JPH0882213A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PURPOSE: To aim at an appropriate deterioration recovery treatment by surely detecting unrecoverable temporary and permanent deterioration in a palladium group catalyst. CONSTITUTION: An exhaust emission control device of an internal combustion device is provided with a catalyst 50 for exhaust emission control carrying mainly palladium, a deterioration degree detection means 51 for detecting deterioration degree of the catalyst 50, an exhaust temperature detection means 52 for detection exhaust temperature flowing in the catalyst 50, a deterioration recovery treatment timing judging means 53 for judging a deterioration recovery treatment timing of the catalyst according to the detected deterioration degree, and a deterioration recovery treating means 54 in which the deterioration of the catalyst is recovered by controlling the air-fuel ratio of exhaust gas to the leaner side than its theoretical air fuel ratio when the detected exhaust temperature is larger than a specified value. It is also provided with a recovery non-treatment judging means 55 for judging whether the recovery of the temporary deterioration is not yet treated or not based on the deterioration degree detected just after the engine is started, and an interrupt means 56 for making the deterioration recover treatment regardless of the deterioration recovery treatment timing, when the judged result shows no recovering treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine using a palladium-based three-way catalyst.

[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 the air-fuel ratio becomes a stoichiometric air-fuel ratio, and HC and C0 are oxidized in the exhaust passage.
A three-way catalyst that simultaneously reduces NO has been widely put into practical use.

The catalytic metal used in this three-way catalyst functions well immediately after starting the engine and within a short time.
A material containing palladium as a main component, which is excellent in low-temperature activity, has been developed (see JP-A-58-189037).

Oxide of palladium (Pd) is stable at room temperature and exhibits a catalytic action as palladium oxide (PdO).

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 (Pd) and the catalytic performance is temporarily deteriorated. Cause

In contrast to this temporary deterioration, when the catalytic performance deteriorates due to a decrease in specific surface area due to thermal deformation of the washcoat or a decrease in the degree of dispersion of the noble metal, it becomes permanent deterioration. Appears prominently.

If the catalyst is temporarily deteriorated, there is a problem that the exhaust gas purifying action is lowered and the exhaust emission is increased during that time, and the applicant of the present application proposes that the catalyst is temporarily deteriorated. If it is determined that the exhaust gas temperature is equal to or higher than a predetermined value, an exhaust gas purifying apparatus that controls the air-fuel ratio of the exhaust gas to a lean side to perform a catalyst deterioration recovery process has been proposed.

In this apparatus, the deterioration recovery treatment timing is determined in relation to the degree of permanent deterioration of the catalyst detected immediately after the engine is started, and the temporary deterioration of the palladium-based catalyst recovered in a high temperature lean atmosphere is completely cooled by leaving it at room temperature. The initial degree of deterioration detected immediately after the engine is started indicates permanent deterioration, which is irrecoverable deterioration of the catalyst, and the degree of deterioration of the catalyst is compared with a reference value according to the degree of initial deterioration. As a result, the above-described deterioration recovery process is performed by determining the time until the total deterioration including the temporary deterioration and the permanent deterioration reaches the allowable range.

[0009]

By the way, in a case such as a hot start in which the engine is restarted immediately after the engine is stopped during the recovery process of the temporary deterioration, the catalyst is sufficiently cooled by leaving it at room temperature. Since it is not performed, the temporary deterioration at the time of the previous start may not be recovered.

However, in the above conventional apparatus, the catalyst is completely cooled by being left at room temperature, and the degree of deterioration is determined based on the catalyst performance immediately after the start of the catalyst, assuming that the temporary deterioration of the catalyst is completely recovered. Therefore, if there is an unrecovered temporary deterioration component in the previous operation, it is judged as if the catalyst has undergone significant permanent deterioration, and the judgment for the deterioration recovery process is erroneously made. Even in the deteriorated state, the deterioration recovery process may be frequently performed.

Therefore, the present invention has been made in view of the above problems, and reliably detects unrecovered temporary deterioration at the time of hot start and the like, and performs deterioration recovery treatment on the catalyst that has caused temporary deterioration, The purpose is to recover the catalyst performance promptly.

[0012]

The first invention, as shown in FIG. 1, is a catalyst 50 for purifying exhaust gas, which mainly carries palladium as a catalyst metal, and a deterioration for detecting the degree of deterioration of the catalyst 50. Degree detecting means 51, exhaust temperature detecting means 52 for detecting the exhaust temperature flowing into the catalyst 50, and deterioration recovery processing timing determining means 53 for determining the time when the catalyst deterioration recovery processing is performed according to the detected catalyst deterioration degree. When the determination result is the deterioration recovery processing time, and the detected exhaust temperature is equal to or higher than a predetermined value, the air-fuel ratio of the exhaust gas is controlled to a deterioration recovery processing air-fuel ratio leaner than the stoichiometric air-fuel ratio. In an exhaust gas purification apparatus for an internal combustion engine, comprising: a deterioration recovery processing means (54) for performing deterioration recovery processing, a recovery undecision is made based on the deterioration degree detected immediately after the engine is started to determine whether the temporary deterioration recovery is unprocessed. A management decision means 55, when the determination result is recovering unprocessed and an interrupt unit 56 for performing the deterioration recovery process regardless the deterioration recovery process time.

The second invention, as shown in FIG.
An exhaust gas-purifying catalyst 50 mainly carrying palladium as a catalytic metal, a deterioration degree detecting means 51 for detecting a deterioration degree of the catalyst 50, and an exhaust temperature detecting means 52 for detecting an exhaust gas temperature flowing into the catalyst 50. Deterioration recovery processing timing determination means 53 for determining the timing for performing the degradation recovery processing of the catalyst 50 according to the detected degree of catalyst degradation, the determination result is the degradation recovery processing timing, and the detected exhaust temperature is a predetermined value. In the exhaust gas purifying apparatus for an internal combustion engine, which includes the deterioration recovery processing means 54 for performing the deterioration recovery processing of the catalyst by controlling the air-fuel ratio of the exhaust gas to the deterioration recovery processing air-fuel ratio leaner than the stoichiometric air-fuel ratio when the above A warm-up determination means 57 for determining whether the engine is warming up, and a recovery unprocessed determination means for determining whether or not the temporary deterioration is unprocessed based on the degree of deterioration detected immediately after the engine is started. 55, an interruption means 56 for performing deterioration recovery processing regardless of the deterioration recovery processing timing when the judgment result is recovery unprocessed, and the judgment results of the recovery unprocessed judgment means 55 and the warm-up judgment means 57 are recovery unprocessed. In addition, warm-up control means 5 that suppresses NO emission during warm-up
8 and.

