JP3520730B2 - Engine catalyst deterioration diagnosis device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine catalyst deterioration diagnosing device, and more specifically, when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, it absorbs NOx in the exhaust gas and the exhaust air-fuel ratio is stoichiometric. N, which releases the absorbed NOx and performs a reduction process when the fuel ratio is richer than the stoichiometric air-fuel ratio
The present invention relates to a technique for diagnosing deterioration of NOx absorption performance of an Ox absorption catalyst.

[0002]

2. Description of the Related Art Conventionally, when the exhaust air-fuel ratio is lean, it absorbs NOx in the exhaust gas, and when the exhaust air-fuel ratio is stoichiometric or rich, the absorbed NOx is absorbed.
NOx absorption catalyst (N
A lean combustion engine equipped with an Ox absorption type three-way catalyst is known (see Japanese Patent Laid-Open No. 7-139397).

On the other hand, as a technique for diagnosing the deterioration of the catalyst, there have been heretofore known JP-A-2-130245 and JP-A-8-140.
There was one disclosed in Japanese Patent No. 30. JP-A-2
The deterioration diagnosis technique disclosed in Japanese Patent Laid-Open No. 130245 detects a delay time of a post-catalyst air-fuel ratio with respect to a pre-catalyst air-fuel ratio during feedback control, and diagnoses deterioration of a three-way catalyst based on the delay time. is there.

The deterioration diagnosis technique disclosed in Japanese Unexamined Patent Publication No. 8-14030 switches the air-fuel ratio of the air-fuel mixture from lean to rich or from rich to lean in a three-way catalyst or a catalyst having NOx absorption performance. From the peak output of the oxygen sensor downstream of the catalyst during the switching period,
The catalyst deterioration is detected.

[0005]

In the deterioration diagnosis technique disclosed in Japanese Patent Laid-Open No. 2-130245, a slight delay in air-fuel ratio change when rich / lean is repeated in a short cycle during air-fuel ratio feedback. Since it is a configuration for diagnosing catalyst deterioration from the above, it is difficult to perform deterioration diagnosis with high accuracy, and it is for diagnosing deterioration of normal three-way performance, and it does not always match the deterioration state of the three-way performance. There was a problem that the deterioration of NOx absorption performance could not be diagnosed.

Further, in the deterioration diagnosis technique disclosed in Japanese Patent Laid-Open No. 8-14030, the diagnosis is made on the basis of the peak value of the detection signal of the oxygen sensor. However, there is a problem in that it is difficult to accurately diagnose the catalyst deterioration because it is affected by the exhaust gas and the like. The present invention has been made in view of the above problems, and an object of the present invention is to provide a deterioration diagnosis device that can accurately diagnose deterioration of the NOx absorption performance of a NOx absorption catalyst.

[0007]

Therefore, the invention according to claim 1 absorbs NOx in the exhaust gas when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. A NOx absorption catalyst that releases the absorbed NOx and performs reduction processing when the fuel ratio is richer than the fuel ratio,
A catalyst deterioration diagnosis device for an engine capable of performing a combustion operation at a lean air-fuel ratio rather than a stoichiometric air-fuel ratio, wherein the NOx absorption amount for the NOx absorption catalyst is estimated during lean combustion, and the exhaust air before the NOx absorption catalyst is also estimated. The delay time until the exhaust air-fuel ratio after the NOx absorption catalyst changes from lean to rich is measured with respect to the change of the fuel ratio from lean to rich, and from the correlation between the estimated value of the NOx absorption amount and the delay time. The configuration is such that deterioration of the NOx absorption performance of the NOx absorption catalyst is diagnosed , and the deterioration based on the delay time is used.
Delay measured at the time of the first rich reversal after engine start
The configuration is based on time only.

According to this structure, the deterioration of the NOx absorption performance is diagnosed from the correlation between the response delay of the lean-to-rich change after the catalyst with respect to the before catalyst and the NOx absorption amount before the rich change. When the air-fuel ratio before the NOx absorption catalyst is changed from lean to rich, the desorption of NOx absorbed during lean combustion is started, but oxygen O ₂ is desorbed at the same time as the desorption of NOx. Therefore, the air-fuel ratio after the catalyst reverses to rich after the desorption of NOx is completed.
The rich inversion after the catalyst is delayed by a time corresponding to the NOx absorption amount with respect to the rich inversion before the catalyst. Therefore, when there is no delay corresponding to the predicted NOx absorption amount, it can be determined that the actual absorption amount is smaller than the predicted NOx absorption amount and the NOx absorption performance of the catalyst is deteriorated.

