JPH0988560A - Diagnostic device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diagnostic device for an engine by which a correct deterioration diagnosis can be executed in a lean engine equipped with NOx absorbing catalyst, by judging the deterioration of the NOx absorbing catalyst on the basis of hour until the output value of a NOx sensor exceeds a slice level after changing over from a theoretical air-fuel ratio to a lean air-fuel ratio. SOLUTION: In a lean engine 1, a target air-fuel ratio is changed over to stoichiometric and lean condition by a control unit 4, and a fuel injection quantity is controlled by feedback control on the basis of the output of an O2 sensor 6 under a stoichiometric condition and controlled by open control under a lean condition. In this case, an NOx sensor 9 is arranged on the downstream side of a catalyst 8 which adsorbs NOx during lean operation and reduces the adsorbed NOx during stoichiometric operation. Reaching time to a slice level is shortened according to the deterioration of the NOx absorptive performance of the catalyst 8, therefore, after changing over from stoic to lean, the deterioration of the catalyst 8 is judged on the basis of hour until the output of the NOx sensor 8 exceeds the slice level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine diagnostic device, and more particularly to a catalyst or air-fuel ratio diagnostic device for a lean engine.

[0002]

2. Description of the Related Art Conventionally, in an apparatus disclosed in, for example, Japanese Unexamined Patent Publication No. 4-116239, a three-way catalyst is provided in an exhaust passage of an engine, and exhaust gas is exhausted upstream and downstream of the three-way catalyst. fuel to the provided upstream O ₂ sensor and the downstream O ₂ sensor outputs a rich lean inversion signal, a predetermined air-fuel ratio based on the output signal of the upstream O ₂ sensor obtained according to the O ₂ concentration while performing the air-fuel ratio feedback control to increase or decrease correcting the fuel injection quantity from the injector, by using the upstream O ₂ sensor and the output value of the downstream O ₂ sensor when the air-fuel ratio feedback control, i.e., the upstream O ₂ The rich / lean inversion frequency f1 of the sensor output signal and the downstream side O
_{2 The} inversion frequency ratio f2 / f1 is obtained based on the rich / lean inversion frequency f2 of the output signal of the sensor, and when the inversion frequency ratio is less than or equal to the set value, the three-way catalyst is normal, and when it is greater than the set value. Is diagnosed as abnormal (deteriorated).

[0003]

By the way, an engine equipped with an air-fuel ratio switching means for switching the air-fuel ratio of the air-fuel mixture supplied to the engine between a stoichiometric air-fuel ratio (stoichi) and a lean air-fuel ratio (lean) according to operating conditions ( In the lean engine, NOx that adsorbs NOx in the exhaust passage during operation at a lean air-fuel ratio (during lean operation) and can reduce the adsorbed NOx during operation at a stoichiometric air-fuel ratio (during stoichiometric operation).
An x-adsorption catalyst is provided, or a lean NOx catalyst that adsorbs HC during stoichiometric operation and is capable of reducing NOx by the adsorbed HC (and HC newly discharged from the engine) during lean operation is provided on the downstream side. A NOx adsorption catalyst is provided.

However, there has been a problem that such a catalyst for a lean engine cannot be diagnosed by the conventional diagnostic device. That is, N of the NOx adsorption catalyst
This is because the deterioration of Ox adsorption performance cannot be determined by the O ₂ concentration, and the deterioration of NOx conversion performance of the lean NOx catalyst cannot be determined by the O ₂ concentration.

The present invention has been made in view of such conventional problems, and an object thereof is to enable diagnosis of a catalyst for a lean engine or the like.

[0006]

Therefore, according to the first aspect of the invention, as shown in FIG. 1 (A), NO is provided in the exhaust passage 5.
In an engine equipped with the x adsorption catalyst 8, a NOx sensor 9 for detecting NOx in the exhaust is provided downstream of the NOx adsorption catalyst 8, while the output value of the NOx sensor 9 is preset to a slice level after switching from stoichiometric to lean. The NOx adsorption catalyst deterioration determining means for determining the deterioration of the NOx adsorption catalyst 8 based on the time until it exceeds is provided to configure the catalyst diagnosis device.