In a third aspect based on the second aspect, the warm-up control means 58 corrects the feedback control coefficient when the air-fuel ratio of the engine is feedback-controlled to the stoichiometric air-fuel ratio to adjust the air-fuel ratio. Shift to the rich side.

Further, in a fourth aspect based on the second aspect, the warm-up control means 58 guides a part of the exhaust gas to the intake passage.

The fifth invention, as shown in FIG.
In any one of the first to fourth inventions,
The recovery unprocessed determination means 55 includes means 59 for detecting the temperature of the catalyst, and when the catalyst temperature detected immediately after the engine is started is equal to or lower than a predetermined value, the degree of deterioration immediately after the start is also determined as permanent deterioration. If not, it is determined that recovery from temporary deterioration is unprocessed.

The sixth aspect of the invention, as shown in FIG.
In any one of the first to fourth inventions,
The unrestored recovery determination means 55 includes means 52 for detecting the temperature of the catalyst 50 and means 60 for learning the degree of deterioration each time the engine is started, and the catalyst temperature detected immediately after the engine is started is below a predetermined value. At the same time, the degree of deterioration immediately after the start is determined as permanent deterioration and the detected degree of deterioration is learned as the degree of permanent deterioration of this time, while the catalyst temperature exceeds the predetermined value and the detected value of the degree of deterioration of this time is the same as the previous time. When it exceeds the learning value of, it is determined that the recovery of the temporary deterioration is unprocessed, and the previous learning value is learned as the degree of permanent deterioration of this time.

[0018]

Therefore, according to the first aspect of the present invention, when it is determined that the degree of deterioration of the catalyst detected immediately after starting is not recovered, the deterioration recovery processing is promptly performed regardless of the deterioration recovery processing timing set according to the degree of deterioration. When the engine shifts to the air-fuel ratio and the exhaust temperature rises above a certain level, it is exposed to a high-temperature lean atmosphere to quickly restore the temporary deterioration remaining on the palladium-based catalyst to the initial state of permanent deterioration, and then detect it while the engine is operating. The deterioration recovery process is performed according to the deterioration recovery process timing that is set according to the degree of deterioration, and the recovery process that responds to the permanent deterioration is promptly recovered after the catalyst whose temporary deterioration has not yet recovered at the time of hot start. Can be done properly.

Further, in the second aspect of the invention, when it is determined that the catalyst has recovered unprocessed temporary deterioration, first, the NO emission is reduced during warm-up of the engine to leave unrecovered temporary deterioration. Temporary deterioration of the catalyst is recovered by promptly performing deterioration recovery processing regardless of the deterioration recovery processing time that is set according to the degree of deterioration when the exhaust temperature rises above a certain value after assisting the deterioration of palladium-based catalyst performance. It is possible to return to the initial state of permanent deterioration by quickly recovering the catalyst whose previous temporary deterioration was not recovered at the time of hot start, etc., and the palladium purification system whose NO purification performance during warming up has deteriorated due to temporary deterioration. Emission of exhaust emission can be suppressed by supplementing the catalyst.

Further, according to the third aspect of the invention, since the warm-up control means shifts the air-fuel ratio to the rich side, NO in the exhaust gas can be reduced during warm-up, and it is reduced by unrecovered temporary deterioration. It is possible to supplement the NO purification performance of the catalyst during warm-up and suppress the emission of exhaust emission.

Further, according to the fourth aspect of the invention, since the warm-up control means recirculates a part of the exhaust gas to the intake passage, NO in the exhaust gas can be reduced during warm-up, which results from unrecovered temporary deterioration. It is possible to supplement the NO purification performance of the catalyst during warm-up and suppress the emission of exhaust emission.

According to a fifth aspect of the present invention, the recovery unprocessed determining means determines the starting state of the engine based on the temperature of the catalyst, and when the catalyst temperature is a cold start below a predetermined value, complete cooling by leaving it at room temperature is performed. If the catalyst temperature exceeds the predetermined value, it is determined that the hot start was insufficient cooling due to standing at room temperature.In this hot start, immediately after the start. It is possible to determine that the degree of deterioration detected in the above includes unrecovered temporary deterioration, and it is possible to easily separate the permanent deterioration of the palladium-based catalyst from the state including unrecovered temporary deterioration to determine the deterioration state of the catalyst. It can be grasped accurately.

In the sixth aspect of the present invention, the determination of whether or not the temporary deterioration is unprocessed is made based on the learning value of the permanent deterioration and the deterioration degree immediately after the start in addition to the engine starting state based on the catalyst temperature. Permanent deterioration and unrecovered temporary deterioration can be reliably separated, and in the case of a cold start where the catalyst temperature is below a specified value, complete cooling is performed by leaving it at room temperature. While learning as deterioration, in the case of hot start, it is determined that temporary deterioration has not been recovered when the degree of deterioration immediately after startup is larger than the previous learning value, and the learning value up to the previous time is used instead of the detected deterioration degree. By learning as the permanent deterioration this time, the learned value can always show the degree of permanent deterioration that does not include temporary deterioration, and by accurately grasping the progress of the degree of deterioration of the catalyst, unrecovered temporary deterioration Can be determined more accurately, it is possible to properly perform the deterioration recovery process.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 3 shows an embodiment of the present invention. A fuel injection valve 5 is arranged in an intake passage 8 of an engine 7 and injects fuel in response to a signal from a controller 4.