[0009] Here, the catalyst temperature becomes high due to changes in operating conditions.
The NOx absorption catalyst can absorb when the temperature changes from low to high.
Change from low temperature to high temperature because the amount of NOx that changes is decreasing
More N under the same temperature conditions than when
Ox will be desorbed, and the accuracy of deterioration diagnosis will decrease.
It Therefore, the diagnosis target is only for the first lean reversal after the start.
As a result, the diagnosis should be made at the transition from high temperature to low temperature.
To avoid. The action of NOx absorption and desorption when barium Ba is used as the NOx absorbing substance can be expressed as follows. Ba (NO ₃ ) ₂ + CO ₂ ⇔ BaCO ₃ + 2NO ₂ + 1 / 2CO ₂

According to the second aspect of the present invention, when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas is absorbed, and when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or is richer than the stoichiometric air-fuel ratio. A catalyst deterioration diagnosis device for an engine, which is equipped with a NOx absorption catalyst that releases the absorbed NOx and performs a reduction process, and is capable of performing a combustion operation at a lean air-fuel ratio rather than a stoichiometric air-fuel ratio, and is absorbed by the NOx absorption catalyst. When the air-fuel ratio of the combustion mixture is temporarily inverted from lean to rich to reduce NOx, the response delay time of the exhaust air-fuel ratio on the downstream side of the NOx absorption catalyst is measured, and the response time is set to the delay time. Based on the delay time, it is configured to diagnose deterioration of the NOx absorption performance of the NOx absorption catalyst based on the above.
The deterioration diagnosis was measured at the first rich reversal after the start.
The configuration is based on only the delay time.

According to this structure, the air-fuel ratio of the combustion mixture is temporarily inverted from lean to rich in order to reduce the NOx absorbed during lean combustion, but at this time,
The NOx absorption performance is diagnosed based on the delay time required for the downstream side of the NOx absorption catalyst to be richly reversed. As described above, the delay time is the time required for desorption of NOx, and since the desorption time changes depending on the actual amount of NOx absorbed, the reduction of the delay time from the initial state is due to NOx absorption. This will indicate a decrease in performance. Also, the beginning
Only the first lean reversal after the movement is targeted for diagnosis, NOx
From the high temperature at which the amount of NOx that the absorption catalyst can absorb decreases and changes
Avoid making diagnostics when transitioning to low temperatures.

According to a third aspect of the present invention, in the second aspect of the present invention, the NOx absorption amount in the NOx absorption catalyst is estimated, and when the estimated NOx absorption amount reaches the saturation amount, combustion mixing is performed. The air-fuel ratio of air is temporarily changed from lean to rich. With this configuration, when the NOx absorption amount increases during lean combustion and reaches the saturation amount, the air-fuel ratio of the combustion mixture is temporarily inverted from lean to rich in order to process NOx.
The deterioration of the NOx absorption performance is diagnosed based on whether or not the change in the air-fuel ratio after the catalyst is delayed by a time commensurate with the saturation amount.

According to a fourth aspect of the present invention, in the first to third aspects of the invention, the deterioration of the NOx absorption performance is diagnosed based on the delay time and the temperature of the NOx absorption catalyst. According to this configuration, deterioration of the NOx absorption performance is diagnosed based on the catalyst temperature at that time as well as the delay time of the air-fuel ratio change after the catalyst with respect to the catalyst before. NOx
The NOx absorption amount in the absorption catalyst correlates with the catalyst temperature and the delay time changes with the catalyst temperature. Therefore, it is necessary to determine whether or not the NOx amount corresponding to the catalyst temperature at that time is actually absorbed. Judging from the time, a decrease in NOx absorption performance is diagnosed.

According to a fifth aspect of the invention, the deterioration diagnosis based on the delay time is performed when the engine temperature at the time of starting is below a predetermined temperature. With this configuration, at the time of high temperature restart when the engine temperature at startup exceeds the predetermined temperature, there is a possibility that the NOx absorbed during the previous operation may have accumulated in the NOx absorption catalyst, and the estimation accuracy of the NOx absorption amount will decrease. Therefore, when the engine temperature at the time of starting is equal to or lower than the predetermined temperature, that is, when NOx at the time of the previous operation is estimated to be not present in the catalyst, N
The deterioration of the NOx absorption performance is diagnosed based on the delay time correlated with the Ox absorption amount.

