due to smoke is determined. The purpose is to:

[0006]

An exhaust gas purifying apparatus for an internal combustion engine according to the present invention is configured as shown in FIG. In FIG. 1, a catalyst is provided in an exhaust system of an internal combustion engine to purify exhaust gas.

The deterioration judgment value storage means stores in advance a judgment value indicating the degree of deterioration of the catalyst due to smoke for each operating condition of the engine, and the operating condition detecting means detects the operating condition of the engine. Then, the judgment value accumulating means accumulates the judgment value retrieved from the deterioration judgment value storage means according to the operating condition detected by the operating condition detecting means.

Here, the smoke deterioration diagnosis means diagnoses the deterioration state of the catalyst due to smoke based on the judgment value integrated by the judgment value accumulation means. Since the degree of deterioration due to smoke (the amount of smoke deposition) differs depending on the operating conditions, the degree of deterioration for each operating condition is determined in advance and stored as a determination value. Integrate the judgment value of each
When the integration result exceeds an allowable level, it is estimated that smoke enough to lower the conversion performance is deposited on the catalyst.

In the invention according to the second aspect, the deterioration determination value storage means allocates a determination value indicating the degree of deterioration for each of a plurality of operating regions classified according to an engine load and an engine rotation speed as the operating conditions. The stored map is configured to be stored. The degree of smoke deposition on the catalyst correlates with the exhaust gas temperature, and the lower the temperature of the exhaust gas, the easier the deposition. Therefore, the determination value is stored in accordance with the engine load and the engine speed correlated with the exhaust gas temperature.

In the invention according to claim 3, the judgment value is:
The configuration is set such that the lower the rotation speed and the lower the load, the greater the degree of deterioration. Since the exhaust temperature becomes lower and the amount of smoke increases as the rotation speed and the load decrease, the judgment value is stored in accordance with the tendency. In the invention according to claim 4, the combustion system of the engine is switched between stratified combustion and homogeneous combustion, and the deterioration determination value storage means stores a determination value according to the engine load and the engine speed. As the map, the determination value map for stratified lean combustion and the determination value map for homogeneous lean combustion are stored, and the determination value integrating means selects a map to be referred to according to the combustion method, and It is configured to search the judgment value.

Since the degree of smoke deterioration differs between homogeneous lean combustion and stratified lean combustion, a map for referencing a judgment value is provided for each combustion method, and the judgment value is determined with reference to a map corresponding to the combustion method at that time. Let me search.
In the invention according to claim 5, the deterioration determination value storage means includes:
A determination value indicating the degree of deterioration is stored according to a catalyst inlet exhaust temperature as the operating condition.

As described above, since the deposition of smoke on the catalyst is greatly affected by the exhaust gas temperature, particularly, the exhaust gas temperature at the catalyst inlet, the judgment value is stored in advance in accordance with the catalyst inlet exhaust temperature, The judgment value is set according to the inlet temperature. In the invention according to claim 6, as shown by the dotted line in FIG. 1, first and second oxygen sensors provided respectively on the upstream side and the downstream side of the catalyst to detect the oxygen concentration in the exhaust gas, A catalyst deterioration diagnosing means for diagnosing the deterioration state of the catalyst based on the fluctuation frequency of the oxygen concentration detected by the oxygen sensor and the fluctuation frequency of the oxygen concentration detected by the second oxygen sensor, The smoke deterioration diagnosing means diagnoses the deterioration state of the catalyst due to smoke on the premise that the catalyst deterioration state is determined by the catalyst deterioration diagnosing means.

The deterioration of the conversion performance of the catalyst can be judged as a decrease in the oxygen storage capacity, and the fluctuation in the oxygen concentration on the upstream side of the catalyst causes a response delay due to the fluctuation in the oxygen concentration on the upstream side of the catalyst. Decreases, the response delay decreases. Therefore, by determining the variation frequency of the oxygen concentration in each of the upstream and downstream of the catalyst and comparing this, the decrease in the oxygen storage capacity of the catalyst and, consequently, the decrease in the conversion performance are diagnosed. Is diagnosed on the basis of the determination value as to whether or not the cause is due to the accumulation of smoke.