That is, as the adsorption performance of the NOx adsorption catalyst deteriorates, the time for the output value of the NOx sensor to reach the slice level becomes shorter after the stoichiometric → lean switching. Therefore, the adsorption performance of the NOx adsorption catalyst is detected by detecting this. Diagnose deterioration. In the invention according to claim 2, FIG.
As shown in (B), in an engine having a lean NOx catalyst 7 in the exhaust passage 5 and a NOx adsorption catalyst 8 on the downstream side of the lean NOx catalyst 7, N in the exhaust gas is exhausted downstream of the NOx adsorption catalyst 8.
While the NOx sensor 9 for detecting Ox is provided, based on the time until the output value of the NOx sensor 9 exceeds the preset slice level after the stoichiometric → lean switching,
A lean NOx that determines the deterioration of the lean NOx catalyst 7 based on the level of the output value of the NOx adsorption catalyst deterioration determination means and the NOx sensor 9 that determines the deterioration of the NOx adsorption catalyst 8.
A catalyst deterioration determination unit is provided to configure a catalyst diagnosis device.

That is, as the adsorption performance of the NOx adsorption catalyst deteriorates, the time τ for the output value of the NOx sensor to reach the slice level after the stoichiometric → lean switching becomes shorter, and the NOx conversion performance of the lean NOx catalyst deteriorates. Since the level of the output value of the NOx sensor increases,
By detecting these, deterioration of the adsorption performance of the NOx adsorption catalyst and deterioration of the conversion performance of the lean NOx catalyst are diagnosed.

According to the third aspect of the invention, as shown in FIG. 1 (A), in the engine having the NOx adsorbing catalyst 8 in the exhaust passage 5, the NO in the exhaust gas is downstream of the NOx adsorbing catalyst 8.
While the NOx sensor 9 for detecting x and the temperature sensor 10 for detecting the temperature of the NOx adsorption catalyst 8 are provided, the stoichiometry →
After lean switching, the NOx adsorption catalyst that determines deterioration of the NOx adsorption catalyst 8 and temporary deterioration due to S poisoning based on the time until the output value of the NOx sensor 9 exceeds a preset slice level and the catalyst temperature. Deterioration determination means is provided to configure a catalyst diagnostic device.

That is, when a large amount of S is deposited on the surface of the NOx adsorbing catalyst, NOx is not adsorbed, so NO
It is known that although the x emission amount increases, the deposition of S is temporary, and if the catalyst is held in a high temperature state, S is decomposed and the deposition amount of S decreases. Therefore, in consideration of the catalyst temperature, permanent deterioration due to heat of the NOx adsorption catalyst and temporary deterioration due to S poisoning are classified and diagnosed.

According to a fourth aspect of the invention, as shown in FIG. 1 (B), in the engine having the lean NOx catalyst 7 in the exhaust passage and the NOx adsorption catalyst 8 further downstream thereof, the NOx adsorption catalyst 8 A NOx sensor 9 for detecting NOx in the exhaust gas and a temperature sensor 10 for detecting the temperature of the NOx adsorption catalyst 8 are provided downstream, while a slice in which the output value of the NOx sensor 9 is preset after stoichiometric → lean switching. Based on the time until the level is exceeded and the catalyst temperature, the NOx adsorption catalyst deterioration determining means for determining the deterioration of the NOx adsorption catalyst 8 and the temporary deterioration due to S poisoning, and the level of the output value of the NOx sensor 9. , Lean NOx catalyst 7
And a lean NOx catalyst deterioration determining means for determining deterioration of the catalyst are provided to configure a catalyst diagnostic device.

According to this, permanent deterioration due to heat of the NOx adsorption catalyst, temporary deterioration due to S poisoning, and deterioration of the lean NOx catalyst can be classified and diagnosed. According to the invention of claim 5, in an engine having a catalyst in an exhaust passage, an upstream NOx sensor for detecting NOx in exhaust gas upstream of the catalyst.
11 is provided, but the upstream NOx sensor 11 during lean operation 11
An air-fuel ratio shift determination unit that determines the shift of the air-fuel ratio based on the level of the output value is provided to configure the air-fuel ratio diagnosis device (see FIGS. 1A and 1B).