On the other hand, according to the sixth aspect of the invention, when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas is exhausted.
And a NOx absorption catalyst that releases the absorbed NOx and performs reduction treatment when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or is richer than the stoichiometric air-fuel ratio, and burns at a leaner air-fuel ratio than the stoichiometric air-fuel ratio. It is a catalyst deterioration diagnosis device for an engine that can be operated, and is configured as shown in FIG.

In FIG. 1, the NOx absorption amount estimating means is
The amount of NOx absorbed by the NOx absorption catalyst during lean combustion is estimated. The enriching means temporarily reverses the combustion mixture from lean to rich when it is determined that the NOx absorption amount estimated by the NOx absorption amount estimating means has reached the saturation amount. The upstream side air-fuel ratio detecting means is a means for detecting the exhaust air-fuel ratio on the upstream side of the NOx absorption catalyst, and the downstream side air-fuel ratio detecting means is a means for detecting the exhaust air-fuel ratio on the downstream side of the NOx absorption catalyst. is there.

Here, the delay time measuring means reverses the exhaust air-fuel ratio by the upstream side air-fuel ratio detecting means from lean to rich when the air-fuel ratio of the combustion mixture is reversed by the enriching means. A delay time from the detection to the detection of reversal of the exhaust air-fuel ratio from lean to rich by the downstream side air-fuel ratio detecting means is measured. Then, the deterioration diagnosing means is configured to perform the first rich reversal after the start by the enriching means.
Only the delay time measured by the delay time measuring means
Based on the above, the deterioration of the NOx absorption performance of the NOx absorption catalyst is diagnosed.

According to this structure, NO is generated during lean combustion.
When it is estimated that the x absorption amount has reached the saturation amount, the air-fuel ratio of the combustion mixture is made rich and the absorbed NOx is increased.
Desorption / reduction of the exhaust gas is attempted. At this time, the delay time from the exhaust air-fuel ratio on the upstream side of the catalyst reversing rich to the exhaust air-fuel ratio on the downstream side of the catalyst reversing rich is measured.
The deterioration of the NOx absorption performance is diagnosed from the delay time correlated with the Ox absorption amount. Also, only at the first lean reversal after starting
NOx that can be absorbed by the NOx absorption catalyst
Diagnosis is performed at the transition from high temperature to low temperature where the amount decreases
To avoid being

According to a seventh aspect of the present invention, there is provided catalyst temperature detection means for detecting the temperature of the NOx absorption catalyst, and the deterioration diagnosis means is based on the delay time and the detected temperature of the NOx absorption catalyst. , NOx absorption performance deterioration is diagnosed. According to this configuration, the NOx absorption performance of the catalyst is diagnosed by taking into consideration the catalyst temperature that correlates with the NOx absorption amount .

According to the eighth aspect of the invention, the deterioration diagnosis means performs the deterioration diagnosis when the engine temperature at the time of starting is equal to or lower than a predetermined temperature. According to this configuration,
Only when the engine temperature at startup is equal to or lower than a predetermined temperature, that is, when it is estimated that NOx during the previous operation is not present in the catalyst, from the delay time of the air-fuel ratio change during the first desorption process,
The deterioration of the NOx absorption performance is diagnosed.

[0021]

According to the invention described in claim 1, the NOx absorption is based on the correlation between the NOx absorption amount and the delay time of the change in the post-catalyst air-fuel ratio with respect to the reversal of the air-fuel ratio before the catalyst from lean to rich. The deterioration of the NOx absorption performance of the catalyst can be accurately diagnosed , and at the time of the first rich reversal after starting.
By setting only the diagnostic condition, NO
x It is possible to avoid a decrease in diagnostic accuracy due to an increase in the desorption amount.
There is an effect.

According to the second aspect of the present invention, when the air-fuel ratio is made rich in order to desorb NOx, NO
By knowing the actual NOx absorption amount based on the delay time required until the rich reversal of the air-fuel ratio after the catalyst indicating the completion of desorption of x, it is possible to accurately diagnose the deterioration of the NOx absorption performance of the NOx absorption catalyst and to start the engine. After the first rich reverse
By setting only the diagnostic condition, NO
x It is possible to avoid a decrease in diagnostic accuracy due to an increase in the desorption amount.
There is an effect.