According to the seventh aspect of the present invention, as shown by a dotted line in FIG. 1, when the smoke deterioration diagnosis means determines that the catalyst has deteriorated due to smoke, combustion at an air-fuel ratio equal to or lower than a predetermined value is forcibly performed. In this case, the catalyst deterioration recovery means is provided for the purpose. When it is determined that the catalyst has deteriorated due to the accumulation of smoke, the combustion is forcibly performed at an air-fuel ratio at which the smoke can be desorbed and burned, thereby recovering the conversion performance of the catalyst.

According to the present invention, the combustion system of the engine is switched between stratified combustion and homogeneous combustion, and the catalyst deterioration recovery means performs homogeneous combustion at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio. The configuration was made to force it. In such a configuration, when deterioration due to smoke of the catalyst is determined,
The stratified combustion is prohibited, and the homogeneous lean combustion is also prohibited. The homogeneous combustion is performed at an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio, so that the smoke deposited on the catalyst is desorbed and burned.

[0016]

According to the first aspect of the present invention, there is an effect that the deterioration state due to the accumulation of smoke on the catalyst can be accurately diagnosed in accordance with the difference in the degree of deterioration depending on the operating conditions. According to the second and third aspects of the present invention, it is possible to determine whether the exhaust gas temperature is low and smoke is easily deposited based on the engine load and the engine rotational speed, thereby diagnosing deterioration of the catalyst due to smoke. There is.

According to the fourth aspect of the present invention, there is an effect that it is possible to accurately diagnose the deterioration of the catalyst due to smoke in accordance with the difference in the degree of deterioration between the homogeneous lean combustion and the stratified lean combustion. According to the fifth aspect of the present invention, it is possible to determine a condition under which smoke is likely to accumulate from the exhaust gas temperature at the catalyst inlet and diagnose the deterioration of the catalyst due to smoke with high accuracy.

According to the sixth aspect of the present invention, it is possible to diagnose whether the conversion performance is low as the oxygen storage capacity of the catalyst is low and then to determine whether the cause is due to the accumulation of smoke. This has the effect of avoiding erroneous diagnosis of smoke deterioration in a state where the conversion performance (oxygen storage capacity) has not actually decreased.

According to the seventh and eighth aspects of the present invention, catalyst deterioration due to smoke accumulation is diagnosed accurately, and when smoke deterioration occurs, combustion at a lean air-fuel ratio is prohibited to reduce exhaust gas temperature. Since the increase is intended, there is an effect that the smoke deterioration of the catalyst can be accurately recovered.

[0020]

Embodiments of the present invention will be described below. FIG. 2 is a system configuration diagram of an internal combustion engine to which the exhaust emission control device according to the present invention is applied. In each cylinder of the internal combustion engine 1, an electromagnetic fuel injection valve 2 for directly injecting fuel into a combustion chamber is provided. And an air-fuel mixture is formed in the cylinder by the fuel injected from the fuel injection valve 2. That is, the engine 1 in the present embodiment is a so-called direct injection internal combustion engine (in-cylinder injection internal combustion engine).

The fuel injection valve 2 injects fuel according to an injection control signal from the control unit 3. In the exhaust passage 9 of the engine 1, oxidation of HC and CO in exhaust gas and N
A three-way catalyst 4 (catalyst for purifying exhaust gas) for simultaneously performing the reduction of Ox is disposed, and a first and a second sensor for detecting the oxygen concentration in the exhaust gas are respectively provided upstream and downstream of the three-way catalyst 4. Oxygen sensors 5 and 6 are arranged.

The control unit 3 receives the detection signals from the first and second oxygen sensors 5 and 6, and receives a water temperature sensor 10 for detecting a cooling water temperature of the engine as operating condition detecting means. Detection signals from an air flow meter 12 for detecting an intake air flow rate on the upstream side of a throttle valve 11 interposed in the passage 8, a rotation speed sensor 13 for detecting a rotation speed of the engine, and the like are also input.

The control unit 3
Referring to a target air-fuel ratio map as shown in FIG. 3, a target air-fuel ratio corresponding to the target torque Tq and the engine speed Ne at that time is set, and stratified combustion is performed in a low load and low speed range. In other operating regions, a homogeneous combustion region is performed. In the homogeneous combustion region, the target air-fuel ratio is controlled to be lean, stoichiometric (stoichiometric air-fuel ratio), and rich. When the stoichiometric (stoichiometric air-fuel ratio) is set to the target air-fuel ratio, the target air-fuel ratio is determined based on the detection signal of the first oxygen sensor 5. Then, the air-fuel ratio feedback control for performing the feedback correction of the fuel injection amount so as to make the actual air-fuel ratio coincide with the stoichiometric air-fuel ratio is executed.

