JP2996084B2 - Exhaust gas purification device for internal combustion engine - Google Patents

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.

[0002]

2. Description of the Related Art In order to purify exhaust gas discharged from an internal combustion engine, feedback control is performed so that an air-fuel ratio becomes a stoichiometric air-fuel ratio, and oxidation of HC and CO and reduction of NO are simultaneously performed in an exhaust passage. Systems in which a three-way catalyst is installed have been widely put into practical use.

As a catalytic metal used in the three-way catalyst, a metal mainly composed of palladium excellent in low-temperature activity, which functions well within a short time after starting the engine, has been developed (Japanese Patent Application Laid-Open (JP-A) No. Sho. 58-189037).

[0004] Palladium (Pd) is an oxide which is stable at room temperature and exhibits a catalytic action as palladium oxide (PdO).

[0005]

When a palladium-based catalyst is exposed to a high-temperature exhaust atmosphere at an air-fuel ratio richer than the stoichiometric air-fuel ratio, it is reduced to metallic palladium, and the catalyst performance is temporarily reduced. So-called temporary deterioration. This temporary deterioration is more remarkable in a catalyst in which permanent deterioration caused by a decrease in the specific surface area due to thermal deformation of the wash coat or a decrease in the degree of dispersion of the noble metal has progressed.

[0006] When the catalyst is temporarily deteriorated, the exhaust gas purifying action is reduced during that time, and the exhaust emission is increased.

[0007] Therefore, an object of the present invention is to recover the catalyst performance by performing a catalyst deterioration recovery process when such temporary deterioration occurs.

[0008]

According to a first aspect of the present invention, as shown in FIG. 14, an exhaust purification catalyst (1) installed in an engine exhaust system mainly supporting palladium as a catalyst metal,
Deterioration degree detecting means 51 for detecting the degree of deterioration of the catalyst (1), exhaust temperature detecting means (13) for detecting the temperature of exhaust gas flowing into the catalyst (1), and a catalyst ( A deterioration recovery processing time determining means 52 for determining the timing of performing the deterioration recovery processing of 1), and determining the air-fuel ratio of the exhaust when the determination result is the deterioration recovery processing time and the detected exhaust gas temperature is equal to or higher than a predetermined value Deterioration recovery processing means 53 for performing a deterioration recovery processing of the catalyst (1) by controlling the air-fuel ratio to a deterioration recovery processing leaner than the stoichiometric air-fuel ratio.

As shown in FIG. 15, a second invention is a catalyst (1) for purifying exhaust gas which is installed in an engine exhaust system mainly supporting palladium as a catalyst metal, and a catalyst for deterioration of the catalyst (1). Deterioration degree detecting means 51 for detecting the degree, exhaust temperature detecting means (13) for detecting the temperature of exhaust gas flowing into the catalyst (1), and deterioration recovery processing of the catalyst (1) according to the detected catalyst deterioration degree. Degradation recovery processing time determination means 52 for determining when to perform; degradation recovery processing time setting means 54 for setting the time for performing the catalyst degradation recovery processing according to the detected degree of catalyst degradation; A deterioration recovery processing means for controlling the air-fuel ratio of the exhaust to a leaner air-fuel ratio than the stoichiometric air-fuel ratio when the exhaust gas temperature is equal to or higher than a predetermined value and performing catalyst deterioration recovery processing; 53 and this Deterioration recovery process ending means ends the deterioration recovery process when the reduction recovery process integration time from the transition to reach the set degraded recovery processing time 55
And

In a third aspect based on the first or second aspect, the deterioration recovery processing timing determining means exposes the catalyst to exhaust gas having a temperature equal to or higher than a predetermined temperature based on a detected value of the degree of catalyst deterioration immediately after starting the engine. Exposure time estimating means for estimating the time until the degree of deterioration proceeds beyond the allowable range when
Exposure time integration means for integrating the time during which the detected exhaust gas temperature is equal to or higher than a predetermined value, and comparison determination means for comparing the integrated exposure time with the estimated possible exposure time to determine the deterioration recovery processing time. Consists of

According to a fourth aspect of the present invention, in the first or second aspect, the deterioration recovery processing timing determining means stores the degree of deterioration detected by the degree of deterioration detecting means immediately after starting the engine as an initial degree of deterioration. A deterioration progress calculating means for calculating a difference between the degree of deterioration detected at predetermined time intervals and the initial deterioration degree, and a deterioration recovery process by comparing the deterioration progress with a reference value set in accordance with the initial deterioration degree. And comparison determination means for determining the timing.