The NOx emission amount from the vehicle depends not only on the performance of the catalyst but also on the NOx emission amount emitted from the engine. Generally, the NOx emission amount is determined by the air-fuel ratio, but there is a range of variation, and if the upper limit of this range is exceeded, it can be diagnosed as an air-fuel ratio rich shift, and if it is less than the lower limit, it can be diagnosed as an air-fuel ratio lean shift. Therefore, upstream NO
In the invention according to claim 6, in which the shift of the air-fuel ratio is diagnosed based on the output level of the x sensor, in addition to the invention according to claims 1 to 4, the upstream side for detecting NOx in the exhaust gas upstream of the catalyst While the NOx sensor 11 is provided, air-fuel ratio shift determination means for determining the shift of the air-fuel ratio based on the level of the output value of the upstream NOx sensor 11 during lean operation is provided (FIG. 1 (A), (See (B)).

According to this, in addition to the actions of the invention according to claims 1 to 4, it is possible to diagnose the shift of the air-fuel ratio.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. [First Embodiment] FIG. 2 is a system diagram. Engine 1
A fuel injection valve 3 is provided in the intake passage 2, and the fuel injection valve 3 is controlled by a control unit 4. An O ₂ sensor 6 is provided in the exhaust passage 5 on the upstream side of a catalyst, which will be described later, and its signal is input to the control unit 4.

The control unit 4 switches the target air-fuel ratio between stoichiometric and lean depending on engine operating conditions, and performs feedback control based on a signal from the O ₂ sensor 6 under stoichiometric conditions and open control under lean conditions. The fuel injection amount of the injection valve 3 is controlled.
A NOx adsorption catalyst 8 is provided in the exhaust passage 5 for purifying the exhaust gas. The NOx adsorption catalyst 8 keeps NO during lean operation.
It is possible to adsorb x and reduce the adsorbed NOx during stoichiometric operation.

Here, a NOx sensor 9 for detecting NOx in the exhaust gas is provided on the downstream side of the NOx adsorption catalyst 8,
The signal is input to the control unit 4.
Incidentally, NOx sensor ^{_{9, In 3+ -TiO 2, WO 3}} , or in which an oxide semiconductor such as Sc ₂ O ₃ -CuO. Fig. 3 shows NOx when switching from stoichiometric to lean
The sensor output is shown. The NOx adsorption performance of the NOx adsorption catalyst has the characteristics shown in the figure, and the time τ to reach the slice level becomes shorter as the NOx adsorption performance deteriorates.
Therefore, by detecting this, deterioration of the adsorption performance of the NOx adsorption catalyst can be diagnosed.

FIG. 4 shows a diagnosis flowchart. In step 1 (denoted as S1 in the figure; the same applies hereinafter), it is determined whether or not the lean condition is met, and the process proceeds to step 2 only when the lean condition is met. In step 2, it is determined whether or not the lean condition is the last time, and if NO, it means that the stoichiometric → lean switching is being performed, and in step 3, the counter CNT for measuring the elapsed time after the switching is cleared. If YES, the counter CNT is incremented in step 4.

In step 5, the output value NOxV of the NOx sensor 9 is read. In step 6, the output value NOxV of the NOx sensor 9 is compared with a predetermined value (slice level) V _0. If NOxV <V ₀ , it is determined in step 8 that the NOx adsorption catalyst is normal. If NOxV ≧ V ₀ , in step 7, the counter CNT is compared with the predetermined value C _0, and CNT
If ≧ C ₀ , it is determined in step 8 that the NOx adsorption catalyst is normal, but if CNT <C ₀ , NOx is determined in step 9.
It is determined that the adsorption catalyst has deteriorated.