In the meantime, smoke is likely to be generated during lean combustion, particularly during lean combustion in stratified operation, and this smoke may accumulate on the three-way catalyst 4 and temporarily lower the conversion performance. As shown in the flowcharts of FIGS. 4 to 8, the catalyst deterioration due to the smoke is diagnosed, and when the smoke deterioration occurs, the conversion performance of the catalyst is restored.

FIG. 4 is a flowchart showing a main routine. First, in S1, the first and second oxygen sensors 5 and 5 are used.
By using 6 to diagnose whether or not the oxygen storage capacity of the three-way catalyst 4 has decreased, catalyst deterioration is diagnosed.
This step S1 corresponds to catalyst deterioration diagnosis means. In S2, the result of the diagnosis is determined, and if the deterioration of the three-way catalyst 4 has been diagnosed, the process proceeds to S3 to determine whether the catalyst deterioration is due to the accumulation of smoke. Setting the value and integrating the judgment value,
In the next S4, a diagnosis of deterioration due to smoke is made based on the integrated value Re of the smoke deterioration determination value.

The step S3 corresponds to the judgment value storage means, and the step S4 corresponds to the smoke deterioration diagnosis means. As will be described later, a map for searching for a deterioration determination value is stored in the control unit 3 in advance, and the memory of the control unit 3 corresponds to a deterioration determination value storage unit. Note that, for convenience, the process proceeds to S3 only when the deterioration is determined in S2, but in practice, the setting and integration of the deterioration degree determination value are performed regardless of the determination in S2. .

At S5, the result of the diagnosis of the smoke deterioration is determined. When the occurrence of the smoke deterioration is diagnosed, the routine proceeds to S6, where the exhaust gas temperature is determined so as to remove and burn out the smoke deposited on the three-way catalyst 4. Is prohibited, stratified combustion and homogeneous lean combustion are prohibited, and only homogeneous combustion at a stoichiometric or rich air-fuel ratio is forcibly performed. Step S6 corresponds to a catalyst deterioration recovery unit.

The deterioration and recovery of the three-way catalyst 4 due to the smoke show a correlation as shown in FIGS. 9 and 10 with respect to the catalyst inlet temperature. When the catalyst inlet temperature is low, the deterioration due to the smoke of the catalyst proceeds, and If the catalyst inlet temperature is high, the deterioration due to smoke does not progress, and conversely, the smoke deposited up to that time is desorbed and burned, so that the catalyst performance can be recovered. Therefore, when a diagnosis of smoke deterioration is made, stratified combustion and lean homogeneous combustion are prohibited in order to secure a high catalyst inlet temperature, and the catalyst performance is restored.

In S7, it is determined whether the conversion performance of the three-way catalyst 4 has actually been recovered by the prohibition of the stratified combustion and the lean homogeneous combustion. Diagnosis is made by using
Proceeding to 8, the deterioration flag and the integrated value Re are reset, and in S9, the prohibition of the stratified combustion and the lean homogeneous combustion is released, and the normal control state is returned.

The flowchart of FIG. 5 shows the details of the above S1. In S11, the cooling water temperature TW is read. In S12, it is determined whether or not the read cooling water temperature TW is equal to or higher than a predetermined temperature T1, and if it is equal to or higher than the predetermined temperature T1, the process proceeds to S13. In S13, it is determined whether or not the current state is in the air-fuel ratio feedback control region. The air-fuel ratio feedback control region is an operation region where the target air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric).

When the air-fuel ratio feedback control is being performed, the process proceeds to S14, where the inversion frequency f1 of the first oxygen sensor 5 is read, and in S15, the inversion frequency f2 of the second oxygen sensor 6 is read. The inversion frequencies f1 and f2 are:
The graph shows the oxygen concentration fluctuation caused by repeating the rich / lean state around the target air-fuel ratio based on the air-fuel ratio feedback control.