The exhaust passage 9 is provided with a three-way catalyst 1 which simultaneously oxidizes HC and CO in the exhaust gas and reduces NO.
The three-way catalyst 1 is composed of a palladium-based catalyst in which alumina is mainly supported by palladium (Pd) as a catalyst metal and other ceria and the like are supported.

A pre-catalyst oxygen sensor 2 and a post-catalyst oxygen sensor 3 are installed upstream and downstream of the three-way catalyst 1 so that the air-fuel ratio becomes the stoichiometric air-fuel ratio based on the output of the pre-catalyst oxygen sensor 2. The fuel injection amount is feedback-controlled.

Further, the number of times the outputs of the pre-catalyst oxygen sensor 2 and the post-catalyst oxygen sensor 3 are inverted to rich and lean, respectively, are compared, and the degree of deterioration of the catalyst is detected based on the inversion frequency, as will be described later. Corresponding to this degree of deterioration, the catalyst deterioration recovery process is executed at a predetermined operation time.

The controller 4 includes a water temperature sensor 12 for detecting the engine cooling water temperature T _W , a temperature sensor 13 for detecting the exhaust temperature flowing into the three-way catalyst 1, and a three-way catalyst 1 for detecting the engine operating state. A signal from the temperature sensor 20 that detects the internal temperature T _B is input. Although not shown, signals representative of operating conditions such as the intake air amount Q of the engine 7 and the rotation speed Ne are also input.

An exhaust gas recirculation passage 14 for recirculating a part of the exhaust gas from the exhaust passage 9 is connected to the intake passage 8, and an exhaust gas recirculation control valve 15 is connected to the engine 7 by the controller 4.
The exhaust gas recirculation amount is controlled according to the operating state of
Decrease O.

The palladium-based three-way catalyst 1 has a characteristic that the catalytic performance is temporarily deteriorated when exposed to a high temperature exhaust atmosphere rich in the stoichiometric air-fuel ratio or higher.

FIG. 4 shows that the three-way catalyst 1 is used for a long time in high-temperature exhaust gas having a temperature of 500 ° C. and an air-fuel ratio of stoichiometric air-fuel ratio (λ = 1).
Represents the state of change in catalyst conversion rate (temporary deterioration) when exposed to, and the catalyst conversion rate decreases with the passage of time, but there is little change in the catalyst A in the figure with little permanent deterioration,
On the other hand, as the catalysts B and C and the permanent deterioration proceeded, the conversion rate decreased remarkably.

Temporary deterioration of the three-way catalyst 1 can be recovered by exposing the three-way medium 1 to a high temperature exhaust atmosphere with a lean air-fuel ratio, and the catalytic performance is recovered to the initial state of permanent deterioration. .

Therefore, when the state of temporary deterioration of the catalyst is determined, the palladium-based three-way catalyst 1 temporarily deteriorated by temporarily controlling the air-fuel ratio to the lean side under the operating condition that the exhaust temperature becomes a predetermined high temperature. Can be recovered.

In order to perform such deterioration recovery processing of the three-way catalyst 1, the controller 4 performs the control shown in FIGS.

First, FIGS. 5 and 6 are control routines for judging the deterioration of the three-way catalyst 1, which are executed only once after the engine 7 is started.

After the engine cooling water temperature T _W and the internal temperature T _B of the three-way catalyst 1 are read in steps S1 and S2, the engine cooling water temperature T _W is, for example, a predetermined value T ₁ or more after completion of warm-up in step S3. Then, in step S4, it is determined whether the air-fuel ratio is in the feedback control region.
If it is in the air-fuel ratio feedback control region after completion of warm-up, the process proceeds to the deterioration diagnosis process after step S5, while if not so, the process returns to step S1.

In steps S5 and S6, the rich and lean inversion frequencies F ₁ and F ₂ of the pre-catalyst oxygen sensor 2 upstream of the three-way catalyst 1 and the post-catalyst oxygen sensor 3 downstream are read respectively.

In step S7, these inversion frequencies F ₁ ,
The ratio Fr of F ₂ is calculated as Fr = F ₂ / F _1. As shown in FIG. 12, the reversal frequency ratio Fr approaches 1 as the deterioration of the three-way catalyst 1 progresses, and when the three-way catalyst 1 is functioning normally, the oxygen in the exhaust gas is stored. Therefore, oxygen contained in the exhaust gas upstream of the three-way catalyst 1 cannot be directly detected downstream of the three-way catalyst 1. on the other hand,
When the three-way catalyst 1 deteriorates, the oxygen storage capacity also decreases, and the oxygen in the upstream exhaust flows as it is to the downstream, so that the output of the post-catalyst oxygen sensor 3 arranged downstream of the three-way catalyst 1 is reduced. The inversion frequency F ₂ is close to the inversion frequency F ₁ of the output of the pre-catalyst oxygen sensor 2. Therefore, the inversion frequency ratio Fr has a value representative of the degree of deterioration of the three-way catalyst 1.

On the other hand, in step S8, the inversion frequency ratio Fr
Frm, which is the learning value up to the previous start of, is read from the storage means (not shown). The learning value Frm is the reversal frequency ratio calculated and learned each time the engine is started, and is represented by, for example, the following moving average value Frm (t).

Frm (t) = aFrm (t−1) + bFr (t) where a and b are constants The learning value Frm read in this way up to the previous startup and the inversion frequency ratio Fr detected after the current startup. Therefore, in step S9, it is determined whether the inversion frequency ratio Fr is equal to or larger than the learning value Frm.

Assuming that the learning value Frm shows permanent deterioration and the reversal frequency ratio Fr shows temporary deterioration, if the reversal frequency ratio Fr is equal to or larger than the learning value Frm, the engine will be completely left at room temperature after the last engine stop. Cooling has not finished,
While it is determined that the three-way catalyst 1 is temporarily deteriorated, the process proceeds to step S11. If not, the learning value Frm is updated with the detected inversion frequency ratio Fr that is determined to be only permanent deterioration. The process proceeds to step S13.