According to the third aspect of the present invention, desorption is performed every time the NOx absorption amount reaches the saturation amount to secure the NOx absorption performance, and the change in the post-catalyst air-fuel ratio corresponds to the saturation amount. NOx based on whether a delay time was required
This has the effect of diagnosing the deterioration of absorption performance.

According to the fourth aspect of the present invention, the deterioration of the NOx absorption amount due to the decrease of the catalyst temperature is reduced by performing the deterioration diagnosis by adding the catalyst temperature correlated with the NOx absorption amount.
It is possible to avoid erroneous diagnosis as deterioration of Ox absorption performance.
There is an effect . According to the invention of claim 5, it is possible to avoid the diagnosis when there is a possibility that the NOx absorbed during the previous operation may remain, and to diagnose the deterioration of the NOx absorption performance with higher accuracy. is there.

According to the sixth aspect of the present invention, when the combustion air-fuel mixture is inverted to rich in order to desorb NOx corresponding to the saturation amount, the exhaust air after the catalyst with respect to the inversion of the exhaust air-fuel ratio before the catalyst is reversed. From the delay time of the reversal of the fuel ratio, it is judged whether or not the saturated amount of NOx was actually absorbed, and thus NOx
The deterioration of the NOx absorption performance of the absorption catalyst can be accurately diagnosed, and the diagnosis condition can be determined only at the first rich reversal after the start.
Depending on the conditions,
The effect of avoiding deterioration of diagnostic accuracy due to increased changes
There is.

According to the invention described in claim 7 , there is an effect that it is possible to avoid erroneous diagnosis of the deterioration of the NOx absorption performance based on the difference in the NOx absorption amount depending on the catalyst temperature.
It According to the invention as set forth in claim 8, the NOx absorbed during the previous operation is unlikely to be accumulated at the time of the first rich reversal after the start, so that the NOx is reduced.
There is an effect that the diagnostic accuracy of the absorption performance can be further enhanced.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 2 is a diagram showing a system configuration of the engine in the embodiment. The intake system of the engine 1 has an air cleaner for purifying intake air from an upstream side, an air flow meter 3 for measuring the intake amount, and an intake amount control. A throttle chamber 4 is installed, and an intake manifold 5 and an injector 6 are provided downstream of the throttle chamber 4.
And are attached.

On the other hand, a water temperature sensor 7 for detecting the cooling water temperature of the engine 1 and a crank angle sensor 8 for detecting the number of revolutions (rpm) of the engine 1 are attached to the engine 1. These water temperature sensor 7 and crank angle sensor The output of 8 is input to the control module 9 together with the output of the air flow meter 3.

The control module 9 leans from the intake air amount detected by the air flow meter 3 and the engine speed detected by the crank angle sensor 8 to the lean,
The basic fuel injection amount during stoichiometric (fuel stoichiometric) combustion is calculated, and the final fuel injection amount is determined by adding the fuel increase value or the like according to the water temperature data detected by the water temperature sensor 7 to the basic fuel injection amount. Then, fuel is injected from the injector 6 into each branch portion of the intake manifold 5. The injector 6 may be a cylinder injection type gasoline engine that directly injects fuel into the combustion chamber of each cylinder.

In the exhaust passage 10 of the engine 1, a NOx absorption catalyst 11 having NOx absorption performance, and the NOx absorption catalyst 11
Upstream oxygen sensor 12 (upstream air-fuel ratio detecting means) and downstream oxygen sensor 13 respectively arranged on the upstream side and the downstream side of the
(Downstream air-fuel ratio detection means) is attached.

The NOx absorption catalyst 11 absorbs NOx in the exhaust when the exhaust air-fuel ratio is lean, and releases the absorbed NOx when the exhaust air-fuel ratio is stoichiometric or rich. NOx that is desorbed and reduced
It is an absorption type three-way catalyst, and a catalyst temperature sensor 14 for detecting the catalyst temperature is attached to the NOx absorption catalyst 11.

The control module 9 calculates the NOx emission amount from the engine 1 during lean combustion from the intake air amount detected by the air flow meter 3 and the engine speed detected by the crank angle sensor 8, When it is detected from the calculated NOx emission amount that the NOx absorbed in the NOx absorption catalyst 10 is in a saturated state (NOx absorption amount estimating means), the fuel increase value is added to the basic injection amount for a predetermined period. The air-fuel ratio of the combustion air-fuel mixture is temporarily inverted from lean to rich to perform the desorption / reduction processing of the absorbed NOx to restore the NOx absorption performance (enrichment means). Further, in the control module 9, the deterioration diagnosis of the NOx absorption performance of the NOx absorption catalyst 11 is performed as follows.