At S16, the read inversion frequencies f1,
The inversion frequency ratio fr = f2, f1 is calculated based on f2. In S17, it is determined whether or not the inversion frequency ratio fr is equal to or more than a predetermined value fra. If the inversion frequency ratio fr is equal to or more than the predetermined value fra, it is determined that the catalyst has deteriorated. Is set to 1. If the inversion frequency ratio fr is less than the predetermined value fra, it is considered that the catalyst has not deteriorated, and the routine proceeds to S19, where 0 is set to the deterioration determination flag F1.

At S2, it is determined whether or not the three-way catalyst 4 has deteriorated, based on the determination of the deterioration determination flag F1. When the conversion performance of the three-way catalyst 4 is reduced,
When the oxygen storage capacity is reduced and the oxygen storage capacity is reduced, the fluctuation frequency of the oxygen concentration on the downstream side approaches the fluctuation frequency of the oxygen concentration on the upstream side of the catalyst 4, so that the reversal frequency ratio fr deteriorates. The value increases as the process proceeds (see FIG. 11). Therefore, when the reversal frequency ratio fr is equal to or greater than the predetermined value fra, it is determined that the oxygen storage capacity has decreased, and thus the deterioration of the three-way catalyst 4 is determined.

However, even if deterioration of the three-way catalyst 4 is determined by the above-mentioned diagnosis, the cause is not limited to the accumulation of smoke. Therefore, as shown in the flowcharts of FIGS. 6 and 7, it is determined whether or not the current catalyst deterioration state is due to smoke accumulation. The flowchart of FIG. 6 shows the details of S3 in detail.
First, in S31, the deterioration degree integrated value Re up to the previous time is read, and in S32, it is determined whether or not the stratified operation is being performed.

If the vehicle is in stratified operation, S33
Then, referring to the map of the deterioration degree determination value Srmn stored in advance corresponding to during the stratification operation (stratified lean combustion), the deterioration degree determination value Srm corresponding to the current operation condition is obtained.
Search for n. In the next S34, the deterioration degree determination value Srmn obtained in S33 is added to the integrated value Re up to the previous time, and the addition result is set in the integrated value Re, thereby sequentially integrating the deterioration degree determination values.

On the other hand, if it is determined in step S32 that the stratified operation is not being performed, and if the homogeneous combustion is being performed, the process proceeds to step S35, and it is determined whether the homogeneous lean operation or the homogeneous stoichiometric rich operation is being performed. When the homogeneous lean operation is being performed, the process proceeds to S36, and the deterioration degree determination value Hrmn corresponding to the current operating condition is determined by referring to a map of the deterioration degree determination value Hrmn stored in advance corresponding to the homogeneous lean operation. Search for.

In the next step S37, S is added to the integrated value Re up to the previous time.
The deterioration degree determination values Hrmn obtained in 36 are added, and the addition result is set in the integrated value Re, whereby the deterioration degree determination values are sequentially integrated. If it is determined in S35 that the vehicle is in the homogeneous stoichiometric / rich operation, it is determined that no smoke has occurred, and the process proceeds to S38, where the integrated value Re up to the previous time is set as the current value.

The judgment values Srmn, referred to in S33 and S36,
As shown in FIGS. 12 and 13, the map of Hrmn is used to determine the judgment values Srmn, Hrmn for each of a plurality of regions divided by the basic fuel injection amount Tp representing the engine load and the engine speed Ne.
Is stored in advance. As shown in FIG. 9, the lower the catalyst inlet temperature, the greater the degree of catalyst deterioration. (A value indicating that the degree of deterioration is greater).

Further, during the homogeneous stoichiometric rich operation, the exhaust gas temperature is high and the degree of catalyst deterioration is sufficiently small as shown in FIG. 9 (smoke accumulation does not proceed).
Therefore, the integrated value Re is not updated. The flowchart of FIG. 7 shows the details of S4 in detail, and diagnoses whether or not smoke deterioration has occurred based on the integrated value Re calculated in the flowchart of FIG. In S41, the integrated value Re is read, and in S42
Then, it is determined whether or not the integrated value Re is equal to or greater than a predetermined value Rea.

If the integrated value Re is equal to or greater than the predetermined value Rea, it is considered that the accumulation of smoke has progressed and the catalyst has deteriorated, and the process proceeds to S43, where 1 is set to the smoke deterioration flag F2. . On the other hand, when the integrated value Re is less than the predetermined value Rea, it is considered that the accumulation of smoke is sufficiently small, and the deterioration of the three-way catalyst 4 is caused by factors other than the smoke.
Set 0 to 2.