When it is determined in step S9 that the deterioration is temporary, that is, when the inversion frequency ratio Fr is equal to or larger than the learning value Frm, the temperature T _B inside the three-way catalyst 1 read in step S2 is the predetermined value T _2. It is determined whether or not the engine 7 is in the hot start state (step S10).

In step S10, the temperature T inside the catalyst is
_{If B} is equal to or greater than the predetermined value T _2, it is determined that the hot start has been performed for a short time since the last engine stop, and the process proceeds to step S11 while the temperature T _B inside the catalyst is less than the predetermined value T ₂ . In this case, similarly, it is determined that the three-way catalyst 1 is in a cold start state in which the three-way catalyst 1 is completely cooled by being left at room temperature after a sufficient time has passed since the last engine stop, and the reversal frequency ratio Fr detected in the same manner as above is permanently deteriorated. Learning value F
In order to reflect it in rm, the process proceeds to step S13, and either hot start or cold start is determined by the temperature T _B of the catalyst immediately after the engine is started, and the degree of deterioration detected immediately after the start is determined according to the engine starting state. Is the primary deterioration or permanent deterioration of the three-way catalyst 1.

When it is determined in step S10 that the hot start is determined and the process proceeds to step S11, the reversal frequency ratio Fr is equal to or higher than the learning value Frm, and the temporary deterioration of the three-way catalyst 1 is recovered. Step S1
In 1, the Hot unrecovered state signal T _Bm is set to 1 to set that the temporary deterioration of the three-way catalyst 1 is unrecovered. Then, in step S12, the reversal frequency ratio Fr detected this time is set.
Is replaced with the learning value Frm indicating the permanent deterioration up to the previous time, and the degree of deterioration detected immediately after this start, that is, the inversion frequency ratio Fr is not reflected in the learning value Frm representing the permanent deterioration.

In this step S12, it can be estimated that the inversion frequency ratio Fr detected this time is after the hot start in which the recovery unprocessed temporary deterioration has occurred and the temporary deterioration is added to the permanent deterioration. The learning value Frm up to the previous time is used as the current permanent deterioration degree instead of being reflected in the learning value Frm shown, and the learning value Frm is treated as a value according to the progress of the permanent deterioration degree in order to suppress the fluctuation of the permanent deterioration degree. Therefore, it is possible to accurately determine the primary deterioration based on the learning value Frm.

After updating the learning value Frm in this way, the routine proceeds to the deterioration detection routine of step S20. On the other hand, if it is determined in step S9 that the reversal frequency ratio Fr indicates permanent deterioration, or if the determination in step S10 is a cold start in which the catalyst bed temperature T _B is less than the predetermined value T ₂ , the learning value is determined in step S13. In order to make Frm correspond to the progress of permanent deterioration of the three-way catalyst 1, the learning value Frm is updated based on the moving average value of the inversion frequency ratio Fr detected this time, and then the inversion frequency ratio Fr is set to the predetermined value Fr in step S14.
It is determined whether it is a or more. Although the learning value Frm is the moving average value of the inversion frequency ratio Fr, it may be simply the inversion frequency ratio Fr at the time of the previous start.

The determination in step S14 is to determine whether the permanent deterioration has progressed to a predetermined value Fra or more. When the inversion frequency ratio Fr is the predetermined value Fra or more, the routine proceeds to the deterioration detection routine of step S20, while If not, the process ends as it is.

Although the above control is executed only once each time the engine 7 is started, immediately after the engine 7 is started, the degree of deterioration (reversal) detected by separating the hot start and cold start depending on the catalyst bed temperature T _B. Frequency ratio Fr:
The degree of initial deterioration (hereinafter, referred to as “degree of deterioration”) can be separately treated as temporary deterioration that can be recovered and permanent deterioration.

Next, in the deterioration detection routine of FIG. 7, in step S21, based on the reversal frequency ratio Fr, from the table shown in FIG. 10, the deterioration degree Rm of the catalyst set in several stages and the allowable range of the catalyst performance are set. Exposure time Tc that can be directly exposed to exhaust gas and a recovery process determination value Tr that corresponds to the deterioration recovery process time that is determined according to the degree of deterioration.
And are read respectively.

The deterioration degree Rm corresponds to the reversal frequency ratio Fr, and the initial deterioration degree detected immediately after the start corresponds to the permanent deterioration degree. Therefore, the exposure possible time Tc of the three-way catalyst 1 is Based on the state of permanent deterioration, when the exhaust temperature is higher than a predetermined value, the addition value with the deterioration degree of the catalyst that is predicted to proceed when the operation is continued until it reaches the allowable limit of the catalyst performance. It is set as time. Then, the recovery process determination value Tr is set according to the exposure possible time Tc.

In step S22, the Hot unrecovery signal Tbm = 1 indicates whether or not it is determined in step S10 that the starting state of the engine 7 is a hot start and it is determined that the temporary deterioration has not been recovered.
If Tbm is 1, the process proceeds to step S23 to compensate for the deterioration of the NO purification performance of the three-way catalyst 1 due to temporary deterioration, while if only Tbm is permanently deteriorated, step S30 is performed. Proceed to the exposure time calculation / recovery processing routine of.

Here, when the Hot unrecovered state signal = 1 in which it is determined in step S23 that the temporary deterioration is unrecovered hot start, the air-fuel ratio feedback control is performed according to the deterioration degree Rm read in step S21. After changing the control constant to the rich side and performing a process of suppressing NO emission, the process proceeds to the exposure time calculation / recovery process routine of step S30. In this case, in the palladium-based three-way catalyst 1 that has undergone primary deterioration, the NO emission amount before the completion of warming up increases due to the deterioration of the catalyst performance. Therefore, the NO-emission amount is reduced by shifting the air-fuel ratio to the rich side according to the degree of deterioration, and the performance of the three-way catalyst 1 before the recovery of the primary deterioration is compensated.

In place of the air-fuel ratio control to the rich side in step S23, the exhaust gas recirculation rate (E) for driving the exhaust gas recirculation control valve 15 to recirculate a part of the exhaust gas to the intake passage 8 (E
GR rate) may be increased, and in this case as well, NO in the exhaust gas is increased.
Can be reduced.