That is, after switching from stoichiometric to lean, N
Based on the time until the output value NOxV of the Ox sensor 9 exceeds a preset slice level V ₀ , if the time is shorter than a predetermined value (C ₀ ), it is determined that the NOx adsorption catalyst 8 has deteriorated. Here, steps 1 to 9 are NO
x Corresponds to the adsorption catalyst deterioration determination means. [Second Embodiment] In this embodiment, a lean NOx catalyst + N is used.
This is the case where an Ox adsorption catalyst is provided.

FIG. 5 is a system diagram. A lean NOx catalyst 7 and a NOx adsorption catalyst 8 are provided in series in the exhaust passage 5. The lean NOx catalyst 7 has an H level during stoichiometric operation.
It is possible to adsorb C and reduce NOx by the adsorbed HC and the HC newly discharged from the engine during lean operation. The NOx adsorption catalyst 8 is capable of adsorbing NOx during lean operation and reducing the adsorbed NOx during stoichiometric operation.

Here, a NOx sensor 9 for detecting NOx in the exhaust gas is provided on the downstream side of the NOx adsorption catalyst 8,
The signal is input to the control unit 4. FIG. 6 shows the NOx sensor output when switching from stoichiometric to lean. As the NOx adsorption performance of the NOx adsorption catalyst deteriorates, the time τ to reach the slice level becomes shorter, and the output level increases as the NOx conversion performance of the lean NOx catalyst deteriorates. Therefore, NOx depends on the time τ.
The deterioration of the adsorption performance of the adsorption catalyst can be diagnosed, and the deterioration of the conversion performance of the lean NOx catalyst can be diagnosed depending on the output level.

FIG. 7 shows a diagnosis flowchart. In step 1, it is determined whether or not the lean condition is met, and the process proceeds to step 2 only when the lean condition is met. In step 2, it is determined whether or not the lean condition is the last time, and if NO, it means that the stoichiometric → lean switching is being performed, and in step 3, the counter CNT for measuring the elapsed time after the switching is cleared. If yes,
In step 4, the counter CNT is incremented.

At step 5, the output value NOxV of the NOx sensor 9 is read. In step 11, the output value NOxV of the NOx sensor 9 is compared with a predetermined value (slice level) V _0. If NOxV <V ₀ , it is determined in step 14 that the NOx adsorption catalyst and the lean NOx catalyst are normal. NOxV ≧
If V ₀ , the output value N of the NOx sensor 9 in step 12
OxV is compared with a predetermined value V ₁ (> V ₀ ), and NOxV <V
_{If 1} , then go to step 13.

At step 13, the counter CNT is compared with a predetermined value C _0. If CNT ≧ C ₀ , it is judged at step 14 that the NOx adsorption catalyst and the lean NOx catalyst are normal, but if CNT <C ₀ . In step 17, it is determined that the NOx adsorption catalyst has deteriorated. If NOxV ≧ V ₁ , step
At 15, it is determined that the lean NOx catalyst has deteriorated. Then, the process proceeds to step 16.

In step 16, the counter CNT is compared with a predetermined value C _0. If CNT <C ₀ , it is determined in step 17 that the NOx adsorption catalyst has deteriorated. That is, stoiki →
After the lean switching, based on the time until the output value NOxV of the NOx sensor 9 exceeds a preset slice level V ₀ , when the time is shorter than a predetermined value (C ₀ ),
When it is determined that the NOx adsorption catalyst has deteriorated and the output value NOxV of the NOx sensor 9 exceeds a predetermined value V ₁ , lean NOx is obtained.
Determined as catalyst deterioration.

Here, steps 1 to 5, 11, 13, 14, 1
Parts 6 and 17 correspond to NOx adsorption catalyst deterioration determination means,
The steps 12 and 15 correspond to the lean NOx catalyst deterioration determination means. [Third Embodiment] In this embodiment, when a NOx adsorption catalyst is provided, temporary deterioration due to S poisoning of the NOx adsorption catalyst can be classified and diagnosed.