FIG. 3 is a control block diagram showing the deterioration diagnosis . The lean operation judging means A judges the lean combustion condition, and when the lean combustion condition is satisfied, NOx is established.
The absorption amount detecting means (NOx absorption amount estimating means) B estimates and calculates the NOx absorption amount in the NOx absorption catalyst 11 from the operating condition of the engine.

Air-fuel ratio increasing means (enriching means)
C is N calculated and estimated by the NOx absorption amount detecting means B.
When the Ox absorption amount reaches the saturation amount, the air-fuel ratio of the combustion mixture is reversed from lean to rich, and the NOx absorption catalyst 11
The fuel injection amount is increased and corrected in order to desorb and reduce the absorbed NOx.

Here, the delay time detecting means (delay time measuring means) D for the post-catalyst air-fuel ratio with respect to the pre-catalyst air-fuel ratio is made rich by the air-fuel ratio increasing means C, whereby the exhaust air-fuel ratio before the catalyst is increased. Is measured from the upstream side oxygen sensor 12 until the exhaust air-fuel ratio after the catalyst detected by the downstream side oxygen sensor 13 is delayed and is then converted into rich state.

The catalyst deterioration detection means (deterioration diagnosis means) E is
Based on the measured delay time and the catalyst temperature detected by the catalyst temperature detecting means F based on the signal from the catalyst temperature sensor 14, the deterioration of the NOx absorption performance of the NOx absorption catalyst 11 is diagnosed. Further, the air-fuel ratio increase number storage means G has NOx estimated by the NOx absorption amount detection means B.
The air-fuel ratio increasing means C counts the number of times the air-fuel ratio of the combustion mixture is temporarily inverted from lean to rich because the absorption amount reaches the saturation amount. Deterioration diagnosis is performed based on the counting result.

FIG. 4 is a flow chart showing the above-mentioned deterioration diagnosis . First, in step 10 (denoted as S 10 in the figure. The same applies hereinafter), the water temperature TWINT at the time of starting is set to a predetermined value.
Determine whether it was below the temperature ITW (eg 40 ℃)
It In the present embodiment, the water temperature Tw is set to the engine temperature
It is used as a representative parameter.

The starting water temperature TWINT is the predetermined temperature IT.
If it exceeds W, there is a possibility of high temperature restart,
NOx absorbed during the previous operation accumulated in the catalyst 11.
There is a possibility that As will be described later, in this embodiment,
Make a diagnosis while repeating NOx absorption and desorption
Instead, NOx was accumulated in the catalyst 11 for the first time after starting.
Sometimes deterioration diagnosis is performed, so NOx from the previous operation is a catalyst.
It is more accurate to make a diagnosis in a state that is not within 11.
improves.

Therefore, the starting water temperature TWINT is the above-mentioned predetermined value.
At the time of a high temperature restart exceeding the temperature ITW and during the previous operation
If there is a possibility that NOx of
Terminates this routine without diagnosis.
It On the other hand, the starting water temperature TWINT is equal to the predetermined temperature ITW.
When it is the following, go to step 11. Step 11
Then, it is determined whether or not the water temperature Tw at that time is equal to or higher than the water temperature TWLEAN (for example, 80 ° C.) that is a condition for lean combustion.

When it is judged at step 11 that Tw≥TWLEAN, it is judged that the lean combustion operation is possible and the routine proceeds to step 12 , where Tw <TWLE.
When it is AN, this routine is finished as it is. In step 12 , the lean combustion flag FLEAN is set to 1 when the engine load condition obtained from the engine speed and the intake air amount is the lean combustion condition.
And if the flag FLEAN is 1, step
Proceed to 13 .

On the other hand, when the flag FLEAN is 0 and the engine load condition is not the lean combustion condition, this routine is ended. Steps 11 and 12 above
This portion corresponds to lean operation determination means A. Step 1
3 (NOx absorption amount detecting means B) calculates the NOx amount discharged from the engine under the engine load condition obtained from the engine speed and the intake air amount, and the NOx absorption catalyst obtained as an integrated value of the NOx amount. The NOx absorption amount NOXADP in 11 and the saturation amount NOXMAX are compared.