The above-described deterioration detection processing routine is performed by the engine 7.
Is repeatedly executed at a predetermined cycle until is stopped (step S24).

8 and 9 show the details of the exposure time calculation / recovery processing routine described above. FIG. 8 shows the exposure possible time calculation and FIG. 9 shows the recovery processing.

First, in step S31, it is determined based on the Hot unrecovered state signal Tbm whether or not the hot start is performed when the three-way catalyst 1 is temporarily deteriorated. If the Hot unrecovered state where Tbm = 1 is established, First, the process proceeds to the deterioration recovery process after step S39 shown in FIG. 9 to promptly recover the primary deterioration of the three-way catalyst 1, while otherwise it is proportional to the time exposed to the exhaust gas at a temperature higher than that in step S32. Exposure time is calculated to detect the primary deterioration.

In step S32, an integrated value Tin, which will be described later, is set.
= 0, and in step S33, the timer Ti is set to 0, and then counting of the timer is started.
4, the weighting coefficient Kc is read from the table of FIG. 11 based on the exhaust gas catalyst inlet temperature T from the temperature sensor 20 at that time.

This weighting coefficient Kc represents the degree of deterioration of the catalyst that progresses per unit time (this also corresponds to the degree of recovery), and strictly speaking, it is a two-dimensional map having exhaust gas temperature and air-fuel ratio as parameters. However, since the influence of the exhaust gas temperature is greater, the table setting may be based only on the temperature.

At step S35, the exhaust gas catalyst inlet temperature T
Is compared with the set temperature range when the weighting coefficient Kc is selected,
The times within this temperature range are integrated in steps S36 and S37. However, this integrated value Tin is Tin = Tin
+ Kc × Ti, and the weighting coefficient Kc calculated based on the catalyst inlet temperature T and the time T when the temperature is within the set temperature range
The integrated value Tin is increased by adding the product of multiplication with i.

When the catalyst inlet temperature T changes from the predetermined temperature range in step S35, the timer Ti is counted in step S36.
Counting is stopped, the process returns to step S33 again via step S37, and the integration of the exposure time is continued.

Then, in step S38, the integrated value Ti
exposure time Tc obtained by reading n in step S21
And step S33 until the time Tc is reached.
The accumulation operation from S37 to S37 is repeated, and the accumulation is continued according to the catalyst inlet temperature T of the exhaust gas at that time. Then, when the integration result is Tin> Tc, step S39 shown in FIG.
The subsequent recovery processing is performed.

Since the primary deterioration of the three-way catalyst 1 progresses according to the time of exposure to the high temperature rich atmosphere, there is a relationship between the exposure time Tin and the exposure possible time Tc that are integrated as in steps S32 to S38. , The progress of deterioration is determined.

Thus, the integrated value Tin is the exposure possible time Tc.
When step S39 has passed, the integrated value Tim is first reset to 0 in step S39, and it is determined in step S40 whether the read catalyst inlet temperature T of the exhaust gas is in a high temperature state above a predetermined value at which deterioration recovery processing is possible. In step S41, the operating condition is a high load rich air-fuel ratio region (KMR region).
Determine if it is in.

In this high load rich air-fuel ratio range, even if an attempt is made to shift the air-fuel ratio to the lean side for catalyst deterioration recovery processing, lean shift can be performed because the KMR range is prioritized in order to ensure drivability. Instead, the process returns to step S39 and the deterioration recovery process up to that point is restarted from the beginning.

On the other hand, when it is not in the KMR range, the deterioration recovery process of the three-way catalyst 1 is performed as follows.

First, in step S42, the timer Ti is reset to 0 and counting is started, and in step S43, the weighting factor Kr is read from the table of FIG. 11 based on the catalyst inlet temperature T of the exhaust gas.

Then, in step S44, the control coefficient (for example, the proportional value or the integral value) of the air-fuel ratio feedback control is changed to shift the control center of the air-fuel feedback control to the lean side, so that the deteriorated three-way catalyst 1 is removed. The primary deterioration is recovered by exposing it to a high temperature lean atmosphere.

At this time, at the same time, the exhaust gas recirculation control valve 15 is driven to increase the exhaust gas recirculation ratio (EGR ratio) and make the air-fuel ratio lean, so that the three-way catalyst 1 cannot perform purification processing.
It reduces the amount of O emission and assists in lowering the exhaust gas purification performance.

As described above, when the temperature of the exhaust gas flowing into the three-way catalyst 1 is high, the palladium catalyst deteriorated by shifting the air-fuel ratio to the lean side recovers from temporary deterioration except permanent deterioration. The three-way catalyst 1 recovers the degree of deterioration to the initial state of permanent deterioration.

In steps S45 to S47, the time during which the temperature of the exhaust gas reaches a certain value or higher is integrated. This integrated value Ti
m is calculated as Tim = Tim + Kr × Ti from the weighting coefficient Kr read in step S43.

When the catalyst inlet temperature T changes from the predetermined temperature range in step S45, the timer Ti is set in step S46.
Counting is stopped, the process returns to step S40 again via step S47, and the integration of the deterioration recovery processing time is continued.

Also in this case, since the recovery of deterioration is greatly influenced by the temperature of the exhaust gas in the lean atmosphere, the weighting factor Kr is set from the table of FIG. 11 which is set depending only on the catalyst inlet temperature T of the exhaust gas. It is possible.

In step S48, it is determined whether the deterioration recovery process is completed by comparing the integrated value Tim with the recovery process determination value Tr read in step S21. In this way, when the deterioration recovery processing time corresponding to the detected degree of deterioration of the three-way catalyst 1 elapses, the temporary deterioration of the catalyst is recovered to the initial state (excluding permanent deterioration) as described above. Then, the process proceeds to step S49, the control coefficient of the feedback control of the air-fuel ratio and the exhaust gas recirculation rate are returned to the values in the normal operating state, and the deterioration recovery process is ended.