In S5, the smoke deterioration flag F
By the determination of 2, it is determined whether or not the deterioration of the three-way catalyst 4 is due to the accumulation of smoke. If the smoke deterioration flag F2 is set to 1 and it is determined that the conversion performance has deteriorated due to the accumulation of smoke on the catalyst, the stratified lean combustion and the homogeneous lean combustion are prohibited, and the stratified lean combustion is originally performed. , By performing the homogeneous stoichiometric combustion or the homogeneous rich combustion in the region where the homogeneous lean combustion is performed, the exhaust temperature is increased, and the smoke deposited on the catalyst 4 during the stratified lean combustion and the homogeneous lean combustion is desorbed / burned out. Thus, the smoke poisoning state of the catalyst is eliminated and the conversion performance is restored.

The flowchart of FIG. 8 shows the details of the above S7. In this routine, it is determined whether or not the conversion performance of the catalyst has recovered as a result of prohibiting stratified lean combustion and homogeneous lean combustion. First, in S71, it is determined whether or not it is in the air-fuel ratio feedback control region. If the air-fuel ratio feedback control is being performed, the process proceeds to S72.

In S72, the reversal frequency f1 of the upstream first oxygen sensor 5 is read, and in the next S73, the downstream second oxygen sensor 5 is read.
The reversal frequency f2 of the oxygen sensor 6 is read. And S
At 74, the inversion frequency ratio fr = f2 / f1 is calculated, and at S75
Then, it is determined whether or not the inversion frequency ratio fr is equal to or less than a predetermined value frb. Since the inversion frequency ratio fr increases as the deterioration proceeds (see FIG. 11), when the inversion frequency ratio fr is equal to or less than the predetermined value frb, the three-way catalyst 4
It can be determined that the conversion performance in has recovered.

Therefore, in S75, the inversion frequency ratio fr
Is determined to be equal to or less than the predetermined value frb, S8
To the deterioration determination flag F1 and the smoke deterioration flag F
2. The integrated value Re is reset, and in S9, the prohibition of the stratified lean combustion and the homogeneous lean combustion is canceled, and the normal control state is returned. According to the above configuration, in a state where it is confirmed that catalyst deterioration has occurred based on the reversal frequency ratio fr, the presence or absence of smoke deterioration is determined in consideration of the difference in the degree of smoke deterioration depending on the engine load and the engine rotation speed. By diagnosing, it is possible to accurately diagnose the deterioration of the catalyst due to smoke accumulation. Based on the result of the diagnosis, if the control for inhibiting the stratified lean combustion and the homogeneous lean combustion and recovering the conversion performance is executed, the recovery can be performed. When the processing is required, the recovery processing can be reliably executed, and it is possible to prevent the lean combustion from being unnecessarily limited and the smoke deterioration state from being left unnecessarily.

In the above embodiment, since the exhaust gas temperature can be estimated from the engine load and the engine speed,
Although the deterioration degree determination value is obtained by using the engine load and the engine speed as parameters, the catalyst inlet exhaust temperature is most correlated with the degree of smoke poisoning of the catalyst.
In order to diagnose the degree of smoke deterioration with higher accuracy,
An exhaust temperature sensor 7 for detecting a catalyst inlet exhaust temperature is disposed upstream of the three-way catalyst 4, and the deterioration degree determination value is obtained based on the catalyst inlet exhaust temperature detected by the exhaust temperature sensor 7. The smoke deterioration may be diagnosed based on the value Re obtained by integrating the values.

The flowchart of FIG. 14 shows a second embodiment for obtaining the deterioration degree judgment value Orn in accordance with the catalyst inlet exhaust gas temperature as described above. Instead of the flowchart of FIG. S3 of the flowchart of 4
It shows the contents of. In the flowchart of FIG. 14, in S301, the integrated value Re up to the previous time is read, and in the next S302, the catalyst inlet exhaust gas temperature detected by the exhaust temperature sensor 7 is read.