When the NOx absorption amount NOXADP is equal to or more than the saturation amount NOXMAX, step 1
4 (air-fuel ratio increasing means C), the atmosphere in the NOx absorption catalyst 11 is made into a reducing atmosphere, and the injection amount increase correction by the air-fuel ratio increasing coefficient KRS in order to desorb and reduce the absorbed NOx. Then, the air-fuel ratio of the combustion mixture is temporarily reversed from lean to rich.

NOx absorption amount NOXADP is saturated amount NOX
When it has not reached MAX, the routine returns to step 12 to repeat the lean combustion condition determination and the NOx absorption amount integration. In step 15, go to step 14
Whether it is the first time after the start that the increase correction is performed.
In order to determine the
Refer to the count flag RSCNT for counting (air-fuel ratio increase count
Number storage means G).

The flag RSCNT is 1
If it is the time of the first increase correction after starting,
16, but the flag RSCNT is 0 and the amount is increased.
If the correction indicates that it is the second time or later, make a diagnosis.
This routine is ended without any action.

Absorption of NOx in the NOx absorption catalyst 11,
When desorption is repeated, the catalyst temperature changes from high to low.
The amount of NOx absorbed may change when the temperature changes to
Thus, when the catalyst temperature shifts from high temperature to low temperature,
More desorption of NOx than when changing from high temperature to high temperature
Therefore, a longer time is measured as the delay time TFR.
The deterioration diagnosis based on the delay time TFR is performed.
The disconnection accuracy decreases.

Therefore, at the first increase correction (desorption) after the start
Deterioration diagnosis based only on the delay time TFR measured in
The catalyst temperature can be changed from high temperature to low temperature
Diagnosis based on the delay time TFR measured at the time of transition
Of the diagnosis based on the delay time TFR.
Improve accuracy.

In step 16 (delay time detecting means D of the post-catalyst air-fuel ratio with respect to the pre-catalyst air-fuel ratio), when the air-fuel ratio of the combustion mixture is inverted to rich by the air-fuel ratio increasing coefficient KRS, the upstream oxygen sensor The delay time TFR from when the reversal to rich is detected at 12 to when the reversal to rich is detected at the downstream oxygen sensor 13 is measured (see FIG. 5).

[0048] When the exhaust air-fuel ratio upstream of the catalyst is initiated release and reduction of NOx in the NOx absorbent catalyst 11 is inverted to the rich, the oxygen O ₂ which leaves at the same time leaving the the NOx catalyst downstream air The fuel ratio is maintained near stoichiometry and NO
After the desorption of x is completed, the exhaust air-fuel ratio on the downstream side of the catalyst will be inverted to the same rich level as on the upstream side, and the delay time of such rich inversion after the catalyst with respect to before the catalyst is as shown in FIG. , NOx absorption catalyst 11 is correlated with the actual NOx absorption amount.

In the case of the present embodiment, the air-fuel ratio is made rich when it is estimated that the NOx absorption amount has reached the predetermined saturation amount. Therefore, in the initial state of the NOx absorption catalyst 11, the saturation is achieved. A delay time commensurate with the amount should be required, and when the delay time becomes shorter than that in the initial state, it can be estimated that the NOx amount that can actually be absorbed has decreased due to deterioration of the NOx absorption performance.

In the three-way catalyst, HC, CO, and O ₂ are bound and converted by the oxygen storage effect, and therefore, as shown in FIG.
As shown in, the air-fuel ratio downstream of the catalyst temporarily becomes substantially stoichiometric until O ₂ in the catalyst is consumed, but the time is extremely shorter than that of the NOx absorption catalyst. This is N
This is a characteristic of an ordinary three-way catalyst having no Ox absorption performance, and even if the delay time is measured as in the present embodiment, this only shows the three-way performance of the catalyst.

In step 17 (catalyst temperature detecting means F), the temperature TCAT of the NOx absorption catalyst 11 is detected based on the detection signal from the catalyst temperature sensor 14. When the catalyst temperature sensor 14 is not provided, the temperature of the catalyst 11 may be estimated from the engine speed and the load condition.
In step 18, as shown in FIG. 7, the delay time T
The deterioration map MAPEAK in which the degree of deterioration of the NOx absorption performance is stored in advance according to the FR and the catalyst temperature is referred to, and in step 19 (catalyst deterioration detection means E), deterioration corresponding to the actual delay time TFR and the catalyst temperature TCAT is performed. Degree NR
Search for EK.