In a fifth aspect based on the first to fourth aspects, the deterioration recovery processing means corrects a feedback control coefficient when the air-fuel ratio of the engine is feedback-controlled to a stoichiometric air-fuel ratio to reduce the air-fuel ratio. Shift to the side.

In a sixth aspect based on the first to fourth aspects, the deterioration recovery processing means introduces secondary air upstream of the catalyst installed in the exhaust passage to reduce the air-fuel ratio of the exhaust gas flowing into the catalyst to the lean side. Shift to

[0014]

According to the first aspect of the invention, when the temporary deterioration of the catalyst is determined, when the exhaust gas temperature is equal to or higher than the predetermined value, the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio, and the catalyst recovery processing is performed. Will be When the palladium-based catalyst is exposed to a high-temperature lean atmosphere, temporary deterioration of the catalyst is removed, and the catalyst performance is restored.

Therefore, when the deterioration of the catalyst is determined, by performing the recovery process of the catalyst in this way, it is possible to provide the catalyst with stable performance for a long time,
A good exhaust purification function can be maintained.

In the second invention, the time required for the deterioration recovery processing is determined according to the degree of deterioration of the catalyst, and the recovery processing is performed only for the set time, thereby accommodating the deterioration recovery processing by making the air-fuel ratio lean. The effect on the operability and the exhaust performance is reduced as much as possible, and the catalyst recovery processing can be performed efficiently.

In the third aspect, the timing of the deterioration recovery processing is determined in relation to the degree of permanent deterioration of the catalyst detected immediately after the start of the engine. Temporary deterioration that recovers in a high-temperature lean atmosphere can be recovered by leaving it at room temperature, and the catalyst recovers when the engine is stopped. Therefore, the initial deterioration degree detected immediately after the start of the engine indicates irrecoverable deterioration of the catalyst, that is, permanent deterioration. The rate of progress of temporary deterioration is
Depending on the degree of permanent deterioration, the higher the degree of permanent deterioration, the faster the progress. Therefore, by estimating the time until the deterioration of the catalyst reaches the allowable range according to the degree of the permanent deterioration, it is possible to accurately determine the deterioration recovery processing time.

In the fourth invention, the deterioration recovery processing time is determined based on a comparison between the initial deterioration degree and the deterioration degree at predetermined time intervals. The difference between the initial deterioration degree and the deterioration degree for each predetermined time, that is, the deterioration progress degree represents the magnitude of the temporary deterioration that has progressed during the operation, and therefore, this deterioration progress degree is a reference based on the initial deterioration degree. By comparing with the value,
It is possible to accurately determine the time until the entire deterioration including the temporary deterioration and the permanent deterioration reaches the allowable range.

In the fifth aspect, the air-fuel ratio is made lean by correcting the control coefficient (for example, proportional value or integral value) of the air-fuel ratio feedback control. Therefore, it is not necessary to add a new hardware configuration for this purpose. .

In the sixth aspect, the air-fuel ratio is made lean by introducing secondary air, so that the engine is operated at an air-fuel ratio within a normal control range such as a stoichiometric air-fuel ratio, and good operability is maintained even during the deterioration recovery process. Can be secured.

[0021]

FIG. 1 shows an embodiment of the present invention. A fuel injection valve 5 is attached to an intake passage 8 of an engine 7 and injects fuel according to a signal from a controller 4. The exhaust passage 9 is provided with a three-way catalyst 1 that simultaneously oxidizes HC and CO in exhaust gas and reduces NO. This three-way catalyst 1
It is composed of a palladium-based catalyst in which palladium (Pd) is mainly supported on alumina as a catalytic metal and ceria or the like is supported.

First and second oxygen sensors 2 and 3 are installed upstream and downstream of the three-way catalyst 1, respectively. The controller 4 determines the stoichiometric air-fuel ratio based on the output of the first oxygen sensor 2. The fuel injection amount is feedback-controlled so as to obtain the fuel ratio. Further, the number of times that the output of the first oxygen sensor 2 and the output of the second oxygen sensor 3 are each inverted in a rich lean manner is compared to detect the degree of deterioration of the catalyst, as described later. Then, the catalyst deterioration recovery process is executed at a predetermined operation time. For this reason, the controller 4
A water temperature sensor 12 for detecting an engine cooling water temperature, and a temperature sensor 13 for detecting an exhaust gas temperature on the inlet side of the three-way catalyst 1.
The signal from is input. Although not shown, a signal representing an operating state such as an engine intake air amount and a rotation speed is also input.