FIG. 8 is a system diagram. The difference from the first embodiment (FIG. 2) is that a temperature sensor 10 for detecting the temperature of the NOx adsorption catalyst 8 is provided and its signal is input to the control unit 4. FIG. 9 shows NOx emission characteristics due to S poisoning of the NOx adsorption catalyst. When a large amount of S is deposited on the surface of the catalyst, the place where BaNO ₃ and NOx are originally adsorbed at the time of lean becomes BaSO ₄ , and NOx is not adsorbed, resulting in a large NOx emission amount. However, the deposition of S is temporary, and the temperature is high (for example, 600
It is known that when the catalyst is held for 30 minutes at 30 ° C., S is decomposed and the amount of S deposited decreases. Therefore, by detecting whether or not the catalyst has been in a high temperature environment for a certain period of time, it is possible to classify and diagnose permanent deterioration due to heat of the NOx adsorption catalyst and temporary deterioration due to S poisoning.

FIG. 10 shows a diagnosis flowchart. Differences from the first embodiment (FIG. 4) will be described. In step 101, the catalyst temperature Tcat is read based on the signal from the temperature sensor 10. Then, in step 102, the catalyst temperature Tcat is compared with a predetermined value T _0, and if Tcat ≧ T ₀ , step 10
The counter TM is incremented by 3. Therefore, the counter TM indicates that the catalyst temperature Tcat is the predetermined value T after the engine is started.
_It indicates the accumulated time in the high temperature state of ₀ or more.

Output value of NOx sensor 9 NOxV ≧ V
_{If 0} and CNT <C ₀ , in the first embodiment, NOx
Although it is determined that the adsorption catalyst is deteriorated, in the third embodiment, the counter TM is compared with the predetermined value TM ₀ in step 104. If TM ≧ TM ₀ as a result of the comparison, it is determined in step 9 that the NOx adsorption catalyst has deteriorated, but if TM <TM ₀ , in step 105 it is determined that S is poisoning.

Here, steps 1 to 9 and 101 to 105 correspond to NOx adsorption catalyst deterioration determining means. [Fourth Embodiment] This embodiment is a lean NOx catalyst + N.
When an Ox adsorption catalyst is provided, temporary deterioration due to S poisoning of the NOx adsorption catalyst can be classified and diagnosed.

FIG. 11 is a system diagram. The difference from the second embodiment (FIG. 5) is that a temperature sensor 10 for detecting the temperature of the NOx adsorption catalyst 8 is provided and its signal is input to the control unit 4. Although the temperature sensor 10 is provided between the lean NOx catalyst 7 and the NOx adsorption catalyst 8 in the drawing, it may be located at a position where the temperature of the NOx adsorption catalyst 8 (or a temperature related thereto) can be detected.

FIG. 12 shows a diagnosis flowchart. Differences from the second embodiment (FIG. 7) will be described. In step 101, the catalyst temperature Tcat is read based on the signal from the temperature sensor 10. Then, in step 102, the catalyst temperature Tcat is compared with a predetermined value T _0, and if Tcat ≧ T ₀ , step 10
The counter TM is incremented by 3. Therefore, the counter TM indicates that the catalyst temperature Tcat is the predetermined value T after the engine is started.
_It indicates the accumulated time in the high temperature state of ₀ or more.

Output value of NOx sensor 9 NOxV ≧ V
₀ and CNT <C ₀ , in the second embodiment, NOx
Although it is determined that the adsorption catalyst has deteriorated, in the fourth embodiment, the counter TM is compared with the predetermined value TM ₀ in step 104. As a result of the comparison, if TM ≧ TM ₀ , it is determined in step 17 that the NOx adsorption catalyst has deteriorated. If TM <TM ₀ , in step 105 it is determined that S is poisoning.

Here, steps 1 to 5, 11, 13, 14, 1
The portions 6, 17, 101 to 105 correspond to NOx adsorption catalyst deterioration determining means, and the portions in steps 12 and 15 correspond to lean NOx catalyst deterioration determining means. [Fifth Embodiment] In this embodiment, the shift of the air-fuel ratio that affects the amount of NOx discharged from the engine is diagnosed.