The NOx absorption amount in the NOx absorption catalyst 11 is influenced by the catalyst temperature, and as shown in FIG. 8, it decreases when the catalyst temperature is too high or too low. Therefore, when the deterioration diagnosis is performed irrespective of the catalyst temperature, the NOx absorption amount decreases because the catalyst temperature is low, for example, and when the delay time TFR becomes short,
There is a possibility of erroneous diagnosis due to deterioration of NOx absorption performance. Therefore, as shown in FIG. 7, the delay time T
The degree of deterioration of the NOx absorption performance is diagnosed from the RF and the catalyst temperature, and the deterioration can be diagnosed by taking into consideration the dispersion of the NOx absorption performance depending on the catalyst temperature.

The diagnosed degree of deterioration of NOx absorption performance is stored as maintenance information, and when the degree of deterioration of the NOx absorption catalyst 11 exceeds an allowable level,
It is possible to take measures such as turning on a warning light indicating catalyst deterioration and prohibiting lean combustion. In addition, the saturation amount may be modified according to the degree of deterioration of the NOx absorption performance, and the timing at which the air-fuel ratio is richly inverted to desorb and reduce NOx may be advanced as the deterioration progresses .

In the above embodiment , the air-fuel ratio is made rich when it is estimated that the NOx absorption amount has reached the saturation amount, and the catalyst 11 of the catalyst 11 is based on the phase difference of the air-fuel ratio change before and after the catalyst at this time. Although the deterioration of the NOx absorption performance is diagnosed, in the deterioration diagnosis, it is not always necessary to absorb the NOx up to the saturation amount, and the estimated value of the NOx absorption amount immediately before the lean combustion to the rich reversal and the post-catalyst The deterioration of the NOx absorption performance can be diagnosed from the delay time of the air-fuel ratio reversal.

In the above embodiment, the delay time is measured from the time when the exhaust air-fuel ratio on the upstream side of the catalyst reverses to rich to the time when the exhaust air-fuel ratio on the downstream side of the catalyst changes to rich. The delay time may be measured from the time when the fuel injection amount is increased until the exhaust air-fuel ratio on the downstream side of the catalyst is reversed to rich.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a catalyst deterioration diagnosing device according to a sixth aspect of the invention.

FIG. 2 is a system configuration diagram of an engine according to the embodiment.

FIG. 3 is a control block diagram showing an embodiment of deterioration diagnosis.

FIG. 4 is a flowchart showing an embodiment of deterioration diagnosis.

FIG. 5 is a time chart showing changes in the air-fuel ratio before and after the catalyst during NOx desorption.

FIG. 6 is a graph showing the correlation between the delay time of the air-fuel ratio change after the catalyst compared to before the catalyst and the NOx absorption amount.

FIG. 7 is a diagram showing a map in which a degree of deterioration is stored according to a catalyst temperature and a delay time.

FIG. 8 is a diagram showing a correlation between catalyst temperature and NOx absorption amount.

[Explanation of symbols]

1 ... engine 2 ... Air cleaner 3 ... Air flow meter 4 ... Throttle chamber 5 ... Intake manifold 6 ... Fuel injection valve 7 ... Water temperature sensor 8 ... Crank angle sensor 9 ... Control module 10 ... Exhaust passage 11 ... NOx absorption catalyst 12 ... upstream oxygen sensor 13 ... Downstream oxygen sensor 14 ... Catalyst temperature sensor

─────────────────────────────────────────────────── --Continued from the front page (56) References JP-A-8-260948 (JP, A) JP-A-8-260949 (JP, A) JP-A-6-200737 (JP, A) JP-A-10- 121944 (JP, A) JP-A-5-195759 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) F01N 3/08-3/36 F02D 41/04 F02D 41/14 F02D 45/00

Claims (8)