Here, when the catalyst temperature T _B detected after the engine 7 is started is a hot start at which the temperature is higher than a predetermined value and the reversal frequency ratio Fr is larger than the previous learned value Frm, the three-way catalyst 1 is left at room temperature. It can be determined that the recovery from the temporary deterioration is insufficient, and such a three-way catalyst 1 shown in FIG.
The performance is degraded as indicated by the broken line in the figure.

Since the amount of NO emission before the warm-up is increased especially for the temporarily deteriorated palladium-based catalyst, it is possible to temporarily change the air-fuel ratio to the rich side before entering the deterioration recovery process as in step S23. In order to compensate for the deterioration of catalyst performance due to deterioration, reduce NO emissions, and in the case of hot start with temporary deterioration, perform recovery processing promptly without calculating the exposure time to achieve the initial stage of permanent deterioration. Since the recovery to the state is performed, the deterioration recovery process of the three-way catalyst 1 can be quickly performed while suppressing the increase of the exhaust emission. In this case, the inversion frequency ratio F detected
Since r is not reflected in the learning value Frm, the learning value Frm does not include temporary deterioration and can be treated as the degree of permanent deterioration at all times, and the deterioration state of the three-way catalyst 1 is divided into primary deterioration and permanent deterioration. It is possible to separate and accurately grasp.

On the other hand, in the case of cold start of the engine 7, the detected reversal frequency ratio Fr indicates the degree of progress of permanent deterioration. Therefore, by reflecting this to the learning value Frm, the degree of permanent deterioration of the three-way catalyst 1 is shown. Of the three-way catalyst 1 that has progressed during operation according to the exposure time to the high-temperature rich atmosphere and the deterioration recovery process is performed, and the low-temperature activity and the economical efficiency are excellent. It is possible to suppress the exhaust emission from the internal combustion engine while recovering the temporary deterioration of the palladium-based catalyst as needed.

Thus, in the case of a hot start in which temporary deterioration has not been recovered, the deterioration recovery process is promptly performed to recover the initial state of permanent deterioration without calculating the exposure time. As described above, unrecovered temporary deterioration is judged as a state where permanent deterioration has significantly progressed, and frequent deterioration recovery processing is no longer performed, while maintaining good drivability without making the air-fuel ratio leaner than necessary. Temporary deterioration of the palladium-based catalyst can be recovered at any time, and if there is unrecovered temporary deterioration during hot start, the air-fuel ratio is shifted to the rich side during warm-up operation to improve catalyst performance due to temporary deterioration. The exhaust emission can be suppressed in a wide operating range by compensating for the decrease in NO.

Next, another embodiment shown in FIGS. 14 and 15 will be described.

Since the degree of progress of deterioration of the three-way catalyst 1 is related to the degree of permanent deterioration, that is, the degree of initial deterioration immediately after engine start detected at cold start, based on the reference value according to this degree of deterioration. The time until the total deterioration of the temporary deterioration and the permanent deterioration reaches the allowable limit is determined.

The process of FIG. 14 is executed only once each time the engine 7 is started, and steps S51 to S58 are executed.
Up to the step S1 to S8 of the processing shown in FIG. 5, the deterioration degree Rm is calculated from the table of FIG. 10 based on the inversion frequency ratio Fr in the step S59.
The initial deterioration degree R is stored in step S60.
Based on mo, the reference value Rmc is read from the table of FIG. This reference value Rmc is determined so that Rmo + Rmc becomes the deterioration limit of the catalyst performance, and the initial deterioration degree Rmo
Becomes larger, Rmc becomes smaller.

That is, here, from the deterioration determination of the catalyst which is performed only once after the engine 7 is started, the deterioration degree R
m is stored as the initial deterioration degree Rmo.

Next, the processing shifts to the processing in FIG. This process is executed every predetermined time after the engine is started, and the degree of deterioration of the catalyst is determined.

Steps S61 to S68 are the same as steps S1 and S3 to S8. Here, the reversal frequency ratio Fr when the catalyst inlet temperature T of the exhaust gas is equal to or higher than a predetermined value is calculated, and then in step S69. Based on this Fr, the deterioration degree Rm is read from the table of FIG.
The progress degree ΔRm of the temporary deterioration represented by the difference between the deterioration degree Rm and the initial deterioration degree Rmo is ΔRm = Rm−Rmo
Calculate as Since the initial deterioration degree Rmo detected immediately after the start of the engine 7 corresponds to the permanent deterioration degree, this ΔR
m represents the temporary deterioration of the recoverable catalyst.

In step S70, the calculated temporary deterioration progress degree ΔRm is compared with the reference value Rmc read in step S60. As the permanent deterioration progresses, the reference value Rmc becomes smaller, and the tolerance of temporary deterioration becomes smaller accordingly.

Here, the temporary deterioration progress degree ΔRm is the reference value R.
If it is not less than mc, the routine proceeds to step S71 to proceed to the catalyst deterioration recovery processing routine, and the recovery processing determination value Tr corresponding to the temporary deterioration progress degree ΔRm is read from the table of FIG.

Then, the process proceeds to step S72, where it is determined in the same manner as in steps S9 to S12 whether or not there is a starting state and temporary deterioration, and then, based on the recovery process determination value Tr obtained in step S71, step S20 is performed as described above. The subsequent deterioration recovery processing is performed.

Thus, based on the reference value Rmc corresponding to the initial deterioration degree Rm detected immediately after the engine 7 is started,
Since the time until the total degree of deterioration including temporary deterioration and permanent deterioration reaches the allowable limit is judged, the catalyst deterioration recovery process should be performed at an appropriate time while accurately judging according to the progress of deterioration. Can be done.

In addition, in order to make the air-fuel ratio of the exhaust gas lean in the deterioration recovery process, in addition to correcting the feedback control coefficient as described above, the secondary is provided upstream of the three-way catalyst 1 and downstream of the pre-catalyst oxygen sensor 2. A device (not shown) for introducing air may be provided, and secondary air may be introduced upstream of the three-way catalyst 1 to make the exhaust gas flowing into the three-way catalyst 1 lean. In this case, the air-fuel ratio of the engine 7 can be set to a normal stoichiometric air-fuel ratio, and good drivability can be secured while performing the deterioration recovery process of the three-way catalyst 1.