FIG. 13 is a system diagram. A NOx adsorption catalyst 8 (or a lean NOx catalyst 7) is provided in the exhaust passage 5. Here, the upstream side of the NOx adsorption catalyst 8 (O
An upstream NOx sensor 11 for detecting NOx in the exhaust gas is provided at the same position as the ₂ sensor 6), and the signal is input to the control unit 4.

FIG. 14 shows the engine air-fuel ratio (A / F) and NO.
The relationship with x is shown. Generally, the NOx emission amount decreases as the A / F becomes leaner, but the NOx emission amount varies Δ due to engine variations, particularly cylinder A / F variations.
There is l. If the NOx value exceeds Δl, this means that the A / F has changed. For example, if the upper limit value max is exceeded, the rich shift is performed, and if the upper limit value max is less than the lower limit value min, the lean shift is performed. Therefore, not the catalyst, but the A / F
Can diagnose shifts.

FIG. 15 shows a diagnosis flowchart. In step 200, it is determined whether or not the lean condition is satisfied, and the process proceeds to step 201 only when the lean condition is satisfied. In step 201, the output value V'of the upstream NOx sensor 11 is read. Step 20
2, the output value V ′ of the upstream NOx sensor 11 is set to the upper limit value V
_If V ′ ≧ V _max is compared with _max , it is determined in step 203 that the A / F rich shift has occurred.

If V '<V _max , the output value V'of the upstream NOx sensor 11 is compared with the lower limit value V _min in step 204, and if _{V'≤V min} , the A / F lean in step 205. Judge as a shift. If V '> V _min , step
At 206, the A / F is judged to be normal. Here, step 200 ~
The portion 206 corresponds to the air-fuel ratio shift determination means.

[Sixth Embodiment] This embodiment is a combination of the first embodiment and the fifth embodiment. FIG. 16 is a system diagram. The difference from the first embodiment (FIG. 2) is that the upstream NOx sensor for detecting NOx in the exhaust gas is located upstream of the NOx adsorption catalyst 8 (at substantially the same position as the O ₂ sensor 6).
11 is provided and the signal is input to the control unit 4.

FIG. 17 shows a diagnosis flowchart. The difference from the first embodiment (FIG. 4) is that steps 201-
206 processing (air-fuel ratio shift determination means) is added. In step 201, the output value V'of the upstream NOx sensor 11 is read. In step 202, the upstream NOx sensor
The output value V ′ of 11 is compared with the upper limit value V _max, and V ′ ≧ V _max
In the case of, it is determined to be A / F rich shift in step 203.

If V '<V _max , the output value V'of the upstream NOx sensor 11 is compared with the lower limit value V _min in step 204, and if _{V'≤V min} , the A / F lean in step 205. Judge as a shift. If V '> V _min , step
At 206, the A / F is judged to be normal. Here, step 201 ~
The portion 206 corresponds to the air-fuel ratio shift determination means.

[Seventh Embodiment] This embodiment is a combination of the second embodiment and the fifth embodiment. FIG. 18 is a system diagram. The difference from the second embodiment (FIG. 5) is that an upstream NOx sensor 11 for detecting NOx in the exhaust gas is provided on the upstream side of the lean NOx catalyst 7 (at substantially the same position as the O ₂ sensor 6), and the signal Is input to the control unit 4.

FIG. 19 shows a diagnosis flowchart. The difference from the second embodiment (FIG. 7) is that the steps 201 to
206 processing (air-fuel ratio shift determination means) is added. The processing contents of steps 201 to 206 are the same as the processing contents in the sixth embodiment. [Eighth Embodiment] This embodiment is a combination of the third embodiment and the fifth embodiment.

FIG. 20 is a system diagram. The difference from the third embodiment (FIG. 8) is that the upstream side of the NOx adsorption catalyst 8 (O
An upstream NOx sensor 11 for detecting NOx in the exhaust gas is provided at the same position as the ₂ sensor 6), and the signal is input to the control unit 4. FIG. 21 shows a diagnosis flowchart.

The difference from the third embodiment (FIG. 10) is that the processing of steps 201 to 206 (air-fuel ratio shift determination means) is added in the middle. The processing contents of steps 201 to 206 are the same as the processing contents in the sixth embodiment. [Ninth Embodiment] This embodiment is a combination of the fourth embodiment and the fifth embodiment.