Then, in S303, as shown in FIG.
Deterioration degree judgment value Or corresponding to catalyst exhaust gas temperature in advance
With reference to a table storing n, a determination value Orn corresponding to the current catalyst inlet exhaust gas temperature is searched. Here, when the catalyst inlet exhaust gas temperature is increased, as shown in FIG. 10, the smoke deposited on the catalyst is desorbed and burned off, and the catalyst performance is restored.As shown in FIG. In the temperature range in which the recovery of the catalyst performance is achieved, the determination value Or
It is preferable that n is set to a negative value and the integrated value Re is reduced and changed in proportion to the recovery amount.

At S304, the judgment value O obtained at S303 is obtained.
rn is added to the integrated value Re up to the previous time, and the added result is newly set as the integrated value Re. In S305, the updated integrated value Re is stored. As described above, if the catalyst inlet exhaust temperature is directly detected and the deterioration degree determination value Orn is set based on the detected catalyst inlet exhaust temperature, the exhaust gas temperature is determined based on the engine load, the engine rotation speed, and the combustion method. Can be diagnosed more accurately than in the first embodiment in which the deterioration degree is estimated and the deterioration degree determination value is set. However, in the case of the first embodiment, there is an advantage that the exhaust temperature sensor 7 is not required.

Incidentally, S in the flowchart of FIG.
If it is determined that the three-way catalyst 4 is not a smoke deterioration, the three-way catalyst 4 is a platinum-based catalyst containing platinum as a main component.
Oxidation of platinum by exposure to a high temperature lean exhaust atmosphere may have caused temporary degradation. The temporary deterioration due to the oxidation of platinum progresses by being exposed to a high-temperature lean exhaust atmosphere, and recovers by being exposed to a high-temperature rich exhaust atmosphere. Therefore, when it is determined in S5 that the deterioration is not the smoke deterioration, the deterioration may be recovered by estimating the temporary deterioration due to the oxidation of the platinum and exposing the catalyst to a high-temperature rich exhaust atmosphere.

Here, even if the air-fuel ratio is rich on the low-load, low-rotation side where the lean combustion is originally performed, the catalyst is exposed to the low-temperature rich exhaust atmosphere. It causes emission deterioration.
Therefore, a deterioration degree determination value Rm is set based on the inversion frequency ratio fr, and a target exhaust temperature at which deterioration recovery is performed is set according to the determination value Rm. Then, a high-load, high-speed region in which the exhaust gas temperature becomes equal to or higher than the target exhaust gas temperature when the stoichiometric combustion is performed is specified as a recovery processing region, while the exhaust temperature when the stoichiometric combustion is performed and the recovery processing region are determined. The air-fuel ratio correction coefficient for obtaining the target exhaust temperature by the minimum lean correction within the recovery processing region based on the exhaust temperature when the combustion is performed at the rich air-fuel ratio under the normal control and the target exhaust temperature. The catalyst is exposed to the rich exhaust atmosphere at the target temperature by setting each region in the processing region and performing correction by the air-fuel ratio correction coefficient.

In general, the correlation between the air-fuel ratio and the exhaust gas temperature is such that the exhaust gas temperature becomes the highest at the air-fuel ratio leaner than the stoichiometric air-fuel ratio by a predetermined value, and the air-fuel ratio is changed from the temperature at which the exhaust gas temperature becomes the highest. There is a characteristic that the exhaust gas temperature decreases as it moves to the side. Therefore, in the high-load, high-speed range where combustion is performed at a rich air-fuel ratio, a minimum necessary lean operation is performed to secure the exhaust gas temperature necessary for catalyst recovery (however, the air-fuel ratio on the rich side of the stoichiometric air-fuel ratio). A high-temperature rich atmosphere required for catalyst recovery is positively generated, and the catalyst is exposed to the high-temperature rich atmosphere to recover the state of temporary deterioration due to oxidation of platinum.

In the case where the above-mentioned temporary deterioration due to the oxidation of platinum is recovered, when the recovery of the catalyst performance is determined based on the inversion frequency ratio fr, the correction of the air-fuel ratio is canceled and the control is returned to the normal control. To do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of an exhaust gas purification device according to the present invention.

FIG. 2 is a system diagram showing a configuration of an internal combustion engine in the embodiment.

FIG. 3 is a diagram showing an air-fuel ratio and a combustion method for each operating condition in the engine of the embodiment.

FIG. 4 is a flowchart showing catalyst deterioration diagnosis and catalyst recovery processing in the embodiment.

FIG. 5 is a flowchart showing a state of a deterioration diagnosis based on the variation frequency of the oxygen concentration in the embodiment.