An exhaust gas recirculation passage 14 for recirculating a part of the exhaust gas from the exhaust gas passage 9 is connected to the intake passage 8, and an exhaust gas recirculation control valve 15 is connected via a controller 4 to an exhaust gas recirculation control valve 15 in accordance with operating conditions. To reduce NO in the exhaust gas.

As shown in FIG. 2, the palladium-based catalyst has a characteristic that the catalyst performance is temporarily deteriorated when exposed to a stoichiometric air-fuel ratio or a high-temperature exhaust atmosphere richer than the stoichiometric air-fuel ratio. Apart from this, permanent deterioration due to physical deterioration of the catalyst also occurs similarly to a general catalyst. The graph shows the state of change (temporary deterioration) of the catalyst conversion when the palladium-based catalyst is exposed to high-temperature exhaust gas having a temperature of 500 ° C. and an air-fuel ratio of stoichiometric air-fuel ratio (λ = 1) for a long time. Represents. In this case, the catalyst conversion rate decreases with the passage of time, but the catalyst A with less permanent deterioration has less change. On the other hand, the catalysts with the more permanent deterioration, catalysts B and C, have a higher conversion rate. The drop is noticeable. The temporary deterioration of the catalyst can be recovered in a high-temperature exhaust atmosphere with a lean air-fuel ratio, and the catalyst performance recovers to the first state of the permanent deterioration. Therefore, when the state of the temporary deterioration of the catalyst is determined, the deteriorated catalyst can be recovered by temporarily controlling the air-fuel ratio to lean under the operating condition where the exhaust gas temperature becomes high.

In order to perform such catalyst deterioration recovery processing, the controller 4 performs the control shown in FIGS.

First, FIG. 3 shows a control routine for determining the deterioration of the catalyst, which is executed only once after the start of the engine.

After reading the engine cooling water temperature Tw in step S1, it is determined in step S2 whether the cooling water temperature Tw is, for example, equal to or higher than a predetermined value T1 after completion of warm-up, and then in step S3, the air-fuel ratio is in a feedback control region. Judge.

If both are different, the process returns to the beginning.

In steps S4 and S5, rich lean inversion frequencies F1 and F2 of the outputs of the first oxygen sensor 2 upstream of the catalyst and the second oxygen sensor 3 downstream are read, respectively. As shown in FIG. 4, the ratio of the inversion frequency, F2 / F1, approaches 1 as the degree of deterioration of the catalyst advances. When the catalyst is functioning normally, the oxygen in the exhaust gas is stored, so that the oxygen contained in the exhaust gas upstream cannot be detected directly downstream of the catalyst. However, when the catalyst deteriorates, the oxygen in the upstream exhaust flows out downstream as it is, so the reversal frequency of the downstream oxygen sensor output is
It approaches the inversion frequency of the upstream oxygen sensor output.

In step S6, the inversion frequency ratio Fr
Is calculated as F2 / F1, and in step S7, the frequency ratio Fr is compared with a predetermined value Fra. Here, the degree of deterioration of the catalyst is determined, and when the detected frequency ratio is larger than a predetermined value, it is determined that the catalyst is deteriorated, and the process proceeds to a deterioration detection routine of step S8.

The above control is performed only once immediately after the start of the engine (but after the activation of the catalyst), but the temporary deterioration of the catalyst naturally recovers at room temperature. The deterioration is recovered during the stop of the operation, and therefore, the degree of deterioration detected at the above timing (frequency ratio Fr: hereinafter referred to as initial deterioration degree) can be regarded as reflecting only the permanent deterioration of the catalyst. .

Next, in the deterioration detection routine of FIG. 5, in step S11, based on the reversal frequency ratio Fr, the deterioration degree R of the catalyst set in several stages from the table shown in FIG.
m, an exposure time Tc during which the catalyst can be directly exposed to the exhaust gas within the allowable range of the catalyst performance, and a recovery processing determination value Tr corresponding to a recovery processing time determined according to the degree of deterioration. Proceed to the calculation / recovery processing routine.