FIG. 22 is a system diagram. The difference from the fourth embodiment (FIG. 11) is that an upstream NOx sensor 11 for detecting NOx in exhaust gas is provided on the upstream side of the lean NOx catalyst 7 (at substantially the same position as the O ₂ sensor 6), and the signal Is input to the control unit 4. FIG. 23 shows a diagnosis flowchart.

The difference from the fourth embodiment (FIG. 12) is that the processing of steps 201 to 206 (air-fuel ratio shift determining means) is added in the middle. The processing contents of steps 201 to 206 are the same as the processing contents in the sixth embodiment.

[0049]

As described above, according to the invention of claim 1, it is possible to accurately diagnose the deterioration of the adsorption performance of the NOx adsorption catalyst. Claim 2
According to the invention of the above aspect, it is possible to accurately diagnose the deterioration of the adsorption performance of the NOx adsorption catalyst and the deterioration of the conversion performance of the lean NOx catalyst.

According to the third aspect of the invention, it is possible to classify and diagnose deterioration of the NOx adsorption catalyst due to heat and temporary deterioration due to S poisoning. According to the invention of claim 4, it is possible to classify and diagnose deterioration due to heat of the NOx adsorption catalyst and temporary deterioration due to S poisoning.
The effect that the deterioration of the catalyst can be diagnosed is obtained.

According to the fifth aspect of the invention, it is possible to accurately diagnose the shift of the air-fuel ratio, which has a great influence on the NOx amount discharged from the engine. According to the invention of claim 6, in addition to the effects of the invention of claims 1 to 4, the effect that the shift of the air-fuel ratio that greatly affects the NOx amount discharged from the engine can be accurately diagnosed. can get.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing the configuration of the present invention.

FIG. 2 is a system diagram showing a first embodiment of the present invention.

FIG. 3 is a characteristic diagram of the first embodiment.

FIG. 4 is a diagnosis flowchart of the first embodiment of the same as above.

FIG. 5 is a system diagram showing a second embodiment of the present invention.

FIG. 6 is a characteristic diagram of the second embodiment.

FIG. 7 is a diagnosis flowchart of the second embodiment.

FIG. 8 is a system diagram showing a third embodiment of the present invention.

FIG. 9 is a characteristic diagram of the third embodiment.

FIG. 10 is a diagnosis flowchart of the third embodiment of the same as above.

FIG. 11 is a system diagram showing a fourth embodiment of the present invention.

FIG. 12 is a diagnosis flowchart of the same as the fourth embodiment.

FIG. 13 is a system diagram showing a fifth embodiment of the present invention.

FIG. 14 is a characteristic diagram of the fifth embodiment of the same as above.

FIG. 15 is a diagnosis flowchart of the above-mentioned fifth embodiment.

FIG. 16 is a system diagram showing a sixth embodiment of the present invention.

FIG. 17 is a diagnosis flowchart of the sixth embodiment.

FIG. 18 is a system diagram showing a seventh embodiment of the present invention.

FIG. 19 is a diagnosis flowchart of the same as the seventh embodiment.

FIG. 20 is a system diagram showing an eighth embodiment of the present invention.

FIG. 21 is a diagnosis flowchart of the eighth embodiment of the same.

FIG. 22 is a system diagram showing a ninth embodiment of the present invention.

FIG. 23 is a diagnosis flowchart of the above-mentioned ninth embodiment.