[0090]

As described above, according to the first aspect of the present invention, an exhaust purification catalyst mainly carrying palladium as a catalyst metal, a deterioration degree detecting means for detecting the deterioration degree of this catalyst, and a catalyst flowing into the catalyst. Exhaust temperature detection means for detecting the exhaust temperature, deterioration degradation processing timing determination means for determining the timing of performing the catalyst degradation recovery processing according to the detected catalyst degradation degree, and the determination result is the degradation recovery processing timing, Further, when the detected exhaust 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 deterioration recovery processing air-fuel ratio leaner than the stoichiometric air-fuel ratio to perform deterioration recovery processing of the catalyst is provided. In an exhaust gas purification apparatus for an internal combustion engine, a recovery unprocessed determination means for determining whether recovery of temporary deterioration is unprocessed based on the degree of deterioration detected immediately after the engine is started, and the result of this determination is recovery unprocessed. In this case, an interrupt means for performing deterioration recovery processing regardless of the deterioration recovery processing time is provided, and after the catalyst whose temporary temporary deterioration is not recovered at the time of hot start etc. is quickly recovered to the initial state of permanent deterioration, It becomes possible to perform recovery processing at a recovery processing time corresponding to permanent deterioration, and it is possible to frequently perform recovery processing by determining unrecovered temporary deterioration as in the case of the conventional example as if the permanent deterioration is significantly advanced. Since it is no longer necessary to make the air-fuel ratio leaner than necessary, good drivability can be secured, and exhaust emission emissions can be reduced while responding to the temporary deterioration characteristics of the palladium-based catalyst. It will be possible.

The second aspect of the invention is directed to an exhaust gas purification catalyst mainly carrying palladium as a catalytic metal, a deterioration degree detecting means for detecting the deterioration degree of the catalyst, and an exhaust gas temperature flowing into the catalyst. Exhaust temperature detecting means, a deterioration recovery processing timing determining means for determining the timing for performing the catalyst deterioration recovery processing according to the detected catalyst deterioration degree, and the determination result is the deterioration recovery processing timing, and the detected exhaust gas Exhaust of an internal combustion engine equipped with deterioration recovery processing means for performing deterioration recovery processing of a catalyst by controlling the air-fuel ratio of exhaust gas to a deterioration recovery processing air-fuel ratio leaner than the stoichiometric air-fuel ratio when the temperature is equal to or higher than a predetermined value. In the purification device, warm-up determination means for determining whether the engine is in warm-up operation, and recovery unprocessed determination means for determining whether recovery of temporary deterioration is unprocessed based on the degree of deterioration detected immediately after starting the engine. When When the determination result is recovery unprocessed, the interrupt recovery unit performs the recovery process regardless of the deterioration recovery process timing, and the determination results of the recovery unprocessed determination unit and the warm-up determination unit are recovery unprocessed and warm-up. NO
It is equipped with a warm-up control means that suppresses the emission of exhaust gas, and promptly restores the catalyst whose previous temporary deterioration has not been recovered at the time of hot start to the initial state of permanent deterioration, and before the deterioration recovery process becomes possible. Exhaust emissions can be reduced while the engine is warming up, and the NO purification characteristics of the palladium catalyst due to unrecovered temporary deterioration can be supplemented, and exhaust emission emissions can be reliably suppressed. Becomes

In a third aspect of the present invention, the warm-up control means corrects the feedback control coefficient when feedback controlling the air-fuel ratio of the engine to the stoichiometric air-fuel ratio, shifts the air-fuel ratio to the rich side, and does not recover. It is possible to supplement the NO purification performance of the catalyst during warm-up, which has deteriorated due to the temporary deterioration, and it is possible to suppress the emission of exhaust emission while corresponding to the temporary deterioration characteristic of the palladium-based catalyst.

Further, in the fourth aspect of the present invention, the warm-up control means guides part of the exhaust gas to the intake passage, so that the NO purification performance of the catalyst during warm-up, which is lowered by unrecovered temporary deterioration, is supplemented. This makes it possible to suppress exhaust emission while dealing with the temporary deterioration characteristic of the palladium-based catalyst.

According to a fifth aspect of the present invention, the recovery unprocessed determining means includes means for detecting the temperature of the catalyst, and when the catalyst temperature detected immediately after the engine is started is below a predetermined value, deterioration just after the engine is started. The degree is judged to be permanent deterioration, but if not, the recovery from temporary deterioration is judged to be unprocessed.Therefore, cold start in which cooling at room temperature is completely performed and cooling at room temperature are insufficient. A reliable hot start can be reliably determined, and in the case of a hot start, it can be determined that unrecovered temporary deterioration is included, and the deterioration recovery processing can be immediately started. The degree of deterioration is surely judged to be a state that includes permanent deterioration and unrecovered temporary deterioration, and the deterioration recovery process corresponding to the temporary deterioration characteristic of the palladium-based catalyst is appropriately executed to execute exhaust emission control. Deployment discharge becomes possible to suppress the.

According to a sixth aspect of the present invention, the unrestored recovery determination means comprises means for detecting the temperature of the catalyst and means for learning the degree of deterioration each time the engine is started. Similarly, when the catalyst temperature is equal to or lower than the predetermined value, the deterioration degree immediately after the start is determined as permanent deterioration and the detected deterioration degree is learned as the current permanent deterioration degree.
When the catalyst temperature exceeds the predetermined value and the detected value of the degree of deterioration of this time exceeds the learned value up to the previous time, it is determined that the recovery of the temporary deterioration is unprocessed, and the previously learned value is set as the degree of permanent deterioration of this time. In order to learn, in addition to the engine starting state based on the catalyst temperature, the deterioration state of the catalyst is accurately determined based on the learning value of permanent deterioration and the degree of deterioration detected immediately after starting, to a state including permanent deterioration and unrecovered temporary deterioration. It becomes possible to separate, and it is possible to more appropriately perform the deterioration recovery process corresponding to the temporary deterioration characteristic of the palladium-based catalyst while accurately grasping the progress of the deterioration degree of the catalyst.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram corresponding to a first invention.