In this case, the deterioration degree Rm of the catalyst corresponds to the reversal frequency ratio Fr, and the initial deterioration degree Rm detected immediately after the start corresponds to the permanent deterioration degree. Based on the state of permanent deterioration, when the exhaust gas temperature is higher than a certain value, the added value with the degree of catalyst deterioration that is predicted to proceed when the operation is continued as it is until the allowable limit of the catalyst performance is reached It is set as time. Then, the recovery processing determination value Tr is set according to the exposure possible time Tc.

This routine is repeatedly executed at a predetermined cycle until the engine stops (step S13).

FIG. 6 shows the details of the exposure time calculation / recovery processing routine described above. In step S21, an integrated value Tin = 0, which will be described later, is set, and in step S22, a timer Ti =
When the count is set to 0, the timer starts counting, and the weight coefficient Kc is read from the table of FIG. 9 based on the catalyst inlet exhaust gas temperature T at that time. This weighting coefficient represents the degree of deterioration of the catalyst that progresses per unit time (this also corresponds to the degree of recovery). Strictly speaking, it is a two-dimensional map using the exhaust gas temperature and the air-fuel ratio as parameters. Since the influence of the temperature is greater, a table setting based on only the temperature may be used.

In step S23, the exhaust gas temperature T is changed to a weight coefficient K.
The time within the set temperature range is compared with the set temperature range when c is selected, and the time within this temperature range is integrated in step S24. However, the integrated value Tin is calculated as Tin = Tin + Kc × Ti, and the integrated value is calculated by adding the multiplication of the weight coefficient Kc obtained based on the exhaust gas temperature T and the time Ti in the temperature range. Will increase.

Then, in step S25, the integrated value Ti
n is compared with the exposure time Tc. Until the exposure time Tc is reached, the integration operation from the above steps S22 to S25 is repeated, integration is continued according to the exhaust gas temperature at that time, and the integration result is Tin> Tc Then, the process proceeds to the catalyst deterioration recovery process of FIG.

The deterioration of the catalyst proceeds in accordance with the time during which the catalyst is exposed to a high exhaust gas temperature. Thus, the progress of the deterioration is determined in relation to the exposure time Tc.

In FIG. 7, in step S26, first, the integrated value Tin is reset to 0, and in step S27, it is determined whether or not the catalyst inlet temperature T is in a high temperature state equal to or higher than a predetermined value at which deterioration recovery processing can be performed. In S28, it is determined whether or not the operating condition is a high load rich air-fuel ratio region (KMR).

In this rich air-fuel ratio region, even if an attempt is made to perform a lean shift for the catalyst deterioration recovery processing, KMR is prioritized from the viewpoint of drivability, and the lean shift cannot be performed. Start over.

If it is not in the KMR, at step S29,
Assuming that the timer Ti is 0, the counting of the timer is started, and the weight coefficient Kr is obtained from the table of FIG.
The control coefficient (for example, proportional value, integral value) of the air-fuel ratio feedback control is changed in step S30, the control center of the feedback control is shifted to the lean side, and the process proceeds to the deterioration recovery process. At this time, the exhaust gas recirculation amount is increased at the same time, and the NO that cannot be purified by the three-way catalyst due to the lean air-fuel ratio is reduced.

As described above, when the exhaust gas flowing into the catalyst is at a high temperature, the air-fuel ratio is made lean, so that the deteriorated palladium-based catalyst can recover the temporarily deteriorated part except for the permanent deterioration. is there.

In steps S31 and S32, the time in a state where the temperature is equal to or higher than a predetermined temperature is integrated. This integrated value Tim is represented by Tim
= Tim + Kr × Ti. Step S3
When the exhaust gas temperature changes from the predetermined temperature range in step 1, the timer is stopped in step S32, the process returns to step S27 via step S33, and the integration of the deterioration processing time is continued.

In this case as well, since the recovery from deterioration is greatly affected by the temperature of the exhaust gas in the lean atmosphere, the weight coefficient Kr can be set from the table of FIG. 9 which is set only depending on the exhaust gas temperature. You can.

In step S33, it is determined whether or not the recovery processing has been completed by comparing the integrated value Tim with the above-described recovery processing determination value Tr. In this way,
If the recovery processing time corresponding to the detected degree of deterioration of the catalyst has elapsed, it is determined that the temporary deterioration of the catalyst has been recovered to the initial state (however, the amount of permanent deterioration has been excluded). Then, the control coefficient of the feedback control and the exhaust gas recirculation rate (EGR rate) are returned to the values in the normal operation state, and the deterioration recovery processing ends.