[Explanation of symbols]

1 engine 2 intake passage 3 fuel injection valve 4 control unit 5 exhaust passage 6 O ₂ sensor 7 lean NOx catalyst 8 NOx adsorption catalyst 9 NOx sensor 10 temperature sensor 11 upstream NOx sensor

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location F02B 77/08 B01D 53/36 101B G01M 15/00

Claims (6)

[Claims] 1. An exhaust passage is provided with N when operating at a lean air-fuel ratio.
Ox is adsorbed and the adsorbed N is adsorbed during the operation at the stoichiometric air-fuel ratio
In an engine equipped with a NOx adsorption catalyst capable of reducing Ox, a NOx sensor for detecting NOx in exhaust gas is provided downstream of the NOx adsorption catalyst, while an output of the NOx sensor is output after switching from a theoretical air-fuel ratio to a lean air-fuel ratio. A diagnostic device comprising NOx adsorption catalyst deterioration determination means for determining deterioration of the NOx adsorption catalyst based on the time until the value exceeds a preset slice level. 2. An exhaust passage is provided with HC during operation at a stoichiometric air-fuel ratio.
Is adsorbed, and the adsorbed HC is adsorbed during operation at a lean air-fuel ratio.
Is equipped with a lean NOx catalyst capable of reducing NOx, and further downstream thereof is equipped with a NOx adsorption catalyst capable of adsorbing NOx during operation at a lean air-fuel ratio and reducing the adsorbed NOx during operation at a stoichiometric air-fuel ratio. In the engine, a NOx sensor for detecting NOx in the exhaust is provided downstream of the NOx adsorption catalyst, while the output value of the NOx sensor exceeds a preset slice level after switching from the theoretical air-fuel ratio to the lean air-fuel ratio. To NOx adsorption catalyst deterioration determining means for determining the deterioration of the NOx adsorption catalyst based on the time until, and lean NOx catalyst deterioration determining means for determining the deterioration of the lean NOx catalyst based on the level of the output value of the NOx sensor. A diagnostic device provided with. 3. The exhaust passage is provided with N when operating at a lean air-fuel ratio.
Ox is adsorbed and the adsorbed N is adsorbed during the operation at the stoichiometric air-fuel ratio
In an engine including a NOx adsorption catalyst capable of reducing Ox, a NOx sensor for detecting NOx in exhaust gas downstream of the NOx adsorption catalyst and a temperature sensor for detecting the temperature of the NOx adsorption catalyst are provided, while After switching from the fuel ratio to the lean air-fuel ratio, the deterioration of the NOx adsorption catalyst and the temporary deterioration due to S-poisoning are performed based on the time until the output value of the NOx sensor exceeds a preset slice level and the catalyst temperature. A diagnostic device provided with NOx adsorption catalyst deterioration determination means for determination. 4. The exhaust passage is provided with HC during operation at a stoichiometric air-fuel ratio.
Is adsorbed, and the adsorbed HC is adsorbed during operation at a lean air-fuel ratio.
Is equipped with a lean NOx catalyst capable of reducing NOx, and further downstream thereof is equipped with a NOx adsorption catalyst capable of adsorbing NOx during operation at a lean air-fuel ratio and reducing the adsorbed NOx during operation at a stoichiometric air-fuel ratio. In the engine, a NOx sensor that detects NOx in the exhaust gas downstream of the NOx adsorption catalyst and a temperature sensor that detects the temperature of the NOx adsorption catalyst are provided, and after switching from the theoretical air-fuel ratio to the lean air-fuel ratio, NOx adsorption catalyst deterioration determining means for determining deterioration of the NOx adsorption catalyst and temporary deterioration due to S poisoning based on the time until the output value of the NOx sensor exceeds a preset slice level and the catalyst temperature, Lean NOx catalyst deterioration determination means for determining deterioration of the lean NOx catalyst based on the level of the output value of the NOx sensor is provided. Diagnostic equipment. 5. In an engine having a catalyst in an exhaust passage, an upstream NOx sensor for detecting NOx in exhaust gas is provided upstream of the catalyst, and an output value of the upstream NOx sensor during operation at a lean air-fuel ratio is set. A diagnostic device comprising an air-fuel ratio shift determining means for determining an air-fuel ratio shift based on a level. 6. An upstream NOx sensor for detecting NOx in exhaust gas is provided upstream of the catalyst, and the air-fuel ratio is shifted based on the level of the output value of the upstream NOx sensor during operation at a lean air-fuel ratio. The diagnostic device according to any one of claims 1 to 4, further comprising an air-fuel ratio shift determining means for determining.