(57) [Claims] 1. When the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas is absorbed, and when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, the absorbed NOx is absorbed. A catalyst deterioration diagnosing device for an engine, comprising a NOx absorption catalyst for releasing and performing reduction processing, capable of performing a combustion operation at a lean air-fuel ratio rather than a stoichiometric air-fuel ratio, wherein the NOx absorption amount for the NOx absorption catalyst during lean combustion is In addition to estimating, the delay time until the exhaust air-fuel ratio after the NOx absorption catalyst changes from lean to rich is measured with respect to the change from the lean air to the rich exhaust air fuel ratio before the NOx absorption catalyst, and the NOx absorption From the correlation between the estimated value of the amount and the delay time, NO in the NOx absorption catalyst
x A structure for diagnosing deterioration of absorption performance , and the delay
Deterioration diagnosis based on time is performed at the first rich reversal after starting.
An engine catalyst deterioration diagnosing device characterized by performing only on the basis of the measured delay time . 2. When the exhaust air-fuel ratio is leaner than the theoretical air-fuel ratio, NOx in the exhaust gas is absorbed, and when the exhaust air-fuel ratio is the theoretical air-fuel ratio or is richer than the theoretical air-fuel ratio, the absorbed NOx is absorbed. A catalyst deterioration diagnosing device for an engine, comprising a NOx absorption catalyst for releasing and reducing the NOx absorption catalyst, capable of performing a combustion operation at a lean air-fuel ratio rather than a stoichiometric air-fuel ratio, wherein NOx absorbed by the NOx absorption catalyst is reduced. Therefore, when the air-fuel ratio of the combustion air-fuel mixture is temporarily inverted from lean to rich, the response delay time of the exhaust air-fuel ratio on the downstream side of the NOx absorption catalyst is measured, and the NOx absorption catalyst is based on the delay time. And a deterioration diagnosis based on the delay time.
Of the delay time measured at the first rich reversal after starting
An engine catalyst deterioration diagnosing device characterized in that it is carried out based only on the above . 3. An NOx absorption amount in the NOx absorption catalyst is estimated, and when the estimated NOx absorption amount reaches a saturation amount, the air-fuel ratio of the combustion mixture is temporarily inverted from lean to rich. The catalyst deterioration diagnosis device for an engine according to claim 2, wherein 4. The engine catalyst deterioration diagnosis according to claim 1, wherein deterioration of NOx absorption performance is diagnosed based on the delay time and the temperature of the NOx absorption catalyst. apparatus. 5. A degradation diagnosis based on the delay time, the engine according to any one of claims 1 to 4, characterized in that to perform when the engine temperature at the start was equal to or lower than the predetermined temperature Catalyst deterioration diagnosis device. 6. When the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, NOx in the exhaust gas is absorbed, and when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or is richer than the stoichiometric air-fuel ratio, the absorbed NOx is absorbed. A catalyst deterioration diagnosing device for an engine, comprising a NOx absorption catalyst for releasing and performing reduction processing, capable of performing a combustion operation at a lean air-fuel ratio rather than a stoichiometric air-fuel ratio, wherein the NOx absorption amount in the NOx absorption catalyst during lean combustion is A NOx absorption amount estimating means for estimating and a rich conversion for temporarily inverting the combustion mixture from lean to rich when it is determined that the NOx absorption amount estimated by the NOx absorption amount estimating means has reached the saturation amount. Means, an upstream air-fuel ratio detecting means for detecting an exhaust air-fuel ratio on the upstream side of the NOx absorption catalyst, and a downstream side air-fuel ratio detecting means for detecting an exhaust air-fuel ratio on the downstream side of the NOx absorption catalyst. And, when the air-fuel ratio of the combustion mixture is inverted to rich by the enriching means, from the lean-to-rich inversion detection of the exhaust air-fuel ratio by the upstream side air-fuel ratio detecting means, the downstream side air-fuel ratio detecting means Delay time measuring means for measuring the delay time from detection of lean to rich reversal of the exhaust air-fuel ratio by means of, and before the first rich reversal after starting by the enriching means.
Based on only the delay time measured by the delay time measuring means
Zui, the catalyst deterioration diagnosis system for an engine, characterized in that said the deterioration diagnosis means for diagnosing the deterioration of the NOx absorbing capacity of the NOx absorbent catalyst, which is configured to include. 7. A catalyst temperature detection means for detecting the temperature of the NOx absorption catalyst, wherein the deterioration diagnosis means deteriorates the NOx absorption performance based on the delay time and the detected temperature of the NOx absorption catalyst. 7. The engine catalyst deterioration diagnosing device according to claim 6 , wherein the engine deterioration is diagnosed. 8. A catalyst deterioration diagnosing device for an engine according to claim 6 or 7 , wherein said deterioration diagnosing means carries out the deterioration diagnosis when the engine temperature at the time of starting is lower than a predetermined temperature.