In order to make the air-fuel ratio lean, instead of correcting the feedback control coefficient, a device for introducing secondary air upstream of the three-way catalyst 1 and downstream of the oxygen sensor 2 is provided.
In step S30, secondary air may be introduced upstream of the catalyst to make the catalyst inflow exhaust gas lean. In this case, the engine air-fuel ratio becomes the normal stoichiometric air-fuel ratio, so that good operability can be ensured even when the catalyst deterioration recovery processing is performed.

Next, another embodiment shown in FIGS. 10 and 11 will be described.

In this embodiment, since the degree of progress of the catalyst deterioration is related to the degree of permanent deterioration, that is, the initial degree of deterioration detected immediately after the engine is started, it is determined based on a reference value corresponding to the degree of deterioration. Then, the time until the total deterioration including the temporary deterioration and the permanent deterioration reaches the allowable limit is determined.

First, the routine of FIG. 10 is executed only once every time the engine is started. Steps S41 to S46 are the same as steps S1 to S6 of the basic routine of FIG. , Step S47
, The degree of deterioration Rm obtained from the table of FIG. 8 by the inversion frequency ratio Fr is stored as the initial degree of deterioration Rmo, and based on this Rmo, the reference value Rmc is read from the table of FIG. This reference value Rmc is
Mo + Rmc is determined to be the deterioration limit of the catalyst performance, and as the initial deterioration degree Rmo increases, Rmc decreases.

That is, here, the degree of this deterioration is stored as the initial deterioration from the catalyst deterioration judgment performed once after the engine is started.

Then, the process proceeds to the routine of FIG. This routine is repeatedly executed at predetermined time intervals after the operation of the engine, and determines the degree of progress of catalyst deterioration. Steps S51 to S54 are the same as steps S2 to S6. Here, when the reversal frequency ratio Fr of the oxygen sensor output when the exhaust gas temperature is equal to or higher than the predetermined value is calculated, step S5 is performed.
At step 5, based on this Fr, the degree of deterioration Rm is read from the table of FIG. 8, and the difference between this and the initial degree of deterioration Rmo, that is, the degree of temporary deterioration ΔRm, is expressed as ΔRm = Rm−
It is calculated as Rmo. Since the initial deterioration degree detected immediately after the start of the engine corresponds to the permanent deterioration degree, this ΔRm
Represents temporary deterioration of the recoverable catalyst.

In step S56, the temporary deterioration progress rate ΔR
m is compared with a reference value Rmc. As the degree of initial deterioration, that is, the degree of permanent deterioration advances, the reference value Rmc becomes smaller. In this case, the tolerance of temporary deterioration also becomes smaller. If the temporary deterioration degree ΔRm is equal to the reference value Rmc
If not, the flow proceeds to step S57 to shift to the catalyst recovery processing routine, reads the recovery processing determination value Tr, and executes the recovery processing operation of step S58.

Note that this recovery processing routine has the same operation contents as steps S26 to S34 in FIG. 7 described above, and reaches the recovery processing determination value Tr by making the air-fuel ratio lean in a high-temperature exhaust atmosphere. During this period, catalyst deterioration recovery processing is performed.

In this manner, the time until the total deterioration including the temporary deterioration and the permanent deterioration reaches the allowable limit is determined based on the reference value corresponding to the initial deterioration degree detected immediately after the engine is started. Control for performing a recovery process on the catalyst can be efficiently performed while accurately determining the state of deterioration.

[0055]

As described above, the first aspect of the present invention is directed to an exhaust gas purifying catalyst installed in an engine exhaust system mainly supporting palladium as a catalytic metal, and a deterioration degree detecting method for detecting the degree of deterioration of the catalyst. Means, exhaust temperature detecting means for detecting the temperature of exhaust gas flowing into the catalyst, deterioration recovery processing time determining means for determining when to perform catalyst recovery processing in accordance with the detected degree of catalyst deterioration, and At the time of deterioration recovery processing and when the detected exhaust gas temperature is equal to or higher than a predetermined value, the air-fuel ratio of the exhaust gas is controlled to the air-fuel ratio leaner than the stoichiometric air-fuel ratio to perform the catalyst deterioration recovery processing. When the exhaust gas temperature is equal to or higher than a predetermined value, the exhaust air-fuel ratio is lean-controlled to perform the catalyst recovery process. Maintain performance It is possible to improve the exhaust emission.

According to a second aspect of the present invention, there is provided an exhaust gas purifying catalyst installed in an engine exhaust system mainly supporting palladium as a catalyst metal, a deterioration degree detecting means for detecting the degree of deterioration of the catalyst, Exhaust temperature detecting means for detecting the temperature of the exhaust gas to be heated, deterioration recovery processing time determining means for determining when to perform the catalyst deterioration recovery processing in accordance with the detected degree of catalyst deterioration, and catalyst in accordance with the detected degree of catalyst deterioration. Degradation recovery processing time setting means for setting a time for performing the degradation recovery processing,
When the determination result is at the time of the deterioration recovery processing and the detected exhaust gas temperature is equal to or higher than the predetermined value, the air-fuel ratio of the exhaust gas is controlled to the air-fuel ratio leaner than the stoichiometric air-fuel ratio to recover the deterioration of the catalyst. A deterioration recovery processing means for performing the processing, and a deterioration recovery processing ending means for ending the deterioration recovery processing when the integrated time from the shift to the deterioration recovery processing reaches the set deterioration recovery processing time, The time required for the deterioration recovery process is determined according to the degree of deterioration of the catalyst, and the recovery process is performed only for this set time, so it is possible to influence the operability and exhaust performance of the deterioration recovery process by making the air-fuel ratio lean. As much as possible, the catalyst can be efficiently recovered.

In a third aspect based on the first or second aspect, the deterioration recovery processing timing determining means exposes the catalyst to exhaust gas having a temperature equal to or higher than a predetermined temperature based on a detected value of the degree of catalyst deterioration immediately after the start of the engine. Exposure time estimating means for estimating the time until the degree of deterioration proceeds beyond the allowable range when
Exposure time integrating means for integrating the time during which the detected exhaust gas temperature is equal to or higher than a predetermined value, and comparison determining means for comparing the integrated exposure time with the estimated possible exposure time to determine the deterioration recovery processing time. With this configuration, it is possible to accurately determine the deterioration recovery processing time by estimating the time until the temporary deterioration reaches the allowable range according to the degree of permanent deterioration of the catalyst.

According to a fourth aspect, in the first or second aspect, the deterioration recovery processing timing determining means stores the deterioration degree detected by the deterioration degree detecting means immediately after the engine is started as an initial deterioration degree. A deterioration progress calculating means for calculating a difference between the degree of deterioration detected at predetermined time intervals and the initial deterioration degree, and a deterioration recovery process by comparing the deterioration progress with a reference value set in accordance with the initial deterioration degree. Since it is composed of a comparison judgment means for judging the timing, by comparing the degree of progress of the catalyst deterioration with the initial deterioration degree, it is possible to accurately determine the time until the total deterioration including the temporary deterioration and the permanent deterioration reaches an allowable range. Can be determined.

In a fifth aspect based on the first to fourth aspects, the deterioration recovery processing means corrects a feedback control coefficient when the air-fuel ratio of the engine is feedback-controlled to a stoichiometric air-fuel ratio to reduce the air-fuel ratio. Shift to the side,
To make the air-fuel ratio lean for the deterioration process, it is unnecessary to add a new hardware configuration, and the configuration is simplified.

In a sixth aspect based on the first to fourth aspects, the deterioration recovery processing means introduces secondary air upstream of the catalyst installed in the exhaust passage to reduce the air-fuel ratio of the exhaust gas flowing into the catalyst to the lean side. Therefore, even if the air-fuel ratio is made lean for the deterioration recovery process, the air-fuel ratio of the engine is within the normal control range, so that good operability can be ensured even during the deterioration recovery process.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a transition state of catalyst performance.

FIG. 3 is a flowchart showing a control operation for detecting catalyst deterioration according to the embodiment.

FIG. 4 is an explanatory diagram of a catalyst deterioration determination.

FIG. 5 is a flowchart showing a control operation for determining deterioration of a catalyst.

FIG. 6 is a flowchart showing a control operation of setting the exposure time of the catalyst.

FIG. 7 is a flowchart showing a control operation of a deterioration recovery process.

FIG. 8 is an explanatory diagram showing a relationship between an inversion frequency ratio and a degree of deterioration.

FIG. 9 is an explanatory diagram showing a relationship between a catalyst inlet temperature and a weight coefficient.

FIG. 10 is a flowchart illustrating a control operation according to another embodiment.

FIG. 11 is a flowchart of a control operation for determining the progress of deterioration of the catalyst.

FIG. 12 is an explanatory diagram showing a relationship between an initial deterioration degree and a reference value.

FIG. 13 is an explanatory diagram showing the relationship between the degree of progress of deterioration and a recovery processing determination value.

FIG. 14 is a configuration diagram of the first invention.

FIG. 15 is a configuration diagram of the second invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Three-way catalyst (palladium catalyst) 2 Oxygen sensor 3 Oxygen sensor 4 Controller 5 Fuel injection valve 9 Exhaust passage 13 Exhaust temperature sensor 51 Deterioration degree detecting means 52 Deterioration recovery processing time determination means 53 Deterioration recovery processing means 54 Deterioration recovery processing time Setting means 55 Degradation recovery processing end means

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akio Isobe 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd. (56) References JP-A-58-1889037 (JP, A) 312024 (JP, A) JP-A-5-248227 (JP, A) JP-A-60-48146 (JP, A) JP-A-6-200766 (JP, A) WO 93/25806 (WO, A1) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) B01J 23/44 B01D 53/86 F01N 3/20 F02D 41/02 305

Claims (6)

(57) [Claims] An exhaust purification catalyst installed in an engine exhaust system mainly supporting palladium as a catalyst metal, a deterioration degree detecting means for detecting a degree of deterioration of the catalyst, and a temperature of exhaust gas flowing into the catalyst. Exhaust temperature detecting means for detecting; deterioration recovery processing time determining means for determining when to perform catalyst recovery processing in accordance with the detected degree of catalyst deterioration; When the exhaust gas temperature is equal to or higher than a predetermined value, deterioration recovery processing means for controlling the air-fuel ratio of the exhaust gas to a leaner-side deterioration recovery processing air-fuel ratio than the stoichiometric air-fuel ratio to perform catalyst deterioration recovery processing is provided. Exhaust purification device for an internal combustion engine. 2. An exhaust gas purifying catalyst installed in an engine exhaust system mainly supporting palladium as a catalyst metal, a deterioration degree detecting means for detecting the degree of deterioration of the catalyst, and a temperature of exhaust gas flowing into the catalyst. Exhaust temperature detecting means for detecting, deterioration recovery processing time determining means for determining when to perform the catalyst deterioration recovery processing in accordance with the detected catalyst deterioration degree, and catalyst deterioration recovery processing in accordance with the detected catalyst deterioration degree A recovery time setting means for setting a time for performing the operation, when the determination result is the deterioration recovery processing time and the detected exhaust gas temperature is equal to or higher than a predetermined value, the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. Degradation recovery processing means for performing a catalyst degradation recovery process by controlling the air-fuel ratio, and when the accumulated time from the shift to the degradation recovery process reaches the set degradation recovery processing time, Exhaust purification system of an internal combustion engine, characterized in that it comprises a deterioration recovery process ending means for ending the reduction recovery process. 3. The deterioration recovery processing timing determining means, based on a detected value of the catalyst deterioration degree immediately after the start of the engine, causes the deterioration degree to exceed an allowable range when the catalyst is exposed to exhaust gas having a temperature equal to or higher than a predetermined temperature. Exposure time estimating means for estimating the time until exposure time, Exposure time estimating means for accumulating the time during which the detected exhaust gas temperature is equal to or higher than a predetermined value, and comparing the accumulated exposure time with the estimated exposure time 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, further comprising a comparison judging means for judging a deterioration recovery processing time. 4. A storage means for storing the degree of deterioration detected by the degree-of-degradation detecting means immediately after the engine is started as an initial degree of deterioration; And a comparison determining means for comparing the degree of deterioration with a reference value set according to the initial degree of deterioration to determine the timing of the deterioration recovery processing. Item 3. An exhaust gas purifying apparatus for an internal combustion engine according to item 1 or 2. 5. A method according to claim 1, wherein said deterioration recovery processing means corrects a feedback control coefficient when feedback-controlling the air-fuel ratio of the engine to the stoichiometric air-fuel ratio to shift the air-fuel ratio to the lean side. An exhaust gas purifying apparatus for an internal combustion engine according to any one of the preceding claims. 6. The deterioration recovery processing means according to claim 1, wherein secondary air is introduced upstream of the catalyst provided in the exhaust passage to shift the air-fuel ratio of the exhaust gas flowing into the catalyst to the lean side. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1.