FIG. 2 is a claim correspondence diagram corresponding to the second invention.

FIG. 3 is a block diagram showing an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a transition state of catalyst performance.

FIG. 5 is a first half of a flowchart showing a control operation for detecting deterioration of a three-way catalyst.

FIG. 6 is the latter half of the flowchart.

FIG. 7 is a flowchart showing a control operation of a deterioration detection routine.

FIG. 8 is a flowchart showing a control operation for setting an exposure time.

FIG. 9 is a flowchart showing a control operation of recovery processing.

FIG. 10 is an explanatory diagram showing the relationship between the inversion frequency ratio Fr and the degree of deterioration and the like.

FIG. 11 is an explanatory diagram showing a relationship between a catalyst inlet temperature and a weighting coefficient.

FIG. 12 is an explanatory diagram showing a relationship between a reversal frequency ratio and deterioration of catalyst performance.

FIG. 13 is a diagram showing the relationship between catalyst temperature and conversion performance.

FIG. 14 is a flowchart of a control operation showing another embodiment.

FIG. 15 is a flowchart of the same.

FIG. 16 is an explanatory diagram showing a relationship between an initial deterioration degree and a reference value.

FIG. 17 is an explanatory diagram showing a relationship between a deterioration progress degree and a reference value.

[Explanation of symbols]

 1 Three-way catalyst 2 Pre-catalyst oxygen sensor 3 Post-catalyst oxygen sensor 4 Controller 9 Exhaust passage 13 Exhaust temperature sensor 20 Catalyst temperature sensor 50 Catalyst 51 Degradation degree detection means 52 Exhaust temperature detection means 53 Deterioration recovery processing timing determination means 54 Degradation recovery processing Means 55 Recovery unprocessed judging means 56 Interrupting means 57 Warm-up state judging means 58 Warm-up control means 59 Catalyst temperature detecting means 60 Learning means

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location F01N 3/24 R ZAB B F02D 41/14 310 C (72) Inventor Akira Tayama 2 Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Address Within Nissan Motor Co., Ltd.

Claims (6)

[Claims] 1. An exhaust gas purifying catalyst mainly carrying palladium as a catalytic metal, a deterioration degree detecting means for detecting a deterioration degree of the catalyst, and an exhaust temperature detecting means for detecting an exhaust temperature flowing into the catalyst. Deterioration recovery processing timing determining means for determining the timing for performing the catalyst degradation recovery processing according to the detected catalyst degradation degree, the determination result is the degradation recovery processing timing, and the detected exhaust temperature is a predetermined value or more. In an exhaust gas purification apparatus for an internal combustion engine, which comprises a deterioration recovery processing unit that controls the deterioration recovery processing of the catalyst by controlling the deterioration recovery processing air-fuel ratio of the exhaust air-fuel ratio to the lean side of the stoichiometric air-fuel ratio at a certain time,
Recovery unprocessed determination means for determining whether the recovery of temporary deterioration is unprocessed based on the degree of deterioration detected immediately after the engine is started, and when the result of this determination is recovery unprocessed, regardless of the deterioration recovery process timing. An exhaust emission control device for an internal combustion engine, comprising: an interruption unit that performs deterioration recovery processing. 2. An exhaust gas purification catalyst mainly carrying palladium as a catalytic metal, a deterioration degree detecting means for detecting a deterioration degree of the catalyst, and an exhaust temperature detecting means for detecting an exhaust temperature flowing into the catalyst. Deterioration recovery processing timing determining means for determining the timing for performing the catalyst degradation recovery processing according to the detected catalyst degradation degree, the determination result is the degradation recovery processing timing, and the detected exhaust temperature is a predetermined value or more. In an exhaust gas purification apparatus for an internal combustion engine, which comprises a deterioration recovery processing unit that controls the deterioration recovery processing of the catalyst by controlling the deterioration recovery processing air-fuel ratio of the exhaust air-fuel ratio to the lean side of the stoichiometric air-fuel ratio at a certain time,
Warm-up determining means for determining whether the engine is warming up, and recovery unprocessed determining means for determining whether recovery of temporary deterioration is unprocessed based on the degree of deterioration detected immediately after starting the engine,
When the result of this determination is that recovery is not yet processed, an interrupt means for performing deterioration recovery processing regardless of the deterioration recovery processing time,
An exhaust gas purification apparatus for an internal combustion engine, comprising: warm-up control means for suppressing NO emission when the determination results of the recovery-unprocessed determination means and the warm-up determination means are recovery-unprocessed and warm-up. . 3. The warm-up control means corrects a feedback control coefficient when feedback-controlling an air-fuel ratio of an engine to a stoichiometric air-fuel ratio, and shifts the air-fuel ratio to a rich side. An exhaust gas purification device for an internal combustion engine as described. 4. The exhaust gas purification device for an internal combustion engine according to claim 2, wherein the warm-up control means guides a part of the exhaust gas to the intake passage. 5. The recovery unprocessed determination means includes means for detecting the temperature of the catalyst, and when the catalyst temperature detected immediately after the engine is started is below a predetermined value, the degree of deterioration immediately after the start is also determined as permanent deterioration. On the other hand, if not so, it is determined that the recovery from the temporary deterioration is unprocessed, and the exhaust emission control system for an internal combustion engine according to any one of claims 1 to 4. 6. The unrestored recovery determination means comprises means for detecting the temperature of the catalyst and means for learning the degree of deterioration every time the engine is started, and the catalyst temperature detected immediately after the start of the engine has a predetermined value. In the following cases, similarly, the degree of deterioration immediately after the start is determined as permanent deterioration and the detected degree of deterioration is learned as the degree of permanent deterioration of this time, while the catalyst temperature exceeds a predetermined value and the detected value of the degree of deterioration of this time is learned. 5. When the value exceeds the value, it is determined that the recovery of the temporary deterioration is unprocessed, and the learning value up to the previous time is learned as the current degree of permanent deterioration, and the learning value according to any one of claims 1 to 4. Exhaust gas purification device for internal combustion engine.