FIG. 6 is a flowchart showing how a deterioration degree determination value is set in the embodiment.

FIG. 7 is a flowchart showing a state of smoke deterioration diagnosis in the embodiment.

FIG. 8 is a flowchart showing a state of a catalyst performance recovery diagnosis in the embodiment.

FIG. 9 is a diagram showing a correlation between a catalyst inlet temperature and a degree of catalyst deterioration.

FIG. 10 is a diagram showing a correlation between a catalyst inlet temperature and a catalyst recovery degree.

FIG. 11 is a diagram showing a correlation between an inversion frequency ratio and a degree of catalyst deterioration.

FIG. 12 is a diagram showing a map of a deterioration degree determination value for stratified combustion in the embodiment.

FIG. 13 is a diagram showing a map of a deterioration degree determination value for homogeneous lean combustion in the embodiment.

FIG. 14 is a flowchart illustrating a second embodiment in which a deterioration degree determination value is set based on a catalyst inlet temperature.

FIG. 15 is a view showing a table of a deterioration degree determination value according to a catalyst inlet temperature in the second embodiment.

FIG. 16 is a diagram showing a correlation between a catalyst inlet temperature and a deterioration degree determination value in the second embodiment.

[Explanation of symbols]

 Reference Signs List 1 internal combustion engine 2 fuel injection valve 3 control unit 4 three-way catalyst 5 first oxygen sensor 6 second oxygen sensor 7 exhaust temperature sensor 8 intake passage 9 exhaust passage 10 water temperature sensor 11 throttle valve 12 air flow meter 13 rotation speed sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 45/00 301 F02D 45/00 301G 368 368F

Claims (8)

[Claims] An exhaust purification catalyst installed in an exhaust system of an internal combustion engine; a degradation determination value storage means for storing in advance a determination value indicating a degree of degradation of the catalyst due to smoke for each operating condition of the engine; Operating condition detecting means for detecting an operating condition of the engine; determining value integrating means for integrating the determination values retrieved from the deterioration determination value storage means in accordance with the operating conditions detected by the operating condition detecting means; An exhaust gas purification apparatus for an internal combustion engine, comprising: smoke deterioration diagnosis means for diagnosing a state of deterioration of the catalyst due to smoke based on the determination value integrated by the value integration means. 2. The deterioration determination value storage means stores a map in which a determination value indicating the degree of deterioration is assigned to each of a plurality of operating regions classified according to an engine load and an engine rotation speed as the operating conditions. 2. The method according to claim 1, wherein
An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the determination value is set to a value indicating that the degree of deterioration is larger at a lower rotation speed and a lower load. 4. The engine according to claim 1, wherein the combustion mode is switched between stratified combustion and homogeneous combustion. The deterioration determination value storage means stores a map of determination values according to the engine load and the engine speed. A determination value map for the stratified combustion,
4. The storage device according to claim 2, wherein the determination value map for the homogeneous lean combustion is stored, and the determination value integrating means selects a map to be referred to in accordance with the combustion method and searches for the determination value. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. 5. The exhaust gas purification system according to claim 1, wherein said deterioration determination value storage means stores a determination value indicating said degree of deterioration according to a catalyst inlet exhaust temperature as said operating condition. apparatus. 6. A first and a second oxygen sensor provided respectively on the upstream side and the downstream side of the catalyst for detecting an oxygen concentration in exhaust gas, and a variation in an oxygen concentration detected by the first oxygen sensor. A catalyst deterioration diagnosing means for diagnosing the deterioration state of the catalyst based on a frequency and a fluctuation frequency of the oxygen concentration detected by the second oxygen sensor. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 5, wherein the smoke deterioration diagnosing means diagnoses a deterioration state of the catalyst due to smoke on the precondition that the determination is made. . 7. A catalyst deterioration recovery means for forcibly performing combustion at an air-fuel ratio equal to or lower than a predetermined value when the smoke deterioration diagnosis means determines the deterioration state of the catalyst due to smoke. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 6. 8. A combustion system of the engine is switched between stratified combustion and homogeneous combustion, and the catalyst deterioration recovery means forcibly performs homogeneous combustion at an air-fuel ratio equal to or lower than a stoichiometric air-fuel ratio. The exhaust gas purifying apparatus for an internal combustion engine according to claim 7, characterized in that: